Preparation and properties of self-compacting alkali-activated slag repair mortar

Abstract

Abstract The alkali-activated slag (AAS) cement has the characteristics of high early strength and high strength, and is especially suitable for preparing repair mortar. The fluidity, setting time, mechanical properties, expansion properties and adhesive property of self-compacting alkali-activated slag repair mortar (SCAASRM) were mainly studied. Moreover, the influence of Dmax of sand on properties of SCAASRM and microstructure of AAS pastes were also studied. Sodium chloride incorporation can improve the fluidity of SCAASRM, especially the 30 min fluidity, although compressive and flexural strength decrease. Amount of Na2SO4 has little effect on fluidity of SCAASRM, although compressive and flexural strength of 1 day increase. With the increase of Dmax, both initial and 30 min fluidity increase a little. SCAASRM with active MgO exhibits microexpansion within 48 h after preparation. With the increase of Na2SO4, adhesive strength of SCAASRM increases. Higher water glass (WG) and higher Dmax of sand result in a little lower adhesive strength. Setting time of SCAASRM is between 65 min and 105 min. Considering the comprehensive properties of SCAASRM, the superior mix design is 4–5% NaCl, 5% WG, 1.5–2% Na2SO4, 2% MgO and 2% PCS. Dmax of sand is 2.36 mm. Water-binder ratio and binder-sand of SCAASRM is 0.40 and 1:1 respectively. Hydrotalcite is formed in the hydration products. NaCl and active MgO improve the crystallinity of the hydration product. With the increase of active MgO, more hydrotalcite appears and surplus active MgO exists in the form of periclase. Also, no brucite is detected. A kind of nepheline is formed in AAS pastes with NaCl.