Influence law and control mechanism of manufactured sand particles derived from tunnel slag on cement hydration

The utilization of tunnel slag processed manufactured sand for high-performance concrete preparation and its application in engineering construction can yield significant economic and social benefits. However, most studies in the field of hydration have predominantly focused on the stone powder, and completely disregarded the influence of sand particles on hydration. To address this research gap, this study investigated the hydration exothermic process of mortar containing different lithologic manufactured sand particles and discussed their underlying mechanisms based on test results. The study revealed that the impact of various lithologic manufactured sand particles was even more significant than the limestone powder content. The exothermic peak value improved by 9.31% and the cumulative heat at 168 h (7 days) increased by 11.81% when the Sphericity (SPHT) of sand particles reduced from 0.867 to 0.817. The signal of the flocculated structure water gradually decreased with the decrease of the SPHT. The strong correlation between the main hydration peak and the SPHT supported the hypothesis that the influence of different lithologic manufactured sand particles on hydration is attributed to their distinct shapes. Moreover, the most probable diameter was smaller apparently in the mortar consisting of manufactured sands, and the hydration products were tiny and more evenly distributed, when compared with NS mortar. Consequently, two mechanisms, including flocculated structure reducing and crystal nucleus dislodged, were proposed to account for the effect of manufactured sand particles on hydration.