WORKABILITY AND STRENGTH OF RETEMPERED SUPERPLASTICIZED CONCRETES

The paper presents the results of a comparative laboratory investigation of the workability of retempered concrete with and without superplasticizer. The effect of mixing time on the strength of superplasticized concrete is also discussed. Both superplasticizer and water were used as retempering agents, and the variables were type of superplasticizer and initial slump of the concrete. Fresh concrete was tested for slump, air content, and unit weight up to 150 min after initial mixing. The hardened concrete was tested compressive strength and modulus of elasticity. The slump of retempered concrete both with and without superplasticizer decreased about equally with time. However, increased workability and subsequent slump loss depended on the type of superplasticizer used and the initial slump level. The results indicate that extended mixing time does not adversely affect the compressive strength of concrete. The large increases in slumps of superplasticized concretes can be maintained for several hours by retempering, which does not reduce the strength of the concrete. The properties of hardened retempered concrete are comparable to those of corresponding unretempered concretes. unretempered concretes.