An investigation of the effects of superplasticizers in steam cured concrete

The ever increasing use of precast and prestressed concrete as structural elements has caused a demand for further research and development in the steam curing process which is used by the precast concrete industry in order to produce structural precast members in short periods of time. The rate of temperature rise in the steam chamber and maximum temperature are critical elements in the process of steam curing concrete. The rate of temperature rise should be controlled and should reach its maximum temperature as quickly as possible without adversely affecting the long-term or short-term strength of the concrete. The maximum temperature should be limited to a temperature that will minimally decrease the 28 day strength of the concrete. Using the results and conclusions from previous research, this investigation examines the effect that an admixture such as a superplasticizer may have on the strengths of the concrete in the steam curing process. A 6000 psi mix design for a mix with a water-cement ratio of 0.40 was used and the w/c ratio was varied to test the effects on different strengths of concrete. The specimens were fabricated in standard 6x12 inch molds and each batch was tested at 24 hours, 3 days, 7 days, and 28 days. There were four batches of 24 cylinders each produced for testing. The use of a superplasticizer in steam cured concrete was found to be beneficial in the strength of the concrete and the rate at which the concrete gains strength between the ages of 7 and 28 days. It was also found to have no adverse effects on the strength of the concrete in comparison to steam cured concrete without a superplasticizer. The early strength of the steam cured concrete did not appear to be any different than the strengths reported in previous investigations.