THERMODYNAMIC APPROACH TO MODELING OF DRYING SHRINKAGE FOR HARDENED CEMENT PASTE

• Published in: Cement Science and Concrete Technology Vol. 66; no. 1; pp. 382 - 389
• Main Authors: SHINHASHI, Yusuke, KOGAWA, Yosuke, GOTOH, Suguru, NAWA, Toyoharu
• Format: Journal Article
• Language: Japanese; English
• Published: Japan Cement Association 25.02.2013
• Subjects: Carbonation; Differential scanning calorimetry; Drying shrinkage; Pore size distribution; Water adsorption-desorption isotherm
• ISSN: 0916-3182; 2187-3313
• DOI: 10.14250/cement.66.382

The hysteresis of water adsorption/desorption isotherms and length change due to drying is investigated both experimentally and theoretically. The hysteresis of water adsorption/desorption isotherms and drying shrinkage was measured using carbonated and not carbonated hardened cement pastes. Carbonation had little effect on the hysteresis of water adsorption/desorption isotherms. In contrast, carbonation strongly influenced the shrinkage；it enhanced the shrinkage and it was also found that the hysteresis of shrinkage during drying and wetting process change became large and was similar to vycor glass that has a simple cylindrical pore. This leads to the expectation that carbonation change the microstructure of hardened cement paste. This could be confirmed the results from microstructure study by using thermoporometry. Considering the disjoining pressure and the wetting of water on pore wall, the model to predict drying shrinkage was built based on the thermodynamic model proposed by Schiller et al. Our proposed model could predict the hysteresis of water adsorption/desorption isotherms for hardened cement paste despite to carbonation. Further, Our model could predict the hysteresis of drying shrinkage for the previous result of vycor glass and carbonated hardened cement paste. However the proposed model with the measured pore distribution failed to explain the hysteresis of drying shrinkage for not carbonated hardened cement paste, which has no pronounced hysteresis. This implied that there exists other factors except for capillary pressure, disjoining pressure and the wetting of water on pore wall.