Embodied Carbon Dioxide Emissions Research Articles

Physio-chemical, mechanical and fracture analysis of ultra-high-performance cementitious composite

The aim of this research was to develop cost-effective and environmentally friendly ultra-high-performance concrete (UHPC) using fly ash (FA) and quartz powder (QP) as sustainable cement replacements. The performance of the various constituents was examined and their influence on fresh and hardened properties was investigated in order to determine the optimum trial mix design. A cube compressive strength of 144 MPa was achieved with 20% FA and 10% QP and other ingredients without any special heat treatment. Advanced characterisation studies, such as the heat of hydration and X-ray diffraction analysis, were performed to gain understanding of the performance of FA-blended UHPC. Various fracture properties (fracture toughness, fracture energy, brittleness etc.) were investigated considering geometrically similar notched beam specimens for UHPC mixes with steel fibre contents of 1.5% and 2.5%. The optimum UHPC mix achieved good scores in terms of the strength index and the embodied carbon dioxide emissions index, indicating that the concrete is eco-friendly and sustainable.

Experimental and Analytical Investigations on Shear Performance of Ambient-Cured Reinforced Geopolymer Concrete Beams

Geopolymer concrete (GPC) has emerged as a sustainable alternative to ordinary Portland cement concrete (OPCC) as GPC significantly reduces embodied carbon dioxide emissions. This study compared the shear behavior of reinforced OPCC beams and GPC beams of the same cross-section and compressive strength. The study tested nine beams under three-point bending to evaluate the effects of concrete type and shear span on the shear strength. The results showed that OPCC and GPC beams exhibited relatively similar reduction rates in the shear strength with increasing a/d ratios, while the failure mode shifted from shear in OPCC beams to shear-flexure in GPC beams. The maximum deflection of GPC beams significantly increased with increasing a/d ratios. Moreover, empirical shear strength equations, intended for OPCC beams in various design codes, underestimated the shear strength of GPC beams by about 11.0-26.9% at the a/d ratio of 4.3 but significantly underestimated the shear strengths of GPC beams by 77% at lower a/d ratios of 1.6 and 2.9. Therefore, modifications are proposed to the existing design OPCC shear strength equations to significantly improve the prediction accuracy for the shear strength of GPC beams.

Green development of fly ash geopolymer via casting and pressing Approaches: Strength, Morphology, efflorescence and Ecological Properties

The high liquid content of cast geopolymer not only limits its strength development and durability but also leads to high energy consumption and carbon dioxide (CO2) emissions. Thus, a study of the cast and pressed geopolymer was performed. The geopolymers were cured for 1, 7 and 28 d before testing and characterizations. With the incorporation of pressure compaction, higher bulk density (2158–2227 kg/m3) was recorded for pressed geopolymer in comparison to cast geopolymer (1842–1854 kg/m3). The dense matrix in pressed geopolymer improved the inter-particle contact, increasing the 28 d degree of reaction to 39.7%, higher than that of cast geopolymer (33.0%). This feature was proved by SEM micrographs wherein the pressed geopolymer was well-compacted and denser in microstructure, with less unreacted/partially reacted fly ash and pores. The compressive and flexural strengths of pressed geopolymer reached 114.2 and 29.9 MPa after 28 d, higher than that of cast geopolymer (60.0 and 6.2 MPa, respectively). The strength reduction of pressed geopolymer (31.7%) after the accelerated efflorescence test was lower than that of cast geopolymer (60.2%). The ecological analysis inferred that pressed geopolymer was ecologically superior to the casting method in terms of embodied energy (EE) and embodied carbon dioxide emission (ECO2), in which 50% and 59% of reductions are acquired. Besides, the embodied carbon index (ECI) of pressed geopolymer was about 21% of cast geopolymer.

Sustainability assessment of cement concrete modified with bagasse ash and calcite powder

The continued global expansion in the built environment has resulted in significant demand for cement as a building and construction material. However, carbon dioxide emissions from the cement manufacturing processes contribute significantly to global warming and climate change. This study evaluates the sustainability of cement concrete mixed with bagasse ash (BA) and calcite powder (CP). A binary mixture of BA (5–15%) and CP (5–15%) was used in a partial replacement level of cement using a 25 MPa concrete mix design. Slump was examined while compressive strengths were tested after 7–28 days of water curing. Embodied energy, embodied carbon dioxide emissions, and sustainability index of the mixed concrete were evaluated after 28 days using the carbon and energy inventory. The results showed a decrease in slump as the replacement of bagasse ash and calcite powder in the mixture increased. In addition, the compressive strength of the mixed concrete decreased slightly as the percentage replacement of BA and CP in the mix increased. However, at 15% BA and 15% CP replacement level, the ternary concrete mix attained the compressive strength of 25.53 MPa compared to 29.45 MPa obtained for the control sample after 28 days. In addition, the blended concrete resulted in lower embodied energy, embodied carbon dioxide emissions, and sustainability index than the control concrete, meaning that cement-based concrete modified with BA and CP is more sustainable than Portland cement concrete.

Shared responsibility of carbon emission for international trade based on carbon emission embodied between developing and developed countries.

Traditional Production-Based Accounting (PBA) principle does not consider the embodied carbon emissions in export and import trade. A multiregional input–output (MRIO) model is constructed to estimate the embodied carbon dioxide emissions of 41 countries and regions worldwide, based on the PBA and shared responsibility approach in this paper. The results indicate that the embodied carbon emissions in 2018 in China’s export trade were 1326 million tons higher than that of import trade. China, India, and the USA have a different carbon coefficient in the 35 sectors, but electricity, gas, and water supply sectors are the largest coefficient for them. A reduction in carbon emission coefficient would contribute to a decrease in imports and exports. Through the empirical analysis of the embodied carbon emissions in China’s import and export trade, it can be seen that China is a major producer of carbon emissions, not a consumer country, and has taken more carbon emissions responsibility for the world. The developed countries should take more shared carbon emission responsibility than the PBA. And it is more reasonable and impartial to assign developed and developing countries carbon emissions responsibility in the light of the shared responsibility method.

Who shapes the embodied carbon dioxide emissions of interconnected power grids in China? A seasonal perspective

With the rapid development of interregional power transmission, the redistribution of fossil and renewable energy resources has changed sharply, and its complexity poses a challenge to the evaluation of power carbon emission responsibility. This study constructs an interprovincial power transmission framework to measure the seasonal carbon emissions embodied in regional electricity consumption over the period of 2008–2015 based on quarterly data. Then, a structural decomposition approach was developed to identify the influential factors of carbon emissions embodied in provincial electricity consumption from a seasonal perspective. The results show that the assessment for embodied emissions of power consumption based on different levels of data may vary by as much as 20%, and the carbon emissions and carbon intensity of power consumption exhibit significant seasonal characteristics. Furthermore, it is revealed that the economic scale in the fourth quarter makes the most significant contribution to the emissions increment, especially in underdeveloped provinces, while the change in energy efficiency of power generation reduces more carbon emissions in the first and second quarters. In addition, the impact of the power transmission scale is more significant in the third and fourth quarters, and it has been close to or even more than the impact of traditional factors in some quarters. Finally, the impact of economic scale, power generation energy intensity, power generation mix and electricity utilization efficiency on the emissions of regional power grids shows a relatively stable increasing trend, but this trend of directional stability is not reflected in the effect of the power transmission structure and transmission scale. This study contributes to the identification of the impact of the power transmission structure and transmission scale. Moreover, this study highlights the importance of considering seasonal characteristics when estimating the carbon emissions of power consumption and formulating specific emission reduction policies. Additionally, it provides a more accurate evaluation of carbon emissions and proposes several prominent recommendations for policy makers.

Robustness of self-compacting concrete incorporating bone china ceramic waste powder along with granite cutting waste for sustainable development

Keeping sustainability at the centre of this work, two solid waste materials have been selected for this study. First is bone china ceramic waste powder (BCCWP) obtained from broken or distorted bone china ceramic waste products, and the second is granite cutting waste (GCW) from the granite cutting and shaping industry. The present study aims at assessing fresh state, mechanical and durability characteristics of the SCC mixes incorporating BCCWP and GCW as cement and fine aggregate replacement, respectively. In a preliminary state, the raw BCCWP was evaluated for various pozzolanic activity tests such as the Frattini test, strength activity index and lime saturation test. SCC mixes were tested for compressive strength, splitting tensile strength, corrosion and chloride resistance tests. SCC mixtures were also tested at elevated temperatures by conducting thermogravimetric analysis (TGA) and differential thermal analysis (DTA) tests. Outcomes of fresh properties were found in the satisfactory limit as per EFNARC standard, except the SCC mix prepared with 30% BCCWP and 40% GCW. SCC mix with 10% BCCWP and 30% GCW showed the maximum strength properties. Moreover, statistical analysis using ANOVA was carried out to find the effectiveness of BCCWP and GCW parameters on various hardened state characteristics. From ecological and economic analysis, lesser embodied energy and embodied carbon dioxide emission, as well as cost reduction, was observed for SCC mixes containing BCCWP and GCW.

Embodied carbon dioxide emissions to provide high access levels to basic infrastructure around the world

Access to infrastructure services is essential to meet human basic needs. However, infrastructure construction requires carbon-intensive materials, first and foremost cement and steel. In this paper, I assess if high level of access to 5 basic infrastructure services – electricity, water, shelter, sanitation and transportation – can be provided at the global scale in 2030 and until 2050 without compromising climate mitigation targets. Following historical patterns, I first quantify the cement and steel requirements in each country associated with providing high access levels. I then estimate the production-based carbon dioxide emissions related to manufacturing the cement and steel needs. To do so, I model influencing factors such as national production technologies mix, trade structure and mitigation actions in the cement and steel industries. Global cumulative material demand (central values) to reach high access level in 2030 is the lowest for water with 8 Gt of cement and 1 Gt of steel and the highest for transportation with 50 Gt of cement and 6 Gt of steel. Most of the cement and steel demand is concentrated in Asia, Middle-East and Africa. I show for all infrastructure services that achieving high access level in 2030 and until 2050 induces cumulative carbon dioxide emissions well below the carbon budgets related to Paris Agreement targets, with central values under baseline scenario from 10 to 53 Gt CO2 depending on the infrastructure service. However, I find providing high sanitation and transportation access in Middle-East and Africa conflicts with existing low-carbon pathways. This calls for on one side implementing material efficiency and substitution towards less carbon-intensive construction materials, and on the other side strengthening mitigation efforts in wealthiest countries to leave enough ’carbon space’ for basic infrastructure development in emerging countries.

Reducing embodied carbon dioxide of structural concrete with lightweight aggregate

An investigation was done into the development of lightweight-aggregate concrete mixes with lower embodied carbon dioxide emissions suitable for structural applications. Production requires the replacement of normal-weight coarse aggregate with a lightweight aggregate. Lytag was considered, which is a good-quality lightweight aggregate manufactured from fly ash. Lightweight-aggregate concrete for structural applications usually contains a high CEM I content owing to the requirements for workability, pumpability and strength. Consequently, its embodied carbon dioxide emissions are generally higher than that of normal-weight concrete. Mixes of LC30/33 class were developed containing up to 60% ground granulated blast-furnace slag, as well as limestone powder, and their fresh and mechanical properties were assessed experimentally. It was found that the embodied carbon dioxide of the investigated mix could be reduced by up to 40% when compared with that of neat CEM I lightweight-aggregate mixes containing Lytag aggregates and to 20% when compared with that of a mix that would be generally used in current practice in the UK containing 40% slag. It was also possible to reduce the CEM I content in the investigated mixes by approximately 40% compared with what would have been normally used.

Regulating embodied carbon dioxide emissions in construction – how to get it right

National regulation of embodied greenhouse gas emissions in construction is inevitable given the world’s growing commitment to achieving net zero. Toby Maclean of UK environmental structural engineers firm Allt says this needs to go beyond simple life-cycle assessments to be effective.

EKC and carbon footprint of cross-border waste transfer: Evidence from 134 countries

Many developing countries, such as China, Malaysia, Vietnam, India, etc., choose to prohibit waste import. Does this mean the inflection point of the Environmental Kuznets Curve (EKC) in these countries has arrived? In this paper, we first calculate the carbon dioxide emission and energy consumption in major resource-based wastes of 134 countries using the Life Cycle Assessment (LCA) method. Second, we test whether the relationship between CO2 (energy consumption) and GDP per capita confirms an EKC's inverted U-shaped curve. Empirical results show that: (1) the relationship between embodied CO2 emissions (energy consumption) of imported wastes and GDP per capita of a country confirms EKC in various robustness checks, including using an alternative, dependent variable and using sub-sample data. (2) The EKC's inflection point on the average embodied carbon dioxide emissions of imported wastes is 36623.88 USD (37181.3 USD for energy). (3) EKC appears in 68 countries out of 134 countries. Most of these 68 countries have crossed the turning point. This research is novel in describing the EKC of waste trade's carbon footprint using the LCA model. This is the first research that provides empirical evidence to the “Waste Haven Hypothesis”. This result empirically explains the evolution of the global waste trade network. That is, waste first transfers from the “North” to the “South” (from US to Europe, and from Europe to Japan and Korea), and then it moves again from the “South” to the “South” (from China to other Asian countries). It reflects the evolution of global pollution haven transfer in the pollution-intensitive sector. Previous research failed to do it because the indicators used for waste transfer limits to trade value (weight) that can not correctly measure waste transfer's environmental pollution. An advantage of using LCA is that it better estimates the pollution generated by the recycling sectors.

Development of an eco-friendly ultra-high performance concrete based on waste basalt powder for Sichuan-Tibet Railway

Generally, tunnel waste is stacked in the slag field nearby for landfilling, which is harmful to sustainable development. The broken rocks and rock powder among the tunnel waste can be recycled to produce machine-made sand, producing many by-products calling rock powder. Based on the practical project, three types of waste basalt powder (BP), from tunnel excavation waste and by-products (rock powder) of machine-made sand producing from tunnel excavation waste in Sichuan-Tibet railway construction sites, was used to prepare an eco-friendly UHPC. The BP is used to replace the cement and is included in the design UHPC based on Modified Andreasen &Andersen particle packing model (MAA). Moreover, the chemical and physical behaviors and ecological evaluation of the designed UHPC and UHPC pasted were discussed. The results showed that when BP (Specific surface area 4.6582 m2/g) replaces up to 15%, the highest compressive strength of designed UHPC (220 MPa) was obtained. Compared with quartz powder, the pozzolanic activity of BP was generally low and increased with the increase of reaction temperature. However, the presence of BP and its fineness in UHPC pastes increased the values of the total autogenous shrinkage and decreased the total heat release at an early age of designed UHPC pastes, this effect is more pronounced with temperature increasing. Based on a quartering method with embodied carbon dioxide emissions and the compressive strength, UHPC with waste BP reduced embodied carbon dioxide and possessed higher compressive strength and lower environmental impact than the control samples of UHPC.

A new circular economy framework for construction projects

Circular economy (CE) is a holistic, viable solution to the ‘take-make-dispose of’ system of the linear model that enhances economic growth without threatening environmental and social value. Its principles are based on product optimisation, waste elimination and regeneration of natural systems. In this paper, a pilot study evaluates the feasibility of implementing CE in construction projects, followed by the development of a new framework with strategies for altering current construction activities for greater circularity. To demonstrate the benefits of implementing a CE model, a critical assessment of its impacts in the industry was made that considers costing, environmental impacts and legislative action. A new comprehensive CE framework was developed that details a set of indicators, action plans and resources allocated to assess the performance of the strategy implementation, specifically designed for building cycles. To address the challenge of monitoring progress on the transition towards circularity, quantitative tools using a life-cycle approach were developed in this study including an embodied carbon dioxide emission calculator and databases for waste and circularity indexing of common construction materials. The framework, accompanied by these tools, was applied to a construction case study to verify its feasibility in combining scientific and policymaking guidelines. Good practice recommendations were also offered, based on the qualitative research undertaken, to enrich the study further.

Analysis of the embodied carbon dioxide in the building sector: A case of China

Many studies and standards in the building sector have often focused on the mitigation of operational carbon with little consideration of the embodied carbon from buildings. Although there exist some studies on embodied carbon, they are analyzed based on the project level or case studies, and few studies explore the embodied carbon dioxide in the building sector. To achieve the peaking of China’s carbon emission by 2030, a process-based approach and a disaggregated input-output model in this study were adopted to estimate the annual embodied carbon dioxide from the China’s building sector, respectively. The results of embodied carbon dioxide emissions were 1421.70 Mt and 1599.62 Mt in the building sector in 2015, respectively. In terms of building types, the embodied carbon dioxide in the residential building sector is about 1.5–2.2 times that of the non-residential building sector. In addition, it is indicated that, unlike the small magnitude of embodied carbon compared with operational carbon in life cycle of buildings, the annual embodied carbon dioxide accounts for roughly one-half in the total carbon dioxide emissions in the building sector in 2015. The study provides an understanding of the embodied carbon and its composition of different industrial materials that would be useful for China to develop its future CO2 emission control plan.

Sustainable use of rice husk ash in cement-based materials: Environmental evaluation and performance improvement

The feasibility of using agricultural waste of rice husk to prepare highly reactive rice husk ash for sustainable cement-based material was explored through five sets of procedures: optimization of rice husk ash with an improved combustion technique, pozzolanic activity evaluation of the prepared rice husk ash, strength development of mortar with rice husk ash, sulfate attack experiment to investigate the potential durability, and environmental evaluation of rice husk ash utilization. From the results, the optimum rice husk ash using improved combustion technique had high pozzolanic activity, it presented the highest lime-ash compressive strength, a violent pozzolanic reaction heat flow as well as rapid Ca(OH)2 consumption ability among different mineral additives. Compressive strengths of mortars have been enhanced with the increase of rice husk ash contents. The results of sulfate attack indicated that paste with 15% rice husk ash improved sulfate resistance by stabilization of C–S–H and the refinement of pore structure. Sustainability analysis including embodied carbon dioxide emission and energy consumption confirmed the environmental friendliness of rice husk ash utilization. This study verified the feasibility of highly reactive rice husk ash from agricultural waste and the potential utilization of it as sustainable mineral admixture in cement-based materials.

Durability studies on ferrochrome slag as coarse aggregate in sustainable alkali activated slag/fly ash based concretes

Utilization of industrial byproducts in concrete reduces carbon footprint, associated with production of ordinary Portland cement (OPC), and also indirectly controls rapid depletion of natural resources in the form of natural coarse aggregate (NCA). This study reports the durability effect of alkali activated slag/fly ash concretes (AASFC) with ferrochrome slag (FCS) as coarse aggregate. Different AASFC mixtures were prepared with two control factors i.e., fly ash (FA) content (0, 25, and 50% by weight as a replacement to Ground granulated blast furnace slag (GGBS)), and FCS content (0, 50, and 100% by volume as a replacement to NCA). Total nine mixtures were examined for three different durability tests i.e., volume of permeable voids (VPV), acid resistant test, and sulphate resistant test. Further, embodied energy (EE), and Embodied carbon dioxide emission (ECO2e) were also utilized to optimize the AASFC mixtures by grey relational analysis (GRA). Analysis of variance (ANOVA) is used as a statistical tool to investigate the effect of FA, and FCS content on the overall durability and ecological performance of AASFC mixtures. Results show that, addition of FA increases the durability performance (in % age), and addition of FCS decreases the durability performance (in % age) in AASFC mixtures. AASFC mixture with composition of 50% GGBS, 50% FA, and 100% FCS is considered as most suitable mixture.

Stochastic Analysis of Embodied Carbon Dioxide Emissions Considering Variability of Construction Sites

The current method of estimating CO2 emissions during the construction phase does not consider the variability that can occur in actual work. Therefore, this study aims at probabilistic CO2 estimation dealing with the statistical characteristics in activity data of building construction work, focused on concrete pouring work and based on field data. The probabilistically estimated CO2 emissions have some differences from CO2 emissions measured by current deterministic methods. The results revealed that the minimum difference was 11.4%, and the maximum difference was 132.7%. This study also used Monte Carlo simulations to derive information on a probability model of CO2 emissions. Results of the analysis revealed that there is a risk of underestimating emissions because the amount of emissions was estimated at a level that exceeds the 95% confidence interval of the simulation results. In addition, the probability that CO2 emissions using the measured activities data were less than the estimated CO2 emissions using the bill of quantity was 73.2% in the probability distribution model.

Comparison of Carbon Dioxide Emissions of the Ordinary Reinforced Concrete Slab and the Voided Slab System During the Construction Phase: A Case Study of a Residential Building in South Korea

The construction industry not only consumes a lot of energy but also emits large volumes of carbon dioxide. Most countries have established target reduction values of the carbon dioxide emissions to alleviate environmental burdens and promote sustainable development. The reduction in carbon dioxide emissions in the construction industry has been taking place in various ways as buildings produce large quantities of the carbon dioxide over their construction life cycle. The aim of this study is to assess and compare the carbon dioxide emissions of an ordinary reinforced concrete slab and the voided slab system applied to a case study involving a commercial-residential complex building in South Korea. Process-based life-cycle assessment (LCA) is adopted to compute the carbon dioxide emissions during the construction phase, which includes all processes from material production to the end of construction. The results indicate that the total CO2 emissions are 257,230 and 218,800 kg CO2 for the ordinary reinforced concrete slab and the voided slab system, respectively. The highest contributor to CO2 reduction is the embodied carbon dioxide emissions of the building materials, which accounts for 34,966 kg CO2. The second highest contributor is the transportation of the building materials, accounting for 3417 kg CO2.

Briefing: Embodied carbon dioxide assessment in buildings: guidance and gaps

The construction industry, through its activities and supply chains as well as the operation of the assets that it creates, is a major contributor to global greenhouse gas emissions. Embodied carbon dioxide emissions associated with the construction of new assets constitute a growing share of whole-life emissions across all project types and make up nearly a quarter of all annual emissions from the UK built environment. Yet these embodied emissions are still rarely assessed in practice, owing to the perceived difficulty and lack of supporting guidance for practitioners conducting an assessment. This briefing paper retraces recent advances in the field of embodied carbon dioxide assessment and highlights existing and forthcoming practical guidance that could support more widespread assessment. The paper constitutes a where-to rather than a how-to, directing assessors towards appropriate resources, of which there are many. Although the paper does highlight some remaining gaps in the field and identifies corresponding research priorities, recent additions to the body of guidance are generally sufficient to support more widespread assessment. Now, the industry must demonstrate its commitment to tackling climate change by using this guidance to drive deeper carbon dioxide reduction.

Embodied carbon minimisation of retrofit solutions for walls

Energy saving in a building is mainly a function of the performance of building insulation and equipment. However, initial embodied carbon dioxide emissions increase as the operational energy decreases, so selecting the best energy retrofit solution should take this into account, together with building-specific needs. Currently there is no regulation of embodied carbon dioxide emissions in the European Union construction industry. The effectiveness of a low-carbon dioxide emission project should be judged by its energy in use together with the building-specific needs, not the total of the energy expended in its retrofit. Three different buildings with different occupant behaviours were studied, and five different retrofit solutions for the external rendering of walls were tested. The objective was to establish a relationship between the initial embodied carbon dioxide of a retrofit solution and the real operational energy consumed. A probabilistic approach was developed to predict the number of years that each solution takes to reduce the embodied carbon dioxide to 0·15 kg/kWh of operational energy in each building. The use of cork in mortars represents the most positive measure to reduce embodied carbon dioxide and increase energy efficiency.