Search Results (1,224)

This paper assesses the feasibility of metakaolin (MK)-based geopolymer (GP) composite as an environmentally friendly substitute for cement-based composite in repair applications. The Taguchi orthogonal array method was used to find the optimum GP mix in terms of mechanical properties and adhesion to concrete substrates. Four key parameters, each with three levels, are investigated including the alkaline activator-to-MK ratio (A/M: 1, 1.2, 1.4), the sodium silicate-to-sodium hydroxide ratio (S/H: 2.0, 2.5, 3.0), sodium hydroxide (SH) molarity (12, 14, 16), and curing temperature (30, 45, 60 °C). The evaluated properties include flowability, compressive strength, splitting tensile strength, flexural strength, ultrasonic pulse velocity, and bond strength under various interface configurations. Experimental results demonstrated that the performance of MK-based GP composite was primarily governed by the A/M ratio and sodium hydroxide molarity. The Taguchi optimization method revealed that the mix design featuring A/M of 1.4, SS/SH of 2, 16 M sodium hydroxide, and curing at 60 °C yielded notable improvements in compressive and bond strengths compared to conventional cement-based composites. Full article

Many transportation structures collapse or sustain severe damage as a result of natural disasters such as earthquakes, floods, wars, and similar attacks. These collapsed or severely damaged structures must be rebuilt and returned to service as quickly as possible. Water is used in the mix for cement-bound concrete roads. It is known that drought problems are emerging due to climate change and that water resources are rapidly depleting. Significant amounts of water are used in concrete production, further depleting water resources. In order to contribute to the elimination of these two problems, the usability of polyurethane resin binder in road pavement construction was investigated. Polyurethane resin binder road pavement is a new type of pavement that does not contain cement or bitumen as binders and does not contain water in its mixture. This new type of road pavement can be opened to traffic within 5–15 min. After determining the aggregate and binder mixture ratios, four different curing methods were applied to the created samples. After the curing, the samples were subjected to compression test, flexural test, Bohme abrasion test, freeze–thaw test, bond strength by pull-off test, ultrasonic pulse velocity (UPV) test, SEM-EDX analysis, XRD analysis, and FT-IR analysis. The new type of road pavement created within the scope of this study exhibited a compression strength of 41.22 MPa, a flexural strength of 25.32 MPa, a Bohme abrasion value of 0.99 cm³/50 cm², a freeze–thaw test mass loss per unit area of 0.77 kg/m², and an average bond strength by pull-off value of 4.63 MPa. It was observed that these values ensured the road pavement specification limits. Full article

Geopolymer concrete (GC) has become apparent as a promising and sustainable alternative to ordinary portland cement (OPC) concrete, presenting notable advantages in both environmental impact and mechanical performance. Despite these benefits, shrinkage remains a critical issue, influencing cracking susceptibility, long-term durability, and structural reliability. While previous investigations have focused on isolated parameters, such as activator concentration or curing techniques, this review provides a comprehensive analysis of the shrinkage behaviour of geopolymer concrete by exploring a broader range of influential factors. Key contributors—including precursor composition, alkali activator concentration, sodium silicate-to-sodium hydroxide ratio, liquid-to-solid ratio, pore structure, and curing conditions—are evaluated and mitigation strategies are discussed. Comparative evaluation of experimental studies reveals key patterns and mechanisms: heat curing around 60 °C consistently limits shrinkage, low-calcium binders outperform high-calcium systems, and chemical additives can reduce shrinkage by as much as 80%. The analysis also highlights emerging, bio-based additives that show promise for simultaneously controlling shrinkage and preserving mechanical performance. By integrating these diverse insights into a single framework, this paper provides a comprehensive reference for designing low-shrinkage GC mixtures. Full article

This study investigates the early-age compressive strength development of concrete incorporating ground granulated blast-furnace slag (GGBFS) under varying water-to-binder (W/B) ratios (35%, 45%, and 55%) and curing temperatures (5 °C, 20 °C, and 35 °C). Concrete mixtures were prepared with 0%, 20%, and 40% GGBFS replacement levels, maintaining a constant slump of 180 mm. The influence of GGBFS on fresh properties was evident, as higher GGBFS content reduced the demand for high-performance air-entraining water-reducing admixture (AEWR) by up to 72% at 40% GGBFS and W/B of 35%. All mixtures maintained target air content within 4.5 ± 1.5%. The Nurse–Saul maturity method was applied to determine the datum temperature $T_0$ (The minimum temperature required for the degree of maturity to increase) for early-age strength prediction. The optimal $T_0$ was found to be −3 °C for both OPC and GGBFS-blended concretes, replacing the conventional −10 °C value. Compressive strength predictions were conducted using Plowman, Logistic, and Gompertz models within the 5–10 MPa range. The Plowman and Gompertz models predicted early-age compressive strength with an error of approximately 10% in the 5–10 MPa range. In the lower strength range of 3–5 MPa, the Gompertz model exhibited superior predictive performance, with prediction errors 0.5–1 MPa lower than those obtained using the Plowman model. These findings will help in enhancing the maturity method’s reliability for low-temperature or time-constrained construction and support the use of GGBFS as a sustainable cement replacement. The study offers practical insights into optimizing early-age performance in blended cementitious systems. Full article

Shotcrete used in underground structures like tunnels is susceptible to sulfate and chloride erosion. In order to systematically study the deterioration law and mechanism of the durability of high-performance shotcrete under a salt erosion environment, the durability test of high-performance shotcrete was carried out by an indoor long-term immersion test using a clear water solution, Na₂SO₄ solution, and Na₂SO₄ and NaCl mixed solution as erosion mediums. A comparative study was conducted on the effects of different curing time, erosion time, erosion medium, and erosion direction on the physical and mechanical properties and SO₄²⁻ content. The microstructure was analyzed to reveal the time evolution process and mechanism of the durability of high-performance shotcrete under coupled erosion. The results show the following: (1) The mass change rate of high-performance shotcrete under the action of coupling erosion increases first, then decreases, and then increases. The compressive strength of the surface perpendicular to the jet direction is better than that of the surface along the vertical jet direction. (2) The diffusion depth of SO₄²⁻ along the injection direction is larger, and the content of SO₄²⁻ is larger at the same depth. The existence of Cl⁻ delays the diffusion of SO₄²⁻ to a certain extent. (3) In the early stage of erosion, the corrosion expansion products generated by the external SO₄²⁻ entering the concrete will fill the original pores and cracks, which improves the durability of the concrete. In the late stages of erosion, the accumulation of corrosion products increases, which accelerates the deterioration of its durability. Full article

Chloride erodes steel bars through concrete pores, seriously affecting the durability of reinforced concrete structures. Improving the binding ability to chloride is an important measure. We explored the effects of W/C, curing age, and premixed Cl⁻ concentration on the compressive strength and Cl⁻ binding capacity in cement pastes. The results indicate that a premixed 5% concentration of Cl⁻ can improve the compressive strength, whereas an excessive Cl⁻ negatively impacts the mechanical properties. The total Cl⁻ content in cement pastes is a crucial factor that influences the binding ability of Cl⁻. When the total Cl⁻ content is within 2% (i.e., the premixed Cl⁻ concentration is 5%), the cement paste has a strong binding ability of Cl⁻. W/C and curing age indirectly affect the binding ability by affecting the total Cl⁻ content. Furthermore, with the increase in content of Cl⁻, the adsorption content of Cl⁻ by C-S-H increased, while the proportion of Cl⁻ bound by Fs to the total bound Cl⁻ initially declines and then tends to stabilize. It is worth noting that a premixed concentration of 5% is a “safety limit” for cement paste, but for reinforced concrete, the presence of free Cl⁻ above normative thresholds should not be underestimated. Full article

Crumb rubber, obtained from discarded tires, presents a sustainable alternative in the construction industry, particularly in rubberized concrete. Treated crumb rubber offers improved mechanical performance; however, limited reports are available on its behavior at elevated temperatures. This study investigates the performance of rubberized concrete containing treated and untreated crumb rubber when exposed to elevated temperatures. The treatments employed are chemical (sodium hydroxide (NaOH)) and physical (cement coating) methods. M30-grade concrete was used as a control mix, and crumb rubber (CR) was added by replacing a portion of the fine aggregate. In order to mitigate the strength reduction, silica fume and polypropylene fibers were added. An optimal mix was determined using Taguchi’s L9 orthogonal array, by varying proportions of crumb rubber, silica fume (SF), and polypropylene (PP) fiber. The ideal mix contained 10% CR, 5% SF, and 0.2% PP fiber based on compressive strength. Specimens were cured for 28 days and exposed to temperatures of 200 °C, 400 °C, 600 °C, and 800 °C for 1 h. Mechanical properties such as compressive strength, split tensile strength, and modulus of elasticity were evaluated, along with an ultrasonic pulse velocity test. The results indicate that treated crumb rubber enhances bonding, improving the mechanical and thermal performance of rubberized concrete under high temperature. Full article

In-situ lunar construction technology is critical for future lunar base development, and the production of geopolymers from lunar regolith—a novel cementitious material with concrete-like properties—has become a vital approach for achieving in-situ resource utilization. This study systematically investigated the influence of basalt fiber content (0–0.4%) on the mechanical properties of lunar regolith simulant geopolymers by controlling key parameters including curing temperature (20 °C and 80 °C), duration (1 d and 7 d), and alkali activator type (strong alkaline solution: a mixture of sodium hydroxide and sodium silicate, and weak alkaline solution: sodium silicate solution). Through testing of 144 specimens, the results revealed that strong alkali-activated specimens with 0.3% fibers cured at 20 °C for 7 d showed optimal ductility with compressive strength of 2.85 MPa and flexural strength of 0.53 MPa, exhibiting characteristic flat stress-strain curves. Specimens with 0.2% fibers under high-temperature curing at 80 °C for 1 d achieved maximum compressive strength of 44.76 MPa and flexural strength of 1.60 MPa but demonstrated brittle failure behavior. Weak alkali-activated specimens containing 0.1% fibers cured at 80 °C for 7 d attained superior comprehensive performance with peak flexural strength reaching 3.88 MPa, showing excellent fiber-matrix synergy. These findings provide important theoretical foundations for optimizing lunar construction materials through customized fiber reinforcement and curing strategies. Full article

This study presents a novel approach to the development of self-compacting concrete (SCC) by partially replacing both cement and fine aggregate (sand) with waste marble sludge (WMS), a byproduct of the marble industry. The research aims to evaluate the feasibility of incorporating this industrial waste into SCC to enhance sustainability without compromising performance. To assess the fresh and hardened properties of the proposed mixtures, a comprehensive experimental program was conducted. Tests included slump flow, T₅₀, and V-funnel for evaluating workability, as well as measurements of specific gravity, compressive strength, flexural strength, Brazilian tensile strength, and water absorption at 28 days of curing. The results demonstrated that the mix containing 5% cement replacement and 20% sand replacement with marble sludge exhibited the highest mechanical performance, achieving a compressive strength of 48.2 MPa, tensile strength of 3.9 MPa, and flexural strength of 4.4 MPa. Furthermore, increasing the percentage of cement replacement led to enhanced flowability, as evidenced by an increase in slump flow diameter and a reduction in V-funnel flow time, indicating improved workability. Overall, the findings suggest that controlled incorporation of WMS can produce SCC with desirable mechanical and rheological properties, offering a promising pathway for sustainable concrete production. In addition to the technical performance, a carbon footprint analysis was conducted to examine the environmental benefits of marble sludge utilization. The mixture with 10% cement and 20% sand replacement exhibited the lowest carbon footprint, while the 7.5% replacement level provided the best balance between strength and sustainability. Full article

With the increasing demand for soil modification technologies in the field of civil engineering, this study employed cement-stabilized soil and MBER (Material Becoming Earth into Rock) stabilized soil as controls to investigate the modification effects of an N-MBER (nanosilica reinforced MBER) stabilizer on the mechanical properties and microstructure of loess. The mechanical and water stability characteristics of N-MBER-stabilized loess under varying moisture contents and compaction degrees were analyzed through unconfined compressive strength (UCS) tests, softening coefficient tests, falling-head permeability tests, and wet–dry cycle tests. Combined with scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance (NMR) techniques, the underlying mechanism of the N-MBER stabilizer in loess stabilization was thoroughly revealed. The results indicate that the N-MBER stabilizer significantly enhances the UCS and softening coefficient of loess. Particularly, under conditions of 28-day curing, a moisture content of 16%, and a compaction degree of 1, the compressive strength achieves a local optimum value of 3.68 MPa. Compared to soils stabilized with MBER stabilizers and cement stabilizers, the N-MBER-stabilized loess exhibits superior water resistance and microstructural density, with a significant reduction in the proportion of pore defects. Specifically, after five wet–dry cycles at a curing age of 28 days, the strength loss rates for MBER-stabilized soil and cement-stabilized soil were 24.4% and 27.54%, respectively, while that for N-MBER-stabilized soil was 18.23%, demonstrating its enhanced water resistance. Additionally, compared to cement-stabilized soil, the N-MBER-stabilized soil exhibited a 21.63% reduction in total pore number, with a 41.64% reduction specifically in large pores. The extremely small particle size and large specific surface area of the nanomaterial enable more effective interactions with soil particles, promoting hydration reactions. The resulting ettringite (AFt) and three-dimensional networked C-S-H gel tightly interweave with soil particles, forming a stable cemented structure. Compared to traditional concrete roads, stabilized soil roads enable the utilization of locally available materials and demonstrate a significant cost advantage. This study provides theoretical support and experimental evidence for the application of nanomaterials in loess improvement engineering. Full article

This study evaluates adhesive bolts (chemical anchors) bonded with epoxy and vinyl ester resins for surface and tunnel excavations in tropical mining environments under static and dynamic loading. Over 300 pull-out tests in concrete and hard rock examined the effects of bolt length, curing time, and substrate condition on load capacity, failure mode, and bond–slip response. Epoxy anchors exhibited higher bond strength, including under early-age and thermally active conditions, while vinyl ester showed improved ductility and post-peak behaviour in fractured rock. Numerical modelling with Rocscience RS2 (Phase 2) and Unwedge simulated excavation responses for bolt lengths of 190–250 mm and spacings of 0.5–2.0 m. Tensile failure dominated at wider spacings, whereas closely spaced anchors enhanced confinement and redistributed stresses. The combined experimental–numerical evidence quantifies chemical-anchor performance in complex subsurface settings and supports their use for early-age support and long-term stability. Findings motivate integration of resin-grouted bolts into modern support designs, particularly in seismically sensitive or hydrothermally variable mines. Full article

The high density of the internal structure of new-generation cementitious composites, such as high-performance and ultra-high-performance concretes, necessitates the use of advanced methods for evaluating their transport properties, particularly those employing a gaseous medium. The developed gas permeability method for cement pastes, based on a modified RILEM-Cembureau approach, has proven to be highly accurate, reliable, and extremely sensitive to changes in the porosity characteristics of such composites. The article contains the results of a study of the mass transport capabilities of blended cement pastes, characterised by variable water–cement ratios. Two types of cements were used in the study: with the addition of fly ash and blast furnace slag. Ordinary Portland cement was used as the reference binder. The tests were conducted after long-term curing under natural conditions, i.e., after 90 days and 2 years. The assessment of open porosity was carried out through three techniques: helium pycnometry, mercury intrusion porosimetry, and water saturation. Permeability, on the other hand, was measured using a customized approach tailored for uniform paste materials. Microstructural changes were also analysed in the context of natural hydration carbonation progress. The results presented allowed a quantitative description of the effects of the w/c ratio, the presence of additives, and the progress of hydration and carbonation on the porosity of pastes and their permeability to gas flow. The two-year curing period of the pastes exposed to natural CO₂ resulted in a reduction of the permeability coefficient k ranging from 11% to 74%, depending on the type of cement and the water-to-cement (w/c) ratio. This decrease was caused by the continued progress of hydration and simultaneous carbonation. The results of the research presented are of interest from both an engineering and scientific point of view in the context of long-term microstructural changes and the mass transport abilities of cement pastes associated with these processes. The extensive range of materials compositions investigated makes it possible to analyse the durability and tightness of many cementitious composites over long periods of service. Full article

With global sustainable construction growth, fully recycled coarse aggregate concrete (RCAC)—eco-friendly for cutting construction waste and reducing natural aggregate over-exploitation—has poor durability in seasonally freezing saline-soil regions (e.g., Tumushuke, Xinjiang): freeze-thaw and salt ions (NaCl, Na₂SO₄) cause microcracking, faster performance decline, and shorter service life, limiting its use and requiring better salt freeze resistance. To address this, a field survey of Tumushuke’s saline soil was first conducted to determine local salt type and concentration, based on which a matching 12% NaCl + 4% Na₂SO₄ mixed salt solution was prepared. RCAC specimens modified with fly ash (FA), silica fume (SF), and polypropylene fiber (PPF) were then fabricated, cured under standard conditions (20 ± 2 °C, ≥95% relative humidity), and subjected to rapid freeze-thaw cycling in the salt solution. Multiple macro-performance and microstructural indicators (appearance, mass loss, relative dynamic elastic modulus (RDEM), porosity, microcracks, and corrosion products) were measured post-cycling. Results showed the mixed salt solution significantly exacerbated RCAC’s freeze-thaw damage, with degradation severity linked to cycle count and admixture dosage. The RCAC modified with 20% FA and 0.9% PPF exhibited optimal salt freeze resistance: after 125 cycles, its RDEM retention reached 75.98% (6.60% higher than the control), mass loss was only 0.28% (67.80% lower than the control), and its durability threshold (RDEM > 60%) extended to 200 cycles. Mechanistic analysis revealed two synergistic effects for improved performance: (1) FA optimized pore structure by filling capillaries, reducing space for pore water freezing and salt penetration; (2) PPF enhanced crack resistance by bridging microcracks, suppressing crack initiation/propagation from freeze-thaw expansion and salt crystallization. A “pore optimization–ion blocking–fiber crack resistance” triple synergistic protection model was proposed, which clarifies admixture-modified RCAC’s salt freeze damage mechanism and provides theoretical/technical guidance for its application in extreme seasonally freezing saline-soil environments. Full article

The urgent need to decarbonize the construction sector has prompted research into sustainable alternatives to conventional concrete. This study compares two industrially produced pulps with contrasting lignin contents: a bleached kraft cellulose pulp with near-zero lignin used in paper production and a thermo-mechanical lignocellulose pulp with high lignin content used in MDF production. Fiber-reinforced composites were produced by partially replacing mineral aggregates with fibers at dosages from 0.1% to 3% by mass and air-curing to simulate practical curing conditions. The specimens were evaluated for density, water absorption, and compressive strength, with compressive strength measured at 7, 28, and 60 days. Results showed a reduction in density for both fiber types, along with increased water absorption and decreased compressive strength at higher fiber contents. Cellulose composites achieved a more favorable mechanical performance than lignocellulose composites but showed markedly higher water absorption, raising concerns about long-term durability. By testing two pulps that differ primarily in lignin content across multiple replacement ratios, the study provides a systematic comparison of their effects on composite properties. The comparison explicitly contrasts the lignin contents of the two industrial pulps—bleached kraft (~0.1%) versus thermo-mechanical (27.4%)—to isolate lignin-driven effects on hydration and property development. A practical air-curing protocol was adopted, leveraging fiber-bound/process water, thereby reflecting use cases where external water curing is constrained. Full article

To investigate the regulatory mechanism of polyoxymethylene (POM) fiber on the workability and mechanical properties of C30-grade coral aggregate concrete (CAC), this study designed six groups of CAC specimens with varying POM fiber volume fractions (0%, 0.2%, 0.4%, 0.6%, 0.8%, and 1.0%). Cube compressive test, axial compressive test, split tensile test, and flexural tests of CAC specimens after 28 days of curing were conducted, while observing their failure modes under ultimate load and stress–strain curves. The experimental results indicate that POM fiber incorporation significantly reduced the slump and slump flow of the CAC mixtures. The cube compressive strength, axial compressive strength, split tensile strength, and flexural strength of CAC initially increased and then decreased with increasing POM fiber volume fraction, peaking at 0.6% fiber content. Compared to the fiber-free group, these properties improved by 14.78%, 15.50%, 17.01%, 46.13%, and 3.69%, respectively. Analysis of failure modes under ultimate load revealed that POM fibers effectively reduced crack quantity and main crack width, producing a favorable bridging effect that promoted a transition from brittle fracture to ductile failure. However, when fiber volume fraction exceeded 0.8%, fiber agglomeration led to diminished mechanical performance. Based on experimental data, the constitutive relationship established using the Carreira and Chu model achieved a goodness-of-fit exceeding 0.99 for CAC stress–strain curves, effectively predicting mechanical behavior and providing theoretical support for marine engineering applications of coral aggregate concrete. This study provides a theoretical basis for exploiting coral aggregates as low-carbon resources, promoting CAC application in marine engineering, and leveraging POM fibers’ reinforcement of CAC to reduce reliance on high-carbon cement. Combined with coral aggregates’ local availability (cutting transportation emissions), it offers a technical pathway for marine engineering material preparation. Full article