A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Civil Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 2001

The prediction method of 28-day compressive strength of normal-cured concrete without admixtures, and with superplasticizers, accelerator, and retarder, based on the accelerated strength by microwave curing technique is investigated. The optimal process involving the optimal power, the penetration resistance level and the rest time are determined and then applied to concrete whose mix proportions obtained from ACI standard mix design. The optimal power at a combination power of P40 (259 watts) for 30 minutes and P30 (197 watts) for 15 minutes is determined to achieve both high early strength and slightly deteriorated later-age strength. The penetration resistance level at 3.45 MPa (500 psi) of sieved mortar is determined and used as the indicator for the starting time of microwave energy application. The rest time at 3 .5 hours is determined to allow continuation of hydration process after microwave curing until the early age test time. The compressive strength of microwave-cured concrete and normal-cured concrete are tested at the early age test time and 28 days, respectively. Eventually, only one equation to predict 28-day compressive strength of concrete containing admixtures can be established from correlation between early strength of microwave-cured concrete and water/cement ratio, and correlation between 28-day strength of normal-cured concrete and water/cement ratio. The prediction is reasonably accurate yielding the average and maximum percentages of error within 6 and ±11 , respectively.