Abstract
This experimental study was conducted with an aim to investigate the effect of the elevated temperature on the mineral phase composition, microstructure and mechanical properties of the thermal insulation lightweight concretes. The first group of experimental concretes was based on the expanded vermiculite and expanded perlite used as lightweight aggregates (in 65 wt%) in combination with either ordinary Portland cement or refractory calcium aluminate cement. The mix-design of the second group of concretes comprised standard quartz aggregate, vermiculite or perlite as aggregate replacement (25 wt%) and binder (PC or CAC). A total of 10 concrete mix-designs were fabricated in form of 40?40?160 mm samples which were submitted to heat-treatment at 400?, 600?, 800? and 1000?C upon standard 28-days period of curing and hardening. The changes in crystallinity and mineral phase composition induced by temperature were monitored by X-ray diffraction technique. Microstructural visualizations of the non-fired and fired concrete samples were conducted by scanning electron microscopy accompanied with EDX analysis. The results indicated that despite the decrease in compressive strengths upon firing, investigated lightweight concretes can be categorized both as thermal insulators and structural materials.
Highlights
Modern civil engineering is continuously imposing new requests regarding the reduction in the weight of structural elements, as well as energy-efficiency and fire safety [13]
The first group of experimental concretes was based on the expanded vermiculite and expanded perlite used as lightweight aggregates in combination with either ordinary Portland cement or refractory calcium aluminate cement
Wollastonite as a calcium inosilicate mineral (CaSiO3) appeared in the mineral phase composition of Portland cement (PC)-P65 as a result of limestone reactions induced by the increasing temperature
Summary
Modern civil engineering is continuously imposing new requests regarding the reduction in the weight of structural elements, as well as energy-efficiency and fire safety [13]. The expanded perlite is characterized by porous structure, high water absorption, low density and good thermal insulation [15,16,17]. Vermiculite is often being mixed with other types of light-weight aggregates such as polystyrene [26], or combined with geopolymer to create lightweight composite panels with improved thermal properties [27]. Expanded vermiculite and perlite were used as lightweight aggregates in a high percentage (65 wt%) in the mix-design of concretes. Prepared composite building materials were compared with another group of thermal insulation concretes in which standard quartz sand has been replaced by either vermiculite or perlite (in 25 wt%). Perlite and vermiculite were alternated as aggregates in the thermal insulation concretes. It is followed by a steep decreasing curve-line, meaning that both vermiculite and perlite were thermally stable up to 1000 °C
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