粉煤灰对碱激发矿渣/粉煤灰体系的作用机理研究

碱激发胶凝材料是以工业固体废弃物为原料制备的一种绿色无机胶凝材料,具有良好的力学性能与耐久性能。粉煤灰因其独特的球体微观结构与其他固废微粉存在本质区别,因此粉煤灰在碱激发胶凝材料体系中的作用机理亟待研究。以矿渣与粉煤灰为原料,利用碱激发剂制备胶凝材料,并对材料进行抗压强度测试,最后采用XRD、FTIR和SEM探究碱激发矿渣/粉煤灰体系的水化反应机理,研究粉煤灰对矿渣/粉煤灰体系的作用机理。结果表明:外掺3%(质量分数)NaOH作为碱激发剂,水固比为0.4时,随粉煤灰掺量减少,抗压强度呈现先上升后下降的趋势;m(矿渣):m(粉煤灰)为4:1时,28 d抗压强度达到峰值(37.1 MPa)。粉煤灰颗粒在不同龄期形成具有不同反应程度与尺寸的嵌入式微观结构,对材料力学性能起到不利影响;但粉煤灰的活化程度随龄期延长逐渐变大,对后期强度发展有持续贡献。碱激发矿渣/粉煤灰体系水化产物中含有Friedel盐、托贝莫来石、钙矾石、C-S-H/C-A-S-H凝胶,以及粉煤灰中残留的α石英相。随粉煤灰掺量增加,托贝莫来石生成量减少,钙矾石向Friedel盐转变,钙矾石生成量减少,Friedel盐生成量增多。

Reaction Mechanism of Fly Ash in Alkali-Activated Slag/Fly Ash System

With excellent mechanical properties and durability, alkali-activated cementitious material prepared by industrial solid waste is a kind of green inorganic cementitious material. Fly ash is essentially different from other solid waste because of its unique spherical microstructure, therefore, the reaction mechanism of fly ash in alkali-activated cementitious material needs to be studied. In this paper, slag and fly ash were used as raw materials to prepare cementitious materials by alkali activator. The compressive strength of the material was tested, and the hydration mechanism of alkali-activated slag/fly ash system was explored by XRD, FTIR, and SEM. The detailed effect of fly ash on alkali-activated slag/fly ash system and related mechanisms were investigated. The results show that, when 3% (mass fraction) NaOH is added as alkali activator, and the water-solid ratio is 0.4, with the decrease of fly ash content, the compressive strength first increases and then decreases. When m(slag):m(fly ash) is 4:1, 28 d compressive strength reaches the peak value of 37.1 MPa. Embedded microstructure of fly ash particles has different reaction degrees and sizes at different ages, which has a negative effect on the mechanical properties of the material. However, the activation degree of fly ash gradually increases with the extension of age, which has a continuous contribution to the later strength development. The hydration products of alkali-activated slag/fly ash system contain Friedel's salt, tobermorite, ettringite, C-S-H/C-A-S-H gel, and residual alpha quartz of fly ash. With the increase of fly ash content, the amount of tobermorite decreases, ettringite transforms into Friedel's salt, the production of ettringite decreases, and the production of Friedel's salt increases.