Producing of Lightweight Concrete from Two Varieties of Natural Pozzolan from the Middle Atlas (Morocco): Economic, Ecological, and Social Implications

The main objective of this work is to evaluate the combined effect of two natural pozzolan varieties (black and red) with different grain sizes (fine powder < 65 mu m and coarse aggregate) on the thermomechanical properties of lightweight concrete. Firstly, the characterization of red and black pozzolan was conducted to determine their chemical and physical compositions. Further experiments were carried out by replacing cement with black pozzolan powder was varying in percentages (0 wt%, 10 wt%, 15wt%, 20 wt%, 25wt%, and 30 %). In the same sense, the replacement of cement by BPP was set at 25 % and then the limestone coarse aggregate was replaced by RPA at 20 %, 40 %, 60 %, 80 %, and 100 % by volume. The results of this study show that with the addition of 25 % black pozzolan powder (BPP), the mechanical strength of concrete increase compared to reference concrete (RC). The compressive and flexural strength of specimen can be increased by 6.7 and 3 % respectively compared to RC at 28 days curing age. Based on the mechanical properties and ultrasonic wave propagation (UWP) results, it is recommended that the optimum substitution of BPP with cement stays at 25 %. The contribution of red pozzolan aggregate (RPA) in concrete reduces the density and thermal conductivity (TC), while all the mechanical properties were also reduced. This occurs due to the vacuolar structure of RPA and its lower density compared to limestone coarse aggregate (LCA). The density and thermal conductivity of specimen S2M100 decreased by 22 and 49 % respectively compared to RC at 28 days. These results indicate that the combined use of two varieties of natural pozzolan in different grain sizes in concrete manufacturing has several advantages: economic, mechanical, and thermal.