Role of shear stress at rest on the viscoelastic response of fresh cement pastes
Role of shear stress at rest on the viscoelastic response of fresh cement pastes
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DOI：
10.1122/1.5129676
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发表时间：
2020-03
影响因子：
3.3
通讯作者：
Siwei Ma;S. Kawashima
中科院分区：
文献类型：
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作者：
Siwei Ma;S. Kawashima
新混凝土由集料和水泥浆组成，水泥浆本身是一种致密的悬浮物，表现出屈服应力，并作为粘合剂通过水泥水化固化。虽然在新鲜状态（即凝固前）反应相对较少，但仍有早期水化产物的形成，影响膏体的流变性。非零静应力广泛存在于混凝土实践中，例如泵送中断、静态模板浇筑和3D混凝土打印，但其对最终粘弹性性能的影响尚未得到很好的了解。在这项研究中，我们研究了不同水平的静应力对新水泥浆的影响，并表明它会显著改变最终的固体性能（即静态屈服应力和刚度）。随着静剪应力的增加，水泥浆体表现出静态屈服应力的增加和弹性行为的增加，其根源与水化的进展有关。将水泥浆体与氧化镁悬浮液（作为惰性模型体系）进行比较，发现前者的静态屈服应力随时间增加的速率加快，而后者则没有。这突出了在非零剪切应力存在下，早期水泥水化对新水泥膏体固化行为的作用。我们进一步支持这一点，表明水泥浆体在外加应力下的结构演化主要归因于弹性极限的增强，这与早期水化有关。研究了两种常用的黏度改性外加剂纳米粘土和地坛胶对这些性能的影响。这项工作证明了在实验室流变实验和工业混凝土应用中考虑静止剪应力的重要性，因为它可以极大地影响最终的凝固行为。新混凝土由集料和水泥浆组成，水泥浆本身是一种致密的悬浮物，表现出屈服应力，并作为粘合剂通过水泥水化固化。虽然在新鲜状态（即凝固前）反应相对较少，但仍有早期水化产物的形成，影响膏体的流变性。非零静应力广泛存在于混凝土实践中，例如泵送中断、静态模板浇筑和3D混凝土打印，但其对最终粘弹性性能的影响尚未得到很好的了解。在这项研究中，我们研究了不同水平的静应力对新水泥浆的影响，并表明它会显著改变最终的固体性能（即静态屈服应力和刚度）。随着静剪应力的增加，水泥浆体的静态屈服应力增加，弹性行为增强，其原因与水螅体的发展有关。
Fresh concrete is composed of aggregates and cement paste, which itself is a dense suspension that exhibits a yield stress and serves as a binder that solidifies through cement hydration. Although there is relatively little reaction during the fresh state (i.e., before setting), there is still the formation of early hydration products that will influence the paste rheology. Nonzero stress at rest widely exists in concrete practice, e.g., interruption during pumping, static formwork casting, and 3D concrete printing, but its impact on eventual viscoelastic properties is not well understood. In this study, we investigated the influence of different levels of applied shear stress at rest on fresh cement pastes and show that it dramatically alters the eventual solid performance (i.e., static yield stress and stiffness). With increasing applied shear stress at rest, the cement paste exhibited increasing static yield stress and increasingly elastic behavior, where the origin was tied to the progression of hydration. Cement pastes were compared against magnesium oxide suspensions, which served as an inert model system, and an accelerated rate of static yield stress increase over time was observed in the former but not in the latter. This highlights the role of early cement hydration on the solidification behavior of fresh cement pastes in the presence of nonzero shear stress at rest. We further support this by showing that the structural evolution of cement paste under applied stress can primarily be attributed to an enhanced elastic limit, which is associated with early hydration. The influence of two common viscosity modifying admixtures, nanoclay and diutan gum, on these properties was also examined. This work demonstrates the importance of taking the shear stress at rest into consideration for laboratory rheological experiments and industrial concrete applications, as it can substantially impact the eventual solidification behavior.Fresh concrete is composed of aggregates and cement paste, which itself is a dense suspension that exhibits a yield stress and serves as a binder that solidifies through cement hydration. Although there is relatively little reaction during the fresh state (i.e., before setting), there is still the formation of early hydration products that will influence the paste rheology. Nonzero stress at rest widely exists in concrete practice, e.g., interruption during pumping, static formwork casting, and 3D concrete printing, but its impact on eventual viscoelastic properties is not well understood. In this study, we investigated the influence of different levels of applied shear stress at rest on fresh cement pastes and show that it dramatically alters the eventual solid performance (i.e., static yield stress and stiffness). With increasing applied shear stress at rest, the cement paste exhibited increasing static yield stress and increasingly elastic behavior, where the origin was tied to the progression of hydra...