Low Carbon Building Materials Research Articles

Strategic Development for a Sustainable Future: Kau Yi Chau Artificial Island Project

The Kau Yi Chau Artificial Island (KYCAI) project is a landmark initiative aimed at addressing Hong Kong's critical land shortage while enhancing its global competitiveness and fostering sustainable development. Situated between Hong Kong Island, Kowloon, and Lantau Island, the project incorporates innovative strategies to balance environmental, social, and economic considerations. Environmental concerns like biodiversity preservation and carbon footprint reduction are tackled through low-carbon building materials, renewable energy, and sustainable transportation. Social justice is promoted by equitable stakeholder engagement, employment opportunities, and fair access to resources. Leadership styles, including transformational and collaborative models, are key to achieving these sustainability goals through effective stakeholder mobilization. The project stands as a testament to strategic planning and collaborative efforts in sustainable urban development, offering valuable insights into balancing environmental, social, and economic goals.

Mechanical properties of geopolymer recycled concrete infilled steel tubes with three sectional types

The steel tubes with geopolymer recycled concrete (GRC) infill are actively seeking environmentally friendly and low-carbon building materials as alternatives in the process of promoting sustainable development, maximizing the use of waste materials and resources, and reducing consumption of natural resources and environmental pollution. In this paper, three types of steel tube specimens with GRC infill were proposed, i.e., the geopolymer recycled concrete-filled steel tube (GRCFST), geopolymer recycled concrete-filled double skin steel tube (GRCFDST), and geopolymer recycled concrete-filled double section steel tubes (GRCFDSST). These GRC-steel tube structures were tested under axial compressive loading, and the influence of some crucial factors on bearing capacity, ductility and strain distribution of specimens was considered, such as the slag content, and the types of steel tube section and the replacement rate of recycled aggregate. The experimental results show that the steel tube can provide effective confinement for geopolymer recycled concrete and thus compensate for the adverse effect induced by recycled aggregate. The slag content has less effect on the bearing capacities of the GRCFDSST specimen compared with the GRCFST and GRCFDST specimens due to the stronger confinement effect of the former. The ductility of GRCFDSST specimens is better than the other steel tube specimens under the same parameter conditions. This study, building on existing literature, provides new insights and design recommendations for the mechanical performance of concrete-filled steel tube structures by using geopolymer recycled concrete as a filling material.

Synthesis of rice husk ash based alkaline activators for geopolymer binder systems: A review

At present, geopolymer binders have been considered to be one of the most promising low-carbon building materials. Apart from low carbon emissions, the production of geopolymer materials also helps in mitigating several industrial solid waste management problems. The geopolymer binder can be produced using any aluminosilicate waste material followed by mixing with an alkaline activator. However, the major limitation associated with geopolymers is their production cost which is slightly higher than traditional cement-based binders. Out of all the ingredients, sodium silicate is found to be the most expensive and least environment friendly material. Several researchers have therefore utilized many silica-rich waste products such as rice husk ash (RHA) based silicate solution as a low-cost alternative to commercial sodium silicate solution. In this regard, this paper provides an in-depth review of the past literature to understand the properties of geopolymer binders produced using RHA-derived alkaline activator. The production process, and the factors affecting dissolution of RHA have been elaborated. Further, the properties such as compressive strength, and microstructure have been detailed. Lastly, the sustainability and lifecycle assessment of geopolymers synthesized using RHA-based sodium silicate solution are presented. The information provided in this study shall encourage the scientific community to adopt RHA-based sodium silicate as a cost-effective, and environment friendly activator to produce geopolymers.

Self-healing analysis of steel slag asphalt mixture under microwave heating through laboratory fatigue-healing test and microscopic characterization method

Steel slag is an eco-friendly low-carbon building material that has been widely used for pavement construction in recent years. In this study, the steel slag aggregate (SSA) is used to replace a part of the basalt aggregate in the porous asphalt mixture to improve its microwave absorption ability. Microwave heating promotes the self-healing capability of steel-slag asphalt mixture. We designed and conducted 16 groups of fatigue-healing tests based on an orthogonal experimental design to analyze the influence of various factors, including the degree of damage, healing temperature, and rest time, on the self-healing ability of the steel slag asphalt mixture. The ratio of the number of cyclic loads after healing (N1) to the number of cyclic loads before healing (N0) is defined as the healing index. The results of the range analysis demonstrate that the healing temperature presents the greatest impact on the healing rate of fatigue damage, followed by the degree of fatigue damage; the rest time has the least impact. The fatigue damage healing rate gradually decreases with the increase in the degree of damage. It first increases and then decreases with the increase in the healing temperature. It increases with the rest time. The optimal healing state of the steel slag porous asphalt mixture involves heating to 80℃ with 60 % degree of damage followed by resting for 8 hours. CT scanning technology is used to observe the crack distribution before and after healing. The CT images and a 3D reconstruction of the asphalt mixture demonstrate that obvious healing of cracks can be observed after microwave heating, and microwave heating does not significantly affect the porosity of the asphalt mixture. The nano-indentation indicates that the Young’s modulus and hardness of the asphalt mortar in the cracking area increased by 16.8 % and 22 %, respectively, after healing due to microwave heating, which can be attributed to the ageing of the asphalt.

Improved macro-microscopic characteristic of gypsum-slag based cementitious materials by incorporating red mud/carbide slag binary alkaline waste-derived activator

The expensive cost and high carbon footprint of commercial alkaline activators hindered the promotion and industrialization of geopolymers. The rising demand for geopolymer as low carbon and excellent building materials will lead to enormous research works towards to low carbon alkaline activator. This study aimed to explore the impact of red mud (RM)/carbide slag (CS) binary alkaline wasted-derived activator (RCA) on the macroscopic and microscopic properties of RCA activated cementitious materials (RCM) prepared with titanium gypsum (TiG) and granulated blast furnace slag (GBFS). It is proposed to adjust the pH value of solid waste powder for calibrating the waste-derived activator, prepare RCM and explore the relationship between its mechanical properties and hydration products. The research showed that the highest flexural and compressive strengths at 28 days occurred with a dosage of 0.8 wt% CS, meeting the strength requirements of 52.5 R Portland cement. It is worth noting that RCM with binary alkaline waste-derived activators with appropriate pH values can exhibit excellent early mechanical properties. Raising the pH of RCA significantly improves the compressive and flexural strength, increasing them to 30.7 MPa and 6.3 MPa at 3 d, and to 60.7 MPa and 10.8 MPa at 28 d. The primary hydration products of RCM include C(N)-A-S-H gels, ettringite, and gypsum crystal phase, which contribute to the development of mechanical strength. Due to the difference in the alkaline environment required for the growth of C(N)-A-S-H gel and ettringite crystal, the increase in RCA pH value has been found to both inhibit the growth of ettringite to a certain extent and promote the precipitation of C(N)-A-S-H gels, improving the chemical structure of the hydration products and the pore distribution characteristics of the RCM. Furthermore, the research has been successfully applied in a pilot test in Jiaozuo, China. RCM introduces a novel concept for the efficient and industrial-scale utilization of solid waste. This study can provide a fundamental academic and industrialized support and a novel concept for the whole solid waste cementitious materials especially from alkaline industrial solid wastes such as RM and CS.

CO2 adsorption properties of aerogel and application prospects in low-carbon building materials: A review

The applications and researches of the aerogel in the field of building materials and building energy conservation had been widely concerned due to its excellent thermal insulation properties. However, it has not been paid attention that the potential application values for excellent CO2 adsorption properties of aerogel in building materials. The CO2 adsorption properties of aerogel and the research progress on utilizing SiO2 aerogel in building materials had been reviewed. And the application prospect of the technologies that exploit the CO2 adsorption properties of aerogel and the carbonization technology to prepare SiO2 aerogel-based low-carbon building materials was discussed. It was shown that the type, morphology, and pore structure of aerogel significantly affect the resulting carbon adsorption performance. Amino modification was an effective method for improving the carbon adsorption capacity of aerogel. The performance of aerogel-incorporated cement-based composites could be optimized by improving the performance of binder materials, modifying the aerogel, or preparing new aggregates by loading aerogel into porous materials with higher strength. In addition, it was feasible to prepare new green low-carbon building materials by using aerogel as thermal insulating aggregate and carbon adsorption material, industrial solid wastes rich in alkali metal ions as cementitious materials, and carbonation curing technology. The purpose of this review was to promote the application of CO2 adsorption properties of aerogel in building materials, and enhance the development of low-carbon (or zero-carbon, or negative-carbon) building materials. This is of great significance for reducing carbon emissions in the construction sector and promoting the "carbon neutrality" of global.

A study of the relevance of seismic steel structures to urban carbon neutrality

Global warming has triggered dramatic climate change and natural disasters. Since the 21st century, the frequency of all kinds of extreme weather has increased significantly. This study, in accordance with the carbon peak targets and stage requirements, improve the building low carbon building standards system, accelerate the formulation, revision and collation of energy-saving design standards for public buildings energy-saving and carbon reduction standards. The application of earthquake-resistant steel structure of the building, the promotion of green low carbon building materials and green construction methods. Actively promote such buildings, the past sixty years each country's carbon emissions intensity have shown a general downward trend, especially South Korea, South Africa and Brazil and other countries due to economic development began to focus attention on environmental issues. In this study, we take Busan, Korea as an example, and use carbon neutral calculations to realize carbon neutrality by designing superstructures with a reduced degree of intensity, so that the reduction of carbon emissions mainly includes emission reductions brought about by a reduction in the amount of steel and cement used. It is hoped that this study will be taken into account, and that the early realization of peak carbon emissions in South Korea will be the current situation to be realized, and will be a challenge not only for developing countries, but also an important issue to be considered by all countries.

Sustainable MgO-calcined clay cementitious material: Reaction mechanism, strength development and performance enhancement via initial CO2 stirring

With the massive utilization of concrete and other cement-based materials worldwide, the high carbon emissions and energy consumption have become severe issues. This study proposes a sustainable cementitious material based on MgO and calcined clay and investigates its reaction mechanism and strength development by combining experimental characterizations and thermodynamic modelling. Furthermore, the performance of the MgO-calcined clay cementitious material is enhanced by CO2 stirring. The results indicated that the introduction of CO2 during stirring generates massive high reactive magnesium carbonate nano/micro-particles. It provides the nucleation sites for promoting the formation of hydration products and reacts with calcined clay to form carbonate-type hydrotalcite. Due to the unique advantages of CO2 stirring in the MgO-calcined clay system, the performance of sustainable cementitious material is remarkably enhanced, providing a new routine for developing high-performance low-carbon building materials.

Mechanical and hygrothermal properties of hemp-silica bio-composites

This research investigated the development of a fast-drying silica-based binder for hemp concrete products with enhanced mechanical and thermal properties. Hemp-silica bio-composites were prepared by mixing hemp shivs with a two-component binder system composed of liquid sodium silicate and tributyl citrate (TBC). Compressive strength, thermal conductivity, moisture buffering value, cyclic moisture resistance and microstructure of hemp-silica composites were analysed, and the results were compared with those of hemp-lime concrete. Hemp-silica blocks with shiv-liquid sodium silicate mass ratio of 1:3.75 and TBC content of 37.5 wt% of sodium silicate dry matter produced a compressive strength of 0.56 MPa only after 3 days of drying and 1.92 MPa after 28 days. These were higher than hemp-lime blocks at the same density range. Hemp-silica panels showed a thermal conductivity of 0.101 W/mK and an excellent moisture buffering value of 3.49. Hemp silica formed an open porosity with large air gaps between the particles and a water-resistance silica-based layer on the shiv surface producing a higher moisture resistance compared to hemp-lime systems. This paper focuses on the development of a novel fast-drying binder system with a potential for use in conjunction with other lingnocellular plant aggregates to form low-carbon and efficient multifunctional building materials.

Thermally Future-Proofing Existing Libyan Housing Stock with Biobased Insulation Materials and Passive Measures: An Empirical and Numerical Study Using a Digital Twin

Thermal refurbishment and retrofitting building envelopes with passive measures such as the optimisation of opaque and transparent fabric performance may play a key role in reducing cooling and heating load and promoting building energy efficiency. Furthermore, to reduce the embodied carbon impact of the building, the refurbishment measures need to consider the use of low-carbon building materials. This paper investigates ways to thermally future-proof typical Libyan houses using biobased materials. Several typical Libyan houses were monitored for one year to investigate the heating and cooling energy use and to thermally retrofit the building envelope. A digital twin was created in the DesignBuilder software using the real building data of one building for digital model calibration. Finally, multi-objective optimisation was carried out with low-impact biobased materials for insulation, including camel hair, sheep wool, and date palm fibre as well as using other optimisation variables such as shading and glazing types. The study reveals that thermally upgrading the building roof and wall with insulation materials and upgrading the windows with energy-efficient glazing and local shadings can achieve a reduction in cooling load from 53.51 kWh/m2/y to 40.8 kWh/m2/y. Furthermore, the heating load reduces from 19.4 kW/m2/y to 15 kW/m2/y without compromising the standard annual discomfort hours.

Unlocking the potential of ordinary Portland cement with hydration control additive enabling low-carbon building materials

Ordinary Portland cement (OPC) is the core ingredient of many construction materials. In 2022, 4.1 billion tons were used worldwide, contributing to ~8% of CO2 emissions ( ~ 3 Gt/year). Nevertheless, the complete strength-generating capacity of OPC remains unrealized due to the restricted conversion of aluminates to ettringite, caused by conventional hydration kinetics. Here we show a hydration control additive that selectively modifies the hydration kinetics, thereby facilitating enhanced dissolution of aluminates (calcium aluminoferrite and tricalcium aluminate) in OPC, which promotes ettringite formation at a desired time. Increasing ettringite content improves packing of the hardened cement, resulting in ~50% higher specific strength and enabling cement reduction. It also increases OPC strength development efficiency, reducing carbon footprint by ~30%. The use of this additive can be combined with methods such as reducing water and/or using supplementary cementitious materials (SCMs) to prepare building materials with significantly fewer CO2 emissions than those from conventional OPC.

Bio-inspired low-carbon building materials: From colonial sandcastles to next-generation constructions

Bio-inspired low-carbon building materials: From colonial sandcastles to next-generation constructions

Environmental Impact Assessment of Building Materials Using Life Cycle Assessment

In pursuit of environmental sustainability in the construction sector, this study employs a comprehensive life cycle assessment (LCA) approach to evaluate the environmental impact of widely used building materials in Iran, with a particular focus on energy consumption and carbon footprint. The investigation encompasses 22 widely used building materials, utilizing the Ecoinvent v3 database and Simapro8 software to assess critical environmental variables, including carbon dioxide (CO2) emission, required primary energy, water consumption, and thermal conductivity. The findings unveil the diverse environmental profiles of these materials, with thermal conductivity typically hovering around zero to 2 W/m.K for most, but with exceptions such as lime, aluminum, rebar, and steel exhibiting significantly higher values. Moreover, aluminum, ceramics, PVC pipe, and expanded polystyrene (EPS) foam are identified as higher energy consumers during their life cycle, in contrast to concrete and cement mortar characterized by lower primary energy demands. The materials identified as high-carbon building materials are steel, stone, plaster, rebar, bitumen, concrete, glass, cement, gravel, and EPS foam. On the other hand, the materials identified as low-carbon building materials are masonry blocks, wood, tiles, bricks, drywall, MDF, and cement mortar. This research provides valuable insights for material selection and sustainable construction practices, emphasizing low-carbon materials to reduce environmental impact and contribute to the global effort to mitigate climate change through responsible construction choices.

An Integrated Workflow for Designing and Fabricating Multi-Functional Building Components through Additive Manufacturing with Clay

This article presents a project that explores the potential of Additive Manufacturing (AM) for designing and fabricating multi-functional building components for improved climate performance. In this project, an innovative façade wall design was developed by using a computational method in an attempt to integrate a displacement ventilation system into the wall. A robotic AM solution is integrated into the workflow as a potentially feasible fabrication method for the resulting wall design with an intricate geometry. Clay is proposed as the AM material, being a potential low-carbon building material. To this end, a material exploration of clay was conducted to develop an appropriate composite for AM. A displacement ventilation system was developed to achieve better indoor air quality by using a Computational Fluid Dynamics (CFD) model. Subsequently, an AM solution was integrated into the workflow to automate the fabrication phase. Finally, a partial prototype of the design was made through AM with clay to demonstrate the feasibility and observe the material qualities of the final product. The proposed workflow proves applicable, highlighting directions for future research.

Three-dimensional Meso-scale virtual strength test of steel slag porous asphalt mixture based on PFC3D

In recent years, steel slag has gained widespread utilization in pavement construction as a green, low-carbon building material. In this study steel slag aggregate (SSA) was used as a partial replacement for basalt aggregate in porous asphalt mixture. To gain an in-depth understanding of the microscopic cracking characteristics of steel slag aggregate porous asphalt concrete (SSA-PAC), laboratory three-point bending tests and numerical simulations were conducted. Based on CT scanning images, 3D models of SSA and basalt aggregates within particle size ranges of 4.75–9.5 mm and 9.5–13.2 mm were generated. These characteristic aggregates were then randomly placed to establish a three-dimensional model using PFC3D (Particle Flow Code in 3 Dimensions). The micro-contact parameters were derived through the conversion and calibration of macro and micro-mechanical parameters. The results of the 3D virtual strength test exhibited a close resemblance to those obtained from laboratory semi-circular bending (SCB) tests. The displacement trend chart of the aggregates revealed three distinct stages: vertical displacement, vertical displacement combined with a small amount of lateral displacement, and lateral displacement. Cracking mainly occurred at the interface between the aggregates and asphalt mortar, which aligned with actual cracking scenarios. The cracking behavior of the asphalt mixture was characterized by evaluating the number of cracks, notch width, and coordination number throughout the loading process. Additionally, the influence of loading rates on cracking behavior was analyzed. The results of this study demonstrated that the established 3D model effectively revealed the cracking characteristics of SSA-PAC.

Crab-claw inspired high performance and flame-retardant magnesium oxychloride cement based adhesive reinforced by 4-arms EDTA and tartaric acid for wood industry

The high CO2 emissions and instability of silicate cement binders during production and use have encouraged the development of low-carbon materials. In this study, an environmentally friendly and flame-retardant building material was produced from magnesium oxychloride cement (MOC) and wood. In practice, the considerable microcracking that forms during the hardening process makes MOC materials very sensitive to water, which limits their further use. Inspired by the predation of crabs, a simple and effective method was proposed to obtain better water resistance and mechanical strength of MOC composite by co-modifying with ethylenediaminetetraacetic acid (EDTA) or disodium ethylenediaminetetraacetic acid (EDTA-Na) in conjunction with tartaric acid. The four –COOH of EDTA and EDTA-Na coordinated well with the 5-phase structure and tightly aggregated the 5-phase crystals, effectively reducing the formation of microcracks. The synergistic effect between EDTA/EDTA-Na and tartaric acid prevented the disruption of 5-phase crystal structures by water molecules, thus improving the water resistance of the MOC composite. The softening coefficients of the MOC composite modified by EDTA and EDTA-Na in cooperation with tartaric acid after soaking for seven days were 0.97 and 0.98, respectively, which is significantly higher than that of the MOC composite modified by tartaric acid alone (0.54). At the same time, the co-modified MOC composite can be utilised as an inorganic adhesive for plywood, and the wet strength of plywood modified with EDTA in cooperation with tartaric acid being 25% higher than that of the unmodified MOC composite. In addition, the resulting composites showed great potential for application in low-carbon building materials, which can help alleviate the environmental impact of construction industries.

Colonial sandcastle-inspired low-carbon building materials

Colonial sandcastle-inspired low-carbon building materials

Multiscale ab-initio modeling and experiment of nano-CaCO3 and fiber synergy on toughening low-carbon geopolymer composites

Although the geopolymer is generally regarded as a solution to low-carbon building materials, the intrinsic high brittleness greatly limits its further engineering practices. Here, we performed multi-scale ab-initio modeling and experiment on synergistic effect of nano- calcium carbonate (NCC) and polyethylene fiber (PEF) on toughening mechanisms of geopolymer composites for the first time. Results showed that NCC significantly improved micro-scale geopolymer gels aggregation on the surface of PEF through the nano-scale calcium (Ca)-triggered electrostatic attractions and high bonding between N/CASH-polyethylene. Due to micro-scale gel aggregation, meso fiber dispersion, geopolymers with 12 mm + 6 mm PE fiber + 1% NCC showed the best synergistic effect on macro- scale bending toughness and multiple cracking characteristics. The relationship of fiber reinforcing index-toughness, toughness-crack amount and toughness-crack fractal dimension tracked good linear, natural log and exponential function, respectively. The crack number and crack fractal dimension are applicable visible indicators of the bending toughness of PEF reinforced GCs.

Thermo-mechanical behavior of cementitious material with partial replacement of Class-II biochar with Accelerated Carbonation Curing (ACC)

Using carbon-neutral materials is a promising way to mitigate the CO2 emissions of the construction industry. Biochar prepared from agricultural waste has a great potential to sequester CO2. This study demonstrates a new sustainable method for preparing biochar from rice husk having class II category as it has less than 60% carbon content and is derived at a temperature of 500 ℃. The prepared biochar was partially replaced in cement paste and cured under a CO2 environment for 7 and 28 d. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) showed that the replacement of biochar promoted cement hydration and mechanical properties. Addition of 3 wt% and 5 wt% biochar increased the compressive strength of the composite by 34.7% and 35.6%, respectively. However, a further addition to 10 wt% biochar reduced the compressive strength by 16.7%. Replacement of up to 5 wt% biochar successfully promoted the carbonation with 10.2% CO2 uptake after 28 d of accelerated CO2 curing. Carbonation of biochar-cement composite substantially improves thermal conductivity, specific heat, and thermal diffusivity compared to control samples at 7 and 28 d. Field Emission Scanning Electron Microscope (FESEM) analysis revealed the numerous cement hydrates which enhance the bond strength after carbonation, and the carbonate densifies the microstructure, considerably enhancing mechanical strength and carbon binding capability. Biochar-cement composites with CO2 could be innovative low-carbon building materials for sustainable engineering applications.

GHG emissions and energy consumption of residential buildings-a systematic review and meta-analysis.

Residential buildings generate significant greenhouse gas (GHG) emissions and consume energy throughout their life cycle. In recent years, research on GHG emissions and energy consumption of buildings has developed rapidly in response to the growing climate change and energy crisis. Life cycle assessment (LCA) is an important method for evaluating the environmental impacts of the building sector. However, LCA studies of buildings show widely varying outcomes across the world. Besides, environmental impact assessment from a whole life cycle perspective has been undeveloped and slow. Our work presents a systematic review and meta-analysis of LCA studies on GHG emissions and energy consumption in the preuse, use, and demolition stages of residential buildings. We aim to examine the differences among the results of diverse case studies and demonstrate the spectrum of variations under contextual disparities. Results show that residential building emits about 2928kg GHG emission and consumes about 7430 kWh of energy per m2 of gross building area on average throughout the life cycle. Residential buildings have an average GHG emission of 84.81% in the use phase, followed by the preuse phase and demolition phase; the mean energy consumption in the use stage occupied the largest share of 84.52%, followed by preuse stage and demolition stage. GHG emissions and energy use vary significantly in different regions due to different building types, natural conditions, and lifestyles. Our study stresses the compelling requirement to slash GHG emissions and optimize energy consumption from residential buildings by use of low carbon building materials, energy structure adjustment, consumer behavior transformation, etc.