TEMPERATURE AND HUMIDITY EFFECT ON THE STRENGTH OF PLAIN AND FLYASH CO NCRETE.

Abstract

This technical note attempts to quantify the effect of temperature and humidity on the strength development of both plain and flyash concrete. Two curing temperatures, 23 degrees celsius and 33 degrees celsius, and two relative humidities, 50 per cent and 75 per cent, were chosen. Interestingly, a 25 per cent increase in the ambient humidity (from 50 per cent to 75 per cent relative humidity) at 23 degrees celsius decreased the seven day strength of all the concretes investigated. In addition, this increase in relative humidity decreased the 91 day strength of plain concrete. In contrast, a 25 per cent increase in the humidity at 33 degrees celsius increased the strength of the concrete at all ages of testing. Overall, the increase in humidity, at both of these temperatures, imparted better strength development characteristics to the flyash concrete as compared with the plain concrete. A 10 degrees celsius increase in temperature (from 23 degrees celsius to 33 degrees celsius) at 50 per cent relative humidity generally decreased the strength of the concretes tested, whereas the same increase in temperature at 75 per cent relative humidity increased the strength of both plain and flyash concretes. A regressive effect, of 33 degrees celsius at 50 per cent relative humidity, on the 91 day strength of concrete was observed. This loss in strength has been attributed to the cessation of hydration due to the drying of the concrete and the development of microcracking (a).