Effect of Internal Curing by Super Absorbent Polymer on the Autogenous Shrinkage of Alkali-Activated Slag Mortars

Abstract

Alkali activated slag (AAS) mortar is becoming an increasingly popular green building material because of its excellent engineering properties and low CO2 emissions, promising to replace ordinary Portland cement (OPC) mortar. However, AAS’s high shrinkage and short setting time are the important reasons to limit its wide application in engineering. This paper was conducted to investigate the effect of internal curing(IC) by super absorbent polymer (SAP) on the autogenous shrinkage of AAS mortars. For this, an experimental study was carried out to evaluate the effect of SAP dosage on the setting time, autogenous shrinkage, compressive strength, microstructure, and pore structure. The SAP were incorporated at different dosage of 0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 percent by weight of slag. The workability, physical (porosity), mechanical, and shrinkage properties of the mortars were evaluated, and a complementary study on microstructure was made. The results indicated that the setting time increased with an increase of SAP dosage due to the additional activator released by SAP. Autogenous shrinkage decreased with an increase of SAP dosage, and was mitigated completely when the dosage of SAP ≥ 0.2% wt of slag. Although IC by means of SAP reduced the compressive strength, this reduction (23% at 56 days for 0.2% SAP) was acceptable given the important role that it played on mitigating autogenous shrinkage. In the research, the 0.2% SAP dosage was the optimal content. The results can provide data and basis for practical application of AAS mortar.

Mitigating Autogenous Shrinkage of Alkali-Activated Slag Mortar by Using Porous Fine Aggregates as Internal Curing Agents

“…As shown in Figure 9, it was more likely that a higher vo mortar would obtain water from MAs with a smaller distance between aggrega which ensured a better internal curing performance. In previous studies [2,26], th enous shrinkage of AAS could be totally eliminated by SAPs and the cenospher could not achieve the same effect, even though the wa/b was higher. This was re the difficulty of releasing all the extra water from MAs.…”

“…In this study, in view of the unstable characteristics of SAP desorption (which leads to great strength reduction [26]), the wide sources of LWA with different properties, and the complex PC manufacturing process, cement was used to prepare standard man-made internal curing agents (MAs) in order to produce active internal curing technology with controllable absorption and desorption, low costs, and easy standardization. We sought to examine the effects of MAs on the autogenous shrinkage, internal relative humidity (IRH), compressive strength, hydration properties, and pore structure of AAS mortars.…”

Effect of borax-modified activator on mechanical properties and drying shrinkage of alkali-activated slag/metakaolin mortar

“…The widely recognized mechanism of DS is that when the water gradually evaporates, surface tension is generated when the menisci are formed in the gel pores and capillary pores, thereby causing an equal compressive stress in the skeleton and causing volume shrinkage 14 , 15 . Current research primarily focuses on reducing the DS of AAMs by incorporating fibers 16 – 18 , chemical admixtures 4 , 19 , and mineral admixtures 20 , 21 , as well as changing the curing system 22 – 24 . Changing the curing system, while effectively reducing shrinkage, may also lead to a decrease in mechanical properties and issues of unstable internal curing humidity 24 .…”

“…Current research primarily focuses on reducing the DS of AAMs by incorporating fibers 16 – 18 , chemical admixtures 4 , 19 , and mineral admixtures 20 , 21 , as well as changing the curing system 22 – 24 . Changing the curing system, while effectively reducing shrinkage, may also lead to a decrease in mechanical properties and issues of unstable internal curing humidity 24 . Adding fibers can enhance the toughness of AAMs and reduce shrinkage, but it also introduces uncertain factors such as uneven fiber distribution and lower fluidity than cement mortar 25 .…”

Improving Self-Healing and Shrinkage Reduction of Cementitious Materials Using Water-Absorbing Polymer Microcapsules

“…Li et al [11] added SAP in cement; the autogenous shrinkage of cement decreased with increasing SAP content. Wang et al [12] found that adding 0.05-0.1% SAPs to alkalized active slag mortar reduced autogenous shrinkage by 4-6 times. Asmann et al [13] found that the shrinkage strain of mortar with a water-to-cement ratio of 0.42 decreased from 85 to 35 µstrain on addition of SAPs.…”