Influence of Polycarboxylate Superplasticizer and Silica Fume on the Properties of Self-compacting Concrete

Abstract

AbstractSelf-compacting concrete is a highly flowing concrete that compacts under self-weight without any vibration effort. To obtain self-compacting concretes with reduced cement consumption and high physical, mechanical and performance characteristics, the use of superplasticizers and mineral additives is required. This paper discusses the effect of a complex additive based on polycarboxylate superplasticizer and silica fume on the properties of self-compacting concretes. According to the study results, self-compacting concrete mixtures with high segregation resistance, high fluidity with a cone flow diameter of more than 700 mm and increased consistency retention of more than 3 h within the slump-flow class SF2 were obtained. The hardening kinetics of self-compacting concrete with a complex additive is characterized by high rates of strength development, even despite the long-term consistency retention of self-compacting concrete mixes. At 1 day, the strength of self-compacting concrete was 31.6 MPa, at 2 days—56.5 MPa, at 28 days—92.5 MPa with a cement consumption of 500 kg/m3. According to the X-ray phase analysis results, it was found that the complex use of polycarboxylate superplasticizer and silica fume at 1 day leads to an acceleration of the hydration processes of alite by 13%, tricalcium aluminate—by 24% and an increase in the content of portlandite by 5%, ettringite—by 14%. At 28 days, the use of complex additive leads to the formation of a cement stone structure with a reduced content of portlandite by 40%, ettringite by 11% and increased content of amorphous low-basic hydrated calcium silicates by 18%, significantly compacting the structure of cement stone and improving its physical and mechanical characteristics.KeywordsSelf-compacting concretePolycarboxylate superplasticizerSilica fumeSand-aggregate ratioSlump-flowConsistency retentionCompressive strengthWater absorptionPhase composition