Cementitious Materials Research Articles

Effect of cementitious capillary crystalline waterproof material on the mechanical behavior of concrete

Cementitious capillary crystalline waterproof material (CCCW) is a material that can react with substances inside the concrete, generating crystals that fill the pores and cracks in the concrete. This chemical reaction is expected to improve the mechanical properties of the concrete. This study investigated the effects of CCCW content and water-cement ratio (W/C) on the compressive behavior of cementitious capillary crystalline waterproof concrete (CCCWC). The results indicated that as the CCCW content increased from 0% to 1.5% for W/C of 0.4, the compressive and tensile strength values of concrete slightly decreased. This is because excessive CCCW generates too many crystals within the concrete, leading to internal matrix expansion and crack formations. However, in the cases of W/C of 0.45 and 0.5, the compressive and tensile strength values of the CCCWC increased wit increasing CCCW content from 0% to 0.5%, but declined with 1.5% CCCWC addition. The reaction between CCCW and concrete generates numerous crystals, which densify the concrete matrix and enhance its strength. Moreover, with increasing W/C, the CCCWC's compressive strength and tensile strength decreased due to the increased porosity of the concrete matrix and the reduced availability of the concrete constituents that react with CCCW. Furthermore, the appropriate choice of CCCW content and W/C can significantly enhance the slope and peak stress of the stress-strain curve. Based on this, a compressive constitutive model of CCCWC was established. The findings showed that the optimal CCCW content varied with W/C. For instance, for a W/C of 0.4, the maximun compressive strength of 54.82 MPa was achieved without any CCCW addition. In contrast, the addition of 0.5% CCCW to concrete produced with W/C of 0.45 and 0.5 resulted in the highest compressive strengths of 50.98 MPa and 44.90 MPa, respectively.

Effect of N, N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid sodium salt and triethanolamine on the hydration and compressive strength of steel slag-cement composite systems: A comparative study

To solve the problem of low cementitious activity of steel slag (SS), N, N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid sodium salt (BES-Na) and triethanolamine (TEA) were used in this study to improve the hydration activity of SS. However, there are no comparative studies on the effects of BES-Na and TEA on the hydration of SS-Portland cement (PC) systems. This study compared the hydration process and strength development of SS-PC systems in the presence of BES-Na and TEA, as well as the complexing ability of BES-Na and TEA. The results showed that both BES-Na and TEA improved the early compressive strength of SS-PC mortar, but TEA did not contribute to the late compressive strength, while BES-Na still improved the late compressive strength. At the same dosage, TEA accelerated aluminates hydration more than BES-Na and retarded/inhibited silicates hydration more than BES-Na. This difference in effect on hydration can be attributed to the difference in their complexing ability. TEA has a stronger complexing ability with metal ions than BES-Na, which is beneficial for accelerating aluminates hydration, but this not only prolonged the hydration induction period but also inhibited silicates hydration. BES-Na has a weaker complexing ability relative to TEA. Although BES-Na has a weaker accelerating effect on aluminates hydration, it has a lesser effect on silicates hydration and even accelerates silicates hydration at low dosage. This study also showed that BES-Na is an alternative additive to TEA, which could help expand the application of BES-Na in cementitious materials.

Recycling and optimum utilization of CRT glass as building materials: An application of low CO2 based circular economy for sustainable construction

The construction industry is the major contributor of CO2 emission around the globe. The rapid advances in the electronics industry have transformed the disposal of cathode ray tube glass waste (CRT-WG) into a prominent environmental concern. Recycling of CRT glasses as building materials can help in the production of sustainable construction. Numerous previous studies have documented that CRT-WG can be utilized either as a component of fine aggregate or binder material as it provides a cleaner solution and reduce carbon emission. Under this cleaner production and low CO2 emission perspective, this paper provides a thorough review of the previous studies on the utilization of CRT glass as a partially and fully substitute of sand and cementitious material in mortar production and propose an application of CO2 based circular economy model for reduce carbon emissions. This paper summarized the fresh, mechanical and durability properties of mortar incorporating treated and un-treated CRT-WG with different mineral additives and w/b ratios. Furthermore, this research explores the optimal proportions of CRT glass that can be use as replacements for sand and cement powder to make eco-friendly and sustainable low carbon mortar suitable for both structural and non-structural applications. More particularly, this review emphasizes the benefits, the need for additional research, and the drawbacks of CRT-WG use in construction building. Overall, this study proposes that incorporating CRT glass into building materials through a low CO2 based circular economy offers significant potential advantages. This study will help in optimization of CRT glass in concrete mix design in combination with waste materials for sustainable construction.

Improved mechanical and microscopic properties of ultra-high-performance concrete with the addition of hybrid alkali-resistant glass fibers

Ultra-high-performance fiber-reinforced concrete (UHPFRC), wherein steel fibers are a primary component, is a new cementitious material with high tensile strength and impact resistance. However, steel fibers are susceptible to corrosion in the alkaline environment of concrete matrices. By contrast, alkali-resistant glass fiber (ARGF) exhibits better corrosion resistance. However, few studies have explored the effects of ARGF on UHPFRC, leaving the optimum ARGF content and its enhancement mechanism unclear. Therefore, this study proposes a UHPFRC design that utilizes AR-GF in place of steel fibers. The effects of different types, lengths, and admixtures of AR-GF are investigated using mechanical tests, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results show that the splitting tensile strength and flexural strength of the UHPFRC increase with fiber length and fiber dosage. The optimum fiber mixing ratio is 30 kg/m3 of 12 mm-long Anti-Crak® 62.4 combined with 0.05 kg/m3 of 6 mm long Anti-Crak® HD, leading to a 23.3 % increase in splitting tensile strength and 15.8 % increase in flexural strength compared to those of undoped concrete. By analyzing the ARGF dispersion pattern at the fracture surface of the flexural test, the ARGF dispersion analysis method was proposed. SEM shows that the ARGF is coated with C-S-H, which increases its adhesion to the concrete matrix. XRD confirms that ARGF does not affect the hydration reaction of the cement in the UHPFRC. Finally, a model of ARGF-reinforced UHPFRC is established to elucidate the reinforcing mechanism. This study provides guidance and a reference for the application of UHPFRC in engineering projects.

Exploring effects of supplementary cementitious materials on setting time, strength, and microscale properties of mortar

The concept of sustainability has become a crucial concern for safeguarding the planet. The current research has focused on developing affordable and eco-friendly mortar by using industrial wastes. This study explores the use of fly ash (FA) and ground granulated blast furnace slag (GGBFS), byproducts of steelmaking and coal burning, in mortar production. It examines their impacts on the compressive strength and setting times, when utilizing varying proportions of the materials. The study also evaluates water requirements for the workability, thus demonstrating the sustainability of these waste products in construction. The cementitious materials were employed in finely ground form and were replaced with further tertiary mixes including both supplements at 10%, 30%, and 50% of each. The mixtures were allowed to cure for 7, 14, and 28 days by immersion in water. The results showed improvements in the compressive strength of mortar samples incorporating FA and GGBFS at various curing ages. However, the water requirement and workability of mortar samples were altered as a result of utilizing these supplementary cementitious materials (SCMs). These findings will serve as a standard for environmentally responsible mortar using GGBFS and/or FA as SCMs.

Self-healing and wave-absorbing functional coupling of nano-Fe3O4 hybridized microcapsules

As a common high-performance wave absorber, the application prospect of nano-Fe3O4 in cementitious materials is limited due to its defects such as easy agglomeration and possible hydration reaction with cement clinker. In this study, self-healing and wave-absorbing functional coupling materials were synthesized by nano-Fe3O4 hybridized microcapsules. The physical and chemical properties of nano-Fe3O4 hybridized microcapsules were characterized by ESEM (Environmental scanning electron microscopy), XRD (X-ray diffractometer) and FTIR (Fourier transform infrared spectrum), etc. The self-healing properties of microcapsules were assessed. The electromagnetic parameters of microcapsules were measured, and the wave-absorbing performance of microcapsules with different matching thicknesses was assessed. The function coupling mechanism of self-healing and wave-absorbing of microcapsules hybridized by nano-Fe3O4 was revealed. The findings revealed that the residual weights of FM0 and FM40 were 1.28 % and 16.44 %, respectively. The hybrid microcapsules demonstrated the amorphous structure of self-healing microcapsules and the crystal structure characteristics of nano-Fe3O4. The highest strength healing rate of cement mortar mixed with microcapsules was 34.2 %. The minimum reflection loss and the corresponding effective bandwidth of the nano-Fe3O4 hybridized microcapsules with a thickness of 3 mm were −20.32 dB and 7.07 GHz, respectively. The nano-Fe3O4 hybridized microcapsules with core–shell structure exhibit excellent wave-absorbing performance through the functional coupling of dielectric loss and magnetic loss.

A cohesive fracture-enhanced phase-field approach for modeling the damage behavior of steel fiber-reinforced concrete

This study introduces a novel computational framework based on the phase-field fracture/damage model (PFM), providing rapid and accurate predictions of the damage behavior of Steel Fiber Reinforced Concrete (SFRC) material. The framework integrates the interfacial cohesive fracture model with the PFM to depict the interaction between the cementitious matrix and fibers, marking the first demonstration that this model adequately captures both local fracture phenomena between fibers and concrete (such as fiber bridging and interfacial debonding) and mesoscopic stress–strain behavior. Additionally, an enhanced geometric approximation is established based on the spatial distribution density function of fibers and particles, allowing for the transformation of the three-dimensions (3-D) fiber-reinforced material structure into an equivalent two-dimensions (2-D) material. This approach enables the reduction of computational time, a significant limitation of the phase-field method, thereby allowing an in-house code to perform various computations with complex material structures such as SFRC. The effectiveness of the approach is demonstrated through four examples involving variations in the microgeometry and material properties of SFRC structures, ranging from the simplest configurations to real experimental material structures. Extensive Monte Carlo simulations of the model are also employed to provide results closer to reality, which are then compared with recent experimental data and numerical models, demonstrating the efficacy of the proposed computational model.

LC3 cementitious binder incorporating microencapsulated phase change materials for self-defrosting traffic surfaces

Exposed surfaces of bridge decks, viaducts and pavements incur ice formation and accumulation of snow in cold seasons, which threatens traffic safety. Mitigating this problem using traditional methods such as deicing salts have caused ecosystem damage and inflicted substantial reinforcement corrosion and surface scaling to bridge decks and pavements, thus compromising their service life and causing colossal economic loss. This paper presents an alternative solution to overcome this problem through the development of a sustainable LC3 cementitious material incorporating micro-encapsulated phase change material (MEPCM) with low phase transition temperature to delay the surface temperature drop and mitigate snow accumulation and ice formation. MEPCM was incorporated in the cementitious matrix at 0 %, 10 % and 20 % by binder mass. Paste and mortar mixtures were prepared to investigate the microstructural, mechanical, physical, and thermal properties. Test results showed that incorporating MEPCM in the LC3 matrix achieved adequate compressive strength. Thermal simulations and visual observations conducted on mortar samples in the laboratory and outdoor exposure showed that MEPCM can effectively regulate the surface temperature of the LC3 matrix and mitigate temperature drops as well as snow accumulation. Analysis of temperature data in the 2023–2024 winter season of Hamilton, Ontario, Canada indicated that the MEPCM incorporated in mortar samples could effectively regulate 40 % of the total days considered and mitigate surface ice formation and snow accumulation, which provides both economic and environmental benefits.

Rheology, shrinkage, mechanical properties and microstructure of ultra-light-weight concrete with fly ash cenospheres

Cenospheres are low-density and hollow microspheres derived from coal-fired power plant fly ash waste. This study aims to prepare ultra-light-weight (<1000 kg/m3 wet density) concrete using fly ash cenospheres (FAC). To begin with, FAC’s shell thickness and the water absorption and desorption were characterized. A mixing procedure was designed to avoid the segregation between the FAC and cement slurry. FAC can affect the rheological properties of fresh mixture over time through absorption and desorption of free water. The presented ultra-light-weight concrete has several advantages compared to the ones prepared using foaming methods. First, shrinkage is significantly reduced due to FAC’s internal restraint and curing effects. Secondly, it has good mechanical performance, especially in bending and is more environmentally friendly due to use of less cement. X-ray computed tomography illustrates that FAC ultra-light-weight concrete has smaller pores of more uniform size compared with those prepared using foaming methods. X-Ray diffraction, thermal gravimetry-derivative thermal gravimetry, fourier-transform infrared spectroscopy and scanning electron microscopy are employed for the hydration products and microstructure characterization. Outcomes prove that FAC can combine well with the cement matrix, and react with calcium hydroxide to produce C-A-S-H through pozzolanic reaction.

An innovative method for mesoscale modelling of moisture diffusion in concrete

Moisture diffusion influences the durability and long-term performance of concrete and whilst it predominantly occurs via the cement matrix and Interfacial Transition Zone, most existing models consider concrete to be homogeneous. This paper introduces a novel micro-meso model that employs random packing and Voronoi tessellation. Rayleigh-Ritz pore distribution and Brunauer-Skalny-Bodor models are combined to determine the radius and fraction of various pores. The results indicate that relative humidity diffuses faster with increasing temperature, decreasing ambient relative humidity and tortuosity. Ambient relative humidity has a greater influence on diffusion compared to temperature and tortuosity. Numerical and experimental comparisons demonstrate that the proposed methodology effectively captures relative humidity distribution across various scenarios. Furthermore, explicit pore network modelling incorporates key parameters for a more accurate analysis. Integrating the proposed methodology into a fully coupled hygro-mechanical framework can potentially yield more accurate predictions of mechanical behaviour; enhancing the reliability of long-term performance assessments and enabling more durable concrete design.

Preliminary investigation on spent garnet as a novel supplementary cementitious material

The escalating global demand for cement, a fundamental material in infrastructure development, has exacerbated environmental challenges, particularly through significant carbon dioxide (CO₂) emissions, which account for approximately 8.3 % of global anthropogenic CO₂ output. This research explores the potential of spent garnet powder, a byproduct of abrasive water jet machining, as a sustainable supplementary cementitious material (SCM) to mitigate these impacts. The spent garnet powder, characterized by a high concentration of silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), and iron oxide (Fe₂O₃), was subjected to rigorous analysis. X-ray Fluorescence (XRF) confirmed its chemical suitability for pozzolanic applications, while laser particle size analysis revealed a finer granulometry relative to Ordinary Portland Cement (OPC), which is advantageous for enhancing pozzolanic reactivity. Scanning Electron Microscopy (SEM) demonstrated the angular and irregular morphology of the garnet particles, which is conducive to improved interfacial bonding within the cement matrix. X-ray Diffraction (XRD) identified active mineral phases that are critical for promoting pozzolanic reactions, and Thermogravimetric Analysis (TGA) demonstrated the material’s superior thermal stability, with minimal decomposition at elevated temperatures. Fourier Transform Infrared Spectroscopy (FTIR) identified strong silicon-oxygen (Si-O) and aluminum-oxygen (Al-O) bond structures, indicative of robust pozzolanic potential. The Strength Activity Index (SAI) and Frattini tests further substantiated the pozzolanic activity, revealing that a 10 % replacement of OPC with SGP not only enhances compressive strength but also meets the stringent requirements of ASTM C618. Additionally, the economic analysis underscores the cost-effectiveness of utilizing spent garnet powder, presenting a viable strategy for reducing both production costs and CO₂ emissions in the cement industry. This study conclusively positions spent garnet powder as a highly promising supplementary cementitious material, with significant implications for advancing sustainable construction practices and reducing the environmental footprint of cement production.

A rheological model for concrete additive manufacturing

The advent of 3D construction printing has ushered in a revolutionary era, demanding deeper insights into the understanding of cementitious fluid materials. Despite notable progress in additive manufacturing technologies, traditional rheological models (i.e., Bingham Plastic and Herschel-Bulkley) due to asymptotic behaviors of its plastic viscosity term fall short in describing the fluid mechanical properties of 3D printable concrete. This poses substantial challenges to achieving precise control and consistency in its boundless possibilities of mix design formulation. In this paper, we introduce an original rheological model that broadly characterizes the physiomechanical behaviours of non-Newtonian fluids, with a primary emphasis on thixotropic 3D printable cementitious pastes. Contrary to conventional representations, it is successfully demonstrated and validated herein that flow characteristics of 3D printable concrete may be described by two distinct viscosity terms, both of which collectively defines an upper and lower bound apparent viscosity with respect to a proposed activation function.

Exploring the role of SAP chemical composition in the internal curing of high-performance cementitious materials

This study investigates the impact of the chemical composition of superabsorbent polymers (SAPs) on their effectiveness in internal curing within high-performance cementitious materials. Although the use of commercial SAPs in cementitious systems has been widely researched, there is still no consensus on how different SAP structures influence material properties. For the first time, this research employs photoinitiated free radical polymerization technology to synthesize three structurally distinct SAPs: SAP with sulfonic acid groups (PAMPS), SAP with amide groups (PAM), and SAP with carboxyl groups (PAAs). The effects of these SAPs on the cement hydration process and microstructure were examined by analyzing their water absorption behavior in cement filtrate. The residual cation content on the SAP surface was evaluated using EDS, while XRD and TGA were used to study how SAP structure affects cement hydration products. Furthermore, the impact of these SAPs on the strength and autogenous shrinkage of the material was investigated. The results indicate that PAMPS, with its sulfonic acid groups, exhibited stable water absorption performance in the alkaline cement environment, promoting hydration reactions and increasing the formation of needle-shaped C-S-H. This stability contributed to mitigating the negative effects on mechanical properties. While the inclusion of SAPs generally reduced the strength of the cement matrix, PAMPS was the most effective in mitigating autogenous shrinkage, achieving a shrinkage mitigation efficiency of 86 %. These findings highlight the importance of SAP chemical structure in influencing cement hydration and material performance, offering insights for the development of effective internal curing agents to enhance high-performance concrete.

Study on High-Temperature Activated Products and Hydration Properties of Aga Soil in Tibet for Cement Concrete.

In order to impart the properties of cementitious material to the Tibetan Agar soil, two high-temperature activation mechanisms (HTMA, HTMB) were designed in this study, and the products and hydration-hardening properties of Tibetan Agar soil high-temperature activation mechanism were analyzed by means of SEM, XRD, and XRF. The results show that the main components of Tibetan Aga soil are calcite and quartz; Aga soil is activated by HTMA high-temperature activation, forming the main products of CaO, C2S, CaSiO3, and CaAl2Si2O8, and its products have both air-hardening and water-hardening characteristics; Aga soil is activated by HTMB high-temperature activation, and when the temperature reaches 1250 °C when the clinker is not found in the CaO, the generation of C2S, C3S, C3A, C4AF, and Mg2SiO4 minerals with good water-hardening cementitious properties occurs when the temperature rises to 1350 °C, although the formation of some inert minerals that do not have the cementitious properties, but this temperature activation products of the thermodynamic properties of the best; Enhancing the value of lime saturation degree (KH) and silicon rate (SM) can promote the formation of the products of the C2S and C3S, increase the reactivity of the Aga soil activation products, and increase the hydration heat as well as compressive and flexural strength, combined with the results of the hydration heat and mechanical test, KH is recommended to be 0.9~0.94, SM is recommended to be 1.8~2.4, and alumina ratio (IM) is recommended to be 1.8~2.4 when Aga soil is used with raw materials.

Rapid carbonate precipitation induced by carbamate coating: A new approach to form impermeable thin barrier and its mechanism

Various coating strategies have been explored in the past to prevent the ingress of aggressive substances into concrete. However, either the durability or performance is still far from satisfaction. Here, carbamate solutions were prepared by pre-absorbing CO2 into amino acid salts (AASs) to carbonize the surface of cementitious materials. The high concentration of carbonate ions provided by the carbamate induced rapid surface carbonation, resulting in the formation of an AAS-CaCO3 composite barrier with a thickness of 2–3 μm and possessing high micromechanical properties. Additionally, it was observed that the barrier's effectiveness depends on the molecular structures of the amino acids employed. Coatings formed by arginine-based carbamates demonstrated excellent performances, likely due to the highly compacted calcite particles they produced. This easy-to-operate and effective strategy has the potential to open new avenues for the development of highly durable and impermeable coating barriers for practical applications.

High-temperature performance of clay-enhanced alkali-activated binders: A sustainable alternative to Portland cement

The cement industry's commitment to reducing CO2 emissions has led to exploring alternative processes and supplementary cementitious materials (SCMs). These include alkali-activated binders or geopolymers, promising cement alternatives due to their pozzolanic properties and superior strength and durability, especially at high temperatures. Using abundant raw materials such as clay further enhances the sustainability of geopolymers by reducing emissions associated with their production. Factors like raw material composition and activator type can affect binder properties, so careful material design is essential. This paper discusses experimental results on the mechanical behaviour of alkaline cements at high temperatures, testing two binders (FA=100 % fly ash and FB=70 % fly ash with 30 % clay) and two activators (WN and WK), selected from previous studies where residual strength after temperature exposure was excellent. Their performance was compared to two Portland types of cement (CEM I 52.5 N/SR and CEM I 42.5 R). Unlike cement pastes, the alkaline cements FA and FB retain and can even improve mechanical strength up to 600 °C. At this temperature, adding clay to the FB alkali cement promotes the formation of a viscous gel capable of filling cracks and voids in the geopolymer, thus increasing its high-temperature strength by 80 % compared to cement pastes.

Influence of silica fume on pore structure, mechanical properties and carbon emission of reactive powder concrete prepared by ice crystal homogenization technology

Under ultra-low water-to-binder ratio conditions, the liquid-bridge effect between powders seriously restricts the development of reactive powder concrete (RPC). Ice crystal homogenization technology fundamentally solves the liquid-bridge problem between powders. However, high carbon emissions still constrain the application of RPC. This paper introduces an innovative RPC material incorporating silica fume (SF) as a supplementary cementitious material to solve environmental concerns and alleviate powder aggregation challenges based on the ice crystal homogenization technology. Experimental results show that there was a significant improvement in compressive and flexural strengths observed, particularly in RPC material containing 15% SF, which exhibited the most notable enhancements: a 19.7% increase in compressive strength to 296.3MPa and a 23.6% increase in flexural strength to 43.8MPa. Moreover, the optimized microstructure was reflected in a substantial reduction in water absorption rate and cumulative pore volume by 44.7% and 54.4%, respectively. Besides, RPC incorporating 15% SF achieved the lowest carbon emissions efficiency, with carbon emissions efficiency could be reduced by 79%~93% compared with conventional UHPC. In conclusion, the use of SF and ice crystal homogenization technology in RPC provides the great potential for developing sustainable construction materials and promoting carbon reduction strategies.

Unveiling the Impact of Absorbent Polymers on Self-healing Efficiency of Sludge-derived Capsules in Cementitious Composites

A novel green capsule for self-healing cementitious material using a combination of waste-based materials with an inorganic substance was developed. A mix of alum sludge (AS), a typical waste from the water industry, and calcium hydroxide were used as the primary healing agents. Also, two types of natural and synthetic absorbent polymers (AP), microcrystalline cellulose (MCC) and sodium polyacrylate (SPA), were added to the core mixture to assess their impact on the healing efficiency. The morphology of the produced capsules, the self-healing proficiency of cracked mortars, and the resulting healing materials were characterised. Outcomes revealed that cracks up to 400µm could be healed by the plain capsule. The closure width was dramatically increased to 500µm and 800µm with the inclusion of MCC and SPA, respectively, mainly in 3 days. The expansion, water retention, and bridging properties of the APs enhanced the sealing performance of the capsules by providing nucleation sites and increasing the reaction rates of core materials to generate further calcium-based products inside the cracks. Therefore, higher recovery rates of mechanical strengths, along with a significant reduction in water ingress were achieved. The main healing products were identified as calcite crystals, C-S-H, calcium silicate, and aluminium-bearing phases.

Physical-chemical performance of coal gasification slag with calcination activation utilized as supplementary cementitious material

The utilization of coal gasification slag to prepare supplementary cementitious materials has garnered considerable interest due to environmental friendliness. In this study, a calcination activation was carried out to enhance the pozzolanic activity of coal gasification slag, and serial sintering temperatures were conducted to activate coal gasification slag in this study. The coal gasification slags were characterized by particle size analyzer, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Furthermore, the pozzolanic activity of coal gasification slag was identified through dilution test and application in blended paste. Results showed that the calcination pretreatment effectively affected the particle size distribution and mineral composition. The setting time and hydration rate were prolonged by incorporating coal gasification slag. It was crucial that the coal gasification slag calcined under 400℃ performed the highest reactivity and its blend presented a 4.75% higher compressive strength than neat cement at 28 d curing. AFt and AFm were mainly generated by pozzolanic reaction, and a denser microstructure that porosity decreased by 26.76% was gained. The achievement of this study proved the feasibility of this treated coal gasification slag in building materials.

Effect of CO2 curing on mechanical and physical properties of the recycled aggregates containing silica fume

CO2 curing is a promising method for enhancing the properties of the recycled concrete aggregates (RCAs) due to its economic and environmental benefits. However, the knowledge about its effectiveness in improving the properties of aggregates derived from blended supplementary cementitious materials (SCMs) remains limited. This study explores the impact of CO2 curing on the mechanical and physical properties, mineralogical composition, and microstructural changes of recycled aggregates incorporating varying amounts of silica fume (SF). The results showed that upon the incorporation with 5wt% SF, CO2 curing increased the compressive strength of the aggregate samples by 17.9%. The microhardness improved from 50 to 56 HV with the addition of 10wt% SF. Moreover, CO2 curing modified the physical characteristics of the samples regardless of SF content. However, it caused mechanical degradation in samples containing 20wt% SF, at both marco- and micro-scale. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) revealed that higher SF dosages led to the formation of poorly crystallised CaCO3 during CO2 curing. Additionally, Low-field 1H nuclear magnetic resonance (LF-NMR), N2 adsorption/desorption, scanning electron microscopy (SEM), and thermodynamic models showed that the carbonation products enlarged the capillary pores, and reduced the solid volume of the hydration products. Those findings underscore the importance of calcium hydroxide in protecting against mechanical degradation in SF-blended recycled aggregates during CO2 curing. This study provides an insight of the carbonation of SF-blended composites, potentially accelerating the application of CO2 curing on RCAs.