Accelerated Carbonation Test By Step Response Method

For three types of concrete (ordinary Portland cement concrete, Portland blastfurnace slag cement concrete, Portland fly ash cement concrete with and without surface coating by emulsion paint, accelerated carbonation test was done, based upon step response method modeling the tendency of increase in the concentration of atmospheric carbon dioxide (CO²) by a step function in which the value increases every month step by step from 5% to 20%. The rates of the progress of carbonation were quantitatively evaluated by the least-square method. It was found that the progress of carbonation under step response condition obeys the linear law concerning time, contrary to the generally accepted parabolic law under the condition of constant concentration of CO². This experimentally obtained fact is well explained theoretically, taking into account of saturation factor for the accelerative effect of CO² concentration in the higher concentration region on the progress of carbonation.