Development and performance of self-consolidating concrete with adapted thixotropy

自固结混凝土(SCC)是一种新兴的混凝土浇筑技术，它不需要传统混凝土所需要的任何机械固结。这可以显著减少浇注时间和劳动力成本，并生产优质混凝土产品。尽管SCC在预制件行业得到了广泛的接受(在北美的市场份额高达30%)，但在预拌行业使用SCC仍然存在一些技术问题，该行业在加拿大混凝土建筑中占据着最大的份额。稳定和坚固的自密实混凝土的日常设计仍然存在技术变化，可以在垂直结构截面(柱、构件、桥墩等)中浇注。而不会对模板施加过大的侧向压力。这一点很重要，因为SCC的行为像液体，与更坚硬的传统混凝土相比，可能会对模板施加更大的侧向压力，从而对建筑成本产生相当大的影响。SCC可以设计成表现出可逆的结构积聚(触变性)，以降低成型压力并确保硬化材料的更大原位均质性。生产高触变性混凝土可能会导致一些表面缺陷(出现施工升降线和成型表面的大气泡)，并需要调整混凝土的流变性以适应浇筑条件。拟议研究计划的目标是：(I)制定测试方案，以评估静态可逆结构积聚；以及特殊测试方法，以评估现场触变性；(Ii)阐明控制触变性的机制；(Iii)开发具有适应的触变性、卓越的工程性能和耐久性的新一代SCC。这项研究的最终目标是开发新一代高流动性混凝土，这种混凝土可能会给加拿大和其他地区的建筑业带来革命性的变化。这样的混凝土可以实现施工过程的优化和自动化，增加对复杂结构的创新设计的使用，并确保高性能建筑和维修材料的安全，以应对在加拿大建设耐用混凝土基础设施的巨大挑战。

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.