Low-content graphite powder for improving the compressive–tensile strength and fracture behavior of recycled aggregate concrete

Analysis of Splitting Tensile Damage Behavior and Deterioration Mechanism of Aluminate Cement-Based Ultrahigh-Performance Concrete under Simulated Fire Temperatures

Traditional portland cement (PC)-based ultrahigh-performance concrete (UHPC) is prone to spalling under fire temperatures due to its dense microstructure, accompanied by severe performance degradation, which hinders its widespread application in engineering. Therefore, this study developed an aluminate cement-based UHPC (AUHPC) with excellent high-temperature resistance and antispalling performance, and systematically investigated the effects of steel fiber type, content, and exposure temperature on the compressive and splitting tensile properties. The results indicate that steam and dry-heat curing effectively inhibit the strength retrogression caused by the transformation of CAH 10 to C 3 AH 6 . Meanwhile, with the increase in temperature, recycled brick powder (RBP) participates in the hydration reaction and forms stable C 2 ASH 8 . At 400°C, the compressive and splitting tensile strengths of AUHPC specimens containing 5% RBP reach the maximum, with the strength of RSF2 specimens increasing by 37.2% and 46.3%, respectively, compared with that at room temperature. When the temperature exceeds 600°C, the number of pores on the specimen surface decreases gradually, while the cracks increase and widen. At 800°C, the splitting tensile strength of NSF2 and RSF2 series specimens decreases by 44.6% and 7.9%, respectively, compared with that at 20°C. At 1,200°C, the holes and channels left by the complete melting of normal steel fibers (NSF) aggravate the high-temperature damage, and the strength decreases with the increase of NSF content, while refractory steel fibers (RSF) exhibit better compatibility with AUHPC matrix.

Effect of graphite content (2–12 wt%) on densification, hardness and compressive response of Cu–8Fe composites

Experimental investigation of the stress-strain behavior of concrete produced with natural perlite aggregate and waste materials

The replacement of conventional aggregates in concrete with alternative and waste-based materials has become an important research area for sustainable construction. This study experimentally investigated the effects of natural perlite aggregate replacement and fiber reinforcement on the mechanical and microstructural properties of concrete. Natural perlite aggregate was used to replace conventional crushed stone aggregate at replacement levels of 0%, 30%, 70%, and 100%, while hemp shives, recycled plastic waste fibers, and polypropylene (PP) fibers were incorporated at volume fractions of 0.0%, 0.5%, 1.0%, and 1.5%. After 28 days of curing, compressive strength, modulus of elasticity, flexural strength, splitting tensile strength, ultrasonic pulse velocity (UPV), compressive stress–strain behavior, and scanning electron microscopy (SEM) analyses were performed. The results showed that 30% perlite replacement increased the compressive strength and modulus of elasticity by approximately 6.67% and 4.08%, respectively, compared with the reference mixture. In contrast, replacement levels of 70% and 100% reduced the mechanical performance due to the porous structure of perlite and the weaker interfacial transition zone. Among the fiber-reinforced mixtures, the optimum fiber content was found to be 1.0%, while PP fibers provided the best overall performance in terms of crack-bridging ability and energy absorption. Overall, the combination of 30% natural perlite aggregate replacement and 1.0% PP fiber was identified as an effective approach for producing low-carbon concrete with balanced mechanical properties.

Uniaxial compressive properties and microstructural failure mechanisms of concrete made with alkali-activated slag and rubber aggregates

Alkali-activated slag–rubber aggregate concrete (Asrac) is a novel green building material in which waste rubber particles partially or fully replace natural aggregates, and alkali-activated industrial slag is used as a substitute for traditional cement. However, studies on the axial compressive mechanical properties of Asrac are limited, restricting its structural applications. Therefore, in this study, the effects of rubber as replacements for natural aggregates and steel fibre (SF) content on the axial compressive behaviour of Asrac were investigated. The results showed that a 100% rubber replacement rate reduced the compressive strength by 58.97–80.52%, but significantly enhanced ductility, as evidenced by a 91.49% increase in peak compressive strain. Optimal performance was achieved at a SF dosage of 1–2%, with 1% SF yielding a maximum strength increase of 64.48% owing to effective crack-bridging mechanisms. A modified axial compressive constitutive model based on a previous model work was developed. By incorporating a rubber softening coefficient, the model accurately captured the complex synergistic interactions within the Asrac, with correlation coefficients exceeding 0.90. X-ray diffraction analysis confirmed that the dominant phases were calcium silicate hydrate (29–35°) and quartz (26.5°), while the absence of calcium hydroxide (Ca(OH)2) indicated that the alkali-activation reaction governed the hydration mechanism.

Mechanical Properties and Modulus Correlations of High-Strength Lightweight Concrete with Fly Ash Cenospheres

Lightweight concrete containing fly ash cenospheres (FAC) approaches a sustainable solution for cutting structural dead loads while maintaining high strength. This study investigates the mechanical properties and hydration behavior of high-strength lightweight concrete (HSLWC) using FAC as a partial sand replacement and supplementary cementitious materials (SCMs), including silica fume (SF), ground granulated blast furnace slag (GGBFS), and nano-silica (nS). Twelve mixes were proposed to evaluate the effects of FAC and SCMs on density, compressive strength, flexural strength, and elastic modulus. The results demonstrated that an increase in FAC content significantly decreased density while enhancing specific strength, highlighting the effectiveness of FAC in lightweight applications. SCMs enhanced the microstructure and mechanical performance via pozzolanic reactions and C─ S─ H formation. The optimal mix, comprising 40% GGBFS and 0.5% nS, achieved a compressive strength of approximately 80 MPa and showed improved flexural strength compared with the control. Thermogravimetric analysis confirmed a marked reduction in Ca(OH) 2 content, indicating active pozzolanic reactions. Unlike previous studies that focused only on strength or density, this work establishes predictive correlations between modulus, strength, and density ( R 2 > 0.94 ), enabling engineering-based performance design of FAC HSLWC. These findings provide valuable insights into the design of high-performance, sustainable, and lightweight concrete.

Structural characteristics of geopolymer concrete beams using alkali-modified blended ash: a comparative evaluation with conventional beams

ABSTRACT This study evaluates the fresh-state rheology and flexural performance of ambient-cured geopolymer concrete (GPC) as a sustainable alternative to M35 grade concrete. Using fly ash and GGBS activated by sodium hydroxide (SH) and sodium silicate (SS), the research investigated a parametric molarity range from 4M to 12M. Fresh-state analysis showed that increasing SH concentration significantly raised dynamic viscosity, reducing slump by up to 79%. An 8M threshold was identified for optimal workability and compaction. Mechanical testing revealed 8M as the robust performance optimum, achieving a 28-day compressive strength of 57.53 MPa (23.7% above control) and a flexural load of 112 kN. While GGBS enabled rapid early-strength gain (reaching up to 93% of 28-day strength within 7 days), the 4M configuration was insufficient for structural use. All GPC beams exhibited an under-reinforced failure mode with extensive strain-hardening, yielding capacity ratios between 1.43 to 2.50. Despite the superior ductility and energy absorption of GPC-8M, the findings are presented as indicative performance trends due to the reliance on single-beam specimens per configuration. Furtheremore, the absence of quantitative Life Cycle Assessment or durability profiles necessitates a cautious interpretation of GPC. These findings establish a deterministic benchmark for optimizing molarity in structural geopolymer applications.