Pore crystallization and expansion of cement pastes in sulfate solutions with and without chlorides

The pore crystallization of ettringite (AFt) and the material expansion are investigated for cement paste subject to external sulfate attack with and without chlorides. Specimens of 2 mm thickness were exposed to solutions of 10 g/L Na2SO4, 10 g/L Na2SO4 + 10 g/L NaCl and 10 g/L Na2SO4 + 19 g/L NaCl. The evolutions of AFt formation, pore structure, transport property and specimen expansion were characterized through27Al NMR, MIP, DVS and micrometer measurements. The analysis of results shows that: (1) chlorides decrease the AFt formation rate and the expansion capacity through depressing the supersaturation of AFt crystals; (2) AFt crystallization alters the pore structure in the whole pore size range, especially through the blockage of ink-bottlepores in micropore range; (3) AFt crystals change the apparent vapor diffusivity by pore-filling and microcracking, and the linear stage of expansion is well captured by poromechanics with pore crystallization pressure incorporated.

Automated summary

This study investigates the pore crystallization and material expansion of cement paste under external sulfate attack with and without chlorides. It is found that chlorides decrease the AFt formation rate and expansion capacity by depressing the supersaturation of AFt crystals; AFt crystallization alters the pore structure in the whole pore size range, especially by blocking ink-bottle pores in the micropore range; AFt crystals change the apparent vapor diffusivity through pore-filling and microcracking, and the linear stage of expansion is well explained by poromechanics with pore crystallization pressure incorporated.