Artificial Lightweight Research Articles

Advancements in Lightweight Artificial Aggregates: Typologies, Compositions, Applications, and Prospects for the Future

Currently, the environment and its natural resources face many issues related to the depletion of natural resources, in addition to the increase in environmental pollution resulting from uncontrolled waste disposal. Therefore, it is crucial to identify practical and effective ways to utilize these wastes, such as transforming them into environmentally friendly concrete. Artificial lightweight aggregates (ALWAs) are gaining interest because of their shift in focus from natural aggregates. Researchers have developed numerous ALWAs to eliminate the need for natural aggregates. This article explores the diverse applications of ALWAs across different industries. ALWAs are currently in the research phase due to various limitations compared to the availability of the various natural aggregates that form more durable solutions. However, researchers have discovered that certain artificial aggregates prioritize weight over strength, allowing for the effective use of ALWAs in applications like pavements. We thoroughly studied the various ALWAs discussed in this article and found that fly ash and construction waste are the most diverse sources of primary material for ALWAs. However, the production of these aggregates also presents challenges in terms of processing and optimization. This article’s case study reveals that ALWAs, consisting of 80% fly ash, 5% blast-furnace slag, and only 15% cement, can yield a sustainable solution. In the single- and double-step palletization, the aggregate proved to be less environmentally harmful. Additionally, the production of ALWAs has a reduced carbon footprint due to the recycling of various waste materials, including aggregates derived from fly ash, marble sludge, and ground granulated blast-furnace slag. Despite their limited mechanical strength, the aggregates exhibit superior performance, making them suitable for use in high-rise buildings and landscapes. Researchers have found that composition plays a key role in determining the application-based properties of aggregates. This article also discusses environmental and sustainability considerations, as well as future trends in the LWA field. Simultaneously, recycling ALWAs can reduce waste and promote sustainable construction. However, this article discusses and researches the challenges associated with the production and processing of ALWAs.

Bloating zone of artificial lightweight aggregates in triaxial whiteware compositions using ME-DOE

This study examines the characteristics of manufactured aggregates by designing an experiment using Mixture Experiments Design of Experiments (ME-DOE) for triaxial whiteware compositions and proposes the optimal mixture for manufacturing artificial lightweight aggregates. The optimal mixture designed using ME-DOE was manufactured in a pilot-scale rotary kiln. The density and water absorption rate of the manufactured aggregates were measured, and the cross-section was observed. Additionally, Mercury Intrusion Porosimetry (MIP) and 3D-CT observation were conducted to observe the pores. The samples designed using the ME-DOE were classified into five types based on the internal microstructure, which had a high correlation with the physical properties of the aggregates. The matrix composition, excluding Fe2O3 and carbon in the area where the black core was created and bloated, was formed in the area of a typical triaxial whiteware mixture. Lightweight aggregates were manufactured at the Pilot Rotary Kiln using a 50:50 mixture of feldspar and ball clay, and the manufactured lightweight aggregates met ASTM C330 standards.

Recycling phosphogypsum to produce artificial lightweight aggregates via stirring and pelleting all-in-one technique: Technical assessment and performance optimization

Currently, production of artificial lightweight aggregates (ALAs) is becoming one of the most promising approaches for solid wastes recycling via pelletization technique. In this study, an innovative stirring and pelleting all-in-one technique (S-pelleting) was employed to prepare the ALAs by using phosphogypsum (PG). The effects of different pelleting techniques on properties of the ALAs were investigated. Furthermore, the NaHCO3, Al2(SO4)3+CaCO3 (Al-Ca) and foamed particles (FP) were introduced as foaming agents to optimize the performance of the ALAs. The specific strength was used as the main assessment index for performance of the aggregates. The results indicated that the specific strength of the aggregates was improved to 10.96 MPa⋅cm3/g by S-pelleting, which was 60.7 % and 35.6 % higher than that of one-step pelleting or double-step pelleting technique. Compared to NaHCO3, the Al-Ca was more conducive to the specific strength development of the aggregates, and the FP addition could further improve the specific strength of the ALAs. When the concentration of Al-Ca was 7% and the mass fraction of FP was 10%, the ALAs with high specific strength of 9.6 MPa⋅cm3/g were obtained in this study. Moreover, the mineral composition, microstructure and pore structure of the ALAs were analyzed and the results reveled that the Al-Ca could promote to form more ettringite and reduce the proportion of harmful pores in the aggregates, which was responsible for the improvement in specific strength. The FP acted as a lightweight skeleton supported inside the aggregates and the well bonded ITZ between FP and the matrix could further improve the specific strength of the ALAs. Finally, the durability and environmental impact of the ALAs were evaluated acceptable. Overall, this study not only provided a green approach for PG recycling, but also presented a new technical scheme for more efficient production of ALAs.

Thermal characteristics of cementitious building materials with carbon and PCM for improved heat storage performance

The thermal properties of cementitious building materials were analyzed by integrating phase change materials (PCMs) and carbon materials to improve their heat storage performance. Four types of carbon materials, namely activated carbon (AC), carbon nanotubes (CNT), exfoliated graphite nanoplatelets (xGnPs), and graphene, were dispersed in PCMs and impregnated into artificial lightweight aggregates via vacuum impregnation to create cement building materials. Various parameters including compressive strength, differential scanning calorimetry (DSC), hydration heat, thermal conductivity, and dynamic heat transfer were evaluated According to the results, the thermal conductivity of PCM was significantly improved by incorporating carbon materials, and the specimen with CNT showed a result of 0.8386 W/m∙K, which is about 20 % higher than that of the specimen without carbon materials. Although the compressive strength decreased with the addition of PCMs, it remained above 20 MPa, thereby ensuring structural integrity. In the dynamic heat transfer test, the carbon/PCM specimen maintained a higher temperature during heat dissipation. It showed a high peak temperature and a time delay of about 2.5 hours during free cooling. The results showed that integrating PCMs and carbon materials into cementitious building materials could effectively improve their thermal performance, potentially saving building energy.

A novel use of incineration bottom ash for H2 aeration in the production of artificial lightweight aggregates

Cold bonding is an energy-efficient method for producing artificial aggregate (AA). However, the relatively high density of AA restricts its use in lightweight concrete products. This study aims to fully upcycle aluminum (Al) content in municipal solid waste incineration bottom ash (IBA) for H2 aeration in the production of lightweight artificial aggregate through alkali activation. To achieve this, the glass particles (GP) in IBA were ground into powder and used as the precursor for NaOH, while the remaining IBA (RIBA), rich in Al, served as the foaming agent. The results showed that RIBA particles (<300 μm) can be used to produce lightweight AA with a loose bulk density ranging from 780 to 840 kg/m3, comparable to sintered fly ash aggregates, and a wide pore size distribution ranging from 0.02 mm to over 1 mm. The inclusion of finer RIBA particles (<75 μm) enhanced the homogeneity of the pore structure, resulting in aggregate strengths of 0.4–0.6 MPa. Moreover, increasing the GP content in IBA up to 40% further boosted the aggregate strength to 1.1 MPa by refining the pore structure and promoting more (C)-N-A-S-H gels with Q4 structures. To ensure sufficient geopolymerization reactions and achieve high strength in the AAs, the alkali concentration should be kept above 3 mol/L. The proposed strategy for lightweight AA production reduced the global warming potential by about 20% compared to the conventional sintered method, offering a more environmentally friendly approach.

Biochar-enabled carbon negative aggregate designed by core-shell structure: A novel biochar utilizing method in concrete

Using carbon-negative biochar is promising for the carbon footprints reduction of construction materials; however, directly utilizing biochar in concrete would negatively influence its mechanical properties, particularly when the utilizing volume exceeds a certain threshold. By designing as a core-shell structure through cold-bonding method, a novel carbon-negative core-shell aggregate (CSA) with a biochar core and a cementitious shell was developed in this study. The aggregate was characterized by strength, density, and water absorption measurements, meanwhile, analyzed by hydration heat, XRD, TGA, SEM/BSE, and X-CT. The results showed that the developed MG80 biochar-CSA attained a loose bulk density of 789 kg/m3. It exhibited a crushing strength of 6.84 MPa, a water absorption value of 19.4 %, and a significantly superior strength efficiency of 8669 Pa·m3/kg compared to commercially sintered artificial lightweight aggregates and other cold-bonded aggregates documented in literature. The carbon emission assessment indicated that producing one ton of MG80 biochar-CSA emitted −69 kg CO2, which was much lower than the commercial sintered aggregates. Concrete developed by replacing natural aggregate with 90 % MG80 biochar-CSA exhibited a compressive strength of 42.2 MPa while maintaining lightweight with density of 1866 kg/m3, which conforms to the standard-classified structural lightweight aggregate concrete.

Characterization of heat-processed artificial lightweight aggregates from polyethylene terephthalate plastic waste

Plastic waste is an undeniable source of pollution that threatens the existence of the earth’s flora and fauna. The bulk of plastic waste generated globally does not go through the proper methods of disposal but is carelessly discarded into the aquatic or terrestrial environment. Current recycling efforts are largely inadequate and disposal in landfills is still fraught with environmental and land use challenges. The proper disposal of plastic waste, as well as mitigating the environmental, social, and health impacts of extracting natural aggregates can be achieved by incorporating plastic waste as aggregates in the construction industry. This paper presents a characterization of aggregates manufactured from polyethylene terephthalate plastic waste using thermal/mechanical methods. From the cost analysis, 24,341.67 Ugx (6.09 USD) was spent to produce 1 kg of PET aggregates. Morphological, intrinsic and mechanical characteristics of the produced aggregates were established using standard procedures and equipment. The results of morphological characterization indicate an irregular shaped aggregate with smooth surface, a dense graded aggregate with a fineness modulus of 4.25, flakiness index of 26%, elongation index of 16% and particle index of 13. Intrinsic characterization yielded particle density of 1330 kg/m3, bulk density of coarse aggregates of 715 kg/m3 and water absorption of 0.445%. Mechanical characteristics of aggregates were evaluated, with compressive strength of 50Mpa, Aggregate Crushing Value of 37%, Ten Percent Fines Value of 71KN, Aggregate Impact Value of 24% and Aggregate Abrasion Value of 20%. The characteristics of PET aggregates confirm their suitability for application in structural lightweight concrete and rigid pavement. The produced PET aggregates can be considered in mix design as a total or partial replacement of natural aggregates in concrete.

Artificial lightweight aggregate made from alternative and waste raw materials, hardened using the hybrid method

Lightweight aggregates are a material used in many industries. A huge amount of this material is used in construction and architecture. For the most part, lightweight construction aggregates are obtained from natural resources such as clay raw materials that have the ability to swell at high temperatures. Resources of these clays are limited and not available everywhere. Therefore, opportunities are being sought to produce lightweight artificial aggregates that have interesting performance characteristics due to their properties. For example, special preparation techniques can reduce or increase the water absorption of such an aggregate depending on the needs and application. The production of artificial lightweight aggregate using various types of waste materials is environmentally friendly as it reduces the depletion of natural resources. Therefore, this article proposes a method of obtaining artificial lightweight aggregate consolidated using two methods: drum and dynamic granulation. Hardening was achieved using combined methods: sintering and hydration, trying to maintain the highest possible porosity. Waste materials were used, such as dust from construction rubble and residues from the processing of PET bottles, as well as clay from the Bełchatów mine as a raw material accompanying the lignite overburden. High open porosity of the aggregates was achieved, above 30%, low apparent density of 1.23 g/cm3, low leachability of approximately 250 µS. The produced lightweight aggregates could ultimately be used in green roofs.

Preparation of carbon-negative artificial lightweight aggregates by carbonating sintered red mud (SRM): CO2 sequestration, microstructure and performance

This study investigated the possibility of employing CO2 curing for the production of cement-free artificial aggregates using low-value sintering red mud (SRM) and fly ash (FA). The effects of different curing methods (CO2 and air curing) and varying FA dosages on the properties of SRM artificial aggregates were analyzed. For SRM artificial aggregates subjected to CO2 curing, the calcium silicates depleted accompanied by precipitation of calcite and aragonite. The carbonated SRM artificial aggregates (CRAAs), exhibited a denser microstructure, with the pores of the SRM filled with carbonation products. For CRAAs with 100 wt% SRM, up to 9.67 wt% CO2 was sequestered and in turn produced calcium carbonate, which resulted in a 149.0% enhancement in crushing strength and a 29.5% reduction in water absorption compared to the similar aggregates under air curing. The introduction of FA led to an accelerated strength development in the CRAAs during subsequent air curing, which was attributed to the formation of carboaluminates as a result of the hydration between the carbonation products and aluminates derived from FA. From the perspective of environment, CRAAs was carbon-negative, with a potential reduction of up to 40.2 kg of CO2 per ton of CRAAs production, presenting a cleaner and sustainable alternative to natural aggregates. The results of the study provided a feasible solution for the effective treatment of SRM on a large scale and can be used as a reference for subsequent studies.

Development of lightweight structural concrete with artificial aggregate manufactured from local clay and solid waste materials

The partial replacement of conventional natural coarse aggregate (NCA) with artificial light weight aggregate (LWA) manufactured from local clay and solid waste to develop a lightweight aggregate concrete (LWAC) for the structural use was studied in this paper. Red clay and Savar clay were used individually with solid wastes like rice husk ash (RHA) and waste glass to produce LWA. The suitability of raw materials and LWA was evaluated by investigating various properties. The mechanical, thermal and durability properties of manufactured LWAC were explored. The results of physical, chemical, thermal and geotechnical properties revealed that Red clay is better than Savar clay for the preparation of LWA. All the physical and mechanical properties of LWA prepared from Red clay are suitable for the preparation of LWAC compared to Savar clay. The test results demonstrated that the concrete manufactured by replacing 30 % of NCA with LWA produced a concrete of lightweight properties. The compressive strength of LWAC for 7 and 28 days was observed as 28 and 48 MPa, respectively. The results of modulus of elasticity, splitting tensile strength, flexural deformation, and creep test of LWAC revealed that these mechanical properties meet the requirements for the structural concrete. The RCP test proves that chlorine permeability of LWAC is comparable with NCA. It was observed that the superior performance of LWAC can be achieved only when the optimized mix designed is followed strictly. The suitability of the replacement of natural aggregate by LWA may be helpful for Bangladesh due to the scarcity of natural coarse aggregate and reusability of solid waste materials.

Converting municipal solid waste incineration bottom ash into the value-added artificial lightweight aggregates through cold-bonded granulation technology

To effective recycle the Municipal solid waste incineration bottom ash (MSWIBA), this study adopts cold consolidation granulation technology to develop eco-friendly artificial lightweight aggregates (ALCBAs), and the materials are over 50 % dosage of MSWIBA, less 50 % fly ash (FA) or ground granulated blast furnace slag (GGBFS), and 10 % ordinary Portland cement (OPC). This study investigated the effects of different binder types and dosages on the properties of ALCBAs, including compressive strength, water absorption rate, bulk density, microstructures, pore development, heavy metal leaching behavior, and sustainability. The feasibility of ALCBAs to design green concrete was also explored. The results show that with higher content of MSWIBA and binders of FA, GGBFS and OPC, the ALCBAs with compressive strength greater than 2.5 MPa, bulk density of about 1000 kg/m3 and water absorption rate greater than 12 % was successfully developed. Increasing the content of FA/GGBFS is beneficial to improve the compressive strength and reduce the water absorption rate and the total porosity and lower the air bubbles percentage of ALCBAs. More importantly, both FA and GGBFS are mixed into ALCBAs, the compressive strength is at 2.5 MPa-3.0 MPa, the water absorption rate is significantly reduced, and the energy consumption, carbon footprint and cost are also significantly reduced. As the content of ALCBAs increases, although the compressive strength and splitting tensile strength are not as good as concrete with natural aggregates, the density of low-carbon concrete with ALCBAs gradually decreases, and the interface transition zone is gradually improved. Overall, ALCBAs can be beneficial to the conservation of natural resources (natural aggregates) and effectively solve the shortage of natural aggregates, and can be used to deal with the accumulation of solid waste in a green way, and it also can open up new channel for solid waste recycling.

Microstructure, XRD, and strength performance of ultra-high-performance lightweight concrete containing artificial lightweight fine aggregate and silica fume

Ultra-high-performance lightweight concrete (UHPLC), a sustainable and environmentally friendly concrete crafted with artificial lightweight aggregates to preserve non-renewable natural resources like river sand, has garnered significant attention due to its exceptional mechanical properties. This study explores the use of artificial lightweight fine aggregate (ALWFA) as a substitute for fine aggregate in UHPLC production, investigating both fresh properties and mechanical performance. Microstructure analysis, utilizing SEM, and crystalline phase evaluation, employing XRD, were also conducted. The study results indicated that due to the irregular shape of ALWA particles with sharp edges, increasing the content of ALWFA led to a reduction in the flowability of UHPLC. Additionally, it was found that increasing the amount of ALWFA as a replacement for fine aggregate negatively affected both the compressive and tensile strength of UHPLC. This reduction in strength can be attributed to the higher porosity and lower intrinsic strength of ALWFA particles, as well as the weaker cohesion between ALWFA particles and the matrix. SEM analysis revealed that elevating the ALWFA content as a replacement for fine aggregate resulted in an increase in both the number and dimensions of voids, which is responsible for the weaker performance of ALWFA concrete. Finally, XRD analysis showed no significant alteration in the crystalline phases as the ALWFA content increased.

Effect of Carbon Nanotubes on Chloride Diffusion, Strength, and Microstructure of Ultra-High Performance Concrete.

This study delved into the integration of carbon nanotubes (CNTs) in Ultra-High Performance Concrete (UHPC), exploring aspects such as mechanical properties, microstructure analysis, accelerated chloride penetration, and life service prediction. A dispersed CNT solution (0.025 to 0.075 wt%) was employed, along with a superplasticizer, to ensure high flowability in the UHPC slurry. In addition, the combination of high-strength functional artificial lightweight aggregate (ALA) and micro hollow spheres (MHS) was utilized as a replacement for fine aggregate to not only reduce the weight of the concrete but also to increase its mechanical performance. Experimental findings unveiled that an increased concentration of CNT in CNT1 (0.025%) and CNT2 (0.05%) blends led to a marginal improvement in compressive strength compared to the control mix. Conversely, the CNT3 (0.075%) mixture exhibited a reduction in compressive strength with a rising CNT content as an admixture. SEM analysis depicted that the heightened concentration of CNTs as an admixture induced the formation of nanoscale bridges within the concrete matrix. Ponding test results indicated that, for all samples, the effective chloride transport coefficient remained below the standard limitation of 1.00 × 10-12 m2/s, signifying acceptable performance in the ponding test for all samples. The life service prediction outcomes affirmed that, across various environmental scenarios, CNT1 and CNT2 mixtures consistently demonstrated superior performance compared to all other mixtures.

Production of Cold-Bonding Pelletized Artificial Expired Cement- Fly Ash Lightweight Aggregates with Various Curing Regime

Expired cement (EC) with fly ash can be recycled in artificial lightweight aggregates (ECFLA) manufacturing to manage industrial waste by mixing with fly ash through a cold bonding process, supplying a sustainable material and contributing to circular economy strategies to produce structural lightweight concrete. Four series of (ECFLA) were divided based on curing conditions and foaming agents, including 20 types of (ECFLA) with control mixes; air and water curing were compared, and their effects were investigated on the (ECFLA) properties. The present study identifies the optimum mix combinations. (EC) mixed with fly ash (FA) in varying amounts of 10, 20, 30, 40, and 50 % by weight of EC with and without foaming agent, it contained approximately 22% water by weight. The (ECFLA) was hardened through a cold-bonding air or water curing process for 28 days, followed by testing at different physical and mechanical properties. Particle crushing strength, impact value, specific gravity, and water absorption were tested on the hardened aggregates. The results indicated that it is possible to produce ECFLA from EC in a cold bonding process. The optimum kind of ECFLA was (20EC80FA) mixed with a foaming agent of loose dry density of 862.13 kg/m3, and particle crushing strength was 2.29 MPa at 28-day for 12 mm diameter. According to test results, cement content significantly affected (ECFLA) strength, consequently influencing lightweight structural concretes’ (LWC) compression strength. The highest 28-day compressive strength of LWCs was 42.3MPa for the (EC50FA50) mix.

Properties of artificial lightweight aggregates prepared from coal and biomass co-fired fly ashes and sewage sludge fly ash

The use of solid waste such as coal and biomass co-fired fly ashes and sewage sludge fly ash instead of clay and other non-renewable resources to produce lightweight aggregates (LWAs) is conducive to sustainable development. In this study, the effects of co-fired fly ashes, sewage sludge fly ash and quartz sand proportion, sintering temperature and sintering time on the physical properties and microstructure of LWAs are studied by single factor experiment. Experimental results show that the optimal experiment conditions are the raw material ratio of co-fired fly ashes: sewage sludge fly ash: quartz sand = 9: 1: 4, 2 wt% SiC as an expansion agent, and sintering at 1060 °C for 10 min. The LWAs obtained under the above conditions have a bulk density of 0.85 g/cm3, an apparent density of 1.84 g/cm3, a 1-h water absorption of 2.71 %, and a compressive strength of 8.68 MPa, which are in accordance with the GB/T17431.1–2010 standard. Besides, the heavy metal immobilization effect of the LWAs is satisfying, where the heavy metal leaching concentrations meet the standard of GB5085.3–2007. In conclusion, it is feasible to use the raw materials to prepare the LWAs under the above sintering conditions, and the prepared LWAs have high strength and low water absorption.

The role of different ratios of biochar in the artificial lightweight cold-bonded aggregates (ALCBAs) containing high volume of red mud (RM)

To explore new channels for the effective recycling of red mud (RM) in the field of construction-related materials, and study the feasibility of applying biochar (BC) and RM into capturing CO2, this study developed the artificial lightweight cold-bonded aggregates mixed with high volume of RM (RM-ALCBAs). Different amount of BC (0%, 5%, 10% and 15%) was also added to the RM-ALCBAs, and a set of quantitative devices for assessing carbon absorption of RM-ALCBAs was innovatively developed. Meanwhile, its compressive strength, water absorption rate and apparent density were tested, and then the microscopic properties of RM-ALCBAs were also investigated by using TGA, XRD, SEM-EDS, MIP. Finally, the sustainability and heavy metal leaning behavior of RM-ALCBAs were assessed. It was found that the total carbon uptake of RM-ALCBAs was about 30.58–33.06 kg/tons, indicating that RM-ALCBAs show the obvious carbon-capturing potential, and when the biochar dosage was increased from 0% to 15%, its compressive strength was 1.28 MPa-1.98 MPa, and the water absorption rate and apparent density of RM-ALCBAs before carbonation were 17.96%-20.46% and 1.85 g/cm3-1.98 g/cm3, while the water absorption rate and apparent density of RM-ALCBAs after carbonation were 16.71%-17.04% and 2.02 g/cm3-1.83 g/cm3, respectively, which is in accordance with the specification of LWAs in China. With the increase of BC doping, the porosity in RM-ALCBAs gradually increased, the proportion of micropores gradually decreased, and the proportion of macropores gradually increased. More importantly, converting RM into RM-ALCBAs can effectively lower the toxic leaching and the concentration of heavy metals is also meet the Chinese requirements. RM-ALCBAs mixed with 5% BC has the lowest energy consumption per-unit compressive strength, carbon emission per-unit compressive strength with about 26.0–29.1 kg/t, and cost per-unit compressive strength with much lower than that of FA-ALCBAs and GGBFS-ALCBAs. Overall, the RM-ALCBAs have obvious eco-friendly potentials and belong to the carbon-negative construction materials that can effectively recycle solid waste of RM, which can provide some new insights and useful data for the development path of low-carbon ALCBAs.

A scientiometric review of artificial lightweight aggregates applying VOSviewer Software

This study aims to conduct a comprehensive scientometric review of Lightweight Artificial Aggregates ( LWAs ), using the Scopus database as the main data source. The choice of Scopus was motivated by the superior availability of documents compared to the "Web of Science", allowing the analysis of more than 510 articles related to the topic. The key expression "artificial lightweight aggregate " was used in the research, and document summaries were read to ensure their relevance to the topic. The justification for this study lies in the need to understand and map the current scientific scenario of LWAs , highlighting their growing importance in civil construction. The analysis Scientometrics adopted scientific mapping as a method, using the VOSviewer software in conjunction with the Scopus analyzer. This approach allowed a detailed assessment of the interconnections between disciplines, authors, publications and institutions, providing a comprehensive view of scientific development related to LWAs . The results revealed the location of 512 relevant articles in the bibliographic search, indicating a significant detection of research on LWAs in the last decade. Although there is progress in this field, it is highlighted that studies on LWAs are still relatively recent compared to commercial aggregates such as expanded clay This comprehensive scientific mapping contributes to a deeper understanding of the research domain, identifying recent advances and areas in need of further exploration, guiding future research and decisions in the construction sector.

Sustainable utilization of concrete slurry waste in eco-friendly artificial lightweight cold-bonded aggregates: An alternative pathway for efficiently sequestrating CO2

Concrete slurry waste (CSW) has the potential of capturing or sequestering CO2. This study designed the low-carbon artificial lightweight cold-bonded aggregates with ultra-high volume of CSW, OSP and MSWIBA (CSW-ALCBAs), and the CO2 sequestrating, compressive strength, and physical properties, leaching toxicity and CO2 emissions of CSW-ALCBAs were investigated. Meanwhile, a novel carbonization device was designed to quantitatively evaluate the potential of CSW-ALCBAs for CO2 adsorption. The results show that both OSP and MSWIBA have the effect of enhancing the CO2 sequestration of CSW-ALCBAs. Besides, the strength, water absorption and apparent density of CSW-ALCBAs also satisfy the demands of GB/T 17461.1–2010. CSW-ALCBAs also exhibit excellent ability to solidify heavy metals and the removal rate of heavy metals is above 80% excepting Cr. ALCBAs with 85% CSW+5% OSP+10% MSWIBA can absorb 29.1313 kg of CO2 (1000 kg ALCBAs), has the highest compressive strength of 1.3 MPa after curing 28 days, water absorption rate is 15.05% and apparent density is 1.3318 g/m3. Overall, this innovative design of CSW-augmented ALCBAs can open up a new area of CSW application that develops technically feasible and cost-efficient carbon-negative building materials.

Sustainable upcycling of artificial lightweight cold-bonded aggregates (ALCBAs) designed by biochar and concrete slurry waste (CSW) into porous carbons materials for CO2 sequestration

CSW (Concrete Slurry Waste) is a hazardous solid waste due to its high alkalinity, and traditional landfill disposal wastes a lot of land. To effectively recycle CSW, this project applied it, ordinary Portland cement (OPC), and Biochar (BC) into designing artificial lightweight cold-bonded aggregates (ALCBAs) by disc granulation. A new test device for evaluating the amount of carbon absorption in ALCBAs was designed and ALCBAs adding ultra-high volume of CSW (CSW-ALCBAs) with BC dosage of 0%, 5%, 10%, and 15% were designed, respectively. The compressive strength, water absorption rate, carbon-sequestration efficiency, pores, hydration phase, and ecological properties of CSW-ALCBAs were also investigated under standard, carbonation, and sealing curing conditions. The results showed that CSW-ALCBAs had obvious carbon-sequestration potential, and the maximum carbon absorption was 18.2 wt% at 15% BC dopsage and the minimum carbon absorption was 16.2 wt% at 5% BC doping. Also, the carbon absorption of CSW-ALCBAs increases with the rise in BC dosage. Besides, the compressive strength in standard and sealed curing conditions peaked at 5% BC dosage, about 2.76 MPa, and then decreased rapidly with increasing BC dosage, and the compressive strength drops to 1.86 MPa at 15% BC dosage. Carbonization condition can improve the mechnaical and physical properties of CSW-ALCBAs with water absorption rate in the range of 6%− 13%, and the maximum compressive strength was about 6.18 MPa. And the compressive strength with the lowest and highest increasing rate in the groups under 28-d carbonized condition were in groups B5 and B10, where the compressive strength increased by 56% and 215%, respectively. Additionally, the total porosity of CSW-ALCBAs is in 13%− 23%, and the BC can provide abundant harmless pores (<50 nm) and store sufficient water. The BC could result in the internal curing effect, and the hydration products such as CH, CC, C-S-H, and AFt could be clearly observed. The choice of 5% BC doping for developing green CSW-ALCBAs is very promising. Overall, this study provides a novel method for the production of carbon-negative aggregates, which not only helps to address the recycling of massive CSW, but also opens up new channels for CSW recycling and CO2 sequestration. Meanwhile, compared with the previous reports about the recycling of CSW has been explored in various ways of utilization and curing regimes, this project explores its potential for carbon capture and investigates the changes in various properties of CSW-ALCBAs after carbonization.

Optimization of the manufacturing process and properties of alkali-activated palm oil fuel ash-based cold-bonded aggregates

Tons of palm oil fuel ash (POFA) are currently being disposed of at landfills or left untreated in the environment, taking up valuable land space and posing significant hazard to the environment. To address this issue, this study investigates the production of artificial lightweight aggregates (LWAs) using POFA as a raw material through a cold-bonded one-part alkali-activation method. High-volume of weakly pozzolanic POFA and different combinations of GGBS (0%, 10%, 30%) as precursors, and Na2SiO3.5H2O (9% and 12%) as the activator were used to produce the artificial LWAs. The granulation process was systematically investigated, where the influence of granulation parameters (the ratio of POFA and GGBS, activator content, water content, rotation angle, and rotation speed) on granulation efficiency and granulation duration were evaluated. The physical properties including loose bulk density, water absorption, and crushing strength were also investigated. In addition, the phase change after alkali-activation was evaluated. Results showed that the water demand for the aggregates with different combination ranged from 0.3 to 0.46. Increasing the GGBS and Na2SiO3.5H2O content improved the granulation efficiency up to 87.4% and shortened the granulation duration to 7 min. Response surface methodology (RSM) modeling revealed that the optimum rotation angle and rotation speed were 55° and 50 rpm, respectively, resulting in a maximum granulation efficiency of 88.2%. The loose bulk density of POFA-based alkali-activated aggregates (PFAAs) was 595.4–730.3 kg/m3, meeting the requirement of LWAs in EN13055. After 28 days curing, the PFAAs with the GGBS replacement of 30% and 12% Na2SiO3.5H2O exhibited crushing strength and water absorption of 2.4 MPa and 22.4%, respectively. Moreover, a stronger alkali-activation was achieved with 30% GGBS replacement, which improved the performance of PFAAs, as evidenced by the phase analysis.