Development and performance of self-consolidating concrete with adapted thixotropy

自固结混凝土（SCC）是一种新兴的技术，它使混凝土的浇筑无需任何机械固结，而使用传统混凝土则需要机械固结。这可以显著减少浇筑时间和人工成本，并生产优质混凝土产品。尽管SCC已经在预制行业获得了广泛的认可（在北美的市场份额高达30%），但在预拌料行业中使用SCC仍然存在一些技术问题，而预拌料行业在加拿大的混凝土建设中占有最大的份额。稳定和坚固的SCC的日常设计中仍然存在技术变化，这些SCC可以在垂直结构部分（柱，元件，桥墩等）中浇筑，而不会对模板施加过大的侧压力。这一点很重要，因为SCC表现得像液体，与更硬的传统混凝土相比，它可以对模板施加更大的侧压力，对建筑成本产生相当大的影响。SCC可以设计成具有可逆的结构堆积（触变性），以降低成型压力，并确保硬化材料的原位均匀性。生产高度触变的混凝土可能会导致一些表面缺陷（施工升降机线的外观和形成表面的大气泡），并且需要调整混凝土的流变特性以匹配放置条件。拟议研究计划的目标是：(i)制定测试方案，以评估静止时可逆的结构积聚和评估现场触变性的特殊测试方法；阐明控制触变性的机制；（iii）开发具有适应触变特性和优越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，这可能会彻底改变加拿大乃至其他地区的建筑行业。这种混凝土可以导致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，并确保高性能的建筑和修复材料，以满足加拿大建造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.