By electrostatic repulsion and steric hindrance, polycarboxylate-based superplasticiser (SP) decreases the water demand for cement hydration in mortar/concrete production. Subsequently, less water is needed for a prescribed flowability, which improves its concurrent design limits of strength and flowability. Nonetheless, SP also introduces unfavourable dilatancy (or shear thickening) in mortar due to the clustering of mobile SP polymers in interstitial voids and adsorbed polymers on cement. Interestingly, the dilatancy does not increase monotonically with SP dosage. Reversal of dilatancy occurs when a threshold SP dosage is reached, and subsequent addition of SP decreases dilatancy because the fine particles in the mortar are better dispersed with adequate SP. Interstitial voids substantially decrease due to deflocculation of the fine particles, which improves the wet packing density (WPD) of mortar. Based on this, it is believed that by blending the cement with fly ash and/or using multi-sized sand, the dilatancy of mortar can be alleviated. In this research, using a coaxial viscometer, a rheology test programme of superplasticised mortar was conducted to determine the threshold SP dosage when dilatancy reversal occurs, to study the effect of using multi-sized powder and sand on mortar dilatancy and to correlate the dilatancy of mortar to its WPD.

中文翻译：

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超塑化水泥砂浆的剪胀逆转

通过静电排斥和空间位阻，聚羧酸减水剂 (SP) 降低了砂浆/混凝土生产中水泥水化的需水量。随后，规定的流动性需要更少的水，这改善了其强度和流动性的并行设计限制。尽管如此，由于间隙空隙中移动的 SP 聚合物和水泥上的吸附聚合物的聚集，SP 也会在砂浆中引入不利的膨胀（或剪切增稠）。有趣的是，膨胀率不会随着 SP 剂量单调增加。当达到阈值 SP 剂量时，膨胀性发生逆转，随后添加 SP 会降低膨胀性，因为砂浆中的细颗粒在足够的 SP 下更好地分散。由于细颗粒的反絮凝，间隙空隙显着减少，提高砂浆的湿堆积密度（WPD）。基于此，相信通过将水泥与粉煤灰混合和/或使用多粒度砂，可以减轻砂浆的膨胀。在本研究中，使用同轴粘度计，进行了超塑化砂浆的流变学测试程序，以确定发生剪胀逆转时的阈值 SP 用量，研究使用多粒度粉末和沙子对砂浆剪胀的影响，并与迫击炮到其 WPD。