Characterizing Lightweight Aggregate Desorption at High Relative Humidities Using a Pressure Plate Apparatus

Abstract

This paper describes the results of an experimental study that was performed to obtain desorption isotherms for a wide range of fine lightweight aggregates that are used commercially in North America. The desorption isotherms were determined for the entire gradation of the fine lightweight aggregates (as received). To obtain the desorption isotherms a pressure plate apparatus (porous plate) was used. The pressure plate enables the desorption isotherm to be measured at high relative humidities (beginning at 100%). In addition to providing experimental results obtained with the pressure plate method, desorption results obtained by gravimetric desorption and dynamic vapor desorption methods are also provided. The gravimetric desorption and dynamic vapor desorption methods are generally used at lower relative humidities (98% and 0% relative humidity). The results indicate that water leaves the fine lightweight aggregates at relative humidities as high as 99.9%. This suggests that internal curing water is available to the cement matrix even at relatively high water-to-cement ratio mixtures when the suction forces exerted by cement paste are small. The results of this work are helpful for the development of mixture proportioning techniques and numerical simulation for internally cured concrete mixtures.