2PAV20110039

53º CONGRESSO BRASILEIRO DO CONCRETO - CBC2011 1

Concrete pavements in Europe:

design, construction and special applications

Lambert Houben

Delft University of Technology, Section Road and Railway Engineering,

P.O. Box 5048, 2600 GA Delft, the Netherlands, email: [email protected]

Abstract Although the majority of the European countries are united in the European Union (EU) neither a standard European Design Method for Concrete Pavements nor a European Code of Practice for concrete pavements does exist. Each country in fact has its own design method and most of these methods are mainly based on experience. Construction practice is however more or less the same throughout the continent. Based on the investigation of the European Long-Life Pavement Group (ELLPAG) in 10 EU-countries, first different aspects of the design of concrete pavements are addressed. These aspects are the nature of the various design methods (empirical vs. analytical), the traffic loadings, the concrete grade, the substructure and a comparison of the required concrete pavement thickness in various countries for a specific design case. Then, as an example of a mainly empirical design method, the German catalogue with standard jointed plain concrete pavement structures is addressed. Next, as an example of a mainly analytical design method, the Dutch design method for both jointed plain and continuously reinforced concrete pavements is explained. The construction of a concrete pavement requires a number of activities which are subsequently briefly described. These activities are the production of the concrete mix, the transport of the concrete mix to the works site, the actual construction of the pavement with a slipformpaver or another type of equipment, creating the texture of the pavement surface, protecting the pavement surface, creating the joints and opening of the pavement to traffic. Furthermore, as an example of a complex and large scale project, the recent rehabilitation of the very heavily loaded Ring Road in the city of Antwerp, Belgium is described. Also some new fields of application are briefly discussed, which are roundabouts, widening of asphalt pavements, and safety barriers. Finally an interesting recent development in the Netherlands is briefly addressed, which is a precast concrete pavement, with or without a porous concrete wearing course. This system is suited both for weak subsoils, subject to settlements, and for settlement-free subsoils.

Keywords: Europe, design, construction, jointed plain concrete pavements, continuously reinforced concrete

pavements, precast concrete pavements, special applications

mailto:[email protected]


1 Introduction

Europe covers 44 countries, 27 of them being united in the European Union (EU). A whole series of EN-standards (EN = European Norms) is available for concrete materials, pavement surface characteristics, dowel bars and tie bars, and joint filling materials. However, neither a standard European Design Method for Concrete Pavements nor a European Code of Practice for Concrete Pavements does exist. Each country in fact has its own design method and most of these methods are mainly based on experience. Construction practice is more or less the same throughout the continent. In this paper first a European overview of several design aspects for concrete pavements is given. Next, as examples the design methods used in 2 European countries are explained in more detail, and these are the mainly empirical German design method for jointed plain concrete pavements and the mainly analytical Dutch design method for both jointed plain and continuously reinforced concrete pavements. Then the modern construction techniques for concrete pavements are summarized. As an example of a complex and large scale project, the rehabilitation of the very heavily loaded Ring Road in the city of Antwerp, Belgium is described. Furthermore, new applications such as roundabouts, the widening of asphalt motorway pavements through extra lanes with a concrete pavement in Germany, and concrete safety barriers are briefly addressed. Finally an interesting recent development in the Netherlands will be briefly explained, which is a precast concrete pavement structure, whether or not with a two-layer porous concrete wearing course.

2 Design of concrete pavements

2.1. Overview of design aspects

2.1.1. Introduction

In 2000 the European Long-Life Pavement Group (ELLPAG) was formed under the auspices of FEHRL (Forum of European National Highway Research Laboratories) to report the current state of knowledge on long-life pavements in Europe. Ten EU countries participated in ELLPAG. The third phase of the project reviewed long-life concrete pavements (HASSAN ET AL, 2006; FEHRL, 2007). The review included design and construction practices of jointed and continuously reinforced concrete pavements, techniques for assessment and upgrading, maintenance and rehabilitation, and economic assessment. Here only the design aspects will be considered, the construction aspects are addressed in 3.1, and the other issues are not discussed in this paper. By definition of ELLPAG a long-life pavement is a well designed and constructed pavement where the structural elements last ‘indefinitely’, provided that the designed maximum individual load is not exceeded and that appropriate and timely surface maintenance is carried out. Concrete pavements comprise a concrete layer as the main structural element, laid onto bound or unbound (sub-)base layer(s). In some countries a thin asphalt layer is used as a surfacing layer (e.g. Porous Asphalt Concrete on motorways in the Netherlands) or as an intermediate layer between the concrete and the (sub-)base


(e.g. on heavily loaded roads in Austria, Belgium and the Netherlands). The most common types of concrete pavements used in Europe include:

Jointed plain concrete pavements (JPCP) are most widely applied in Europe. A JPCP does not have any reinforcement at all. By means of longitudinal and transverse contraction joints the concrete pavement is divided into slabs with horizontal dimensions usually not exceeding 5 m. More or less square slabs are applied, i.e. the ratio of length and width is limited to about 1.3. Dowel bars are applied in the transverse joints for better load transfer across the joints and for better longitudinal evenness at long term. Tie bars are applied in the longitudinal joints to limit the joint width. The joints are mostly sealed, although for minor roads for reasons of costs sealing is not always done.

Continuously reinforced concrete pavements (CRCP) where a small amount of longitudinal reinforcement (around 0.7%) is applied to control the crack pattern, i.e. the crack width and the crack spacing. The reinforcement is located (about) mid-depth within the concrete layer. A CRCP does not contain any transverse joint, longitudinal contraction and/or construction joints are however present. In general, compared to JPCP, the CRCP investment costs are higher and the maintenance costs are lower. In practice the application of CRCP is limited to heavily loaded pavements.

The amount of concrete pavements on the main road network varies for the individual European countries. A relatively large share of concrete pavements, considering the length of the total national network, is found in Austria and Belgium with 36% and 35%, respectively, followed by Germany with 25%. France, the Netherlands, Poland, Spain, Switzerland and the United Kingdom have values less than 10%. The limited use of concrete pavements in Europe is mainly associated with the relatively high investment costs compared to other types of pavement (asphalt pavements and small element pavements). However, a long-life concrete pavement with an improved long-term performance, thus less maintenance, can significantly lower the whole life costs.

2.1.2. Design methods

European design methods for concrete pavements rely heavily on empirical data from the observed performance of experimental and in service roads taken at a number of full-scale sites, and from the determination of deflections and stresses in the pavement, supplemented by results from laboratory tests on specimens taken from the pavement. The interpretation of data has lead to the development of analytically-generated design methods, which are based on realistic traffic predictions and the characterization of parameters contributing to the structural performance of the pavement. These include the type of pavement, the material and structural properties of the pavement layers and the combined effects of traffic and temperature loading. There are a variety of approaches to concrete pavement design currently used in the European countries. For example, the United Kingdom has developed a set of concrete thickness curves for different base types, concrete strengths and for different cumulative traffic loadings. The Netherlands (see 2.3) and France have developed analytical design


tools for the calculation of the concrete pavement thickness in relation to the concrete fatigue strength and, for CRCP, the amount of steel reinforcement and the crack width and crack spacing. Other countries, e.g. Germany (see 2.2) specify a range of concrete thicknesses in relation to the traffic loading.

2.1.3. Traffic loading

The traffic parameters in the various national road guidelines relating to the design of concrete pavements are maximum axle load, standard design axle load, the design period and the maximum cumulative traffic loading. The maximum axle load for the different countries ranges between 105 and 130 kN, with the highest value being specified in Belgium, France and Spain. The range of standard axle load used to calculate the cumulative traffic loading is from 80 to 130 kN, with the highest value for France and the lowest for the United Kingdom. The Netherlands adopt a different approach by designing to an axle load spectrum (see 2.3). The majority of the European countries design concrete roads for a 30 to 40 years life. A comparison of the design criteria in the national road guidelines shows that most countries design on a cumulative number of standard axles, although the equivalent standard axle load (ESAL) varies between countries. Design criteria in million standard axles (msa) with maximum national values of 80 and 400 msa are used in Austria and the United Kingdom, respectively. Belgium uses other design criteria such as an annual average daily traffic (AADT) flow. The Netherlands uses the total number of truck axles together with the axle load frequency distribution in the concrete fatigue analysis. Despite the similarity of traffic loading specification in many countries, it is not easy to make a direct comparison between them because of the variations of the ESAL and the maximum traffic loading within the design period of the pavements.

2.1.4. Concrete grade

Concrete is mainly classified by its strength properties as compressive strength, flexural tensile strength or indirect (splitting) tensile strength. A summary of the concrete design values for the different countries is given in table 1. The majority of the countries use compressive and/or flexural tensile strength values, only France uses the indirect tensile strength. For the various countries the design compressive strength varies from 25 to 62.5 MPa (the latter value used in Belgium after 90 days) and the design flexural tensile strength varies from 3.5 to 6 MPa.

2.1.5. Substructure

The substructure of a concrete pavement consists of the subgrade, the sub-base (capping layer) and/or the base. In concrete pavements the traffic induced stresses are spread over a large area of the subgrade due to the high bending stiffness of the concrete layer. Therefore, variation in the


Table 1. Design concrete strength values in various European countries.

Country Age of testing (days)

Concrete Strength (MPa)

compressive flexural tensile indirect (splitting) tensile

Austria 28 35 / 40 5.5 -

Belgium 90 62.5 - -

Czech Republic 28 25 / 35 3.5 – 4.5 -

France 28 - - 2.7

Germany 28 30 / 37 - -

The Netherlands

28 35 / 45 - -

Poland 28 - 4 - 6 -

Spain 28 - 3.5 – 4.5 -

Switzerland 28 30 5.5 -

United Kingdom 28 - 4.5 - 6 -

subgrade stiffness and strength has only little influence upon the structural capacity of the pavement. When the subgrade comprises very low strength material it is often necessary to improve the bearing capacity to allow construction of the upper layers. This can be achieved by applying an unbound granular layer, in the form of a sub-base, or by in-situ stabilization of the subgrade. In Austria and Germany the minimum subgrade static elastic modulus, determined by the static plate load test, is 35 MPa and 45 MPa, respectively, and in Switzerland a static elastic modulus of 22.5 MPa to 45 MPa is required. In Spain, for the heaviest traffic the subgrade must be stabilized with cement. A sub-base is applied in 2 countries being the Netherlands, where a sand sub-base with a thickness of at least 0.5 m is applied, and the United Kingdom where a granular sub-base (CBR-value at least 15%) is required when the CBR-value of the subgrade is less than 5%. In France, the subgrade dynamic elastic modulus must be more than 120 MPa when heavy traffic is to be carried. The base is the platform upon which the concrete layer is constructed. The United Kingdom specifies a hydraulically bound material only for use in concrete pavements, to ensure a durable, stiff and strong base to resist erosion from the ingress of surface water through joints and cracks. In France, the base is also a lean concrete except when heavy traffic is to be carried. However, owing to frequent erosion problems, the trend in France, Belgium and the Netherlands is to use a 50 to 90 mm thick asphalt concrete interlayer between a CRCP and the base. Countries that allow a variety of base materials are Austria, Belgium, Germany, Poland and Switzerland. Belgium specifies a 200 mm lean concrete base on the most heavily trafficked roads, with 200 mm granular base as an option for less heavily trafficked roads. In Spain the situation is similar but with 150 mm lean concrete base on the most heavily trafficked roads and 200 to 400 mm granular base on less heavily trafficked roads. Austria, Germany, Poland and Switzerland specify either cement-bound or granular bases, with appropriate adjustments to the overlying concrete thickness. In the Netherlands either a


150 mm lean concrete base or a 250 mm granular base is usually applied, where the granular base material is mainly mix granulate (recycled demolition waste, mixture of 50% to 80% (by mass) crushed concrete and crushed masonry).

2.1.6. Concrete thickness

In concrete pavement design the major design output is the thickness of the concrete layer. Figure 1 shows a comparison of the thickness designs for JPCP, based on the following prescribed set of parameters:

Traffic of 5000 commercial vehicles per day on the design traffic lane

Concrete with compressive strength 32 MPa, flexural tensile strength 4 MPa, indirect tensile strength 2.7 MPa

Base modulus amounts 100 MPa

Figure 1. JPCP design thickness for different European countries.

Figure 1 shows that the JPCP design thickness ranges between 220 mm and 310 mm, with Switzerland having the thinnest concrete slab and the United Kingdom having the thickest slab, however the United Kingdom no longer constructs JPCP. In France, the Netherlands and Spain the use of concrete pavements for heavily trafficked roads is limited to CRCP. With the exception of these 3 countries, the JPCP design thickness varies between 220 mm and 280 mm. The same design parameters were also used to derive the CRCP thickness. The results for the 5 countries using such designs show that the CRCP thickness ranges between 200 mm in Belgium and France and 250 mm in the Netherlands, Spain and the United Kingdom.

2.1.7. European Standards

With respect to concrete pavements, in the European Union standards (EN = European Norms) are available for (JOFRÉ, 2006):

materials for concrete pavements

functional requirements and test methods for concrete pavements


dowel and tie bars

joint fillers and sealants Concerning materials for concrete pavements, i.e. the concrete mix and its constituents (aggregates, cement, additions, water, admixtures), the standard EN 13877-1 ‘Concrete pavements – Part 1: Materials’ is valid. This standard is in agreement with the general standards on concrete, i.e. EN 12620 ‘Aggregates for concrete’ and EN 206-1 ‘Concrete – Part 1: Specification, performance, production and conformity’. The standards on the functional requirements and test methods, the dowel and tie bars, and the joint fillers and sealants have been developed by Working Group WG3 of the Technical Committee TC227 in the period between 1991 and 2006. The standards related to the functional requirements, and the test methods thereof, for concrete pavements deal with the strength, thickness, density, freeze-thaw resistance and resistance to wear by studded tires of the concrete as well as with the bond between 2 layers. In the Appendix an overview of the relevant EN standards is given. An in-depth discussion of these 33 standards is outside the scope of this paper.

2.2. Example of mainly empirical design method: Germany

In Germany there is a large scale experience with concrete pavements over a period longer than 100 years. Besides of that, especially in the seventies and eighties quite some numerical analyses, especially into the effects of temperature gradients on the design and performance of Jointed Plain Concrete Pavements, have been done at the Technical University of Munich (EISENMANN ET AL, 2003). Mainly based on experience, guidelines for the design of asphalt pavements, small element pavements and Jointed Plain Concrete Pavements (JPCP) are published and revised on a regular basis since 1925. The most recent guidelines, the so-called RStO 01 (FGSV, 2001), have been published in 2001 and the standardized concrete pavements in those guidelines are briefly discussed here. RStO 01 contains standard JPCP structures as a function of the traffic loading and the type of base material (figure 2). The first row in figure 2 indicates the road class, ranging from class SV (most heavily loaded roads, such as motorways) down to class VI (very lightly loaded rural roads and residential streets). The second row in figure 2 gives the traffic loading during the desired pavement life on the design traffic lane, expressed as the cumulative number of equivalent 100 kN (10 ton) standard axle loads (in millions). The third row in figure 2 gives the required total thickness (in cm) of non frost susceptible materials, which include concrete pavement, cement bound bases, asphalt bases and granular (sub-)bases. The total thickness varies depending on the road class and the


Figure 2. Standard JPCP structures in the German Guidelines RStO 01.

location of the pavement within the country (in the north of Germany there is a relatively mild sea climate while in the east and south there is a colder land climate). The first column in figure 2 refers to the type of base applied below the concrete pavement:

‘1’ indicates a cement-bound base; ‘1.1’ is lean concrete that should have an average compressive strength of at least 12 MPa; ‘1.2’ and ‘1.3’ are lower quality cement-bound granular materials, that should be applied in greater thickness; in contrast to the earlier Guidelines, in RStO 01 a plastic sheet is applied between the concrete pavement and the cement-bound base to prevent reflective cracking from the base into the pavement

‘2’ indicates an asphalt base

‘3’ indicates a granular base


The numbers around the standard JPCP structures are explained for the most upper left structure. The numbers at the right sight of the structure (27, 15 and 42) are the thicknesses (in cm) of the concrete pavement, the base, and the concrete pavement plus the base, respectively. The numbers below the structure are the minimum thicknesses (in cm) of the non frost susceptible sub-base, to fulfill the requirement given in the third row of figure 2. The numbers at the left sight of the structure (45 and 120) are the required minimum value of the ‘deformation modulus’ Ev2 at the indicated level within the structure. This Ev2 is an equivalent modulus for all the underlying layers. A general requirement is that at the top of the subgrade Ev2 should have a value of at least 45 MPa. Ev2 is determined by means of a so-called static plate loading test, in which a stiff circular steel plate is slowly loaded to a specified level and then unloaded, and this load cycle is repeated a number of times. Ev2 is then calculated by means of the equation (based on Burmister’s theory):

2

1.5* *v

p aE

y (MPa) (Equation 1)

where: Ev2 = deformation modulus (MPa) p = applied maximum stress (MPa) a = radius of circular plate (= 150 mm) y = measured rebound (elastic) deformation (mm) during unloading at the 2nd load cycle During construction of the pavement structure Ev2 is actually measured. If the required value is not present, the contractor should take such measures (stabilization, extra compaction, etc.) that the required Ev2-value is met. Only then the contractor is allowed to construct the next pavement layer (this procedure is also followed in Austria and Switzerland). On motorways usually slabs are applied with a length of 5 m and a width of around 4 m, taking into account the lane width and the location of the markings. It is tried to realize more or less square slabs. The length of the slabs should be smaller than 25 times the thickness of the slabs, and should never exceed 7.5 m, to limit the temperature gradient stresses. The limited slab length also limits the joint width variations due to temperature changes and increases the lifetime of the joint filling material. Non-profiled steel dowel bars (diameter 25 mm, length 500 mm), with a plastic coating to prevent corrosion and bond to the concrete, are applied at transverse contraction joints at mid-depth of the concrete pavement at a spacing of 250 mm for better load transfer. Profiled steel tie bars (diameter 20 mm, length 800 mm), 3 bars per 5 m slab length, with a plastic coating at the central ⅓ part, are applied at longitudinal contraction joints at ⅔ of the concrete depth to limit the width of the longitudinal joint.


2.3. Example of mainly analytical design method: the Netherlands

2.3.1. Introduction The current Dutch method for the structural design of jointed plain concrete pavements (JPCP) and continuously reinforced concrete pavements (CRCP), subjected to normal road traffic, is available as a software package called VENCON2.0 that was released early 2005 by CROW (CROW, 2005; HOUBEN ET AL, 2006; HOUBEN ET AL, 2007). The structural design of JPCP is based on a fatigue strength analysis, performed for various potentially critical locations on the pavement, i.e. the free longitudinal edge, the longitudinal joint(s) and the transverse joint in the centre of the wheel tracks. The analysis includes the traffic load stresses (calculated by means of a Westergaard-equation, taking into account the load transfer in the joint or at the edge) and the temperature gradient stresses (calculated by means of a modified Eisenmann theory). For the determination of the thickness of CRCP the pavement is considered as a JPCP, however with modified horizontal ‘slab’ dimensions (because of the presence of transverse cracks instead of joints) and a greater load transfer over the relatively small transverse cracks. Having found the concrete thickness, the required longitudinal reinforcement (to control the crack widths) is then determined. Figure 3. Flow chart of the structural design of jointed plain/reinforced concrete pavements according to the

Dutch VENCON2.0 design method.

Figure 3 gives a scheme of the input and calculation procedure of the VENCON2.0 design method. The items 8 to 10 are not discussed here, reference is made to (HOUBEN ET AL, 2007). The items 1 to 7 mentioned in figure 3 are subsequently discussed in the

1. TRAFFIC LOADINGS: Axle loads Directional factor Design traffic lane Traffic at joints

2. CLIMATE: Temperature gradients

3. SUBSTRUCTURE: Modulus of substructure reaction

5. TRAFFIC LOAD STRESSES: Load transfer at joints Westergaard equation

6. TEMPERATURE GRADIENT STRESSES: Eisenmann/Dutch method

7. THICKNESS PLAIN/REIN- FORCED PAVEMENT: Miner fatigue analysis

9. REINFORCEMENT OF REINFORCED PAVEMENTS: Shrinkage and temperature Tension bar model Crack width criterion

8. ADDITIONAL CHECKS PLAIN PAVEMENTS: Robustness (NEN 6720) Traffic-ability at opening

10. ADDITIONAL CHECKS REINFORCED PAVEMENT: Robustness (NEN 6720) Traffic-ability at opening Parameter studies

4. CONCRETE: Strength Parameters Elastic modulus


paragraphs 2.3.2 to 2.3.8. Some calculation results of the VENCON2.0 design method for JPCP are given in paragraph 2.3.9.

2.3.2. Traffic loadings

The traffic loading is calculated as the total number of axles per axle load group (> 20 kN) on the design traffic lane during the desired life of the concrete pavement. In the calculation is included:

the division of the heavy vehicles per direction; for roads having one carriageway the directional factor depends on the width of the carriageway, for roads having two carriageways the directional factor is taken as 0.5;

in the case that there is more than 1 traffic lane per direction: the percentage of the heavy vehicles on the most heavily loaded lane (the design traffic lane); this percentage varies from 100% (1 lane per direction) till 80% (4 lanes per direction);

the average number of axles per heavy vehicle (table 2). In the case that no real axle load data is available, for a certain type of road the default axle (wheel) load frequency distribution, given in table 2, can be used. These frequency distributions are based on axle load measurements on a great number of provincial roads in the Netherlands in the years 2000 and 2001. In the design method all the truck axles are taken into account. Note that the highest axle load group in table 2 is 200-220 kN! Table 2 makes clear that also in the Netherlands there are quite some overloaded axles and these really should be taken into account when designing a concrete pavement.

Table 2. Default axle load frequency distributions for different types of roads.

Axle load group (kN)

Average wheel load P (kN)

Axle load frequency distribution (%) for different types of road

heavily loaded motorway

normally loaded motorway

heavily loaded provincial road

normally loaded provincial road

municipal main road

rural road

public transport bus lane

20-40 15 20.16 14.84 26.62 24.84 8.67 49.38 -

40-60 25 30.56 29.54 32.22 32.45 40.71 25.97 -

60-80 35 26.06 30.22 18.92 21.36 25.97 13.66 -

80-100 45 12.54 13.49 9.46 11.12 13.66 8.05 -

100-120 55 6.51 7.91 6.50 6.48 8.05 2.18 100

120-140 65 2.71 3.31 4.29 2.70 2.18 0.38 -

140-160 75 1.00 0.59 1.64 0.83 0.38 0.38 -

160-180 85 0.31 0.09 0.26 0.19 0.38 0.00 -

180-200 95 0.12 0.01 0.06 0.03 0.00 0.00 -

200-220 105 0.03 0.01 0.03 0.00 0.00 0.00 -

Av. nr. of axles per heavy vehicle

3.5 3.5 3.5 3.5 3.5 3.1 2.5

Different types of tire are included in the VENCON2.0 design method:

single tires, that are mounted at front axles of heavy vehicles;

dual tires, that are mounted at driven axles, and sometimes at trailer axles;

wide base tires, that are mostly mounted at trailer axles;

extra wide wide base tires, that in future will be allowed for driven axles.


Every tire contact area is assumed to be rectangular. In the Westergaard equation for calculation of the traffic load stresses, however, a circular contact area is used. The equivalent radius a of the circular contact area of the tire is calculated by:

* 0.0028* 51a b P (mm) (Equation 2)

where: b = parameter dependent on the type of tire (table 3) P = average wheel load (N) of the axle load group

Some default tire type frequency distributions are included in the design method (table 3).

Table 3. Value of parameter b (equation 2) for different types of tire.

Type of tire Width of rectangular contact area(s) (mm)

Value of parameter b of equation 2

Frequency distribution (%)

roads public transport bus lanes

Single tire 200 9.2 39 50

Dual tire 200-100-200 12.4 38 50

Wide base tire 300 8.7 23 0

Extra wide wide base tire 400 9.1 0 0

2.3.3. Climate

With respect to the climate especially the temperature gradients in the concrete pavement are important. In the years 2000 and 2001 the temperature gradient has continuously been measured on a stretch of the newly build motorway A12 near Utrecht in the centre of the Netherlands. The continuously reinforced concrete pavement has a thickness of 250 mm and the measurements were done before the porous asphalt wearing course was constructed. Based on these measurements it was decided to include the default temperature gradient frequency distribution shown in table 4 in the current design method.

Table 4. Default temperature gradient frequency distribution.

Temperature gradient class (ºC/mm)

Average temperature gradient ΔT (ºC/mm)

Frequency distribution (%)

0.000 – 0.005 0.0025 59

0.005 – 0.015 0.01 22

0.015 – 0.025 0.02 7.5

0.025 – 0.035 0.03 5.5

0.035 – 0.045 0.04 4.5

0.045 – 0.055 0.05 1.0

0.055 – 0.065 0.06 0.5


2.3.4. Substructure

The rate of support of the pavement by the substructure is an important parameter in the structural design of concrete pavements. The substructure includes all the layers beneath the concrete pavement, so the base, the sub-base and the subgrade. The rate of support is represented by the modulus of substructure reaction k at the top of the base. Starting point for the calculation of the k-value is the modulus of subgrade reaction ko at the top of the subgrade. Among other things table 5 shows the ko-values that are used in VENCON2.0.

Table 5. Modulus of subgrade reaction ko of Dutch subgrades.

Subgrade Cone resistance qc (N/mm2)

CBR-value (%)

Dynamic modulus of elasticity Esg (N/mm2)

Modulus of subgrade reaction ko (N/mm3)

Peat 0.1 - 0.3 1 - 2 25 0.016

Clay 0.2 - 2.5 3 - 8 40 0.023

Loam 1.0 - 3.0 5 - 10 75 0.036

Sand 3.0 - 25.0 8 - 18 100 0.045

Gravel-sand 10.0 - 30.0 15 - 40 150 0.061

To obtain the modulus of substructure reaction k at the top of the base, equation 3 has to be applied for each layer (first the sub-base, then the base):

3 54

1 2 42.7145*10 *( * * )C C

k C C e C e (N/mm3) (Equation 3)

where: C1 = 30 + 3360*ko C2 = 0.3778*(hb – 43.2) C3 = 0.5654*ln(ko) + 0.4139*ln(Eb) C4 = -283 C5 = 0.5654*ln(ko) ko = modulus of subgrade/substructure reaction at top of underlying layer (N/mm3) hb = thickness of layer under consideration (mm) Eb = dynamic modulus of elasticity of layer under consideration (N/mm2) k = modulus of substructure reaction at top of layer under consideration (N/mm3) The boundary conditions for equation 3 are: 1. hb ≥ 150 mm (bound material) and hb ≥ 200 mm (unbound material) 2. every layer has an Eb-value that is greater than the Eb-value of the underlying layer 3. log k ≤ 0.73688*log(Eb) – 2.82055 4. k ≤ 0.16 N/mm3 The second boundary condition implies that in the case of the application of a very light-weight fill of Expanded Polystyrene Foam, EPS (that has a dynamic modulus of elasticity of not more than Eb = 6 to 10 N/mm2, depending on its volume weight), this layer has to be considered as the subgrade in the calculation of the modulus of substructure reaction k.


2.3.5. Concrete

Various concrete grades are applied in the top layer of concrete pavements (table 6). In the old Dutch Standard NEN 6720 (1995), valid until July 1, 2004, the concrete grade was denoted as a B-value where the value represented the characteristic (95% probability of exceeding) cube compressive strength after 28 days for loading of short duration1 (f’ck in N/mm2). In the new Standard NEN-EN 206-1 (NEN, 2001), or the Dutch application Standard NEN 8005 that is valid since July 1, 2004, the concrete grade is denoted as C-values where the last value represents the characteristic (95% probability of exceeding) cube compressive strength after 28 days for loading of short duration while the first value represents the characteristic cylinder compressive strength at the same conditions (table 6).

Table 6. Concrete grades used in road construction in the Netherlands.

Concrete grade Characteristic (95% probability of exceeding) cube compressive strength after 28 days for loading of short duration, f’ck (N/mm2) B-value C-values

B35 B45

C28/35 C35/45

35 45

Generally on heavily loaded jointed plain concrete pavements, such as motorways and airport platforms, the concrete grade C35/45 is used. On lightly loaded jointed plain concrete pavements (bicycle tracks, rural roads, etc.) mostly concrete grade C28/35 and sometimes C35/45 is applied. In continuously reinforced concrete pavements mostly the concrete grade C28/35 is applied and sometimes the concrete grade C35/45. According to both the CEB-FIP Model Code 1990 (CEB, 1993) and the Eurocode 2 (EUROCODE, 2002) the mean cube compressive strength after 28 days for loading of short duration (f’cm) is:

' ' 8cm ckf f (N/mm2) (Equation 4)

For the structural design of concrete pavements not primarily the compressive strength but the flexural tensile strength is important. In accordance with the Eurocode 2, in the VENCON2.0 design method the mean flexural tensile strength (fbrm) after 28 days for loading of short duration is defined as a function of the thickness h (in mm) of the concrete slab:

16001.3*[ ]*[1.05 0.05*( ' 8)]/1.2

1000brm ck

hf f

(N/mm2) (Equation 5)

1 loading of short duration: loading during a few minutes loading of long duration: static loading during 103 to 106 hours, or dynamic loading with about 2.106 load cycles


The mean flexural tensile strength (fbrm) is used in the fatigue analysis (see paragraph 2.3.8).

Except the strength also the stiffness (i.e. Young’s modulus of elasticity) of concrete is important for the structural design of concrete pavements. The Young’s modulus of elasticity of concrete depends to some extent on its strength. According to NEN 6720 (NEN, 1995) the Young’s modulus of elasticity Ec can be calculated with the equation:

22250 250* 'c ckE f (N/mm2) with 15 ≤ f’ck ≤ 65 (Equation 6)

For the two concrete grades applied in concrete pavement engineering, table 7 gives some strength and stiffness values. Besides some other properties are given, such as the Poisson’s ratio (that plays a role in the calculation of traffic load stresses, see paragraph 2.3.6) and the coefficient of linear thermal expansion (that plays a role in the calculation of temperature gradient stresses, see paragraph 2.3.7).

Table 7. Mechanical properties of (Dutch) concrete grades for concrete pavement structures.

Property Concrete grade

C28/35 (B35)

C35/45 (B45)

Characteristic* cube compressive strength after 28 days for loading of short duration, f’ck (N/mm2)

35 45

Mean cube compressive strength after 28 days for loading of short duration, f’cm (N/mm2)

43 53

Mean tensile strength after 28 days for loading of short duration, fbt (N/mm2)

3.47 4.01

Mean flexural tensile strength after 28 days for loading of short duration, fbrm (N/mm2): concrete thickness h = 180 mm h = 210 mm h = 240 mm h = 270 mm

4.92 4.82 4.71 4.61

5.69 5.57 5.45 5.33

Young’s modulus of elasticity, Ec (N/mm2) 31000 33500

Density (kg/m3) 2300 - 2400

Poisson’s ratio ν 0.15 – 0.20

Coefficient of linear thermal expansion α (°C-1) 1∙10-5 – 1.2∙10-5 * 95% probability of exceeding

2.3.6. Traffic load stresses

The tensile flexural stress due to a wheel load P at the bottom of the concrete slab along a free edge, along a longitudinal joint, along a transverse joint (jointed plain concrete pavements) and along a transverse crack (continuously reinforced concrete pavement) is


calculated by means of the ‘new’ Westergaard equation for a circular tire contact area (IOANNIDES ET AL, 1987):

3

2 4

3 1 4 11.84 1.18 1 2

3 100 3 2

cal cP

P E h al n

h k a l

(Equation 7)

where:

P = flexural tensile stress (N/mm²) Pcal = wheel load (N), taking into account the load transfer (equation 8) a = equivalent radius (mm) of circular contact area (equation 2 and table 3) Ec = Young’s modulus of elasticity (N/mm²) of concrete (equation 6 and table 7)

= Poisson’s ratio of concrete (usually taken as 0.15) h = thickness (mm) of concrete slab k = modulus of substructure reaction (N/mm3) (Equation 3)

l = 3

42

*

12*(1 )*

cE h

k = radius (mm) of relative stiffness of concrete slab

The load transfer W at edges/joints/cracks is incorporated in the design of concrete pavement structures by means of a reduction of the actual wheel load P to the wheel load Pcal (to be used in the Westergaard equation) according to:

1 0.5* /100 * 1 *200

calW

P W P P

(Equation 8)

The contribution of the base to the load transfer W has been determined by means of the model for a slab on a Pasternak-foundation (VAN CAUWELAERT, 2003). In the VENCON2.0 design method the following values for the load transfer W are included:

free edge of jointed plain or continuously reinforced concrete pavement (at the outside of the carriageway): - W = 20% in the case that a unbound base is applied; - W = 35% in the case that a bound base is applied;

longitudinal joints in jointed plain or reinforced concrete pavements: - W = 20% and 35% respectively at non-profiled construction joints without tie bars

in jointed plain concrete pavements on a unbound and a bound base respectively; - W = 50% and 60% respectively at non-profiled construction joints with tie bars and

dowel bars respectively in jointed plain concrete pavements; - W = 50% at non-profiled construction joints with transverse reinforcement in

continuously reinforced concrete pavements; - W = 35% at contraction joints without any load transfer devices in jointed plain and

continuously reinforced concrete pavements; - W = 70% and 80% respectively at contraction joints with tie bars and dowel bars

respectively in jointed plain concrete pavements;


- W = 70% at contraction joints with transverse reinforcement in continuously reinforced concrete pavements;

transverse joints/cracks in jointed plain or continuously reinforced concrete pavements: - W = 90% at cracks in continuously reinforced concrete pavement; - W = 20% and 35% respectively at non-profiled construction joints without dowel

bars in jointed plain concrete pavements on a unbound and a bound base respectively;

- W = 60% at construction joints with dowel bars in jointed plain concrete pavements;

- W = 80% at contraction joints with dowel bars in jointed plain concrete pavements; - W according to equation 9 at contraction joints without dowel bars in jointed plain

concrete pavements:

2 2[5*log( . ) 0.0025* 25]*log 20*log( * ) 0.01* 180W k l L Neq k l L (Equation 9)

In equation 9 is: W = joint efficiency (%) at the end of the pavement life L = length (mm) of concrete slab k = modulus of substructure reaction (N/mm3) l = radius (mm) of relative stiffness of concrete slab Neq = total number of equivalent 50 kN standard wheel loads in the centre of the wheel track during the pavement life, calculated with a 4th power, i.e. the load equivalency factor leq = (P/50)4 with wheel load P in kN

2.3.7. Temperature gradient stresses

In VENCON2.0 the stresses due to positive temperature gradients are only calculated along the edges of the concrete slab (as, from a structural point of view, the weakest point of the pavement always is somewhere at an edge and never in the interior of the concrete slab). Starting point for the calculation of the temperature gradient stresses is a beam (of unit width) along an edge of the concrete slab (LEEWIS, 1992).

In the case of a small positive temperature gradient T the maximum upward displacement due to curling of the beam is smaller than the downward displacement due to the compression of the substructure (characterized by the modulus of substructure reaction k) because of the deadweight of the beam. In this case the beam remains fully supported over the whole length. The flexural tensile stress σT at the bottom of the concrete slab along the edge, joint or crack is then equal to (figure 4 – left):

** *

2cT

h TE

(Equation 10)

where: σT = flexural tensile stress (N/mm2) at the bottom of the concrete slab due to a small


positive temperature gradient ΔT (°C/mm) h = thickness (mm) of the concrete slab α = coefficient of linear thermal expansion of concrete (usually taken as 1.10-5 ºC-1) Ec = Young’s modulus of elasticity (N/mm²) of concrete (equation 6 and table 7)

Figure 4. Effect of small (left) and great (right) positive temperature gradient on the behavior of a concrete

pavement.

In the case of a great positive temperature gradient T the maximum upward displacement due to curling of the beam is greater than the downward displacement due to the compression of the substructure because of the deadweight of the beam. In this case the beam is only supported over a certain length C at either end. The flexural tensile stress σT

at the bottom of the concrete slab along the edge, joint or crack (assuming a volume weight of the concrete of 24 kN/m3) is then equal to (figure 4 – right):

longitudinal edge: 5 '21.8*10 * /T L h (Equation 11a)

transverse edge: 5 '21.8*10 * /T W h (Equation 11b)

The slab span in the longitudinal direction (L’) and in the transverse direction (W’) is equal to:

' 2*

3L L C (Equation 12a)

' 2*

3W W C (Equation 12b)

where: L = length (mm) of the concrete slab W = width (mm) of the concrete slab C = supporting length (mm), which is equal to (4):


4.5**

hC

k T

if C << L (Equation 13)

The actually occurring flexural tensile stress at the bottom of the concrete slab due to a temperature gradient ΔT at a free edge, joint or crack is the smallest value resulting from the equations 10 and 11a (free edge or longitudinal joint) or the smallest value resulting from the equations 10 and 11b (transverse joint or crack).

2.3.8. Slab thickness of JPCP and CRCP

In the case of a JPCP on a 2-lane road the fatigue strength analysis is carried out for the following locations of the design concrete slab:

the wheel load just along the free edge of the slab;

the wheel load just along the longitudinal joint between the traffic lanes;

the wheel load just before the transverse joint. In the case of a multi-lane road (e.g. a motorway) the strength analysis is also done for:

the wheel load just along every longitudinal joint between the traffic lanes;

the wheel load just along the longitudinal joint between the entry or exit lane and the adjacent lane.

In the case of a CRCP the strength analysis is done for two locations of the design concrete ‘slab’:

the wheel load just before a transverse crack;

the wheel load just along a longitudinal joint.

Both for JPCP and CRCP the flexural tensile stress (Pi) at the bottom of the concrete slab due to the wheel load (Pi) in each of the mentioned locations is calculated by means of the Westergaard equation (equation 7), taking into account the appropriate load transfer (joint efficiency W, equations 8 and 9) in the respective joints/cracks.

Both for JPCP and CRCP the flexural tensile stress (Ti) at the bottom of the concrete slab due to a positive temperature gradient (ΔTi) in each of the mentioned locations is calculated by means of the equations 10 to 13. In the case of JPCP the horizontal slab dimensions (length L, width W) are predefined. In the case of CRCP the width W of the ‘slab’ is predefined (distance between free edge and adjacent longitudinal joint or distance between two adjacent longitudinal joints), the length L of the ‘slab’ is arbitrarily taken as 1.35*W, with L ≤ 4.5 m. Both for JPCP and CRCP the structural design is based on a fatigue analysis for all the mentioned locations of the pavement. The following fatigue relationship is used (CROW, 1999):

max

max

min

12.903*(0.995 / )log 0.5 / 0.833

1.000 0.7525* /

i

i

brm

brmibrm

fN with f

f

(Equation 14)


where:

Ni = allowable number of repetitions of wheel load Pi i.e. the traffic load stress Pi till

failure when a temperature gradient stress Ti is present

mini = minimum occurring flexural tensile stress (= Ti)

maxi = maximum occurring flexural tensile stress (= Pi + Ti) fbrm = mean flexural tensile strength (N/mm2) after 28 days for loading of short duration (equation 5) The design criterion (i.e. cracking occurs), applied on every of the above-mentioned locations of the JPCP or CRCP, is the cumulative fatigue damage rule of Palmgren-Miner:

1.0i

i i

n

N (Equation 15)

where:

ni = occurring number of repetitions of wheel load Pi, i.e. the traffic load stress Pi,

during the pavement life combined with a temperature gradient stress Ti due to the temperature gradient ΔTi

Ni = allowable number of repetitions of wheel load Pi, i.e. the traffic load stress Pi, till

failure combined with a temperature gradient stress Ti due to the temperature gradient ΔTi Lateral wander within a traffic lane is taken into account when analyzing a transverse joint or crack, with 50% to 100% of the traffic loads driving in the centre of the wheel track. When analyzing a longitudinal free edge or longitudinal joint the number of traffic loads just along the edge or joint is limited to 1% to 3% (free edge) or 5% to 10% (every longitudinal joint) of the occurring total number of traffic loads on the carriageway (so not the design traffic lane).

2.3.9. Design examples for JPCP

In this paragraph, for a JPCP design results obtained by means of the program VENCON2.0 for a specific case will be presented. The case concerns a 7.5 m wide 2-lane provincial road. Because the width of the pavement is more than 4.5 to 5 m a longitudinal contraction joint is required in the road axis to prevent uncontrolled (‘wild’) longitudinal cracking. Tie bars are applied in the longitudinal joint, resulting in the load transfer W = 70% (see paragraph 2.3.6). The following JPCP structure is taken into account:

plain concrete slabs, width 3.75 m (equal to the lane width) and length 4.5 m (to limit the ratio of length and width of the slabs); the transverse contraction joints are


provided with dowel bars, which means that the load transfer W = 80% (see paragraph 2.3.6);

250 mm thick cement-bound base (E = 6000 MPa), that is not bonded to the concrete slabs (safe assumption); the bound base results in a load tranfer at the free edge of the pavement W = 35% (see paragraph 2.3.6);

500 mm sand sub-base (E = 100 MPa);

subgrade with E = 100 MPa which equals a modulus of subgrade reaction ko = 0.045 N/mm3.

The modulus of substructure reaction (k-value of subgrade, sub-base plus base) is equal to the maximum value k = 0.16 N/mm3 (see paragraph 2.3.4, equation 3). The default temperature gradient frequency distribution of VENCON2.0 is applied (table 4). With respect to the traffic loading, it is assumed that heavy vehicles are driving on the road on 300 days per year. The heavy traffic is equally divided over the 2 traffic lanes. The traffic growth is 3% per year. On average a heavy vehicle has 3 axles. The default frequency distribution of the types of tire of VENCON2.0 is used (see table 3, one but last column). It is assumed that 50% of the heavy vehicles on a traffic lane drive exactly in the centre of the wheel track. It is furthermore assumed that 2% of the heavy vehicles on the road drive exactly along the edge of the pavement and that 10% of the heavy vehicles on the road drive exactly along the longitudinal joint. In the calculations the following parameters are varied:

the concrete grade: C28/35 or C35/45 (see paragraph 2.3.5);

the axle load frequency distribution on the provincial road: heavily loaded provincial road (table 2, 5th column) or normally loaded provincial road (table 2, 6th column);

the number of heavy vehicles per day on a traffic lane in the 1st year: 10, 100 or 1000;

the design life of the pavement: 20, 30 or 40 years. The calculation results (thickness of the concrete slabs) for the JPCP are given in table 8. The mentioned thicknesses include 15 mm extra concrete on top of the minimum thickness calculated by means of the VENCON2.0 program.

Table 8. Design thickness (mm) of JPCP for 2-lane provincial road according to VENCON2.0.

Concrete grade C28/35 (B35) C35/45 (B45)

Axle load frequency distribution on provincial road

Heavy Normal Heavy Normal

Number of heavy vehicles per day on traffic lane in 1

st year

10 100 1000 10 100 1000 10 100 1000 10 100 1000

Design life 20 years 234 247 263 224 238 253 208 221 235 199 212 227




In this case study the centre of the free edge of the pavement is always governing the thickness design of the JPCP. The centre of the longitudinal joint and the centre of the wheel track at the transverse joint are never decisive for the design. Table 8 shows that the most influencing factors on the JPCP thickness are:

the concrete grade: concrete C35/45 results in 25 to 30 mm thinner slabs compared to concrete C28/35 (due to the better fatigue behaviour, see table 7 and equation 14);

the heavy axle load frequency distribution (highest axle load group 200-220 kN, see table 2) requires about 10 mm thicker concrete slabs than the normal axle load frequency distribution (highest axle load group 180-200 kN);

the number of heavy vehicles: a 10 times greater number of heavy vehicles requires about 15 mm thicker concrete slabs;

the design life: a 2 times longer design life requires only 5 to 10 mm thicker concrete slabs.

2.4. Concluding remarks on design methods for concrete pavements

It has to be emphasized that one has to be careful with the application of empirical design methods. They only can be applied with confidence in those areas where all relevant local circumstances (such as climate, type of traffic, axle loads, material properties, construction details, drainage measures, construction techniques and equipment, etc.) are (nearly) the same as those in the areas/countries for which the method was developed. Certainly when there is a lack of experience with concrete pavements an analytical concrete pavement design procedure is preferable above an empirical design method. However, the quality of such an analytical design procedure is totally dependent on:

the reliability of the values to be used for the various input parameters, such as the temperature gradient frequency distribution, the number of repetitions of every axle load group, the concrete layer characteristics (especially the flexural tensile strength and the fatigue relationship), the joint/crack (load transfer) characteristics and the substructure characteristics (especially the resistance to erosion of the base and the modulus of substructure reaction);

the quality of the theory or method used to calculate the flexural tensile stresses (and deflections) due to external loadings, such as traffic loadings, temperature gradients and unequal subsoil settlements; the finite element method is assumed to give the most accurate calculation results.

It will be clear that it requires extensive material and analytical research to develop a sound analytical concrete pavement design method for local circumstances.

3 Construction of concrete pavements

3.1. Modern construction techniques

The construction of a concrete pavement requires a number of activities which are briefly described in this paragraph (CROW, 2004). These activities are the production of the concrete mix, the transport of the concrete mix to the works site, the actual construction of


the pavement, creating the texture of the pavement surface, protecting the pavement surface, creating the joints and opening of the pavement to traffic.

3.1.1. Mixing plants

Stationary concrete mixing plants are readily available in most European countries. As these plants also have to serve other clients their capacity for road construction works is mostly limited. Stationary plants are thus only an option for small scale construction works. This might result in longer transport distances which increases the transport costs and the risk for delayed delivery (e.g. when the trucks are stuck in traffic jams) and stand-still of the construction equipment. For larger scale works one or more mobile concrete mixing plants are erected close to the works site. Such mobile plants have a capacity of a few hundred tons per hour. In this case the transport distances are very limited. However, such plants require large areas for stockpiles of raw materials (figure 5) and supplies such as water and electricity which in the densely populated European countries usually are available in the vicinity of the works site.

Figure 5. Overview of mobile concrete mixing plant (CROW, 2004).

3.1.2. Transport The means of transport of the concrete mix to the construction equipment depends on the required consistency of the concrete. A slipformpaver requires a rather dry concrete (water/cement-ratio 0.40 to 0.45) which is transported in open trucks. The fresh concrete mix is covered by canvas to protect it against wetting (rain) and drying (sun, wind). A rolling finisher and manual construction require a concrete mix with a higher slump. This mix is normally transported by truck mixers and brought into the works site by the mixers themselves or by means of a concrete pump. The required number of trucks depends on the capacity of the mixing plants, the capacity of the trucks, the loading time at the mixing plant, the maximum travel distance from the mixing plant to the works site vice versa, the dumping time at the mixing plant, and the capacity of the construction equipment at the works site.


If there are no obstacles in front of the construction equipment the concrete mix can be dumped just in front of the construction equipment (figure 6-left). If there are however obstacles, such as dowel bars and tie bars installed prior to pouring of the concrete (JPCP) or reinforcement (CRCP), then the concrete has to be dumped from the side (figure 6-right).

Figure 6. Dumping of the concrete mix just in front of construction equipment (left) or from the side (right) (CROW, 2004).

3.1.3. Construction equipment

The normal equipment to construct concrete pavements in Europe is the slipformpaver. For special projects a rolling finisher is applied. Manual construction is only done in special cases.

3.1.3.1. Slipformpaver

A slipformpaver is a (very) heavy piece of construction equipment and is provided therefore with tracks. During construction of the concrete pavement the slipformpaver is driving over the base which therefore not only needs to be strong enough to carry the equipment but also needs to be about 0.5 m wider than the concrete pavement. A slipformpaver runs with a speed of 0.5 to 1.0 m/minute. The formwork for the concrete pavement is within the slipformpaver which means that the concrete mix is only a few minutes within the formwork and after that the concrete has to ‘stand upright’. Therefore the water/cement-ratio has to be quite low (0.40 – 0.45). Figure 7 shows a top view and a side view of a slipformpaver. The letters in figure 7 point to the following components of a slipformpaver: a = tracks g = supersmoother b = 4 hydraulic sensors for height h = distributing unit c = 2 hydraulic sensors for direction j = hydraulic leveling plate d = vibrating dowel bar inserter k = high frequency vibrating needles e = vibrating tie bar inserter l = stamping knife f = vibrating leveling beam m = adjustable profile pan (formwork top/sides) Slipformpavers are available in different sizes (table 9). Examples are shown in figure 8, where the small size slipformpaver at the right is constructing the kerb of a roundabout..


Figure 7. Top view (above) and side view (below) of a slipformpaver (CROW, 2004).

Table 9. Some characteristics of different sized slipformpavers (CROW, 2004).

Size Large Medium Small

Weight (tons) 60 – 100 20 – 45 10 – 20

Width of pavement (m) 6 – 18 3 – 8 ≤ 4

Thickness of pavement (m) 0.2 – 0.6 0.15 – 0.25 ≤ 0.2

Applications motorways provincial roads large areas

provincial roads rural roads roundabouts airport platforms

small rural roads bicycle tracks safety barriers kerbs, gutters

Figure 8. Large, medium and small slipformpaver (from left to right) (CROW, 2004).


Slipformpavers are guided, with respect to the direction of travel and the height of the concrete surface, through sensors running over steel wires at both sides of the pavement (figure 9). The steel wires have to be positioned and leveled very accurately, and during construction of the concrete pavement their position and level have to be checked continuously.

Figure 9. Sensors of slipformpaver (at centre bottom of pictures) running over steel wire.

The slipformpavers are provided with automatic dowel bar and tie bar inserters (figure 10-left).

Figure 10. Positioning dowel bars by means of vibrating them in by slipformpaver (left) or by installing them

on chairs prior to pouring of the concrete (right) (CROW, 2004).

In case of a JPCP, at the predefined locations the dowel bars (transverse contraction joints) and tie bars (longitudinal contraction joints) are vibrated into the fresh concrete down to the required depth, generally mid-depth of the concrete layer. The round dowel bars usually consist of FeB 220 HWL and have a length of 500 to 600 mm and a diameter of 25 mm. The dowel bars are coated to prevent bond to the concrete and thus allowing horizontal movements of the concrete slabs due to temperature variations without any structural damage. The profiled tie bars (usually 3 per slab length) consist of FeB500 HWL, have a length of 800 mm and a diameter of 16 or 20 mm. The central ⅓ part of the tie bars is coated to spread the movement of the longitudinal joint (due to shrinkage of the


concrete and temperature variations) over greater length to prevent the tie bar from yielding. Sometimes the dowel bars and tie bars are placed on ‘chairs’ prior to pouring of the concrete (figure 10-right). In this case the chairs have to be very well fixed to the base layer and the bars have to be very well fixed to the chair to prevent their movement during pouring of the concrete. In case of CRCP the longitudinal reinforcement, supported by a small amount of transverse reinforcement, is installed prior to pouring of the concrete (figure 8-left and figure 9-right). The transverse reinforcement continues at the location of the longitudinal contraction joints, so no tie bars are applied there. In case of longitudinal construction joints the tie bars can be ‘shooted’ in the fresh concrete (figure 11-left and –middle) or can be glued in holes drilled in the hardened concrete (figure 11-right).

Figure 11. Inserting tie bars in longitudinal construction joints (CROW, 2004).

Modern slipformpavers are provided with a so-called supersmoother (figure 7 and figure 12-left) to obtain a better longitudinal evenness (figure 12-right).

Figure 12. Supersmoother at backside of slipformpaver (left) and endproduct of slipformpaver (right) (CROW,

2004).

3.1.3.2. Rolling finisher

A so-called rolling finisher is used to construct special projects, e.g. roundabouts (figure 13-left). The concrete, brought into the works site by means of a truck mixer or a concrete


pump, is constructed between a formwork or between earlier made/placed kerbs or gutters. The rolling finisher is guided through sensors running over steel wires. Compaction of the concrete is done by means of vibrating needles and leveling the concrete surface is done through rollers (figure 13-right). The production rate of a rolling finisher is lower than that of a slipformpaver.

Figure 13. Rolling finisher (CROW, 2004).

3.1.3.3. Manual construction

Manual construction of concrete pavements is only done on small scale in Europe. However, in case of very small scale or irregular projects manual construction is the only option, e.g. concrete pavements with varying width, thin concrete layers (< 100 mm, thin overlays), connections and repair works. The concrete is poured between an existing pavement (figure 14-left), formwork (figure 14-right), kerbs or gutters. Manual construction requires vibrating needles and a vibrating leveling beam.

Figure 14. Manual construction of concrete pavements (CROW, 2004).

3.1.4. Texture

Immediately after pouring of the concrete the pavement surface needs to be textured to obtain sufficient skid resistance. Texturing is normally done manually by means of a fine


brush and should result in a texture depth (as measured by means of the sand patch method) of 0.7 to 1.0 mm (figure 15-left). The traffic rolling noise level of such a textured concrete pavement surface is around 2 dB(A) higher than that of a dense asphalt concrete pavement surface.

Figure 15. Normal concrete pavement surface texture resulting from brushing (left) and ‘exposed aggregate’

surface texture (centre and right).

In European countries where reduction of traffic noise is (becoming increasingly) important, such as the Netherlands, Belgium and Germany, another type of concrete pavement surface treatment is applied more and more. This special treatment is called ‘exposed aggregate surface’. Immediately after pouring of the concrete a liquid retarder (which retards the concrete hardening and also acts as a curing compound) is spread at the concrete which then has to be covered, both at the top and at the sides of the pavement, with a plastic sheet to prevent drying out of the fresh concrete (figure 16-bottom). After about 1 day the non-hardened cement paste at the pavement surface is removed by brushing (figure 15-centre). After brushing the concrete pavement surface has to be protected further against drying out of the concrete by means of the application of a curing compound (see paragraph 3.1.5). From the point of view of traffic noise reduction the best result is obtained if rather fine coarse aggregate (with a discontinuous grading) 4/7 mm or 5/8 mm is applied in the concrete mix and the maximum texture depth, measured with the sand patch method, is about 1.4 mm (figure 15-right). In this case the traffic rolling noise is 1 to 2 dB(A) lower than that of a dense asphalt concrete pavement surface. Further reduction of traffic noise is possible through the application of porous concrete. In situ constructed porous concrete has been tried on a few roads in Germany and the Netherlands but has not been very successful. However, in the Netherlands an innovative precast concrete pavement has been developed and recently applied within a junction between 2 motorways, which is promising in this respect (see chapter 4).

3.1.5. Protection of fresh concrete

After pouring of the concrete, some kind of measure has to be taken to protect the fresh concrete primarily against drying out (that would result in a lot of fine surface cracks) due to high temperatures, sun radiation and wind.


The most widely used protection measure is to uniformly apply, mechanically or manually, a curing compound which is mostly based on paraffin. This has to be applied in an amount of 150 to 200 grams/m2, not only at the pavement surface but also at the pavement sides (figure 16-top). Sometimes a plastic sheet is applied, also at the surface and sides of the concrete pavement. However, a plastic sheet may disturb the surface texture. Occasionally burlaps (that have to be kept wet) or a roof, fixed or pulled by equipment, are applied. Especially a roof protects the fresh concrete pavement surface against mechanical damage.

Figure 16. Application of curing compound (top) and plastic sheet after spreading of a retarder for ‘exposed

aggregate surface’ (bottom).

3.1.6. Joints

Four types of joints in concrete pavements can be distinguished: 1. contraction joints 2. construction joints 3. ‘day’ joints 4. expansion joints Contraction joints are required at predefined locations to prevent uncontrolled cracking of the concrete pavement due to shrinkage of the concrete and decrease of the temperature of the concrete. In JPCP both transverse and longitudinal contraction joints are present, in CRCP only longitudinal contraction joints. The contraction joints are obtained by sawing the concrete pavement until a depth of 35% to 40% (longitudinal joints) or 30% to 35%


(transverse joints) of the concrete pavement thickness (figure 17-left); the width of the saw cut is 3 mm. Sawing must be done as soon as possible, but not later than 12 to 24 hours after pouring of the concrete. Usually all of the longitudinal contraction joints and most of the transverse contraction joints really crack through (figure 17-centre). Contraction joints can also be made by pushing a plastic strip into the fresh concrete (figure 17-right), but this is done rarely, also because the obtained joints are not very straight. A construction joint occurs when 2 adjacent concrete strips are constructed at different times. At the side of the eldest concrete strip tie bars have to be inserted in case of a road (figure 11) or dowel bars in case of an airport platform as that can be loaded in any direction (figure 18).

Figure 17. Sawing a contraction joint (left), a cracked contraction joint (centre) and the use of a plastic strip to

create a contraction joint (right) (CROW, 2004).

Figure 18. Dowel bars in a construction joint of an airport platform (CROW, 2004).

So-called ‘day joints’ are required if the construction of the concrete pavement stops for whatever reason (end of the production day, shortage of concrete, breakdown of equipment). In this case the last part of the concrete has to be removed, holes have to be driven mid-depth in the hardening concrete, dowel bars have to be glued and then construction can be continued (figure 19). Such a day joint should not be closer than 1 m to a regular transverse contraction joint.


Figure 19. Day joint (CROW, 2004).

Expansion joints are required when the concrete pavement is ending, e.g. before a bridge or another type of pavement, and also before and after curves with a rather small radius (figure 20-right). Usually 2 or 3 expansion joints are applied. Each expansion joint has a width of 25 to 30 mm, is provided with dowel bars for load transfer and is filled with compressible material (figure 20-left).

Figure 20. Construction of an expansion joint prior to pouring of the concrete (left) and expansion joint near a

roundabout (right) (CROW, 2004).

Figure 21: Joint filling materials: warm bituminous material (left), cold material (centre) and premanufactured

profile (right) (CROW, 2004).


In major roads the joints are usually filled to prevent the intrusion of water, dust, fine aggregates, etc. In minor roads the joints normally remain unfilled. When joints are filled, first the upper part of the 3 mm wide contraction joint has to be widened to 8 or 12 mm to limit the relative deformations within the joint filling material due to contraction and expansion of the concrete slabs due to shrinkage of the concrete and temperature changes. The widened joints have to be cleaned carefully with high pressure air before application of the filling. Three types of joint filling can be applied: • Warm bituminous material (figure 21-left).

The bottom of the widened joint first has to be closed by means of a chord. The material has to be applied strictly according to the supplier’s guidelines. The horizontal strain (relative deformation) of the jointing material must be smaller than 15%.

• Cold material (figure 21-centre). Also in this case the bottom of the widened joint first has to be closed by means of a chord. Again the material has to be applied strictly according to the supplier’s guidelines. The material mostly is a 2-component polysulfide mass.

• Profiles (figure 21-right). Premanufactured profiles are especially applied in expansion joints. The profiles mostly consist of EPDM (Ethylene Propylene Diene M-class rubber), a type of synthetic rubber. The required width of the profile depends on the expected changes of the joint width.

3.1.7. Opening to traffic

A concrete pavement cannot be trafficked immediately after construction. In case a normal type of cement is applied in the concrete mix, the following rules of the thumb are valid: • Pedestrians and bicycles are allowed on the pavement as soon as the joints have

been sawn; • Luxury cars are allowed after 3 days; • All cars, in limited numbers, are allowed after 7 days. In case a fast hardening type of cement is used, of course the traffic can be allowed earlier.

3.2. Concrete pavement construction example: rehabilitation of Antwerp Ring Road in Belgium

3.2.1. Introduction

The urban motorway Ring Road R1 around the city of Antwerp in Belgium was opened to traffic in 1969. The R1 has a total length of 14.2 km and includes the 690 m long Kennedy Tunnel (2*3 traffic lanes) below the river Schelde and the 1700 m long Viaduct Merksem (2*4 traffic lanes), see figure 22. Six radial motorways are tying into the R1. The total length of access and exit ramps on the interchanges amounts 30 km. During a partial rehabilitation in 1976 and 1977 some stretches of the R1 were widened up to 7 traffic lanes. After this rehabilitation, except of the Kennedy Tunnel the number of traffic lanes per direction varied between 4 and 7.


The original pavement structure as well as the structure constructed during the rehabilitation of the R1 was an asphalt pavement structure (see figures 23 and 25). In 2004 the traffic intensity on the most heavily trafficked parts of the R1 had increased to around 200,000 vehicles per day, including 25% of trucks. The capacity of the R1 was reached and after 35 years of service the asphalt pavement suffered for serious damage (such as cracking, raveling and patching), there was a severe problem with respect to the surface run-off, and the concrete pavement in the Kennedy Tunnel suffered from severe cracking (figure 23). The R1 is very important for the harbour of Antwerp (the second largest harbour of Europe) and for the international through traffic. Based on an extensive testing program (visual condition survey, Falling Weight Deflection measurements, investigation of cores) it was decided to perform a major rehabilitation to realize a safe, modern and efficient Ring

Figure 22. Overview of Ring Road R1 in Antwerp, Belgium .

Figure 23. Damages on the Ring Road R1 in Antwerp, Belgium in 2004.


Road with a service life of at least 35 years and with only minor pavement maintenance during this period. The rehabilitation of the Eastern carriageway was done between June and November 2004, and the rehabilitation of the Western carriageway was done between April and September 2005. In the following paragraphs some interesting aspects of this major rehabilitation project are discussed (DEBAERE ET AL, 2006).

3.2.2. Traffic regulation during the rehabilitation works

Because of the importance of the R1 (the green road in figure 24-left) for the international through traffic, all local entrances and exits (the purple crosses in figure 24-left) were closed. Local traffic had to use the at grade city ring, called Singel (the red road in figure 24-left), that was temporarily equipped with pre-manufactured fly-over structures (the blue stretches in figure 24-left).

Figure 24. Closure of local entrances and exits on the Ring Road R1 and upgrading the city ring, called Singel, in Antwerp, Belgium.

All through traffic was detoured by means of minimum 2*2 traffic lanes on that carriageway which was not under rehabilitation. From and to this carriageway a thoroughfare with a


minimum width of 1 lane had to be provided for the through traffic to and from the interchanges with the radial motorways. As a result of this regulation the carriageway being rehabilitated became available for construction over its full width and length, with the exception of the at grade thoroughfares to the interchanges. This allowed a maximum construction efficiency and minimum construction time. The execution of the works, the possible hindrance and the partial rerouting of traffic was communicated very frequently to the road users, not only in the city of Antwerp but in the whole of Belgium and even in the neighbouring countries (the Netherlands, Germany, France and United Kingdom). As a result the hindrance for traffic was limited and traffic jams hardly occurred.

3.2.3. Choice of type of pavement

Considering the limited space because of the requirement to maintain traffic on at least 1 traffic lane and due to the small radii of the alignment curves it was immediately decided to apply an asphalt pavement structure on the ramps of the interchanges. For the new pavement on the actual Ring Road R1 a thorough comparative study was made of an asphalt pavement and a continuously reinforced concrete pavement (CRCP). In a Life Cycle Cost Analysis the Net Present Value over an infinite horizon was used, i.e. it was determined how much money one has to reserve now for the construction today and the maintenance and reconstruction in the future. The construction costs appeared to be lowest for the asphalt pavement and the maintenance and reconstruction costs appeared to be lowest for the CRCP. The Net Present Value for both types of pavements appeared to be comparable. Other aspects (traffic noise, recycling of materials, driving comfort, traffic safety, construction time, etc.) were evaluated by means of a Multi Criteria Analysis. The result for CRCP was slightly better than the score for an asphalt pavement and would only be worse if absolute priority was given to the construction time. Based on these studies a CRCP was chosen for the Ring Road, with the exception of the asphalt pavement on the Viaduct Merksem. In the Kennedy Tunnel a jointed plain concrete pavement (JPCP) was applied because of the difficulties with the supply of fresh concrete in case of a CRCP.

3.2.4. Recycling

A major purpose of the rehabilitation project was to recycle the broken up materials to the maximum possible, given the very large quantities of broken up and recyclable materials, the short construction periods, and the decision not to create additional traffic flows by hauling broken up materials and by supplying new materials. As a result of a recycling study the existing asphalt pavement was recycled: • partly in new asphalt mixes • partly in the new cement-bound coarse granular base; 15% to 20% sand had to be

added to obtain a continuous grading and a maximum density


The existing base (mainly lean concrete and locally coarse aggregate) was broken up and recycled in the new granular sub-base.

3.2.5. Structural design of CRCP

The thickness design of the CRCP was done according to the Belgian Guidelines, which include an asphalt interlayer between the CRCP and the cement-bound base. The design is based on the traffic loading (cumulative number of equivalent 100 kN standard axle loads on the design lane during the design period), the CBR-value of the subgrade, the lane distribution factor and the design speed. The CRCP pavement structure together with the existing asphalt pavement structure is shown in figure 25.

Figure 25. Existing asphalt pavement and designed CRCP of Ring Road R1 in Antwerp, Belgium.

To reduce traffic noise, an exposed aggregate surface texture was chosen for the CRCP which requires a rather fine concrete mix (see 3.1.4). The specifications for the concrete mix were as follows: • The stone grading to be used is 4/7, 7/14 and 14/20 mm. The amount of 4/7 mm

aggregates has to be at least 20% of the total granular mix (sand and coarse aggregates). The percentage of sand should be as low as possible as far as compatible with an adequate workability.

• The water/cement-ratio is less than 0.45. • The minimum cement content is 400 kg/m3. • The use of an air-entraining additive is compulsory. The total amount of (longitudinal plus supporting transverse) reinforcement amounts 0.74%. The arrangement of the reinforcement steel is shown in figure 26. The longitudinal reinforcement consists of steel bars (BE 500 S, diameter 20 mm, spacing 0.18 m) with a minimum length of 14 m. When splicing longitudinal steel the minimum lap


is 35 bar diameters (35*20 mm = 700 mm = 0.7 m) with a skewed splice pattern. Having more than one splice in a transverse cross-section is kept to a minimum. The transverse reinforcement consists of steel bars (BE 500 S, diameter 12 mm, spacing 0.7 m) that are supported by steel chairs, which are placed on the asphalt interlayer. The transverse steel bars are placed at an angle of 60° to the longitudinal bars. When placed at a right angle it was expected that the transverse bars could be crack-inducing and could thus influence the crack pattern. Tie bars with diameter 16 mm are applied in every longitudinal construction joint. The tie bars are chemically anchored in holes that are drilled at a right angle to the longitudinal joint mid-depth in the concrete layer. The spacing of the tie bars varies from 0.80 to 0.85 m to avoid interference with the transverse reinforcement steel bars.

Figure 26. General arrangement of reinforcing steel (top) and actual transverse supporting reinforcement (bottom-left) and complete reinforcement (bottom-centre and –right) on the

Ring Road R1 in Antwerp, Belgium.

3.2.6. End of CRCP

At the ends a CRCP is subjected to changes in length due to changes in temperature. The so-called active length mainly depends on the friction between the CRCP and the


underlying asphalt interlayer and the magnitude of the temperature changes and was estimated as about 125 m. There are 2 possible solutions to cope with these horizontal end movements: • Restrain the end movements by means of end anchorages. This can be realized by

applying a number of transverse lugs which are anchored in the subgrade (figure 27). This expensive solution was chosen for auxiliary traffic lanes adjacent to the main road where the CRCP does not undergo any horizontal movements.

• Accommodate the end movements in one or more transverse expansion joints. Figure 28 shows the (relatively cheap) expansion joint, with a neoprene joint profile, that was applied at the end of the CRCP of the main road, between the CRCP and the adjacent asphalt pavement structure. In principle this expansion joint is similar to the one applied in bridges.

Figure 27. Anchorage lugs to restrain the end movement of a CRCP.


Figure 28. Expansion joint to accommodate the end movement of a CRCP.

3.2.7. Construction

The construction period of the rehabilitation of the Eastern carriageway was limited to 140 calender days and to 150 days for the Western carriageway. For the main road the working time was 16 hours per day, 7 days per week. The rehabilitation works in the Kennedy Tunnel were carried out continuously, i.e. 24 hours per day, 7 days per week. Along with the pavement rehabilitation works, 170 km of storm water sewers and drainage pipes, 9 utility tunnels below the Ring Road and many bridges had to be rehabilitated. A separate temporary haul road was built over the entire length of the project. This road was also intended for use by emergency vehicles. Two construction plants were erected on the works site to recycle the broken up materials and to supply the concrete. The construction of the CRCP had to be split up in many phases, both longitudinally and transversally, requiring a detailed scheduling and coordination of the placement of both the reinforcement steel and the concrete. It was impossible to construct the CRCP at once over its full width. In principle the 4 through lanes were cast (from the middle of the Ring Road to the outer edge) in widths of 2 lanes (2*3.75 m) or 1 lane plus a shoulder. The casting widths varied according to the number of lanes, the presence of a shoulder in CRCP and/or the necessity to apply an overwidth at those locations where either no shoulder was available or the shoulder had an asphalt pavement. The concrete was cast with a CMI HVW 2000 slipformpaver that is able to construct a variable width up to a maximum of 10 m.


The figures 29 to 32 show some pictures of the construction of the JPCP in the Kennedy Tunnel, the construction of the CRCP of the main Ring Road R1, and the completed Ring Road R1 in Antwerp, Belgium.

Figure 29. Installation of dowel bars and construction of JPCP in Kennedy Tunnel.

Figure 30. Construction of CRCP on main Ring Road R1.

Figure 31. Sawing longitudinal contraction joint (left), drilling holes for tie bars in construction joint (centre) and filling longitudinal construction joint (right).


Figure 32. General overview of the works site (left) and the in-service CRCP (centre and right) of the Ring Road R1 in Antwerp, Belgium.

3.3. Roundabouts

In comparison to a normal traffic junction, a roundabout improves the traffic flow and increases the traffic safety, also because of the reduced vehicle speed at roundabouts. Therefore, in Western Europe an increasing number of roundabouts are realized during the last decades, not only within built-up areas (figure 33-top and -centre) but also on major road crossings in rural areas (figure 33-bottom). The outside radius of roundabouts usually is in the order of 15 to 30 m, although larger radius roundabouts are also applied. Depending on the required traffic capacity these roundabouts have 1 lane (figure 33-centre and -bottom) or 2 lanes (figure 33-top). The smaller the radius of the roundabout, the wider the lane(s) should be. Normally the lane width is 4 to 5.5 m. At the inner side of the roundabout a so-called drive-over lane, width 2 to 2.5 m, is constructed that is incidentally used by long vehicles. Especially when the roundabout will be used by a large number of trucks then often a concrete pavement is applied on the roundabout, even when an asphalt pavement is applied on the crossing roads (figure 33-top). The reason for this is that, in comparison to an asphalt pavement, a concrete pavement can better withstand the huge horizontal forces resulting from (non-steered) multi-axles which are for instance mounted on trailers. Both jointed plain concrete pavements and continuously reinforced concrete pavements are applied on roundabouts (CROW, 2004). The applied concrete grades are C28/35 and C35/45. The concrete pavement thickness design can be done in a similar way as for roads, and normally a concrete pavement thickness of 230 to 250 mm is applied on top of a base. Between the concrete pavement of the roundabout and the pavement of the crossing roads always an expansion joint should be applied (figure 34).


Figure 33. Examples of roundabouts (with concrete pavement) in the city of Eindhoven, the Netherlands (top), the city of Genk, Belgium (centre) and on the N277 in the Netherlands (bottom).


Figure 34. Expansion joint between concrete road and concrete roundabout (CROW, 2004).

In case a jointed plain concrete pavement is applied on a roundabout, contraction joints are made in the traffic lane with a maximum spacing of 5 m, resulting in more or less square slabs (figure 35). In the drive-over lane contraction joints are made every 2 to 2.5 m, again resulting in more or less square slabs, and also 4 expansion joints are constructed. Between the traffic lane and the drive-over lane, and also at the outside of the roundabout, a kerb of in-situ placed concrete or precast concrete elements is constructed.

Figure 35. Example of a 1-lane roundabout with a jointed plain concrete pavement (CROW, 2004).


In case of a continuously reinforced concrete pavement on the traffic lane of the roundabout, an asphalt interlayer is applied between the pavement and the base. Table 10 gives some data about the longitudinal reinforcement. The transverse reinforcement, mainly to support the longitudinal reinforcement, amounts about 0.06%. The reinforcement bars consist of steel FeB 500 HWL. In this case the structures applied on the drive-over lane as well as for the kerbs are similar to those described above. Table 10. Longitudinal reinforcement for a continuously reinforced concrete pavement on a roundabout in the

Netherlands (CROW, 2004).

Concrete pavement thickness 230 mm 250 mm

Concrete grade C28/35 C35/45 C28/35 C35/45

Minimum percentage of reinforcement (%) 0.59 0.70 0.59 0.70

Minimum amount of reinforcement (mm2/m) 1357 1610 1475 1750

Reinforcement bars with diameter 16 mm

Spacing of bars (mm) 145 125 135 115

Amount of reinforcement (mm2/m) 1387 1608 1489 1748

Overlap length (mm) 420 375 420 375

Reinforcement bars with diameter 20 mm

Spacing of bars (mm) 225 195 210 180

Amount of reinforcement (mm2/m) 1396 1611 1496 1745

Overlap length (mm) 510 450 510 450

3.4. Widening of pavements

In Western-Europe the motorway network has largely been completed in the last decades, only a limited number of new motorways will be constructed. Traffic intensities in parts of countries like Germany, Italy, Great Britain, Belgium and the Netherlands have however grown such high that many existing motorways, including their junctions, have reached their capacity. Certainly in case of disturbing factors (bad weather conditions, accident, road maintenance) heavy traffic jams do occur. Extension of motorway junctions and widening of the most heavily trafficked motorways therefore are becoming major construction activities. When the subsoil is free of settlements both asphalt and concrete pavements can be widened with an asphalt pavement or with a concrete pavement (table 11). In Germany widening of a motorway asphalt pavement with a concrete pavement has become rather common practice, and then the heavy vehicles are mainly driving over the new concrete pavement. An example is the motorway A4 between the cities of Aachen and Cologne that was widened from 2*2 lanes to 2*3 lanes (figure 36). The existing asphalt pavement on the emergency lane was removed and JPCP was applied on the new 3rd lane and emergency lane.


Table 11. Possible combinations of pavement structures for existing road and widening (CROW, 2010).

Existing pavement structure + wearing course

Pavement structure for widening

Asphalt concrete (AC)

JPCP CRCP

Brushed or exposed aggregate surface

AC wearing course

Brushed or exposed aggregate surface

AC wearing course

AC JPCP JPCP + AC CRCP CRCP + AC

X X X X X

X X - - -

X - X - -

X - - X -

X - - - X

Figure 36. JPCP widening of asphalt pavement on motorway A4 in Germany during and after construction (CROW, 2010).

Special attention must be given to the longitudinal joint between the asphalt pavement and the concrete pavement. This joint must be filled and below the joint a drainage facility has to be built that is directly connected to the underlying permeable granular base (figure 37).

Figure 37. Basic solution for the longitudinal joint between asphalt and concrete widening (CROW, 2010).


3.5. Safety barriers

Traditionally in Europe galvanized steel safety barriers are applied (figure 38-left). However, in case of a collision they get damaged (bended) and the required repair is not only expensive and time-consuming but on heavily trafficked roads it also causes traffic delays. Besides, at long term the barriers loose heavy metals that may pollute the subsoil and the groundwater. Therefore, in a number of European countries (such as Belgium, France, Germany, Great Britain, Spain and Italy) concrete safety barriers are applied more and more (figure 38-right).

Figure 38. Traditional steel safety barrier (left) and concrete safety barrier (right).

The original concrete barrier was applied first in New Jersey, USA, in 1955 and is therefore called the New Jersey barrier (figure 39-left). Nowadays also a somewhat different barrier, called step barrier, is widely applied (figures 38-right, 39-right and 40). The shapes are optimized to guide colliding vehicles along the barrier in the direction of travel. Both types of barrier have a weight of 700 to 800 kg per meter length and they are able to withstand the heaviest vehicles without any serious damage. Usually 2 to 4 reinforcement bars are applied in the upper part of the barrier to increase the strength of the barrier in case of a collision. The barrier has to be constructed on a base (such as an unbound base, a lean concrete base or an asphalt layer) and embedded in the adjacent pavement for sufficient lateral support. A concrete safety barrier is constructed by means of a small slipformpaver or a dedicated machine (figure 40) (WIRTGEN GROUP, 2009). In both cases the machine is equipped with a special feeder unit and steel mould to yield the correct shape of the barrier. The protection of the fresh concrete (grade C28/35 or C35/45) of the barrier is similar as the protection of concrete pavements (see paragraph 3.1.5). Usually contraction joints are made in the concrete barrier every 4 to 10 m by saw cutting the barrier over a depth of 20 to 30 mm. At specific locations, e.g. besides bridges, expansion joints are required.


Figure 39. New Jersey barrier (left) and step barrier (right).

Figure 40. Construction of a step barrier by means of a slipformpaver (left) or dedicated machine (right).

4 Example of new development: Modieslab precast concrete pavement in the Netherlands

In this chapter four full-scale applications of a new type of precast concrete pavement in the Netherlands are shortly described. The pavement system, called ‘Modieslab’, was originally developed in 2001 and extensively tested in the period from 2001 till 2006 (HOUBEN ET AL, 2006). The precast concrete slabs are provided with a structural reinforcement for bearing capacity and a porous concrete wearing course for reduction of traffic noise can be applied.

4.1. Full-scale test section in motorway

Based on the quite good functional and structural performance of the Modieslab system in the testing period 2001 till 2006 (HOUBEN ET AL, 2006), in 2007 a 100 m full-scale test section was constructed in a bypass within the junction ‘Oudenrijn’ near the city of Utrecht in the centre of the Netherlands. Oudenrijn is the junction between 2 of the most important


Dutch motorways, i.e. the A2 (running from the capital city Amsterdam to the south of the country and further to Belgium) and the A12 (running from the government city The Hague to the east of the country and further to Germany) (figure 41). The precast concrete slabs are provided with two-layer porous concrete.

Figure 41. Location of the junction ‘Oudenrijn’ within the Dutch main road network (left) and location of the Modieslab test section within the junction ‘Oudenrijn’ (right).

The applied Modieslab structure has the following characteristics:

Lane-wide slabs have been applied to improve longitudinal evenness and to allow repair, if necessary, lane by lane. This means that in case of repair only 1 lane needs to be closed. The applied slab dimensions are: length * width * thickness = 7.2 * 3.6 * 0.38 m.

The slabs are heavily reinforced as they are designed as a bridge with very short span.

The junction ‘Oudenrijn’ is located in an area with a very weak, compressible subsoil, and therefore the slabs had to be founded on driven concrete foundation piles. On top of the piles pre-manufactured headers were applied.

The voids content of the two-layer porous concrete amounts 20%-22%. The 30 mm thick upper porous concrete layer has a fine grading 2/8 mm and the 55 mm thick lower porous concrete layer has a somewhat coarser grading 2/11 mm.

Figure 42 gives an impression of the Modieslab system. The pictures in figure 43 give an idea about the construction process, which includes hammering the foundation piles into the subsoil, placing the headers, placing the precast concrete slabs and the accurate leveling of the slabs onto the headers. The functional properties of the Modieslab test section ‘Oudenrijn’ have been measured immediately after construction. The results were very satisfying (table 12).

A12

A2


Figure 42. Artist impression of the Modieslab system applied on the bypass within the junction ‘Oudenrijn’.

Figure 43. Construction of the Modieslab test section on the bypass within the junction ‘Oudenrijn’.


Table 12. Functional properties of Modieslab pavement structure.

Required Measured

Deceleration during emergency brake > 5.2 m/s2 7.1 m/s2

Friction coefficient > 0.4 0.51 – 0.57

Raveling (rolling surface abrasion test) < 20 grams 1.7 grams

Permeability < 20 seconds 15 seconds

Noise level reduction at 100 km/h 6 – 7 dB(A)

Evenness Very good

Mid 2011, so 4 years after construction, no damage has been observed on this Modieslab test section that every day is trafficked by around 40,000 vehicles including about 15% trucks.

4.2. Applications within built-up areas

In the autumn of 2009 a Modieslab type of pavement has been constructed on 7 junctions during the reconstruction of a heavily loaded access road, called Diamantstreet, to an industrial area within the built-up area of the city of Hengelo, in the east of the Netherlands (figure 44). During 7 subsequent weekends each time one junction was reconstructed. Each junction in the 2*2-lane road has an area of 2,000 to 2,500 m2.

Figure 44. Overview of the Diamantstreet in the city of Hengelo, the Netherlands.


The subsoil on that location is sand, which is quite good for Dutch conditions. Therefore, subsoil settlements were not an issue on this project. In this case the precast concrete slabs were not founded on precast concrete foundation piles but on an asphalt layer (figure 45). The applied (rectangular and non-rectangular) precast concrete slabs are so-called Modieslab LS (Low Speed) slabs, which have especially been developed for low traffic speeds (up to 80 km/h). A porous concrete toplayer is not applied because that would be severely damaged in a short period of time due to the high friction forces applied by turning trucks. On average each slab has an area of around 15 m2. The slabs are interconnected by means of concave-convex connections.

Figure 45. Construction of Modieslab on junctions in Diamantstreet in the city of Hengelo, the Netherlands.

During 3 days in October 2010 in total 1,234 m2 of Modieslab LS slabs were applied on a 2-lane bus road in the centre of the city of Haarlem in the Netherlands (figure 46). The slabs are resting on a newly laid asphalt layer. Except of the slabs on a traffic junction, the slabs have horizontal dimensions of 8 * 4 m. The thickness of the slabs is 400 mm. The upper part does not contain any reinforcement, which allows to make gutters to install tramway rails (‘embedded rail’) if the local politicians would ever decide to transform the bus road into a tramway.

Figure 46. Construction of Modieslab on a bus road in the city of Haarlem, the Netherlands.

Such an embedded tramway structure for silent public transport already was constructed in November 2008 in the city of Blankenberge in Belgium. In this case the gutters for the tram rails already were made during the manufacturing of the slabs (figure 47). A two-layer porous concrete wearing course is applied to yield a reduction of the tram noise of 6 dB(A).


Figure 47. Modieslab slabs for a silent tramway in the city of Blankenberge, Belgium.

References

CEB (COMITÉE EURO-INTERNATIONAL DU BÉTON). CEB-FIP Model Code 1990. Bulletin d’information 213/214, London, Thomas Telford, 1993. CROW. Uniform evaluation method for concrete pavements (in Dutch). Publication 136, CROW, Ede, the Netherlands, March 1999 CROW. Concrete Pavements on Roundabouts (in Dutch). Publication 193, CROW, Ede, the Netherlands, March 2004. CROW. Manual for Construction of Concrete Pavements (in Dutch). Publication 195, CROW, Ede, the Netherlands, July 2004. CROW. VENCON2.0 software for the structural design of jointed plain and continuously reinforced concrete pavements (in Dutch). CROW, Ede, the Netherlands, January 2005. CROW. Concrete Pavements on road widening (in Dutch). Publication 286, CROW, Ede, the Netherlands, May 2010. DEBAERE, P.; DIEPENDAELE, M.; DE GOOF, D.. The challenging rehabilitation of the Antwerp Ring Road in CRCP 2004 – 2005. Proceedings 10th International Symposium on Concrete Roads, Brussels, Belgium, 18-22 September 2006. EISENMANN, J.; LEYKAUF, G.. Concrete pavements, 2nd edition (in German). Ernst, Wilhelm & Sohn, Verlag für Architektur und Technische Wissenschaften GmbH, Germany, 2003. EUROCODE 2 (prEN 1992-1-1). Design of concrete structures – Part 1: General rules and rules for buildings. Comitée Européen de Normalisation (CEN), Brussels, July 2002.


FEHRL. Making best use of long-life pavements in Europe – Phase 3: A guide to the use of long-life rigid pavements. FEHRL Report 2007/Y, FEHRL, Brussels, 2007. FGSV. Guide for the Standardisation of Road Pavement Structures RStO 01 (in German). Forschungsgesellschaft für Strassen- und Verkehrswesen, Köln, Germany, 2001. HASSAN, K.E.; FERNE, B.W.; WISTUBA,; GORSKI, M.; OULD-HENIA, M.. European long-life rigid pavement. Proceedings 10th International Symposium on Concrete Roads, Brussels, Belgium, 18-22 September 2006. HOUBEN, L.J.M.; BRAAM, C.R.; VAN LEEST, A.J.; STET, M.J.A.; FRÉNAY, J.W.; BOUQUET, G.Chr.. Backgrounds of VENCON2.0 software for the structural design of jointed plain and continuously reinforced concrete pavements. Proceedings 6th International DUT-Workshop on Fundamental Modelling of Design and Performance of Concrete Pavements, held September 15-16, 2006 in Old-Turnhout, Belgium; Delft University of Technology, Section Road and Railway Engineering, Delft, the Netherlands, 2006. HOUBEN, L.J.M.; POOT, S.; HUURMAN, M.; VAN DER KOOIJ, J.. Developments on the Modieslab innovative concrete pavement concept. Proceedings 10th International Symposium on Concrete Roads, Brussels, Belgium, 18-22 September 2006. HOUBEN, L.J.M; VAN LEEST, A.J.; STET, M.J.A.; FRÉNAY, J.W.; BRAAM, C.R.. The Dutch structural design method for plain and continuously reinforced concrete pavements. Proceedings International Workshop on Best Practices for Concrete Pavements, Recife, Brazil, October 21-23, 2007. IOANNIDES, A.M.; THOMPSON, M.R.; BARENBERG, E.J.. The Westergaard Solutions Reconsidered. Workshop on Theoretical Design of Concrete Pavements, 5-6 June 1986, Epen. Record 1, CROW, Ede, the Netherlands, 1987. JOFRÉ, C.. The European standards on materials for concrete pavements. Proceedings 10th International Symposium on Concrete Roads, Brussels, Belgium, 18-22 September 2006. LEEWIS, M.. Theoretical knowledge leads to practical result (in Dutch). Journal ‘BetonwegenNieuws’ no. 89, September 1992, pp. 20-22. NEN 6720:1995, TGB 1990. Concrete Standards – Structural requirements and calculation methods (VBC 1995), 2nd edition with revisions A2:2001 and A3:2004 (in Dutch). Netherlands Normalisation Institute NNI, Delft, the Netherlands, 1995.


NEN-EN 206-1:2001. Concrete – Part 1: Specifications, properties, manufacturing and conformity (in Dutch). Netherlands Normalisation Institute NNI, Delft, the Netherlands, 2001. VAN CAUWELAERT, F.. Pavement Design and Evaluation. ISBN 2-9600430-0-6, Federation of the Belgian Cement Industry, Brussels, Belgium, 2003. WIRTGEN GROUP. Concrete Slipform Paving Manual – Part 1: Curb, barrier, sidewalk and multipurpose applications. Wirtgen GmbH, Windhagen, Germany, 2009.


Appendix: Overview of European Standards (EN) related to Concrete Pavements

Materials, requirements and dowel bars for concrete pavements EN 13877-1 Concrete pavements – Part 1: Materials EN 13877-2 Concrete pavements – Part 2: Functional requirements for concrete pavements EN 13877-3 Concrete pavements – Part 3: Specifications for dowels to be used on concrete pavements EN 13863-1 Concrete pavements, test methods for functional requirements – Part 1: Test method for the determination of the thickness of a concrete pavement by survey method EN 13863-2 Concrete pavements, test methods for functional requirements – Part 2: Test method for the determination of the bond between two layers EN 13863-3 Concrete pavements, test methods for functional requirements – Part 3: Determination of the thickness of a concrete slab EN 13863-4 Concrete pavements, test methods for functional requirements – Part 4: Determination of wear resistance to studded tires

Joint fillers and sealants EN 14188-1 Joint fillers and sealants – Part 1: Specifications for hot applied sealants EN 14188-2 Joint fillers and sealants – Part 2: Specifications for cold applied sealants EN 14188-3 Joint fillers and sealants – Part 3: Specifications for preformed joint seals EN 13880-1 Hot applied joint sealants - Part 1: Test method for the determination of density at 25°C EN 13880-2 Hot applied joint sealants - Part 2: Test method for the determination of cone penetration at 25°C EN 13880-3 Hot applied joint sealants - Part 3: Test method for the determination of penetration and recovery (resilience) EN 13880-4 Hot applied joint sealants - Part 4: Test method for the determination of heat resistance – Change in penetration value EN 13880-5 Hot applied joint sealants - Part 5: Test method for the determination of flow resistance EN 13880-6 Hot applied joint sealants - Part 6: Test method for the preparation of samples for testing EN 13880-7 Hot applied joint sealants - Part 7: Function testing of joint sealants EN 13880-8 Hot applied joint sealants - Part 8: Test method for the determination of the change in weight of fuel resistance joint sealants after fuel immersion EN 13880-9 Hot applied joint sealants - Part 9: Test method for the determination of compatibility with asphalt pavements


EN 13880-10 Hot applied joint sealants - Part 10: Test method for the determination of adhesion and cohesion following continuous extension and compression EN 13880-11 Hot applied joint sealants - Part 11: Test method for the preparation of asphalt test blocks used in the function test and for the determination of compatibility with asphalt pavements EN 13880-12 Hot applied joint sealants - Part 12: Test method for the manufacture of concrete test blocks for bond testing (recipe methods) EN 13880-13 Hot applied joint sealants - Part 13: Test method for the determination of the discontinuous extension (adherence test) EN 14187-1 Cold applied joint sealants – Part 1: Test method for the determination of the rate of cure EN 14187-2 Cold applied joint sealants – Part 2: Test method for the determination of tack free time EN 14187-3 Cold applied joint sealants – Part 3: Test method for the determination of self-levelling properties EN 14187-4 Cold applied joint sealants – Part 4: Test method for the determination of the change in mass and volume after immersion in test fuel EN 14187-5 Cold applied joint sealants – Part 5: Test method for the determination of the resistance to hydrolysis EN 14187-6 Cold applied joint sealants – Part 6: Test method for the determination of the adhesion/cohesion properties after immersion in chemical liquids EN 14187-7 Cold applied joint sealants – Part 7: Test method for the determination of the resistance to flame EN 14187-8 Cold applied joint sealants – Part 8: Test method for the determination of the artificial weathering by UV-irradiation EN 14187-9 Cold applied joint sealants – Part 9: Function test EN 14840 Test methods for preformed joint seals

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