Effect of retarding superplasticizers on the properties of cement paste, mortar and concrete

Abstract

Chemical admixtures are becoming increasingly popular as these could improve several properties of concrete, both in plastic and hardened condition. However, improper use of admixture may lead to the inferior performance of produced concrete. Effects of admixtures dosage on the properties of cement paste, mortar and concrete were studied in this research. The most recently developed polycarboxylic ether (PCE)-based admixtures from different manufacturers were used. The trial dosages were fixed considering their properties and suppliers’ specifications. Firstly, the effect of retarding on cement setting times was evaluated using cement paste and then flow test was carried out on cement mortars to examine change in workability, i.e., superplasticizing effect with this. Compressive and tensile strength test on mortar cube and briquette samples was conducted to evaluate variation in strength with different dosage of admixture while keeping other materials’ proportions same. Finally, the dosage effect on workability (slump retention) of fresh concrete was studied for every 15-min interval up to 1.5 h. Effect of slump retention using admixture on compressive strength was also evaluated. Experimental results show that a small variation in admixture dosage changes these properties significantly. It was concluded that properties of cement paste, mortar and concrete could be improved with an optimum dosage for each particular type of admixture; however, higher or lower dosage than this may put adverse effect. Within the usable time, there might be other chemical effects that enhance/decrease the concrete performance while keeping all other quantity and parameters the same for all these concrete mixes.