Review of Several Experimental Methods for Characterization of Micro- and Nano-Scale Pores in Cement-Based Material
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nternational Journal of Concrete Structures and Materials Open Access
RESEARCH
Review of Several Experimental Methods for Characterization of Micro‑ and Nano‑Scale Pores in Cement‑Based Material Abudushalamu Aili1* and Ippei Maruyama1,2
Abstract Mechanical properties and durability of cement-based materials are largely affected by pore structures. This paper provides an overview of several experimental techniques to characterize pore size distribution and specific surface area, with focus on pores in calcium silicate hydrates. The reviewed experimental techniques are nitrogen and water vapor sorption isotherm, proton nuclear magnetic resonance (1H-NMR) and small-angle scattering (SAS). Different pretreatment methods are compared for sorption measurements. Pore size distribution and specific surface area are analyzed using data from different methods to understand difference and consistency of these methods. It is found that pore size distribution calculated from sorption isotherm is very sensitive to adsorption model. Though specific surface areas from different techniques are quite different from each other, they are all able to detect the microstructural alteration due to long-term drying. Keywords: cement, pore size distribution, specific surface area, sorption isotherm, 1H-NMR, SAS 1 Introduction Cement paste and concrete are porous material composed from solid skeleton and pores, with the size of pores varying from several micrometers to nanometers. These pores are of great importance for not only mechanical properties but also for durability of cementbased materials. Most of the chemical agents, that are triggers of degradation, invade into the material through pores. Chemical reactions then takes place inside the pores, causing different results based on the size of the pores. For instance, during salt attack in cement paste, crystallization pressure is different in larger pores and smaller pores (Scherer 1999, 2004). It was confirmed in Sasano et al. (2018) that drying shrinkage reduced the performance of reinforced concrete structure. This drying shrinkage is caused by three different mechanisms in *Correspondence: [email protected]‑u.ac.jp 1 Graduate School of Environmental Engineering, Nagoya University, Furocho, Chikusa‑ku, Nagoya 461‑8603, Aichi, Japan Full list of author information is available at the end of the article Journal information: ISSN 1976-0485 / eISSN 2234-1315
different pores at different relative humidities (Hansen 1987). In larger pores at higher relative humidity, capillary pressure causes the drying shrinkage (Feldman and Sereda 1970; Powers 1965, 1968). When relative humidity continues to decrease, disjoining pressures of water in smaller pores play main role (Bazant 1972; Wittmann 1973); whereas, at even lower relative humidity in much smaller pores, the shrinkage is caused by surface energy (Feldman and Sereda 1964; Powers 1965). Therefore, characterizing pore size and pores structure is necessary to better estimate the durability of cementitious materials and
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