Effects of retempering methods on the compressive strength and water permeability of concrete

Retempering of concrete is a common practice in ready-mixed concrete industries for adjusting the workability that might adversely affect strength and durability properties in hot climates. In this paper, the effects of retempering with melamine sulphonate naphthalene-based superplasticizer (RS), water (RW) and withhold water (RWW) on the compressive strength and water permeability (WP) of concrete, are experimentally investigated. The results of this study indicated that the compressive strength of concrete retempered with superplasticizer and withhold water, enhanced by increasing the delay in casting, while retempering with water, resulted in a substantial decrease. Moreover, it was found that RS improved the water permeability of retempered concrete much more than RWW, whereas RW diversely increased this parameter. Although RWW imposed a slight slump loss, RWW and RS are generally proposed for the retempering of concrete, due to the suitable strength and permeability results.