Influence of mixing time and superplasticizer dosage on self-consolidating concrete properties

Abstract

Self-compacting concrete (SCC) requires specific properties, such as fillability, flowability, and passability. It also needs to resist bleeding and segregation, which may be caused by increased water or superplasticizer (SP) content. In addition, long periods of mixing deteriorate the properties of fresh SCC and causes difficulty in filling structure sections. This study investigates the effect of different mixing periods (e.g., 15, 30, 60, and 90min from the addition of water to the mixture) and increased SP doses (e.g., 1.5%, 2%, 2.5%, and 3% of cement mass) on the properties of SCC mixtures. The properties of fresh concrete were assessed by seven tests, namely, slump flow, V-funnel, slump flow T50, V-funnel T5, L-box, bleeding, and segregation. Hardened concrete was assessed on the basis of compressive, indirect, and flexural strengths. Results showed that compared with the slump flow under 15min mixing time, the 30, 60, and 90min increase in mixing time reduced slump flow by 6%, 19%, and 27%, respectively. Findings also showed that results of SCC segregation and bleeding decreased when increased mixing time. The results also appeared that compressive strength of SCC slightly decreased compared with that under 15min mixing time. The increase in dosage of superplasticizer has mitigated the negative effect for long mixing periods on the properties of concrete.