Emerging CO2 utilization technologies for construction materials: a review

The construction industry is a major contributor of CO2 emissions. Carbonation, involving the reaction of CO2 with alkaline reactants, immobilizes CO2 into thermodynamically stable carbonates used in construction materials such as concrete and aggregates. The utilization of CO2 in construction materials is considered as one of the most promising routes for carbon sequestration, with a $400 billion market opportunity and a potential to reduce annual CO2 emissions by up to 3 Gt by 2030. This paper reviews the current status of the utilization of CO2 in construction materials from the perspective of scientific research and commercial applications. The explanation of the fundamental carbonation reaction mechanisms was extended to cover different binder systems involving Portland cement, non-hydraulic calcium silicate, industrial solid wastes and magnesium-based materials. Factors affecting the kinetics of the carbonation reaction and properties of the final products were reviewed. Furthermore, the current state of research and commercial initiatives involving the utilization of CO2 in the production of various building components were presented. Finally, key issues regarding the challenges faced in the scaling up of CO2 utilization technologies from the perspective of academia, industry and relevant regulatory bodies were highlighted. Recommendations to address the current utilization dilemma and promote large-scale application of CO2 in the production and development of construction materials were provided

Maximising the benefits of calcium carbonate in sustainable cements: opportunities and challenges associated with alkaline waste carbonation

Cement production significantly contributes to global climate change and implementation of carbon capture, utilisation and storage (CCUS) in construction materials is considered a crucial step toward achieving net-zero emissions. Substituting Portland cement (PC) clinker with limestone has been demonstrated to effectively reduce CO2 emissions while enhancing the properties of cement and concrete. Beyond limestone extraction, quarrying, and crushing, various types of alkaline waste materials generated from industrial processes can serve as valuable resources for producing diverse forms of calcium carbonate, simultaneously capturing a substantial amount of CO2. In this context, we contend that due to the distinct characteristics of various calcium carbonate forms, there exists the substantial potential to maximise their technical, economic, and environmental advantages in the production of sustainable cements. We reviewed existing studies of the effects of different calcium carbonate forms on cement properties and underscored the viability of utilising various alkaline wastes to produce different calcium carbonate products. As a promising approach for CO2 reduction, waste management, and resource recovery, we addressed the opportunities and challenges associated with advancing CCUS through the utilisation of carbonated alkaline wastes in sustainable cements. To achieve real-world impacts, we emphasised the necessity for interdisciplinary research collaborations, active involvement from industry stakeholders, regulatory bodies, and governmental support to facilitate the large-scale adoption of these innovative practices

Temporal effect of MgO reactivity on the stabilization of lead contaminated soil

Elevated soil lead (Pb) concentrations are a global concern owing to the toxic effects of this heavy metal. Solidification/stabilization (S/S) of soils using reagents like Portland cement (PC) is a common approach for the remediation of Pb contaminated sites. However, it has been reported that under long-term field conditions, the performance of PC treatments can diminish significantly. Therefore, novel reagents that provide longer-term stabilization performance are needed. In this study, four magnesium oxide (MgO) products of different reactivity values were applied (5 wt%) to a Pb contaminated clayey soil. The short-term (1–49 days) and long-term (25–100 years) temporal stabilization effects were investigated by laboratory incubation and accelerated ageing methods, respectively. The concentration of Pb in Toxicity Characterization Leaching Procure (TCLP) leachate was ~14 mg/L for the untreated soil; ~1.8 times higher than the TCLP regulatory level (5 mg/L). Only one day after treatment with MgO, the leachate concentration was reduced to below the regulatory level (a reduction of 69.4%–83.2%), regardless of the MgO type applied. However, in the long-term accelerated ageing experiments, only treatments using the most reactive MgO type could provide leachate concentrations that were consistently below the TCLP threshold throughout the 100 years of simulated ageing. The soil treated with the MgO of lowest reactivity was the first to exceed the regulatory level, at simulated year 75. It is thus demonstrated that MgO reactivity has a significant effect on its long-term effectiveness for contaminated soil stabilization. This is attributed to differences in their specific surface area and readiness to carbonate, which may facilitate the immobilization of Pb in the long term. It is also noteworthy that compared to PC, reactive MgO is more environmentally friendly owing to lower energy consumption and reduced CO2 emissions during its manufacture

Effects of MgO Expansive Agent and Steel Fiber on Crack Resistance of a Bridge Deck

To prevent cracks caused by shrinkage of the deck of the Xiaoqing River Bridge, MgO concrete (MC) and steel fiber reinforced MgO concrete (SMC) were used. The deformation and strength of the deck were measured in the field, the resistance to chloride penetration of the concrete was measured in the laboratory, and the pore structure of the concrete was analyzed by a mercury intrusion porosimeter (MIP). The results showed that the expansion caused by the hydration of MgO could suppress the shrinkage of the bridge deck, and the deformation of the deck changed from −88.3 × 10−6 to 24.9 × 10−6, effectively preventing shrinkage cracks. At the same time, due to the restriction of the expansion of MgO by the steel bars, the expansion of the bridge deck in the later stage gradually stabilized, and no harmful expansion was produced. When steel fiber and MgO were used at the same time, the three-dimensional distribution of steel fiber further limited the expansion of MgO. The hydration expansion of MgO in confined space reduced the porosity of concrete, optimized the pore structure, and improved the strength and durability of concrete. The research on the performance of concrete in the in-situ test section showed that MgO and steel fiber were safe for the bridge deck, which not only solved the problem of shrinkage cracking of the bridge deck but also further improved the mechanical properties of the bridge deck

Influence of Combined Action of Steel Fiber and MgO on Chloride Diffusion Resistance of Concrete

To improve the chloride diffusion resistance and durability of concrete, a new kind of steel fiber reinforced MgO concrete (SFRMC) was made by adding steel fiber and MgO to concrete simultaneously. With steel fiber for load bearing and expansion limiting, MgO as the expander, SFRMC has both the advantages of fiber reinforced concrete and expansion concrete. The influence of steel fiber and MgO on the strength and chloride diffusion resistance of concrete was evaluated by splitting tensile test and chloride diffusion test. Mercury intrusion porosimeter (MIP) and scanning electron microscopy (SEM) were used to study the microstructure of SFRMC. The results showed that the combined action of steel fiber and MgO reduced the porosity of concrete and the chloride diffusion coefficient (CDC), which could not be achieved by steel fiber and MgO separately. In the free state, the expansion energy produced by the hydration of MgO made the concrete expand outwards. However, under the constraint of steel fiber, the expansion energy was used to tension the fiber, resulting in self-stress. In this way, compared to reference concrete RC, the tensile strength of SFRMC-1, SFRMC-2, and SFRMC-3 increased by 3.1%, 61.3%, and 64.5%, CDC decreased by 8.8%, 36.7%, and 33.1%, and the porosity decreased by 6.2%, 18.4%, and 20.6%, respectively. In addition, the SEM observations demonstrated that the interfacial transition zone (ITZ) between fiber and matrix was denser in SFRMC, which contributed to reduce the diffusion of chloride ions in the concrete

Effects of Steel Slag Powder and Expansive Agent on the Properties of Ultra-High Performance Concrete (UHPC): Based on a Case Study

In view of the performance requirements of mass ultra-high performance concrete (UHPC) for the Pang Gong bridge steel cable tower in China, the UHPC incorporating of steel slag powder and hybrid expansive agents is optimized and prepared. The effects of steel slag powder and hybrid expansive agents on the hydration characteristics and persistent shrinkage of UHPC are investigated. The results indicate that 15 wt.% steel slag powder and 5 wt.% hybrid expansive agents can effectively reduce the drying shrinkage deformation of UHPC with a slight decrease of strength. Heat flow calorimetry results show that the incorporation of steel slag powder and expansive agents decreases the hydration heat at three days. Moreover, the obtained adiabatic temperature rise of UHPC is 59.5 °C and the total shrinkage value at 180 days is 286 με. The hydration heat release changes of large volume UHPC in the steel-concrete section of cable tower is agreed with the result of adiabatic temperature rise in the laboratory

Influence of Polyvinyl Alcohol Powder on the Mechanical Performance and Volume Stability of Sulfoaluminate–Portland Cement Composite

Cement quick repair materials generally have the defects of brittleness and early shrinkage. The modification of composite cement mortar by water-soluble glue powder—polyvinyl alcohol (PVA)—was studied in the condition of settled water cement ratio. At 90 days, the maximum flexural strength of mortar was 15.4 MPa, which was 1.3 times of the group without PVA and there was no strength shrinkage phenomenon. Through the analysis of the porosity, PVA improved the total porosity; high porosity could play a better role of buffering and absorbing the impact stress, effectively improving the toughness of mortar. At 28 days, the maximum impact resistance was 1.72 J/cm2, which was 1.75 times of the group without PVA. In addition, the increased total porosity also greatly absorbed the shrinkage stress at the early stage, and reduced the mortar self-shrinkage. When the PVA content was 1%, the volume self-shrinkage of mortar decreased from the initial 3360 μm·m−1 to 700 μm·m−1. According to the analysis of hydration heat, the addition of PVA effectively reduced the early hydration heat release rate and alleviated the concentrated heat release phenomenon to a certain extent. In this paper, the hydration reaction of composite cement and the action mechanism of PVA in composite cement were studied by means of X-ray diffraction, infrared spectrum and hydration heat analysis

Alkanolamines-activated steel slag for stabilization/solidification of heavy metal contaminated soil

Steel slag (SS) is a byproduct discharged from steel-making industry with less than 25% utilization rate in China. The low utilisation rate of SS is associated with its low hydration activity in cement and concrete. In this study, four different alkanolamines (TEA, TIPA, EDIPA and DEIPA) were used to activate SS to improve its cementitious properties and metal binding performance, and hence its capacity on treating heavy metal-contaminated soils containing Cd, Cu, Ni, Pb and Zn. Compared with the reference SS without activators, concentrations of leached Cd, Cu, Ni, Pb, and Zn have reduced by 87.2%, 78.8%, 62.4%, 73.6% and 64.5% by using 0.1% TIPA-activated SS after 28 days, and they were all below their respective regulatory limits by Standard for Pollution Control on the Hazardous Waste Landfill (GB 18598–2019) in China, and the unconfined compressive strength (UCS) of the treated soil at 28 days was enhanced by 237.7% using 0.1% TIPA-activated SS. To elucidate the activation mechanism, the hydration process of SS was thoroughly followed via isothermal calorimetry (IC) and conductivity analysis, and the nature of hydration products was studied by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). It was concluded that alkanolamines facilitated the dissolution of minerals in SS and formation of hydration products (e.g., C-S-H, C-A-H, C-F-H and Mc), and hence significantly enhanced the microstructural development and engineering properties of SS. This work demonstrated a promising way of upcycling SS as an effective and sustainable S/S agent for handling complex heavy metal contaminated soil, with the potential of enhancing the SS utilization significantly

Effects of Lightly Burnt MgO Expansive Agent on the Deformation and Microstructure of Reinforced Concrete Wall

Compensation for shrinkages with three kinds of lightly burnt MgO expansive agent (LBMEA) is used in a reinforced concrete wall poured in the summer. Influences of the internal temperature history on the expansion of concrete and the microstructure of cement paste containing LBMEA were investigated. The results showed that LBMEA exhibited significant expansion around the end of the fall temperature stage; then, the expansion rate declined obviously, and concrete containing LBMEA with low hydration reactivity (140 s and 220 s) showed larger expansion than LBMEA with high hydration reactivity (60 s). Microstructural analysis indicated that brucite preferentially forms in the pores in cement paste containing LBMEA with high reactivity, but brucite mainly grows on the surface of the MgO particles in cement paste containing LBMEA with low reactivity during the early age. Paste containing LBMEA with low reactivity showed a larger volume of single brucite crystal than LBMEA with high reactivity, which further led to larger expansion in the latter than the former. The results revealed the expansion process of LBMEA and can help engineers select suitable LBMEA for application to actual engineering