Abstract
This paper presents results from experimental work on mechanical properties of geopolymer concrete, mortar and paste prepared using fly ash and blended slag. Compressive strength, splitting tensile strength and flexural strength tests were conducted on large sets of geopolymer and ordinary concrete, mortar and paste after exposure to elevated temperatures. From Thermogravimetric analyzer (TGA), X-ray diffraction (XRD), Scanning electron microscope (SEM) test results, the geopolymer exhibits excellent resistance to elevated temperature. Compressive strengths of C30, C40 and C50 geopolymer concrete, mortar and paste show incremental improvement then followed by a gradual reduction, and finally reach a relatively consistent value with an increase in exposure temperature. The higher slag content in the geopolymer reduces residual strength and the lower exposure temperature corresponding to peak residual strength. Resistance to elevated temperature of C40 geopolymer concrete, mortar and paste is better than that of ordinary concrete, mortar and paste at the same grade. XRD, TGA and SEM analysis suggests that the heat resistance of C–S–H produced using slag is lower than that of sulphoaluminate gel (quartz and mullite, etc.) produced using fly ash. This facilitates degradation of C30, C40 and C50 geopolymer after exposure to elevated temperatures.
Highlights
Concrete is by far the most widely used construction material today
The geopolymer was synthesized from materials of geological origin or by-product materials, such as metakaolin [9,10] blast furnace slag [11] and fly ash [10,12] that are rich in silicon and aluminum using alkali activation
Considering that the concrete structure is likely to be exposed to fire and an elevated temperature environment during the service stage, performance evaluation of geopolymer concrete after exposure to elevated temperature is important to determine its suitability for engineering applications [14,15,16]
Summary
Concrete is by far the most widely used construction material today. The most commonly used binder material for conventional concrete is ordinary Portland cement (OPC) [1]. It has been shown that curing of a fly ash-based geopolymer at ambient temperature could be greatly accelerated after addition of a small proportion of slag [26,27,28,29,30] or OPC [25], with high CaO content. It has been found that a fly ash and slag blend-based geopolymer exhibits better elevated temperature resistance than cement-based materials [20]. The fly ash and slag blend-based geopolymer mortar cured in 70 ◦C condition was proved to possess the similar properties with the change of slag content after high temperatures [33]. An experimental study of the mechanical, mineralogical and micro-structural properties of high-volume fly ash-based geopolymer concrete, mortar and paste after exposure to elevated temperature has been conducted. Thermogravimetric analysis (TGA), X-ray diffractometry scanning electron microscope (SEM) were conducted to investigate the ma nent transformation and micro-structural changes of geopolymer paste, re Polymers 2021, 13, 1473
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