The strength of Portland cement concrete is dependent on the strength of the cement paste binding the aggregates together. An understanding of the cement paste is the first step to assess the concrete strength. To this end, a program for strength testing of cement paste was implemented for water to cement ratios of 0.35 and 0.40. The compressive strength was evaluated using two inch cubes and four inch diameter cylinders; while the tensile strength evaluation was based on flexure and direct tension tests. All the specimens were cured in the mold the first day, followed by curing in sealed vacuum bags for the remaining of the time. The total curing time ranged from three, seven, fourteen and twenty-eight days. Three replicate specimens were prepared, cured, and tested for each combination of water to cement ratio, type of specimen, and time of curing. The results of the testing program show that while the compressive strength increases for increasing curing time, the tensile strength shows a consistent decline. These results indicate that the sealed curing forced that further hydration caused “self-desiccation” of the CSH, inducing new cracks or extension of existing cracks that would be responsible for the loss of tensile strength.
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