Polypropylene Fiber Reinforced Concrete Research Articles

Modelling and optimisation of the structural performance of lightweight polypropylene fibre-reinforced LECA concrete

Lightweight fibre-reinforced concrete integrates the advantages of lightweight aggregates with the strength-enhancing properties of fibres, resulting in a lighter composite with enhanced impact and mechanical performance. However, achieving an optimal balance between structural weight, and performance remains a challenging endeavour. This study investigates the mechanical properties, impact energy absorptions, flexural toughness, and crack resistance of lightweight fibre-reinforced concrete with the coarse aggregate entirely replaced with lightweight expanded clay aggregate (LECA). Concrete mixes containing 0 %, 0.5 %, 0.75 %, and 1.0 % Polypropylene fibre (PPF) and 10 % micro-silica were experimentally investigated. Predictions for concrete mixes with up to 2 % PPF were made using regression models developed from experimental data. The experimental and predicted results were analysed using response surface methodology. The findings reveal significant enhancements of up to 300 % and 570 % in toughness indices I5 and I10 at 1 % PPF, coupled with a 55.4 % increase in residual strength. Furthermore, an optimised slab thickness of 47 mm containing 1.73 % PPF yielded optimal impact energy absorption of 680 J and 2384 J and crack resistance of 3823 MPa and 16279 MPa at service and ultimate loading, respectively. These metrics represent improvements of 4.8, 15.2, 37, and 56 times, respectively, compared to the control samples. These substantial advancements highlight the potential of lightweight fibre-reinforced LECA concrete in engineering applications where balancing impact energy absorption, crack resistance, and structural weight is crucial. This innovative approach promises a transformative impact on the construction industry, paving the way for more efficient and resilient infrastructure.

Bond‐slip behavior between polypropylene fiber concrete and corroded reinforcement

AbstractIn this paper, the bond‐slip behavior and bond‐slip constitutive model of corroded reinforcement embedded in polypropylene fiber‐reinforced concrete (PFRC) were investigated. The central pullout test was conducted for 36 specimens. The effects of the corrosion level of reinforcement and the volume fraction of polypropylene (PP) fibers in concrete on the damage mode and bond‐slip process between reinforcement and concrete were studied. Based on the experimental data, a modified bond‐slip constitutive model considering the corrosion level of reinforcement and the volume fraction of PP fibers in concrete was proposed, and the proposed modified bond‐slip constitutive model was used in finite element analysis. The results showed that the addition of PP fibers effectively improved the ultimate bond strength, peak slip and bond toughness of reinforcement and concrete. The enhancement of the bonding properties of the specimens by the PP fibers remained significant after the reinforcement was corroded. The proposed modified bond‐slip constitutive model agreed well with the experimental results. The validity of the proposed model was further verified by finite element analysis.

Flexural behaviour and post-cracking performance of polypropylene fibre-reinforced waste cardboard blended concrete

The requalification of recycled materials has become of significance owing to a global shift towards net zero emissions and the severe environmental impact of misused recyclable waste. Cardboard and polypropylene have evolved into significant waste products, and the purpose of the study was to focus on the repurposing of both waste materials in determining the structural behaviour of an eco-efficient fibre-reinforced waste concrete. The study extended upon the findings of a precursor study in the development of an eco-efficient fibre-reinforced waste concrete mix. Finely processed municipally collected waste cardboard and recycled polypropylene macro-fibres were incorporated into a concrete mix design for which an experimental program was realised. To achieve this, uniaxial compressive strength, modulus of rupture, modulus of elasticity, and indirect tensile strength of the waste and reference mixtures were determined for 7- and 28-day intervals. Crack mouth open displacement testing was achieved to assess the post-cracking response, and retaining wall beams were prepared and loaded to determine the efficacy of the concrete mixture for low load-bearing structures. Mechanical and post-cracking properties of the hybrid waste concrete underscored excellent performance in comparison to other waste fibre-reinforced concrete mixtures, and superior to those blended with similar kraft fibre volume fractions. Moreover, the structural performance of beams cast from the hybrid mixture closely matched those of the reference mixture, emphasising the viability of the mixture and the role waste materials have in the construction and building industry.

An experimental study on mechanical and fracture characteristics of hybrid fibre reinforced concrete

This research investigates the impact of polypropylene and glass fibres on the mechanical and fracture properties of concrete. Prepared specimens consisted of plain concrete (PC), polypropylene fibre-reinforced concrete (PPFC), glass fibre-reinforced concrete (GFC), and polypropylene-glass hybrid fibre-reinforced concrete (HFC). The specimens were evaluated for their mechanical and fracture properties. PPFC indicated a little drop in compressive strength and GFC demonstrated a moderate gain; HFC, as a result of synergistic effect of polypropylene fibre and glass fibre, demonstrated a marginal increase in compressive strength. The substantial increase in flexural and split tensile strength was observed in all the fibre reinforced concrete specimens, compared to plain concrete. The incorporation of polypropylene fibre yields the greatest improvement in concrete's split tensile strength, whereas the incorporation of glass fibres results in the highest improvement in concrete's flexural strength. The fracture characteristics also showed significant improvement in fibre incorporated concrete. The coaction of polypropylene and glass fibre in HFC resulted in 30.1 % increase in first crack strength and a threefold rise in flexural toughness compared to plain concrete. Compared to plain concrete, the critical crack tip opening displacement of PPFC, GFC, and HFC increased by 43.90 %, 26.25 %, and 39.02 %, while the critical stress intensity factor increased by 15.73 %, 13.10 %, and 14.22 %. Subsequently, it was determined that the fracture energies of PPFC, GFC, and HFC were 3.35, 1.78, and 2.50 times those of PC, respectively. In addition, the synergistic effect of polypropylene and glass fibres in concrete was studied, and it was found that when used together, the fibres have better fracture characteristics than when used alone, without compromising mechanical strength. Subsequently, different bilinear softening curves were used to predict fracture parameters, and it was seen that the computed values agreed with the experimental values.

Experimental research on PPF anti-cracking effect in scale model of hollow rigid frame bridge

The hollow rigid frame bridge has many advantages, such as being lightweight, having strong spanning ability, and having slight deflection in span. This type of bridge has a broad potential for application in regions of many canyons and hills. While there has been less research into the application of this type of bridge, some of the bridges in early service have cracking problems. To satisfy the demand for cracking resistance of the Yunnanzhuang large-span hollow rigid frame bridge, our group proposed using Polypropylene Fibers (PPF) to enhance the strength of concrete against cracking. After analyzing the structure of the whole bridge, we gave the critical sections of the bridge and carried out a series of tests to give the PPF dosage that applies to the project. This paper focuses on the use of reduced-size bridge model tests to investigate the effect of PPF on the cracking resistance of hollow rigid frame bridges under bending.In this paper, the similarity criterion between the actual bridge and the model was calculated by the method of magnitude analysis, according to which scale-down model beams of the upper chord S4 segment and mid-span jointing segment of Yunnanzhuang Bridge were designed under the geometry of 1:5. We respectively made these models using the same C55 concrete as the actual bridge and Polypropylene Fibre Reinforced Concrete (PPFRC) with 0.3 % volumetric admixture of PPF in the same mix ratio, and three-point bending static load tests were performed on these models. To make up for the insufficiency of test groups, we performed a finite element analysis using ABAQUS and the CDP constitution, which led us to some reliable conclusions.Considering that concrete materials have size effect, directly using the results of model tests to predict the cracking stresses of the actual bridge is not accurate. In this paper, some theories on size effects were examined. Finally, the Size Effect Model (SEM), Boundary Effects Model (BEM), and Weibull's brittle strength theory were selected to correct the test results.The results show that PPF can increase the cracking load of the test beams, ranging from 11.22 % to 13.49 %. After using selected size effect theories to predict the cracking stresses in actual bridges, the results show that PPF can enhance the cracking strength of C55 concrete, with an increase ranging from 9.15 % to 18.75 %. Combined with the results of the structural analysis of the whole bridge, the critical section has a cracking stress between 2.6 MPa and 3.5 MPa when using C55 concrete, which has a certain risk of cracking. However, when using PPFRC, the cracking stress ranges from 3.1 MPa to 4.2 MPa, with no risk of cracking in most unfavorable cases, which can satisfy the demand for concrete cracking resistance of Yunnanzhuang Bridge.

Influence of Polypropylene Fiber on Concrete Permeability under Freeze-Thaw Conditions and Mechanical Loading.

Polypropylene fiber reinforcement is an effective method to enhance the durability of concrete structures. With the increasing public interest in the widespread use of polypropylene fiber reinforced concrete (PFRC), the necessity of evaluating the mechanism of polypropylene fiber (PF) on the permeability of concrete has become prominent. This paper describes the influence of PF on the concrete permeability exposed to freeze-thaw cycles under compressive and tensile stress. The permeability of PFRC under compressive and tensile loads is accurately measured by a specialized permeability setup. The permeability of PFRC under compressive and tensile loads, the volume change of PFRC under compressive load, and the relationship between compressive stress levels at minimum permeability and minimum volume points of PFRC are discussed. The results indicate that the addition of PF adversely affects the permeability of concrete without freeze-thaw damage and cracks. However, it decreases the permeability of concrete specimens exposed to freeze-thaw cycles and cracking. Under compressive load, the permeability of PFRC initially decreases slowly and follows by a significant increase as the compressive stress level increases. This phenomenon correlates with the volume change of the specimen. The compressive stress level of the minimum permeability point and compressive stress level of the minimum volume point of PFRC exhibit a linear correlation, with a fitted proportional function parameter γ ≈ 0.98872. Under tensile load, the permeability of PFRC increases gradually with radial deformation and follows by a significant increase. The strain-permeability curves of PFRC under loading are studied and consist of two stages. In stage I, the permeability of PFRC gradually decreases with the increase of strain under compressive load, while the permeability increases with the increase of strain under tensile load. In stage II, under compressive load, the permeability of PFRC increases with the increase of freeze-thaw cycles, whereas under tensile load, the permeability gradually decreases with the increase of freeze-thaw cycles. The reduction of PF on the permeability of PFRC under tensile load is greater than that under compressive load. In future research, the relationship between strain and permeability of PFRC can be integrated with its constitutive relationship between stress and strain to provide a reference for the application of PF in the waterproofing of concrete structures.

Compressive Properties of Basalt Fibers and Polypropylene Fiber-Reinforced Lightweight Concrete.

With the development of high-rise and large-scale modern structures, traditional concrete has become a design limitation due to its excessive dead weight. High-strength lightweight concrete is being emphasized. Lightweight concrete has low density and the characteristics of a brittle material. This is an important factor affecting the strength and ductility of the lightweight concrete. To improve these shortcomings and proffer solutions, a three-phase composite lightweight concrete was prepared using a combination of tumbling and molding methods. This paper investigates the various influencing factors such as the stacking volume fraction of GFR-EMS, the type of fiber, and the content and length of fiber in the matrix. Studies have shown that the addition of fibers significantly increases the compressive strength of the concrete. The compressive strength of concrete with a 12 mm basalt fiber (BF) (1.5%) admixture is 9.08 MPa, which is 62.43% higher than that of concrete without the fiber admixture. The compressive strength was increased by 27.53 and 21.88% compared to concrete containing 3 mm BF (1.5%) and 0.5% BF (12 mm), respectively. Fibers can fill the pore defects within the matrix. Mutually overlapping fibers easily form a network structure to improve the bond between the cement matrix and the aggregate particles. The compressive strength of lightweight concrete with the addition of BF was 16.71% higher than that with the addition of polypropylene fiber (PPF) with the same length and content of fibers. BF has been shown to be more effective in improving the mechanical properties of concrete. In this work, the compressive mechanism and optimum preparation parameters of a three-phase composite lightweight concrete were analyzed through compression tests. This provides some insights into the development of lightweight concrete.

Utilizing bio-based and industrial waste aggregates to improve mechanical properties and thermal insulation in lightweight foamed macro polypropylene fibre-reinforced concrete

This research intends to examine the potential of incorporating waste materials in place of coarse aggregates to augment the mechanical characteristics and thermal insulation of lightweight foamed concrete (LWFC), along with the inclusion of polypropylene (PP) fibres. The PP fibre exhibits excellent tensile strength and enhancement on thermal insulation properties of cementitious materials. In this study, eco-friendly bio-based oil palm shell (OPS) and robust solid polyurethane (SPU) aggregates derived from industrial waste were utilized as substitutes for conventional aggregates. Additionally, silica fume was partially incorporated as supplementary cementitious materials. The addition of PP fibre impacted the workability of the LWFC with the inverted slump value decreased by 1.7 %–17.5 %. The inclusion of PP fibre proportion increased from 0 % to 0.5 % revealed a positive result in mechanical properties and thermal insulation performance. The OPSSPU/0.5 showed the significantly increment of 40.4 % compressive strength, 102.9 % of splitting tensile strength, and 70.8 % flexural strength, respectively. The optimum result was obtained in the OPSSPU/0.5 mixture, which exhibited 3.74 MPa residual compressive strength. Furthermore, utilizing PP fibres brought about a significant reduction in thermal conductivity in the environmentally sustainable LWFC, leading to improvements ranging from 0.2 % to 16.3 % when compared to the control composition. Thus, these findings are essential for encouraging the adoption of such practices in the construction industry and contributing to the reduction of environmental impacts associated with sustainable concrete production.

Study on the Effect of Post-Freezing Mechanical Properties of Polypropylene Fibre Concrete Based on BAS-BPNN

An indoor accelerated freezing and thawing test of polypropylene fibre-reinforced concrete in chloride and sulphate environments was conducted using the “fast-freezing method” with the objective of investigating the damage law of the post-freezing mechanical properties of hydraulic concrete structures and studying the effects of different mixing amounts of polypropylene fibres on the mechanical properties of concrete. Furthermore, in order to reduce the cost of concrete tests and shorten the time required for conducting concrete tests, a backpropagation neural network based on a Beetle Antenna Search algorithm (BAS-BPNN) was established to simulate and predict the mechanical properties of polypropylene fibre-reinforced concrete. The accuracy of the model was verified. The results indicate that the order of improvement in the macro-physical properties of concrete due to fibre doping is as follows: PPF1.2 exhibited the greatest improvement in macro-physical properties of concrete, followed by PPF0.9, PPF1.5, PPF0.6, and PC. When the freezing and thawing medium and the number of cycles are identical, all four assessment indexes (R2, RMSE, SI, MAPE) demonstrate that the four groups of polypropylene fibre concrete exhibit superior performance to the control group of ordinary concrete. This indicates that polypropylene fibre can enhance the mechanical properties and freezing resistance of the concrete matrix, delay the process of freezing and thawing damage to the matrix, and extend the lifespan of the matrix, yet cannot prevent the ultimate failure of the matrix. The application of intelligent algorithms to optimise the parameters of an artificial neural network model can enhance its capacity to generalise and predict the mechanical properties of concrete. In terms of the coefficient of determination (R2), the Beetle Antenna Search algorithm (0.9782) outperforms the Particle Swarm Optimization (PSO; 0.9676), the Genetic Algorithm (GA; 0.9645), and the backpropagation neural network (BPNN; 0.9460). The improved backpropagation neural network based on the Beetle Antenna Search algorithm not only avoids the trap of local optimality but also improves the model accuracy while further accelerating the convergence speed. This approach can address the complexity, non-linearity, and modelling difficulties encountered during the freezing process of concrete. Moreover, it offers relatively accurate prediction outcomes at a reduced cost in comparison to traditional experimental methodologies.

Study on early-age cracking resistance of multi-scale polypropylene fiber reinforced concrete in restrained ring tests

The primary cause of early-age cracking is high tensile stress resulting from restrained shrinkage of concrete structures. This study examined the shrinkage performance of polypropylene fiber reinforced concrete (PFRC) through restrained ring and free shrinkage tests. The impact of polypropylene fiber on shrinkage deformation and restrained shrinkage stress of concrete was analyzed. Furthermore, the mechanism of multi-scale polypropylene fiber to improve the crack resistance of PFRC was discussed. Test results demonstrated that adding polypropylene fiber to concrete significantly reduced the possibility of early cracking in concrete matrix. Plain concrete (A0) showed the highest potential for early-age cracking. At 28 days of age, the cracking risk factor of single-doped, double-doped, multi-doped polypropylene fiber reinforced concrete (A1, A2, and A3) was 0.851, 0.793, and 0.665, which decreased by 7.1%, 13.43%, and 27.4% compared with A0, respectively, suggesting the effect was better positive in reducing the crack risk when multi-scale polypropylene fiber hybridized.

Flexural fatigue performance and damage evolution analysis of multiscale polypropylene fiber‐reinforced concrete

AbstractAs an excellent concrete reinforcement material, polypropylene fiber has a high potential for bulk‐scale applications. In this study, a comprehensive experimental campaign was carried out to assess the flexural fatigue performance of multiscale polypropylene fiber‐reinforced concrete (MPFRC). Two types of fine polypropylene fiber (FPF) and one type of coarse polypropylene fiber (CPF) were selected for single doping or hybridization into concrete. The fatigue deformation damage mechanism of polypropylene fiber reinforced concrete (PFRC) was analyzed through acoustic emission (AE) and scanning electron microscopy. Results indicated that the incorporation of polypropylene fibers could significantly improve the strength of concrete, with the best results for MPFRC, where the compressive, tensile, and flexural strength were increased by 13.12%, 20.59%, and 25.49%, respectively, compared to the plain concrete. The fatigue life of PFRC obeyed the Weibull distribution at different stress levels, with the mean fatigue life of MPFRC increasing by up to 6.37 times. The fatigue strain‐to‐cycle ratio curves coincided with the cumulative AE ringing count‐to‐cycle ratio curves, both showed that the fatigue damage process of MPFRC underwent three distinct stages, accounting for 5%, 85%, and 10% of the total fatigue life, respectively. By forming a three‐dimensional mesh structure inside the concrete, polypropylene fibers effectively mitigated internal damage and improved the fatigue performance of the concrete.

Study on the tensile and compressive mechanical properties of multi-scale fiber-reinforced concrete: Laboratory test and mesoscopic numerical simulation

To investigate the tensile and compressive mechanical properties of multi-scale polypropylene fiber-reinforced concrete (PFRC), two-dimensional microscopic finite element models of PFRC were established, and their reliability was verified using laboratory test results. The failure development process and tensile and compressive behaviors of multi-scale PFRC were simulated. In addition, the influence of the length and dosage of polypropylene fibers (PFs) on the mechanical properties of concrete was investigated using mesoscopic numerical simulations. The numerical models established in this study fill the gap in existing research by revealing both the distribution of multi-scale PFs and the true shape of the aggregates. The results predicted by the proposed numerical models were in good agreement with the experimental results. Moreover, the ideal PF length was 30 or 40 mm, and the optimum fiber dosages of two fine polypropylene fibers (FPF1, FPF2) and coarse polypropylene fiber (CPF) were 0.6 kg/m³, 0.6 kg/m³, and 4.8 kg/m³, respectively. This study reveals the influence of parameters such as the length and dosage of multi-scale PFs on the mechanical properties of concrete, providing a reference for engineering applications.

Experimental study on the effect of polypropylene fiber on compressive strength and fracture properties of high-strength concrete after elevated temperatures

Polypropylene fibers improve the toughness of concrete and reduce the susceptibility of high-strength concrete (HSC) to high temperature spalling. And the mechanical properties of polypropylene fiber reinforced concrete (PFRC) become important after exposure to high temperatures, especially in situations related to engineering uses or repairing concrete structures damaged by fire. This paper presents an experimental study on the compressive strength and fracture properties of PFRC experiencing different temperatures with different fiber contents and lengths. It was shown that the fracture path of concrete becomes longer after experiencing high temperatures. The rate of debonding of mortar and coarse aggregate increases with the temperature rising. The compressive strength of concrete and the peak load and fracture energy of three-point bending beams were both increased by the addition of polypropylene fibers at room temperature, and the compressive strength increased with the increase of fiber content. The addition of polypropylene fibers is able to increase the compressive strength of concrete compared to the control group at experiencing temperatures less than 300 oC. The peak forces of the three-point bending of the concrete beams all show a decreasing trend with the increase in the experienced temperature. The initial slopes of the rising part of the force-loading point displacement and force-crack mouth opening displacement (CMOD) curves all decrease with increasing of temperature, and curves gradually become slower. Addition of polypropylene fibers decreases the peak force of concrete after high temperature. There is no significant pattern in the effect of polypropylene fiber content and length on the peak force and fracture energy of concrete three-point bending beams.

Study on bending failure and crack characteristics in ductile fiber‐reinforced concrete beams

AbstractIn this study, we designed six polypropylene fiber‐reinforced concrete (PP‐FRC) beams and three reinforced concrete (RC) beams for experimental studies. Then, we analyzed the effects of incorporating PP fibers on the cracking performance of PP‐FRC beams from the perspectives of load‐displacement response, crack distribution, crack depth, crack width, crack spacing, and deformation coordination. The research results showed that the cracking load and number of cracks were positively correlated with the volume ratio of PP fibers, while the maximum crack width, average crack spacing, and average crack depth were negatively correlated with the volume ratio of PP fibers. Due to the bridging effect of fibers, the PP‐FRC beam body and reinforcement could deform in a coordinated manner within a specific loading range after cracking, which increased the deformation coordination ability between the body and reinforcement. In this study, the cracking mechanism of PP‐FRC beams was investigated. Firstly, the formula for calculating the cracking moment of PP‐FRC beams was derived from the perspective of equivalent bending tensile strength. Then, based on the fiber bridging law and the bond strength between PP‐FRC and reinforcement, theoretical formulas were proposed to predict the average crack spacing and maximum crack width of PP‐FRC beams. Finally, through comparison, it was found that the proposed formulas could be used for characteristic crack prediction.

Experimental Study on the Mechanical Properties of Hybrid Basalt-Polypropylene Fibre-Reinforced Gangue Concrete

Incomplete data indicate that coal gangue is accumulated in China, with over 2000 gangue hills covering an area exceeding 200,000 mu and an annual growth rate surpassing 800 million tons. This accumulation not only signifies a substantial waste of resources but also poses a significant danger to the environment. Utilizing coal gangue as an aggregate in the production of coal-gangue concrete offers an effective avenue for coal-gangue recycling. However, compared with ordinary concrete, the strength and ductility of coal-gangue concrete require enhancement. Due to coal-gangue concrete having higher brittleness and lower deformation resistance than ordinary concrete, basalt fibre (BF) is a green, high-performance fibre that exhibits excellent bonding properties with cement-based materials, and polypropylene fibre (PF) is a flexible fibre with high deformability; thus, we determine if adding BF and PF to coal-gangue concrete can enhance its ductility and strength. In this paper, the stress–strain curve trends of different hybrid basalt–polypropylene fibre-reinforced coal-gangue concrete (HBPRGC) specimens under uniaxial compression are studied when the matrix strengths are C20 and C30. The effects of BF and PF on the mechanical and energy conversion behaviours of coal-gangue concrete are analysed. The results show that the ductile deformation of coal-gangue concrete can be markedly enhanced at a 0.1% hybrid-fibre volume content; HBPRGC-20-0.1 and HBPRGC-30-0.1 have elevations of 53.66% and 51.45% in total strain energy and 54.11% and 50% in dissipative energy, respectively. And HBPRGC-20-0.2 and HBPRGC-30-0.2 have elevations of 31.95% and 30.32% in total strain energy and −3.46% and 28.71% in dissipative energy, respectively. With hybrid-fibre volume content increased, the elastic modulus, the total strain energy, and the dissipative energy all show a downward trend. Therefore, 0.1% seems to be the optimum hybrid-fibre volume content for well-enhancing the ductility and strength of coal-gangue concrete. Finally, the damage evolution and deformation trends of coal-gangue concrete doped with fibre under uniaxial action are studied theoretically, and the constitutive model and damage evolution equation of HBPRGC are established based on Weibull theory The model and the equation are in good agreement with the experimental results.

Finite Element Modelling of Polypropylene Fibre Reinforced Concrete Beams Reinforced with Steel under Bending

Application of the fibre-reinforced concrete has manifested a wider acceptability over time for its contribution towards significantly improving the flexural performance of structural members. A lot of work has been done to understand the influence of fibres on the mechanical and structural behaviour of reinforced concrete. Towards this end, several researchers have experimentally investigated the residual flexural strength to characterize the fibre-reinforced concrete. The number of influencing parameters to be investigated through experiments is mostly limited because of the time and cost implications. Consequently, validation of the experimental investigations through analytical models and further utilizing these models to study the behaviour in greater detail is a viable option for researchers. As part of this work, an analytical investigation has been performed to investigate the performance of full-scale polypropylene fibre-reinforced concrete beams. The models have been validated through comparison with the observed performance during an experimental investigation where tests on twelve full-scale FRC beams were performed. Three-dimensional finite element models of the beams under 4-point loading were prepared and the post-cracking flexural performance of FRC beams has been investigated by varying the dosage of polypropylene fibres obtained from shredding medical face masks.

Application of artificial intelligence in predicting the residual mechanical properties of fiber reinforced concrete (FRC) after high temperatures

The practical application of Artificial Intelligence (AI) approaches in estimating the mechanical properties of fiber-reinforced concrete (FRC) subjected to high temperatures was initiated by developing a dataset including concrete mixtures, geometrical and mechanical properties of fiber, and temperatures. The dataset contains compressive strength, tensile strength, and modulus of elasticity of concrete with two distinct types of fiber, i.e., steel and polypropylene with an extensive range of temperatures from 100 to 1200 ℃. The dataset determined the gaps in the literature and showed FRC with high fiber aspect ratios and higher content of fiber (>0.8%) are not studied enough. The AI-based models showed that steel fiber-reinforced concrete (SFRC) has higher residual compressive strength compared with polypropylene fiber-reinforced concrete (PFRC). An increase in steel fiber diameter and length resulted in a higher compressive strength ratio at all temperatures. Moreover, higher PP fibers content and longer PP fibers decrease the rate of tensile strength degradation. A large probabilistic analysis was performed, and it showed that the failure probability (Pf) for PFRC is independent of W/B ratios and is almost 50%;. In contrast, for SFRC, W/B ratios between 0.4 to 0.5 have lower failure probability in comparison with other W/B ratios. Moreover, Pf for both fibers at a W/B ratio of 0.5 is almost independent of fiber content. Furthermore, the critical temperature resulting in failure (defined as the residual strength ratio less than 0.5) for SFRC and PFRC is 550 ℃ and 430 ℃, respectively.

Effect of free and embedded polypropylene fibres recovered from concrete recycling on the properties of new concrete

This study aims at investigating the effect of incorporating different quantities of polypropylene fibres recovered during concrete recycling or embedded in recycled aggregates on the mechanical properties of new polypropylene fibre-reinforced concrete (PPFRC). Both recovered fibre (at replacement ratios of 0 %, 10 %, 30 % and 100 %) and recycled coarse aggregate (0 %, 100 %) were used in new concrete. Polypropylene fibre contents of 3 and 9 kg/m3 (0.33 % and 1.0 % by volume, respectively) were chosen for all concretes. The properties of recovered and virgin fibres were tested to determine the effect of recycling on fibre properties. The compressive strength, elastic modulus and stress–strain behaviour in compression were tested and a constitutive model was developed to fit the stress–strain behaviour of the PPFRC with mixed recovered and virgin fibres. The residual tensile strength was also tested for concretes with recovered fibres and fibres embedded in recycled aggregate. The results show that mixing of recovered and virgin fibres is feasible without significant effect on mechanical properties of concrete. At the same time, inclusion of recycled coarse aggregate from PPFRC recycling contributes to residual tensile strength through the presence of fibres embedded in the aggregate.

Mesoscale modeling of polypropylene fiber reinforced concrete under split tension using discrete element method

This study is proposed to determine the effectiveness of the discrete element method (DEM) in predicting the tensile properties of polypropylene fiber-reinforced concrete (PFRC). To calibrate and validate the proposed PFRC simulation model, splitting tensile tests were performed on limestone (granite)-polypropylene fiber reinforced mortar (PFRM) hybrid samples to investigate the effects of polypropylene fiber (PF) contents and aggregate types on the tensile properties of the interfacial transition zone (ITZ). The test improved the particle contact mode in the PFRC discrete element model. Based on DEM software (PFC3D), a multi-phase microscopic discrete element model was created, and the tensile properties of PFRC were predicted by simulating a splitting tensile test. The simulation results revealed that the proposed model could be more efficient in predicting the splitting tensile responses of PFRC. The improved flat joint-softening contact model is more accurate and stable for the bridging effect simulation of PF after concrete cracking.

Post-Cracking Properties of Concrete Reinforced with Polypropylene Fibers through the Barcelona Test.

The Barcelona method was developed as an alternative to other tests for assessing the post-cracking behavior of fiber-reinforced concrete, with the main advantage being that it uses significantly smaller specimens compared to other methods. For this reason, it can provide a solution for characterizing concrete in hard-to-reach constructions such as roads and tunnels. On the other hand, polypropylene (PP) fibers have gained increased attention in recent years within the scientific community due to their high tensile strength and cost-effectiveness. This research aimed to understand the influence of PP fiber volume, slenderness (l/d), and reinforcement index on post-cracking properties of concrete, including toughness and residual strength (f_res), using the Barcelona method. Three fiber volumes, 0.4%, 0.8%, and 1.2%, and three slenderness ratios, 46.5, 58.1, and 69.8, were employed in normal-strength concrete. In addition to the reference mixture without fibers, 10 mixtures were prepared with 10 specimens each, resulting in a total of 100 specimens. Pearson's hypothesis test was employed to determine the existence of correlations between variables, followed by scatter plots to generate predictive equations between post-cracking properties and fiber attributes. The results indicated no direct correlation between fiber slenderness and post-cracking properties. Regarding fiber volume, there was a correlation with residual strength but not with toughness. However, the combined effect of volume and slenderness, the reinforcement index, correlates with the post-cracking properties of concrete. Finally, four predictive equations for toughness and residual strength were derived based on the reinforcement index. These equations can prove valuable for designing structures made of polypropylene fiber-reinforced concrete.