Polypropylene Fiber Content Research Articles

Effect of Polypropylene and Straw Fiber Materials on the Unconfined Compressive Strength of Tailings and Wasted Stone Mixed Backfill.

Ensuring the mechanical performance of backfill materials while reducing cementation costs is a key challenge in mine backfill research. To address this, fiber materials such as polypropylene (PP) fiber and rice straw (RS) fiber have been incorporated into cement-based mixtures for mine backfilling. This study investigates the effects of PP and RS fibers on the mechanical properties, flow characteristics, and microstructure of Tailings and Wasted Stone Mixed Backfill (TWSMB). A series of orthogonal experiments were designed to evaluate the influence of variables, including the cement-sand ratio, solid mass concentration, wasted stone mass concentration, fiber content, and fiber length on the TWSMB properties. The results indicate that the influence of cement-sand ratio and solid mass concentration have a more significant impact on strength than fibers, though the fibers show a stronger effect than the wasted stone mass concentration. Both fiber types enhanced the strength of the specimens, with PP fiber exhibiting a stronger reinforcing effect than RS fiber. Furthermore, the effect of PP fiber content was more pronounced than that of fiber length, whereas the opposite trend was observed for RS fiber. The optimum fiber parameter levels were determined for each type: PP fiber performed best at a mass concentration of 1.5% and a length of 6 mm, while RS fiber showed optimal performance at a mass concentration of 1.0% and a length of 5-10 mm. Macroscopic damage analysis indicated that the structural integrity and residual compressive strength of the TWSMB specimens were preserved even after surpassing the ultimate compressive strength, due to the crack-bridging effect of the fibers. Microstructural analysis showed that PP fiber-reinforced specimens exhibited a dense structure formed through reactions with other hydration products. In contrast, the surface of RS fibers was nearly fully encapsulated by hydration products, resulting in the formation of a physical skeleton structure. This study provides new insights into minimizing cement consumption and reducing backfilling costs in mining operations.

Mechanical properties of soil reinforced by fiber and alkaline-activated rice husk ash, and rainfall erosion model tests.

Rice husk ash is an industrial waste produced by biomass power plant to generate electricity, which contains a lot of silica. The accumulation of rice husk ash not only consumes land resources, but also causes environmental pollution. It is an urgent problem to explore the resource utilization of rice husk ash. In order to reuse rice husk ash, this study focuses on the application of polypropylene fiber and alkaline activated rice husk ash to slope reinforcement. Polypropylene fiber has the advantages of good toughness and corrosion resistance. Reinforced soil can effectively improve soil toughness and mechanical properties of soil engineering. NaOH solution was selected as the alkaline activator, and rice husk ash and polypropylene fiber were used to stabilize and strengthen the clay, which was consistent with the principles of sustainable development and circular economy. Through unconfined compressive strength test, the effects of ash content, polypropylene fiber content, NaOH concentration and curing age of rice husk on soil strength characteristics were studied. In addition, the mechanical properties and curing reinforcement mechanism of alkali-activated rice husk ash fiber-reinforced soil were studied by using dry-wet cycle test, rainfall erosion model test and microstructure analysis. The results show that the curing effect is best when 5 % rice husk ash is used, and the unconfined compressive strength of rice husk ash reinforced soil is the highest when the fiber content is 0.7%. NaOH solution improve soil strength, with maximum strength observed at a concentration of 0.6mol/L. The resistance to dry-wet damage of rice husk ash fiber reinforced soil is better than that of unreinforced soil, but the strength loss after dry-wet cycle by alkali activation is greater. In addition, the surface erosion of fibrous soil slope is the smallest, and the erosion amount is much lower than that of unreinforced soil. Fiber can effectively improve the erosion resistance and slip resistance of slope. The microscopic test analysis confirms the strength test results, and the addition of 5% rice husk ash will produce more hydration products, reduce soil porosity and improve soil strength. NaOH can effectively stimulate the active ingredients in soil particles, and the hydration products produced by the reaction can effectively fill the soil pores and significantly enhance the soil strength. The staggered network structure of polypropylene fibers improves the integrity of the soil, providing significant reinforcement.

Mechanical properties of polypropylene fiber reinforced concrete short columns under freeze-thaw cycles

To investigate the effect of polypropylene fibers on the mechanical properties of concrete structures in cold regions, obtain an appropriate amount of polypropylene fiber content, and improve the frost resistance of the structure, freeze-thaw cycle tests were conducted on three groups of reinforced concrete short column specimens with different polypropylene fiber contents. The depth of surface damage of the specimen was detected using ultrasonic method. The stress process and failure of the specimen were analyzed through axial compression test, and the corresponding changes in compressive toughness were discussed. A formula for calculating the axial compressive bearing capacity of polypropylene fiber reinforced concrete short columns after freeze-thaw cycles was established. The test results indicate that the addition of polypropylene fibers can reduce the compressive bearing capacity of reinforced concrete short columns. An appropriate amount of polypropylene fiber can enhance the frost resistance, ductility and toughness of concrete components, and the recommended volume fraction of polypropylene fiber is 0.08–0.12%.

Experimental and numerical simulation study on the dynamic behavior of basalt-polypropylene fibers reinforced coral aggregate concrete

This study investigates the failure mode, dynamic compressive strength, strain rate effect and critical strain of basalt-polypropylene fiber-reinforced coral concrete (BPRCAC) under impact load using a 75 mm diameter split Hopkinson pressure bar (SHPB). The Holmquist-Johnson-Cook (HJC) model is modified to obtain parameters such as strain rate effect and strength based on the test results, utilizing LS-DYNA for numerical simulation analysis. The results indicated that the dynamic compressive strength and critical strain of BPRCAC significantly respond to the strain rate, increasing with the strain rate. A relationship between the dynamic increase factor (DIF) and the strain rate of BPRCAC is developed, showing that the DIF increases linearly with the decimal logarithm of the strain rate. However, the critical strain of BPRCAC increases linearly with the strain rate. The addition of basalt fiber (BF) and polypropylene fiber (PF) improves the strain rate sensitivity of the dynamic compressive strength, with increases of 19.21 %, 7.37 %, 22.60 %, and 11.37 % observed for BCAC-0.1, PCAC-0.1, BPCAC-0.1, and BPCAC-0.2, respectively, compared to CAC at a strain rate of 133 −143 s−1. The combined content of BF and PF has a more significant effect on the strain rate sensitivity of the critical strain, with BPCAC-0.2 exhibiting a critical strain 50.79 %−74.42 % higher than that of the other groups compared to CAC. The stress-strain curves and failure modes of the specimens simulated by LS-DYNA agree with the experimental results, verifying the applicability of the improved HJC model to BPRCAC.

Fiber Showdown: A Comparative Analysis of Glass vs. Polypropylene Fibers in Hot-Mix Asphalt Fracture Resistance

Cracks in asphalt mixtures compromise the structural integrity of roads, increase maintenance costs, and shorten pavement lifespan. These cracks allow for water infiltration, accelerating pavement deterioration and jeopardizing vehicle safety. This research aims to evaluate the impact of synthetic fibers, specifically glass fiber (GF) and polypropylene fiber (PPF), on the crack resistance of Hot-Mix Asphalt (HMA). An optimal asphalt binder content of 5% was used in all sample designs. Using the dry mixing technique, GFs and PPFs were incorporated into the HMA at dosages of 0.50%, 1.00%, and 1.50% by weight of the aggregate. The effects of these fibers on the mechanical fracture properties of the HMA were assessed using Semi-Circular Bending (SCB), Indirect Tensile Asphalt Cracking Tests (IDEAL-CTs), and Three-Point Bending (3-PB) tests. This study focused on fracture parameters such as fracture work, peak load, fracture energy, and crack indices, including the Flexibility Index (FI) and Crack Resistance Index (CRI). The results from the SCB and IDEAL-CT tests showed that increasing GF content from 0.5% to 1.5% significantly enhances the flexibility and crack resistance of HMA, with FI, CRI, and CT Index values increasing by 247.5%, 55%, and 101.35%, respectively. Conversely, increasing PPF content increases the mixture’s stiffness and reduces its crack resistance. The PP-1 mixture exhibited higher FI and CT Index values, with increases of 31.1% and 10%, respectively, compared to the PP-0.5 mixture, based on SCB and IDEAL-CT test results. The SCB, IDEAL-CT, and 3-PB test results concluded that fibers significantly influence the fracture properties of bituminous mixtures, with a 1% reinforcement dosage of both PPFs and GFs being optimal for enhancing performance across various applications.

A Comparative Study of the Rheological Properties of a Fly Ash-Based Geopolymer Reinforced with PP Fiber for 3D Printing: An Experimental and Numerical Approach

The present study investigates the flow characteristics of fly ash-based (FA) geopolymers reinforced with polypropylene (PP) fibers during the extrusion process in three-dimensional printing. By applying the Herschel–Bulkley rheological model, this research provides a sound theoretical basis to understand the flow behavior of these materials under various conditions. The Herschel–Bulkley model describes the relationship between shear stress and the shear rate in non-Newtonian fluids, capturing yield stress and flow consistency. A combination of experimental and numerical techniques based on the Finite-Element Method (FEM) in COMSOL has been used in this study. The results of both experimental and simulation approaches are compared to examine the material behavior during extrusion. The experimental results indicate that PP fiber content significantly affects the rheological properties. Mixtures with high fiber content encountered issues such as high static yield. However, mixtures with moderate fiber content showed smoother extrusion processes, suggesting an optimal fiber addition range that balances mechanical properties and extrudability. The numerical simulations generally agreed with the experimental data up to a certain fiber content level, beyond which more complex interactions necessitate further model refinements. The investigation identified a 0.25% to 0.5% fiber content range that enhances performance without complicating the extrusion process, facilitating the production of properly printed structures.

EFEKTIVITAS PENAMBAHAN SERAT POLYPROPYLENE TERHADAP KUAT LENTUR BETON GEOPOLIMER dengan SUPERPLASTICIZER

Geopolymer concrete is concrete composed of a mixture of coarse and fine aggregate without Portland cement binder. Fly ash is used as a substitute, because it contains a lot of silica and alumina. Geopolymer concrete has good strength and durability, but concrete also has disadvantages, namely brittleness, workability and often cracking due to tensile loads. Superplasticizer (SP) is used at 2% of fly ash weight to improve workability. The SP used is Sika viscocrete 1003. The addition of polypropylene fiber is one way to overcome brittle properties and the appearance of fine cracks in concrete. In this paper using Sika fiberforce 48mm polypropylene fiber which has a tensile strength of 465N/mm2(MPa) at a dose of 0%, 0.5%, 1%, 1.5% and 2%. The alkaline activator used is a mixture of NaOH and Na2SiO3 solutions. The molarity of the NaOH solution used is 8M with a ratio of NaOH/Na2SiO3 2: 3. From the test results, it is known that the influence of polypropylene fiber is effective for increasing the bending strength of geopolymer concrete. The bending strength value of geopolymer concrete with the addition of polypropylene fibers increased by 60.19%. The polypropylene fiber content will be maximum at a percentage of 0.5% of the total volume of the mixture.Keywords: Fiber, Flexural Strength, Fly Ash Geopolymer Concrete, Polypropylene, Superplasticizer

Properties of Fiber-Reinforced Geopolymer Mortar Using Coal Gangue and Aeolian Sand.

Geopolymers, as a novel cementitious material, exhibit typical brittle failure characteristics under stress. To mitigate this brittleness, fibers can be incorporated to enhance toughness. This study investigates the effects of varying polypropylene fiber (PPF) content and fiber length on the flowability, mechanical properties, and flexural toughness of coal gangue-based geopolymers. Microstructural changes and porosity variations within the Fiber-Reinforced Geopolymer Mortar(GMPF) matrix were observed using scanning electron microscope (SEM) and Low field NMR(LF-NMR) to elucidate the toughening mechanism of PPF-reinforced geopolymers. The introduction of fibers into the geopolymer matrix demonstrated an initial bridging effect in the viscous geopolymer slurry, with a 3.0 vol% fiber content reducing fluidity by 5.6%. Early mechanical properties of GMPF were enhanced with fiber addition; at 1.5 vol% fiber content and 15 mm length, the 3-day flexural and compressive strengths increased by 30.81% and 17.4%, respectively. Furthermore, polypropylene fibers significantly improved the matrix's flexural toughness, which showed an increasing trend with higher fiber content. At a 3.0 vol% fiber content, the flexural toughness index increased by 198.35%. The data indicated that a fiber length of 12 mm yielded the best toughening effect, with an 84.03% increase in the flexural toughness index. SEM observations revealed a strong interfacial bond between fibers and the matrix, with noticeable damage on the fiber surface due to frictional forces, and fiber pull-out being the predominant failure mode. Porosity testing results indicated that fiber incorporation substantially improved the internal pore structure of the matrix, reducing the median pore diameter of mesopores and converting mesopores to micropores. Additionally, the number of harmless and less harmful pores increased by 23.01%, while the number of more harmful pores decreased by 30.43%.

Research on axial compressive performance of ceramic concrete reinforced with HTPP fibers

This study investigates the influence of High-Toughness Polypropylene (HTPP) fiber content (0 %, 0.3 %, 0.6 %, 0.9 %) on the axial compressive performance of ceramsite concrete. Four sets of ceramsite concrete cube and prism specimens were prepared, and the cube compressive strength and full stress-strain curves for each set were tested. Based on the experimental results, it analyzed the variation characteristics of HTPP fibers on the stress-strain curve of ceramic concrete at different stages, studied the peak stress, peak strain, elastic modulus, toughness, and energy absorption capacity of ceramic concrete. Finally, the stress-strain curve has been fitted. The results indicate that: HTPP fibers can significantly enhance the strength and toughness of ceramic concrete, the compressive strength of the cube increased by 23.8 %, the axial compressive strength increased by 19.0 %, the residual stress increased by 143.0 %, the absolute modulus increased by 164.1 %, the toughness increased by 51.5 %, and the energy dissipation coefficient increased by 9.4 %. By fitting the experimental curve, the mathematical expression for the uniaxial compressive stress-strain curve of ceramic concrete reinforced with high tenacity polypropylene (HTPP) fibers has been proposed. The model matches well with the experimental results, which provides a theoretical basis for the structural analysis and design of this type of concrete.

Exploring enhanced high-temperature resistance: Analyzing the combined impact of fibers and nanoparticles in mortars

This study aims to explore the potential synergistic effect of polypropylene (PP) fiber and different types of nanoparticles to improve the high-temperature resistance of cementitious materials. For that, mortar samples with different PP fiber percentages, 0.6 wt% and 1.2 wt%, were produced. Different percentages of both colloidal nano-silica (CNS), 0.3 %, 0.6 %, and 0.9 %, and nano calcium carbonate (NCC), 0.5 %, 1 %, and 2 %, were used in the study. To test the resistance to elevated temperatures, mortar samples were exposed to different peak temperatures of 300°C, 600°C, and 900°C for 2 h, using unexposed samples as reference. Flexural and compressive strength, water absorption, surface electrical resistivity, and thermogravimetric analysis (TGA) of the heated and unheated samples were conducted. Results showed that, at 300°C heating regime, all samples with 0.6 % PP fiber exhibited an increase in flexural and compressive strength compared to their corresponding reference samples. For instance, specimens containing 0.6 % PP fiber and 2 % NCC content exhibited a 19 % increase in flexural strength compared to the unheated sample, whereas samples with 0.6 % PP fiber and 0.5 % NCC increased 32 % their compressive strength. In contrast, at 600°C, there was a major decline in mechanical properties in all samples, with samples containing NCC exhibiting the lowest amount (average of 61 % reduction in flexural strength and 32 % decrease in compressive strength). In general, a higher dosage of nanoparticles and lower PP fiber content will be better to resist temperatures up to 600 °C.

Study on static and dynamic mechanical properties and microstructure of silica fume-polypropylene fiber modified rubber concrete

Through tests and micro-observations, the static and dynamic mechanical properties and microstructure of rubber concrete samples modified with varying amounts of silica fume and polypropylene fiber content were explored. The results indicate that incorporation of silica fume and polypropylene fiber can effectively enhance the performance of rubber concrete. Moreover, at 10% and 0.1% of silica fume and polypropylene fiber content respectively, rubber concrete’s compressive strength, splitting tensile strength, flexural strength, and dynamic compressive strength reached maxima. Furthermore, microstructure characteristic analysis indicated that inadequate adhesion between rubber particles and the matrix is responsible for compromised bearing capacity in unmodified rubber concrete. However, with the addition of silica fume and polypropylene fiber, the fiber binds the rubber particles closely with the matrix, while the silica fume fills the gaps between the matrix components. This combination results in rubber concrete with a denser internal structure and enhances its bearing capacity significantly.

Behavior of Polypropylene Fibre Reinforced Fly Ash Concrete RC Beams in Flexure

This paper presents an experimental investigation on the polypropylene fibre reinforced fly ash concrete RC beams under flexure. The variables of study include the polypropylene fibre content (0.2 % & 0.4%). The polypropylene fibre and 10% of Fly ash as cement replacement are incorporated in all the concrete mix proportions considered in this study. The experimental test results showed that the compressive strength of concrete increases with the increasing percentage of fibre. The flexural strength of polypropylene fibre reinforced fly ash concrete beams increased considerably than the control concrete beams.

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.

Effect of Varying The Content And Length Of Fibers In The Behavior of A Cemented Soil Efecto del Contenido de Fibra y la Variación de Longitud en el Comportamiento de un Suelo Cementado

This study presents the results of the effects of variation in the content and length of polypropylene fibers, when inserted into a soil-cement mixture, aiming its use as a primary coating for dirt roads. In this study, the experimental models were used: 5% fast-curing cement, clay sand of the Barreiras geological formation and polypropylene fibers of 6 mm and 24 mm lengths, at levels from 0.25%, 0.50% and 0.75% relative to the total dry soil-cement mass. After completion of the unconfined compression tests and tensile strength by diametrical compression, it was found that increasing fiber content in the soil-cement matrix provides: increase in resistance of the materials, increase on the voids content and the strain, but, significantly reduces the initial tangent modulus making the more ductile material. In the terms of length, it observed clearly that the 24 mm fiber has a stronger influence on the mechanical behavior when inserted into the matrix of the developed composite material.

Study on the flexural performance and microstructure of lithium feldspar tailings cementitious filler using mixed fibers

The brittle fracture and toughness of cemented tailings backfill (CTB) are not conducive to underground mining projects. Incorporating fibers may enhance the flexural properties of the CTB. This study used glass (GS) and polypropylene (PP) fibers to fabricate fiber-reinforced cemented lithium feldspar tailing backfill (FCLTB) specimens. The flexural strengths and microstructures of the specimens were analyzed using a three-point flexure test and scanned electron microscopy (SEM). Following a three-point bending test, it was observed that Upon decreasing the amount of GS fiber, the bending strength of the FCLTB specimens initially decreased and then increased. However, with an increase in the PP fiber content, the average bending module of the FCLTB specimens initially reduced and then rose. The combined use of GS and PP fibers significantly improved the toughness of the CLTB samples after the peak. Composite fibers resist the formation of cracks under load.

Impact of Recycled Polypropylene Fibers on the Density and Strength of Unreinforced Concrete

Polypropylene (PP) is widely used in the construction industry to produce a variety of materials. Accordingly, a huge amount of waste is produced during or after the construction activity. The PP fiber provides a good alternative solution to enhance concrete properties and more sustainable concrete produced in terms of isolation and weight reduction. In this study, 24 concrete cubic samples are cast by adding different PP fiber content to characterize this fiber effect on concrete density and unconfined compressive strength (UCS). The results demonstrate that using higher fiber content of 2%, 6%, and 10% leads to a mass reduction that equals to 59, 157, and 290 kg compared to normal concrete per one cubic meter. However, at higher PP fiber content, the unconfined compressive strength decreases compared to the controlled samples. The concrete mix with 2% PP fiber revealed a higher value of compressive strength with increment by (10-12)% at age (7-28) days compared to normal concrete. The outcomes imply that using PP fiber contributes to the protection of the environment by reducing the quantity of PP waste from construction materials.

Influence of key design variables on dynamic material properties of iron tailing porous concrete under impact loading

Iron tailing porous concrete (ITPC) is a new foamed concrete material that using iron ore tailing powder to partially replace the cement. Previous investigations on ITPC primarily focused on its mechanical properties under static loads or low strain rate conditions, leaving a significant gap in its impact resistance performance at high strain rates. This study employed the split Hopkinson pressure bar (SHPB) to test ITPC specimens under impact loading with strain rate around 120 s−1. Density, water-binder (W/B) ratio, iron tailing powder content, polypropylene fiber length and content were taken as key design variables to prepare the ITPC specimens with different mix ratios and study their effects on the dynamic material properties of ITPC. Specifically, the failure modes, stress-strain relations, elastic moduli, compressive strengths and energy dissipation densities of the ITPC specimens with various design variables were recorded and compared. The test results indicate that the material density, fiber length and content have strong influences on the impact failure modes of ITPC. The elastic modulus, compressive strength and energy dissipation density of ITPC exhibit exponential growth with the material density. These parameters, however, show an initial growth followed by a decrease with the rising W/B ratio, fiber length and fiber content, and they reach the peak values at around 0.70, 9 mm and 2.0%, respectively. Moreover, the iron tailing powder content of 25% is recommended for ITPC for maintaining good impact resistance.

Properties of fiber incorporated concrete blocks manufactured using recycled aggregates

The construction and demolition industry generates a significant quantity of concrete waste, presenting an environmental challenge. The concrete waste generated can be processed to produce Recycled Aggregates (RA) of various sizes. Utilization of Recycled Aggregates (RA) as a substitute to conventional aggregates in concrete has captured considerable attention in the past few years, owing to its promising environmental and economic advantages. However, the combined utilization of recycled fine and coarse aggregate in the production of concrete for low-strength application has not been adequately explored. In this article, an attempt is made to investigate the characteristics of concrete blocks made with RA and polypropylene fiber (PF) are investigated for different cement content. Cement and PF content varied from 8 to 12% and 0% to 2% respectively in production of concrete blocks using Recycled Fine Aggregates (RFA) and Recycled Coarse Aggregates (RCA) at different replacement intervals. Water absorption of blocks manufactured across all replacement intervals of RA was less than 10%. Blocks containing 75% RFA and 25% RCA resulted in improved compressive strength of the order more than 3.8 MPa. Rate of improvement in compressive strength of block was 11% to 20% and 6.5% to 8.2% when the fiber dosage was increased from 0.5% to 1% and 1% to 2% respectively. The optimal fiber dosage was found to be 1%, beyond which no notable improvement in mechanical properties of blocks was observed. Use of RA in concrete blocks reduced embodied energy by 19% to 24% for varying cement content from 8 – 12%. Cost of blocks was found to be reduced by 10 – 15% when made with PF dosage of 0 to 2% with 8% cement content.

Enhancing the physical properties of cemented ultrafine tailings backfill (CUTB) with fiber and rice husk ash: Performance, mechanisms, and optimization

A series of experiments was conducted to study the performance and mechanisms of Cemented Ultrafine Tailings Backfill (CUTB). Firstly, the optimum fiber type was selected by single factor multilevel test. Secondly, the effects of cement content, rice husk ash content, fiber content and fiber length on backfill properties were analyzed by orthogonal test and microstructure test, and the influence mechanism of fiber and rice husk ash content was revealed. Finally, fuzzy mathematics theory is used to optimize the ratio parameters. The results show, compared to glass and basalt fiber, polypropylene fiber yields the most substantial enhancement in backfill strength. The increase of cement content, polypropylene fiber content and length can reduce slump, but the change of rice husk ash content has no obvious effect. Increased cement or fiber content effectively restrained the formation of primary fractures in CUTB, thus enhancing its integrity. Adding an optimal dosage range of 0–4 % of rice husk ash boosted the early compressive strength, albeiting at the expense of later compressive strength. Fiber addition with the optimum content range between 0.1 and 0.4 % enhanced the strengthening effect of cement content on compressive strength. Fiber primarily enhances the macroscopic strength of backfill through the dispersion and co-loading of forces, whereas rice husk ash enhances strength by optimizing void structure distribution. The optimal ratio parameters of a cement content of 310 kg/m³, rice husk ash content of 8.0 %, fiber content of 0.4 %, and fiber length of 9 mm were proposed finally.

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.