Research for alternative binders has become a necessity due to cement's embodied carbon, climate change, and depletion of natural resources. These binders could potentially reduce our reliance on cement as the sole binder for concrete while simultaneously enhancing the functional characteristics of concrete. Theoretically, the use of finer particles in the cement matrix densifies the pore structure of concrete and results in improved properties. To validate this hypothesis, current research was designed to investigate how the value-added benefits of nano-silica (NS) and metakaolin (MK) in fly ash (FA)-blended cement affect the mechanical and durability characteristics of concrete when used as ternary and quaternary blends. Additionally, the cost-benefit analysis and environmental impact assessment were conducted. It was observed that the synergy of MK and NS used in FA-blended cement had a greater impact on enhancing the functional characteristics of concrete, while 10% MK as ordinary Portland cement (OPC) replacement and 1% NS as an additive in FA-blended OPC concrete was the optimum combination which achieved 94-MPa compressive strength at the age of 91 days and showed more than 25% increment in the flexural and splitting tensile strengths compared to the control mix (MS00). The ultrasonic pulse velocity and dynamic modulus of elasticity were significantly improved, while a significant reduction in chloride migration of 50% was observed. In terms of environmental impact, MS100 (30% FA and 10% MK) exhibited the least embodied CO2 emissions of 319.89 kgCO2/m3, while the highest eco-strength efficiency of 0.268 MPa/kgCO2·m-3 with respect to 28-day compressive strength was exhibited by MS101. In terms of cost-benefit, MS00 was determined the cheapest, while the addition of MK and NS increased the cost. The lowest cost of producing 1 MPa was exhibited by MS01 with a merely 0.04-$/MPa/m3 reduction compared to MS00.
This experimental research was conducted to study the combined effect of agricultural by-product wastes on the properties of concrete. The coconut shell ash (CSA) was utilized to substitute cement content ranging from 0 to 20% by weight of total binder and sugarcane bagasse ash (SCBA) to substitute fine aggregates (FA) ranging from 0 to 40% by weight of total FA. In this regard, a total of 300 concrete specimens (cylinders and cubes) were prepared using 1:1.5:3 mix proportions with a 0.52 water-binder ratio. The study investigated the workability, density, permeability, and mechanical properties in terms of compressive and splitting tensile strengths. Additionally, the total embodied carbon for all mix proportions was calculated. It was observed that with an increase in CSA and SCBA contents, the workability, density, and permeability reduced significantly. Due to CSA and SCBA being pozzolanic materials, a gain in compressive and splitting tensile strengths was observed for certain concrete mixes, after which the strength decreased. The increase in embodied carbon of SCBA increased the total embodied carbon of concrete; however, it can be said that C15S40 which consists of 15% CSA and 40% SCBA is the optimum mix that achieved 28.75 MPa and 3.05 MPa compressive and tensile strength, respectively, a reduction of 4% total embodied carbon.
Cement production emits a significant carbon dioxide (CO2) gas, dramatically influencing the environment. Furthermore, a large amount of energy is consumed during the cement manufacturing process; since Pakistan is already facing an energy crisis, this high energy consumption by the cement industry puts further stress on Pakistan's energy sector. Hence, the price of cement is rising day by day. Furthermore, waste disposals and concrete ingredients' restoration after demolition have adversative effects on the environment. Therefore, using these wastes decreases cement manufacturing, thereby reducing energy consumption, but it also aids in safeguarding the environment. The study aimed to determine the concrete properties by partially replacing cement with only eggshell powder (ESP) and combining ESP and silica fume (SF) in a ternary binder system in the mixture. However, workability, water absorption, compressive strength, split tensile strength, and flexural strength were all investigated in this study. In this experimental study, cement was replaced as 5, 8, 11, 15, and 20% of ESP, along with 5, 10, and 15% of silica by weight of cement in concrete. Approximately 21 mixes were prepared, from which 01 control mix, 05 mixes of ESP alone, and 15 mixes designed with a blend of ESP and SF with a 1:1.25:3 mix ratio and 0.5 water-cement ratios. Study parameters advocate the substitution of 11% ESP and 10% SF as the optimal option for maximum strength. Furthermore, combining ESP and SF diminishes the composite concrete mixture's workability and dry density greatly.
The production of cement contributes to 10% of global carbon dioxide (CO2) pollution and 74 to 81% towards the total CO2 pollution by concrete. In addition to that, its low strength-to-weight ratio, high density and thermal conductivity are among the few limitations of heavy weight concrete. Therefore, this study was carried out to provide a solution to these limitations by developing innovative eco-friendly lightweight foamed concrete (LFC) of 1800 kg/m3 density incorporating 20-25% palm oil fuel ash (POFA) and 5-15% eggshell powder (ESP) by weight of total binder as supplementary cementitious material (SCM). The influence of combined utilization of POFA and ESP on the fresh state properties of eco-friendly LFC was determined using the J-ring test. To determine the mechanical properties, a total of 48 cubes and 24 cylinders were prepared for compressive strength, splitting tensile strength and modulus of elasticity each. A total of 24 panels were prepared to determine the thermal properties in terms of surface temperature and thermal conductivity. Furthermore, to assess the environmental impact and eco-friendliness of the developed LFC, the embodied carbon and eco-strength efficiency was calculated. It was determined that the utilization of POFA and ESP reduced the workability slightly but enhanced the mechanical properties of LFC (17.05 to 22.60 MPa compressive strength and 1.43 to 2.61 MPa tensile strength), thus satisfies the ACI213R requirements for structural lightweight concrete and that it can be used for structural applications. Additionally, the thermal conductivity reduced ranging from 0.55 to 0.63 W/mK compared to 0.82 W/mK achieved by control sample. Furthermore, the developed LFC showed a 16.96 to 33.55% reduction in embodied carbon and exhibited higher eco-strength efficiency between 47.82 and 76.97%. Overall, the combined utilization of POFA and ESP as SCMs not only enhanced the thermo-mechanical performance, makes the sustainable LFC as structural lightweight concrete, but also has reduced the environmental impacts caused by the disposal of POFA and ESP in landfills as well as reducing the total CO2 emissions during the production of eco-friendly LFC.
Rapid urbanization and 'concretization' have increased the use of concrete as the preferred building material. However, the production of cement and other concrete-related activities, contribute significantly to both the carbon dioxide emissions and climate change. Agro-industrial wastes such as Palm Oil Fuel Ash (POFA) and Eggshell Powder (ESP) have been utilized in concrete as supplementary cementitious materials, to reduce the cement content, in order to minimize the carbon footprint and the environmental pollution associated with the dumping of waste. Both POFA and ESP have been utilized in ternary binder foamed concrete; however, higher content of cement replacement tends to reduce the concrete's strength significantly. Therefore, this research was conducted to study the influence of ternary binder foamed concrete, incorporating 30% POFA and 5-15% ESP by weight of the total binder, when reinforced with polypropylene (PP) fibres. Based on the results, the ternary binder foamed concrete showed better strength than the control foamed concrete due to the pozzolanic reaction and the addition of PP fibres slightly improved the strength. Furthermore, ternary binder foamed concrete can reduce up to 33.79% of the total CO2 emissions. In terms of cost, all ternary binder foamed concrete mixes reduced the overall cost of the mix. The lowest cost per 1 MPa was achieved by ternary binder foamed concrete mix which incorporated 30% POFA, 5% ESP and 0.20% PP fibres. However, the optimum S5 ternary binder foamed concrete mix, which incorporated 30% POFA, 10% ESP and 0.20% PP fibres, exhibited a cost of $3.74 per 1 MPa strength, which was $1.1 lower than the control foamed concrete. PP reinforced ternary binder foamed concrete is an eco-efficient and cost-effective concrete that can be used in numerous civil engineering applications, mitigating the environmental and the emissions generated by agro-industrial waste.
The production of cement releases an enormous amount of CO2 into the environment. Besides, industrial wastes like silica fume and fly ash need effective utilization to reduce their impacts on the environment. This research aims to explore the influence of silica fume (SF) and fly ash (FA) individually and combine them as binary cementitious material (BCM) on the hardened properties and embodied carbon of roller compacted concrete (RCC). A total of ten mixes were prepared with 1:2:4 mix ratio at the different water-cement ratios to keep the zero slump of roller compacted concrete. However, the replacement proportions for SF were 5%-15%, and FA were 5%-15% by the weight of cement individually and combine in roller compacted concrete for determining the hardened properties and embodied carbon. In this regard, several numbers of concrete specimens (cubes and cylinders) were cast and cured for 7 and 28 days correspondingly. It was observed that the compressive strength of RCC is boosted by 33.6 MPa and 30.6 MPa while using 10% of cement replaced with SF and FA individually at 28 days, respectively. Similarly, the splitting tensile strength of RCC is enhanced by 3.5 MPa at 10% cement replaced with SF and FA on 28 days, respectively. The compressive and splitting tensile strength of RCC is increased by 34.2 MPa and 3.8 MPa at SF7.5FA7.5 as BCM after 28 days consistently. In addition, the water absorption of RCC decreased while using SF and FA as cementitious material individually and together at 28 days. Besides, the embodied carbon of RCC decreased with increasing the replacement level of SF and FA by the mass of cement individually and combined.
With the recent increase in demand for high-strength concrete, higher cement content is utilized, which has increased the need for cement. The cement industry is one of the most energy-consuming sectors globally, contributing to 10% of global carbon dioxide (CO2) gas emissions and global warming. Similarly, with rapid urbanization and industrialization, a vast number of by-products and waste materials are being generated in abundance, which causes environmental and health issues. Focusing on these two issues, this study aimed to develop an M50-grade eco-friendly high-strength concrete incorporating waste materials like marble dust powder (MDP) and fly ash (FA) as partial cement replacement. 2.5%, 5%, 7.5%, and 10% MDP and FA by weight of total binder was utilized combinedly, such that the 5%, 10%, 15%, and 20% cement content was replaced, respectively. The fresh state properties in terms of workability and hardened state properties in terms of compressive and flexural strengths were evaluated at 7, 14, 28, 56, and 90 days. Furthermore, to assess the environmental impact of MDP and FA, the embodied carbon and eco-strength efficiency were calculated. Based upon the results, it was observed that a combined 10% (5% MDP and 5% FA) achieved the highest strength; however, 15% (7.5% MDP and 7.5% FA) substitution could be optimal. Furthermore, the combined utilization of FA and MDP also enabled a reduction in the total embodied carbon. It decreased the cost of concrete, resulting in an eco-friendly, high-strength concrete.