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Due to the large amount of old hardened cement mortar attached to the surface of aggregate and the internal micro-cracks formed by the crushing process, the water absorption, apparent density, and crushing index of recycled coarse aggregate are still far behind those of natural coarse aggregate. Based on the performance requirements of different qualities of recycled coarse aggregate, the performance differences of recycled coarse aggregate before and after physical strengthening were observed. The results showed that the physical strengthening technique can remove old hardened mortar and micro powder attached to the surface of recycled coarse aggregate by mechanical action, which can effectively improve the quality of recycled coarse aggregate. The optimum calcination temperature of the recycled coarse aggregate was 400 °C and the grinding time was 20 min. The contents of the attached mortar in recycled coarse aggregates of Class I, II, and III were 7.9%, 22.8%, and 39.7%, respectively. The quality of recycled coarse aggregate was closely related to the amount of mortar attached to the surface. The higher the mortar content, the higher the water absorption, lower apparent density, and higher crushing index of the recycled coarse aggregate. [ABSTRACT FROM AUTHOR]

Compared with nanosilica collected in a gaseous state, nanosilica sol has great economic value and application significance for improving the performance of concrete and mortar. In this study, the influence of nanosilica sol on the hydration process of different kinds of cement is studied by means of hydration heat analysis, X-ray diffraction analysis (XRD) and other methods, and the properties of mortar such as setting time, mechanical properties and porosity are also studied to characterize the influence of nanosilica sol on the macroscopic properties of mortar. The experimental results show that nanosilica sol can accelerate the hydration rate of two kinds of cement and promote the hydration reaction degree of cement, and this promotion effect increases with the increase in nanosilica sol content. At the same time, nanosilica sol can significantly shorten the setting time of the two kinds of cement, and it is more obvious with the increase in content. Excessive content of nanosilica sol will adversely affect the permeability resistance of mortar. It may be caused by the weak interval formed by nanosilica particle clusters in the mortar matrix, which can be supported by the mortar pore structure distribution test. At the same time, the influence of nanosilica sol on the hydration of the two kinds of cement is different, and the compressive strength of HBSAC cement mortar increases first and then decreases after adding nanosilica sol; However, the compressive strength of P·O 42.5 cement mortar increases gradually after adding nanometer silica sol. This shows that nanosilica sol does not effectively promote the hydration of β-C2S in high belite sulfoaluminate cement (HBSAC) mortar. Based on the above experimental results, it can be concluded that when the content of nanosilica sol is about 1%, it has the best promotion effect on the hydration of the two kinds of cement and the performance of mortar. [ABSTRACT FROM AUTHOR]

Improving the adaptability of polycarboxylate superplasticizers (PCE) in high-clay content mortar is of great significance in enhancing the workability and mechanical properties of mortar containing clay. In this study, the potassium-based alkaline electrolyzed water (AEW) was used as mixing water for cement mortar. The excellent properties of AEW enabled PCE to be more compatible in cement mortar containing montmorillonite (MT) or kaolin (GL), improving the performance of mortar containing clay. The results showed that compared with ordinary tap water (OTW), the adsorption rate of clay minerals on PCE decreased in the AEW environment, and the clay interlayer spacing of MT was also reduced. AEW can inhibit the intercalation and adsorption of PCE molecular side chains by clay minerals to some extent. However, due to its unique crystal structure, the adsorption of MT on PCE was still significantly higher than that of GL. At the same time, increasing the content of clay mineral led to a decrease in mortar performance. Compared with the GL series, the MT series had a more significant negative impact on mortar fluidity and strengths. AEW also can promote hydration reactions, release more hydration heat, and produce more hydration products to encapsulate clay particles, thereby improving the workability and mechanical properties of cement paste containing clay. Furthermore, the high-activity AEW is rich in positively charged metal ions that can interact with clay minerals preferentially over cement particles, which enables the clay interlayer structure to be quickly saturated by AEW water molecules, effectively hindering the adsorption of PCE by clay minerals. However, in both the OTW and AEW environments, the intercalation effect of GL on PCE molecular side chains was not significant. Therefore, AEW has great potential in improving the adaptability of PCE in muddy cement pastes, which can help to enhance the workability and mechanical properties of muddy cement composites. This study provides theoretical references for preparing high-performance anti-clay concrete. • The excellent properties of AEW enabled PCE to be more compatible in cement-based materials containing montmorillonite (MT) or kaolin (GL). • AEW can mitigate the adsorption of MT to the PCE molecular side chains, while the interlayer of GL is both basically not intercalated with PCE molecular side chains. • For different clay minerals series of mortar, AEW mortar both exhibits significantly higher fluidity and strengths than ordinary tap water (OTW) mortar. [ABSTRACT FROM AUTHOR]