Cotton textile waste (CW) and crushed bricks (CB) are wastes generated by the textile and construction industries that cause adverse effects on the environment. This paper explores the effect of adding 1, 2, 5, and 10 wt.% of CW and CB, instead of natural sand under 1 mm (50 to 100 vol.%), on the properties of concrete. The study included the analysis of workability, density, water absorption, thermal conductivity, mechanical strengths, and electron microscopy. The results show that the presence of CW and CB increased the water required to obtain the same slump value as reference, R. Concretes with CW provided better performance in terms of density, water absorption (for 1 wt.%), and splitting strength (for 1 to 2 wt.%). The 28 days of compressive strength decreased with increasing CW (33.3 MPa for R and 26.9 MPa for 2 wt.% of CW). The partial substitution of sand decreased the workability and density and increased the mechanical strength of concrete. The presence of both CW and CB decreased workability, density, and mechanical strengths. Regarding the ability of concrete to transfer heat, the addition of CW and CB decreased the thermal conductivity value (e.g., 0.32 W/(m·K) for 1 wt.% of CW compared to 0.37 W/(m·K) for reference).

In the transition to zero waste and sustainable development, it becomes essential to use phase change materials and recycled cement in construction projects to improve energy efficiency and encourage sustainable building practices. The primary goal of this study is to determine how the properties of expanded perlite mortars are affected when Portland cement is partially replaced with recycled cement, produced by thermally treating concrete waste at 550 °C. Recycled cement substituted Portland cement in various percentages (10 %, 30 %, and 50 %). Also, microencapsulated phase change material (m-PCM) was incorporated into the mortar in a proportion of 2 wt% and 5 wt%. Cement-based mortars with a 1:3 aggregate volume ratio have been developed for evaluation. The mortars were analyzed in terms of mechanical strength (flexural and compressive), water absorption, thermal properties, differential scanning calorimetry, and microstructure. The experimental results revealed a decrease in mechanical strength values when Portland cement is substituted by recycled cement, regardless of percentage. Recycled cement in proportion of 30 % positively influenced the water absorption. The thermal conductivity of reference mortar was higher than that of 30 % recycled cement. The reference mortar's specific thermal conductivity values were 0.466 W/(m·K) at 25 °C, 0.525 W/(m·K) at 30 °C, and 0.589 W/(m·K) at 35 °C. On the other hand, the mortar containing 30 % recycled cement exhibited much lower heat conductivity throughout these temperatures, suggesting superior insulating qualities. DSC analysis verified that adding m-PCM to the mortars increased their thermal storage capacity, which is essential for raising the energy efficiency of building materials. Nevertheless, the mechanical strength decreased as m-PCM was added. Despite decreases, all mortars satisfied the SR EN 998–1 standard's CS IV classification for interior plaster applications, which is based on compressive strength requirements. Overall, this study shows how using m-PCM and recycled materials can improve the performance of cement-based materials.

This study aimed to obtain and characterize a mortar with perlite aggregate and thermal-treated materials that could substitute for Portland cement. First, the thermally treated materials were obtained by calcinating old Portland cement (OC-tt) and concrete demolition waste (CC-tt) at 550 °C, for 3 h. Second, plastic mortars with a perlite: cement volume ratio of 3:1 were prepared and tested for water absorption, mechanical strength, and thermal conductivity. The microstructure was also analyzed. Portland cement (R) was partially substituted with 10%, 30%, and 50% OC-tt. Thermal-treated materials negatively influenced the compressive and flexural strengths at 7 and 28 days. With an increase in the substitution percentage to 50%, the decrease in the compressive strength was 40% for OC-tt and 62.5% for CC-tt. The presence of 10% OC-tt/CC-tt positively influenced the water absorption. The thermal conductivity of the tested mortars was in the range of 0.37–0.48 W/m·K. SEM analysis shows the expanded perlite pores remained unbroken.

This study develops a transient mathematical model for predicting the outlet air temperature of a modular solar air collector integrating recycled concrete as sensible heat storage. The reference prototype used 18.8 kg of recycled concrete storage, with a volume of 0.01033 m³, density of 1820 kg/m³, and measured thermal conductivity of 0.885 W/(m·K). The model connects absorber, airflow, storage, external convection, and radiative heat-transfer mechanisms using a 600 s time step and measured meteorological boundary conditions. Validation was performed for clear, overcast, and scattered cloud conditions, producing absolute MBE values below 0.38 °C, MAE values of 0.64–1.17 °C, RMSE values of 0.87–1.39 °C, and R² values of 0.83–0.96. The expanded uncertainty of the measured outlet temperature was ±0.58 °C, placing the lowest model error close to the experimental uncertainty level. The results support the use of recycled demolition concrete as a sensible storage medium and provide a modeling framework for subsequent investigation of different storage masses, geometries, airflow rates, and longer multi-day operating periods.