ORCID Profile
0000-0001-5896-6375
Current Organisations
Texas State University
,
University of California Davis
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Publisher: Elsevier BV
Date: 02-2022
Publisher: Elsevier BV
Date: 04-2022
Publisher: Springer Science and Business Media LLC
Date: 24-04-2023
Publisher: Elsevier BV
Date: 08-2022
Publisher: Elsevier BV
Date: 05-2022
Publisher: MDPI AG
Date: 07-03-2023
DOI: 10.3390/SU15064722
Abstract: Calcium aluminate cements (CACs) are a group of rapid-hardening hydraulic binders with a higher aluminum composition and lower ecological footprint compared to their ordinary Portland cement (CEM) counterparts. CACs are commonly known to have higher thermo-durability properties but have previously been observed to experience a major strength loss over time when exposed to thermal and humidity conditions due to the chemical conversion of their natural hydrated products. To address this, in this study, silica fume is added to induce a different hydration phase path suggested by previous studies and utilized in conjunction with fiber-reinforced lightweight pumice to produce lightweight concrete. To closely evaluate the performance of the produced s les with CAC compared to CEM, two different types of cement (CEM and CAC) with different proportions of pumice and crushed stone aggregate at temperatures between 200 and 1000 °C were tested. In this context, sieve analysis, bulk density, flowability, compressive and flexural strength, ultrasonic pulse velocity and weight loss of the different mixes were determined. The results of this study point to the better mechanical properties of CAC s les produced with pumice aggregates (compared to crushed stone) when s les are exposed to high temperatures. As a result, it is found that CACs perform better than CEM s les with lightweight pumice at elevated temperatures, showing the suitability of producing lightweight thermal-resistant CAC-based concretes.
Publisher: Wiley
Date: 26-09-2022
Abstract: Structural optimization is a broad term in the construction sector, whereby material efficiency, as well as cost effectiveness of structures, are optimized. In concrete technology, high‐performance lightweight concrete structures often represent such optimized properties, including cost‐effectiveness and ease of application, while having a lower structural dead load. Although the use of lightweight concrete is often viewed as a sustainable practice, it does not address the high use and dependance on Portland cement, which has a high ecological footprint. In this regard, this study evaluates the engineering properties of structural lightweight concrete containing expanded shale and clay, as coarse aggregate, with a high quantity of coal fly ash (class F and C). For this purpose, a total of 15 mixes have been produced and a comprehensive series of physico‐mechanical and durability tests have been conducted. Based on the results, it is found that expanded clay outperforms expanded shale in terms of physico‐mechanical and durability properties of the resulting concrete, potentially due to its lower particle size distribution (used in this study) and the resulting porosity compared to expanded shale. Nonetheless, comparable physico‐mechanical properties are achieved when expanded shale and clay are used, as a full replacement of limestone. In turn, the performance of class C fly ash is found to be better in mechanical, but lower in certain durability variables, compared to their class F companions. The result of this study is found significant and point to suitability of using expanded shale and clay in combination with high‐volume fly ash.
Publisher: Wiley
Date: 30-12-2022
Abstract: As an alternative to ordinary Portland cement (OPC), alkali‐activated materials (AAMs) have more recently been studied and found to have certain suitability in reducing ecological footprint of OPC binding systems. Nonetheless, due to recent concerns over the availability of certain precursors used AAMs (such as the reduction of coal fly ash availability), this study utilized marble powder in various quantities to replace the naturally available kaolin as precursor. This composite use of natural precursors has been entertained to assimilate the production of carbon zero AAMs. To evaluate the physico‐mechanical and microstructural characteristics of the materials, 48 mixes with different sodium (Na) concentrations, curing temperatures, and marble powder content have been used. The results show that rising curing temperature is more effective than other variables, such as the Na and marble powder content on the physico‐mechanical performance of tested geopolymers. In this regard, it is found that a very high Na content can have adverse effect on the properties, potentially due to altered Na/Si, Na/Al ratio in the mixes. Furthermore, the inclusion of marble powder is found to be effective in decreasing the overall porosity up to ~31% and enhancing the physico‐mechanical properties of the specimens cured at 20 and 80°C. Nonetheless, results show that when specimens containing marble powder are exposed to higher curing temperatures (above 80°C) the presence of marble powder adversely affects physico‐mechanical properties. It is concluded that this phenomenon is caused by the dehydration of chemically bound water in higher temperatures when marble powder is used. This result is further confirmed by microstructural tests.
Publisher: MDPI AG
Date: 04-12-2022
DOI: 10.3390/SU151411045
Abstract: Recent growth in materials science and engineering technologies has pushed the construction industry to engage in new applications, such as the manufacturing of smart and electrically conductive products. Such novel uses of conductive construction materials would potentially allow their use in conjunction with various fields, such as those referred to as “Industry 4.0.” The following study uses iron oxide (Fe3O4)-multi-walled carbon nanotubes (MWCNTs) nanocomposites synthesized by chemical vapor deposition (CVD) and incorporated into the cementitious mortars as a substitute for sand at 1, 2, and 3% ratios to enhance the electrical conductivity. Results reveal that the electrical resistivity of cementitious composites decreases (due to the increase in electrical conductivity) from 208.3 to 61.6 Ω·m with both the Fe3O4-MWCNTs nanocomposites ratio and the increasing voltage. The lowest compressive strengths at 7 and 28 days are 12.6 and 17.4 MPa for specimens with 3% Fe3O4-MWCNTs and meet the standards that comply with most applications. On the other hand, the highest porosity was reached at 26.8% with a Fe3O4-MWCNTs rate of 3%. This increase in porosity caused a decrease in both the dry unit weight and ultrasonic pulse velocity (from 5156 to 4361 m/s). Further, it is found that the incorporation of Fe3O4-MWCNT nanocomposites can have a negative effect on the hardening process of mortars, leading to localized air cavities and an inhomogeneous development of cementing products. Nonetheless, the improvement of the electrical conductivity of the s les without significantly compromising their physico-mechanical properties will allow their use in various fields, such as deicing applications with low-voltage electric current.
Publisher: MDPI AG
Date: 18-06-2022
DOI: 10.3390/SU14127458
Abstract: In construction industry, phase change materials (PCMs), have recently been studied and found effective in increasing energy efficiency of buildings through their high capacity to store thermal energy. In this study, a combination of Capric (CA)-Palmitic acid (PA) with optimum mass ratio of 85–15% is used and impregnated with recycled concrete powder (RCP). The resulting composite is produced as foam concrete and tested for a series of physico-mechanical, thermal and microstructural properties. The results show that recycled concrete powder can host PCMs without leaking if used in proper quantity. Further, the differential scanning calorimetry (DSC) results show that the produced RCP/CA-PA composites have a latent heat capacity of 34.1 and 33.5 J/g in liquid and solid phases, respectively, which is found to remain stable even after 300 phase changing cycles. In this regard, the indoor temperature performance of the rooms supplied with composite foams made with PCMs, showed significantly enhanced efficiency. In addition, it is shown that inclusion of PCMs in foam concrete can significantly reduce porosity and pore connectivity, resulting in enhanced mechanical properties. The results are found promising and point to the suitability of using RCP-impregnated PCMs in foam composites to enhance thermo-regulative performance of buildings. On this basis, the use of PCMs for enhanced thermal properties of buildings are recommended, especially to be used in conjunction with foam concrete.
Publisher: Springer Science and Business Media LLC
Date: 15-07-2022
DOI: 10.1007/S11356-022-21837-Z
Abstract: Due to the increased population in the urbanized areas, considerable attention is being paid on the development of energy-efficient buildings. In construction, the use of insulating foams has grabbed considerable attention in recent decades due to their porous structure that can reduce thermo-acoustic conductivity leading to higher energy efficiency. Nonetheless, the production of certain foams (e.g., polymer foams) is based on harmful chemical substances, such as isocyanate, as well as having difficulty being recycled. In this regard, this study adopted the use of hydrodesulfurization (HDS) spent catalyst, which is a byproduct of petroleum industry and is known to be a hazardous solid waste material, to produce a more environmentally friendly composite foam with lower thermal conductivity. In this sense, a series of material property tests, as well as thermal conductivity test, have been conducted. In addition, to further confirm the impact of HDS inclusion in the produced foams, energy cost savings and CO
Publisher: Elsevier BV
Date: 08-2023
Publisher: Elsevier BV
Date: 10-2023
Publisher: MDPI AG
Date: 19-10-2022
DOI: 10.3390/SU142013496
Abstract: Recent trends in reducing the ecological footprint of the construction industry have increased the attention surrounding the use of alternative binding systems. Among the most promising are geopolymer binders, which were found to have the capability to substantially reduce the environmental impact of Portland cement use. However, even the use of this alternative binding system is known to be heavily dependent on the use of industrial byproducts, such as precursors and an alkaline source, produced through an energy intensive process. To address this and provide a greener route for this binding system, this study adopts the use of natural kaolin and raw ceramic powder as the main precursors. The activation process is performed by using solid potassium hydroxide in conjunction with sodium and magnesium sulfate, which are naturally available, to produce geopolymers. To assess the resulting geopolymer s les, 28 mixes are produced and a series of physico-mechanical and microstructural analyses is conducted. The results show that the use of ceramic powder can improve the physico-mechanical properties by reducing porosity. This, however, requires a relatively higher alkalinity for activation and strength development. These findings are further confirmed with the XRD and FTIR results. Nonetheless, the use of ceramic powder with sodium and magnesium sulfate is found to result in a more coherent and homogenous microstructure, compared to the geopolymers produced with potassium hydroxide and kaolin. The findings of this study point to the suitability of using sodium and magnesium sulfate for the cleaner production of kaolin and ceramic powder-based geopolymers.
No related grants have been discovered for Mehrab Nodehi.