Sulfate resistance of Portland dolomite cement: performance and mechanisms
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ORIGINAL ARTICLE
Sulfate resistance of Portland dolomite cement: performance and mechanisms Ji Lu
. Aiwen Xu . Jiangtao Xu . Duyou Lu . Zhongzi Xu
Received: 12 May 2020 / Accepted: 17 September 2020 / Published online: 29 September 2020 Ó RILEM 2020
Abstract This study investigated the sulfate resistance of Portland-dolomite cement (PDC) cured at different temperatures. Mortars of Portland cement (PC) and PDC with different dosages of dolomite, 10, 20, 30% by weight, were cured in water at 20 °C and 60 °C for 28 days before immersed in 50 g/L Na2SO4 solution at 20 °C. In addition to monitoring the length changes of mortars, MIP and XRD were performed to investigate microstructure and evolution of phase assemblages. Results show that PDC mortars cured at 20 °C give a poorer sulfate resistance than PC, and the higher the dosage of dolomite, the worse the sulfate resistance. On the contrary, when cured at 60 °C, PDC gives a much better sulfate resistance than PC, and the higher the dosage of dolomite, the better the sulfate resistance. The increases of critical pore size and porosity with the incorporation of dolomite lead to a poor sulfate resistance of PDC cured at 20 °C. However, for PDC cured at 60 °C, it is not the pore structure but the lack of available aluminate caused by the formation of hydrotalcite contributes to its sound sulfate resistance. The higher the dosage of dolomite from 10 to 30%, the larger amounts of hydrotalcite
J. Lu A. Xu J. Xu D. Lu (&) Z. Xu (&) College of Materials Science and Engineering, Nanjing Tech University, No. 30 Puzhu Road(S), Nanjing 210009, China e-mail: [email protected] Z. Xu e-mail: [email protected]
formation and the better the sulfate resistance. Hydrotalcite is stable in the presence of sulfate. Keywords Portland-dolomite cement Sulfate attack Hydrotalcite Mechanism
1 Introduction Cementitious materials exposed to external sulfate sources will suffer from significant deterioration due to the interactions between hydrate phases and external sulfates, which is knowns as the external sulfate attack (ESA) [1–4]. ESA on cement mortar or concrete may lead to the precipitation of ettringite, gypsum and/ or thaumasite, resulting in expansion, cracking, softening and strength loss. Many variables influence the sulfate resistance of cementitious materials such as curing temperature, humidity, aggressive environments (type and concentration of sulfate) and cement compositions [5–8]. More recently, Portland dolomite cement (PDC) has attracted great attention as a promising alternative to ordinary Portland cement due to its potential economic and technical benefits [9–14]. It has been reported that the incorporation of dolomite powder can improve the workability and early-age strength of mortar, and promote the formation of hemicarbonate and monocarbonate and consequently the stabilization of ettringite, which is similar
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Materials and Structures (2020) 53:125
to the effect of limestone in ble
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