DETERMINATION OF OPTIMAL PROCESS FOR MICROWAVE CURING OF CONCRETE

Operations such as precasting and repair of concrete can benefit signi ficantly from rapid strength development. Previous investigations have shown that microwave curing is an effective means to develop high ear ly strength in concrete. Moreover, with certain combinations of proces sing parameters (including microwave power, application time and durat ion of microwave), the later age strength (at 7 days) can be comparabl e to that of specimens cured at room temperature. The present investig ation illustrates how optimal processes, which provide high strength a t both the early and later stage, can be obtained with the help of fee dback temperature control. Using 0.4 w/c ratio concrete as an example, the optimal power history (in terms of a continuously varying curve) is identified. To enable processing with low cost microwave generators (such as the ones in the domestic oven), the optimal power curve is a pproximated with discrete power levels. The discretized optimal power is found to give very good results for concrete with 0.4 w/c and below . Compared with the use of fixed power, the use of variable discrete p ower can provide better combinations of early age and long term streng th with less energy consumption. As examples, at the early age of 4.5 hrs, compressive strength of 29.5 MPa and 35.4 MPa are achievable with w/c equal to 0.40 and 0.325 respectively. In both cases, the strength at 7 day shows no deterioration compared with specimens cured at room temperature. (C) 1997 Elsevier Science Ltd.