This study investigates the effects of steel fiber and silica fume on the mechanical and fracture properties of ultra-high performance geopolymer concrete (UHPGC). Four volume fractions of steel ...fiber (0%, 1%, 2% and 3%) and four contents of silica fume by the mass of total binders (5%, 10%, 20% and 30%) were used. The mechanical and fracture properties evaluated include the compressive, splitting tensile and ultimate flexural strengths, modulus of elasticity, flexural behavior, fracture energy and stress intensity factor. In addition, the correlations among the compressive and splitting tensile strengths, and compressive strength and elastic modulus were studied. The results indicated the increase of steel fiber dosage resulted in the decrease of the workability, but the continuous improvement of mechanical and fracture performance of UHPGC. The empirical equations for predicting elastic modulus of conventional ultra-high performance concrete overestimated the elastic modulus of UHPGC, however some prediction formulas for the splitting tensile strength of PC-based concretes could be applied for UHPGC. Silica fume had a complicated influence on workability and hardened properties of UHPGC, which is strongly dependent on its amount. The inclusion of 10% silica fume induced the increase of the flowability, but the sharp degradation of the mechanical performance, while the specimens with 20% and 30% silica fume possessed the superior mechanical characteristic to that with 5% silica fume. The steel fiber dosage could be decreased without sacrificing the mechanical and fracture performance of UHPGC, via the increase of silica fume content.
•The development in fracture mechanics models of concrete is presented.•Various determination methods of fracture parameters for FRCC are summarized.•Different factors affecting the fracture ...properties of FRCC are reviewed systematically.•Reinforcement mechanism of FRCC on fracture properties is discussed.•Future work on fracture properties of FRCC is suggested.
Fiber reinforced cementitious composites (FRCC) have been widely used in the field of civil engineering in terms of high-performance building material. The fracture mechanics has been generally considered as an effective way to perform the stability analyses of cracks and safety assessment of concrete structures. This review article first introduces several theoretical models of fracture mechanics and different testing methods of fracture parameters for FRCC. Then the factors affecting fracture properties of FRCC are reviewed respectively, including fiber type, fiber content (Vf), water-to-cement ratio (w/c), maximum aggregate particle size (dmax), aggregate type, initial crack length (a0), high temperature and freeze–thaw cycle times. Furthermore, the reinforcement mechanism of fiber to improve fracture properties of FRCC is discussed, and future work is recommended. This review provides fundamentals on measuring fracture properties, also is to understand the fracture behaviors of FRCC.
•137 papers are reviewed on basalt fiber-reinforced concrete (BFRC).•Influences of basalt fiber (BF) on the mechanical properties and fracture properties of BFRC are reviewed.•Effects of BF on the ...durability and the microstructure of BFRC are discussed.•Further suggestions for the research and application of BFRC are proposed.
In recent years, basalt fiber (BF) has been extensively used as a reinforced fiber to improve the mechanical properties and durability of concrete because of its excellent mechanical properties, high-temperature resistance, acid and alkali resistance, availability of raw materials, and environmentally friendly production processes. Based on a thorough review of recent literature, the current research status of basalt fiber-reinforced concrete (BFRC) in terms of the basic mechanical characteristics, fracture performance, and durability under different test conditions were reviewed in this study, and future research directions and trends were predicted and analyzed. It is shown that the reasonable addition of BF with a diameter of approximately 10–20 μm, length of approximately 12–20 mm, and an optimal volume fraction of approximately 1 % in concrete can better improve the mechanical properties of concrete. Furthermore, BF significantly improves the fracture toughness, fracture energy, and maximum deflection of concrete, effectively increasing the impermeability, resistance to concrete chloride erosion, and sulfate attack. In addition, the advancements in methods for the numerical simulation of concrete fractures and calculation of the chloride ion permeability coefficient were also summarized in this paper. Based on the shortcomings of the current study, it is suggested that future studies should focus on the mechanical properties and durability of BFRC under high-temperature and after damage. The toughening mechanism of BF on hydraulic concrete concrete should be studied, with the objective of laying the theoretical foundation for its application in practical engineering.
•The incorporation of RAP reduced the fracture toughness and energy at −15 °C while it resulted in an increase in these fracture properties at 25 °C under different loading modes.•The use of ...recycling agents increased the fracture toughness and energy at subzero-temperature under different loading modes.•The fracture toughness and energy of mixtures at mid-temperature decreased by addition of recycling agents.•The efficacy of recycling agents on the fracture properties depending on the type and origin of recycling agents.
This paper aims to evaluate the influence of two recycling agents (RAs) on the cracking behavior of warm mix asphalt (WMA) containing up to 50% reclaimed asphalt pavement (RAP). Two chemically different types of recycling agents, namely aromatic extracts and triglycerides/fatty acids, together with a WMA additive (Sasobit®) were introduced to the mixture. A hot mix asphalt (HMA) mixture (as control mixture) and seven WMA mixtures containing three different dosages of RAP (0, 25, and 50%) and modified by two RAs were prepared. The fracture toughness and energy of the above-mentioned asphalt mixtures were evaluated under pure modes of I and II and mixed mode I/II using the semi-circular bending (SCB) test at mid and subzero temperatures. The results indicated that the cracking resistance of the WMA mixtures without RAP is better than the HMA mixtures under different modes of fracture regardless of the temperature (−15 °C and 25 °C). In addition, at −15 °C, the presence of RAP in the WMA mixtures reduced the fracture toughness and energy while at 25 °C, it results in an increase in fracture toughness and energy. Moreover, the addition of RAs to the WMA mixtures containing RAP increased the fracture toughness and energy at −15 °C. Although RAs decreased the fracture toughness and energy of the RAP blended WMA mixtures at mid-temperature, the performance of these mixtures was better than the HMA mixture.
•The effects of cyclic loading paths on the fracture behaviors of granite are studied experimentally.•The characteristics of AE and FPZ under different loading paths are obtained and compared.•The ...strengthening/weakening mechanisms of granite under cyclic loading are revealed.
To investigate the impact of cyclic loading paths on the Mode I fracture characteristics of granite, a series of fracture tests were conducted on semi-circular bend (SCB) specimens using acoustic emission (AE), digital image correlation (DIC) and 3D scanning. The tests included monotonic loading, variable amplitude (VA) cyclic loading, and tiered constant amplitude (TCA) cyclic loading. The results demonstrated that VA cyclic loading leads to an average enhancement of 5.6% in fracture toughness, whereas TCA cyclic loading results in an average reduction of 3.7% in fracture toughness. During cyclic loading and unloading, the TCA loading path exhibits a higher rate of cumulative plastic deformation growth and greater magnitude cumulative plastic deformation compared to the VA loading path. Additionally, detailed observations from 3D scanning revealed that under cyclic loading, the fracture trajectories and surface morphology exhibit more tortuosity and roughness compared to monotonic loading, particularly in the case of TCA cyclic loading. Furthermore, according to the AE and DIC analysis, the proportion of microcrack initiation and stable propagation stage, cumulative AE counts and fracture process zone (FPZ) size generated under VA cyclic loading are greater than those generated under TCA cyclic loading, displaying a consistent variation pattern with fracture toughness. The changes of fracture properties can be attributed to a competition between the compaction-induced hardening effect and the cracking-induced damage effect. A higher cyclic upper limit and incomplete unloading are more likely to accelerate the growth of the irreversible crack damage and rapid crack extension, resulting in weakened rock fracture properties. These findings provide important references for rock instability control in underground rock engineering.
Growing amount of agricultural waste and its burning in open environments is contributing towards the carbon emissions and triggering serious health hazards. It can be reduced by beneficially ...employing the wastes, as carrier media of calcite (CaCO3) precipitating microbes, into the concrete. Instant formation of CaCO3 in micro-cracks using bio-inspired concrete prevents aggressive ions to penetrate into the inside concrete, hence boosting the durability. In the present study, Bacillus subtilis (BS) were immobilized with nano-micro sized carbonaceous solid material, bagasse ground biochar (GBC), to enhance the CaCO3 precipitation. The mechanical behavior of the samples was investigated in terms of bending and compression. Biochar immobilized BS concrete (BSCM) exhibited promising flexural behavior, higher strain energy storing capability, and higher modulus of fracture toughness. Moreover, 23.18% enhancement in compressive strength was achieved after 56 days of curing in comparison to the control samples. Furthermore, autonomous cracks closure mechanism was monitored as the function of time, the BSCM showed effective crack healing with maximum 100% and 68% sealing of 500 μm and 800 μm wider cracks respectively, in the selected time frame. The BSCM samples revealed higher ultrasonic pulse velocities and lesser sorptivity due to the densified microstructure of concrete by bacterial precipitated CaCO3. The x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy and thermal gravimetric analysis confirmed the existence of CaCO3 inside the cracks. Consequently, immobilizing BS with bagasse GBC could be considered as a promising solution for prompt cracks repairing and enhancing the mechanical properties of concrete.
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•Biochar was produced from bagasse using one step pyrolysis method and used as immobilizer for Bacillus subtilis in concrete.•Detailed micro forensic analysis was conducted for produced ground biochar.•Efficient cracks closure was observed in concrete by the immobilized bacterial spores.•Enhanced flexural and compressive responses were seen for the bio-immobilized samples.•Wider cracks (maximum of 500 μm) healing mechanism has been developed and achieved 95% compressive strength recovery.
Recycled aggregate concrete (RAC) made from construction and demolition wastes has several environmental benefits. Fire is one of the most common disasters in buildings, and RAC is a brittle ...construction material; therefore, the bearing capacity of RAC structures under high temperatures should be considered. According to previous studies, crumb rubber made of waste tires can further reduce damages to RAC under high temperatures. Meanwhile, fracture behaviors are one of the key characteristics of concrete materials that need to be considered, but few studies have focused on their behavior when subjected to elevated temperatures. Rubber-modified RAC (RRAC) notched beam specimens with three recycled aggregate substitutions (0%, 50%, and 100%), and four rubber contents (0%, 2%, 4%, and 6%), exposed to high temperatures (200 °C, 400 °C, and 600 °C), were tested using the three-point bending test. The fracture behaviors of the RRAC, including the crack mouth opening displacement, fracture energy, and fracture toughness were analyzed. The results show that the effect of rubber particles on the unstable fracture toughness is greater than that on the initial cracking toughness of RAC after exposure to high temperatures. However, the enhanced effect of rubber on the fracture resistance decreases after subjecting it to a high-temperature treatment owing to the softening and eventual decomposition of rubber at high temperatures. Consequently, in order to avoid the drawbacks introduced by rubber, a rubber content of more than 4% is not recommended considering the mechanical and fracture performance of RRAC.
•The fracture behaviors of rubber-modified recycled concrete (RRAC) were studied.•Thermal damage increases the fracture energy and fracture toughness of RRAC.•Double-K criterion was employed to analyzed the fracture performance of RRAC.•The mesostructure of RRAC after high-temperature treatment was explored.•The optimal ratio of rubber content was obtained.
•TPB test was performed to explore the effect of basalt fiber on geopolymer concrete.•The strengthening mechanisms of basalt fiber were explored by SEM.•A decrease in crack length of basalt ...fiber–reinforced FAGCs was observed via DIC.•MTH method was used to analyze elastic properties of basalt fiber–reinforced FAGCs.
A comprehensive experimental study was conducted to explore the fracture characteristics of basalt fiber–reinforced fly ash geopolymer concretes (FAGCs) with different fiber contents (0.025%, 0.05%, 0.1%, 0.15%). The fracture behaviors of the basalt fiber–reinforced FAGCs, such as load-crack mouth opening displacement curve, fracture toughness, fracture energy, crack propagation length, were investigated by three-point bending tests, and their strengthening mechanisms were explored by scanning electron microscopy. In addition, the Mori–Tanaka homogenization (MTH) method was introduced to analyze the elastic properties of the basalt fiber–reinforced FAGCs. It was found that the addition of basalt fibers improved the peak load, fracture toughness, and fracture energy of the basalt fiber–reinforced FAGCs, and the most significant improvements were noticed in the concrete with the basalt fiber content of 0.05%. Moreover, a decrease in the crack length of the basalt fiber–reinforced FAGCs was observed before the load level of the post-80% peak load. The elastic properties of the basalt fiber–reinforced FAGCs were analyzed based on the MTH theory, and numerical results were found to be in good agreement with experimental findings.
•HVFA mortar with 0–1.5 wt% NS and 0–1.0 vol% PVA fibers were studied.•NS greatly improves the fracture properties of PVA fiber-reinforced HVFAM.•NS significantly increases the 28-day mechanical ...strength of HVFAM.•NS condenses the interfacial transition zone between matrix and PVA fibers.
Using nano-silica (NS) in cement-based materials has attracted extensive attention. However, whilst most studies focused on the hydration, fresh, mechanical and durability properties, there is limited information on the effect of NS on the fracture properties of fiber-reinforced high-volume fly ash mortars (HVFAM). In this paper, a series of experiments were carried out to evaluate the effect of NS on the fracture and mechanical properties of polyvinyl alcohol (PVA) fiber-reinforced HVFAM, with the fly ash/binder ratio fixed at 50% by weight. Four NS/binder weight ratios of 0% 0.5%, 1.0% and 1.5%, and four PVA fiber volume dosages of 0%, 0.2%, 0.5% and 1.0% were adopted. Compared to 0.2–1.0 vol% PVA fiber-reinforced HVFAM without NS, the addition of 0.5 wt% NS could further increase the flexural strength, fracture energy, fracture toughness, critical crack tip opening displacement and brittleness index by 3–5%, 8–29%, 17–28%, 18–38% and 34–95%, respectively; the addition of 1.0 wt% NS could increase the flexural strength, fracture energy, fracture toughness, critical crack tip opening displacement and brittleness index by 4–9%, 15–41%, 26–46%, 18–48%, and 62–79%, respectively. The mineralogy and microstructure characterizations showed that the NS condensed the fiber/matrix interface. These findings provide insights into designs and applications of fiber-reinforced high-volume pozzolan cement-based materials with nano-particles.
