Mehrab Nodehi

Bio: Mehrab Nodehi is an academic researcher from Texas State University. The author has contributed to research in topics: Materials science & Durability. The author has an hindex of 4, co-authored 12 publications receiving 39 citations.

Alkali-Activated Materials and Geopolymer: a Review of Common Precursors and Activators Addressing Circular Economy

Abstract: The vast increase in CO2 and waste generation in recent decades has been a major obstacle to sustainable development and sustainability. In construction industry, the production of ordinary Portland cement is a major greenhouse gas emitter with almost 8% of total CO2 production in the world. To address this, Alkali-activated materials and geopolymer have more recently been introduced as a green and sustainable alternative of ordinary Portland cement with significantly lowered environmental footprints. Their use to replace Portland cement products generally leads to vast energy and virgin materials savings resulting in a sustainable concrete production. In doing so, it reuses the solid waste generated in industrial and manufacturing sectors, which is aligned with circular economy. In turn, it reduces the need for ordinary Portland cement consumption and its subsequent CO2 generation. To provide further insight and address the challenges facing the substitution of ordinary Portland cement, this article reviews different types, mechanisms, and result of mechanical and durability properties of alkali-activated materials and geopolymer reported in literature. Finally, it discusses future projections of waste materials that have cementitious properties and can replace ordinary Portland cement and be used in alkali-activated materials and geopolymer.

A systematic review of bacteria-based self-healing concrete: Biomineralization, mechanical, and durability properties

Abstract: Cracking is one of the major deteriorating causes of concrete, which allows the entrance of chemicals and can lead to the loss of physico-mechanical and durability properties of concrete structures. To protect, repair, and rehabilitate concrete structures, the application of different surface coating agents and sealants, binding agents, as well as adhesives has been commonly practiced. Although such techniques have mostly been applicable, due to their inherent mechanism difference, major challenges such as delamination and lack of cost effectiveness have resulted in searching for alternative methods of crack sealing or self-healing. One of the novel self-healing mechanisms is using bacterial induced calcite precipitation in concrete mixtures to heal concrete cracks. In this technique, bacterial mineralization (biomineralization) is performed through decomposing urea and calcium to produce calcium carbonate (CaCO 3 ), which can fill cracks. To review the mechanisms ruling this precipitation, this article aims to present an in-depth analysis of biomineralization, CaCO 3 precipitation, physico-mechanical, durability and microstructural properties of bacterial concrete. To do this, over 70 research articles have been reviewed and their data including the types and dosage of bacteria, mixture proportions, as well as the result of mechanical and durability tests are gathered, provided and analyzed. Based on this review, it is found that the biomineralization is mostly dependent on factors such as the applying method and consistent preservation of the living bacteria. In addition, the environmental impact of bacterial concrete is found to be directly linked with the urea content in the concrete mixture. • A review of bacteria-based calcium carbonate precipitation for self-healing of concrete is presented. • In bacterial concrete , alkaliphiles bacteria is mostly used due to their high resistance to alkalinity. • Bacterial concrete has an enhanced mechano-durability properties due to high compaction and reduced defects. • The environmental impact of bio-concrete is directly linked with the amount of urea used.

Sustainable concrete for circular economy: a review on use of waste glass

Abstract: As a result of socio-economic growth, major increase in solid waste generation is taking place which can lead to resource depletion and environmental concerns. To address this inefficient cycle of make, use and dispose, the concept of circular economy has recently been proposed that de-linearizes the current relationship between economic growth, environmental degradation and resource consumption thorough its 6Rs (Reuse, Recycle, Redesign, Remanufacture, Reduce, Recover). In the construction sector, currently the production of binding agents and transportation of virgin aggregates is associated with considerable environmental pollution. As a result, major attempts are taking place to substitute such ingredients with more sustainable and potentially cheaper materials. With waste glass having a production of roughly 100 million tons annually, and its low recycling rate of 26%, there is a growing number of studies unlocking its potential as an eco-friendly substitute for Portland cement (with particle size of below $$100\ \upmu \hbox {m}$$ ) or fine aggregate (with size of below 4.75 mm) in concrete. As a result, this article intends to review the connection of construction sector and circular economy with recycled glass in its center. Accordingly, by partially replacing cement or aggregate with recycled glass, on average, up to 19% greenhouse gas, and 17% energy consumption reduction as well as major cost savings can be made. Additionally, in technical concrete terms, better fresh properties and fire resistance, as well as lower permeability, and in fine grades, favorable cementitious properties are reported as major benefits of using waste glass as a sustainable construction material.

Environmental Performance Index

Abstract: Yale’s Environmental Performance Index (EPI) has emerged as the premier framework of national-scale metrics for global environmental policy analysis. Data and indicators from 180 countries gauge progress on 20+ environmental public health and ecosystem vitality goals. The framework offers a policy-relevant scorecard that highlights leaders and laggards in environmental performance, gives insight on best practices, and provides guidance for countries that aspire to be leaders in sustainability. The Yale Center for Environmental Law & Policy (YCELP) is looking for research assistants to contribute to the 2018 release of the next EPI report. For more information, visit epi.yale.edu.

Alkali-Activated Materials and Geopolymer: a Review of Common Precursors and Activators Addressing Circular Economy

Abstract: The vast increase in CO2 and waste generation in recent decades has been a major obstacle to sustainable development and sustainability. In construction industry, the production of ordinary Portland cement is a major greenhouse gas emitter with almost 8% of total CO2 production in the world. To address this, Alkali-activated materials and geopolymer have more recently been introduced as a green and sustainable alternative of ordinary Portland cement with significantly lowered environmental footprints. Their use to replace Portland cement products generally leads to vast energy and virgin materials savings resulting in a sustainable concrete production. In doing so, it reuses the solid waste generated in industrial and manufacturing sectors, which is aligned with circular economy. In turn, it reduces the need for ordinary Portland cement consumption and its subsequent CO2 generation. To provide further insight and address the challenges facing the substitution of ordinary Portland cement, this article reviews different types, mechanisms, and result of mechanical and durability properties of alkali-activated materials and geopolymer reported in literature. Finally, it discusses future projections of waste materials that have cementitious properties and can replace ordinary Portland cement and be used in alkali-activated materials and geopolymer.

Fracture Performance of Cementitious Composites Based on Quaternary Blended Cements

Abstract: This study presents test results and in-depth discussion regarding the measurement of the fracture mechanics parameters of new concrete composites based on quaternary blended cements (QBC). A composition of the two most commonly used mineral additives, i.e., fly ash (FA) and silica fume (SF), in combination with nanosilica (nS), has been proposed as a partial replacement for ordinary Portland cement (OPC) binder. Four series of concrete were made, one of which was the reference concrete (REF) and the remaining three were QBC. During the research, the main mechanical parameters of compressive strength (fcm) and splitting tensile strength (fctm), as well as fracture mechanics parameters and the critical stress intensity factor KIcS, along with critical crack-tip opening displacements (CTODc) were investigated. Based on the tests, it was found that the total addition of siliceous materials, i.e., SF + nS without FA, increases the strength and fracture parameters of concrete by approximately 40%. On the other hand, supplementing the composition of the binder with SF and nS with 5% of FA additive causes an increase in all mechanical parameters by approximately 10%, whereas an increase by another 10% in the FA content in the concrete mix causes a significant decrease in all the analyzed factors by 10%, compared to the composite with the addition of silica modifiers only.