Cool road pavements contribute to mitigating urban heat islands. To evaluate the heat balance in paved surfaces and to select appropriate road construction materials that help suppress heat islands, an accurate understanding of heat transport parameters such as thermal conductivity (λ) and heat capacity (HC) is important. Recycled aggregates from construction and demolition waste, including scrap construction materials and industrial by-products, are often used for road construction; however, λ and HC of recycled aggregates especially for roadbeds are not fully understood. This study involved a series of laboratory tests to measure λ and HC of recycled concrete and clay brick aggregates (<40 mm) and their mixtures with autoclaved aerated concrete grains (<2 mm) under varied moisture conditions. The measured λ and HC increased with increasing volumetric water content (θ). Closed-form models for estimating λ(θ) were proposed using normalized thermal conductivity (λ_e) and effective saturation (S_e). The new λ_e(S_e) models performed well for the measured data compared to previously proposed models and would be useful to evaluate λ of recycled aggregates for roadbed materials.

Road base layers play an important role in bearing, transmitting, and distributing part of the load to the underground. Unbound aggregates crushed from natural rock are the most popular materials used to construct the base layers of the pavements. However, nowadays the sources of natural materials have been increasingly exhausted and the pollution from construction and demolition waste (CDW) is a big problem in Vietnam. Therefore, the utilization of CDW for recycling is a crucial issue to reduce the generation amount of CDW and consumption of natural resources. With regards to the applicability of recycled concrete aggregates (RCA) to unbound roadbed materials, many studies have been done to investigate the effect of grading of particles on mechanical properties. However, the effect of other factors such as maximum particle size (Dmax) and fines content (Fc in wt.%; typically, with particle size less than 0.075 mm) have not been fully understood. In this study, concrete waste taken from a CDW landfill in Vietnam and was crushed and sieved to prepare graded RCA samples for a series of laboratory tests to characterize mechanical properties such as compaction, bearing capacity, and saturated hydraulic conductivity. The graded RCA samples with two different Dmax, 25 and 37.5 mm, and four different Fc values ranging from 0 to 20 %, were prepared. This study showed that maximum dry density (MDD) and CBR value of graded aggregates with Dmax = 25 and 37.5 mm reached the highest values at Fc = 5%. Except for the sample with Fc = 20 % and Dmax = 25 mm, the measured CBR values of tested samples satisfied the technical requirements of Vietnamese and Japanese standards. Besides, the particle breakage of aggregates and saturated hydraulic conductivity were highly controlled by Fc and both values decreased with increasing in Fc.

Nghiên cứu này giới thiệu bổ sung giải pháp đắp nền bằng cát biển có sử dụng vải địa kỹ thuật để gia cố, giúp hạn chế được các đặc tính dễ bị rửa trôi, mất ổn định cục bộ của cát biển. Bên cạnh đó, nghiên cứu cũng tiến hành kiểm toán ổn định của nền đường với các giải pháp khác nhau, chiều cao đắp khác nhau (Hđ = 3, 6, 12m). Nghiên cứu chỉ ra rằng, giải pháp đắp nền đường bằng cát biển gia cố vải địa kỹ thuật có hệ số ổn định cao hơn so với giải pháp đắp bằng đất đắp chọn lọc. Trong quá trình thi công thực tế, cần có so sánh luận chứng về kinh tế - kỹ thuật để lựa chọn được giải pháp đắp phù hợp. Đồng thời, cần phải có thêm các nghiên cứu để xác định khả năng nhiễm mặn của môi trường xung quanh khi sử dụng cát biển đắp nền đường trước khi áp dụng thi công thực tế.