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CEMENT GROUTED BITUMINOUS MACADAM1

1.0 Introduction

Flexible, composite and rigid pavements are the most common types of pavement used for highways in India and in the rest of the world. There may be another type of pavements

which can be obtained by grouting of open graded bitumen treated aggregates with cement (or polymer based slurry), and are known as grouted bituminous macadam. The present guideline deals with cement grouted bituminous macadam (CGBM).

In such layer, first, the single sized (preferably cubic) aggregates mixed with bituminous binder is used to prepare the aggregate skeleton. This aggregate skeleton should have voids (VMA) 25% or more, which is quite high compared to the traditional mixes. Sometimes fibres are added to prevent draindown of binder. Then, sufficiently flowable cement grout is

introduced to fill up the voids by gravity. This cement grout is prepared by mixing suitable proportions of cement, fine sand and water. Additives like micro silica, flyash,

superplasticizer may be added so that the grout flows into the voids and attains the required strength. Flowability of the grout plays an important role in developing the strength of the CGBM. A typical CGBM mix contains 10 mm single size (75% of the aggregates are between 10 mm passing and 6.3mm retained) aggregates, typical bitumen content is about 3% by weight of the aggregates.

CGBM is generally used as surfacing (Oleveira et. al. 2008), but it also has potential to be used as base course (Oleveira et. al. 2007). It seemed to have been developed in France during 1960s and was known as resin modified pavement (Wu 2011, Gawedzinki 2008, Anderton 2000). In USA it is first applied during 1987 (Anderton 2000). Various countries where CGBM has been used includes France, USA, Germany, Japan, Spain, Portugal, Sweden, Norway, Finland, Saudi Arabia, South Africa, Austria and so on (Anderton 2000). CGBM has been reportedly used in bus stations, parking areas, warehouses etc (Al-Qadi et al. 1994), roads and aprons (Wu 2011). Some of the advantages of CGBM are (Anderton 2000, Oleveira et. al. 2006, 2007, 2009, Wu 2011): 1 Draft document developed by Dr. B. B. Pandey and Dr. Animesh Das

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o Resistance to fuel spillage

o Resistance to permanent deformation o Resistance to abrasion/ wearing o Resistance against water damage o Flexibility

o Absence of joint o High static bearing capacity and distribution of stress

o High thermal susceptibility o Impermeability o Good skid resistance property o Quick constructability and opening to traffic

These advantages enable CGBM mix to take care of the some of the individual limitations

associated with cement concrete and bituminous mix. Past researchers have conducted laboratory studies on stiffness (Anderton 2000, Oliveira et al. 2006, 2009), tensile and compressive strength (Anderton 2000), Marshall stability (CRRI 2002), thermal expansion coefficient (Anderson 2000), low temperature fracture (Oliveira et al. 2006), fatigue (Oliveira et al. 2006, 2008 and 2009) properties of CGBM and found to show satisfactory performance. The consistency and quantity of binder, size and gradation of the aggregates,

loading frequency, grout strength and shrinkage potential, temperature etc are observed to affect these properties (Oliveira et al. 2006, 2008 and 2009).

Scope of the guideline

This guidelines lay down recommendation for CGBM that may be used as a wearing course

for low volume roads. For high volume roads, bitumen coated binder and base layers also can be grouted with cement slurry to obtain a durable pavement. Properties of grout, method

of construction of cement grouted bituminous layer as well as pavement design principles are also included in the guidelines. Due to lack of extensive performance data of pavements with such materials, pavement performance data should be periodically recorded in order to revalidate or revise the guidelines.

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2.0 Materials

The CGBM mix consists of aggregates, bituminous binder and cement grout. The recommended specifications for these materials are mentioned in the following:

2.1 Aggregates

The aggregates shall be open-graded asphalt and they shall consist of clean, sound, tough angular and durable particles obtained from crushing of rocks. The physical properties of the

aggregates shall be tested as per the IS 2386 and they should satisfy the specifications of the MoRT&H Specifications (2013). Since open graded aggregates coated with a binder is compacted by a road roller, Los Angeles Abrasion value should be less than 30% to eliminate crushing of aggregates during the rolling.

Any gradation of surface dressing, open graded premix carpet, stone matrix asphalt (specified by MORT&H guidelines) which can result in air voids (in terms of VMA) of 25% or more can be considered as suitable gradation for CGBM (Suresha et al. 2007).

2.2 Bituminous binder

The binder can be bitumen or modified bitumen satisfying IS 73 (2006) and IRC: SP:53 (2010) standards. The binder type should be chosen according to the location of the site and the weather conditions. The effect of the binder type on grout penetration is not quite significant, but use of stiffer binder will result in stiffer mixes.

2.3 Cementitious grout

Cementitious grout consists of cement, sand, water and additives, such as flyash, micro-silica,

super plasticizer in suitable proportion so as to produce a material that it can flow easily into the voids of the bituminous mix and subsequently achieve strength. Though aggregates

bridges over the mortar and bears most of the load applied by traffic, the grout should be strong enough to resist the stresses caused by traffic without crumbling.

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Ordinary Portland cement, Portland Pozzolanic Cement, Slag cement etc. which are used for normal concrete road construction, can be used in preparation of the cement grout. The

specifications should follow IS-12269 (1987).

The fine sand to be used in the cement grout should pass 0.6mm size so that the grout can enter into the voids easily.

Fly ash, silica, super plasticizer etc. can be used so as to increase the performance and also

can be used to get the required fluidity at the lower water contents for cement grout.

The grout should satisfy the following criteria:

o It should be sufficiently flowable so that it can occupy the void space of the aggregate skeleton. If however the viscosity is low, the grout will flow down

through the aggregate pores and strength will not be achieved. o The small particles present in the grout should not pose difficulty for the easy

flow of the grout through the aggregate voids.

The flowability of cement grout is to be measured in Marsh flow cone (Al-Qadi et al. 1994, ASTM C476 2010) as shown in Fig.1. The cement grout should satisfy the following properties:

Property Guidelines Value

Flowability measured in

Marsh flow cone

ASTM C476 2010 7-9 seconds for 1 litre grout

Compressive strength ASTM C109 2010 Minimum 15 MPa for 70.7mm 70.7mm 70.7mm cube

Flexural strength Minimum 7 MPa

Initial setting time

Final setting time

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Fig. 1: Schematic diagram of the Marsh flow cone

3.0 Laboratory mix design for CGBM

Binder content for cement grouted bituminous mix should be about 2.0 to 2.5% by weight of the aggregates so that there is a minimum of 25% air voids in mineral aggregates (VMA) after the compaction by a road roller.

For preparing the samples, requisite compaction should be applied (in three tamping stages) on the mix placed in a mould. The samples are air-cooled overnight while these remained inside the mould. Cement grout (prepared as per Section 2.3) is slowly poured at the top of the sample. The collar of the Marshall sample helps to hold the liquid grout on the top of the sample. A portion of the top surface is kept empty, so that air (displaced by grout) can move out. Grout is poured on this portion is poured at the end when grout has occupied most of the accessible air-voids within the mix. This has been schematically explained in Figure 2.

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(a) compacted bituminous mix sample

(b) grout is poured to the sample

(c) grout occupies all the accessible voids in the mix

Fig 2: Preparation of laboratory CGBM sample

The sample subjected to moist curing for 2 days and then taken out from the mould. The mix should satisfy the following recommended values

Test Guidelines Recommended value

Indirect tensile strength ASTM D 4123 Min 100 kPa (at 40oC)

Compressive strength ASTM C 109 6-8 MPa (one day) 10-14 MPa (28 days)

Retained IDT (in water) ASTM D 1075 90% Modulus of rupture ASTM C 78 1500 kPa

Loss of material in 7 days of immersion in diesel oil

Abrasion resistance IS:9284

The optimum grout content (composition) and optimum bitumen content will be finalized for the mixes which satisfies the above requirements.

4.0 Pavement design

Elastic layered analysis applied for the analysis of flexible pavements can be used for the design of composite pavement also. Various parameters for design are CBR of the soil,

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elastic moduli of the granular layers, elastic moduli of the grouted bituminous layers, Poisons ratio of different layers, design traffic in terms of standard axles. Temperature has

less effect of the elastic modulus of the grouted bituminous layers due to the presence of cementitious grout, and hence may be neglected in the design process.

The fatigue equation obtained at Nottingham University (Oliveira et al. 2008) from four point bending test at 10 hz frequency is given as,

9718.39107.2 = tN Eq.1

where, N= fatigue life in number of standard axle repetitions and t= tensile strain at the bottom of the CGBM layer. Equation 1 has a shift factor of 45, this takes care of the calibration due to field performance. Thickness of pavement using CGBM can be done using the fatigue Equation 1. Modulus of different types of bases, subbases and subgrades can be taken from IRC:37:2012.

Based on studies done at Nottingham University and IIT Kharagpur, the elastic modulus of CGBM can be taken as 8000 MPa (Oliveira et al. 2008). After the expiry of the fatigue life, the elastic modulus of the CGBM layer may be assumed to be reduced by 50%.

If a low volume road has CGBM premix carpet, its contribution to the pavement strength may be neglected. Such wearing course however may last longer than the conventional seal coat due to its resistance to water damage.

4.1 Design example

4.1.1 Design problem

Design a pavement with CGBM surfacing for design traffic 50msa. The elastic modulus of subbase and subgrade can be taken as 300 MPa and 100 MPa, respectively.

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4.1.2 Design solution 1

A three layer pavement structure constituted with CGBM, granular base and subgrade layer assumed. The allowable tensile strain at the bottom of the CGBM layer is obtained from Eq.

1 as 61080 .

Assuming sub-base thickness as 400 mm, the CGBM layer thickness is iteratively obtained as

175 mm (for allowable strain as 61080 ). Subgrade strain is obtained to be much lower than what is permitted by IRC:37;2012.

4.1.2 Design solution 2

A four layer pavement structure constituted with CGBM, DBM granular base and subgrade layer assumed. The thickness of CGBM layer and sub-base layers are assumed as 35mm and 400 mm respectively. The elastic modulus of DBM is taken as 1700 MPa (VG40 bitumen at 35oC average annual pavement temperature). The allowable tensile strain at the bottom of the CGBM layer is obtained from Eq. 1 as 61080 . The allowable tensile strain at the bottom of the DBM layer for 50 msa traffic and 80% reliability is obtained as (from IRC:37 2012)

6104.235 .

For a thickness of 100 mm of DBM, the horizontal tensile strain the bottom of CGBM layer

is obtained as 6101.43 and the horizontal tensile strain 6104.235 . Thus, the pavement structure can be designed as CGBM 35 mm, DBM 100 mm, sub-base 400 mm and subgrade.

5.0 Construction

CGBM can be constructed on any stable bituminous/ concrete layer. The following construction steps are to be followed.

o Heating of the aggregates and bitumen are done in hot mix plant. o The porous asphalt mix is laid. o When the temperature comes down to 50-60oC, cement mortar is applied on the

prepared porous asphalt surface. It should automatically occupy the voids due to

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gravity. Roller in vibration mode may be used to facilitate the process. Grout work should not proceed in rainy or snowy environment.

o No construction joint is necessary for CGBM construction. o Moist curing needs to be done in accordance with **. o The road can be opened to traffic after 3 days. If the traffic is pedestrian it can be

opened after 1 day. If the traffic axle load is expected to be higher the curing period should longer.

o The surface should be mechanically/ manually broomed to create texture on the surface.

o The surface texture should be evaluated with sand patch testing in accordance with ** and the average texture depth should be more than **.

o The skid resistance should be evaluated using British Pendulum Tester and the minimum skid resistance value should ** for dry condition and ** for wet condition.

6.0 Maintenance

References

Al-Qadi, I., Gouru, H., and Weyers, R. E., Asphalt Portland cement concrete composite: laboratory evaluation, Journal of Transportation Engineering, 120(1), 1994, pp.94-108.

Anderton, G. L., 2000, Engineering properties of resin modified pavement (RMP) for mechanistic design, Geotechnical Laboratory, U. S. Army Engineering Research and Development Center, ERDC/GL TR-00-2. , last accessed July 12, 2013.

ASTM C109, Standard Test Method for Compressive Strength Hydraulics Cement Mortar 50mm Cube, ASTM International, West Conshohocken, 2010.

ASTM C 476-10, Standard Specification for Grout for Masonry, ASTM International, West Conshohocken, 2010.

ASTM C937-10, Standard Specification for Grout Fluidifier for Preplaced Aggregate Concrete, ASTM International, West Conshohocken, 2010.

CRRI, Evaluation of ACC Marg overlaid road sections, report submitted by Central Road Research Institute, sponsored by Associated Cement Companies India Pvt. Ltd., Research and Consultancy Directorate, Thane, 2002.

IS-73, Specifications for Paving Bitumen, Bureau of Indian Standards, New Delhi, 2006.

IS-12269, Specification for 53 grade ordinary Portland cement, Bureau of Indian Standards, New Delhi, 2008.

IS:9284, Method of test for abrasion resistance of concrete, Bureau of Indian Standards, New Delhi 2007.

IS: 2386, (Part IV), Friction tester, Bureau of Indian Standards, New Delhi, 1963.

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IRC: SP 53, Tentative guideline on use of polymer and rubber modified bitumen in road construction, Indian Roads Congress, New Delhi, 2002.

Gawedziniki, M., (2008) Evaluation of semi-flexible (resin modified) pavement 12008-1, Illinois Department of Transportation Bureau of Materials and Physical Research.

MORT&H, (2013) Specifications for Roads and Bridge Works, 5th Revision, Ministry of Surface Road Transport and Highways, Government of India, published by IRC.

Oliveira, J. R., Zoorob, S. E., Thom, N. H., and Pereira, P. A., (2007) A simple approach to the design of pavements incorporating grouted macadams, 4th International Conference Bituminous Mixtures and Pavements, Thessaloniki, Greece.

Oliveira, J. R., Thom, N. H., and Zoorob, S. E., (2006) Fracture and Fatigue Strength of Grouted Macadams, 10th International Conference on Asphalt Pavements, Quebec City, Canada, vol. 1, pp. 225-34.

Oliveira J. R., Sangiorgi C., Fattorini G., and Zoorob S. E., (2009) Investigating the fatigue performance of grouted macadams, Transport, 162(TR2), pp. 115-123.

Oliveira, J. R., Thom, N. H., and Zoorob, S. E., (2008) Design of Pavements Incorporating Grouted Macadams, Journal of Transportation Engineering, ASCE, 134(1), pp. 7-14.

Suresha, S. N., Ravi Shankar, A. U., George, V., Investigation of porous friction courses and mixes: a brief overreview, Indian Highways, July 2007.

Wu, D. Q., The semi-rigid pavement with higher performances for roads and parking aprons, CAFEO 29, Sustainable Urbanization Engineering Challenges and Opportunities, November 27-30, 2011, Brunei Darussalam, pp.1-7.