Impact of graphene oxide and highly reduced graphene oxide on cement based composites

This study examines and compares the performance of two specific forms of graphene nanomaterials in the cement based composite, namely graphene oxide (GO) and reduced graphene oxide (rGO). A typical forms of GO with the average C:O ratio of 54:46 and a rGO with the average C:O ratio of 82:18 were used in the cement based paste composites. rGO was treated with superplasticizer to improve its dispersibility in water. Both GO and rGO were used as 0.02, 0.04, 0.06 wt% of cement. The effect of GO and rGO on workability, early age hydration, microstructure, mechanical and transport properties was determined. Different characteristics of GO and rGO such as molecular structure, functional groups, d spacing, size and physical strength influenced the properties of the cement based composites. The workability and final setting time of composite gradually decreased compared to 100% PC (control) with higher dosages of GO up to 0.06 wt% (of cement), which is due to the dominant oxygen functional groups and the hydrophilic nature of GO. To the contrary, the workability and final setting time increased in the rGO composites compared to the control mix due to the almost hydrophobic nature of rGO and the presence of superplasticiser. The XRD and TGA quantification of the hydration products shows that GO composites have a greater content of Ca(OH)2 and C-S-H compared to rGO composites measured at 1, 7 and 28 days. Micropores (smaller than ∼10 µm) in GO composites were observed to be filled with calcium silicate hydrate (C-S-H) gel and crystalline compounds. Random pore filling nature was observed in rGO composites and ettringite was more common element in those pores. Meso and gel pores

MAT-759: PARTICLE SIZE ANALYSIS AS A MEANS TO BETTER UNDERSTAND THE INFLUENCE OF FLY ASH VARIABILITY IN CONCRETE

Fly ash is generated from thermal power stations as an industrial by-product of coal combustion materials. Its particles are generally glassy, spherical in shape, and typically range in size from 0.5-300 µm. Coal fly ash is widely used as a partial cementitious material in concrete, which not only offers economic and environmental benefits but also improves concrete performance. However, variability of the physical description and chemical composition of fly ash has been considered to be a major barrier to its increased use in cement and concrete. In this study the variability and properties of fly ash are characterized with an emphasis on particle size analysis as a means for fly ash producers to better understand material properties in relation to the process of production, classification, and potential modes of utilization. Fly ash samples were collected from different coal-fired power plants from certain Indian and Canadian sources. The particle size analysis results using Laser Diffraction Technique showed a wide variation between the particle size distributions of the studied sources. However, no correlation between the varied size distributions and chemical compositions of fly ash samples was found. Laboratory experiments on the selected fly ash samples are being undertaken to correlate fly ash characteristics and their effects on the performance of concrete mixtures with cementitious replacement level up to 50%

Nano-cement composite with graphene oxide produced from epigenetic graphite deposit

This study presents the development of a nano-cement composite with graphene oxide (GO) carbon-based nanomaterials synthesized from a high-purity epigenetic graphite deposit. Diamond drill sampled graphite mineralization was upgraded through beneficiation and purification to recover a high-purity graphite product (99.9% graphitic carbon “Cg”). An alternate and improved chemical oxidation process based on the Modified Hummers method was adopted for the synthesis of GO from high-purity graphite. Microstructural analysis were performed to characterise GO. The GO consists of single bondOH, single bondC=O, single bondCOOH, and C-O-C functional groups with a layer thickness of 1.2 nm, 2 to 3 layers of graphene, an interlayer distance of 0.90 nm and a Raman (ID/IG) ratio of 0.79. The effect of 0.02, 0.04, and 0.06 wt% GO of cement on the composite workability, hydration, microstructure, mechanical and transport properties was determined. Increasing the concentration of GO in the composite decreased the workability due to the hydrophilic nature of the 2D planar surface. The rate of hydration accelerated and the cumulative hydration heat increased with the increasing proportions of GO in the composite. GO dosages about 0.02 and 0.04 wt% of cement in the composites resulted the maximum enhancement of compressive and flexural strength by 83 and 26%, respectively, compared to the control mix (0 wt% GO). The microstructural investigation shows that GO enhanced the hydration of calcium hydroxide (CH) and calcium silicate hydrate (C-S-H) during the nucleation and growth stages, filled pores, bridged micro-cracks and created interlocking between the cement hydration products. Collectively, these effects ultimately improved the mechanical properties of the composites. Also, in this process, the 0.02 and 0.04 wt% GO cement composite increased the electrical resistivity by 11.5%, and decreased the sorptivity by 29%, respectively, both of which improved the overall performance of the composite

Environmental impacts of using desalinated water in concrete production in areas affected by freshwater scarcity

Up to 500 litres of water may be consumed at the batching plant per cubic meter of ready mix concrete, if water for washing mixing trucks and equipment is included. Demand for concrete is growing almost everywhere, regardless of local availability of freshwater. The use of freshwater for concrete production exacerbates stress on natural water resources. In water-stressed coastal countries such as Israel, desalinated seawater (DSW) is often used in the production of concrete. However, the environmental impacts of this practice have not yet been assessed. In this study the effect of using DSW on the water and carbon footprints of concrete was investigated using life cycle assessment. Water footprint results highlight the benefits of using DSW rather than freshwater to produce concrete in Israel. In contrast, because desalination is an energy intensive process, using DSW increases the greenhouse gas intensity of concrete. Nevertheless, this increase (0.27 kg CO2e/m3 concrete) is small, if compared to the life cycle greenhouse gas emissions of concrete. Our results show that using untreated seawater in the mix (transported by truck from the coast) in place of DSW, would be beneficial in terms of water and carbon footprints if the batching plant were located less than 13 km from the withdrawal point. However, use of untreated seawater increases steel reinforcement corrosion, resulting in loss of structural integrity of the reinforced concrete composite. Sustainability of replacing steel with non-corrosive materials should be explored as a way to reduce both water and carbon footprints of concrete

Nano reinforced cement paste composite with functionalized graphene and pristine graphene nanoplatelets

This study examines and compares the workability, hydration, mechanical, microstructure and transport properties of cement paste composites containing the three forms of graphene-based 2D nanomaterials synthesised from epigenetic graphite deposit, namely, graphene oxide (GO), reduced graphene oxide (rGO), and pristine graphene nanoplatelates (G). Graphene materials were used from 0.01% to 0.16% of cement weight. The rGO and G were treated with salt and surfactant, respectively during synthesis, to improve dispersion in water. Characteristics and physical strength vary among GO, rGO and G, which have influenced the properties of nano reinforced graphene-cement composites (GCCs). The 28-day compressive and flexural strength of graphene (GO, rGO and G) cement composite improved by 28% and 81%, 30% and 84%, and 39% and 38%, respectively, compared to the control mix (cement paste without graphene materials). Finally, microscopic analysis, dynamic vapour sorption (DVS), electrical resistivity and water sorptivity results suggested that graphene materials densify and reinforce the composite microstructure

Graphene-based anti-corrosive coating on steel for reinforced concrete infrastructure applications: Challenges and potential

Steel corrosion has been a major perpetual issue of concern for durability and structural integrity of steel and reinforced concrete infrastructure. Polymeric, zinc-galvanic and chromate conversion coatings are commonly applied to protect typical steel materials such as structural steel, reinforcing steel bar (rebar), mild steel and light gauge steel used in infrastructure. Yet, due to physical integrity, long-term performance and environmental concerns, their applications have been limited. In recent years, graphene has garnered considerable attention in the field of anti-corrosive coatings and substantial progress has been achieved in the development of particular graphene-based monolithic (single/few-layer graphene and graphene oxides) as well as laminate and nanocomposite coatings. Despite considerable efforts dedicated towards fundamental research, the laboratory to industry transition of graphene-based anti-corrosive coatings remains challenging. To this end, this report reviews the state-of-the-art on graphene-based coating technology with application to steel surfaces and discusses, both, experimental studies and theoretical aspects. Specifically, this review presents (i) production of different forms of graphene-based materials and the coating process; (ii) corrosion resistance and anti-corrosive coating performance of graphene-coated steel materials, (iii) key potential areas and challenges pertaining to the application of graphene-based coating to structural steel and rebar; and (iv) potential future directions towards corrosion protection and smart coatings

Five recommendations to accelerate sustainable solutions in cement and concrete through partnership

Though the technical knowledge to make cement and concrete more sustainable already exists, implementation of solutions lags behind the rate needed to mitigate climate change and meet the targets set by the Sustainable Development Goals. Whilst most of the focus around the built environment is on embodied carbon, we stress an important but neglected dimension: partnership (SDG17). Effective partnerships can be powerful enablers to accelerate sustainable solutions in cement and concrete, and let such solutions transfer from academia to the market. This can be achieved through knowledge generation, solution implementation, and policy development, among other routes. In this article, we share five recommendations for how partnerships can address neglected research questions and practical needs: 1) reform Science, Technology, Engineering and Mathematics (STEM) education to train “circular citizens”; 2) map out routes by which cementitious materials can contribute to a “localization” agenda; 3) generate open-access maps for the geographical distribution of primary and secondary raw materials; 4) predict the long-term environmental performance of different solutions for low-CO2 cements in different geographical areas; 5) overhaul standards to be technically and regionally fit for purpose. These approaches have the potential to make a unique and substantial contribution towards achieving collective sustainability goals

Taxonomy of uncertainty in environmental life cycle assessment of infrastructure projects

Environmental life cycle assessment (LCA) is increasingly being used to evaluate infrastructure products and to inform their funding, design and construction. As such, recognition of study limitations and consideration of uncertainty are needed; however, most infrastructure LCAs still report deterministic values. Compared to other LCA subfields, infrastructure LCA has developed relatively recently and lags in adopting uncertainty analysis. This paper presents four broad categories of infrastructure LCA uncertainty. These contain 11 drivers focusing on differences between infrastructure and manufactured products. Identified categories and drivers are: application of ISO 14040/14044 standards (functional unit, reference flow, boundaries of analysis); spatiotemporal realities underlying physical construction (geography, local context, manufacturing time); nature of the construction industry (repetition of production, scale, and division of responsibilities); and characteristics of infrastructure projects (agglomeration of other products, and recurring embodied energy). Infrastructure products are typically large, one-off projects with no two being exactly alike in terms of form, function, temporal or spatial context. As a result, strong variability between products is the norm and much of the uncertainty is irreducible. Given the inability to make significant changes to an infrastructure project ex-post and the unique nature of infrastructure, ex-ante analysis is of particular importance. This paper articulates the key drivers of infrastructure specific LCA uncertainty laying the foundation for future refinement of uncertainty consideration for infrastructure. As LCA becomes an increasingly influential tool in decision making for infrastructure, uncertainty analysis must be standard practice, or we risk undermining the fundamental goal of reduced real-world negative environmental impacts