During the summer concrete producers, particularly in the south, encounter problems with low strength and with slump loss that is rapid enough to require retempering. Retempering lowers strength even further. Unfortunately, these seasonal problems occurs during the peak construction period. They are quite costly because cement requirements must be increased to maintain strength levels and because construction is delayed while concrete quality is being verified or while low strength concrete is reinforced or replaced. The culprit is high temperature which accelerates the hydration of cement compounds, especially in the first 24 hours. For this reason ASTM Specification C 94 for Ready Mixed Concrete and ACI Recommended Practice 605 for Hot Weather Concreting require that the concrete temperature not exceed 90 degrees F. Besides keeping the concrete below this temperature there are two other ways of slowing early hydration. One method is to use chemical admixtures that slow it by reducing mixing water requirements. Any such admixtures should be carefully screened to verify satisfactory performance with the particular brand of cement used. The other method is for the cement manufacturer to reduce the fineness or increase the sulfate content of the cement or both. The latter method, now possible because of the relaxation of ASTM and AASHO specifications, is the more effective and improves the performance characteristics of cement in combination with various chemical admixtures.