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SCM's potential to lower Australia's greenhouse gas emissions profile
Abstract
Under the Kyoto Accounting rules, Australia's National Greenhouse Gas Inventory Report emissions for 2002 was 550.1 Mt carbon dioxide equivalent (CO 2 -e) being a net increase of 1.3% on the 1990 level. This increase is largely attributed to the stationary energy, transport and industrial process sectors, offset with significant reductions from reduced land clearing. For the construction sector additional mitigation strategies could be employed to further reduce Australia's net CO 2 -e emissions. For example through increased use of mineral resources like coal combustion products such as; fly ash, iron blast furnace slag and amorphous silica, or commonly referred to as supplementary cementitious materials (SCM's), used with Portland cement in the manufacture of concrete. For Australia, the manufacture and delivery of one tonne of cement results in the emission of approximately 0.82 tonne of CO 2 -e or 6.5 Mt of CO 2 -e emitted for total cement sales in 2002. Using data collected from companies processing fly ash and iron blast furnace slag, life cycle analyses were conducted to demonstrate the reduced embodied energy and resultant CO 2 -e signature for one cubic meter of concrete containing various combinations of fly ash and iron blast furnace slag. From the resultant data and analysis a simple CO 2 -e estimator has been developed to assist architects, designers and consulting engineers to specify eco-friendly structures. For the construction of a domestic dwelling (four bedroom home) using approximately 130 cubic meters (m3) of 25 MPa concrete containing binder ratios of 35% Portland cement and 65% ground granulated blast furnace slag cement, the total savings in CO 2 -e emissions was 17.03 tonnes, or equivalent to emissions from a four-cylinder car for 5.68 years. The paper will briefly discuss Australia's current National Greenhouse Gas Inventory Report in the context of how increased use of SCM's in the construction sector can further lower greenhouse gas emissions, whilst still delivering improved durability performance.
... However, the capture, milling and grinding, drying and transportation of FA causes energy consumption. Based on the literature, the reported values of CO 2 -eq/kg for FA was in the range of 0.007 to 0.027 kg (Heidrich et al., 2005;Phetchuay et al., 2016). Moreover, as RM is a waste by-product, and there were not any consuming energy activities for it in this study, the CO 2 -eq of RM is related to its transportation. ...
... Coarse aggregates 0.0408 (Turner & Collins, 2013) k gC O 2 -eq/kg 0.019 $/kg material Fine aggregates 0.0139 (Turner & Collins, 2013) k gC O 2 -eq/kg 0.012 $/kg material Fly ash (F-type) 0.027 (Heidrich et al., 2005) k gC O 2 -eq/kg 0.045 $/kg material Red mud 0.00518 (Heidrich et al., 2005) k gC O 2 -eq/kg 0 $/kg material Crumb rubber -0.103 (Farina et al., 2017) k gC O 2 -eq/kg 0.05 $/kg material Chipped rubber 0.0195 (Farina et al., 2017) k gC O 2 -eq/kg 0.031 $/kg material Sodium hydroxide 1.915 (Duxson et al., 2007) k gC O 2 -eq/kg 0.2 $/kg material Sodium silicate 1.514 (Duxson et al., 2007) k gC O 2 -eq/kg 0.4 $/kg material RM30FGC-CR90 with the highest amounts of RM and chipped rubber were determined to be the most environmentally friendly and economical specimen among the others, but its mechanical properties were the lowest. Therefore, the necessity of multicriteria optimization was sensed among these conflicting responses to establish a trade-off. ...
... Coarse aggregates 0.0408 (Turner & Collins, 2013) k gC O 2 -eq/kg 0.019 $/kg material Fine aggregates 0.0139 (Turner & Collins, 2013) k gC O 2 -eq/kg 0.012 $/kg material Fly ash (F-type) 0.027 (Heidrich et al., 2005) k gC O 2 -eq/kg 0.045 $/kg material Red mud 0.00518 (Heidrich et al., 2005) k gC O 2 -eq/kg 0 $/kg material Crumb rubber -0.103 (Farina et al., 2017) k gC O 2 -eq/kg 0.05 $/kg material Chipped rubber 0.0195 (Farina et al., 2017) k gC O 2 -eq/kg 0.031 $/kg material Sodium hydroxide 1.915 (Duxson et al., 2007) k gC O 2 -eq/kg 0.2 $/kg material Sodium silicate 1.514 (Duxson et al., 2007) k gC O 2 -eq/kg 0.4 $/kg material RM30FGC-CR90 with the highest amounts of RM and chipped rubber were determined to be the most environmentally friendly and economical specimen among the others, but its mechanical properties were the lowest. Therefore, the necessity of multicriteria optimization was sensed among these conflicting responses to establish a trade-off. ...
... (1) Where is the dosage of raw materials (kg/m 3 ), i refers to cement, fly ash, fine aggregate, coarse aggregate, water and superplasticiser, and is the emission factor of different raw material (kg CO 2 -e/kg), they are 0.92 [5] , 0.027 [6] , 0.0408 [7] , 0.0139 [5] , 0.000213 [8] and 0.72 [9] , respectively. ...
... By applying Bo Weidema's system expansion methodology, the GGBFS (Product B) is assigned the intermediate processing impacts (grinding of GBFS into GGBFS) and credited with the avoidance of the waste treatment (landfill). Inventory data for the grinding of GGBFS was adopted from (Heidrich et al., 2005). In this article, the emissions due to milling and drying of 1 tonne of slag were 0.064 tonne (electricity) and 0.049 tonne (natural gas), respectively. ...
... CCPs can complement the use of local quarried materials in large-scale civil applications. The use of CCPs has environmental benefits in allowing the conservation of depleting natural resources (Heidrich, Hinczak et al. 2005). ...
This paper discusses how a supply chain approach to turning under utilised coal combustion product resources into solutions is resulting in new networks, new collaborations and new products. This paper discusses how the industry is exploring new product options using a supply chain approach with participants. The Sustainability Capacity Building Program has elements of both innovation and organisational change because it engages corporations in thinking about sustainability issues, their culture, their business environment, their desired future and new product opportunities. Depending on the position of the organisation in the coal combustion product (CCPs) supply chain, there are different imperatives, trade-offs and barriers. To build understanding across the supply chain a staged approach was undertaken. Stage one (1) establishes mutual understanding about their different business models and operational imperatives. Stage two (2) was to learn about the production processes, constraints and opportunities. Stage three (3) focused on the developing strategic interventions to fill the knowledge gaps with the ultimate objective of increasing the utilisation of CCPs in products. Documenting lessons learned and implementing organisational wide changes underpinned all stages. This paper discusses the staged approach using survey's, workshops and webinars to establish new products and systemic learning with industry stakeholders in the CCPs supply chain.
... Fly ash is a waste by-product arising from coal-burning power stations and therefore some studies have considered the raw material to contribute zero CO 2 -e [14]. However energy expenditure occurs during fly ash capture, milling and grinding, drying, and transport [29] and an emission factor of 0.027 kg CO 2 -e/kg for fly ash has been calculated. Compared with OPC and the alkali activators, fly ash has a significantly lower emission factor. ...
... Cement manufacture is a large source of CO 2 emissions. The substitution of 1 ton of fly ash for Portland cement reduces CO 2 emissions for the overall process of concrete production by about 1 ton (Heidrich et al., 2005). ...
Thermal power plants (TPPs) that burn fossil fuels emit several pollutants linked to the environmental problems of acid rain, urban ozone, and the possibility of global climate change. As coal is burned in a power plant, its noncombustible mineral content is partitioned into bottom ash, which remains in the furnace, and fly ash, which rises with flue gases. Two other by-products of coal combustion air-pollution control technologies are flue gas desulfurization (FGD) wastes and fluidized-bed combustion (FBC) wastes. This paper analyzed and summarized the generation, characteristics and application of TPP solid wastes and discussed the potential effects of such solid wastes on the environment. On this basis, a review of a number of methods for recovery of metals from TPP solid wastes was made. They usually contain a quantity of valuable metals and they are actually a secondary resource of metals. By applying mineral processing technologies and hydrometallurgical and biohydrometallurgical processes, it is possible to recover metals such as Al, Ga, Ge, Ca, Cd, Fe, Hg, Mg, Na, Ni, Pb, Ra, Th, V, Zn, etc., from TPP solid wastes. Recovery of metals from such wastes and its utilization are important not only for saving metal resources, but also for protecting the environment.
A green building certification system (GBCS) is essential for sustainable city development. However, the building's embodied energy (EE) and thermal insulation have often been overlooked in GBCSs. The correlation of thermal insulation envelopes to EE and operational energy (OE) has also yet to be extensively investigated. This study adopts life cycle energy assessment methodology to evaluate the EE and OE of non-green and green-rated non-residential buildings with hotspot analysis and analyse the trade-offs between EE production and OE saving for five types of insulation envelopes. Taking Malaysia as a reference, results show EE holds 16–19% of total energy in non-green and green-rated non-residential buildings; hence EE should not be neglected in GBCS. The material consumption phase incurs half a quarter of the total EE, indicating that major recycled and low-embodied building materials (e.g., recycled steel and green cement) should be rewarded with higher points in GBCS. Insulated building envelopes save 84–87% of cooling demand than non-insulated walls, with cellulose fibre insulators consuming the least EE. It is hoped that this study can provide evidence-based outcomes to policymakers when formulating the proportion of EE and OE, and integrating insulation envelopes in GBCS to enhance energy savings further.
Rammed earth (RE) is an eco-friendly building material and has been capturing special attention among researchers. Many of the recently studied RE additives are extremely resource- and energy-consuming. On the other hand, the usage of fly ash (FA), which is a sustainable replacement for cement, has been scarcely investigated in RE construction. In this paper, an experimental investigation was performed on the physical and mechanical properties of RE materials stabilized with the combination of cement and alkali-activated FA. This scrutiny consists of density measurements, pulse velocity tests, unconfined compression tests, and direct shear tests. Additionally, the carbon dioxide emission and unit cost of each mix were estimated using the available literature. Finally, a multi-objective optimization was performed using the response surface method to determine the optimum mixture. The optimization goals were the maximization of strength parameters in addition to minimization of cost, density, and carbon footprint. Based on the optimization criteria, it was found that 0.7% of cement and 6.5% of FA was the suitable stabilizer choice for RE contractors.
Soil-cement-bentonite (SCB) vertical cutoff walls are commonly used to control the flow of contaminated groundwater at polluted sites. However, conventional backfill consisting of ordinary portland cement (OPC) is associated with a relatively high CO 2 footprint. Potential chemical interactions between OPC and bentonite could also undermine the long-term durability of SCB materials. This paper proposes an innovative backfill material for cutoff walls that is composed of MgO-activated ground granulated blast furnace slag (GGBS), bentonite, and soil. The OPC-soil, OPC-bentonite-soil, and OPC-GGBS-bentonite-soil backfill materials are also tested for comparison purposes. The workability of fresh backfills and unconfined compressive strength of aged backfills are investigated. The hydraulic conductivities of aged backfills permeated with tap water, Na 2 SO 4 , and Pb-Zn solutions are assessed. The unconfined compressive strength and hydraulic conductivity of the proposed backfill permeated with tap water are in the range of 230-520 kPa and 1.1 × 10 −10 to 6.3 × 10 −10 m=s after 90 days of curing, respectively, depending on the mix composition. The hydraulic conductivity of the proposed MgO-GGBS-bentonite-soil backfill permeated with sodium sulfate (Na 2 SO 4) or lead-zinc (Pb-Zn) solution is well below the commonly used limit, while the OPC-bentonite-soil backfill shows a significant loss in impermeability. Environmental and economic analyses indicate that, compared with conventional backfill made from OPC-bentonite-soil mixtures, the proposed backfill reduces CO 2 emissions by approximately 84.7%-85.1% and costs by 15.3%-16.9%. The environmental and economic advantages will promote the use of MgO-activated GGBS-bentonite mixtures in cutoff walls and lead to their increased application in land remediation projects.
An innovative cutoff wall backfill consisting of reactive MgO, ground granulated blast furnace slag (GGBS), bentonite and local clayey sand (MSB) was developed recently for land remediation applications. This paper investigates the engineering characteristics (e.g. strength and permeability) and reaction mechanisms of the MSB backfills with various MgO-activated GGBS (i.e., the binder) and bentonite contents. A series of analytical techniques are employed to identify the hydration products in this complex system. The engineering properties are tested via the unconfined compressive strength (UCS) test and flexible-wall permeation test. Results show that UCS and dry density decrease with increasing bentonite content, while the opposite trends are observed when increasing the binder content. The UCS values increase with curing time and become plateaued after ∼90 days. Meanwhile, the hydraulic conductivity (k) decreases distinctly with the increase of the binder content and bentonite content. All backfills reach UCS of >100 kPa UCS and k <10−8 m/s at 28 days while curing for 90 days leads to increase of UCS by >1.5 times and reduction of k by nearly one order of magnitude. The major hydration products of MSB backfills are identified as hydrotalcite-like phases (Ht), calcium silicate hydrates (C-S-H), monosulfate (AFm) and portlandite (CH). The hydration products, binding adjacent soil particles, filling pores, together with the swelling of bentonite, contribute to the mechanical performance and impermeability of the backfills.
Soil–cement–bentonite (SCB) vertical cutoff walls are commonly used to control the flow of contaminated groundwater at polluted
sites. However, conventional backfill consisting of ordinary portland cement (OPC) is associated with a relatively high CO2 footprint.
Potential chemical interactions between OPC and bentonite could also undermine the long-term durability of SCB materials. This paper
proposes an innovative backfill material for cutoff walls that is composed of MgO-activated ground granulated blast furnace slag (GGBS), bentonite, and soil. The OPC–soil, OPC–bentonite–soil, and OPC–GGBS–bentonite–soil backfill materials are also tested for comparison purposes. The workability of fresh backfills and unconfined compressive strength of aged backfills are investigated. The hydraulic conductivities of aged backfills permeated with tap water, Na2SO4, and Pb–Zn solutions are assessed. The unconfined compressive strength and hydraulic conductivity of the proposed backfill permeated with tap water are in the range of 230–520 kPa and 1.1 × 10−10 to 6.3 × 10−10 m=s after 90 days of curing, respectively, depending on the mix composition. The hydraulic conductivity of the proposed MgO–GGBS–bentonite–soil backfill permeated with sodium sulfate (Na2SO4) or lead–zinc (Pb–Zn) solution is well below the commonly used limit, while the OPC–bentonite–soil backfill shows a significant loss in impermeability. Environmental and economic analyses indicate that, compared with conventional backfill made from OPC–bentonite–soil mixtures, the proposed backfill reduces CO2 emissions by approximately 84.7%–85.1% and costs by 15.3%–16.9%. The environmental and economic advantages will promote the use of MgO-activated GGBS–bentonite mixtures in cutoff walls and lead to their increased application in land remediation projects.
This chapter addresses potential alternatives for base raw materials as well as potential solutions for sustainability in mass concrete. Issues like material selection and environment, material properties and mix design, durability, carbon footprint and life cycle analysis (LCA) of mass concretes are reviewed. The focus is put on recycling. Besides the use of conventional SCMs, non-conventional biomass pozzolans, based on combustion of renewable source of energy, like woody ashes, sugarcane bagasse ash and rice husk ash are covered. The synergic use of several mineral SCMs as a partial substituent of Portland cement is addressed. Furthermore, reuse of aggregates from construction–demolition waste as well as natural fiber alternatives to steel and synthetic reinforcements is discussed in detail. Materials selections and the consequence of it on the properties that affect the mix design and material properties specifically related to durability are summarized. An introduction on life cycle assessment (LCA) is given with its pros and cons, followed by its review on different mass concrete mixtures, separately addressing LCA of binders, aggregates, concretes and reinforced concrete structures with placement technologies. Limitations and further research directions are highlighted.
The production of one tonne of Portland cement requires 1.5 tonnes of raw material. The production of Portland cement is highly energy intensive, consuming 4 to 7 MJ of fossil fuel energy per kg, and releases approximately one tonne of carbon dioxide for manufacture of each tonne of Portland cement. The production of cement contributes 5% of the global greenhouse gas emissions.Utilisation of unused industrial by-products such as slag, which otherwise would contribute to land pollution, as Portland cement substitute in concrete, results in less energy for the manufacture of cement while also reducing the emissions arising from the burning of fossil fuels. The paper discusses the greenhouse gas emission reductions which can be achieved by the use of slag as a partial replacement of Portland cement (blended cements) and as a full replacement of Portland cement by the use of alkali activated slag concrete.
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