Explore the vast range of titles available.

Structural lightweight concrete (SLWC) is crucial for reducing building weight, reducing structural loads, and enhancing energy efficiency through lower thermal conductivity. This study explores the effects of incorporating silica fume (SF), micro-polypropylene (micro-PP), and macro-PP fibers on the workability, thermal properties, and strength of SLWC. SF was added to all mixtures, substituting 10% of the Portland cement (PC), except for the control mixture. Macro-PP fibers were introduced alone or in combination with micro-PP fibers at volumetric ratios of 0.3% and 0.6%. The study evaluated various parameters, including slump, Vebe time, density, water absorption (WA), ultrasonic pulse velocity (UPV), thermal conductivity coefficients (k), compressive strength (CS), and splitting tensile strength (STS) across six different SLWC formulations. The results indicate that while SF negatively impacted the workability of SLWC mortars, it improved CS and STS due to the formation of calcium silicate hydrate (C-S-H) gels from SF’s high pozzolanic activity. Additionally, using micro-PP fibers in combination with macro-PP fibers rather than solely macro-PP fibers enhanced the workability, CS, and STS of the SLWC samples. Although SF had a minor effect on reducing thermal conductivity, the use of macro-PP fibers alone was more effective for improving thermal properties by creating a more porous structure compared to the hybrid use of micro-PP fibers. Moreover, increasing the ratio of micro- and macro-PP fibers from 0.3% to 0.6% resulted in lower CS values but a significant increase in STS values.

Producing self-compacting concrete with lightweight aggregates is a difficult task. Mixtures with a high content of expanded aggregate tend to separate. It is possible to evaluate the possibility of producing self-compacting lightweight concrete with low average density. This work presents the results of a study of self-compacting lightweight concrete on hollow microspheres. The ability of a lightweight concrete mixture on hollow microspheres with low density (ρ = 1450 ± 25 kg/m3) to self-compact has been established. The closeness in the values of the spreading diameter before and after shaking on the table Dsp,1 → Dsp,2 confirms this. The dependences (regression equations) of mobility, coefficients of the Ostwald–Weil equation, and density and strength on the W/C ratio and plasticizer concentration for lightweight concrete with a volume content of hollow microspheres of 46.4% have been established. The limits for homogeneity of lightweight concrete mixtures on hollow microspheres are W/C ≤ 0.6 and CPl ≤ 1.0%. The dispersion of quartz sand (varying the Sp/Sf ratio) in an amount of 8.7% in the composition of lightweight concrete does not have a significant effect on the self-compaction criterion and physical and mechanical properties. Changes in the physical and mechanical properties of lightweight concrete on hollow microspheres in the selected range of varying the W/C ratio and plasticizer concentration are in the following ranges: ρ = 1403–1485 kg/m3, Rfl = 3.34–5.90 MPa, Rcom = 29.6–45.7 MPa. The presence of delamination at W/C ≥ 0.6 does not allow one to correctly establish the influence of variable factors.

This comprehensive study investigates the development of lightweight structural concrete with enhanced thermal and durability properties by strategically incorporating nano-silica (NS) and expanded polystyrene (EPS) granules. This research aims to design a high-performance concrete composite that can achieve superior thermal insulation, improved water permeability, and maintain structural integrity. NS was strategically incorporated at varying dosages of 0.75, 1, and 1.25% by weight of cement, while EPS was used to replace fine aggregates at 25, 50, 75, and 100% replacement levels. The thermal performance of the concrete mixtures was systematically evaluated using the advanced transient plane source method, providing insights into thermal conductivity, thermal diffusivity, and volumetric heat capacity. The experimental results demonstrate that the addition of NS led to a significant 15% reduction in thermal conductivity, attributed to the filler effect and pozzolanic reactivity of nano-silica. The incorporation of EPS granules exhibited an even more pronounced impact, decreasing the thermal conductivity of concrete by up to 80.5% as the replacement level increased. Notably, the combined use of NS and EPS resulted in a synergistic effect, achieving a remarkable 39–86% reduction in thermal conductivity, 28–71%, and 28–79% reductions in thermal effusivity and diffusivity, respectively, compared to the control mix. Furthermore, the optimal NS content of 1–1.25% was found to enhance the compressive strength by up to 36.5% and reduce the water permeability by 40–52%, indicating improved mechanical and durability properties. These findings highlight the transformative potential of this composite material in developing high-performance, thermally-efficient, and sustainable concrete for energy-efficient buildings, reducing operational energy demands and carbon footprints.

This study explores the possibility of producing sustainable structural lightweight concrete (LWC) based on limestone calcined clay cement (LC³) using waste from construction and demolition. The main innovation is the dual substitution of waste-derived materials for traditional LC³ constituents: crushed brick powder (CBP) was used in place of metakaolin (MK), and recycled concrete powder (RCP) was used in place of limestone powder (LSP). To achieve lower densities, nine concrete mixtures were created using crushed brick as both fine and coarse aggregates in addition to an air-entraining agent. Flowability, dry density, ultrasonic pulse velocity, compressive strength, resistance to magnesium sulfate attack and high temperatures (200 and 400 degrees Celsius), water absorption, and porosity were all assessed through an extensive experimental program. With only a small drop in 28-day compressive strength (5–8%) and a slight increase in water absorption (10–12%), the results showed that CBP is a very promising substitute for MK. All mixtures met the structural LWC requirements of DIN EN 1045-1 (dry density of 1650–1850 kg/m³ and strength > 24 MPa), but substituting RCP for LSP resulted in a more noticeable decrease in 28-day compressive strength (15–20%) and an increase in water absorption (13–18%). Additionally, after 180 days of sulfate exposure, all LC³ systems showed very little mass loss (< 0.7%) and maintained over 80% of their residual strength at 400 °C. According to the study, CBP and RCP can effectively and sustainably replace MK and LSP in LC³-based LWC, allowing for a 60% reduction in clinker while preserving structural integrity and promoting waste valorization.

The article presents a recognition of the current state of the art in the field of bridge structures made using concrete on lightweight aggregate. The article aims to show the reader why aggregate with low mechanical parameters and high absorption can be used in demanding bridge constructions. Divided into two parts, the first presents the history of both topics and compiles the parameters of currently used lightweight aggregates by considering the guidelines applicable in the EU, China, and America concerning bridge construction. The literature review conducted highlighted both the advantages and disadvantages of using lightweight aggregates, presented the knowledge accumulated to date in this area, and identified important research gaps regarding lightweight aggregates. The second part discusses existing or planned bridge structures, taking into account their shapes and material properties. In summary, the challenges involved in the development of lightweight aggregate for bridge structures. The results obtained from the analysis will provide a basis for further research into the development of original lightweight aggregate for bridge structures.

The development of self-compacting lightweight concretes is associated with solving two conflicting tasks: achieving a structure with both high flowability and homogeneity. This study aimed to identify the technological and rheological characteristics of the flow of concrete mixtures D1400…D1600 based on hollow microspheres in comparison with heavy fine-grained D2200 concrete and to establish their structural and physico-mechanical characteristics. The study of the concrete mixtures was carried out using the slump flow test and the rotational viscometry method. The physical and mechanical properties were studied using standard methods for determining average density and flexural and compressive strength. According to the results of the research conducted, differences in the flow behaviors of concrete mixtures on dense and hollow aggregates were found. Lightweight concretes on hollow microspheres exhibited better mobility than heavy concretes. It was shown that the self-compacting coefficients of the lightweight D1400...D1600 concrete mixtures were comparable with that of the heavy D2200 concrete. The rheological curves described by the Ostwald–de Waele equation showed a dilatant flow behavior of the D1400 concrete mixtures, regardless of the ratio of quartz powder to fractionated sand. For D1500 and D1600, the dilatant flow behavior changed to pseudoplastic, with a ratio of quartz powder to fractional sand of 25/75. The studied compositions of lightweight concrete can be described as homogeneous at any ratio of quartz powder to fractional sand. It was shown that concrete mixtures with a pronounced dilatant flow character had higher resistance to segregation. The value of the ratio of quartz powder to fractional sand had a statistically insignificant effect on the average density of the studied concretes. However, the flexural and compressive strengths varied significantly more in heavy concretes (up to 38%) than in lightweight concretes (up to 18%) when this factor was varied. The specific strength of lightweight and heavy concrete compositions with a ratio of quartz powder to fractional sand of 0/100 had close values in the range of 20.4...22.9 MPa, and increasing the share of quartz powder increased the difference between compositions of different densities.

In this paper, Structural Lightweight Concrete (SLC) containing Recycled Lightweight Aggregate (RLA) is described. Damaged lightweight concrete was used as RLA by crushing it into fine particles, and used to replace fine limestone aggregate of up to 45% by weight. To enhance the strength development of SLC, silica fume and a superplasticizer were incorporated into the mixture. The compressive strength, density, water absorption, porosity, modulus of elasticity, and thermal conductivity of the concrete were tested. The results show that SLC with satisfactory 28-day compressive strengths of between 16.5 and 30.5 MPa, and densities of between 1600 and 1800 kg/m 3 , were obtained. The compressive strength, modulus of elasticity, and thermal conductivity decreased with an increase in RLA content, and the water absorption and porosity increased. Water absorption of 3.28–7.87%, porosity of 6.82–13.87%, modulus of elasticity of 16.5–25.2 GPa, and thermal conductivity of 0.49–0.75 W/mK were found to be within the working range of SLC.

The freeze–thaw cycles lead to cumulative damage and gradual strength deterioration in concrete, which cannot be accurately represented by traditional empirical models. To address this issue, shale-based lightweight structural concrete (LSC) specimens with four strength grades (LSC20-LSC50) were subjected to basic mechanical performance and freeze–thaw cycle experiments. The study investigated the patterns of mass loss, relative dynamic elastic modulus, and loss of compressive strength in LSC subjected to varying numbers of freeze–thaw cycles. Furthermore, the correlation between the dynamic modulus of elasticity and compressive strength was examined. A Gamma process-based stochastic degradation model for the compressive strength of LSC was then developed. The results show that the compressive strength degradation of LSC under freeze–thaw cycles follows a monotonically increasing trend that gradually stabilizes, with low-strength LSC deteriorating faster than high-strength LSC. After 200 cycles, the compressive strength degradation of LSC30 and LSC50 was only 32.66% and 29.79% of that of their corresponding ordinary concretes (C30 and C50). The proposed Gamma process model showed high fitting accuracy for all strength grades of LSC (R2 > 0.96, RMSE < 0.25 MPa, MAPE < 11%). The research results provide a scientific basis for the structural design of concrete in cold regions.

Plastic is a widely consumed material with a high decomposition time, occupying significant space in landfills and dumps. Thus, strategies to reuse plastic waste are imperative for environmental benefit. Plastic waste is a promising eco-friendly building material for cement-based composites due to its reduced specific gravity and thermal conductivity. However, this waste reduces the composites’ mechanical strength. This work aims to produce and evaluate lightweight concretes made with only lightweight aggregates and mostly recycled plastic aggregates. Initially, an optimized dosage approach for lightweight concrete is presented. The mixture proportion of the lightweight concrete was based on the performance of mortars with the complete replacement of natural aggregate by recycled polyethylene terephthalate (PET) aggregates. The PET aggregates showed irregular shapes, impairing workability and providing lightweight concretes with around 18% water absorption and 21% void index. However, the concretes presented significantly low-unit weight, approximately 1200 kg/m3. This work presented a structural lightweight concrete (ACI 213-R) using only lightweight aggregates and mostly plastic waste aggregate, with a compressive strength of up to 17.6 MPa, a unit weight of 1282 kg/m3, and an efficiency factor of 12.3 MPa·cm3/g. The study shows that with an optimum dosage, reusing plastic waste in concrete is a viable alternative contributing to environmental sustainability.

The use of structural lightweight concrete in the construction industry is on the rise in the last few decades mainly because of the higher strength per unit density, as it reduces the total deal load of the structural elements as compared with normal strength concrete. In addition, the environmental concerns of the concrete industry have gained supreme importance in recent times, demanding vital and effectual steps. In this regard, the current study was carried out to formulate an alternative approach for producing a sustainable lightweight structural concrete. The study followed two stages: initially, the selection of optimized manmade plastic aggregates based on trial concrete mixes, and finally, to gauge the physical-, mechanical- and durability related properties of the concretes integrating optimized manmade aggregate series at different replacement fractions. As a result of the first phase: two aggregate series out of eight were selected based on the compressive strength and durability properties of their concretes. In the next stage, all the properties for the optimized aggregate concrete were analyzed in terms of compressive strength. It was noted that the physical, mechanical and chloride penetration resistances have generally displayed a decreasing trend, with an increase in the manmade plastic aggregate replacement fractions as compared with reference lightweight concrete. However, the two aggregates, i.e., 70% DS-30% LLDPE and 50% QF-50% PET at the replacement fractions of 25% and 100%, were found to be the best two contenders that fulfilled the criteria for structural lightweight concrete, i.e., ASTMC330/C330M-14, and were proposed for structural lightweight purposes with low and relatively high strength and chloride resistance-based durability requirements, respectively. In addition, the brittleness ratios and structural efficiency parameters for the concretes of the 70% DS-30% LLDPE and 50% QF-50% PET also supplemented the aforementioned findings. Overall, this study presents a sustainable approach for the effective utilization of plastic waste for producing structural lightweight concrete.