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Most geopolymer research claims a substantial reduction in carbon dioxide emissions compared with ordinary portland cement concrete. However, geopolymer concretes are not all equally eco-friendly. The environmental benefits of geopolymer concrete cannot be taken for granted. Modeling emissions is necessary to assess the environmental impact of each geopolymer mix. Unfortunately, only studies concerned with carbon dioxide emissions care to provide sophisticated emissions modeling. Such modeling is practically nonexistent for other geopolymer studies; because function-oriented geopolymer research tends to assume the environmental eminence of their designed mixes. This research reviews the last 7 years of geopolymer concrete research to assess the sustainability of the mixes designed by researchers worldwide and to highlight any bad environmental practices in the mix design. The nominal CO2-e equivalent emissions for geopolymer concrete mixes varied from 56 to 661 kg-CO2/m3 for the surveyed mixes. SOx and NOx emissions reached 1,865 g-SOx/m3 and 1,161 g-NOx/m3 , respectively. Finally, this paper recommends a simple method for estimating a nominal carbon dioxide emissions value, which can be easily implemented in future geopolymer research. [ABSTRACT FROM AUTHOR]

This paper reports the results of an initial attempt of using iron ore tailings (IOTs) to develop greener engineered cementitious composites (ECCs). ECC is a unique class of high-performance fiber-reinforced cementitious composites featuring high tensile ductility and durability. However, the high cement usage in ECC limits the material greenness and increases the material cost compared with normal concrete. In this paper, IOTs in powder form are used to partially replace cement to enhance the environmental sustainability of ECC. Mechanical properties and material greenness of ECC containing various proportions of IOTs are investigated. The newly developed versions of ECC in this paper, with a cement content of , exhibit a tensile ductility of 2.3-3.3%, tensile strength of 5.1-6.0 MPa, and compressive strength of 46-57 MPa at 28 days. The replacement of cement with IOTs results in 10-32% reduction in energy consumption and 29-63% reduction in carbon dioxide emissions in green ECC compared with typical ECC. Thus, the feasibility of producing greener ECC with significantly reduced environmental impact using IOTs, and maintaining the mechanical properties of typical ECC, is experimentally demonstrated in this paper. [ABSTRACT FROM AUTHOR]

The portland cement (PC) industry is responsible for approximately 7% of all carbon dioxide (CO2) emissions in the world. Blast furnace slag (BFS) has been increasingly used as a substitute for PC, due to the efficient disposal of steel industry waste and reductions in CO2 emissions. The present work investigated the environmental benefits of cementitious materials with large volumes of BFS (up to 90% PC replacement for the S90 mixture) and the influence on porosity and compressive strength. By X-ray computed microtomography and mercury intrusion porosimetry, pore size distribution was assessed. Porosity was also evaluated by water absorption. The environmental impacts were investigated by analyzing the embodied CO2 emissions (ECO2) and embodied energy (EE) by using life cycle assessment methodology. Reductions of around 40% in the compressive strength of S90 were found, while reductions in EE and ECO2 were above 80%. The S90 showed higher porosity at the age of 28 days, but then promoted a more active pore closing effect over time, being nevertheless feasible for use in terms of porosity. The use of S90 is expected to increase durability due to its thinner porous matrix, and contribute to reducing environmental impact and advancing cleaner production. Practical Applications: Today, there is a global call to action to end poverty, protect the environment and climate, and ensure that people everywhere can enjoy peace and prosperity. Objectives set for the United Nations aim to help developing countries, like Brazil, achieve the 2030 Agenda for Sustainable Development. A highlight is given to "Sustainable Development Goal 9: Industry, Innovation and Infrastructure" (SDG 9), which aims to build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation. The portland cement (PC) industry is responsible for approximately 7% of all carbon dioxide (CO2) emissions in the world. The study carried out here points to the feasibility of using blast furnace slag (BFS) to replace up to 90% of PC clinker, and demonstrates the environmental advantages in terms of reducing CO2 emissions and energy consumption. In this context, the use of clinkers with higher concentrations of BFS, up to 90%, has emerged as a way to contribute to the sustainable development proposed by SDG 9. [ABSTRACT FROM AUTHOR]

Environmental issues, such as global warming and pollution, could be solved by reducing the carbon dioxide (CO2) footprint on the surrounding atmosphere. Utilizing by-products as a cement substitute in cement production, such as cement kiln dust (CKD), could reduce CO2 emissions from burning raw materials in cement plants. This study investigated the effect of cement kiln dust on cement mortar's physical, flow, and mechanical properties. Cement was replaced with CKD up to 100% (by weight of dry cement). The optimum content of CKD was determined based on compressive strength; loss on ignition (LOI); and chloride (Cl), sulfate (SO3), and magnesium oxide (MgO) contents. Standard sand with a maximum diameter of 2 mm was used in this study, with a sand-to-binder ratio (s/b) of 3∶1. Three different models—multiexpression programming (MEP), nonlinear regression (NLR), and an artificial neural network (ANN)—were employed for estimating the compressive strength of CKD-modified cement mortar using the present study data (110 data sets) and 152 data collected from other research studies. The compressive strength of cement mortar was predicted as a function of water-to-binder ratio (w/b), sand-to-binder ratio, cement kiln dust content, silicon dioxide content in the binder, calcium oxide content in the binder, the maximum aggregate diameter (MDA), and curing ages (t). Based on the statistical assessments, the ANN models outperformed the MEP and NLR models in the testing phase. According to the sensitivity analysis, curing time is the most critical parameter affecting the compressive strength of CKD-modified cement mortar, and the SiO2 content percentage affected the compressive strength more than did the CaO content percentage. [ABSTRACT FROM AUTHOR]

Utilization of fly ash in concrete reduces the use of virgin materials and offers benefits of reduced landfill materials and CO2 emissions avoidance-fly ash therefore contributes to industrial sustainability. This paper presents a method to optimize the cement and fly ash contents in concrete on the basis of the hardened concrete properties testing and environmental effects. Such fly ash concrete would develop an adequate 1-day and 28-day compressive strength and would be as durable as the ordinary portland cement concrete. Nine concrete mixtures with fly ash contents ranging from 15-60% and cementitious material contents from 338-391 kg/m3 (570-705 lbs/cu yd) were investigated. Environmental life cycle assessments (LCA) were completed by using a model developed for Denver, Colorado. The optimized fly ash concrete was selected to yield a similar 28-day compressive strength and durability to that of Colorado Department of Transportation (CDOT) Class D structural concrete. The durability aspects investigated included the resistance to rapid chloride-ion penetration and the resistance to the rapid cycles of freezing and thawing. The results show that the mixtures with cementitious material content lower than 365 kg/m3 (615 lbs/cu yd) and fly ash content higher than 40% meet the CDOT Class D structural concrete strength and durability requirements. On the basis of the structural performances of the concrete mixtures and environmental effects, the optimized cementitious material content and the maximum possible cement replacement percentage with the fly ash was selected to be 338 kg/m3 (570 lbs/cu yd) and 50%, respectively. The optimized concrete mixture exhibited excellent characteristics in compressive strength (32.0 MPa, 4,635 psi at 28 days), resistance to chloride-ion penetration (moderate at 28 days of age) and freeze-thaw (96, average durability factor after 300 cycles). The mixture with optimum fly ash and cementitious content had the minimum embodied energy and greenhouse gas (GHG) emission among the nine mixtures. The embodied energy and GHG emission of the optimized concrete mixture (per cubic meter) were 2,643 MJ and 361 kgCO2E, respectively, which are 32.8 and 35.2% less than the mixture with the most embodied energy and GHG emission. [ABSTRACT FROM AUTHOR]