مقاله انگلیسی رایگان در مورد خواص حرارتی بتن RCA زبر در دمای بالا – الزویر 2018

A large amount of construction and demolition waste has been generated all over the world in recent years [1, 2], of which waste concrete is the main component. Crushing waste concrete to produce coarse recycled concrete aggregates (RCA) for new concrete is regarded as an effective way to deal with the problem of increasing construction waste [3, 4]. This new concrete is henceforth termed ‘coarse RCA concrete’ for simplicity in this paper. To date, coarse RCA concrete has mainly been applied to non-structural project, such as pavement base and back-fill for retaining walls [5, 6]. In the past few years, our research group has also carried out research on both material [7, 8] and structural [9-14] performances of the coarse RCA concrete, proving that it is feasible to apply the coarse RCA concrete to composite structural members, such as concrete-filled steel tubular columns or composite slabs. This also has been confirmed by some researches on reinforced concrete beams [15, 16], columns [17] and joints [18]. Given the increasing use of coarse RCA concrete in structural members, it is critically important to study its properties at elevated temperatures, including thermal, mechanical and deformation properties. For evaluating fire resistance performance of structures made with coarse RCA concrete, the temperature distribution in the structural members under fire exposure should be calculated first. The elevated-temperature thermal properties of coarse RCA concrete are essential for such a calculation. These thermal properties that determine the temperature distribution include thermal conductivity and specific heat at elevated temperatures. Thermal expansion is another important thermal property that influences the thermal stresses in the concrete at elevated temperatures. Concrete is a composite material produced with aggregates, cement, water and superplasticizer. Aggregates, representing almost 70% of the volume in concrete, have an important effect on the elevated-temperature thermal properties of concrete [19, 20]. Coarse RCA concrete may have different thermal properties when compared to concrete made with coarse natural aggregate (NA), as coarse RCA has higher mortar content, more porosity and cracks than coarse NA. Currently, the information on the elevated-temperature thermal properties of coarse RCA concrete is still limited. Laneyrie et al. [21] tested the thermal conductivity and specific heat of coarse RCA concrete for temperature up to 300 °C. Two water/cement (w/c) ratios of 0.3 and 0.6 and two coarse RCA replacement percentages of 0% and 100% were considered in the experiment. It was concluded that the thermal conductivity of concrete with 100% coarse RCA was about 10-20% lower than that of coarse NA concrete in 20-300 °C range, which was attributed to the higher porosity of coarse RCA concrete.