Influence of Retempering with Superplasticizer on Fresh and Hardened Properties of Prolonged Mixed Concretes Containing Supplementary Cementitious Materials

Abstract

Ready-mixed concrete suffers in terms of fresh and hardened properties as a result of prolonged mixing, hot weather concreting and/or possible delays in construction site. To overcome these problems, this study focused on the provision of sufficient workability with the retempering of concrete mixtures during prolonged mixing periods with use of superplasticizer (SP). Four mixtures with substitution of different mineral admixtures such as blast furnace slag (BFS), fly ash (FA), ground clay brick (GCB) and natural pozzolan (NP) and control mixture were designed. 5, 60, 120, 180 and 240 minutes mixing periods were applied on the mixtures. 15 ± 2 cm slump value was targeted after the retempering. In addition, air content, 7 and 28 day compressive and splitting tensile strength of the mixtures were tested. Results showed that slump values fall to zero after prolonged mixing when mixtures were not retempered, while slump loss was completely eliminated after retempering with SP. The air content of the mixtures decreased significantly as a result of the stiffening of the concrete after prolonged mixing. After the retempering process, compressive and splitting tensile strengths of the mixtures slightly increased. Also, the fresh and hardened properties of concrete improved with the use of high amounts of mineral admixtures.

Keywords

• air entrainment
• mineral admixture
• prolonged mixing
• ready mixed concrete
• retempering
• superplasticizer