Geopolymer concrete (GPC) is a novel and environmentally friendly type of concrete that eliminates the use of cement, resulting in a significant reduction in carbon emissions and a more sustainable construction material. Alkaline activators are used in GPC to achieve rapid strength development. The most popular alkaline activators are sodium/potassium silicate and sodium/potassium hydroxide, which are known contributors to carbon emissions, hence limiting the advantages of GPC; therefore, reducing the amount of these alkaline activators that contribute to carbon emissions is necessary for developing a more sustainable geopolymer concrete. In this study, the influence of the variation in sodium hydroxide molarities on the performance of fly ash/sugarcane bagasse ash-based-geopolymer concrete was investigated. The different molarities used were 10 M, 12 M, 14 M, and 16 M sodium hydroxide solutions. In addition, the effect of sugarcane bagasse ash content (0%, 5%, 10%, 15%, and 20%) on the fresh and hardened geopolymer concrete properties were examined. The slump test, compression test, split tensile test, and flexure test were conducted on the cast samples. The results of this study showed that raising the concentration of NaOH from 10 M to 16 M while maintaining a sodium silicate to sodium hydroxide ratio of 2.5 resulted in a 3.75–10.2% improvement in compressive strength after 28 days. It is worth noting that, even at a concentration of 10 M, the concrete still achieved high strength.

The need for concrete is increasing exponentially due to the growing population and fast urbanization. The primary constituent in concrete is ordinary Portland cement (OPC). Producing cement involves a significant quantity of embodied energy and leads to the release of greenhouse gases. Geopolymer concrete (GPC) was created to address the adverse environmental effects of carbon dioxide emissions (CO₂) and the overdependence on fossil fuels in cement production. In addition to reducing environmental consequences, geopolymer concrete shows outstanding resistance to higher temperatures compared to OPC concrete, which maintains temperatures up to 1200 °C. This review investigates the field of GPC, focusing on its ability to withstand high temperatures. It briefly reviews geopolymer concrete's mechanical properties at high temperatures. It has been observed that residual compressive strength, which is essential in high-temperature GPC studies, generally increases to 150–350 °C but decreases beyond 400 °C because of microcrack formation. Moreover, enhanced tensile strength is demonstrated up to 300 °C, with a noticeable decrease above 800 °C. This study emphasizes the potential of geopolymer concrete for improving fire protection measures in the building industry.

Structural response of composite concrete filled plastic tubes in compression composite structures;compressive loads;concrete filled plastics;plastics;stub columns; Kenya has recently experienced worrying collapse of buildings during construction largely attributable to the poor quality of in-situ concrete and poor workmanship. The situation in the country is further compounded by rapid deterioration of infrastructure, hence necessitating the development of alternative structural systems such as concrete filled unplasticized poly vinyl chloride (UPVC) tubes as columns. The work herein adds on to the very limited and scanty work on use of UPVC tubes in construction. This study presents the findings of experimental and analytical work which investigated the structural response of composite concrete filled UPVC tubes under compressive load regime. UPVC pipes are cheaper than steel tubes and can be used as formwork during construction and thereafter as an integral part of column. Key variables in this study included the strength of infill concrete, the length to diameter ratio (L/D) of the plastic tube, as well as the diameter to thickness ratio (D/2t) of the plastic tube. Plastic tubes having varying diameters and heights were used to confine concrete of different strengths. Results obtained in the study clearly demonstrate the effectiveness of UPVC tubes as a confining medium for infill concrete, attributable to enhanced composite interaction between the UPVC tube and infill concrete medium. It was determined that compressive strength of the composite column specimens increased with increased concrete strength while the same decreased with increased column height, albeit by a small margin since all the columns considered were short columns. Most importantly, the experimental confined concrete strength increased significantly when compared to unconfined concrete strength; the strength increased between 1.18 to 3.65 times the unconfined strength. It was noted that lower strength infill concrete had the highest confined strength possibly due to enhanced composite interaction with the confining UPVC tube. The study further proposes an analytical model for the determination of confined strength of concrete.

The structural performance of reinforced concrete (RC) deep beams in both ultimate and serviceability limit states (ULSs/SLSs) is influenced by beam size effects and the adopted reinforcement ratios. In this study, the effects of cotton waste fibres (CWFs) and beam depth were studied using a four-point load test on five sets of 400 mm and 500 mm CWF high-strength RC deep beams with a 0.3% web reinforcement ratio. Control unnotched and notched, and notched specimens with 0–0.75% CWF content in each specimen set, were studied. The failure modes, stirrup and strut-and-tie zones’ strains, shear capacity, and load-deflection were analyzed. It was observed that the beam failure evolved from shear-compression in unnotched specimens to the web-splitting failure phenomenon in notched ones, coupled by 27.44% and 0.17% decline in ultimate shear capacity ($V_u$) in notched 400 mm and 500 mm beam sets, respectively. The notched RC deep beam specimens, mimicking the SLS shear performance parameters, showed a 34.28% and 14.71% $V_u$ increase in 400 mm and 500 mm depth beams, respectively. The crack opening load increased from 13.87 kN to 44.63 k and from 11.88 kN to 35.19 kN in these beam sets, respectively. In a similar analysis, 84.76% and 38.39% stiffness increase, and 49.15% and 39.95% shear ductility index increase in the outer-most stirrup, were observed in the respective specimen sets. The contribution factor of the shear reinforcement to $V_u$ improved from 0.31 to 0.94, and from 0.87 to 0.97 in 400 mm and 500 mm, with 0% and 0.75% CWF, respectively. These experimental results confirm the contribution of beam size effect and fibres to the shear performance properties of RC deep beams. The feasibility of using CWF in structural concrete is confirmed by its improvement of the SLS properties of the studied RC deep beam specimens with light shear reinforcement.