镁钙碳酸盐胶凝材料微结构的形成机制及调控

Preparation of novel low-carbon binder is an important way for developing green construction materials. Mg/Ca carbonate binder is a kind of novel cementing material based on Mg or Ca-bearing carbonates, which has many advantages associated with low carbon emissions, waste utilization, environmental friendly, durable performance, good mechanical properties and so on. To carbonate Mg/Ca containing raw materials efficiently and hence produce mechanical performance rapidly is key to use the carbonate binder. However, the mechanism of microstructure formation in the binder during carbonation has not been well understood, and there is a lack of principle for adjusting the microstructure to improve its binding performance, hindering its further development and application. In this project, MgCl2 solution, the industrial byproducts produced during the extracting process of potassium salt from saline solution, will be used to react with Ca(OH)2 firstly to prepare Mg(OH)2. Then the Mg/Ca carbonate binder will be synthesized via accelerated carbonation of the Mg(OH)2/Ca(OH)2 with CO2 of high concentration and high pressure. Reaction kinetic of the carbonation will be studied to investigate the effects of carbonation conditions in terms of temperature, CO2 concentration and pressure, characteristic of Mg(OH)2, compositions of raw materials, and carbonation additive (biocarbonate salt) on the rate of carbonation, composition and microstructures of carbonate products. Based on that, the formation mechanism of the carbonates will be revealed. The intrinsic relationship between the microstructure evolution and mechanical property development of the carbonated binder will be examined to demonstrate the nature of its binding performance. In addition the principle for adjusting the microstructures of carbonates will be developed. This study will lay a scientific base and technical guidance for developing Mg/Ca carbonate binders by using the waste liquid Mg-containing wastes, and moreover provide a new safe and economical way for CO2 storage.

开发新型低碳胶凝材料是发展绿色建材的重要途径。镁钙碳酸盐胶凝材料是一种以镁、钙碳酸盐为胶结组分的新型胶凝材料，具有低碳、利废、环保、耐久、力学性能好等优点。高效碳化镁钙原料快速产生强度是该材料应用的关键。但碳化时该胶凝材料微结构形成机制尚不明晰，缺少调控微结构提高力学性能的理论依据，制约了它的开发及应用。项目利用氢氧化钙与盐湖提钾工业副产品氯化镁反应制取氢氧化镁，采用高浓度高压CO2碳化手段合成镁钙碳酸盐胶凝材料。从碳化反应动力学角度探究碳化条件(如温度、CO2浓度和压力)、碳化调节剂(碳酸氢盐)、氢氧化镁微结构和原料组成对其反应速率、产物组成和微结构的影响规律，揭示碳化产物微结构形成机制。通过探究碳酸盐产物微结构演变与力学性能发展的内在关系，探明其胶凝性能本质，并揭示微结构的调控机理。研究为利用含镁液体废弃物开发镁钙碳酸盐胶凝材料提供理论支撑和技术指导，并提供安全经济储存CO2的新方法。

开发新型低碳胶凝材料是发展绿色建材的重要途径。镁钙碳酸盐胶凝材料是一种以镁 、钙碳酸盐为胶结组分的新型胶凝材料，具有低碳、利废、环保、耐久、力学性能好等优点。本项目利用氢氧化钙与盐湖提钾工业副产品氯化镁反应制取高比表面积(68.2m2/g)氢氧化镁，经高浓度（40%-99.9%）CO2加速碳化合成镁钙碳酸盐胶凝材料。研究了原材料配比、试件成型压力、碳化时间和CO2浓度等因素对镁钙碳酸盐胶凝材料微结构与力学性能的影响规律。对比研究加速碳化不同类型富含镁钙的工业废渣(钢渣和镁渣)制备碳酸盐胶凝材料的微结构与性能，探究碳酸盐胶凝材料微结构的形成机制及其产生胶凝性能的本质原因。研究表明，盐湖MgCl2制取的Mg(OH)2、富含钙镁的钢渣和镁渣在高浓度CO2环境中均具有高碳化活性，其加速碳化可以制备出强度高达187.1MPa或119.2MPa的以碳化产物MgCO3.3H2O或CaCO3、MgxCa(1-x)CO3为主要胶结组分的碳酸盐胶凝材料。碳酸盐产物形成所导致的微结构致密化、碳酸产物优良微观力学性能及碳化产物与未碳化矿物颗粒构建的强化胶结基质是碳酸盐胶凝材料产生力学强度的本质原因。碳化产物的生成使胶凝材料的孔径细化、孔体积减小、产物相互胶结更好。碳酸盐产物具有很高的纳米压痕弹模和硬度，碳化镁含量较高的镁渣所制备的碳酸盐胶凝材料中产物基体弹性模量为 50.5±9.5GPa，压痕硬度为2.2±0.6GPa，均高于镁含量较低的钢渣碳化产物的弹模(37.6±10.4GPa)和硬度（1.4±0.6GPa）。通过选用不同镁钙含量的废渣原材料或改变试件中Mg(OH)2的含量能够调控胶凝材料的微结构，进而改变其力学强度。本项目的研究成果为资源化环保利用含镁液体、固体工业废弃物制备镁钙碳酸盐胶凝材料提供理论支撑和技术指导，并提供安全经济储存 CO2的新方法，具有重要的应用前景。