Dynamic modulus of Portland cement paste and mortar as affected by ambient relative humidity

Results are given of an investigation into the influence of drying and wetting on changes in weight and dynamic modulus of paste and mortar specimens dried at different relative humidities at room temperature. Drying causes a significant drop in the dynamic modulus probably due to moisture stress gradients and removal of interlayer water which is recovered from subsequent wetting of the specimens. This suggests that drying-induced microcracking is unlikely to occur. The percentage reduction in dynamic modulus of prisms (2·5 mm × 10 mm × 75 mm) increases with increasing aggregate concentration and decreases with increasing water/cement ratio.