Improving internal curing efficiency through adjusting ab- and desorption curve of superabsorbent polymer in cement pastes using sodium carbonate

Superabsorbent polymer (SAP) has a prominent effect on relieving autogenous shrinkage of low w/c cement -based materials. It is quite important to improve internal curing efficiency of SAP considering the concrete performance and economic cost. In this paper, proper Na2CO3 dosage by cement mass was added into cement pastes to improve internal curing efficiency of SAP. Through X-ray radiography, the ab-and desorption curves of SAP in cement pastes with different Na2CO3 dosage were characterized. Through corrugated tube method, the autogenous shrinkage curves in SAP-containing cement pastes with and without optimal Na2CO3 dosage were obtained. From the view of effective internal curing water content of SAP, internal curing efficiency of SAP with 0.2 wt% SAP dosage and optimal 0.4 wt% Na2CO3 dosage can be improved by 52.3%, compared to that without Na2CO3. From the view of autogenous shrinkage curves, to achieve same internal curing effect, 0.4 wt% SAP dosage can be approximately reduced to 0.3 wt% SAP dosage, with 25% reduction rate of SAP dosage through adding 0.4 wt% optimal Na(2)CO(3)dosage. Further, the mechanism of improving internal curing efficiency of SAP with proper Na(2)CO(3)dosage is revealed.