Khaled Shwekat

Bio: Khaled Shwekat is an academic researcher from Wayne State University. The author has contributed to research in topics: Total cost & Fly ash. The author has an hindex of 1, co-authored 1 publications receiving 17 citations.

Benefit-cost analysis model of using class F fly ash-based green cement in masonry units

Abstract: Green Cement (GC) is considered as a potential alternative to Ordinary Portland Cement (OPC). There are major drawbacks associated with OPC, such as the emission of greenhouse gasses and high-energy consumption from cement production. Recycling fly ash and using it to replace cement has positive impacts on our environment, such as conserving landfill spaces, conserving natural resources, reducing CO2 emissions, and saving energy. Fly ash can be further recycled into value-added building products by developing fly ash-based green cement. This study presents an examination of the Benefit-Cost Analysis Model (BCAM) to characterize the environmental impact of masonry units produced from OPC or GC. Output from BCAM includes the monetary value of energy use, raw materials, atmospheric emissions, social costs of CO2, tax costs of carbon's emissions, and avoiding land filling of fly ash. This study has found that Mix (1) which is for OPC has a direct cost of raw materials only, on average $0.460/square foot, and an indirect cost (the monetary value of benefit-cost analysis model, as a result of negative impacts) of on average $0.152/square foot. Therefore, the total cost is $0.612/sf. Mix (2) which is for GC with NaOH as an activator has a direct cost of raw materials only, on average $2.28/sf, and a saving (the monetary value of benefit-cost analysis model, as a result of positive impacts) of on average $-1.057/sf. Therefore, the actual cost (direct cost - savings) is on average $1.222/sf. Mix (3) which is for GC with Na2SO4 as an activator has a direct cost of raw materials only, on average $0.943/sf and a saving of on average $-1.057/sf. Therefore, the actual cost is on average $-0.114/sf. The negative cost means that there is a saving as a result of monetary value of the positive impacts.

Sustainable criterion selection framework for green building materials – An optimisation based study of fly-ash Geopolymer concrete

Abstract: Green materials are considered as one of the prominent elements in designing an environmentally sustainable construction project. Studies have highlighted cement replacement is a popular method of reducing greenhouse gas (GHG) emissions and replacing virgin materials in concrete. These options incur cost implications through sophisticated designs and technologies. The importance of maintaining a balance between environmental and economic benefits of a green design is critical for the decision making stakeholders in a construction project. However, designers often lack the resources and tools to initiate informed decision making for the optimum selection of a green material. In order to systemize the optimising process, the current study suggests a multi-objective optimisation based decision making framework for optimising the cement replacement materials in concrete. The study aims to present a sustainable criterion optimisation framework that could well be adopted to assess the sustainability of green materials in concrete production. A case study using fly ash geopolymer concrete in Melbourne demonstrated a reduction of 3.63% to 41.57% and 23.80% to 30.25% can be achieved for GHG emissions and production cost respectively if the developed optimisation based framework is implemented. The scenario results highlighted around 3% to 8% GHG and cost increase if material is not available locally. A similar approach can be utilised to optimise the environmental and cost savings of other cement replacement materials. Further studies are encouraged on comparing environmental and cost savings of other cement replacement materials using the developed framework. The framework will be valuable for designers in making decisions on sustainable cement replacement materials.

An integrated approach using AHP and DEMATEL for evaluating climate change mitigation strategies of the Indian cement manufacturing industry

Abstract: Concrete, a cement-based product is the highest manufactured and second highest consumed product after water on earth. Across the world, production of cement is the most energy and emission intensive industry hence, the cement industry is currently under pressure to reduce greenhouse gases emissions (GHGEs). However, reducing the GHGEs of the cement industry especially for developing country like India is not an easy task. Cement manufacturing industry needs to focus on significant climate change mitigation strategies to reduce the GHGEs to sustain its production. This study aims at identifying significant climate change mitigation strategies of the cement manufacturing industry in the context of India. Extant literature review and expert opinion are used to identify climate change mitigation strategies of the cement manufacturing industry. In the present study, a model projects by applying both AHP and DEMATEL techniques to assess the climate change mitigation strategies of the cement industry. The AHP technique help in establishing the priorities of climate change mitigation strategies, while the DEMATEL technique forms the causal relationships among them. Through AHP, the results of this research demonstrate that Fuel emission reduction is on top most priority while the relative importance priority of the main remaining factors is Process emission reduction - Electric energy-related emission - Emission avoidance and reduction - Management mitigation measures. The findings also indicate that the main factors, Process emission reduction, and Fuel emission reduction are categorized in cause group factors, while the remaining factors, Electric energy-related emission, Emission avoidance and reduction and Management mitigation measures are in effect group factors. Present model will help supply chain analysts to develop both short-term and long-term decisive measures for effectively managing and reducing GHGEs.

Pozzolanic reaction on alkali-activated Class F fly ash for ambient condition curable structural materials

Abstract: Despite considerable efforts focused on the utilization of industrial wastes, the application of low-calcium fly ash to the construction industry is limited to the partial substitution to ordinary Portland cement. High-temperature curing is a method via which fly ash can be completely utilized as an alkali-activated construction material; however, additional energy is required. In this study, the dual reaction of alkali activation and the pozzolanic reaction was proposed to manufacture ambient-condition-curable structural mortars. For this purpose, calcium hydroxide was used in fly ash activated by sodium hydroxide and sodium silicate solutions. A series of experiments, including compressive strength tests, X-ray diffraction, thermogravimetric analysis, heat of reaction, and mercury intrusion porosimetry, were conducted. The continuous pozzolanic reaction on the pre-formulated geopolymeric skeleton was found to significantly enhance the material properties. By the addition of silica fume and a 7:3 mixture of sodium hydroxide and sodium silicate solutions, the material strength increased to greater than 60 MPa at 56 days. The added silica fume as well as the reduced alkali content of the solution enhanced the reactions due to the active participation of the calcium ion supplied by the added hydrated lime in a high pH environment.

Interfacial design of nano-TiO2 modified fly ash-cement based low carbon composites

Abstract: An enhanced use of fly ash in cement composites can decrease energy consumption, reduce related CO2 emissions, and conserve natural resources. However, low activity fly ash reduces the degree of early-age hydration and early strength of cement composites. This paper presents a facile processing method to increase the reactivity of fly ash and improve the early strength of low-carbon composites. Fly ash is mixed with TiO2 nanoparticles through ball milling, and the resulting roughened particles are used as supplementary cementitious materials (20 wt%) in a cement matrix. The TiO2 nanoparticles coated on the surface of fly ash improve the interfacial interlocking between fly ash and cement, and increase the early-age pozzolanic activity of fly ash. At a nano-TiO2 composition of 1 wt% of the binder materials, the early flexural strength and compressive strength of the paste exhibit a dramatic increase (of 37.74% and 39.11%, respectively) over those of a paste without nano-TiO2. A hydration heat evaluation of the fly ash–cement pastes conducted by an isothermal calorimeter indicates that the TiO2 nanoparticles coated on the surface of fly ash increase the hydration rate and hydration extent of the early hydration reaction of fly ash–cement paste. The thermogravimetric analysis results indicate that the TiO2 nanoparticles coated on the surface of fly ash promote the reaction of fly ash with calcium hydroxide (hydration products). This study illustrates the effectiveness of the interfacial design by this facile ball-milling process in overcoming the low reactivity of class-F fly ash and improving the early strength of low-carbon composites. More importantly, the proposed strategy can be conveniently extended to other waste materials, which could potentially improve the waste recycling efficiency.

High adsorption activated calcium silicate enabling high-capacity adsorption for sulfur dioxide

Abstract: Porous materials with developed pore structures are vital to obtaining high adsorption properties. Fly ash is rich in silicon with high porosity and a large specific surface area, and it is an excellent precursor for porous silica-based sorbents. Here, we report activated calcium silicate (ACS), which was prepared by fly ash and a two-step hydrothermal method to greatly enhance the activity of the pozzolanic reaction. Of importance, the adsorption capacity of ACS for sulfur dioxide (SO2) is up to 38.2 mg g−1. The results show that ACS has a honeycomb-like structure with high porosity and a large specific surface area. The adsorption process of SO2 on ACS involves the coexistence of physical and chemical adsorption. In particular, SO2 is first attached to the surface of ACS, and then diffused into the interior of ACS. At the same time, oxygen and water vapor are adhered to the surface of ACS, and SO2 is further oxidized to sulfuric acid and sulfate. In addition, the cycling performance of ACS can remain 71.2% through the adsorption–regeneration cycle for 20 cycles, forecasting the excellent cycle stability of ACS. The ACS material can be considered a new type of adsorbent with great development potential in the removal of fly ash and sulfur dioxide from coal-fired power plants.