Ez-Zaki Hassan, Marangu Joseph Mwiti, Bellotto Maurizio, Dalconi Maria Chiara, Artioli Gilberto, Valentini Luca
CIRCe, Department of Geosciences, University of Padova, Via G. Gradenigo 6, 35131 Padova, Italy.
Department of Physical Sciences, Meru University of Science & Technology, Meru P.O. Box 972-60200, Kenya.
Materials (Basel). 2021 Jun 3;14(11):3037. doi: 10.3390/ma14113037.
In this work, the factors controlling the fresh state properties of limestone calcined clay cement (LC) are assessed and compared to Portland and binary cements, extending the scope of previous research by combining rheological measurements with setting time determination and the evaluation of plastic shrinkage by a novel method. Yield stress and elastic modulus are considered indicators for the structural build-up/breakdown process when stress is applied to the system. On the other hand, plastic shrinkage occurs from the mixing to the setting of fresh paste and plays an important role in governing microstructural changes due to settlement and evaporation. Evaluation of the rheological properties with time was appropriate to give an overview of the influence and behavior of different added materials. The elastic modulus of all binders (clinker, LC, clinker-limestone, and clinker-calcined clay) was increased from mixing to 60 min of curing as follows: 5.27 × 10 to 9.50 × 10 Pa, 5.94 × 10 to 9.87 × 10 Pa, 6.89 × 10 to 5.62 × 10 Pa and 7.85 × 10 to 1.27 × 10 Pa, respectively. Moreover, during the first three hours of curing, LC exhibited a reduction of plastic shrinkage by more than a factor of 2 compared to clinker cement. The use of calcined clay with clinker increases the elastic modulus of the system due to the flocculation effect and increased water absorption, while a dilution effect is contributed due to deflocculation and a free-water increase in the system when a high fraction of limestone is present in the binary cement. The combination of limestone and calcined clay with clinker can induce additional chemical reactions, which control the early age properties, such as plastic shrinkage. The obtained results can contribute to optimizing the fresh state properties of ternary blends of OPC, calcined clay, and limestone through a knowledge-based approach.
在本研究中，对控制石灰石煅烧黏土水泥（LC）新拌状态性能的因素进行了评估，并与波特兰水泥和二元水泥进行了比较，通过将流变学测量与凝结时间测定以及采用新方法评估塑性收缩相结合，扩展了先前研究的范围。当对体系施加应力时，屈服应力和弹性模量被视为结构形成/破坏过程的指标。另一方面，塑性收缩发生在新拌浆体从搅拌到凝结的过程中，并且在控制由于沉降和蒸发引起的微观结构变化方面起着重要作用。随时间对流变性能进行评估，有助于全面了解不同外加材料的影响和行为。所有胶凝材料（熟料、LC、熟料 - 石灰石和熟料 - 煅烧黏土）的弹性模量从搅拌到养护60分钟时均有所增加，具体如下：分别从5.27×10到9.50×10 Pa、5.94×10到9.87×10 Pa、6.89×10到5.62×10 Pa以及7.85×10到1.27×10 Pa。此外，在养护的前三小时内，与熟料水泥相比，LC的塑性收缩降低了两倍多。煅烧黏土与熟料的使用由于絮凝作用和吸水率增加而提高了体系的弹性模量，而当二元水泥中存在高比例石灰石时，由于解絮凝作用和体系中自由水增加，会产生稀释效应。石灰石和煅烧黏土与熟料的组合可引发额外的化学反应，从而控制早期性能，如塑性收缩。所得结果有助于通过基于知识的方法优化普通硅酸盐水泥、煅烧黏土和石灰石三元混合材的新拌状态性能。
