Search Results (97)

Xanthan gum (XG) has potential application prospects as a biopolymer in soil reinforcement engineering. However, there remains a lack of relevant research on its influence on the mechanical properties, microscopic mechanism, and pH value changes in clay. In this study, the effects of different XG dosages (0%, 5%, 10%, 15%, and 20%) on the microscopic mechanism, pH value, and mechanical strength of clay at the 7-day curing age were investigated through tests including Zeta potential, infrared spectroscopy, scanning electron microscopy (SEM), pH value, unconfined compressive strength, and triaxial shear strength. The results show that the addition of XG can not only promote charge exchange to generate hydrogen bonds and increase the bonding force between clays but can also form flocculent aggregates between the matrices, cementing the clay, filling the pores, and reducing the porosity of the samples. It can significantly increase the mechanical strength of the sample. When the content of XG is 20%, the unconfined compressive strength (UCS) and cohesion of the sample reach their maximum, increasing by 296% and 806%, respectively, compared with the reference group without XG. The conclusions drawn from this research can not only provide a theoretical reference for improving soft clay foundations but also expand the application research of XG in clay. Full article

Despite the availability of various materials for chimney applications, ongoing research seeks alternatives with improved thermal and chemical resistance. Geopolymers are a promising solution, exhibiting exceptional resistance to high temperatures, fire, and aggressive chemicals. This study investigates fly ash-based lightweight geopolymer concretes that incorporate expanded clay aggregate (E.C.A.), perlite (P), and foamed geopolymer aggregate (F.G.A.). The composites were designed to ensure a density below 1200 kg/m³, reducing overall weight while maintaining necessary performance. Aggregate content ranged from 60 to 75 wt.%. Physical (density, thickness, water absorption), mechanical (flexural and compressive strength), and thermal (conductivity, resistance) properties were evaluated. F.G.A. 60 achieved a 76.8% reduction in thermal conductivity (0.1708 vs. 0.7366 W/(m·K)) and a 140.4% increase in thermal resistance (0.1642 vs. 0.0683). The F.G.A./E.C.A./P 60 mixture showed the highest compressive strength (18.069 MPa), reaching 52.7% of the reference concrete’s strength, with a 32.3% lower density (1173.3 vs. 1735.0 kg/m³). Water absorption ranged from 4.9% (REF.) to 7.3% (F.G.A. 60). All samples, except F.G.A. 70 and F.G.A. 75, endured heating up to 800 °C. The F.G.A./E.C.A./P 60 composite demonstrated well-balanced performance: low thermal conductivity (0.2052 W/(m·K)), thermal resistance up to 1000 °C, flexural strength of 4.386 MPa, and compressive strength of 18.069 MPa. The results confirm that well-designed geopolymer lightweight concretes are suitable for chimney and flue pipe linings operating between 500 and 1000 °C and exposed to acidic condensates and aggressive chemicals. This study marks the initial phase of a broader project on geopolymer-based prefabricated chimney systems. Full article

Mortar is widely used in civil construction. The inclusion of expanded clay as a lightweight aggregate reduces the density of mortar, enabling lighter structural elements and potentially lowering material and energy requirements during construction. This research aims to produce lightweight mortars by partially replacing fine aggregate with proportions of expanded clay. Six mortar formulations were prepared with varying proportions of expanded clay. The constituent materials of the mixtures and the mortars were characterized according to regulatory prescriptions. The results indicated that the increase in the replacement of fine aggregate with expanded clay reduced the consistency and density of the mass in the fresh state. No significant differences were observed in water absorption by immersion among the mortars in the hardened state. Regarding mechanical tests, most mortars’ tensile strength in bending remained stable. On the other hand, compressive strength decreased. The tensile adhesion was also reduced with the incorporation of expanded clay. After exposure to sodium sulfate solution, all tensile strength results in bending improved. The coefficient of the constructive quality indicated that the ideal replacement formulation is 20% expanded clay. These mortars represent a viable technical alternative, complying with current standards and contributing more efficiently and sustainably to civil construction. Full article

The growing demand for lightweight aggregates (LWAs) in the construction industry is driving the development of sustainable alternatives based on the reuse of solid industrial waste. The aim of this study was to assess the technical feasibility of using red ceramic waste (RCW) as a partial or total substitute for red clay (RC) to produce lightweight expandable aggregates. Six formulations were made with different proportions of RCW and RC and sintered at four temperatures (1100, 1150, 1200 and 1250 °C). They were characterised using physical, thermal, morphological, chemical and mechanical analyses, according to standard protocols. The results showed that almost all the formulations sintered at 1200 and 1250 °C had a positive bloating index (BI > 0), particle density of less than 2.0 g/cm³, low water absorption of less than 2% and mechanical strength of more than 5.4 MPa, revealing strong potential for use in lightweight structural and non-structural concrete. The main conclusion is that RCW, even used in isolation, has physicochemical and mineralogical properties suitable for the production of lightweight aggregates under optimised thermal conditions, contributing to the development of sustainable materials with a competitive technical performance compared to commercial LWAs. Full article

The elastic modulus is one of the fundamental parameters controlling the mechanical behaviour of concrete. In this study, the Movable Cellular Automata (MCA) method is applied to predict the Young’s modulus of concrete based on the properties of its components. Each automaton represents one component: cement paste, fine aggregate, or coarse aggregate. A parametric sensitivity analysis was performed using Grey System Theory (GST) on hypothetical concrete modeled with the MCA method. The analysis showed that the coarse aggregate type, coarse aggregate-to-total aggregate ratio, and water-to-cement ratio have the greatest impact on the Young’s modulus. To test the effectiveness of the MCA method in modelling concrete, results of numerical simulations were compared with experimental data available in the literature. The first numerical simulations were conducted for mortars containing cement paste and sand as well as for concretes produced by adding granite to them. Two approaches were used to perform the simulations; in the first approach, a sample contained automata representing cement paste, sand, and granite, while in the second the automata represented mortar and granite. High consistency was achieved, with results from both approaches differing by only 0.6%. Subsequent simulations focused on concretes with different water-to-cement ratios (0.45, 0.55, and 0.65), the origin of the basaltic aggregate, and various aggregate contents (60%, 54%, 48%, and 42%). Results showed high agreement between simulations and experimental data, confirmed by a high coefficient of determination R² of 0.84 and mean squared error of 2.43 GPa². Finally, simulations were performed for lightweight expanded clay aggregate concrete, resulting in an R² of 0.86 and mean squared error of 0.81 GPa², which demonstrates the effectiveness of the MCA method in predicting the static elastic modulus of concrete. Full article

The quantity of construction demolition waste (CDW) has been increasing due to the demolition of many old buildings throughout the world. So far, all the statistics indicate that there is a very large generation of CDW, which increases annually. The increasing amount CDW in landfills will cause a scarcity of landfill space and will also increase pollution and cost due to transportation. Recycled brick aggregate concrete (RBAC) incorporating polystyrene (EPS) aggregate beads has emerged as an alternative lightweight material with numerous obvious sustainable benefits, suitable for a future circular economy. The goal of this paper is to assess the feasibility of obtaining lightweight aggregate concrete of structural grade with recycled brick aggregate (RBA) as a coarse aggregate and the incorporation of polystyrene beads in a certain percentage by conducting an experimental study on the dry and apparent density, compressive strength, split-tensile strength and elasticity modulus. In addition, the effects of the w/c ratio and cement content on these properties were studied to provide useful information for the performance optimization of this concrete with RBA and polystyrene (EPS) beads. The properties were investigated for two cement contents, 400 and 360 kg/m³, and two ratios between water and cement, 0.43 and 0.39, respectively. The RBAC mixtures containing EPS beads in 15%, 25% and 35% replacement percentages were evaluated through a comprehensive test program based on the European standards. The results showed that, in general, the use of polystyrene (EPS) beads decreased the mechanical properties of the recycled brick aggregate concrete; however, the outcome indicates the potential for producing lightweight concrete of different grades, including structural classes. It was found that the developed lightweight concrete presents a uniform distribution of the polystyrene granules in the hardened volume of concrete. Also, it was found that the recycled brick aggregate with a 16 mm maximum size did not negatively influence the uniform distribution of the EPS beads, avoiding concentrations of beads. With the increase in the percentage of EPS beads, the properties of the recycled brick aggregate concrete were found to be less sensitive to the water-to-cement ratio. Full article

Microbial-induced carbonate precipitation technology allows concrete to detect and diagnose cracks autonomously. However, the concrete’s compact structure and alkaline environment necessitate the adoption of a proper carrier material to safeguard microorganisms. In this study, various bacterial strains, including Bacillus subtilis, Bacillus sphaericus, and Bacillus megaterium, were immobilized in lightweight expanded clay aggregates (LECA) to investigate their effect on the self-healing performance, mechanical strength, and freeze–thaw durability. Self-healing concrete specimens were prepared using immobilized LECA, directly added bacterial spores, polyvinyl acetate (PVA) fibers, and air-entraining admixture (AEA). The pre-cracked prisms were monitored for 224 days to assess self-healing efficiency through ultrasonic pulse velocity (UPV) and surface crack analysis methods. A compressive strength restoration test was conducted by pre-loading the cube specimens with 60% of the failure load and re-testing them after 28 days for strength regain. Additionally, X-ray diffraction and scanning electron microscopy (SEM) were conducted to analyze the precipitate material. The findings revealed that self-healing efficiency improved with the biomineralization activity over the healing period demonstrated by the bacterial strains. Compression and flexural strengths decreased for the bacterial specimens attributed to porous LECA. However, restoration in compression strength and freeze–thaw durability significantly improved for the bacterial mixes compared to control and reference mixes. XRD and SEM analyses confirmed the formation of calcite as a self-healing precipitate. Overall, results indicated the superior performance of Bacillus megaterium followed by Bacillus sphaericus and Bacillus subtilis. The findings of the current study provide important insights for the construction industry, showcasing the potential of bacteria to mitigate the degradation of concrete structures and advocating for a sustainable solution that reduces reliance on manual repairs, especially in inaccessible areas of the structures. Full article

The construction sector’s reliance on traditional cement significantly contributes to CO₂ emissions, underscoring the urgent need for sustainable alternatives. This study investigates fine (0–4 mm), rounded, uncoated, porous-surfaced lightweight expanded clay aggregate (LECA)-based geopolymers, which combine the low-carbon benefits of geopolymers with LECA’s lightweight and insulating properties. Geopolymers were synthesized using lignite-rich fly ash with varying ratios of LECA to aggregate. Mechanical testing revealed that the reference mixture without LECA (REF-GEO) achieved the highest compressive strength of 37.89 ± 0.75 MPa and flexural strength of 7.62 ± 0.11 MPa, while complete substitution of the aggregate with LECA (LECA-100%) reduced the compressive strength to 17.31 ± 0.88 MPa and flexural strength to 3.41 ± 0.11 MPa. The density of the samples decreased from 2.06 g/cm³ for REF-GEO to 1.31 g/cm³ for LECA-100%, and thermal conductivity dropped significantly from 1.15 ± 0.07 W/mK to 0.38 ± 0.01 W/mK. Microstructural analysis using XRD and SEM-EDX highlighted changes in the material’s internal structure and the increase in porosity with higher LECA content. Water vapor permeability increases over time, particularly in samples with higher LECA content. These findings suggest that LECA-based geopolymers are suitable for low-load or non-structural elements. They are ideal for sustainable, energy-efficient construction that requires lightweight, insulating, and breathable materials. Full article

Used tires (UTs) are a global problem, especially in developing countries due to inadequate management systems. During retreading, when the worn tread is replaced, waste is generated in the form of tire fibers (TFs) and particles, which can be reused as raw materials to produce economically and environmentally low-cost prefabricated elements. Using TFs as a lightweight aggregate in nonstructural geopolymer-based elements is a sustainable valorization option. This study aims to valorize used tires by incorporating them as TFs into lightweight geopolymer mixes and analyzing their physico-mechanical, thermal, and thermography properties for building and civil engineering applications. The geopolymer is produced from a precursor (spent catalyst residue from catalytic cracking, FCC) and an alkaline activator composed of rice husk ash (RHA), sodium hydroxide, and water. The control sample’s (mortar with siliceous sand, CTRLSIL) compressive strength came close to 50 MPa, while the TF mixes ranged from 32 to 3 MPa, which meet the masonry standards. The thermal conductivity and thermography analyses showed that increasing the TF content reduced the heat transmission and achieved a similar performance to expanded-clay concrete and better performance than for conventional concrete. Full article

The use of artificial porous aggregates for the production of lightweight cement concrete is widespread and used everywhere. In most cases, lightweight artificial aggregates are used to produce concrete of the standard structure using vibration technology. However, there is currently no knowledge base on the use of these aggregates for the production of concrete using centrifugation technology. The purpose of this work is to develop and obtain a new composition of variotropic concrete with a combined coarse aggregate and microsilica. A total of 17 concrete elements of the annular cross-section were manufactured using centrifugation technology. The optimal ratio of 60% crushed stone (CrS) and 40% expanded clay gravel (EC) was determined. It was found that replacing CrS with EC improves such properties as density and thermal conductivity, and negatively affects the strength of the composite. Modification of lightweight centrifuged concrete on a combined aggregate with microsilica (MS) in dosages from 2% to 10% had a positive effect on its mechanical properties. The most effective MS dosage was 6%. The compressive strength of lightweight concrete increased by 14.75%, from 36.6 MPa to 42.0 MPa, which is comparable to the compressive strength of centrifuged concrete on a heavy aggregate of 43.4 MPa. The density value was 2148 kg/m³. The thermal conductivity coefficient was 1.270 W/m×°C. As a result, a new centrifuged concrete of variotropic structure with reduced material consumption, density, thermal conductivity coefficient, and the required mechanical properties was developed. Full article

Toxic cyanobacterial blooms are a growing environmental problem, persisting in freshwater bodies globally, and potentially hazardous to populations that rely on surface freshwater supplies. Nature-based solution units (NBSUs) are effective and sustainable approaches for water treatment, with sorption being an important process. The purpose of this study was to evaluate unmodified agro-based waste materials (rice husks, olive pulp pomace pellets (OP), cork granules) and the benchmark NBSU substrates (biochar, light expanded clay aggregate (LECA), and sand) for their microcystin-LR (MC-LR) and cylindrospermopsin (CYN) sorption potential. The kinetics and sorption mechanism of the two best sorbent materials were studied for future incorporation into NBSUs. Pre-screening of the sorbents showed highest sorption with biochar (>86% MC-LR and >98% CYN) and LECA (78% MC-LR and 80% CYN) and lower sorption with rice husk (<10%), cork (<10%), and sand (<26%). Leaching from OP made them unsuitable for further use. The sorption of both the cyanotoxins onto biochar was rapid (8 h), whereas onto LECA it was steadier (requiring 48 h for equilibrium). The pseudo-second-order kinetic model fit the sorption of both cyanotoxins onto biochar and LECA (R²: 0.94–0.99), suggesting that the sorption rate is limited by chemisorption. The sorption of MC-LR and CYN to biochar and LECA fit the Freundlich and D–R models better, suggesting multilayer sorption, high heterogeneity, and porosity in the sorbents (which was also confirmed by SEM/EDS). The sorption capacity was observed to be higher for biochar (K_f: MC-LR = 0.05, CYN = 0.16) than LECA (K_f: MC-LR = 0.02, CYN = 0.01). Full article

Lightweight concrete (LWC) is a long-standing development in the area of construction materials. LWC has become increasingly important for sustainable construction due to its reduced susceptibility to cracking. However, when exposed to extreme temperatures during fires, LWC can lose its compressive strength and ductility. This study investigates the performance of lightweight expanded clay aggregate (LECA) concrete T-beams exposed to elevated temperatures. The research also focuses on the use of an engineered cementitious composite with a basalt fiber-reinforced polymer grid (ECCBFG) as a rehabilitation method for fire-damaged T-beams. Key variables considered include the concrete cover thickness (20 and 30 mm), fire exposure duration (30 and 60 min), and thickness of the ECCBFG layer. Thermocouples were installed at various points within the beams to monitor the heat gradient across the cross-section. Fourteen concrete beam specimens were tested, including control beams, fire-damaged beams, and beams strengthened with the ECCBFG layer. Key performance parameters, such as the energy absorption, cracking load, ductility index, maximum load capacity, and corresponding displacement, were analyzed. The experimental results showed that the strengthened beams outperformed the fire-damaged beams, closely matching the performance of undamaged reference beams in most aspects, except energy absorption. The findings suggest that further research is needed to optimize certain performance indicators and address challenges in strengthening fire-damaged beams. Full article

Self-compacting concrete (SCC) is a relevant technology and an alternative to conventional concrete in complex structures due to its exceptional workability. The rheological parameters demonstrated by SCC provide high fluidity and cohesion, resulting in high mould-filling capability and segregation resistance, as well as optimising concreting processes and reducing costs. In view of this, self-compacting lightweight concrete (SCLC) has emerged as a possible alternative as it combines the benefits of SCC and lightweight aggregate concrete (LWAC). In the production of LWC, the most widely used lightweight aggregate in the world, and also in Brazil, is still expanded clay; however, Brazilian production is restricted to the southeast region. In this context, previous studies have verified the feasibility of producing lightweight aggregates from the sintering of industrial waste and regional raw materials (Rio Grande do Norte/Brazil), such as sugarcane bagasse ash (SBA), scheelite mining residue (SMR), and local clay. Therefore, this study evaluates the influence of three lightweight aggregates, analysing their performance in comparison with SCLC produced with commercial lightweight aggregate (expanded clay). The concretes studied were subjected to characterisation tests in a fresh state; fluidity, apparent viscosity, visual stability, and passing ability were assessed through slump flow tests, flow time (T500), visual stability index, and J-ring, respectively, as well as measurement of the fresh specific mass. In the hardened state, tests were carried out to determine the compressive strength at 7 and 28 days, the dry specific mass, the chloride ion diffusion coefficient, and the thermal conductivity. The new concretes had density values ranging from 1.94 to 2.03 g/cm³ and compressive strength values at 28 days between 26.11 and 36.72 MPa. The results obtained show that it is feasible to produce SCLC with unconventional lightweight aggregates based on sugarcane bagasse waste and scheelite mining waste. Full article

Objectives: This study aims to evaluate the potential of lightweight concrete mixtures incorporating sustainable materials, such as nopal mucilage and aloe vera, to enhance thermal and structural performance while promoting eco-friendly construction practices. The objective is to analyze their effects on physical, mechanical, and thermal properties to optimize mixture design. Methods/Analysis: Six lightweight concrete mixtures were prepared using varying dosages of tuff, expanded clay, nopal mucilage, and aloe vera as lightweight and stabilizing agents. To assess their performance, a series of physical tests (bulk density, water absorption, and slump), mechanical tests (compressive strength), and thermal characterizations (conductivity, heat capacity, and resistivity) were conducted. Fractal analysis was employed to evaluate the structural complexity of the mixtures. Findings: The results revealed significant differences based on the materials used. Mixtures with aloe vera exhibited extreme water absorption (up to 11.472%) and varying consistency, from fluid (“spreads”) with tuff to workable with expanded clay. When combined with expanded clay, Nopal mucilage-based mixtures showed lower workability but higher compressive strengths (up to 11.447 MPa). Expanded clay increased bulk density and enhanced thermal efficiency, with mixtures incorporating aloe vera or nopal mucilage demonstrating high heat retention and structural complexity. The compressive strengths ranged from 7.343 MPa (aloe vera-tuff) to 12.207 MPa (water-tuff), highlighting the impact of stabilizing agents on mechanical performance. Novelty or Improvement: This study introduces a novel evaluation of lightweight concrete mixtures using nopal mucilage and aloe vera, focusing on their synergistic effects with lightweight aggregates such as tuff and expanded clay. The findings provide valuable insights into optimizing eco-friendly concrete mixtures with improved thermal retention, workability, and mechanical properties, offering a sustainable alternative for modern construction. Full article

The paper presents the results of experimental and numerical tests on barrel vaults with backfill material. The thickness, internal span, and rise of the vaults were 125 mm, 2000 mm, and 730 mm, respectively. In experimental studies, vaults with backfill of expanded clay aggregate or granite aggregate were tested. Moreover, three types of extrados finishing were considered in the experiments: masonry with flush joints, PVC film, and steel angles attached to the bricks. The numerical simulations increased the number of cases analyzed by conducting a parametric analysis for four additional backfill materials with varying bulk density or internal friction angle, as well as modifying the friction coefficient at the backfill-vault interface for each of the analyzed materials. The main goal of the analyses was to investigate the impact of the bulk density, the internal friction angle of the backfill material, and the friction coefficient between the backfill and the vault on the load-bearing capacity of the buried vault. Both the laboratory tests and numerical simulations indicate a significant impact of the internal friction angle, bulk density of the backfill materials, and the finishing method of the extrados of the vault on the load-bearing capacity of buried vaults. Full article