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Maintaining a high quality of water resources is always the top priority as water is highly essential in many aspects. However, contamination of water resources, especially due to the improper discharge of industrial wastewater is drawing attention. Poorly or untreated industrial wastewater is usually severely polluted with hazardous materials such as heavy metals. Therefore, this study intended to prepare a facile-fabricated porous geopolymer sphere and investigate its potential as an adsorbent for the removal of Ni(II) from wastewater. Porous geopolymer spheres can be beneficial for direct use in packed bed systems and can be retrieved easily upon being exhausted. Results demonstrated that at the equilibrium contact time of 48 h, the Ni(II) uptake capacity of porous geopolymer spheres was approximately 3.4 times greater than non-foamed geopolymer spheres. The large pore size and open porosity network that exist in porous geopolymer spheres enhance the adsorption performance as these factors allow easy penetration of Ni(II). The optimum pH was found to be pH 5. The pH can greatly affect the removal performance, where low pH results in competition for binding sites between H+ and Ni(II), while high pH induces the precipitation of Ni(OH)2. The maximum Ni(II) removal capacity obtained from the isotherm study was 19.94 mg/g.

This paper studies the role of CO2 treatment and the impact of particle size (

Recycled concrete aggregate (RCA) derived from demolition waste has been widely explored for use in civil engineering applications. One of the promising strategies globally is to incorporate RCA into concrete products. However, the use of RCA in high-performance concrete, such as self-consolidating concrete (SCC), has only been studied in the past decade. This paper summarizes recent publications on the use of coarse and/or fine RCA in SCC. As expected, the high-water absorption and porous structure of RCA have posed challenges in producing a high-fluidity mixture. According to an analysis of published data, a lower strength reduction (within 23% regardless of coarse RCA content) is observed in SCC compared with vibrated concrete, possibly due to the higher paste content in the SCC matrix, which enhances the weak surface layer of RCA and interfacial transition zone. Similarly, SCC tends to become less durable with RCA substitution although the deterioration can be minimized by using treated RCA through removing or strengthening the adhered mortar. To date, the information reported on the role of RCA in the long-term performance of SCC is still limited; thus, a wide range of research is needed to demonstrate the feasibility of RCA—SCC in field applications.

Recycled concrete aggregate (RCA) obtained from construction and demolition waste has been widely studied for its feasible uses to replace natural aggregate in different types of concrete products. For the past few decades, efforts have been made to modify or/and improve conventional mixing approaches for the use of RCA in concrete, such as two-stage mixing approach, paste wrapped recycled aggregate approach, etc. However, there was no direct comparison between these approaches. Therefore, this paper investigates the synergistic effect of pre-carbonated slurry and concrete mixing sequence on the performance of self-compacting modified mortar (SMM) containing RCA and aims to compare with other four mixing approaches. Fresh properties and mechanical strengths of SMM and the characterization of interfacial transition zone were studied and compared. Results proved that a denser matrix and an interfacial transition zone (ITZ) with a better quality reflected a better mechanical performance. Among five mixing approaches, SMM samples produced by pre-carbonation approach had slightly larger drying shrinkage, but exhibited enhanced flowability and reduced permeable voids. The compressive strength and flexural strength increased by about 12.3% and 12.0% compared to those made by normal mixing sequence. Backscattered electrons (BSE) images and Vickers microhardness results also revealed a denser interface between new cement matrix and RCA for the sample prepared with pre-carbonation approach.

Several attempts have been made to achieve considerable energy savings in concrete buildings by using phase change materials (PCMs). However, PCM leakage can affect both the PCMs’ efficiency and the overall properties of concrete which consequently limit their application in buildings. To overcome this issue, this study proposes to develop a novel core-shell structured phase change material aggregates (AGGsPCM) to capture and store solar energy in the building envelope for space heating and cooling applications. The thermophysical properties of AGGsPCM and the thermal performance of AGGsPCM in concrete panels under the actual climate conditions of southern China were tested. The obtained results demonstrate significant PCM leakage prevention and enhancement of the thermal performances of the concrete panel. The AGGsPCM-concrete panel was able to reduce the peak temperature by 1 °C, indicating improved thermal comfort and electricity saving potential. Better performances could be achieved by increasing the mPCMs content into AGGsPCM or by selecting a PCM with a more suitable phase transition temperature to allow a more efficient heat storage and release process.

The aim of this paper is to investigate the effect of carbonation on the microhardness and mechanical-related properties of carbonated and uncarbonated layers of cement pastes. The microhardness and mechanical property changes were examined 1 day after demolding and then 3, 7, 14, and 28 days with further CO2 and water curing. CO2 treatment yielded substantial impacts on the microstructure and densification of the surface layer of the paste by consuming calcium hydroxide and forming calcium carbonates. The maximum carbonation depth of 5 mm was recorded at 28 days, and the microhardness of the surface layer was significantly enhanced compared to the internal layer as well as uncarbonated paste samples. However, despite improved surface hardness, the overall compressive strength of carbonated sample was lower than that of water-cured samples, probably due to the non-preconditioning (to remove excess water for carbonation) of the carbonated samples and better hydration in the internal layer of the samples cured in water. In addition, the thin denser surface layer of the carbonated samples could decrease the cement hydration process. However, the denser and lower surface water absorption relation to CO2 treatment could facilitate long-term durability performance of concrete structures.

This paper presents an experimental investigation on lightweight aggregate mortars containing high volume cement replacement materials. For this purpose, expanded perlite (EP) and expanded vermicul...

Early-age carbonation can make a significant difference in the formation of hydration products in cement-based materials and alter the microstructural and mechanical performances. To understand in detail the impacts and their contribution to cement hydration, dry-mix cement pastes were exposed to instant carbonation with 0.04 %, 1%, 3%, 10 %, 20 % CO2 concentrations for 2 h prior to further water curing. By increasing the CO2 concentration, an increment in strength gain of samples at 2 h (right after early carbonation) as well as being prolonged by water curing at 1, 3, 7 days was noticed. This agrees with TGA and XRD results, demonstrating that the increases in CO2 concentration resulted in a higher carbonation reaction and hydration degree. 29Si NMR results also indicate that the higher the CO2 concentration the lower the calcium to silica ratio (Ca/Si); thus, there is a higher degree of polymerization to promote early hydration. It can be concluded that early carbonation of 2 h in particular with a high CO2 concentration can be beneficial for further cement hydration due to the consumption of calcium hydroxide (CH) and nuclei site effect of calcite crystals, resulting in better microstructural properties and mechanical performance.

Along with the growing development of countries around the world, there are huge amounts of construction and demolition works which produce large volumes of recycled concrete aggregate (RCA) and these are increasing over the past few decades. One of the more practical ways to manage the RCA wastes is through re-using them as aggregate to produce concrete. In this paper, 5–10 mm crushed RCA was used at different ratios (0, 25%, 50%, 75%, and 100% by weight) in modified self-compacting concrete (SCC) to study its feasibility as natural aggregate (NA) substitute. The results show that while the presence of RCA reduced the mechanical strengths and increased the water absorption as well as permeable voids of SCC, these effects were less pronounced compared to the use of RCA in normal vibrated concrete. Although the micro-hardness of the RCA-mortar interface was lower, the thickness of the ITZ was similar as that for NA-mortar interface. These findings suggested that SCC is a suitable matrix for incorporating RCA and based on the investigated properties, it is recommended that the maximum replacement level of RCA to be 25%.

The final publication is available at Springer via http://dx.doi.org/10.1617/s11527-022-01927-7 Many (inter)national standards exist to evaluate the resistance of mortar and concrete to carbonation. When a carbonation coefficient is used for performance comparison of mixtures or service life prediction, the applied boundary conditions during curing, preconditioning and carbonation play a crucial role, specifically when using latent hydraulic or pozzolanic supplementary cementitious materials (SCMs). An extensive interlaboratory test (ILT) with twenty two participating laboratories was set up in the framework of RILEM TC 281-CCC ‘Carbonation of Concrete with SCMs’. The carbonation depths and coefficients determined by following several (inter)national standards for three cement types (CEM I, CEM II/B-V, CEM III/B) both on mortar and concrete scale were statistically compared. The outcomes of this study showed that the carbonation rate based on the carbonation depths after 91 days exposure, compared to 56 days or less exposure duration, best approximates the slope of the linear regression and those 91 days carbonation depths can therefore be considered as a good estimate of the potential resistance to carbonation. All standards evaluated in this study ranked the three cement types in the same order of carbonation resistance. Unfortunately, large variations within and between laboratories complicate to draw clear conclusions regarding the effect of sample pre-conditioning and carbonation exposure conditions on the carbonation performance of the specimens tested. Nevertheless, it was identified that fresh and hardened state properties alone cannot be used to infer carbonation resistance of the mortars or concretes tested. It was also found that sealed curing results in larger carbonation depths compared to water curing. However, when water curing was reduced from 28 to 3 or 7 days, higher carbonation depths compared to sealed curing were observed. This increase is more pronounced for CEM I compared to CEM III mixes. The variation between laboratories is larger than the potential effect of raising the CO2 concentration from 1 to 4%. Finally, concrete, for which the aggregate-to-cement factor was increased by 1.79 in comparison with mortar, had a carbonation coefficient 1.18 times the one of mortar. The authors would like to thank HeidelbergCement AG for the supplied cements and the chemical and physical analysis. H. Vanoutrive has received internal funding from KU Leuven which made this interlaboratory study possible. P. Van den Heede, N. Alderete and Z. Liu are funded by the Research Foundation—Flanders (FWO) (project No. G062720N, 12ZG820N and G0F3619N). The financial support of FWO is gratefully acknowledged. Peer Reviewed This report has been prepared by members of the working groups 1 and 2 within a framework of RILEM TC 281-CCC ‘‘Carbonation of concrete with supplementary cementitious materials’’ and further reviewed and approved by all members of the RILEM TC 281-CCC. TC Membership Chair: Prof. Nele De Belie. Deputy Chair: Prof. Susan Bernal Lopez. Members: Natalia Alderete, Carmen Andrade, Ueli Angst, Tushar Bansal, Ve´ronique Baroghel-Bouny, Muhammed P.a. Basheer, Nele De Belie, Susan Bernal Lopez, Hans D. Beushausen, Leon Black, Aires Camöes, Servando Chincho´n-Paya, Özlem Cizer, Gisela Paola Cordoba, Martin Cyr, Patrick Dangla, Yuvaraj Dhandapani, Katja Dombrowski-Daube, Vilma Ducman, Yogarajah Elakneswaran, Jan Elsen, Juan Manuel Etcheverry, Miren Etxeberria, Ana Maria Fernandez-Jimenez, Lander Frederickx, Isabel Fuencisla Saez del Bosque, Cassandre Le Galliard, Ine`s Garcia Lodeiro, Daniel Geddes, Christoph Gehlen, Mette Geiker, Guoqing Geng, Bahman Ghiassi, Gregor Gluth, Cyrill Grengg, Elke Gruyaert, R. Doug Hooton, Bruno Huet, Andres Idiart, Ivan Ignjatovic, Kei-Ichi Imamoto, Shiju Joseph, Siham Kamali-Bernard, Antonis Kanellopoulos, Xinyuan Ke, Sylvia Kessler, Heejeong Kim, Arto Ko¨lio¨, Juan Li, Ning Li, Tung Chai Ling, Qing-Feng Liu, Zhiyuan Liu, Barabare Lothenbach, Isabel Martins, Jose´-Fernando Martirena-Hernandez, César Medina Martinez, Fabrizio Moro, Shishir Mundra, Marija Nedeljkovic, Kolawole A. Olonade, José Pacheco, Christian Paglia, Angel Paloma, Ravi Patel, Janez Perko, Quoc Tri Phung, John L. Provis, Francisca Puertas, Nuria Rebolledo, Marlene Sakoparnig, Javier Sancez Montero, Francesco Santoro, Sriram Pradeep Saridhe, Karen Scrivener, Marijana Serdar, Zhenguo Shi, Kosmas K. Sideris, Ruben Snellings, Matteo Stefanoni, Charlotte Thiel, Karl-Christian Thienel, Michael D.A. Thomas, Ilda Tole, Luca Valentini, Philip Van den Heede, Hanne Vanoutrive, Yury Andre´s Villagran Zaccardi, Talakokula Visalakshi, Anya Vollpracht, Stefanie Von Greve-Dierfeld, Brant Walkley, Fazhou Wang, Ling Wang, Jinxin Wei, Lia Weiler, Bei Wu, Yan Yao, Guang Ye, Maciej Zaja˛c, Zengfeng Zhao, Semion Zhutovsky. Hanne Vanoutrive and Philip Van den Heede have contributed equally to this work.

In this study, municipal solid waste incineration fly ash (MSWIFA) was pretreated with CO

In light of concerns relating to improper waste disposal and resources preservation, reclamation of the discarded glass in construction materials had been extensively carried out since 1963. In the past decade, although more than 100 papers associated with the use of glass powder (GP) in the micron level scale were published, comprehensive review of all practical applications in cement-based materials and construction products is not available. This paper therefore provides a summary of the body of knowledge on the interaction and effects of using GP in cement-based and extended construction materials. This review concludes that GP is an innovative and promising eco-supplementary cementitious material. Beyond that, use of GP is demonstrated to be potentially beneficial as a precursor in geopolymer and suitable for manufacturing eco-cement, artificial lightweight aggregate and composite phase change material. The multiple applications of GP are seen as an important step towards waste glass recycling as a sustainable construction material and for the overall betterment of the industry.

Carbonation for the curing of cement-based materials has been gaining increased attention in recent years, especially in light of emerging initiatives to reduce carbon dioxide (CO2) emissions. Carbonation method or CO2 curing is founded on the basis of the reaction between CO2 and cement products to form thermally stable and denser carbonate, which not only improves the physical and mechanical properties of cement-based materials, but also has the ability to utilize and store CO2 safely and permanently. This study aims to assess the effect of CO2 curing technology on the high-temperatures performance of cement blocks. Upon molding, dry-mix cement blocks were cured under statically accelerated carbonation condition (20% CO2 concentration with 70% relative humidity) for 28 days, followed by exposure to elevated temperatures of 300 °C to 800 °C in order to comprehensively study the principal phase changes and decompositions of cement hydrates. The results indicated that CO2 curing improved the performance of cement blocks, such as enhancement in the residual compressive strength and reducing the sorptivity. At 600 °C, the scanning electron microscopy (SEM) revealed a denser microstructure while thermal analisis and X-ray diffraction (XRD) analysis also clearly demonstrated that higher amounts of calcium carbonate were present in the cement blocks after CO2 curing, suggesting better high-temperature performance compared to natural cured cement blocks. In general, an improved high-temperature performance, specifically at 600 °C of the dry-mixed cement blocks was demonstrated by adopting the CO2 curing technology. This confirms the potential of utilizing CO2 curing technology in not only improving quality of cement blocks, new avenue for storing of CO2 in construction material can be realized at the same time.

The high temperature properties of glass aggregates (i.e. thermal conductivity and melting temperature) play important roles on the performance of the glass concrete. It has been known that when glass aggregates are incorporated in concrete and the concrete is subjected to elevated temperatures, the melted glass surface could act as a binding material to mitigate the high temperature damages in the interfacial transition zone (ITZ) between the cement paste and the glass aggregates. In this study, the influence of the particle size of the glass aggregates on the properties of dry-mix glass concrete blocks after exposure to elevated temperatures of up to 800 °C was investigated. In order to avoid the influence of the pozzolanic reaction of the glass, glass particles of

Paraffin as a phase change material showed a great potential to promote energy efficiency in buildings due to its unique thermo-physical properties. However, its low thermal conductivity can negatively impact the charging-discharging process and affect the heat transfer efficiency. Previously, many researchers have focused on using shape-stabilized materials and additives to form paraffinic phase change materials (PPCM) with a high thermal conductivity. However, these techniques resulted in the reduction of the total amount of paraffin incorporated into the PPCM and thus lowered the overall thermal efficiency. Based on the analyzed literature data, this paper suggests that the paraffin content in the PPCM should be equal or higher than 50.0% to achieve better performances. Therefore, exploring novel composites and additives to form thermally stable and efficient PPCM with enhanced heat transfer could be a topic of interest to encourage and implement more sustainable practices in the building industry.

Steel slag is a calcium-rich but hydration-inactive material. Accelerated carbonation is an effective method to activate its reactivity. In this study, a kind of widely available steel slag, basic oxygen furnace slag (BOFS), was used as the sole material for fabricating dry-mixed compacts; the interactions of casting pressure, water to solid (w/s) ratio and carbonation duration were investigated in terms of their effects on CO2 uptake and compressive strength, with the emphasis of finding the parametric interdependence and the optimized parameters. The results suggested that the casting pressure and water addition determined the framework i.e., initial air voids for BOFS activation. The initial air voids inherent in different sample preparation scenarios described the CO2 uptake and strength behavior. It was found that the optimal casting pressure and w/s for BOFS carbonation to achieve the highest compressive strength (45.57 ± 2.10 MPa) and sequestrate considerable amount of CO2 (9.56 wt%) were 15 MPa and 0.13, respectively. Additionally, adopting optimized parameters enabled the exemption of preconditioning and could simplify the curing process at plant setting. It was also highlighted in this study that the maximized density did not correspond to the highest strength since over compactness of the matrix could restrain the CO2 diffusion for carbonation. Also, portlandite, brucite, larnite, tricalcium aluminate, brownmillerite and some amorphous phases were the critical reactive phase towards carbonation while metal oxides and their solid solution were inert. This study provided insight into the development of CO2-activated BOFS-based construction products towards either environment- or property highlighted purposes.

Residual hydrated cement powder (HCP) produced from recovering recycled concrete is usually restricted from being directly reused in concrete due to its high water absorption and porous str...