Capillary absorption of cracked strain-hardening cement-based composites

Abstract

Cracks in strain-hardening cement-based composites (SHCC) will significantly influence the capillary absorption of the material when its surface is exposed to water. An analysis model is presented which is based on the decomposition of the absorbed water volume into three portions: water absorbed by the outer surface, water filling the cracks, and water absorbed by the crack surfaces. The crack pattern in SHCC, normally consisting of numerous fine cracks, affects these three water absorption portions in different ways. In order to quantify the contributions of the cracks, appropriate crack pattern parameters have been defined and used for developing the analysis model. For parameter identification and model verification, water absorption tests of uncracked, cracked, and fractured SHCC surfaces were conducted. In addition, the water absorption of thin slices made of SHCC was measured to adequately consider the influence of the crack spacing distribution in the model. The prediction of the capillary absorption by means of the model is based on the actual crack pattern observable at the respective SHCC surface. Since these surface cracks do not necessarily continue throughout the entire cross-section of the specimen, the model tends to overestimate the capillary absorption. Accordingly, the deviation from the measured values becomes smaller with decreasing specimen depth.