超细粉煤灰和偏高岭土对高强混凝土耐热性能的影响

Effect of Ultra-fine Fly Ash and Metakaolin on Heat Resistance of High Strength Concrete

以普通硅酸盐水泥为主要胶凝材料,超细粉煤灰和偏高岭土作为辅助胶凝材料制备了高强混凝土,研究了其在400℃热处理前后的力学性能,分析了浆体物相组成、断面形貌的变化。结果表明,超细粉煤灰和偏高岭土的引入可以明显改善高强混凝土受热条件下的力学性能,同时引入30wt%超细粉煤灰和5wt%偏高岭土可制备出常温抗压强度、残余强度分别为87.18 MPa、109.72 MPa的高强混凝土。微观分析发现,在热处理过程中,未掺加辅助胶凝材料的试样浆体中氢氧化钙和硅钙石分解,浆体结构劣化,力学性能退化明显;掺加超细粉煤灰可以改善试样浆体的孔结构,且超细粉煤灰可在高温下与氢氧化钙及其分解产生的氧化钙反应生成更多的硅钙石以及耐高温矿物相,改善了加热过程中由于氢氧化钙和部分硅钙石分解而产生的结构缺陷,进而提升材料耐热性能,使得混凝土热处理后的残余强度不降反升;在掺加超细粉煤灰的同时复掺偏高岭土,可以在常温下水化生成更多的水化硅酸钙凝胶,使得粉煤灰微珠与浆体的界面结合更加紧密,并在高温下进一步加快水化反应速率,在浆体中生成大量硅钙石、钙铝榴石与蓝晶石三种耐高温物相,进而大幅度提升混凝土的耐热性能,使得混凝土高温残余强度更高。

High strength concrete(HSC)was prepared by using ordinary Portland cement as the main cementing material,ultra-fine fly ash(UFFA)and metakaolin(MK)as supplementary cementitious materials(SCMs).The mechanical properties before and after heat treatment at 400℃were studied.The changes of hardened paste phase compositions and cross-sectional morphology were analyzed.Results show that the introduction of UFFA and MK significantly improve the mechanical properties of HSC at high temperature.HSC with compressive strength and residual strength of 87.18 MPa and 109.72 MPa have been prepared by using 30wt%UFFA and 5wt%MK together.Microscopic analysis shows that portlandite and hatrurite decompose in the hardened paste without SCMs during heat treatment,which resulting in deterioration on hardened paste structure.And the mechanical properties of samples are greatly degraded.The addition of UFFA improves the pore structure of the hardened paste.More hatrurite as well as high temperature resistant mineral phases are manufactured by the reaction of UFFA with portlandite and calcium oxide at high temperature.The heat resistance of samples improve due to the repair of structural defects caused by decomposition of portlandite and hatrurite in the heating process,so that the residual strength of the HSC increases after heat treatment More hydrated calcium silicate gel is generated at room temperature with blending of UFFA and MK,which making the interface transition zone between the fly ash beads and hardened paste tightly.The hydration reaction rate is further accelerated under high temperature.A large number of high temperature resistant phases of hatrurite,grossular and kyanite are generated in hardened paste.The heat resistance of concrete greatly improves,which making the concrete own higher residual strength at high temperature.