Origin of Drying Shrinkage of Hardened Cement Paste: Hydration Pressure

Abstract

The driving force of drying shrinkage of hardened cement paste has been attributed to RTln(h)/v with external relative humidity h and water molar volume v in theories of capillary tension and disjoining pressure. However, these theories fail to explain the considerable hysteresis observed in length-change isotherms. In this study, the sorption isotherm and length-change isotherm of cement pastes were determined with different water-to-cement ratios and cement types, and internal pressure of shrinkage Π was calculated using the measured strain and elastic modulus of the skeleton. This internal pressure is a kind of disjoining pressure originated from hydration force and built up within adsorbed water films as a result of interactions between the hydrophilic solid surface and water molecules. Changes in internal surface energies of hardened cement pastes due to hydration, drying and temperature history result in a different statistical thickness of the adsorbed water layer under the same equilibrium relative humidity. The proposed model gives a rational explanation for the hysteresis in length-change isotherm.

Numerical Approach towards Aging Management of Concrete Structures: Material Strength Evaluation in a Massive Concrete Structure under One-Sided Heating

“…Water vapor isotherm of hardened cement paste is modeled based on S H2O , which confirm the following experimental characteristics: 1) long-term desorption data under a 40% RH range obtained by a gravity method is reversible (Helmuth and Turk 1967;Maruyama 2010), and it is almost identical to that of the desorption process obtained by a volumetric method; 2) the water vapor BET surface area in the adsorption process has a linear relation with that under the desorption process by a volumetric method ; 3) long-term drying affects S H2O (Maruyama et al 2014c); 4) temperature affects S H2O ; and 5) a sorption amount at 98% RH in the desorption branch is affected by the drying or heating condition of a sample (Igarashi and Maruyama 2012). Background data and resultant fitted data with regard to 3) and 4) are shown in Fig.…”

“…This equation also gives the distribution of degree of hydration in a concrete member by coupling with heat transfer phenomenon of which details of modeling is introduced in 3.1. These factors and parameters are determined by experiments in which the degree of hydration of each cement mineral in cement paste with different water-to-cement ratios and different types of Portland cement is examined (Maruyama andIgarashi 2011a, 2014). The applied temperature histories of the experiments are shown in Fig.…”

“…Based on experimental data (Maruyama andIgarashi 2011a, 2014) and vast existing discussions regarding cement reaction (Osbaeck 1992;Bentz 1997;Taylor 1997), the following equations are applied to the proposed phase composition model: 1) Molecular weight of C-S-H when the Ca/Si atomic ratio is assumed to be 1.7 is listed 2) Jennings (2000), Taylor (1986) 3) Feldman and Ramachandran (1982) 4) In the present study, the adsorbed water at the condition above 11% RH is assumed to behave like bulk water 5) Zhou and Glasser (2001), Tennis and Jennings (2000) 6) Tennis and Jennings (2000), Pöllmann et al (1993) 7) Motzet and Pöllmann (1999), Tennis and Jennings (2000) 8) Allmann (1977) 9) Kuzel (1969) 10) Fischer and Kuzel (1982), Schwiete and Ludwig (1969) 11) Fischer and Kuzel (1982) 12) This has been reported to become C 4 AH 19 at a RH of 88% or higher, but C 4 AH 13 is used for the present study due to its easy decomposition. 13) Due to missing data, the density was calculated by assuming the same crystal structure as C 4 AH 7 .…”

“…13 Calculation results of the sorption model using Equations 27 -36 and experimental data integrated from Maruyama (2010) and Maruyama and Igarashi (2010). Fig.…”

The Use of Sorption Balance for the Characterization of the Water Retention Curve of Cement-Based Materials

“…In these areas it has been proven that the use of sorption balance is able to obtain similar results to other common techniques (Johannesson and Janz 2002;Arlabosse et al 2003;Fei et al 2006). Over the last 10 years, sorption balances have been put to use more and more for cementitious materials (Anderberg and Wadsö 2008;Johannesson and Utgenannt 2001;Johannesson 2002;Robens et al 2002;Espinosa and Franke 2006;Åhs 2008;Scheffler et al 2009;De Belie et al 2010;Maruyama 2010;Dubina et al 2011;Pavlík et al 2012;Dubina et al 2014;Saeidpour and Wadsö 2015;Jennings et al 2015;M. Wu et al 2014;Kumar et al 2014;Snoeck et al 2014;Baquerizo et al 2016;Aktas et al 2015;Maruyama et al 2015).…”