To ameliorate shrinkage problems in concrete, the most common route is to cut down the cementitious paste volume. This study proposed and demonstrated the strategy of filling industrial waste powder into the voids among aggregate particles in order to effectively fulfill the target of reduction in cementitious paste volume without air entrapment in concrete. The workability, strength and shrinkage of concrete mixes with 0-12.5% industrial waste powder content to replace cementitious paste at 0.35-0.60 water/cement ratio have been measured through slump, flow, cube strength, prism shrinkage tests. Results disclosed that utilization of industrial waste powder to replace cementitious paste significantly lowered the ultimate shrinkage strain by as high as 58.3% and prolong the shrinkage half-time by as high as 47.1%. In-depth analysis revealed that ultimate shrinkage strain was governed mainly by the cement content whereas shrinkage half-time was governed mainly by the water content.

This study develops a cost-effective, mass-producible blast-resistant concrete (BRC) that combines high dynamic performance with excellent workability with a low steel fiber content. To improve practical applicability, locally sourced river sand was used to partially replace quartz sand. The steel fiber volume fraction was limited to 1%, enabling high flowability suitable for ready-mixed concrete production while maintaining ultra-high compressive strength exceeding 180 MPa. A two-stage experimental program was conducted. First, river sand particle size distributions were optimized based on fresh properties and quasi-static mechanical performance. Second, the effects of steel fiber geometry-micro-straight (S), hooked (H), and wavy (W)-on compressive, flexural, and tensile behavior were systematically investigated under both quasi-static and high strain-rate load conditions, including impact tests and high-speed direct tensile tests. The results demonstrate that strain rate significantly enhances strength, stiffness, and energy absorption for all mixtures. Deformed fibers substantially improve post-cracking behavior and dynamic resistance due to enhanced mechanical interlocking and fiber-matrix bonding. Compared with straight fibers, H- and W-type fibers exhibit higher dynamic peak strength, strain capacity, and toughness. Among them, W-type fibers show superior energy absorption and more stable post-peak behavior. Based on the experimental data, strain rate-dependent dynamic increase factor (DIF) models for compressive and tensile strengths were established, explicitly incorporating steel fiber type. These fiber-type-dependent DIF models constitute the main novelty of this study and provide practical input for blast-resistant structural design and numerical simulations.

This study examined the impact behavior and failure mechanism of corroded reinforced concrete (RC) beams strengthened with fiber reinforced polymers (FRP) grid-ultra-high-performance concrete (UHPC) composites. Finite element (FE) models were developed and thoroughly validated against existing experimental data. Furtherly, the effects of corrosion rate, strengthening scheme, and impact velocity were systematically analyzed. The results indicate that corrosion of longitudinal rebars concentrated flexural damage in the impact region and increased deformation. Both pure UHPC and FRP-UHPC strengthening enhanced flexural resistance and reduced sectional damage factor by up to about 44%. While minimally affecting the first peak impact force, both strengthening significantly increased the second peak. However, the high stiffness of FRP-UHPC layer induced stress concentration at the UHPC-normal concrete (NC) interface, leading to premature debonding. Transverse U-shaped anchors mitigated debonding, though local debonding might persist in unanchored zones. Increasing interfacial bond strength, simulating rebar planting, could effectively prevent interface debonding, but required approximately twice the normal strength. Therefore, a combined strategy employing interfacial rebar planting and transverse U-shaped anchors at a spacing less than 1.0h0 (h0 is the beam effective depth) is recommended to suppress debonding and fully utilize the material potential of FRP and UHPC.

Microwave-assisted crushing of coarse aggregate is a promising future development trend in the technology for producing recycled coarse aggregates. This paper presents an innovative approach that combines finite element and discrete element methods to simulate and investigate the process of microwave-assisted crushing of concrete under various conditions, including different coarse aggregate content and microwave power levels. The finite element method is utilized to examine the distribution of electromagnetic fields and temperatures within the microwave field, while the discrete element method focuses on studying the cracking mechanism of concrete in this environment. Experimental validation confirms the accuracy of simulation results and evaluates the impact of microwave-assisted crushing on concrete by determining its reduction in strength after irradiation. The study reveals that changes in coarse aggregate content and microwave power influence multiple aspects during specimen crushing, such as electric field, power density, temperature, and crack distribution evolution. Uniaxial compression tests demonstrate both the magnitude of reduction in compressive strength caused by microwave radiation and energy consumption per unit mass for a 1 MPa decrease in concrete strength. These findings indicate that pre-irradiation with microwaves can effectively reduce concrete strength during waste concrete crushing processes while facilitating resource recycling.

This study investigates the mechanical and microstructural behavior of lightweight engineered geopolymer composites (LWEGCs) containing nano tubes under high temperatures. LWEGCs were fabricated using fly ash, silica fume, slag, metakaolin, and fly ash microspheres as binders, with ceramsite-based lightweight aggregates (LAs) such as clay-based (CBC), granulated blast furnace slag-based (GBC), and shale-based (SBC) aggregates. Compressive stress and mass loss were assessed after exposure to temperatures extending from 200℃ to 800℃. Scanning electron microscopy (SEM), X-ray Diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were used to assess the phase assemblage of the produced LWEGC mixes. Results depicted that matrix compaction increased the compressive stress of LEGC-REF by 27.27% at 200℃, while thermal deterioration caused a considerable decrease of 43.47% at 600℃ and 135.71% at 800℃. With mass loss increasing to 22.54% at 800℃, LEGC-CBC exhibited the lowest thermal stability, whereas LEGC-SBC had superior stability with 20.1% mass loss. The material's integrity was diminished by the development of cracks and a honeycomb structure at high temperatures, according to SEM research. By strengthening the geopolymer matrix and bridging microcracks, MWCNTs enhanced microstructural cohesiveness despite degradation. This study emphasizes how LWEGCs can be used in high-temperature applications and how LAs and MWCNTs can enhance mechanical and fire resistance.

In the high exterior temperature, the cracking possibility due to hydration heat and drying shrinkage also increases, and the ion penetration and the related corrosion increase since the ions move rapidly. In this study, the sulfate diffusion behavior with increasing temperature was evaluated and its activation energy was derived for evaluating the deterioration behavior in the NPP (Nuclear Power Plant) concrete for sulfate ion ingress. After obtaining the materials used in the NPP, concrete samples were prepared, and the temperature-dependent sulfate diffusion coefficients were obtained while elevating the temperature from 20℃ to 50℃ with 10℃ interval. During the process of temperature elevating, the diffusion coefficient increased to a level of 3.4 times, and the activation energy range was measured to 19.4-28.9 KJ/mol with average of 22.3 KJ/mol, which had no significant differences from the those of chloride diffusion results. Finally, the sulfate ion ingress behavior was simulated considering effect of temperature, repairing thickness, and cover depth, which showed a significant sulfate intrusion due to elevated temperature.