Abstract

Saline intrusion is a critical issue in building material because of the severe damages caused by the salt precipitation/dissolution process, especially for the porous material, which has good connectivity. When porous material is exposed to aggressive ambient, the pore structure, not only porosity but also pore size distribution, will be altered by salt precipitation/dissolution. As one of the most significant characteristics in the porous material, pore size distribution is always paid much attention in many literatures. However, a quantitative and practical determination method is still absent. This work aims to establish a probabilistic model to investigate the pore size distribution induced by solid-phase precipitation/dissolution. First, a lognormal distribution is proposed for the simulation of initial pore size distribution tested by the MIP method. Then we develop a probabilistic-based porous network to represent the evolution of microstructure due to precipitation/dissolution. To this end, two different transformation models are constructed to interpret the relation between initial pore radius and modified pore radius before and after precipitation/dissolution. With this probabilistic-based porous network, we could illustrate the precipitated profiles that evolve near the capillary interface during the salt precipitation/dissolution process for a given porosity and water saturation degree. Such a method could be used to interpret the mechanism of the local precipitation/dissolution process in pore scales, which cannot be implemented by experimental measurements.

Abstract

Expansive additives (EAs) have been widely used to reduce the risk of cracking due to shrinkage. Such additives cause early age expansion of concrete due to the formation of Portlandite and Ettringite in the pores of the cement paste, which affects the cement paste's microstructure. The presence of external restraints in the form of reinforcement and support affects the expansion and, ultimately the microstructure of cement paste. In the current study, the microstructure of cement paste with expansive additives is studied using mercury intrusion porosimetry (MIP). A free lime-based EA, with 10 and 15% (by weight) cement replacement ratios, is studied in the current study. The porosity and pore size distribution of the cement paste with EA were studied under free and restrained conditions. Results show that the under the stress-free condition, the porosity of the paste increased, while under the restrained condition, the porosity remained much similar to the reference case of OPC. Further, the pore size distribution of the cement paste with EA under free and restrained conditions is explained, and the effect of EA and restraint on the microstructure is discussed.