Abstract
In recent decades, relevant environmental and economic reasons have driven an increasing interest in using a large amount of recycled aggregate in replacement of natural ones to produce mortar and concrete. The present study aims to investigate the effect of substituting 100% of natural sand with recycled aggregate on fresh properties, mechanical properties, and the durability of a thixotropic and a self-leveling mortar. Recycled aggregate was characterized using X-ray diffractometry and energy-dispersive X-ray spectroscopy. Its morphology was investigated using scanning electron microscopy and automated morphological imaging. Recycled aggregate mortars showed a moderate decline in initial workability, as well as higher shrinkage and porosity than the control ones. The compressive strength of self-leveling mortars produced with recycled aggregate was only 6% lower than mortars produced with natural sand. The gap increased to 40% in the case of thixotropic mortars. The self-leveling recycled aggregate mortar showed equivalent resistance to freeze–thaw cycles and better sulfate resistance than the control one. The thixotropic recycled aggregate mortar showed comparable sulphate resistance and only slightly lower resistance to freeze–thaw cycles than the control one. Their capacity to relief stresses, due to hydraulic pressures and the formation of expansive products, arises from their higher porosity. Thermal stability of the prepared mortars, after a curing period of 90 days, up to 700 °C, was also investigated. A significant decrease in ultrasonic pulse velocity is observed in the 200–400 °C interval for all the mortars, due to the dehydration–dehydroxylation of calcium silicate hydrate. The overall decline in the strength of both the recycled aggregate mortars was comparable to the control ones. The results reported in the present investigation suggest that the selection of high-quality recycled aggregate helps to obtain good-quality mortars when a large amount of natural sand is replaced.
Highlights
The construction industry consumes around 40% of all extracted natural resources, produces large amount of waste from building demolition, and consumes a lot of energy [1].Several approaches have been carried out to mitigate the environmental impact of construction practices, such as investigating on more sustainable binders [2,3] and reusing demolition waste [4,5]
The use of pre-saturated RS prevented the absorption of free water during the mixing
The thixotropic and self-leveling mortars produced with recycled aggregate showed porosities of 35.6% and 32.6%, respectively
Summary
The construction industry consumes around 40% of all extracted natural resources, produces large amount of waste from building demolition, and consumes a lot of energy [1]. Based on the aforementioned information, authors evaluated the fresh and hardened properties and the durability of two commercial products, a self-leveling and a thixotropic mortar, whose mix design includes two specific chemical admixtures kits They compared the results with those obtained when their mix design was modified by replacing the 100% the natural sand with recycled aggregate. This improves the bonding strength of repairing mortar to the substrate, fills in capillary pores, enhances the freeze–thaw resistance, improve resistance to water and chemicals, and reduces surface cracking [51] They provide a protective film on the surfaces of aggregates, and form a link with the hydration products of cement.
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