Design and Application of Low Compaction Energy Concrete for Use in Slip-form Concrete Paving

The United States Department of Transportation (USDOT) has outlined key research goals for the future of this country's crumbling infrastructure. The first three goals include 1) safety, 2) reduction in congestion and 3) global connectivity. The project proposed for continuation herein aims to contribute to all three of these major goals. The slip-form paving process has made highway construction considerably quicker and more cost-effective since its development in Iowa in the late 1940s. Different from the fixed-form paving, slipform paving brings together concrete placing, casting, consolidation, and finishing into one unique process. The stiff concrete used in slip-form paving machines requires extensive internal vibration. Although this streamlined process has been able to cut down on construction time, one of the major problems associated with slip-cast paving concerns durability. It has been shown that over-consolidation caused by the internal vibrators during the construction process contribute to the formation of premature cracks. Typically, pavements are designed to last 25-30 years, however in several instances in the United States, slip-cast pavements have shown significant cracks at three years, and requiring expensive and time consuming repairs leading to closures and congestion. For cast-in place and pre-cast concrete construction, it has been shown that material selection and mix design of concrete can be tailored to provide sufficient compaction without internal vibration. This approach is based on the principles of selfconsolidating concrete (SCC). This proposal is focused on optimizing the consolidation properties and shape stability of fresh concrete in order to eliminate internal vibration in the slip-form paving process. This new concrete is termed Slip-Form SCC (SF-SCC). SF-SCC is not as fluid as conventional SCC, but it will (1) be workable enough for machine placement, (2) be compactable with minimal external energy, (3) hold shape after extrusion from a paver, and (4) have comparable performance properties (strength and durability) to the current pavement concrete. Such a durable concrete will increase time between maintenance and reduce congestion and associated risks involved for construction workers. A study conducted by the Center for Advanced Cement-Based Material (ACBM) at Northwestern University with the Center for Portland Cement Concrete Pavement Technology (PCCPT) at Iowa State University concluded that is it possible to slip-cast pavements without internal vibration through manipulation of mix designs by adding fine materials and chemical admixtures. The feasibility study was supported by a consortia consisting of members from the FHWA, state DOTs and concrete material/admixture suppliers. Considering the keen interests and needs of the concrete paving industry, the research team has divided the following work among the two research centers: Proposed work to be delivered by ACBM under funding from ITI in 2009/2010 will include: 1. Pinpoint mechanisms responsible for dramatic increases in green strength associated with small additions of clays including water absorption, chemical influences and particle packing; 2. Investigate possible use of wave-reflection, acoustics emission and temperature methods to quantify flocculation processes in order to gain fundamental insight into how cement-based materials develop green strength immediately after casting; 3. Investigate segregation mechanisms in concrete using computational fluid dynamics modeling in order to explain relationships garnered from the slump-flow; 4. Continued refinement of SF-SCC design methodology and acceptance criteria (shared with PCCPT) Work to be delivered by PCCPT: 5. Development of SF-SCC design methodology and acceptance criteria (shared with ACBM); 6. Conduct small-scale field paving trials; 7. Investigate durability and mechanical property issues concerning SF-SCC; 8. Full-scale field investigation of SF-SCC paving in collaboration with PCCPT Tasks 1-4 will be delivered by ACBM, under funding from ITI. Tasks 4-7 will be conducted by the PCCPT with support from ACBM concerning material and modeling background. Task 4 is shared between both research centers. Each center has developed different sets of acceptance criteria. These methods will be compared in order to determine the best solution. This new technology will have revolutionary impacts on environment, economics, and pavement sustainability, which is extremely important to the overall public view. The potential benefits of having such a new type of SF-SCC include the following: * Eliminate the vibrator trails and large cracks in concrete pavement and improve pavement durability. * Enhance the quality, especially the uniformity of concrete pavements by reducing the problems resulting from inconsistent vibration of concrete. * Improve pavement smoothness with minimum surface finishing requirements. * Expedite construction speed and reduce construction energy and noise that are consumed and generated by the vibrator. * Increased durability and decreased maintenance of pavements, thus reducing congestion and road closures. * Increase awareness in tailorability of concrete for a wide range of applications, such as SCC mixes that exhibit lower formwork pressure due to green strength. * Insight into fundamental processes involved in the green strength development in fresh state concrete. * Implementation of field friendly quality control tests. The research results will benefit not only slip-cast paving but also slip-form construction of pipes, tanks, towers, silos, and high-rise buildings.