Water sensitivity of cement‐based materials

Abstract

Cement-based materials are the most widely used construction materials on the planet. Cementbased materials play a fundamental role in modern civilization and will for the foreseeable future.Although great efforts have been devoted to discovering the behaviors and optimizing their performances, several long-standing controversies persist for the fundamental water-related properties of cement-based materials, which hinder theoretical researches and mislead technological developments. Inspired by the decreasing water permeability of clay-bearing rocks, the term "water sensitivity" in geophysics is borrowed and proposed for cement-based materials. The lamellar structure of negatively charged nanoparticles is responsible for swelling in clay-based reservoir rocks. Amorphous calcium silicate hydrate gels in cement-based materials have similar microstructural characteristics. They probably swell upon wetting and contract upon drying, making the pore structure of cement-based materials dependent on water content. More importantly, several unexplained behaviors of cement-based materials can be rationalized using water sensitivity.Thorough exploration of both the micro-structural characteristics and performances validate the use of water sensitivity for cement-based materials. Because water participates in or regulates almost all physical and chemical processes of cement-based materials, water sensitivity can be a part of the interpretations of almost all of their properties and performances.

Using water vapour and N2 isotherms to unveil effects of SCMs on nanopores and evaluate hydration degree

“…The detected volume of LGP by N 2 sorption is much lower than that by water vapour sorption. The vacuum or high-temperature drying method induces severe damage of the layer structure of C-S-H, so it results in the contraction of the interlayer space and coarsening of some of the gel pores [16,20,72]. In CEM I and ternary hcps, we can observe an evident increase in capillary pores resulting from the coarsening of the gel during the drying treatment in this study.…”

“…There is no such difference in the S w and S N of building materials with other binders such as gypsum, lime or autoclaved lime and silica [24,53]. C-S-H, as the main hydration product of Portland cement-based materials, has a similar structure to that of clay (such as montmorillonite), so it is sensitive to the water content [20]. During the drying treatment of samples for the N 2 sorption test, the interlayer space will be narrowed due to the removal of water [54][55][56].…”

“…A treatment to remove the water in the materials is required in most of these measurements. Currently, there is no such method that can remove the nonbound water without damage to the structure of the C-S-H. During the process of water removal (drying process), the mesoscale pore structure [19,20] and the chemical structure after a certain extreme drying [15] will be altered due to the change of forces and interactions in the matrix. For measuring the mesoscale pores, the most widely-used methods are the sorption isotherms of N 2 and water vapour (static or dynamic [11,21]).…”

Deformations in Cement Pastes during Capillary Imbibition and Their Relation to Water and Isopropanol as Imbibing Liquids

“…Taylor et al [ 53 ] also attributed this anomaly in Portland cement-based materials to the swelling occurring during the transport process. In general, reported data [ 51 , 52 , 53 , 54 ] indicates that absorption results when testing non-aqueous liquids are always larger than when testing with water due to swelling of C-S-H gels [ 11 ].…”

“…This normally results in a decrease in surface energy and expansion. However, when taking the water sensitivity of cementitious materials into account, generally an anomalously lower water uptake is reported in comparison to other fluids [ 51 , 52 , 53 , 54 ]. Then, these differences are also reflected in the deformations measured, as when testing with IPA the registered values are much less in comparison to water.…”