Kejin Wang, Surendra P. Shah, and Thomas Voigt 1

A NOVEL SELF-CONSOLIDATING CONCRETE FOR SLIP-

FORM APPLICATION

Kejin Wang

Associate Professor Department of Civil, Construction, and Environmental Engineering

Iowa State University 492 Town Engineering Building

Ames, IA 50011, Phone 515-294-2152 FAX 515-294-8216 kejinw@iastate.edu

Surendra P. Shah

Professor Department of Civil Engineering

Northwestern University Room A130 Tech Building

2145 Sheridan Road Evanston, IL60208-4400

Phone: 847-491-3858 Fax: 847-467-1078

s-shah@northwestern.edu

Thomas Voigt Research and Technology Innovation Center

USG Corporation 700 North Highway 45

Libertyville, IL 60048, USA Phone: 847-970-5102 Fax: 312-214-1466

tvoigt@usg.com

August 1, 2006

Word count: text 2420, table 500, figure 1750, total 4670

Author for correspondence

TRB 2007 Annual Meeting CD-ROM Original paper submittal - not revised by author.

mailto:s-shah@northwestern.edumailto:tvoigt@usg.com

Kejin Wang, Surendra P. Shah, and Thomas Voigt 2

ABSTRACT In this paper, a novel concrete that can not only self-consolidate but also hold its shape right after casting is introduced. Such a concrete may have a great potential for slip form paving providing more workable concrete, smoother and more durable pavement, and higher rates of production. In the consideration of the self-consolidating concrete for slip form paving application (SF SCC), the significances, version, and challenge of this innovative study are discussed. The research approach to the novel concrete through tailoring concrete materials and mixture proportions is described. The preliminary research activities, involving concrete flow ability, compactibility, and shape-holding ability studies, are briefly presented. The results indicate that the newly developed SF SCC does possess sufficient self-consolidating ability and timely shape stability. The set time and strength of the SF SCC is comparable to those of conventional concrete. A lab simulation of the field slip form paving process has also demonstrated that such a SF SCC is feasible for field application.

TRB 2007 Annual Meeting CD-ROM Original paper submittal - not revised by author.

Kejin Wang, Surendra P. Shah, and Thomas Voigt 3

INTRODUCTION Slip form construction has been extensively used by the worldwide paving industry. Different from the fixed form paving, slip-form paving brings together concrete placing, casting, consolidation, and finishing into one unique process without requirement for formwork. In this process, concrete mixture with a slump less than 2 is placed in front of a paver. As the paver moves forward, the mixture is spread, leveled, consolidated (by equally spaced internal vibrators), and then extruded. After extrusion, the fresh concrete slab can hold in shape without any lateral support for further surface finishing, texturing, and curing until the concrete sets. Because of the low consistency of the mixture, a great deal of vibration is needed to move entrapped air and consolidate the concrete.

Over consolidation of pavements is noted visually in finished pavements. Longitudinal trails are observed on the surface of the concrete pavements (Figure 1). These trails are also called vibrator trail, and they run parallel to each other with spacing similar to that of vibrators on pavers. Cores taken from vibrator trails of some pavements have revealed in many instances the hardened concrete contains less than 3% air, rather than 6-7% as designed, thus significantly reducing concrete freeze-thaw durability 1 . Although some measures are taken to monitor frequency of the vibrators, improper vibrations are sometime still inevitable.

(a) Vibrator trials (b) Segregation of concrete on a vibration trial

FIGURE 1: Vibrator trails on concrete pavements. (Photo courtesy: Robert F Steffes, CP Tech Center, Iowa State University)

VISION It is believed that it will be a revolutionary advance in paving technology if vibration of the slip-form paved concrete can be eliminated. Such a new self-consolidating concrete for slip-form application (SF SCC) would permit the concrete paving industry to have not only more

TRB 2007 Annual Meeting CD-ROM Original paper submittal - not revised by author.

Kejin Wang, Surendra P. Shah, and Thomas Voigt 4

uniform, durable, and smoother pavements but also much faster, safer, and quieter construction. Such concrete technology could also be applied to slip form construction of many other structures, such as water towers and tanks. CHALLENGE Todays concrete research and practice has shown that material selection and mix design of concrete can be tailored to provide a good consolidation without the need for vibration. This principles of self-consolidating concrete (SCC) has been widely used in precast as well as cast-in-place construction. SCC has generated tremendous industrial interest since its initial introduction in Japan (1990). Due to its excellent flowability and stability (segregation resistance), SCC has been used for many different applications, including bridge decks and pavement repairs. SCC can be cast and compacted in small dimension and/or heavily reinforced formwork without vibration. Use of SCC technology also increases the speed of the construction, improves the quality of the concrete (without segregation and loss of air), and reduces the cost of labor, energy, and environmental impacts caused by vibration and/or noise.

A challenge in developing SF SCC is that the new SCC needs to possess not only excellent self-compactibility without segregation before extrusion but also extraordinary shape stability to sustain its self-weight, or to hold the slab in shape, without support from any framework right after casting. It is understood that to obtain self-consolidating ability, a concrete mixture must overcome the stress generated by the friction and cohesion between the aggregate particles; while to hold the freshly cast products in shape, the fresh concrete must have certain strength or stability. A key issue is to achieve these two conflicting needs for the concrete at appropriate time. APPROACH Concrete is a shear-thin material. At a high shear rate (such as during mixing), concrete microstructure is disturbed, and its yield stress and viscousity are reduced. Thus, the concrete becomes more flowable and self-compactible. While at a low (or zero) shear rate, concrete microstructure can be re-built, green strength will develop, and the concrete becomes less deformable. Extrusion process, even at a low pressure, will help concrete consolidation and green strength development by rearranging solid particles for packing. Based on the current knowledge of concrete materials, a rational balance between compactibility and shape stability of a concrete mixture can be achieved timely by tailoring concrete materials and mix design, and there is a great potential for development of a desirable SF SCC. An approach to the concrete mix design development is to start from a conventional SCC mix design and then modify it gradually with fine materials and/or chemical admixtures so as to achieve improved its shape stability without loss of its self-compactability.

TRB 2007 Annual Meeting CD-ROM Original paper submittal - not revised by author.

Kejin Wang, Surendra P. Shah, and Thomas Voigt 5

CRITERIA Based on the discussion above, the novel SF SCC may not be as fluid as the conventional SCC but it will be (1) workable enough for machine placement, (2) self-consolidating without segregation, (3) able to hold shape right after casting, and (4) of compatible (or superior) performance properties (strength and durability) to (or over)

conventional concrete. PRELIMINARY STUDY The research on the SF SCC development is in progress, which is conducted by the collaborative research team members from the National Concrete Pavement Technology Center (CP Tech Center) at Iowa State University (ISU) and the Center for Advanced Cement Based Materials (ACBM) at Northwestern University (NU). As a preliminary study, the research team has investigated the effects of materials and proportions on concrete flowability, consolidation, and shape stability. This investigation has focused on the effects of supplementary cementitious materials (SCMs) (mainly fly ash), clays, and chemical admixtures (superplasticizers and viscosity modifiers) on flow behavior of pastes and concrete. Modified slump cone test, modified flow table test, compaction factor test, and green strength test have been performed. A mini-paver is also developed at the CP Tech Center to simulate field paving using SF SCC in laboratory. Detailed studies have been or will be presented in different publications2, and selected results are summarized below:

FIGURE 2 Effectiveness of different fine materials on shape stability of cement pastes.

TRB 2007 Annual Meeting CD-ROM Original paper submittal - not revised by author.

Kejin Wang, Surendra P. Shah, and Thomas Voigt 6

Effect of Fine Materials on the Flowability of Cement Pastes As mentioned before, the SF SCC mix design development started with a common self-consolidating concrete (SCC). This SCC was modified by gradually adding different fine materials, such as fly ash, clay and cement, until the concrete reached a shape stable condition. Figure 2 shows the effects of different fine materials on flowability and shape stability of concrete pastes, where the paste flow was measured by the flow drop table as described in ASTM C 230. The high effectiveness of the fine materials in shape stability improvement appeared closely related to the finer particle size. With the fine material addition, a high flowable, low shape stability paste was changed into a non-flowable, highly shape stable paste.

(a) Loosely-filled slump cone test

(b) Modified compaction test

FIGURE 3 Illustration of loosely-filled slump cone and modified compaction tests.

750 mm Slump

Spread

300 mm

Slump Cone

750 mm

Measure

TRB 2007 Annual Meeting CD-ROM Original paper submittal - not revised by author.

Kejin Wang, Surendra P. Shah, and Thomas Voigt 7

Interrelation between Concrete Flow Ability and Compactibility As shown in Figure 3, a loosely-filled slump cone test, using the cone as described in ASTM C 143 without rodding the sample, was employed to evaluate the concrete flow ability and self-compacting ability. The test results (Table 1) indicate that concrete mixtures made with different materials and mix proportions displayed different slump, spread, and shape right after the slump cone was removed. Some concrete mixtures may have a similar slump value but different spread values and shape stability. Proper balance among slump, spread, and shape might provide the concrete with proper ability to self-compact and hold shape. TABLE 1 Concrete flow ability and compaction ability Compaction Factor

Slump/Spread Shape of the Concrete Mixture after the Loosely-filled Slump Cone Test

0.8 50-150 mm/ 200-275 mm (2-6/ 8-11) Irregular Shape

1.0 175-225 mm)/

200-275 mm (3-7/ 12-15) Regular Cone Shape

Green Strength The investigators believe that the shape stability of fresh concrete is related to its green strength - the strength of concrete at the plastic or green state. The concrete green strength is associated with the friction and cohesion among the cement-coated aggregate particles. Concrete having higher green strength may have better the shape stability. However, as mentioned before, concrete shape stability combats with its flow ability. In order to achieve a proper SF SCC, a minimum shape stability or green strength of the concrete shall be obtained while sufficient flow ability is maintained for self-consolidation. As a result, the study on concrete green strength was aimed at finding out the minimum green strength required for the concrete shape stability and the factors that affect concrete green strength.

The green strength of fresh concrete has been evaluated by the research team with two different methods: (1) A simple, sand loading method In this simple test, as illustrated in Figure 4, a plastic cylinder mold (4 in. x 4 in. or 10 cm x 10 cm, without bottom) was used for concrete casting. During the casting, the SF SCC mixture was poured into the cylinder molds at a given height (12 in or 30 cm) with no

TRB 2007 Annual Meeting CD-ROM Original paper submittal - not revised by author.

Kejin Wang, Surendra P. Shah, and Thomas Voigt 8

additional consolidation applied. Immediately after the cast, the plastic mold was removed and the shape of the concrete sample was examined. If a mixture demonstrated little or no deformation after the mold was removed, the mixture was considered to have good shape-holding ability, and the green strength test of the sample was then pursued. A large plastic cylinder (6 in. x 12 in. or 15 cm x 30 cm) was placed on the top of the fresh concrete sample. A small amount of sand was then slowly but continuously poured into the large plastic cylinder until the sample collapsed. The total amount of sand applied during the test divided by the loading area of the sample defined the green strength of the concrete. It was observed that the newly developed SF SCC (without rodding or vibration) could hold its shape very well right after demolding (Figure 4c) while its green strength was only 2.3 kPa (0.35 psi), much less than that of the compacted conventional pavement concrete (8.8 kPa or 1.33 psi)2.

(a) Test setup: slump cone placed on top

of a plastic mold without the bottom (b) Casting: mold is filled with fresh

concrete without rodding or vibration

(c) Demolding: after plastic mold is

removed, some concrete holds its shape

(d) Loading: a big cylinder is placed on top of fresh concrete sample; sand is then gradually loaded into cylinder until sample fails

FIGURE 4 The simple, sand loading test method for concrete green strength. (2) A modified flow table method A standard flow table as described in ASTM C 230 was used to prepare samples for evaluation of the green of concrete. During the test, a 4x8 inch cylinder was loosely filled with fresh concrete, and then placed on the drop table. After 25 drops, the cylinder was turned over and demolded. The shape stability of the demolded cylinder was visually evaluated. A vertical force was then applied to the cylinder until the specimen collapsed. The maximum force was used to calculate the green strength of the tested cylinder. Figure 5 shows the flow table used for the green strength test and a specimen before and after the test.

TRB 2007 Annual Meeting CD-ROM Original paper submittal - not revised by author.

Kejin Wang, Surendra P. Shah, and Thomas Voigt 9

Drop Table Test Green StrengthShape Stability

after compaction in cylinder mold (2x4 in) on drop table (25 drops)

FIGURE 5 The flow table used for green strength test (left) and a specimen before and after the test (right).

Table 2 presents some test results from the modified flow table tests3. In the table, the Plain concrete mix had a proportion of water:cement:gravel:sand:naphthalene plasticizer (by weight) = 0.38:1.00:1.67:1.54:0.004. The Class F fly ash and clays were used as additives. The results in Table 2 indicate that when compared with the Plain mix, addition of Class F fly ash increased the concrete flow but decreased the concrete green strength. Different clay modified the concrete properties in a different way. Addition of 1.5 % Clay 1 increased concrete green strength considerably but slightly reduced the concrete flow. Addition of 1.5 % Clay 2 did not change the concrete green strength but increased concrete flow slightly. As expected, concrete green strength generally decreased as the concrete flow increased. TABLE 2 Concrete green strength and flow measured from the modified flow

table test Concrete Mixture Green Strength

(kPa) Flow

(% at 25 drops) Plain (Reference) 3.4 75 Plain +10% FA (class F) 0.0 110 Plain + 23% FA (class F) 1.2 83 Plain + 33% FA (class F) 1.2 63 Plain +1.5% Clay 1 (metakaolinite) 8.8 69 Plain +1.5% Clay 2 (kaolinite, illite, silica) 3.4 88 Laboratory Simulation To investigate whether or not this new SF SCC was applicable to field paving, a simple mini-paver was developed at the CP Tech Center to simulate field paving using SF SCC in laboratory. Figure 6 illustrate the configuration of the mini-paver.

TRB 2007 Annual Meeting CD-ROM Original paper submittal - not revised by author.

Kejin Wang, Surendra P. Shah, and Thomas Voigt 10

18

36

24

Platform

L-box

6

FIGURE 6 Mini-paver used for lab simulation of slip form paving.

To start paving, fresh concrete was pushed from a platform into the vertical leg of the box up to a certain height, which generated a pressure to consolidate the concrete. Then, the mini-paver was pulled forward by a crank system at a designed speed (3-5 ft/min) and the concrete slab was extruded at the end of the mini-paver.

(a) SF SCC slab cast by the mini-paver (b) Cross-section of the SF SCC slab

FIGURE 7 SF SCC pavement slab produced using mini-paver.

Selected SF SCC mixtures were tested with the minipaver, and Figure 7 displays one

of the final mini-paver test products. With no additional consolidation applied during the test, the SF SCC not only flowed and consolidated well but also held the shape of the slab very well, especially at edge. The 9-day compressive strength of the 2 cylinders cored from the slab was 4900 psi and the splitting tensile strength was 420 psi.

Working table

Crank

Towing cable

6

4-6

Concrete in

Slab out

Stop plate

TRB 2007 Annual Meeting CD-ROM Original paper submittal - not revised by author.

Kejin Wang, Surendra P. Shah, and Thomas Voigt 11

MAJOR FINDINGS The preliminary results of the present research have indicated the following:

Newly developed SF SCC has sufficient self-consolidating ability and timely shape stability

The set time and strength of the SF SCC is comparable to those of conventional concrete.

The mini-paver test has demonstrated that such a SF SCC for field application is feasible.

Different from the conventional self-consolidating concrete (SCC), which has very high flowability and requires formwork for construction, this new type of self-consolidating concrete for slip-form paving (SF SCC) will have sufficient flowability for self-consolidation but be stiff enough to hold its shape right after paving, thus not requiring formwork for construction. Currently the research team is conducting the field trial tests using SF SCC for small pavements such as bike roads. Further studies on the concrete mix design procedure, field paving application, specification, and performance monitoring are under development. ACKNOWLEDGEMENT Five state departments of transportation (Iowa DOT, Kansas DOT, Nebraska DOR, New York State DOT, and Washington State DOT), industry (W. R. Grace and Active Minerals Company), the Federal Highway Administration (FHWA), and the CP Tech Center participated in and sponsored the feasibility study of this project. The authors greatly appreciate the technical inputs and financial supports from the participants on the research project. Special thanks are extended to Tom Cackler at the National CP Tech Center and Sandra Larson at Iowa DOT for their management and strong support throughout the project.

REFERENCES 1 S. Tymkowicz and R. F. Steffes, Vibration Study for Consolidation of Portland Cement

Concrete, Semi-sesquicentennial Transportation Conference, Iowa State University, 1996

2 Kejin Wang, Surendra P. Shah, Thomas Voigt, Bekir Yilmaz Pekmezci, David J. White, Joseph Gray, Lu Gang, Jiong Hu, and Clinton Halverson, Self-Consolidating ConcreteApplications for Slip-Form Paving: Phase I (Feasibility Study), Final Report, TPF-5(098), Center for Portland Cement Concrete Pavement Technology, November 2005

3 Thomas Voigt, Bekir Yilmaz Pekmezci, Kejin Wang, Surendra P. Shah, Low Compaction Energy Concrete for Improved Slip Form Casting of Concrete Pavements, (Accepted by ACI Materials Journal, 2006)

TRB 2007 Annual Meeting CD-ROM Original paper submittal - not revised by author.

A NOVEL SELF-CONSOLIDATING CONCRETE FOR SLIP-FORM APPLICATIONEffect of Fine Materials on the Flowability of Cement Pastes