Development and performance of self-consolidating concrete with adapted thixotropy

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Self-consolidating concrete (SCC) is an emerging technology that enables the casting of concrete without any mechanical consolidation which would be required when using conventional concrete. This can lead to remarkable reduction of casting time and labour cost and the production of premium concrete products. Although SCC has gained wide acceptance in the precast industry (up to 30% of the market share in North America) some technical issues remain at hand for the use of SCC in the ready-mix industry, which holds the largest segment of concrete construction in Canada. Technical changes remain in daily designs of stable and robust SCC that can be cast in vertical structural sections (columns, elements, bridge piers, etc.) without exerting excessive lateral pressure on the formwork. This is important given the fact that SCC behaves like a liquid and could exert greater lateral pressure on formwork compared to stiffer conventional concrete, with considerable impact on construction cost. SCC can be designed to exhibit a reversible structural build-up (thixotropy) to reduce form pressure and secure greater in-situ homogeneity of the hardened material. Producing highly thixotropic concrete could lead to some surface defects (appearance of construction lift lines and large entrapped air bubbles at formed surfaces) and would necessitate adapting the rheological properties of the concrete to match placement conditions. The objectives of the proposed research program are to (i) develop test protocols to evaluate the reversible structural build-up at rest and special test methods to assess thixotropy in the field; (ii) elucidate mechanisms governing thixotropy; (iii) develop new generation of SCC with adapted thixotopy and superior engineering properties and durability. The ultimate goal of the research is to develop new generation of highly flowable concrete that could revolutionize the construction industry in Canada and beyond. Such concrete can lead to optimization and automation of the construction process, increase the use of innovative designs for complex structures, and secure high-performance construction and repair materials to meet the great challenge of building durable concrete infrastructure in Canada.