Case Studies in Construction Materials最新文献

Carbon fibers (CFs) reinforced alkali-activated (AA) ground granulated blast furnace slag (GGBFS) geopolymer composites have excellent mechanical and thermoelectrical properties, as well as low energy consumption and low CO₂ emissions during their production. However, the dispersion of CFs in the geopolymer matrix is always a technical issue in the preparation of the green composite material. Therefore, this study comparatively investigated various dispersion methods, including, mixing sequence (pre-mixing and after-mixing methods), dispersing agent (nano silicon dioxide [nSiO2]), and ultrasonic treatment time (0, 15, 30, and 45 min), as well as CFs content (0.5, 1.0, and 1.5 wt% of GGBFS). The distribution of CFs was then qualitatively and quantitatively evaluated by a series of tests, such as flowability, electrical resistivity, flexural strength, scanning electron microscope (SEM) analysis, and X-ray computed tomography (CT). The experimental results showed that the proposed pre-mixing method provided excellent dispersion characteristics for CFs compared with the after-mixing method. The introduction of nSiO₂ can enhance the dispersion of CFs and the mechanical and electrical properties of AA GGBFS geopolymer composites. At a carbon fiber content of 1.5 %, the pre-mixing method and the addition of nSiO₂ dispersant reduced the resistivity of the 28-day geopolymer composites by 17.0 % and 38 %, respectively, compared with the after-mixing method. It is feasible to use X-ray CT scanning with the gray-scale frequency map to analyze the dispersion effect of CFs in AA GGBFS geopolymer composites. However, the results were not intuitive when less agglomeration of CFs occurred for the low content of CFs. The scanning method is more applicable to the sample with over 1.0 wt% CFs. The average pixel areas of uniformly dispersed CF bundles in the 2D images of the pre-mixing method and the addition of nSiO₂ dispersant specimens were 3.32 % and 6.55 % higher than those of the after-mixing method, respectively. The 2D and 3D scanning results from the dispersion characteristics of CFs were consistent. 2D scanning could provide a time-consuming option for the measurement of CFs dispersion characteristics.

The incorporation of steel reinforcement in cast concrete can effectively enhance the ductility and strength of the concrete. In this paper, the steel wires reinforced 3D printed mortar (3DPM) was utilized as the external restraint for two series of short concrete columns (S-series: square section, C-series: circular section). Three different wire diameters (fine, medium, and thick) were considered as experimental variables. The experimental results indicate that the specimens reinforced with medium steel wires in both series exhibited strengths comparable to or superior to those of the unreinforced specimens. In terms of crack control, the specimens with the appropriate reinforcement ratio exhibited excellent performance, showing the smallest crack widths for both C-M and S-M specimens. It is found that in both S and C series that an appropriate reinforcement ratio positively influences the load-bearing capacity of the restrained columns. Furthermore, a calculated model for the uniaxial compression model of ECC confined concrete was proposed. The findings reveal that the calculated model is conservative and effective in predicting the compressive strength of the short column, with the exception of the C-F specimen.

While 3D printing of concrete (3DCP) has gained increasing interest in the construction industry, steel reinforcement remains a significant obstacle to 3D printing (3DP) construction. To address this concern, Engineered Cementitious Composites (ECC), also recognized as Strain-Hardening Cementitious Composites (SHCC), can provide structural performance and integrity, safety, durability, and strength without steel reinforcement. The article reviews scientific works on 3DCP using ECC and proposes further investigations to lead to better development. As a result, generally, Poly-Ethylene (PE) fibers are used more frequently because of their strength. Mix design parameters have been extensively examined in relation to fresh ECC rheological characteristics. Due to the printing process, fiber orientation may affect ultimate tensile strain. As compared to casted ones with random fiber orientation, fiber orientation aligned with tensile stress resulted in a higher ultimate tensile strain. Additionally, research showed that ECC including up to 2 % fiber can be mixed, extruded, and built. Morovere, results highlighted the comparison between printed ECC containing PVA and PE fibers, the influence of mix design parameters on extrudability, and the impact of fiber length and volume fraction on strain-hardening properties. The text also covers the effects of fiber orientation and nozzle distance on tensile performance and ultimate tensile strain, as well as the anisotropic properties of 3DP-ECC. As well as this, there are some areas that require further research, such as durability and response to a variety of loading conditions, such as seismic loading.

A novel type of solid waste based artificial aggregate which holds promise for a good synergy between mechanical properties and self-healing capacity is designed with using the core-shell structure concept. The artificial aggregate is designed with a high self-healing potential core and a high strength shell, to achieve the high-performance application of artificial aggregates in concrete. The basic properties and potential self-healing capacity of artificial aggregates were comprehensively analyzed. The results indicated that the artificial aggregates were eligible considering the 28-d single particle compressive strength of exceeding 5.0 MPa, low water absorption and high volumetric stability. The crack-healing ratio of artificial aggregate is up to 94.5 % after 7-d curing in the simulated concrete pore solution (i.e., saturated Ca(OH)₂ solution). The primary self-healing product was detected as calcium-aluminate-silicate-hydrate (C-A-S-H) gel due to the secondary hydration reactions of core materials.

Cement plays a pivotal role in the production of semi-flexible pavement (SFP), however, it contributes to 8 % of global carbon dioxide emissions. Consequently, reducing cement usage in grout production for porous asphalt mixtures is highly desirable to mitigate the overall carbon footprint. Additionally, the substantial generation of agricultural, industrial, and hazardous waste often ends up in environmental disposal without recycling. This research aims to repurpose glass waste powder (GWP) and date palm seed ash (DPSA) as partial substitutes for cement in SFP, aiming to curtail environmental pollution from cement production, decrease costs, and enhance waste and landfill management. Novel cement grouts were formulated by partially replacing Portland cement with GWP and DPSA at varying ratios (10 %, 20 %, and 30 %). These grout blends were assessed for flow characteristics and compressive strength. Furthermore, SFP samples were prepared by integrating 5 % styrene-butadiene-styrene (SBS)-modified bitumen into a porous asphalt structure, subsequently filled with predefined cement grouts. Comparative analysis of compressive strength, Marshall stability, skid resistance, and moisture damage resistance indicated that SFP specimens modified with GWP and DPSA exhibited superior performance over conventional counterparts. Optimal results were achieved with a combination of 20 % GWP and 10 % DPSA replacement ratio, yielding denser microstructure, enhanced skid resistance, and improved adhesion and tensile strength, thereby enhancing overall SFP performance.

Utilizing activated sludge as a partial substitute for cement can both curb cement consumption and address sludge reuse in an economically and environmentally-friendly manner. This study delves into the pozzolanic activity of mechanically-thermal (MT) activated sludge and alkali-mechanical-thermal (AMT) activated sludge, employing the strength activity index (SAI) method. Microscopic insights provided by X-ray diffraction (XRD), scanning electron microscopy (SEM), and laser particle size analysis aid in the interpretation of observed phenomena. The findings underscore the superiority of MT activation over AMT activation, with an SAI of 97 %. Optimal pozzolanic activity is achieved through a 2-hours holding time, slow heating at 10 °C/min, and rapid cooling. A calcination temperature of 800 °C effectively promotes the decomposition of active minerals and enhances the sludge's pozzolanic activity. Additionally, a ball milling time of 2 minutes proves sufficient to meet practical demands, as prolonged ball milling has a limited impact on sludge pozzolanic activity.

Given the rise in sustainable use of recycled aggregate concrete (RAC) in new construction, weaker properties may compromise the integrity of structural components, including the slab-column connections. Low-strength concrete can be encountered, not only by using weak RAC in new construction, but also in the case of normal concrete in aged and deteriorated historic or conventional structures. To uphold the sustainable use of such materials in critical structural components, the need for restoring the strength via external strengthening using near-surface-mounted (NSM) fiber-reinforced polymer (FRP) bars is presented in this study. The paper experimentally investigates the behavior of NSM FRP strengthening against punching shear failure in slab-column connections produced from RAC and steel fibers with low structural strength. The three variables studied are steel fiber addition, recycled aggregate replacement, and FRP bar material type – Glass FRP (GFRP) versus Carbon FRP (CFRP). Five tests were conducted, utilizing three and two specimens strengthened with GFRP and CFRP bars, respectively. The three GFRP bar strengthened specimens differ in the type of concrete used, namely, ordinary concrete without steel fibers, ordinary steel fiber reinforced concrete (FRC), and RAC without steel fibers. The two CFRP bar strengthened specimens were of ordinary concrete and RAC, both with steel fibers, resulting in recycled aggregate FRC. RCA’s incorporation positively affected the results of the ultimate punching shear, flexural stiffness, and the maximum displacement due to the likely role of the recycled aggregate angularity in resisting the punching shear better. Due to higher flexural stiffness of the NSM CFRP, it entails more likelihood of debonding failure that limits its full utilization in increasing the punching shear capacity compared to that of NSM GFRP. However, both the NSM strengthening materials appear promising in low-strength (f’_c ≤ 17 MPa) concrete slabs to reach acceptable capacities. Assessment based on different design code provisions and an analytical model revealed better accuracy of the Critical Shear Crack Theory (CSCT) and the fib Model Code in predicting punching shear capacity for NSM strengthened ordinary concrete column-slab connections, but with some slight deviations when applied to specimens made of RAC.

The escalating global energy demand and the imperative to combat climate change necessitate urgent action to reduce energy consumption in the building sector. This research focuses on advancing the development of lightweight construction materials with enhanced thermal insulation properties to address the growing energy demands of residential buildings. The study explores using vermiculite, perlite, and aluminium powder as additives to traditional cement bricks, aiming to improve thermal performance while maintaining structural integrity. The research employs a multifaceted approach, combining experimental and simulation methods. The experimental phase involves fabricating solid cement bricks with varying proportions of vermiculite, perlite, and aluminium powder. The bricks' mechanical, physical, and thermal properties are systematically evaluated. The simulation study employs Design Builder software to assess the real-world thermal performance and energy efficiency of lightweight bricks in a virtual residential building, replicating the harsh desert climate of New Cairo, Egypt. The research found that incorporating vermiculite, perlite, and aluminium powder into cement bricks significantly reduced their thermal conductivity, improving thermal insulation properties. While this incorporation decreased compressive strength, indicating a trade-off between weight reduction and structural integrity, the simulation study demonstrated substantial energy savings and reduced carbon footprints associated with using these lightweight bricks in a virtual residential building model, highlighting their potential for sustainable construction.

This study examines the microstructure and mechanical properties of foamed concrete modified by natural fibers (basalt, coir, and sisal) in concentrations ranging from 0.15 % to 0.45 %. The objective was to develop high-performance natural fiber-reinforced foamed concrete (NFRFC). Comprehensive experimental analyses were performed, including assessments of micromorphology, phase composition, water absorption, compressive and flexural strength, as well as durability. The results indicate that coir fibers markedly enhance the compressive strength of NFRFC, outperforming sisal and basalt fibers. Optimal compressive strength, an increase of 42.19 % over the control, was achieved with a coir fiber content of 0.3 %. Conversely, excessive fiber addition was found to enlarge pore size and connectivity, adversely affecting the NFRFC’s microstructure. All fiber variations significantly improved the flexural properties, with basalt fibers providing the most effective reinforcement. Additionally, while freeze-thaw and wet-dry cycles generally diminished the performance of foam concrete, the inclusion of natural fibers like coir mitigated micro-cracking and enhanced durability. The study suggests incorporating suitable quantities of coir or sisal fibers into foamed concrete to achieve durable, high-performance NFRFC suitable for various engineering applications.

This paper investigates experimentally the short-term behavior of natural hydraulic lime (NHL) mortars reinforced with ballast fiber for use as structural repair mortars in historic and contemporary buildings. The physical and mechanical properties of mortar mixes reinforced with 0.143–0.215 mm equivalent thick and 12 mm long fibers in volumetric percentages of 1 %, as well as of unreinforced mortars, produced with different compaction methods and cured under different environmental conditions, have been evaluated. A cost-effectiveness analysis has also been carried out to determine the economic impact of these factors in their practical application. It is found that basalt fiber reinforcement provides lower water absorption coefficients and significantly improves the shore hardness, compressive strength, and post-critical flexural behavior of NHL mortars at early ages. Furthermore, it is observed that the compaction procedure can improve the packing density of the mortars providing higher densities, lower water absorption coefficients and higher mechanical strength values. Finally, it is verified that the curing parameters affect unevenly the basalt fiber reinforced NHL mortars and unreinforced NHL mortars, with greater deterioration being observed in the former when sufficient moisture is not ensured. Decreases in hardness, flexural and compressive strength, as well as increases in the water absorption coefficient are important. Consequently, the economic profitability of basalt fiber reinforcement depends on ensuring optimal moisture conditions during curing, especially when the mixes have already lost excess water after the first 2–3 days. The study provides quantitative and qualitative data to determine the appropriate curing parameters for basalt fiber reinforced NHL mortars that are viable in practice for their industrial performance.