基于5•1•7相为主要水化相的MgO-MgSO4-H2O三元胶凝体系的微观结构与水化机理研究

MgO-MgSO4-H2O ternary cementitious system, based on 5•1•7 (5Mg(OH)2•MgSO4•7H2O ) phaseas the main hydration phase, is a kind of additives modified magnesia-based cement. It has many advantages such as high strength, low density and good water resistance, causing the extensive concern by magnesium industry. However, problems such as slow setting and hardening, high hydration heat and low initial strength, may usually occur when using this ternary cementitious system to produce magnesite products. In this work, microstructure and hydration mechanism of this ternary cementitious system will be studied to make further improvement to its properties. The changes of hydration phase composition, microtopography, pore-size distribution and pore solution composition of the ternary cementitious system at different hydration ages will be analyzed to study the strength development mechanism. The hydration exothermic regularity will be measured to partition the hydration processes and analyze the controlling factors of the different hydration stages. The formation principle of 5•1•7 phase is to be explored through studying the adsorption mechanism of additives on the hydration layer, the possible gelatinous structure before the formation of 5•1•7 crystal phase and the thermal dynamic data of the hydration processes. This study would state the hydration mechanism of MgO-MgSO4-H2O ternary cementitious system based on 5•1•7 phase as the main hydration phase at the molecular lever, and could provide the theoretical basis for resolving some problems of magnesite production.

以5•1•7相（5Mg(OH)2•MgSO4•7H2O）为主要水化相的MgO-MgSO4-H2O三元胶凝体系是一种新型镁质胶凝材料，具有高强、轻质、抗水等优点，引起菱镁行业的广泛关注。但这种镁质胶凝材料用于水泥制品生产时，往往存在凝结缓慢、水化热高、早期强度低等问题。本项目将研究其微结构和水化机理，为进一步改善其性能提供科学依据。通过分析该不同水化龄期三元胶凝体系的水化相组成、微观形貌、孔径分布、孔隙溶液组成，研究其力学强度发展的微观机理；通过研究该三元胶凝体系的水化放热规律，划分其水化历程并分析其各反应阶段的控制因素；通过研究水化层对外加剂的吸附机理和5•1•7相形成之前的凝胶结构，并结合水化的热动力学数据，探明5•1•7的形成机制。通过本项目的研究，从分子水平上阐明以5•1•7为主要水化相的三元胶凝体系的水化机理，进而为解决菱镁制品生产中所遇到的一些常见问题提供理论基础。

以5•1•7相为主要水化相的Mg-MgSO4-H2O的三元胶凝体系（碱式硫酸镁水泥，BMSC）具有高强高韧性等优点，但其水化机理尚不明确。本项目采用了XRD、SEM-BSE、水化热、FTIR、TG/DSC、MIP、EIS、Zeta电位、液相组成化学分析等手段对水化机理和微观结构进行了分析，并研究了氧化镁来源或活性、温度、摩尔比、减水剂、矿物掺合料等因素的影响规律。研究结果，BMSC中5•1•7相形成经历了MgO稳定水化层形成、Mg-O骨架柱撑结构的前躯体形成、5•1•7相成核和生长的过程，水化宏观上表现为诱导前期、诱导期、加速期、减速期和稳定期五个阶段；外加剂在5•1•7相的形成过程中，起控制MgO水化速率、稳定MgO水化层、Mg-O八面体骨架柱撑和增大Mg(OH)2生成的活化能并抑制其形成的作用。BMSC的结构为晶须状5•1•7相互交错的网状结构，内部孔隙主要为晶间孔（孔径>20nm），且MgO活性越低或者添加晶种可促进5•1•7相生长并提高其结晶程度。高强度BMSC具有高含量高结晶程度的5•1•7相；合适的外加剂应对水合镁离子具有合适的络合能力，其结构特点一般为可溶性的多羟基羧酸或磷酸（磷酸）。本项目的研究，为进一步提高BMSC性能、指导BMSC制品和新型镁盐晶须产品的生产提供理论指导。