The relationship between capillary pressure and tensile strength of fresh cementitious materials under water evaporation

Tensile strength is a crucial parameter for understanding the plastic shrinkage cracking of concrete. It is difficult to characterize tensile strength at early age due to its very small value. In this study, the tensile strength of the cementitious paste was measured using a horizontal direct tensile device, and corresponding capillary pressure was simultaneously tested under a high evaporation rate (>1.0 kg/m2/h). Thereafter, the relationship between capillary pressure and tensile strength was studied when the negative capillary pressure of the paste was 0–70 kPa. The results indicate that when the negative capillary pressure is lower than a specific value (approximately 14.0 kPa), the tensile strength rapidly increases and is higher than the corresponding value of the negative capillary pressure. Subsequently, the growth of tensile strength slows down, and the tensile strength is less than the value of the negative capillary pressure. At 70 kPa, the tensile strength is about 30 kPa. Meanwhile, the tensile strength evolution for pastes with various mix proportions was consistent when tensile strength was plotted as a function of the negative capillary pressure. Furthermore, a fitting model based on capillary pressure was created to predict the tensile strength. Consequently, due to the simplicity of capillary pressure measurement, the model proposed in this paper can predict the tensile strength of cementitious materials in the plastic stage without conducting tensile testing.