Search Results (303)

Concrete is a cornerstone material in the construction industry owing to its versatile performance; however, its inherent brittleness, low tensile strength, and poor permeability resistance limit its broader application. Graphene, with its exceptional thermal conductivity, stable lattice structure, and high specific surface area, presents a transformative solution to these challenges. Despite its promise, comprehensive studies on the multifunctional properties and underlying mechanisms of graphene-enhanced concrete remain scarce. In this study, we developed a novel concrete composite incorporating cement, coarse sand, crushed stone, water, and graphene, systematically investigating the effects of the graphene dosage and curing duration on its performance. Our results demonstrate that graphene incorporation markedly improves the material’s density, brittleness, thermal conductivity, and permeability resistance. Notably, a comprehensive analysis of scanning electron microscopy (SEM) images and thermogravimetric (TG) data demonstrates that graphene-modified concrete exhibits a denser microstructure and the enhanced formation of hydration products compared to conventional concrete. In addition, the graphene-reinforced concrete exhibited a 44% increase in compressive strength, a 0.7% enhancement in the photothermal absorption capacity, a 0.4% decrease in maximum heat release, a 0.8% increase in heat-storage capacity, and a 200% reduction in the maximum penetration depth. These findings underscore the significant potential of graphene-reinforced concrete for advanced construction applications, offering superior mechanical strength, thermal regulation, and durability. Full article

This study investigates the effects of incorporating recycled concrete powder (RCP) as a supplementary cementitious material in Portland cement composites at replacement levels of 5–30% by weight. A comprehensive characterization using isothermal calorimetry, electrical conductivity measurements, thermogravimetric analysis, FT-IR spectroscopy, and scanning electron microscopy revealed that RCP modified the hydration behavior and microstructural development. The results showed a linear 16.5% reduction in the total heat of hydration (from 145.38 to 121.44 J/g) at 30% RCP content, accompanied by a 26.5% decrease in peak electrical conductivity (19.16 to 14.08 mS/cm) and delayed reaction kinetics. Thermal analysis demonstrated an increased stability of hydration products, with portlandite decomposition temperatures rising by up to 10.8 °C. Microstructural observations confirmed the formation of denser but more amorphous C–S–H phases alongside increased interfacial porosity at higher RCP contents. The study provides quantitative evidence of RCP’s dual functionality as both an inert filler and a nucleation agent, identifying an optimal 20–25% replacement range that balances performance and sustainability. These findings advance the understanding of construction waste utilization in cementitious materials and provide practical solutions for developing more sustainable building composites while addressing circular economy objectives in the construction sector. Full article

Ground granulated blast-furnace slag (GGBS), a waste product generated during steel production, can be added as a substitute for cement in concrete to mitigate the environmental impact of the cement and steel industries. However, the use of GGBS is limited because it decreases the early strength development of cement or concrete. This study evaluated the performance of incorporating synthesized C-S-H nanoparticles to enhance the compressive strength, early hydration, and microstructure of cement composite. The synthesized C-S-H nanoparticles were produced at standard atmospheric pressure and room temperature. Heat of hydration, X-ray diffraction, and thermogravimetric analyses were conducted to investigate the hydration and mechanical properties of the cement containing the C-S-H nanoparticles. Further, mercury intrusion porosimetry was conducted to examine the pore structures. The experimental finding demonstrated that adding C-S-H nanoparticles accelerated the early hydration progress in the cement composites, thereby increasing their initial compressive strength. Full article

To address the challenges of concrete construction in polar regions, this study investigates the feasibility of fabricating cement-based materials under severely low temperatures using electric-induced heating curing methods. Cement mortars incorporating fly ash (FA-CM), ground granulated blast furnace slag (GGBS-CM), and metakaolin (MK-CM) were cured at environmental temperatures of −20 °C, −40 °C, and −60 °C. The optimal carbon fiber (CF) contents were determined using the initial electric resistivity to ensure a consistent electric-induced heating curing process. The thermal profiles during curing were monitored, and mechanical strength development was systematically evaluated. Hydration characteristics were elucidated through thermogravimetric analysis (TG), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) to identify phase compositions and reaction products. Results demonstrate that electric-induced heating effectively mitigates the adverse effect caused by the ultra-low temperature constraints, with distinct differences in the strength performance and hydration kinetics among supplementary cementitious materials. MK-CM exhibited superior early strength development with strength increasing rates above 10% compared to the Ref. specimen, which was attributed to the accelerated pozzolanic reactions. Microstructural analyses further verified the macroscopic strength test results that showed that electric-induced heating curing can effectively promote the performance development even under severely cold environments with a higher hydration degree and refined micro-pore structure. This work proposes a viable strategy for polar construction applications. Full article

Researchers are exploring eco-friendly alternatives to Portland cement, such as geopolymers, which require reactive aluminosilicate sources. This study evaluated the reactivity of six calcined clays (heated at 700 °C) in the presence of an alkaline solution. The calcined samples from kaolinite quarries in Kamboinsé, Kandarfa, Saaba, Sabcé, Selogo, and Tougou were subjected to chemical and mineralogical analyses. The results indicated a high aluminosilicate content (>50%), with kaolinite reaching up to 83.1%, and an amorphous fraction of up to 31.8%, a key factor influencing reactivity. Geopolymer pastes, prepared using a 12 M NaOH solution and each of these calcined clays, exhibited varying setting times: 24 h for the Saaba clay (the most reactive) compared with 48 h or even up to 7 days for the least reactive. The evaluation of the compressive strength of the geopolymer pastes revealed varying performances depending on the composition of clay. The Saaba clay showed the highest strength (14 MPa), attributed to its high kaolinite content (83.1%) and amorphous phase (31.8%), and thus reactivity. This was followed by Kamboinsé with 10.5 MPa (58.3% kaolinite; 24.3% amorphous phase), Selogo with 4.6 MPa (42.9%; 20.4%), Tougou with 1.4 MPa (44.1%; 20.4%), Kandarfa with only 0.7 MPa (31.3%; 19.2%), and Sabcé, which did not set with 0 MPa (24.1%; 13.7%). A discussion between the chemical and mineralogical compositions of the different clays and the mechanical characteristics of the synthesized pastes highlighted the importance of kaolinite content and its amorphous nature on the reactivity of the geopolymer binders. These findings highlight its potential for applications such as stabilized bricks or geopolymer concrete, offering a low-carbon alternative to traditional materials. Full article

Thermal Energy Storage (TES) technologies improve solar power dispatchability by addressing the important challenge of energy intermittency. Sensible heat energy storage technology using materials based on Ordinary Portland Cement (OPC) is the simplest and most economical. However, the operation of these materials is limited to temperatures below 400 °C due to the structural degradation of OPC at this temperature. This paper investigates the design and development of inorganic polymers based on Construction and Demolition Waste (CDW) as a sustainable, low-cost, and environmentally friendly alternative to OPC-based materials for high-temperature sensible TES applications. Based on the ternary systems Na₂O-SiO₂-Al₂O₃ and K₂O-SiO₂-Al₂O₃, representative compositions of CDW-based inorganic polymers were theoretically designed and evaluated using the thermochemical software FactSage 7.0. The experimental verification of the theoretically designed inorganic polymers confirmed that they can withstand temperatures higher than 500 and up to 700 °C. The optimized materials developed compressive strength around 20 MPa, which was improved with temperatures up to 500 °C and then decreased. Moreover, they presented thermal capacities from 600 to 1090 J kg⁻¹ °C ⁻¹, thermal diffusivity in the range of 4.7–5.6 × 10⁻⁷ m² s⁻¹, and thermal conductivity from 0.6 to 1 W m⁻¹ °C⁻¹. These properties render the developed inorganic polymers significant candidates for TES applications. Full article

In this study, multi-walled carbon nanotubes (MWCNTs) were uniformly applied to polyethylene terephthalate (PET) film using a bar-coating method to fabricate conductive thin films, and their transmittance, surface morphology, and effects on the heating and electrical properties of cement composites were analyzed. The experimental parameters considered were the mixing method, MWCNT concentrations, use or absence of coating films, applied voltages, and electrode spacings. Considering these parameters, the cement composites were divided into a total of four groups and then fabricated. Group 1 is a method for fabricating plain cement composites (PCCs), while Group 2 is a method for fabricating PCC using only MWCNT-coated films. Group 3 is a method for fabricating PCC by adding only MWCNT dispersion, and finally, Group 4 is a method for fabricating PCC using both MWCNT dispersion and MWCNT-coated films. Furthermore, field emission scanning electron microscope (FE-SEM) image analysis confirmed that MWCNT were evenly distributed across the entire front surface of the PET film and formed a dense network structure. The experimental results of cement composites using these showed that when both MWCNT dispersion and MWCNT-coated films were used, the electrical resistance was significantly reduced and the heating performance was improved. In particular, when the electrode spacing was 40 mm and the applied voltage was 30 V, the MDCF-0.75 specimen exhibited the highest heating performance and the lowest electrical resistance. Full article

The cement industry faces increasing energy costs and environmental pressures, driving the adoption of alternative fuels derived from waste materials. In Togo, approximately 350,000 t of end-of-life tires (ELT) are generated annually, creating significant environmental and health hazards through uncontrolled disposal and burning practices. This study investigated the technical feasibility and economic viability of incorporating waste tires as an alternative fuel in cement manufacturing. Tire-derived fuel (TDF) performance was evaluated by comparing pre-processed industrial tires with unprocessed ones, focusing on clinker production loss, elemental composition, heating values, and bulk density. The results demonstrate that TDF exhibits superior performance characteristics, with the highest heating values, and meets all the required specifications for cement production. In contrast, whole tire incineration fails to satisfy the recommended criteria, necessitating blending with conventional fuels to maintain clinker quality and combustion efficiency. The investigation revealed no significant adverse effects on production processes or clinker quality while achieving substantial reductions in nitrogen and sulfur oxide emissions. The experimental results were compared with the theoretical burnout times to optimize the shredding operations and injection methods. However, several challenges remain unaddressed, including the absence of streamlined handling processes, limited understanding of long-term ecological and health impacts, and insufficient techno-economic assessments. Future research should prioritize identifying critical aging points, investigating self-rejuvenating behaviors, and quantifying long-term environmental implications. These findings provide a foundation for developing computational models to optimize the mixing ratios of alternative and fossil fuels in cement manufacturing, offering significant environmental, economic, and societal benefits for the cement industry. Full article

This study investigates the early hydration characteristics and kinetics of ordinary Portland cement (OPC) and calcium sulfoaluminate cement (CSA) composite pastes. The hydration mechanisms of OPC-CSA systems with different proportions are analyzed through zonal analysis and the Krstulović–Dabić method. The experimental results show that in OPC-dominated systems, an appropriate amount of CSA promotes the rapid hydration of ye’elimite and optimizes the cumulative hydration heat and pore structure. However, excessive CSA inhibits hydration due to alkalinity imbalance. In CSA-dominated systems, 10% OPC increases the alkalinity, promoting ye’elimite to hydrate into ettringite. Higher OPC content hinders the hydration process due to ion concentration imbalance. The kinetics model indicates that CSA accelerates the interfacial reaction and diffusion in the OPC system, while OPC reduces the overall hydration rate of the CSA system. Microscopic analysis confirms that the composite system improves the pore structure through mineral interaction. In the OPC-dominated area, the pore structure is mainly composed of small and dense pores. In the CSA-dominated area, the characteristics of large pores are affected by the expansion properties of CSA and hydration heat. This study constructs a coupling mechanism of alkalinity regulation and crystal nucleus generation, providing a theoretical basis for the design of high-performance composite cement materials. Full article

A structure of composite cement with 15 wt.% thermally activated clay shales has been developed. The phase composition and properties of aluminosilicate rocks of the Kazakhstan deposits—Mynaral and Kuyuk—have been studied. It has been shown that aluminosilicates are related to clay shales by their composition. The regularities of thermal activation processes of aluminosilicates have been established, and it has been shown that pozzolanic activity increases for all compositions with an increase in the heat treatment temperature from 700 to 900 °C. The clay shale of the Mynaral deposit is characterized by the highest activity. The physicomechanical properties of the obtained composite cements–including Portland cement clinker, gypsum, and thermally activated clay shale—have been studied. It has been shown that when replacing up to 15 wt.% Portland cement clinker with thermally activated clay shales, there is no decrease in the strength properties of the composite cement. The obtained results allow us to consider heat-treated clay shales as active mineral additives. Full article

The use of binders in construction dates back to antiquity, with lime-based materials historically playing a significant role. However, the 20th century brought the widespread replacement of lime with Portland cement (PC), for its superior mechanical strength, durability, and faster setting time. Despite these advantages, the restoration of historic masonry structures has revealed the incompatibility of PC with traditional materials, leading to damage due to increased brittleness, stiffness, and reduced permeability. Consequently, lime mortars remain the preferred choice for heritage conservation. To enhance their durability while maintaining compatibility with historic materials, the incorporation of carbon-based nanoparticles has gained attention. This study investigated the impact of the carbon nanotubes (CNTs) additive on two types of lime-based mortars, calcium lime (CL) and hydraulic lime (HL), evaluating structural and mechanical properties, heat transport characteristics, and hygric properties after modification by CNTs with dosages of 0.1%, 0.3%, and 0.5% binder weight. Incorporation of CNTs into CL mortar resulted in an increase in mechanical strength and slight reduction in heat transport and water absorption due to changes in porosity. The addition of CNTs into HL mortars reduced porosity, pore size distribution, and other depending characteristics. The utilisation of CNTs as an additive in the investigated lime-based composites has been identified as a potentially effective approach for the reinforcement and functionalisation of these composite materials, as they exhibited enhanced mechanical resistance while preserving their other engineering properties, making them well suited for use as compatible mortars in building heritage repairs. Full article

Geopolymers possess good mechanical properties and durability, and their partial replacement of traditional Portland cement is noteworthy for promoting the development of low-carbon building materials. To clarify the influence mechanism of the mechanical properties of slag-fly ash-based geopolymer mortar, this paper investigated the hydration heat, composition, and morphology of hydration products with various contents and moduli of waterglass. The results showed that the compressive strength of geopolymer mortar increased with increasing waterglass content, and first rose and then fell as the waterglass modulus raised, while its flexural strength increased and then decreased with the growth in both. The compressive and flexural strength of geopolymer mortar with 1.2-modulus waterglass at 20 wt% cured for 28 days were 88.4 MPa and 9.0 MPa, respectively. The hydration temperature and cumulative hydration heat of geopolymer mortar was elevated with the increase in waterglass content, and declined with the rising waterglass modulus. The hydration products of the geopolymer consisted of dense amorphous and flocculent structures wrapped around each other. The microstructure of the geopolymer cured for 3 days was loose when the content of 1.4-modulus waterglass was 5 wt%. The relative areas of the flocculation in the geopolymer cured for 28 days increased while the waterglass modulus was greater than 1.4, forming an interface with the dense amorphous structure generated during the early hydration stage, leading to a decrease in its mechanical properties. Therefore, it is recommended for slag-fly ash geopolymer mortar that the waterglass modulus is between 1.2 and 1.4 and its content is no less than 10 wt% to ensure suitable mechanical properties. This study also provided a referenceable time period for the pouring and operation of the engineering application of slag-fly ash-based geopolymer repair mortar. Full article

Titanium nitride (TiN) is a widely used industrial hard coating material, known for its excellent hardness and chemical stability. However, its relatively high coefficient of friction (COF) often leads to interfacial heat accumulation and adhesive wear during service, limiting its applicability in high-temperature tribological environments. To enhance its tribological performance, a TiN–WS₂ soft–hard composite coating was fabricated on cemented carbide substrates using reactive co-sputtering magnetron deposition. By adjusting the sputtering parameters and target power ratio, a synergistic deposition of the hard (TiN) and lubricating (WS₂) phases was achieved and compared with a pure TiN coating. The results revealed that the incorporation of WS₂ significantly reduced the COF at both room temperature (25 °C) and an elevated temperature (200 °C), with the average values decreasing from 0.61 to 0.39 at 25 °C and from 0.53 to 0.36 at 200 °C. A white light interferometry analysis showed that the TiN–WS₂ coating exhibited narrower wear tracks and less surface damage than TiN at elevated temperatures, demonstrating superior friction-reducing and wear-resistant capabilities. In terms of mechanical properties, the composite coating showed a reduction in the hardness, the reduced elastic modulus (Er), and the adhesion strength by 27.3%, 19.8%, and 9.5%, respectively, compared to pure TiN. These findings indicate that the introduction of a quantitatively controlled lubricating WS₂ phase allows for a balance between nanoscale hardness and wear resistance, offering promising potential for engineering applications under complex working conditions. Full article

Alongside technological advancement, there is a growing need for materials that are easier to obtain and process and that offer multiple uses, thereby reducing environmental impact. Such materials are generally subject to mechanical, resistance and fatigue studies, often without considering their thermal properties, which could potentially expand the range of applications for the studied compound. The current study aims to analyze possible fluctuations and deviations from linearity in temperature flow curves, as well as their impact on the conductivity coefficient. These studies are conducted on a new type of panel made of fiberglass, a low-cost material with significant recycling potential, using foam elements recycled from packaging insulations and a cement biding mixture. This study considers the time variation of the different thermal coefficients and the temperature curves obtained from the experimental measurements. These data are analyzed and used to simulate heat variation in order to observe the heat flux fluctuations within the plate. The results suggest that the proposed composite plate can serve as an alternative to classical insulating panels. Full article

This study investigates the effects of nano-metakaolin and fly ash contents, the water-to-binder ratio, and other factors on autogenous shrinkage, internal relative humidity, and resistivity. Hydration heat, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry, and other micro-testing techniques were employed to characterize the hydration process, phase composition, and pore structure of cementitious materials. The experimental results show that lower water-to-binder ratios lead to faster and more significant decreases in internal relative humidity within cement pastes. When nano-metakaolin and fly ash are combined, fly ash effectively mitigates the excessive autogenous shrinkage caused by nano-metakaolin under low water-to-binder ratios. Lower water-to-binder ratios result in faster resistivity growth in cement pastes. Specifically, when the water-to-binder ratio decreased from 0.35 to 0.30 and 0.25, the 28-day resistivity of nano-metakaolin–fly ash cement pastes increased by 8.08% and 7.33%, respectively. Additionally, the water-to-binder ratio has a relatively minor impact on the autogenous shrinkage and resistivity of fly ash cement pastes. Higher water-to-binder ratios accelerate the hydration rate and increase porosity, leading to the gradual coarsening of pore distributions. When the water-to-binder ratio increased from 0.25 to 0.35, the 28-day porosity increased by 50.31%. In hydration systems with lower water-to-binder ratios, internal relative humidity decreases more rapidly, pores become refined, capillary stresses increase, and autogenous shrinkage behavior becomes more pronounced. This research provides a practical foundation for studying the early-age autogenous shrinkage behavior of cementitious materials. Full article