Effect of retempering on the compressive strength of ready-mixed concrete in hot-dry environments

The practice of retempering in hot-dry environments is frequently performed to increase slump beyond typical specification’s limits (of 100 ± 25 mm) in order to cope with the need for expediting the casting operations and reducing the consolidation effort. In this study, the effect of retempering on the workability and strength of ready-mixed concrete (RMC) in hot-dry environments was investigated. This study covered 12 construction sites with concrete delivered by 11 different RMC suppliers. The results indicate that the reduction in strength due to water addition is proportional to the associated increase in slump. In cases where water was added to restore the slump to the specification’s limits (100 ± 25 mm), the reduction of strength was below 10%. However, when water was added to increase slump beyond these limits, the reduction of strength may be as high as 35%. The study shows the change in slump can be used to predict reduction of strength due to jobsite water additions when practical considerations preclude accurate determination of the w/c ratio.