Incorporating Polypropylene Fibers Research Articles

Enhancing Fatigue Performance of Coal Gangue Concrete (CGC) through Polypropylene Fiber Modification: Experimental Evaluation.

Coal gangue is a byproduct of coal mining and processing, and according to incomplete statistics, China has amassed a substantial coal gangue stockpile exceeding 2600 large mountains, which poses a serious threat to the ecological environment. Utilizing gangue as a coarse aggregate to produce gangue concrete (GC) presents a promising avenue for addressing the disposal of coal gangue; however, gangue concrete presents several challenges that need to be tackled, such as low strength and poor resistance to repeated loads. In this study, polypropylene fibers (PPFs) were incorporated into gangue concrete to enhance its utilization rate. Uniaxial compressive and repeated loading experiments were then conducted to investigate the uniaxial strength and fatigue properties of polypropylene fiber-reinforced gangue concrete (PGC) with varying gangue substitution rates (20%, 40%, and 60%) and different polypropylene fiber admixtures (0, 0.1%, 0.2%, and 0.3%). The findings indicate that incorporating gangue at a substitution rate of 40% could notably enhance the uniaxial compressive strength of PGC, resulting in a maximum increase of 19.4%. In the repeated loading experiments, the ductility of PGC was enhanced with the incorporation of PPFs, resulting in a reduction of 33.76% in the damage factor and 19.42% in residual strain for PGC-40-0.2 compared to PGC-40-0. A PPF content of 0.2% was found to be optimal for enhancing the fatigue performance of PGC. Scanning electron microscope (SEM) testing proved the improvement effect of polypropylene fiber on gangue concrete from a microscopic perspective. This study provides crucial experimental data and a theoretical foundation for the utilization of gangue concrete in complex stress environments.

Strength Performance of Concrete Containing Rice Husk Ash as Cement Replacement in Presence of Polypropylene Fiber

This study focuses on the utilization of Rice Husk Ash (RHA) as partial replacement of Ordinary Portland Cement (OPC) in concrete in addition with Polypropylene (PP) fiber. The main goal of this study was to decrease dependence on OPC and address environmental waste generated through rice mills. This study considered concrete cubes prepared through 1:2:4 ration with 0.50 water-cement ratio with and without RHA and PP fibers. The water curing was done for 7 and 28 days, with three specimens for each proportion, and the average value was considered as the result. It was observed that the compressive strength of M2 concrete which containing 10% RHA was noticed 7% higher than the control mix concrete and declared as 10% RHA as optimum dosage. Next, the performance in terms of compressive strength of concrete containing optimum dosage of RHA in presence of PP fibers of three different lengths were also evaluated and found that the 0.1% of PP fiber of 0.5 inches length gives the 25% higher strength performance as compared to the control mix and 17% higher than the concrete containing 10% RHA only at the age of 28days. Hence, this study concluded that the replacing OPC cement with 10% RHA produces satisfactory strength performance and incorporation of PP fiber gives better strength performances.

Mechanical Properties and Microstructure of Polypropylene-Glass-Fiber-Reinforced Desert Sand Concrete.

In order to improve the performance of desert sand concrete, polypropylene fiber (PF) and glass fiber (GF) were used to prepare desert sand concrete (DSC) with different fiber and volume content, and the basic mechanical properties, such as cube compressive, tensile and flexural strengths, were tested and studied. Based on the mercury injection method (MIP) and scanning electron microscopy (SEM), the evolution of pore structure and interface structure was analyzed. The mechanism of fiber toughening was revealed at the microscopic level. The results show that the slump of DSC decreases with the increase in fiber content. The slump of glass-fiber-reinforced DSC (GFRDSC) is smaller than that of polypropylene-fiber-reinforced DSC (PFRDSC). The strength enhancement of DSC by fibers is in the order of flexural strength > split tensile strength > compressive strength. The flexural strength of hybrid-fiber-reinforced DSC (HyFRDSC) (0.1% PF + 0.1% GF) is increased by 40.7%. Meanwhile, fibers can improve the toughness of DSC. The MIP results show that the porosity of HyFRDSC decreased by 50.01%, and the addition of fiber can effectively refine the large pore size. The SEM results show that the incorporation of PF and GF causes the formation of a uniform and dense structure between the fibers, cement and aggregate. The two can give full play to the crack-resisting and toughening effect in different loading stages, thus improving the macromechanical properties of DSC.

Influence of polypropylene fibers on the mechanical properties of radiation shielding concrete with barite aggregates

The brittleness of barite aggregates leads to inferior strength and toughness of radiation shielding concrete with barite aggregates (RSBC), which limits its application in high-pressure and high-heat nuclear engineering. This study aims to investigate the influence of polypropylene fibers on the mechanical properties of RSBC, and the effects of fiber type (PR40 and TMA20) and fiber content (3–9 kg/m3) on the mechanical properties of RSBC with water-to-binder (w/b) ratios of 0.44 and 0.39 are discussed. The microstructure of polypropylene fiber-reinforced RSBC was analyzed through scanning electron microscopy, revealing the underlying reinforcement mechanism of polypropylene fibers. The applicability of prediction formulas from typical codes was evaluated based on experimental data, and a reliable prediction model for the mechanical properties of RSBC was established. The findings showed that incorporating polypropylene fibers can significantly improve the compressive strength, splitting tensile strength, and flexural strength of RSBC. The addition of 9 kg/m3 PR40 and TMA20 fibers increased the 28-day compressive strength of RSBC by 17.9%–19.8% and 9.5%–16.2%, respectively; the 28-day splitting tensile strength increased by 12.1%–27.7% and 9.3%–26.1%, respectively; and the 28-day flexural strength increased by 19.3%–25.0% and 7.0%–13.5%, respectively. Adding PR40 fibers with a lower slenderness ratio yielded significantly better mechanical properties. Polypropylene fibers form a three-dimensional network structure in the concrete, acting as a bridge between the aggregate and cement mortar, enhancing the stability of interfacial transition zones, thereby effectively improving the macroscopic mechanical performance of RSBC. The mechanical property prediction models of EC 2 and GB 50010 for RSBC exhibit deviations, while the ACI 318 splitting tensile strength model and the flexural strength model established in this research demonstrate good predictive performance.

Effects of Curing Conditions on Splitting Tensile Behavior and Microstructure of Cemented Aeolian Sand Reinforced with Polypropylene Fiber.

Aeolian sand is widely distributed in the Takramagan Desert, Xinjiang, China, which cannot be directly used as railway subgrade filling. It is beneficial for environmental protection to use fiber and cement-reinforced aeolian sand as railway subgrade filling. The present work is to explore the enhancement of tensile strength in cemented aeolian sand via the incorporation of polypropylene fibers under conditions of elevated temperature and drying curing. The purpose Is to delve into the examination of the temperature's impact on not only the mechanical attributes but also the microstructure of cemented aeolian sand reinforced with polypropylene fiber (CSRPF). For this, a comprehensive set of tests encompassing splitting tensile strength (STS) assessments and nuclear magnetic resonance (NMR) examinations is conducted. A total of 252 CSRPF specimens with varying fiber content (0, 6‱, 8‱, and 10‱) are tested at different curing temperatures (30 °C, 40 °C, 50 °C, 60 °C, 70 °C, and 80 °C). The outcomes of the NMR examinations indicate that elevating the curing temperature induces the expansion of pores within CSRPF, both in size and volume, consequently contributing to heightened internal structural deterioration. STS tests demonstrate that the STS of CSRPF decreases as the curing temperature increases. Meanwhile, the STS of CSRPF increases with fiber content, with optimal fiber content being 8‱. Regression models accurately predict the STS, with the curing temperature exhibiting the greatest influence, followed by the fiber content according to sensitivity analysis. The research results provide a valuable reference for the use of CSRPF as railway subgrade filling under high temperature and drying conditions.

Combined effect of fly ash and fiber on spreadability, strength and water permeability of foam concrete

Strength and permeability are the two critical properties of interest for various applications of foam concrete (FC). These properties are well known to be highly dependent on parameters such as density, mix composition and microstructure of FC. Among various measures to enhance the strength and permeation characteristics of FC, incorporation of fly ash and polypropylene fiber has been proven to be effective solutions by various studies. In terms of permeability, though the measurement of air/water permeability has been suggested by various methods, usually such measurements are limited to a pressure of 3 bar. For higher pressures (as recommended in codal provisions) no to limited work is available. In this paper, variation in spreadability, permeability, compressive strength and split tensile strength of FC due to replacement of 50% of sand with Class F fly ash and incorporation of polypropylene fiber is investigated on a systematic basis. For the measurement of permeability at higher pressures (>3 bar), use of novel sealing mechanism using 5 mm thick rubber membrane as sealant with iron spiral cylinder and clamp as casing, is attempted in this work. The present study is first of kind of study using the above-mentioned sealing mechanism for measurement of permeability of FC at higher pressures. Further, only scanty literature is available on permeation behavior of FC with fly ash (as filler) and polypropylene fiber. As per the present findings, particularly in lower density mixes (say density 1000 kg/m3) tested at age of 56 days, replacement of 50% of fine aggregate (by weight) by Class F fly ash results in 114% enhancement in compressive strength and 69% reduction in permeability. In addition, mixes with 0.05% of total solids replaced with polypropylene fiber (by weight) show 25% reduction in compressive strength and 500% increase in permeability in comparison to FC mixes without fly ash and polypropylene fibers. Thirdly, considering mixes with addition of fly ash and polypropylene fibers both, it is found that the effect of fly ash is more predominant from strength perspective than fiber. From permeability perspective however, the fibers control the permeability significantly due to their higher impact on microstructure of FC.

Effect of polypropylene fiber on frost resistance and carbonation resistance of manufactured sand concrete

Mixing fiber into manufactured sand to prepare concrete can effectively reduce the consumption of natural sand resources, improve concrete performance, improve the life of the whole building structure, and bring considerable environmental and economic benefits. To better apply it to engineering practice, this research studied the effect of polypropylene fiber (PPF) on the frost and carbonation resistance of manufactured sand concrete (MSC). In this research, PPF with different volume content (0.8%,1.0%,1.2%)and length(6 mm,12 mm,18 mm) are incorporated into (MSC). Through the design of compressive strength test, splitting tensile strength test, rapid freeze–thaw test, and carbonation test to analyze and evaluate strength, dynamic elastic modulus, and carbonation depth of MSC by Response Surface Methodology (RSM). The experimental findings demonstrated that PPF can effectively improve the compressive strength and splitting tensile strength of MSC. Compared with the control group (natural-sand concrete, NC), the compressive strength increased by 18.18% at most and 1.72% at least, and the splitting tensile strength increased by 32.14% at most and 17.86% at least. when the volume content of PPF is 1.0%, the damage of compressive strength and splitting tensile strength of MSC is the lowest, and the frost resistance is the best. The carbonation depth is the lowest (1.94 mm) when the volume content of PPF is 1.0% and the length is 12 mm, and compared with NC, the flexural strength and dynamic elastic modulus of MSC were increased by 4.65% and 16.3%, respectively. Through XRD and SEM analysis, the incorporation of PPF with moderate volume content can slow down the carbonation reaction of MSC and improve the carbonation resistance of MSC. From RSM analysis, the effect of PPF on the frost resistance of MSC is volume content > length; the effect of PPF on the carbonation resistance of MSC is length > volume content. The optimized prediction results are consistent with the analysis results: the incorporation of PPF can improve the durability of MSC, reaching or even exceeding NC specimens, which provides a theoretical basis for the promotion of PMSC in engineering. When the volume content of PPF is 1.0 % and the length is about 12 mm, the frost resistance and carbonation resistance of MSC are the best.

Early-age autogenous shrinkage, tensile creep, and restrained cracking behavior of ultra-high-performance concrete incorporating polypropylene fibers

Ultra-high-performance concrete (UHPC) as a kind of progressive cement-based material has attracted wide attention in the field of concrete engineering due to its superior performance. Nonetheless, the high early-age cracking potential of UHPC under restrained conditions due to the considerable autogenous shrinkage (AS) becomes one major impediment. Polypropylene fibers have been added to UHPC for increasing the tensile strength. However, the influence of polypropylene fibers on the cracking potential of UHPC under restrained conditions is not well studied. The restrained cracking behavior of UHPC incorporating polypropylene fibers was examined by the temperature stress test machine tests in the present study. To study the influencing mechanism of polypropylene fibers on the cracking potential of UHPC, workability, mechanical properties, shrinkage-induced stress, AS, and tensile creep were investigated. Results indicated that the incorporation of polypropylene fibers improved the tensile strength and flexural toughness, decreased the elastic modulus and AS, and increased the tensile creep of UHPC. The shrinkage-induced tensile stress obtained from test was reduced by 64.9%, 65.9%, 67.8%, and 67.5% attributed to creep when compared to the calculated theoretical stress for UHPC incorporating 0%, 1%, 2%, and 3% volume proportion of polypropylene fibers, respectively. As a result, the cracking potential of UHPC under uniaxial restrained condition estimated by the integrated criterion decreased by 21.7%, 60.7%, and 44.1% with the increasing volume proportion of polypropylene fibers from 0% to 1%, 2%, and 3%, respectively.

The effect of polypropylene fiber on the curing time of class G oil well cement and its mechanical, petrophysical, and elastic properties

The cement paste is subjected to various loads throughout a well’s life, which may compromise some of its essential characteristics and impair its performance. When the cement paste is first being formed and the cement’s characteristics have not yet fully matured, these loadings take on greater importance. In this study, the early properties of cement used in oil wells that contains polypropylene fiber are assessed. Five different curing times were used to prepare ten cement samples (6, 12, 24, 48, and 72 h). Five samples contained polypropylene fiber, while the remaining five samples were without polypropylene fibers. After the samples were prepared, the examination of several early cement properties took place. Nuclear magnetic resonance (NMR) was used to describe each sample in order to determine how the curing times affected the cement’s porosity. The findings demonstrated that both cement systems’ compressive and tensile strengths increased with curing time, and that adding polypropylene fiber enhanced the cement’s strength. The porosity and permeability of the cement specimens were significantly reduced with the incorporation of polypropylene fibers, as well as with time during the curing process for both cement samples. The reduction of Young’s modulus and the increase in Poisson’s ratio show that the addition of polypropylene fibers also makes the cement more elastic. To express variations in porosity as well as compressive and tensile strengths, logarithmic relationships were constructed. While the Poisson’s ratio, Young’s modulus, density variations, and permeability were precisely modeled by power-law equations.

Dynamic response characteristics of coral reef sand concrete under impact loading

The dynamic mechanical properties, energy evolution characteristics, breakage modes, and damage mechanism of coral reef sand concrete (CRSC) are distinctly different from those of land-sourced aggregate concrete. Because structures made of CRSC may suffer damage due to earthquakes and artillery shells, it is significant to investigate the impact resistance and dynamic response characteristics of CRSC. In this study, macroscopic and microscopic testing techniques were used to compare the dynamic response characteristics of CRSC, CRSC with polypropylene fibers (PFs), and CRSC with basalt fibers (BFs) under impact loading. The results showed that with increasing strain rate, the dynamic compressive strength and dynamic increase factor (DIF) of the CRSC increased via power and logarithmic functions, respectively. Furthermore, the PFs and BFs improved the dynamic compressive strength at medium and low strain rates. The damage modes of the CRSC and CRSC with BFs were primarily fragmentation damage, while the damage mode of the CRSC with PFs was core retention damage. The failure cracks of all three types of concrete developed through the coral coarse aggregate, cement mortar, and slurry near the interfacial bonds. Nanoindentation test results revealed the great bonding performances at the coral aggregate–slurry bond. The incorporation of PFs or BFs changed the form and content of the C–S–H in the interfacial transition zone of the CRSC, which in turn affected the mechanical properties of the CRSC. In practical engineering, however, PFs and BFs could still improve the seismic and blast-resistant performances of CRSC.

Effects of air-entraining agent and polypropylene fiber on the mechanical properties, autogenous shrinkage, and fracture properties of fully recycled aggregate concrete

The effects of air-entraining agent (AEA) and polypropylene fiber (PPF) on the autogenous shrinkage and fracture properties of fully recycled aggregate concrete (FRAC) are studied to obtain FRAC with low density, low autogenous shrinkage, and superior fracture properties. Six groups of FRAC with different AEA (0, 5%, 10%) and PPF (0, 1.2 kg/m3) contents were prepared for test. The results illustrate that AEA can slightly reduce density but that it has an adverse effect on the strength and fracture properties of FRAC. The incorporation of PPFs can reduce the adverse effect of AEA on compressive strength and splitting tensile strength, but it will increase the adverse effect on fracture properties. Furthermore, the addition of PPFs alone will significantly reduce compressive strength and splitting tensile strength, whereas flexural strength and fracture properties are increased. The addition of AEA can improve the adverse effect of PPFs on compressive strength and splitting tensile strength, but flexural strength and fracture properties will decrease rather than increase. The addition of 10% AEA can greatly reduce autogenous shrinkage, and 5% AEA can reduce autogenous shrinkage at an early age. Incorporating PPFs can further reduce autogenous shrinkage. The study mainly examines the effects of AEA and PPF on the autogenous shrinkage of FRAC, and provides some new ideas for producing high-performance FRAC. At the same time, the cooperative effect of AEA and PPF on the properties of FRAC is also studied.

Effect of fiber type, shape and volume fraction on mechanical and flexural properties of concrete

An experimental work was herein presented focusing the effect of different type, shape and volume fraction of fibers on the hardened properties of concrete including compressive, splitting tensile and flexural strengths at 7 and 28 curing days. A control concrete mixture including no fiber was prepared and six fiber-reinforced concrete (FRC) mixtures were designed by using two different fiber types and volume fractions. Two types of steel fibers having different shapes (short straight and long hooked end) and polypropylene fiber were used with the volume fraction of 0.4% and 0.8%. The load-deflection curves and toughness of the specimens were analyzed based on ASTM C1609. The results showed that the utilization of short straight steel fibers with 0.8% volume fraction was most efficient at enhancing the compressive strength with 9.98% while the use of 0.8% long hooked end steel fibers provided better splitting tensile and flexural strengths with 33.33% and 30.35%, respectively, compared to specimen with no fiber at 28 curing day. Besides, the long hooked end steel fibers with the volume fraction of 0.8% contributed to an excellent deflection hardening behavior resulting in higher load deflection capacity and higher toughness values at peak load, L/600 and L/150. On the other hand, with incorporation of polypropylene fiber, all strength values decreased regardless of the volume fraction and curing days.

Effect of Fiber Type, Shape and Volume Fraction on Mechanical and Flexural Properties of Concrete

An experimental study was herein presented focusing the effect of different type, shape and volume fraction of fibers on the hardened properties of concrete including compressive, splitting tensile and flexural strengths at 7 and 28 curing days. A control concrete mixture with no fiber was prepared and six fiber reinforced concrete mixtures were designed by using two different types of fibers which were steel fibers with different shapes (short straight and hooked end) and polypropylene fiber with the volume fraction of 0.4% and 0.8%. The load-deflection curves and toughness of the specimens were analyzed based on ASTM C1609. The results showed that the utilization of short straight steel fibers with 0.8% volume fraction was most efficient at improving the compressive strength while the use of 0.8% long hooked end steel fibers provided better splitting tensile and flexural strengths. Besides, the long hooked end steel fibers with the volume fraction of 0.8% contributed to an excellent deflection hardening behavior resulting in higher load deflection capacity and toughness at peak load, L/600 and L/150. On the other hand, with incorporation of polypropylene fiber, all strength values were decreased regardless of the volume fraction and curing days.

Mechanical and thermal properties of fibrous rubberized geopolymer mortar

Nowadays, geopolymers play an important role in developing eco-friendly construction materials to avoid the pollution that comes from the Portland cement industry. Geopolymers show enhanced mechanical properties while ductility tends to be relatively low. Moreover, the thermal properties of construction materials are important in terms of energy-saving and sustainability. On the other hand, by increasing the used rubber tires and with low recycling processes, these wastes become a serious environmental problem. So, this work is directed to develop and investigate enhanced rubberized geopolymer composites regarding ductility as well as thermal properties. To achieve these targets, reusing Crumb Rubber (CR) from used rubber tires as a partial replacement of sand by volume was investigated with (10 %, 20 %, and 30 %) replacement ratios and different CR particle sizes (0–1 mm, 1–3 mm, 4 mm, and 0–4 mm). Parallel with using CR, polypropylene fibers with different volume fractions of (0.5 %, 1.0 %, and 1.5 %) were implemented. The effect of CR content and size on the Physical, mechanical, and thermal properties have been investigated. Additionally, the effect of incorporating polypropylene fibers in rubberized geopolymer mortar has been studied. The results indicated that despite the mechanical properties of rubberized geopolymer mortars tend to be lower, the mode of failure, toughness, and performance under flexural due to the synergistic influence of rubber and fibers have been improved remarkably. Additionally, the results of the transient plane source method indicated that thermal conductivity, thermal diffusivity, and heat capacity have been significantly enhanced in terms of heat insulation. Incorporating 20 % CR with 1 % fibers increases the flexural toughness by 27.5 % more than the mix containing 1 % fiber only. Incorporating 30 % CR decreased the thermal conductivity by about 39.7 %. Furthermore, the regression analysis by developing numerous relationships was proposed. The results of the regression model revealed that the models developed were adequate in explaining the effect of the independent parameters on the responses. It will be helpful to the engineers in deciding the levels of the fibrous rubberized geopolymer composites parameters for desired performance properties serving some environmentally friendly construction applications.

Effect of exposure temperatures on chloride penetration resistance of concrete incorporating polypropylene Fibers, silica fume and metakaolin

• The diffusion resistance of silica fume (SF) concrete was 1.4–7.3 less than OPC concrete. • The diffusion resistance of metakaolin (MK) concrete was 1.2–3.9 less than OPC concrete. • The effect of 10% SF on migration resistance was almost similar to that of 15% MK. • Models to predict the service life of RC structures in hot environments were developed. Rapid degradation of reinforced concrete (RC) has become a serious concern due to its reduction of life span and high unexpected maintenance cost. Chloride penetration and subsequent corrosion are the primary causes of such concrete deterioration. This study investigated the effects of polypropylene fibers, metakaolin and silica fume on chloride diffusion and migration resistance of concrete at different exposure temperatures. Eight concrete mixes were prepared using a water/binder ratio of 0.38, cement replacement of 0, 5, 10, and 15 % by either silica fume (SF) or metakaolin (MK) with zero or 0.6 kg/m 3 polypropylene fibers (PPFs). Furthermore, concrete resistance to chloride diffusion at four different exposure temperatures (23, 38, 53 and 68 °C) and chloride migration at 23 °C was evaluated. The results showed that both pozzolanic admixtures, SF and MK, significantly reduced apparent chloride diffusion coefficient (D a ) and chloride migration coefficient (D nssm ). However, PPFs concretes incorporating MK showed inferior chloride diffusion than those containing SF. D a for PPFs concretes incorporating SF and MK were 1.4–7.3 and 1.2–3.9 times less than Type I cement concrete, respectively. While D nssm for PPFs concretes incorporating SF and MK were 1.7–6.3 and 1.5–3.2 times less than Type I cement concrete, respectively. The results also showed that the effect of 15 % MK on D nssm and D a was almost similar to that of 10 % SF. The D a increased slightly at exposure temperatures of 23 and 38 °C. However, at higher exposure temperatures of 53 and 68 °C, a significant increase in D a was noted. Eight models were developed using regression analysis and were validated by comparing the predicted apparent chloride diffusion coefficient values with the measured ones. The validation of the developed models showed that the predicted D a values were within ± 7 % error margin. The developed chloride diffusion models in the current study allow us to predict and quantify the long life of future realizations of RC structures in marine hot environments.

Mechanics, hydration phase and pore development of embodied energy and carbon composites based on ultrahigh-volume low-carbon cement with limestone calcined clay

Engineered cement-based composites exhibit excellent deformability, mechanical behavior, fresh performance and durability. However, the traditional cement-based composites incorporating high volume ordinary Portland cement would lead to high carbon footprint. In this study, a new and eco-efficient engineered cement-based composites was designed by incorporating Polypropylene fibers (PPF) and eco-friendly cement with limestone calcined clay (LC3-ECCs). The LC3-ECCs were analyzed and discussed in terms of mechanical properties, microscopic morphology, hydration products and porosity. The study found that the 28-days compressive behavior was above 44.2 MPa, and the flexural strength remained above 4.8 MPa. Because of the formation and gathering of highly polymerized compound products (C-S-H gel, C-A-S-H gel) in the matrix and plenty of ettringite, the bonding effect between PPF and LC3 cementitious matrix is better. Additionally, the LC3-ECCs with 1.5 % volume content of PP fiber showed less porosity beneficial to the mechanical behavior. This study suggests that low-carbon LC3 has the potential to be successfully utilized as the alternative to OPC and is suitable to design sustainable ECCs, and this low-carbon construction product can be also generally applied into some area with the abundant clay sources.

Research on Dynamic Compressive Performance of Polypropylene Fiber-Reinforced High-Strength Concrete under Freeze-Thaw Environment

Existing studies have proved that the incorporation of polypropylene fiber can effectively improve the impact resistance of concrete. In this paper, the split Hopkinson pressure bar and digital pulse shaping technology are used to further study the dynamic compression performance and constitutive relationship of concrete in the cold regions under the deteriorating effect of freeze-thaw cycle, and obtain the dynamic increase factor. Studies have shown that polypropylene fiber-reinforced high-strength concrete has a strain rate enhancement effect. The number of freeze-thaw cycle times at low strain rates has an obvious effect on concrete deterioration, and the effect is weaker at higher strain rates. By comparing three typical dynamic strength growth factor models with the test results, after revising the model, the dynamic increase factor equations under different freeze-thaw circulation times were fitted. This research provides a basis for the design of durability and robustness of building structures in cold regions.

Experimental study on mechanical properties, microstructural of lightweight concrete incorporating polypropylene fibers and metakaolin at high temperatures

The main purpose of this experimental research is to investigate the effect of high temperature between 200 and 600 °C on microstructural and mechanical properties of lightweight concrete containing Polypropylene fibers (PP) and Metakaolin. This study includes 12 mixing samples. The percentage replacement of cement by Metakaolin considered in this experimental study are 0, 10, and 20% by weight of cement and percentage of PP fiber content between 0.1% and 0.8% by volume of concrete. The mechanical properties encompass the compressive and tensile strengths, ultrasonic pulse velocity (UPV) test, impact test, and SEM analysis. An impact test was performed to evaluate the ductility index. The results show that the compressive strength of 28-day specimens decreases with increasing temperature. Also, water absorption decreased by 6.8% in samples without PP fibers and 10% Metakaolin (P0M10) at temperatures from 200 °C to 400 °C. PP fibers with 0.4% and 0.8% in the mixing design reduces cracking of concrete and makes the concrete durable at high temperatures. The sample with 0.8% PP fibers and 10% Metakaolin (P0.8M10) showed 233.34% increase in absorption energy compared to the sample of P0M0 at 20 °C in impact test.

Experimental Investigation on the Mechanical Properties of Polypropylene Hybrid Fiber-Reinforced Roller-Compacted Concrete Pavements

To explore the effect of multi-scale polypropylene fiber (PPF) hybridization on the mechanical properties of roller-compacted concrete (RCC), the early-age (3, 7, 14, 28 days) compressive strength, splitting tensile strength and uniaxial tensile test of RCC reinforced with micro-, macro- and hybrid polypropylene fibers were investigated. Then, the tensile stress–strain curve of polypropylene fiber-reinforced roller-compacted concrete (PFRCC) and the corresponding tensile parameters were obtained. The uniaxial tensile constitutive equation of PFRCC and fiber hybrid effect function was also proposed. Finally, the enhancement mechanism of fiber hybridization on mechanical properties of RCC was analyzed. The results indicated that the strength and toughness of PFRCC improved with the incorporation of PPF, showing obvious plastic failure characteristics of PFRCC. Before curing the concrete for 7 days, micro-PPF played a major role in strengthening RCC, while macro-PPF played a major role in reinforcing concrete after that. Moreover, the tensile strength and toughness indexes of multi-scale PFRCC performed the best, indicating the positive hybridization of three types of PPF. The proposed PFRCC uniaxial tensile constitutive equation and fiber hybrid effect function based on existing researches were also well matched with the experimental results.

Highly nonlinear mathematical regression for polypropylene material strength prognostication

Concrete features high fragility, moderate bending strength, and endurance. Strain energy in the form of mechanical properties of polypropylene such as compressive strength, flexural strength, and split tensile strength are correlated via mathematical algebraic functions. Polynomial function, Exponential function , Fourier function , Gaussian function, the sumofthesinefunction, and Power function are used for correlation. Furthermore, fifteen customs equations are considered in this work. The application of polypropylene fibers to concrete could strengthen such unsatisfactory output. The polypropylene fiber reinforced cement concrete matrix has expanded dramatically due to its operational superiority. The paper examines concrete statistical properties by incorporating polypropylene fibers as reinforcing material. Seven fiberconcrete combinations with a limit of 0%, 0.2%, 0.35%, 0.5%, 0.75%, 1%, and 1.5% polypropylene fiber were prepared on a volume basis. Single w/c ratio provided 0.4 for all concrete compositions. The results indicated a considerable change in the mechanical characteristics of the concrete. The experimental results found the mechanical properties of the concrete increase up to 0.5 % of the polypropylene content in the concrete. Compressive strength, split tensile strength, and flexural strength of the polypropylene concrete are increased by 17 %, 15.58%, and 7.53%, respectively, compared to conventional concrete. Regression coefficients were calculated for the best match in various linear and nonlinear functions. The numerical comparisons of mechanical strengths in linear and nonlinear regression determination coefficients revealed a significant relationship between strengths. Since the formal association between compressive and flexural strength of concrete, the compressive strength is about 8–11 times the flexural strength. The equation predicted values were within the required range, a technical possibility with a constant geometry of the polypropylene fiber presented for the strength of fiber-reinforced concrete. The suggested model and the experimental findings are in moderate correlation.