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论文类型：期刊论文

发表时间：2016-11-01

发表刊物：CEMENT AND CONCRETE RESEARCH

收录刊物：SCIE、EI、Scopus

卷号：89

页面范围：63-71

ISSN号：0008-8846

关键字：Dispersion; Hydration products; Microstructure; MgO; Silica fume

摘要：The extent of reaction between magnesium oxide (MgO) and silica fume (SiO2) is normally limited and mixes require high water contents to give suitable rheology. The use of considerably lower water contents and the formation of magnesium silicate hydrate (M-S-H) gel as a binding phase is made possible by adding sodium hexametaphosphate (Na-HMP) to the mix water prior to the addition of MgO and SiO2. This results in the formation of extensive reaction products and cured samples with high compressive strength and low porosity. In this work, the effect of Na-HMP on the hydration of MgO/SiO2 mixes is investigated using high water to solids ratio samples to allow monitoring of pH and the solution chemistry during hydration. It is shown that a relatively small amount of Na-HMP inhibits the formation of Mg(OH)(2) when MgO is hydrolyzed. It is proposed that this is due to adsorption of phosphate species on the MgO which inhibits the nucleation of the Mg(OH)(2). This gives rise to high Mg2+ species in solution and elevated pH (>12) conditions relative to when Mg(OH)(2) forms. In contrast, the phosphate does not suppress formation of M-S-H gel. In combination with the enhanced dissolution rate of SiO2 at high pH, M-S-H gel can form quickly without competition for Mg2+ ions by Mg(OH)(2) precipitation. Incorporating the optimum concentration of Na-HMP into the mix water therefore transforms the properties of cement paste and mortar samples formed by reacting MgO and SiO2. (C) 2016 Elsevier Ltd. All rights reserved.