Mohamed Abo El-Naga Kandil

The amount of agricultural waste has grown as agricultural output has expanded globally. Therefore, in order to protect the environment, agricultural waste needs to be disposed of appropriately. Many studies used various types of agricultural wastes in concrete production as a partial replacement of cement to reduce carbon footprint. In order to produce sustainable high-strength concrete (SHSC), this study focusses on employing two promising pozzolanic materials: rice sugarcane leaf ash (SLA) and sugar beetroot ash (SBA) in SHSC production with different replacement levels up to 20%. This research provides a wide-ranging assessment of the mechanical, physical, durability and microstructural characteristics of SHSC. With a focus on advancing eco-friendly construction, the study also includes fly ash (FA) to assess its combined effects on SHSC’s mechanical and durability characteristics. SHSC mixtures were exposed to various tests to evaluate the influence of replacement from different aspects: slump test, compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity, chloride penetration resistance, sorptivity, water permeability and scanning Electron Microscopy (SEM). According to the findings, replacing cement with SLA and FA up to 20% presented the optimum tests results, which led to significant enhancements in all physical, mechanical and durability properties of SHSC. Additionally, the inclusion of SBA with replacement level of 10% resulted significant enhancements to all SHCS characteristics whereas, compressive strength increased by 16%, tensile splitting strength increased by 10.8%, flexural strength increased by 12.4% and modulus of elasticity increased by 7.66% compared to the control specimens. With 20% FA replacement level, the optimum durability levels ware obtained; the lowest chloride permeability by 1342 Coulomb, the lowest sorptivity coefficient by 0.051 mm/√s and the lowest water permeability by 2.61 × 10^–11 cm/sec. In addtion, these improvements extended to FA replacement level of 10% mixtures’, including mechanical properties and also obtained lower durability terms results. Generally, cement replacement in all mixtures caused decrease in slump values comparing to control mixture. The SBA replacement level of 20% is technically useless, did not led to the expected improvement in all tested properties, and affected negatively SHSC mixtures. SEM images of new SHSC mixtures revealed that adding agricultural waste improved the SHSC’s microstructure by decreasing pore size, forming a denser SHSC structure and increasing the production of C–S–H. This study confirms the potential of SLA, SBA and FA as valuable supplementary cementitious materials, offering a sustainable alternative for producing durable SHSC with significant minimizing environmental impact.

The incorporation of construction and demolition (C&D) waste in concrete production has gained great importance toward sustainability, especially in geopolymer concrete. In this study, ground granulated blast-furnace slag (GGBFS) and fine aggregate of normal geopolymer concrete were partially replaced by clay brick powder (CBP) and fine clay brick (FCB) derived from C&D waste, respectively, aiming to produce high-strength geopolymer concrete (HSGC). Fly ash (FA) was also used as a partial replacement for GGBFS in normal geopolymer concrete. Twenty HSGC mixtures were designed using the response surface methodology with three variables, including CBP (0–25%), FA (0–25%), and FCB (0–50%). The performance of the proposed HSGC mixtures was assessed by measuring several mechanical and durability properties. In addition, a variety of physicochemical methods, including X-ray fluorescence spectroscopy, X-ray diffraction, and scanning electron microscopy, were used to examine the mineralogical and microstructural characteristics of the control and the developed mixtures. The findings revealed that the compressive, splitting tensile, and flexural strengths of the HSGC made with C&D waste ranged from 38.0 to 70.3 MPa, 4.1 to 8.2 MPa, and 5.2 to 10.0 MPa, respectively. The results also indicated that the incorporation of FA is an essential parameter to eliminate the negative impacts of C&D waste addition on concrete workability. The optimal proportions for the HSGC were 5% for CBP, 5% for FA, and 40% for FCB, which were determined to generate the optimized HSGC with the highest mechanical performance, according to the verified models and optimization findings. The physicochemical analyses showed that the thick amorphous geopolymeric gel predominated the nonporous structure of the optimized HSGC, which had good mechanical characteristics. Furthermore, the anti-carbonation performance and freezing resistance of the optimal HSGC increased by 17.7% and 14.6%, respectively, while the apparent porosity decreased by 8.4%.

This study investigates the effects of changing in the properties of face and core wythes in structural sandwich panels (with dimensions of 500 500 mm and 120 mm total height). Concrete face wythes of three grades (80, 70, 37) MPa, thicknesses of (25, 35, and 45) mm, and three types of core materials (high density foam, polyethylene foam, and palm bark) were used in the production of panels. Steel shear connectors were installed in the panels with angle of 45º. Three-point bending load test was carried out on all panels and results were compared with both of the theoretical extremes capacities of non- composite and fully-composite states and ANSYS software results. The degree of composite action (%) and the (strength/weight) ratio were the main parameters that judged the specimens. It was found that upgrading concrete increased overall strength of slabs especially in high strength concrete (80 MPa), however the use of lightweight concrete (70 MPa) caused high (strength/weight) ratio due to very lightweight. Results revealed that decreasing thickness of concrete face wythes had a positive effect on strength/weight ratio (although the ultimate loads decreased) that enhanced the performance of panels as lightweight structural panels. The optimum face wythe thickness is that of 2.5 cm and has high (strength/weight) ratio. It was noticed that adding polyethylene foam as a core material results in positive effect and high (strength/weight) ratio. Results revealed that high strength concrete (80 MPa) and light-weight concrete (37 MPa) are very successful in the production face wythes of precast light-weight sandwich panels that can obtain high (strength/weight) ratio and high percent of composite action.