Abstract
This novel study was triggered by a lack in the international literature of the simultaneous use of ground recycled concrete (GRC) as a cement replacement and mixed recycled aggregate as part of the granular skeleton in recycled concrete. It explores the thermal behaviour of concrete mixes bearing 10 wt% or 25 wt% GRC as a cement replacement and 25 wt% or 50 wt% mixed recycled aggregate (MRA) sourced from construction and demolition waste (CDW). The experimental programme conducted assessed concrete’s dry density, open porosity, electrical and thermal conductivity and specific heat capacity. The findings showed that the use of 10% and 25% GRC, in conjunction with 50% MRA, reduced thermal conductivity by 7.9% to 11.8% and raised specific heat capacity by 6.0% to 9.1% relative to concrete with 100% natural aggregate (NA). A cross-property analysis revealed that improved thermal performance was linearly related to lower density and higher porosity. The results also support the conclusion that these new recycled aggregate concrete mixes are more energy-efficient construction materials than conventional concrete.
Highlights
Concrete production is responsible for serious environmental impacts worldwide. These impacts can be divided into two main problems: use of natural aggregates, and Portland cement production, which leads to an average consumption of 125 kW/h of electricity and results in an emission to the atmosphere of 800 kg of CO2
That behaviour was consistent with the findings reported by Cantero et al [10] in a study of concrete mixes prepared with both 25% ground recycled construction and demolition waste (CDW) (RC-CDW) as a cement replacement and 50% mixed recycled aggregate (MRA)
The declines recorded were steeper than the up to 20% reported for compressive strength and up to 24% for splitting tensile strength in a study [10] of concrete mixes with ground fired clay-based materials recycled from CDW, which were more reactive than the present ground recycled concrete (GRC), and 50% of a harder MRA (LA < 36 wt%) than the one used here (LA = 46 wt%)
Summary
Concrete production is responsible for serious environmental impacts worldwide. These impacts can be divided into two main problems: use of natural aggregates, and Portland cement production, which leads to an average consumption of 125 kW/h of electricity and results in an emission to the atmosphere of 800 kg of CO2. Ge et al [7], Kannan et al [8] and Vejmelková et al [9] investigated the durability of concrete with the use of ceramic powders as binders instead of cement, having studied maximum replacement ratios of 30%, 40% and 60%, respectively. Liu et al [11] evaluated the use of hybrid recycled powder from demolished concrete solids and clay bricks as supplement for cement This investigation obtained a decrease in the mechanical performance of these cementitious materials. The authors concluded that the effect of using RA is quite variable depending on their nature Despite this variation, several other investigations [13,14,15,16,17] point to decreases in thermal conductivity higher than 20% in mixes with the replacement of natural aggregates with RA from concrete or glass.
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