A comprehensive review of deactivation and modification of selective catalytic reaction catalysts installed in cement kilns.

After the ultralow emission transformation of coal-fired power plants, cement production became China's leading industrial emission source of nitrogen oxides. Flue gas dust contents at the outlet of cement kiln preheaters were as high as 80-100 g/m3, and the calcium oxide content in the dust exceeded 60%. Commercial V2O5(-WO3)/TiO2 catalysts suitable for coal-fired flue gas suffer from alkaline earth metal Ca poisoning of cement kiln flue gas. Recent studies have also identified the poisoning of cement kiln selective catalytic reaction (SCR) catalysts by the heavy metals lead and thallium. Investigation of the poisoning process is the primary basis for analyzing the catalytic lifetime. This review summarizes and analyzes the SCR catalytic mechanism and chronicles the research progress concerning this poisoning mechanism. Based on the catalytic and toxification mechanisms, it can be inferred that improving the anti-poisoning performance of a catalyst enhances its acidity, surface redox performance-active catalytic sites, and shell layer protection. The data provide support in guiding engineering practice and reducing operating costs of SCR plants. Finally, future research directions for SCR denitrification catalysts in the cement industry are discussed. This study provides critical support for the development and optimization of poisoning-resistant SCR denitrification catalysts.

B-nZVI optimization of strength and heavy metal stability of lead-contaminated soil solidified by Portland cement.

Traditional cement solidifying or stabilizing heavy metal-contaminated sites often face issues like alkalinity loss, cracking, and poor long-term performance. Therefore, bentonite-supported nano-zero-valent iron (B-nZVI) was introduced to optimize the remediation effect of cement in this paper. The effects of B-nZVI, ordinary Portland cement (OPC), and B-nZVI + OPC on the chemical stability of heavy metals and the physical strength of lead-contaminated soil were compared using semi-dynamic leaching methods, BCR tests, unconfined strength analysis, and micro-assisted analysis. Results demonstrated that the addition of B-nZVI effectively enhanced the remediation efficacy of OPC on lead-contaminated soil. The combination of B-nZVI and OPC exhibited a synergistic repair effect, offering superior physical strength and chemical stability for lead remediation. B-nZVI facilitated the adsorption and enrichment of Pb2+, thereby reducing oxidizable lead and enhancing short-term stabilization. Meanwhile, OPC precipitation and silicate gelling stabilized exchangeable lead into the residual form, necessitating repeated hydration gelling. Additionally, B-nZVI's sealing effect via water absorption delayed the leaching of exchangeable lead, thereby reducing lead migration. Even with only 1% B-nZVI added to the 12% OPC base, the leaching amount of Pb2+ decreased significantly from 67.6 to 6.59 mg/kg after 7 d of curing. The unconfined strength of contaminated soil treated with the composite solidifying agent for 7 d was 12.87% higher than that of OPC alone, and for 28 d, it was 36.48% higher. This optimization scheme presents a promising approach for effective and sustainable remediation of heavy metal-contaminated sites.

Eco-friendly concrete: Combining treated wastewater and recycled aggregates.

The concrete industry is a significant consumer of drinking water and natural aggregates, such as sand and gravel. However, the scarcity of water and aggregate resources and the challenges associated with the disposal of construction and demolition waste prompted the exploration of alternative materials. This study investigates the feasibility of incorporating secondary treated wastewater from UASB reactors followed by trickling filters and mixed recycled aggregates as potential alternatives. To assess the viability of these alternatives, the study considered the replacement of 100% potable water with treated wastewater, as well as varying proportions of recycled gravel (20, 40, 60, 80, and 100%) and recycled sand (10, 20, 30, 40, and 100%). Physical and mechanical properties were negatively affected, but it was possible to reach compressive results over 40 MPa and splitting tensile strength over 4 MPa for almost all mixes. Regarding physical properties, the use of alternative materials caused poorer outcomes for density, water absorption, and air-void ratio. The limited magnitude of these detrimental effects indicates the potential of manufacturing concrete with the addition of combined treated wastewater and recycled aggregate as a viable strategy while enhancing reuse practices.

Alkalinity control in sludge propels the conversion of concrete slurry waste into micro- and nano-sized biogenic CaCO3.

The utilization of Bacillus sp. for the production of bio-CaCO3 in concrete crack repair and strength enhancement has attracted considerable attention. However, microbial-induced calcium carbonate precipitation (MICP) has yet to be explored as a precedent with activated sludge. Here calcium sourced from concrete slurry waste (CSW) and carbon from sludge microbial ß-oxidation under alkaline were used to generate micro/nano CaCO3. The results indicate that the main crystalline form of the generated precipitated particles is calcite, with a particle size ranging from 0.7 to 10 µm. Minimal heavy metals were found in the supernatant following settling. And at the optimum pH of 8.5-9, carbon capture reached 743 mg L-1, and CaCO3 production reached 1,191 mg L-1, and dominant phylum were Proteobacteria and Bacteroidota, with Thauera being a prevalent genus adept in ß-oxidation. Mass balance analysis showed that alkali promotes microbial ß-oxidation of organisms to produce CO2 and facilitate storage. Thus, the alkaline regulation of metabolism between microbe and CSW provides a novel way of sludge to initiate MICP.

Acoustic performance analysis of wooden structure building wall by integrating BIM technology and impedance tube method.

With the increasing demand for building acoustic performance, accurately evaluating the acoustic performance of building walls has become an important research topic. However, existing research has mostly focused on general building materials such as concrete, iron and steel, and glass. For wooden structure wall, due to the sound absorption performance of the materials themselves and the complexity of structural design, the analysis of their acoustic performance is still relatively weak. Moreover, there is a lack of quantitative description of their spectral characteristics and acoustic impedance. To analyze the acoustic performance of wooden structure building walls, Building Information Model (BIM) and impedance tube method were integrated to construct a building wall performance testing system with BIM technology. The impedance tube method was applied and testing functions for sound absorption and insulation performance were designed. The outcomes indicated that in the error test, the error range between the experimental group and the control group was [0.01, 0.18], indicating a high reliability of the experimental results. In the calculation of sound insulation of different specimens at different sound frequencies, when the frequency was 1600Hz, the sound insulation of the control group and experimental group was 65.30dB and 70.14dB, proving the effectiveness of the design method. The above results demonstrate the practicality of integrating BIM technology and impedance tube method in the acoustic performance analysis of wooden structure building walls. This study provides strong technical support for reducing the indoor environment of wooden buildings and improving the comfort of people's living environment.

Molecular Insights into Adhesion at Interface of Geopolymer Binder and Cement Mortar.

The degradation of concrete and reinforced concrete structures is a significant technical and economic challenge, requiring continuous repair and rehabilitation throughout their service life. Geopolymers (GPs), known for their high mechanical strength, low shrinkage, and durability, are being increasingly considered as alternatives to traditional repair materials. However, there is currently a lack of understanding regarding the interface bond properties between new geopolymer layers and old concrete substrates. In this paper, using advanced computational techniques, including quantum mechanical calculations and stochastic modeling, we explored the adsorption behavior and interaction mechanism of aluminosilicate oligomers with different Si/Al ratios forming the geopolymer gel structure and calcium silicate hydrate as the substrate at the interface bond region. We analyzed the electron density distributions of the highest occupied and lowest unoccupied molecular orbitals, examined the reactivity indices based on electron density functional theory, performed Mulliken charge population analysis, and evaluated global reactivity descriptors for the considered oligomers. The results elucidate the mechanisms of local and global reactivity of the oligomers, the equilibrium low-energy configurations of the oligomer structures adsorbed on the surface of C-(A)-S-H(I) (100), and their adsorption energies. These findings contribute to a better understanding of the adhesion properties of geopolymers and their potential as effective repair materials.

Assessing heavy metal contamination and health risks in playground dust near cement factory: exposure levels in children.

Heavy metals pose significant threats to human health, particularly children. This study aimed to assess heavy metal pollution in children's playgrounds using surface dust as an indicator and to ascertain the associated exposure levels and health risks. A total of one hundred twenty dust samples were collected from the surface of playground toys in areas surrounding the cement factory in Bursa, Türkiye, on precipitation-free days. The heavy metal content of the samples was analyzed using ICP-MS. The average total concentration of heavy metals ranged from 2401 to 6832 mg/kg across the sampling sites, with the highest values observed at PG4, PG3, PG2, and PG1, respectively. The most commonly detected heavy metals in the samples included Cr, Mn, Fe, Co, Cu, Zn, Pb, Cd, As, and Ni. Statistical analysis revealed significant positive correlations (p < 0.01) among Cr, Mn, Fe, Co, Cu, Pb, As, and Ni, with Cu and Pb also showing correlation (p < 0.05). PCA analysis identified three principal components explaining 79.905% of the total variance. The Hazard Quotient (HQ) and Hazard Index values for heavy metals were found to be below the safe threshold (HQ < 1). Quantitative techniques such as the geoaccumulation index and enrichment factor are used to determine pollution levels at the sampling sites. Overall, the results indicate that cement factories significantly contribute to heavy metal pollution, with observed values varying based on proximity to the emission source.

Effects of different roughness on Brazilian splitting characteristics of rock-concrete interface.

In order to study the tensile properties of rock-concrete composite disc specimens with different roughness, the surface of the gray-white sand specimen was artificially grooved, and six different roughness were configured. The test results show that the roughness size and roughness mode jointly control the tensile strength of the rock-concrete interface. With the increase of roughness, the tensile strength of the sample changes from the initial decrease to the increase and then decrease, and the tensile strength reaches the highest when the roughness is f3. The variation trend of pre-peak energy accumulation and post-peak energy accumulation of the sample is opposite, and the dissipation energy is closely related to the crack propagation strain. The roughness and crack closure strain, crack peak strain, crack propagation strain and crack closure stress show a sinusoidal periodic variation. The crack propagation strain is closely related to the change of dissipation energy. The change trend of crack closure stress is basically consistent with the change trend of tensile strength. Therefore, in the actual project, grasping the period of roughness variation and selecting the construction position can make the rock-concrete interface stable and get twice the result with half the effort.

Research on the expansion, shrinkage properties and fracture evolution of red clay stabilised with phosphogypsum under dry-wet cycles.

In view of the special engineering properties of red clay and the waste of phosphogypsum resources, the expansion and contraction deformation and fissure evolution of phosphogypsum stabilized red clay under different conditions were investigated by laboratory tests and image processing system. The research results show that: (1) the absolute expansion and absolute shrinkage of phosphogypsum stabilized red clay are positively correlated with the compaction degree, the number of dry and wet cycles and the cement dosage, and negatively correlated with the initial water content and the phosphogypsum dosage; (2) the fissure rate increases with the increase of the number of dry and wet cycles, and decreases with the increase of the initial water content, the compaction degree, the cement, and the phosphogypsum dosage; (3) The relationship among absolute expansion rate (absolute shrinkage), degree of compaction and fracture rate can be fitted by the equation f(x,y) = ax+by+cx2+dy2+e; (4) Phosphogypsum has an obvious inhibiting effect on the expansion, shrinkage and cracking of the mix. It is recommended that the cement mixing amount of 6% and phosphogypsum: red clay = 1:1~1:2 as roadbed filler.

Experimental and numerical study on the model of hybrid fiber phase change concrete frozen shaft wall.

In this study, phase change materials (PCMs) were innovatively incorporated into hybrid fiber concrete. The properties of PCMs, which absorb and release heat during phase transitions, enable the concrete to actively respond to complex and varying temperature environments. This integration reduces the internal temperature differentials within the concrete, thereby preventing temperature-induced cracks in deep wellbore structures. Through the temperature control model test of the frozen shaft wall, it can be seen that the hybrid fiber phase change concrete (HFPCC) significantly reduces the internal temperature difference, and the maximum temperature difference along the radial direction is 35.84% lower than that of benchmark concrete (BC). The numerical simulation results indicate that a moderate phase transition temperature should be selected in engineering. The phase change temperature should not be close to the ambient temperature and peak temperature. The peak temperature can be reduced by 9.32% and the maximum radial temperature difference can be reduced by 30.89% by selecting an appropriate phase change temperature. The peak temperature and radial maximum temperature difference are both proportional to the latent heat of phase change. The temperature control performance of phase change concrete can be further improved by increasing the latent heat of phase change materials.

An investigation on the physical properties of cementitious pastes modified with low dosage of waste glass powder and silica fume.

Portland cement (PC) production is among the industrial activities that most emit harmful gases. Its replacement to green binders turns into a timely issue to face the global restrictions due to climate changes. In this study, some properties of cementitious pastes prepared with waste packing glass powder (GP) and silica fume (SF) were characterized in line with a prefixed alkaline equivalent limit. These materials were obtained in Northeastern Brazil. Grinding operations used to produce GP into four size ranges ([45-75] µm, < 45 µm; [25-45] µm, < 25 µm) were disclosed. X ray diffraction showed that GP and SF substitutions did not change the hydration products commonly observed in PC pastes. The portlandite content measured with thermogravimetry was affected by GP size in both unitary and binary substitutions. The compressive strength measured after 56 days of curing was dependent on portlandite and void index contents measured in hardened pastes. Scanning electron microscopy coupled to energy dispersive spectroscopy were useful to show the effect of the particle size on the pozzolanic activity. It was found that 5% of PC replacement for GP < 25 µm was enough to raise the compressive strength by ~5%. For binary substitution, the strength increasing was ~ 20 %. The collectors of solid residues are the main players of waste glass recycling in Brazil. It is expected that the results of this study contribute to take out these workers from the fringes of the citizenship.

Evolutionary game and simulation analysis of construction waste recycling from the perspective of stakeholders.

In current construction waste resource management processes, the effect of government supervision is unclear, and illegal treatment and low-quality reproduction of recycling and reprocessing enterprises by construction units are common. To improve the degree of resource utilization of construction waste and deeply explore the role of its key influencing factors, a tripartite evolutionary game model of construction waste resource treatment in which the government, construction units, and recycling and reprocessing enterprises are the research objects that considers public participation factors to be established. MATLAB is used to simulate the sensitivity of relevant parameters. The results show that: (1) An increase in government fines can regulate the behavior of enterprises; (2) Low government subsidies are conducive to the development of a tripartite stability strategy; and (3) An increase in the cost difference between the two strategies of the enterprise will weaken its willingness to carry out green operations (and after the cost difference exceeds the threshold, the enterprise will refuse to carry out green operations); (4) The reputation value brought by the public and the additional value added by reputation under the contrast effect have an incentive effect on the enterprise and the government; and (5) The peak value of the inverted U-shaped curve of government strategy choice is affected by the degree of public participation. Therefore, the government should propose rectifications in terms of fines and subsidies, and both companies can use technological innovation to reduce costs. At the same time, it is necessary to raise stakeholders' awareness of resource utilization and encourage the public to actively participate in supervision. The research conclusions can provide a decision-making reference for improving the utilization of construction waste resources and the efficient treatment of construction waste resources.

The oxidative stress-dependent pulmonary inflammation of inhalable multi-walled carbon nanotube-containing nano-concrete dust and its comparison with conventional concrete dust and DQ12.

Nano-concrete, which is an admixture of nanomaterials in concrete recipes, has been investigated to overcome the limitations of existing concrete, such as its stability and strength. However, there is no information on the human health effects of broken-down dust released during the construction and demolition efforts. In this study, we prepared an inhalable fraction of multi-walled carbon nanotube-containing nano-concrete dust and performed comparative toxicity studies with conventional concrete dust and DQ12 using a rat intratracheal instillation model. Although the recipes for concrete and nano-concrete are entirely different, the pulverized dust samples showed similar physicochemical properties, such as 0.46-0.48 µm diameter and chemical composition. Both concrete and nano-concrete dust exhibited similar patterns and magnitudes, representing acute neutrophilic inflammation and chronic active inflammation with lymphocyte infiltration. The toxicity endpoints of the tested particles at both time points showed an excellent correlation with the reactive oxygen species levels released from the alveolar macrophages, highlighting that alveolar macrophages are the primary target cells and that the oxidative stress paradigm is the main toxicity mechanism of the tested particles. In addition, the toxicity potentials of both concrete and nano-concrete dust were more than 10 times lower than that of DQ12.

Mechanical performance and anisotropic analysis of rubberised 3D-printed concrete incorporating PP fibre.

The research investigates the effects of substituting sand with rubber particles derived from waste tyres-up to 40% by volume-and the inclusion of polypropylene (PP) fibres. Unlike steel fibres, which can cause operational challenges and surface irregularities in the printing process, PP fibres' flexibility integrates well within the concrete matrix. This integration ensures smooth extrusion and a high-quality surface finish, enhancing the printability of the concrete. The study's findings reveal that including rubber particles and PP fibres impacts the concrete's properties, showing a general decline in compressive and flexural strengths as the rubber content increases. Nevertheless, the PP fibre-enhanced mixtures maintain sufficient structural strength, demonstrating an anisotropic compressive strength above 30 MPa and a flexural strength of 4 MPa. These results underscore the feasibility of using rubberised 3D-printed concrete with PP fibres in sustainable construction practices, aligning with standards (ACI 318:2018) and contributing to eco-friendly and innovative construction methodologies.

Use of antioxidants to retard aging of bitumen: A review.

Oxidative aging of bitumen is an inevitable and irreversible phenomenon. Exposure to detrimental factors such as sunlight, oxygen, and UV radiations accelerates the aging of bitumen and bituminous pavement. The aging process induces hardening and embrittlement in bitumen, leading to premature pavement failure. Therefore, for constructing sustainable long-lasting pavements anti-aging additives are used. Among the available additives, the use of antioxidants has emerged as a promising solution to mitigate the aging of bitumen. The current review aims to summarise the existing literature for a comprehensive understanding of the effectiveness of these additives as aging inhibitors. It provides an overview of the chemical pathway involved during bitumen oxidation and various quantification techniques to measure the effect of aging. This review also highlights the potential use of antioxidants in bitumen and elaborates on the working mechanism of different types of antioxidants to prevent bitumen aging. Further, the effect of modification in bitumen at micro, macro, and mixture levels are discussed. Additionally, cost analysis and future prospects on the use of antioxidants for bitumen are presented.

Sustainable utilization of mine wastes in mortar production as a part of aggregates: a case study on calcareous wastes of Angoran lead and zinc mine.

This study investigated the feasibility of large-scale utilizing calcareous wastes (CW) of Angoran lead and zinc mine as aggregates in mortar production with the maximum possible substitution of natural aggregates. The main goal was to produce mortar (concrete with fine aggregates as fine as sand or smaller) from Angoran mine's calcareous wastes for maintenance in its underground spaces. Compared to concrete, such mortars with better fluidity can enter narrow spaces more easily. In addition, it can be used to build various structures around the mine. Therefore, multiple samples were prepared by replacing 0% (as the control sample), 20%, 40%, 60%, 80%, and 100% of natural aggregates with CW. Subsequently, compressive strength, flexural strength, water absorption, slump, and TCLP tests were conducted on these samples. The results revealed that the mortar sample with 80% CW exhibited significantly higher compressive strength at 3, 14, 28, and 56 days compared to both the control sample and other samples. Specifically, the compressive strength of this sample reached 35.5 MPa at 56 days, representing an 18.4% increase over the control sample. This indicates that the hydration of cement and the growth of C-S-H gel were enhanced. Analysis of the workability and slump of the samples indicated that as the percentage of natural aggregate replaced by CW increased, the fluidity of the mortar slightly decreased. In addition to mechanical properties like compressive strength, environmental aspects like heavy metal stabilization are also very important. So, TCLP tests conducted on the four heavy metals lead, zinc, copper, and cadmium demonstrated that the released amounts of these elements from all the samples were below the EPA standard limits. These findings confirm the effective stabilization of heavy metals in mortar samples. A comparison of SEM images revealed that the mortar sample made with 20% CW (with minimum compressive strength) exhibited a higher presence of ettringite compared to the sample made with 80% CW (with maximum compressive strength) after 28 days.

Application of solid waste materials in cold bitumen emulsion mixtures for cleaner pavement industry: a comprehensive review.

There is a global concern with continuous waste production, and efforts are underway to use these wastes in the construction sector. The negative effects of excessive waste production and the use of virgin materials and energy in Hot Mix Asphalt (HMA) construction are challenging and require attention. The right step towards developing resilient road infrastructure is using cold bitumen emulsion mixtures (CBEMs), a cold mix asphalt (CMA). A long-term fix to issues with waste generation and the creation of flexible pavements with HMA can be found by incorporating wastes into CMA. This work reviews the utilization of numerous wastes from different sectors (agricultural, industrial, construction and demolition, and municipal) that are well-known but underutilized and could be used as potential fillers in cold asphalt mixtures. Focus is given to the critical analysis of wastes' physiochemical characteristics and how these affected the effectiveness of mixtures against primary distresses like stability, stiffness, rutting, cracking, fatigue, and moisture susceptibility. Almost all waste materials incorporation reported enhancement in the mechanical performance of CBEM mixes concerning conventional CBEM mixes. The paper sums up the impact on various mechanical properties of CBEM mixes utilizing waste material filler, presents research gaps and a way forward to inspire researchers, and serves as a guideline for using waste materials as fillers in CBEM mixes. This will improve environmental quality and promote sustainability in the paving industry.

Advances in microbial self-healing concrete: A critical review of mechanisms, developments, and future directions.

The self-healing bioconcrete, or bioconcrete as concrete containing microorganisms with self-healing capacities, presents a transformative strategy to extend the service life of concrete structures. This technology harnesses the biological capabilities of specific microorganisms, such as bacteria and fungi, which are integral to the material's capacity to autonomously mend cracks, thereby maintaining structural integrity. This review highlights the complex biochemical pathways these organisms utilize to produce healing compounds like calcium carbonate, and how environmental parameters, such as pH, temperature, oxygen, and moisture critically affect the repair efficacy. A comprehensive analysis of recently published peer-reviewed literature, and contemporary experimental research forms the backbone of this review with a focus on microbiological aspects of the self-healing process. The review assesses the challenges facing self-healing bioconcrete, including the longevity of microbial spores and the cost implications for large-scale implementation. Further, attention is given to potential research directions, such as investigating alternative biological agents and optimizing the concrete environment to support microbial activity. The culmination of this investigation is a call to action for integrating self-healing bioconcrete in construction on a broader scale, thereby realizing its potential to fortify infrastructure resilience and sustainability.

Reported exposures to respirable crystalline silica during construction tasks and guidance for harmonizing future research.

Airborne respirable crystalline silica (RCS) has been a widely recognized hazard in the United States for nearly 100 years, yet it continues to pose a risk to construction tradespersons, among others. RCS exposures vary widely depending on site conditions and tools and materials used. The proper use of engineering, administrative, and personal protective equipment (PPE) controls can effectively reduce exposure to RCS. Historically, others have reviewed available RCS exposure data among construction trades and reported that there were considerable data gaps and variability that needed to be addressed. This current assessment aimed to synthesize available peer-reviewed exposure studies to determine potential RCS exposures during the use of common construction materials and evaluate to what extent data gaps and variability persist. Twenty-eight studies were identified that reported RCS exposure during construction tasks. After conversion to the unit of µg/m3, reported measurements from samples collected for varying durations ranged from 6.0 to 75,500 µg/m3 for work with concrete, 80 to 4,240 µg/m3 for work with brick, <59 to 10,900 µg/m3 for work with mortar, 90 to 44,370 µg/m3 for work with engineered stone, and 70 to 380 µg/m3 for work with roof tile. To better facilitate pooling data across studies, future researchers should report their sample duration, clarify how time-weighted average (TWA) exposure data are calculated, report the silica content of the material being manipulated, and specify whether samples were collected while the task was performed in isolation or on a worksite where other silica-containing materials were also actively handled. When reporting results as respirable quartz, it is important to note whether any other polymorphic forms of silica were detected. It is ultimately the employer's responsibility to train employees and monitor and control RCS exposures on construction worksites. To do this effectively, it is important to have a clear understanding of the tasks, materials, and site conditions where intervention is most urgently needed.