粉煤灰-偏高岭土基地质聚合物的孔结构及抗压强度

地质聚合物因其优异的力学性能、化学稳定性、耐高温等性能,在建筑、耐火、有毒有害离子固化等领域备受关注。本研究通过压汞法(MIP)、FT-IR、SEM测试分析了粉煤灰-偏高岭土基地质聚合物的孔径分布、凝胶结构及断裂方式,探讨了偏高岭土掺量对其结构与性能的影响。结果表明:地质聚合物的孔径分布随水灰比的调整存在大范围的变化,最可几孔径由几个纳米到100nm。当水灰比固定时,偏高岭土掺量由25%(质量分数)增加至60%(质量分数),地质聚合物中气孔均以凝胶孔为主,最可几孔径由40nm减小至26nm,总气孔率无显著变化,但有害孔的孔隙率明显由3.6%降至0.09%。偏高岭土掺量的增加,提高了凝胶相多元环结构中[AlO_4]的数目,使材料呈均匀化、致密化结构,尤其是改善了未反应粉煤灰颗粒与凝胶相之间的界面结合。偏高岭土掺量为60%时,裂纹在粉煤灰颗粒堆积气孔或薄弱界面周围的快速扩展得到有效控制,抗压强度显著提高,7d龄期时强度达到75.5 MPa。

Pore Structure and Compressive Strength of Fly Ash-Metakaolin Based Geopolymer

The great advantages of geopolymers, such as excellent mechanical property, chemical stability, high temperature resistance properties and so on, have been attracted much attention in recent years. They are gradually deemed to be potentially revolutionary materials in the field of building, fire resistance and stabilization radioactive and toxic wastes. This study was aimed to investigate the structure and compressive strength of geopolymer with high content of metakaolin and the metakaolin dosage affecting them. The pore structure (including pore diameter distribution and porosity), reaction products structure and fracture behavior of geopolymers, were characterized respectively by MIP, FT-IR and SEM. The pore diameter distribution was influenced obviously by the water to binder mass ratio, the diameter of the most probable pore was dispersedly distributed in the region of several nm to one hundred nm. As water/binder ratio was constant and metakaolin dosage increases from 25%(mass fraction) to 60%(mass fraction), abundant gel pores were detected in all samples, whereas the diameter of the most probable pore was diminished from 40 nm to 26 nm. In addition, although the total porosity was not much different, the porosity of harmful pore decreased from 3.6% to 0.09%. An increase in the metakaolin content promoted the number of [AlO₄] in a ring of aluminasilicate gel, which resulted in the structure more denser and more homogenous, especially improved the interface bonding performance between unreacted fly ash particles and the gels. The substitution of 60% fly ash by metakaolin, the crack propagation around the pore or weak interface of fly ash particles was effectively controlled, thus significantly improving the compressive strength and at 75.5 MPa after 7 d curing.