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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. [ABSTRACT FROM AUTHOR]

To popularize the complete replacement of natural sand with manufactured sand, a study was performed to determine the effect of adding polypropylene fibres (PPFs) to increase the bending strength and carbonization resistance of manufactured sand concrete (MSC). A 2 × 3 factorial design with the content and length of PPF as variables was used to establish a carbonization depth prediction model and a response surface model (RSM). The phase composition and microstructure of polypropylene-fibre-reinforced manufactured sand concrete (PPF-MSC) were analysed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show the addition of PPF with different contents and lengths increases the bending strength of PPF-MSC to varying degrees, while reducing the carbonization depth and increasing the dynamic elastic modulus after 28 days of carbonization. The highest bending strength (6.12 MPa) and carbonization resistance of PPF-MSC are obtained by the addition of 1 kg/m3 of 12 mm PPF, while the carbonization depth and an increase in the dynamic elastic modulus after 28 days of carbonization are maintained at a minimum of 2.26% and 1.94 mm, respectively. A prediction model was established to obtain a formula for the PPF-MSC carbonization depth in terms of the content and length of PPF and the carbonization time. The following results were obtained from the RSM: compared to the PPF length, the PPF content has a larger impact on the PPF-MSC bending strength and a smaller impact on the PPF-MSC carbonization resistance; there is no significant interaction between the content and length of PPF; and the predicted and measured values are close, indicating that the model is highly reliable. A comparison of the XRD patterns and SEM micrographs of PPF-MSC and MSC after 28 days of carbonization show a lower peak intensity of CaCO3 in the pattern for the carbonized area for PPF-MSC than for MSC and considerably fewer surface pores and cracks in PPF-MSC than in MSC. These results indicate that the addition of PPF increases the compactness of MSC and creates an effective resistance to the erosion by water molecules and carbon dioxide (CO2), thus enhancing the bending strength and carbonization resistance of MSC. [ABSTRACT FROM AUTHOR]

Recently, Fibre Cement Board (FCB) due to its lightness and speed in construction and execution has been highly considered. In this paper, numerical and experimental studies have been carried out to achieve eco- friendly FCB. A total of 20 mixtures were prepared. Limestone powder (LP) and silica fume (SF) were used, as a partial replacement for cement, and perlite (PLT) as a replacement for sand in the predetermined mixtures. Polypropylene fibre (PP) and fibre-glass mesh (FGM) were also used to improve the mechanical behavior. The flexural strength, modulus of elasticity, density, and water absorption of the specimens were evaluated.. Numerical analysis was also implemented to simulate the testing configuration for the full-scaled FCB. The results showed that the minimum density corresponded to the perlite specimen, reinforced by 0.75% polypropylene fibre. In contrast, the flexural strength and modulus of elasticity were increased by 48% and 51%, respectively, compared to the reference one.. The results declared that using LP, with and without SF, should be limited by 5%. The numerical results of the small FCB model were precisely validated by the experimental specimens, which can be considered an appropriate assessment method to evaluate the performance of full-scaled FCB. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the appropriateness of polypropylene fibres (PP) to decrease the brittleness of high-performance self-compacting concrete (HPSCC). The influence of PP fibre content on the fresh and mechanical assets of PP-fibre-reinforced HPSCC was investigated. PP fibres were applied with 0, 0.025, 0.05, 0.075, 0.125, 0.25% contents to the HPC blends with high cement replacement by ground granulated blast furnace slag (GGBS). The impact of PP fibre fraction on fresh properties of HPSCC, counting passing capability as well as filling parameters is discussed. In addition, the mechanical properties, i.e., compressive, splitting tensile, and flexural strengths, were evaluated after 7 and 28 days of specimens' maturation in water. The higher content of PP fibres gradually reduced the HPSCC workability and improved the mechanical properties. The high performance of fresh and hardened ecological HPSCCs containing 46% GGBS instead of cement with 0.025–0.25% PP fibre content proves the great potential of using these composites in various applications in the construction industry. The advantages of the potential recycling of GGBS include, among others, the reduced use of cement in a durable material, reduced amount of waste in landfill and lower emission levels of greenhouse gases. [ABSTRACT FROM AUTHOR]

The durability of the self compacting concrete is one of the prominent areas of concern in recent years since it has become prevalent due to its ease of handling in the construction industries. However, there is a lack of detailed durability study of M-sand self compacting concrete with polypropylene fibres in the literature. In this paper, self compacting concrete made by Portland pozzolana cement with natural sand and M-sand, different percentages of volume fraction (0%, 0.1%, 0.15% and 0.2%) polypropylene fibres with M-sand is thoroughly investigated for fresh properties, hardened properties, drying shrinkage, water absorption, permeability, acid resistance and corrosion crack initiation time. Further, SEM analysis was carried out to know the effect of polypropylene fibre on the concrete microstructure. The results confirmed that the use of M-sand has improved the fresh, hardened and durability properties of the self compacted concrete than natural sand. Also, it is observed that the addition of polypropylene fibres has reduced the fresh properties of self compacted concrete. However, M-sand with 0.15% polypropylene fibres has slightly improved the strength of self compacting concrete, compression strength by 6.97%, split tensile by 8.68% and flexure strength by 3%. Further, it has reduced the drying shrinkage by 40%, water absorption by 30%, water penetration by 33.33%, and increased the chemical resistance, surface crack initiation period than the natural sand self compacting concrete. Finally, this study concludes that M-sand with 0.15% polypropylene fibres improves the durability of self compacting concrete by reducing effect from aggressive environments and in turn contributes to increased corrosion resistance of reinforcements embedded in concrete. Thus, the study supports the use of self compacting concrete with M-sand and optimum amount of polypropylene fibres to achieve required sustainability in terms of strength and durability. [ABSTRACT FROM AUTHOR]

Recycled concrete aggregate has been widely researched to be capable of replacing natural coarse aggregate in concrete, however, with some inadequacies in its concrete's ability to attain the same feat in mechanical properties as normal concrete. This research work attempts to improve the strength characteristics of concrete containing recycled coarse aggregate with the addition of admixtures (Micro-Silica and Superplasticizer) and Polypropylene fibre. Results showed that admixtures significantly improved the workability and mechanical properties of CRCA at all RCA replacement levels. Addition of PPF had significant effect on the flexural and splitting tensile strengths of CRCA, but not much impact on the compressive strength. [ABSTRACT FROM AUTHOR]

Pervious concrete remains a sustainable solution for effective water management in urban scenarios. Owing to the absence of fine aggregates, properties of pervious concrete rely much on the properties of aggregates and porosity. This article is aimed at determining the effect of aggregate size on the performance of pervious concrete mixes using 12.5 and 20 mm nominal-sized aggregates. In addition to that, the effects of polypropylene and glass fibre were experimented by varying their proportion in volumetric increments of 0.1% up to 0.4%. The aggregate to cement ratio and water to cement ratio were retained constant at 3.54 and 0.35, respectively. Results indicated that the fall in aggregate size improves mechanical properties but decreases porosity and permeability values. The presence of fibres in pervious concrete mixes was observed to improve flexural and split tensile strength but has no significant effect on the compressive strength, porosity and permeability. [ABSTRACT FROM AUTHOR]

Wet-laid nonwovens are now increasingly used in various technical applications. Fibres of short cut length which are usually discarded as waste are now used to produce valuable products. In the present study, polypropylene (PP) fibrous nonwoven webs were prepared by using a wet laid technique. Carbon fibres used as filler were added to PP fibrous web in the proportion of 10% on the weight of the Web. The effect of stacking sequence of the wet-laid nonwovens during composite preparation on the flexural and impact properties of composite laminates was studied. The addition of carbon fibre fillers led to an improvement of 63% in flexural strength and 17% in impact strength compared to the pristine samples prepared with PP. The addition of carbon fibre fillers to the nonwovens has resulted in the increased realisation of flexural and impact strength of composites. [ABSTRACT FROM AUTHOR]

This research investigates the potential use of waste white cement by pass dust (WCBPD) in producing roller-compacted concrete (RCC). Fifteen RCC mixes were casted in which cement was partially replaced by WCBPD at (10, 20, 30 and 40%) with addition of polypropylene fibre in two percents (0.25 and 0.5%). The mechanical properties of RCC mixes were evaluated using compressive and splitting tensile strength, modulus of elasticity and ultrasonic pulse velocity. The durability behaviour was evaluated through water absorption, dynamic modulus of elasticity and freeze–thaw resistant. Test results have shown that Increasing WCBPD to 20, 30 and 40% repalcement of cement has degraded the mechanical properties of RCC mixes. Even though, all RCC mixes reached a compressive strength greater than 27.6 MPa except mix with 40% WCBPD replacement level. All RCC mixes have shown a satisfactory durability. The addition of PPF has improved the mechanical and durability properties of RCC mixes with WCBPD. It is recommended to use waste WCBPD in producing RCC for up to 30% as a main base layer. Using WCBPD (as a replacement of cement) in producing RCC will effectively reduce the production cost and reduce environmental pollution by decreasing the disposal of this waste material in landfills. [ABSTRACT FROM AUTHOR]

Oil palm shell (OPS) is a renewable resource obtained from agricultural solid end products via the extraction of palm oil. A study on preparing the lightweight concrete (LWC) using heat-treated and non-treated OPS aggregate has been investigated. High performance polypropylene fibre (HPPF) was incorporated in this oil palm shell concrete (OPSC) in different volume fraction (Vf) (0, 0.25, 0.5, 0.75 and 1%). The performance of heat-treated and non-treated OPS fibre-reinforced concrete (FRC) mixtures was evaluated by conducting comprehensive series of tests on fresh and hardened properties as well as durability properties and drying shrinkage. The Vee-Bee, density, compressive strength and stress-strain behaviour have been measured and evaluated. Rapid chloride penetration test (RCPT), porosity measurement, water absorption, initial surface absorption (ISA) and drying shrinkage tests have been performed in order to signify the effects of heat-treated OPSFRC on durability properties. The results showed that the ideal amount of HPPF has enhanced the durability of concrete by reducing chloride diffusion, porosity and water absorption. Hence, the findings of this investigation revealed the novelty of heat treatment method on OPS by incorporating HPPF, with promising durability properties and drying shrinkage of LWC as the sustainable solution in the construction industry. [ABSTRACT FROM AUTHOR]

Synthetic fibre reinforced granular soils, particularly fine to medium sands have the benefits of improved shear strength and permeability and as a result found wide application as fill and backfill material. However, not much work is reported on coefficient of elastic uniform compression (Cu) of fibre reinforced sand. Cu is used in determination of soil spring stiffness and is an important essential parameter in design of machine foundations and structures subjected to cyclic loads. Hence, in the present study, the effect of addition of polypropylene fibre in fine sand is assessed by conducting small scale cyclic load tests in the laboratory. The study is also intended to evaluate the effect of shape of loading plate on Cu of fibre reinforced sand. Fibres of 6 mm and 12 mm length in proportions of 0.5%, 1.0% and 1.5% by weight are mixed with fine sand in the study. The study yielded the optimum percentage of fibre for stabilization as 1%, with 12 mm fibre more effective than 6 mm fibre. No shape effect on Cu of fibre reinforced fine sand is observed in contrast to unreinforced fine sand for which Cu of circular plate is 0.85 times the Cu of square plate of same size. [ABSTRACT FROM AUTHOR]

In this study, different dosages of carbon black (CB) and polypropylene (PP) were added to develop functional cementitious composites as cement-based sensors. The results show that electrical conductivity increased with the amount of PP fibres, due to the enclosed CB nanoparticles and more conductive passages. The compressive strength slightly decreased, while the flexural strength was significantly increased with the increased amount of PP fibres. The improvement is mainly achieved by the reduced CB concentration in cement matrix and the excellent tensile strength of PP fibres. Under the cyclic compression, the piezoresistivity increased by three times for 0.4 wt% PP fibres filled CB/cementitious composite, regardless of the loading rates. The flexural stress sensing efficiency was considerably lower than that of compressive stress sensing, but it increased with the amount of PP fibres. Moreover, fitting formulas were proposed and used to evaluate the self-sensing capacity, with the attempts to apply cement-based sensors for structural health monitoring. Unlabelled Image • Enclosed CB nanoparticles on the surface increase the conductive passages by PP fibres. • Carbon black agglomerations were more significant to affect the mechanical properties. • Flexural strength of specimen considerably improved with the increase of PP fibres. • Compressive stress sensing efficiency linearly increased with the increase of PP fibre. • Flexural failure can be recorded by suddenly increased electrical resistivity of the specimen. [ABSTRACT FROM AUTHOR]

This paper reports the influence of fibre inclusion on the hydro-mechanical properties of bentonitic mixtures at varying compaction states. Pond ash–bentonite and sand–bentonite mixtures are synthesized by adding 20% commercial bentonite to pond ash and sand respectively. Discrete polypropylene fibres ranging from 0 to 1% are added to the mixtures. The hydro-mechanical properties of specimens; compacted to either standard or modified Proctor density; are investigated for a wide range of molding water content varying from dry to wet side of optimum. Though the inclusion of fibre has insignificant effect on optimum moisture content and maximum dry density of mixtures, the compressive strength, failure strain, unit cohesion and frictional angle of the compacted specimens are found to increase whereas the volumetric shrinkage strains are found to decrease irrespective of the molding water content. Both unreinforced and reinforced specimens exhibited the maximum unconfined compressive strength at relative water contents of 90% and 80% when compacted to standard and modified Proctor density respectively. With an addition of 1% fibre, these values are found to increase by 2 to 3 times. The specimens compacted at dry of optimum did not show any significant variation in hydraulic conductivity whereas specimens compacted at wet of optimum exhibited an increased hydraulic conductivity with fibre content. However, specimens compacted at optimum moisture content showed an insignificant change in hydraulic conductivity with increase in fibre content. Furthermore, the increase in volumetric shrinkage strain with relative water content is reduced as the fibre content increases. [ABSTRACT FROM AUTHOR]

Self-compacting concrete presents good workability to fill complicated forms without mechanical vibrations. This concrete is often reinforced with fibres to improve the strength and toughness. This study investigated the use of nickel -titanium (NiTi) shape memory alloy fibres in comparison with polypropylene and steel fibres in 2055 The performances of the fresh fibre–reinforced self-compacting concrete are explored by slump flow and J-ring experiments. Meanwhile, the static and cyclic flexural tests are conducted to estimate the bending resistance strength performance, residual deformation and recovering capacity of shape memory alloy, polypropylene and steel fibre–reinforced self-compacting concrete. Moreover, the flexural toughness of the shape memory alloy, polypropylene and steel fibre–reinforced self-compacting concrete is calculated using four different codes. The shape memory alloy fibre–reinforced self-compacting concrete with 0.75% volume fraction presents the largest flexural strength, re-centering ability and toughness in comparison with polypropylene and steel fibre–reinforced self-compacting concretes. The experimental results demonstrated the beneficial influence of the shape memory and superelastic properties of NiTi in postponing initial crack formation and restricting the crack widths. [ABSTRACT FROM AUTHOR]

This study was conducted to experimentally demonstrate the control the nano-, micro- and macro-scale cracking in cement-based composites by using nano-, micro- and macro-scale fibres. While micro, macro and hybrid system polypropylene (PP) fibres were used in concrete designs, micro-scale PP and multi-walled carbon nano tubes (MWCNT) were utilized in mortar mixtures. The progression of the cracks was monitored in accordance with a well-known standard and also with a modified method which enabled the investigation of plastic and restrained shrinkage. Fracture energy, flexural strength, compressive strength, modulus of elasticity and ultrasonic pulse velocity of the samples were also determined as the mechanical properties of the composites. Results showed significant improvements in the reduction of cracks, especially with hybrid fibres system. • Cracks at three levels (nano, micro and macro level) were controlled. • Effects of hybrid PP fibres on shrinkage and mechanical properties. • MWCNT dispersion without ultrasonification. • Modified test method was used for combined plastic and restrained shrinkage. • Flexural strength and fracture energy were improved by the use of fibres. [ABSTRACT FROM AUTHOR]

The use of various types of fibres within concrete matrix for enhancing structural performances of concrete or reinforced concrete (RC) members has been gaining interest in recent years. While a considerable amount of research has been conducted for using steel fibres, the studies on the other types of fibres are limited. For the purpose of extending our knowledge on polypropylene fibres in RC beams, an experimental programme was carried out for investigating the shear behaviour of polypropylene fibre-reinforced concrete (PFRC) beams. This paper presents the results of beams with web reinforcement divided into three groups according to the shear span-to-effective depth ratio and the amount of web reinforcement. Each group consists of a reference RC beam and three beams with fibre contents of 1.0, 2.0 and 3.0%. The simply supported beams were loaded at mid-span. Experimental results show that the addition of polypropylene fibres enhanced the shear behaviour of RC beams with web reinforcement. Furthermore, an expression for the contribution of web reinforcement was derived by considering the effectiveness of web reinforcement and it was introduced to the equation proposed previously for predicting the shear strength of PFRC beams without web reinforcement. The predictions agree with the experimental results. [ABSTRACT FROM AUTHOR]

In this study, the strength and flexural toughness of Fibre Reinforced High Strength Concrete (FRHSC) beam containing different combinations of polypropylene and steel fibres are represented. Polypropylene fibre with 0.2% and 0.4% by weight of cement and steel fibre with 0.25%, 0.50%, 0.75% and 1% by volume of concrete were added to the concrete individually and in combination. To obtain the flexural strength of concrete beam, an experimental study was conducted in beam specimens of size 100 x 150 x 1200 mm were subjected to four point loading test. The flexural toughness factor was obtained according to JCI method. The test results from this study indicate concrete containing 0.2% of polypropylene fibre and 0.75% of steel fibre in individual fibre form, and 0.2% of polypropylene fibre + 0.75% of steel fibre in hybrid fibre composites show desired strength and flexural toughness under four point loading test. [ABSTRACT FROM AUTHOR]

Geopolymer offers significant promise to the construction world as a possible alternative to ordinary Portland cement (OPC). Like conventional Portland cement concrete, the matrix brittleness in geopolymer composites can be reduced by introducing suitable fibre reinforcement. A few investigations on fibre reinforced geopolymer composites are available. However there is still a gap to comprehend and enhance their performance. This paper describes the effect of incorporating micro polypropylene fibres on the strength and durability characteristics of geopolymer concrete. The engineering and durability properties like workability, compressive strength, split tensile strength, flexural strength, modulus of elasticity, and sorptivity of geopolymer concrete reinforced with micro polypropylene fibres is presented. The effect of the sulfuric acid attack on Geopolymer Concrete reinforced with micro polypropylene fibres is also discussed. The results show that hydrophobic characteristics of the micro polypropylene fibre led to weak contact with the geopolymer binder and hence weakened the mechanical performance of the fly ash based geopolymer matrix. However significant improvements in durability properties were noted. [ABSTRACT FROM AUTHOR]

Abstract The aim of this research is to establish the fracture properties of high performance concrete (HPC) containing hybrid – basalt (B) and polypropylene (P) fibres. The experimental investigation consisted of tests on cubes, beams and notched prismatic specimens made of plain HPC and fibre reinforced HPC with 1% and 2% of basalt and/or polypropylene fibres. Extensive data on the compressive and tensile splitting strength, flexural behaviour, as well as fracture energy are determined and analyzed. The experimental investigations show that HPC with hybrid B/P fibres display a more ductile behaviour compared to that of plain HPC. The results of the bending tests revealed extended post-peak softening behaviour. The shape of the descending branch depended on the mechanical properties of the fibres, and volume content used. The results illustration the positive effect of high modulus basalt and low modulus polypropylene fibres on HPC fracture energy growth. Moreover the results indicate that a combination of fibres may contribute more effectively to increasing the flexural strength, flexural toughness and fracture energy than using a single type of fibre. [ABSTRACT FROM AUTHOR]

The article presents the results of research work aimed at testing the use of hybrid steel-polypropylene fibre as a strengthening solution to upgrade reinforced high-performance concrete (HPC) beams with openings (BO1 ÷ BO3) and without (B1 ÷ B3). A total of six simply supported beams were tested under four-point bending. The test beams had a cross section of 200 × 400 mm and a total length of 2500 mm. Two square openings in each shear span were located symmetrically about the mid-point in three BO beams. Research was carried out with regard to the quantity and type of reinforcement. Beams B1 and BO1 were constructed with traditional reinforcement made of steel bars. As regards the remaining beams, instead of stirrups and compressive bars, fibre reinforcement of varying fibre volume contents was applied. In the analysis, a non-contact system for three-dimensional measurements of strain and displacement was used. Analysis of the behaviour of the beams under static load was based on the measurements of cracks, deflections and strains. The test results show that the first diagonal crack and the ultimate shear strength increase significantly as the fibre content increases. The above study showed that the hybrid fibres have a positive effect, reducing crack width and ensuring an increase in the load-bearing capacity. [ABSTRACT FROM AUTHOR]

Dynamic compressive behaviour of basalt–polypropylene fibre-reinforced concrete (BPFRC) was experimentally investigated using a 75-mm-diameter split-Hopkinson pressure bar. The results showed that the addition of basalt fibre (BF) and polypropylene fibre (PF) is effective at improving the impact-resistance behaviour of concrete. The dynamic compressive strength, critical strain, and energy absorption capacity of BPFRC increased with increasing strain rate. At strain rates of 20–140 s −1 , the addition of BF and PF significantly increased the dynamic compressive strength, critical strain, and energy absorption capacity of concrete. The dynamic increase factor of BPFRC increased linearly with the decimal logarithm of strain rate. The hybrid addition of BF and PF significantly improved the strain rate effect of the dynamic compressive strength. The strengthening and toughening mechanisms of BF and PF are discussed in detail. The proposed dynamic damage constitutive model can be used to accurately describe the dynamic stress–strain relationship of BPFRC. [ABSTRACT FROM AUTHOR]

In this study, the effects of steel and polypropylene fibre hybridization on the flexural performance of fibre-reinforced geopolymer were investigated. Fibre reinforcement has emerged as a way to improve the brittleness of geopolymer. There are currently several types of fibres available on the market. When polypropylene fibre is used, it usually yields a large drop in strength immediately after the first crack, as well as a lower post-peak response, owing to its high flexibility and low stiffness. To resolve these issues, a hybrid system is introduced using fibre with high strength and stiffness such as steel fibre. In the present study, two hybridization systems are investigated: replacement and addition systems. For a replacement system, the polypropylene fibre is replaced gradually with steel fibre at a rate of 0.2% by volume. For an addition system, the steel fibre is added into the mixture at the same rate. The results indicate that the hybridization of steel fibre can improve the flexural response, toughness, and residual strength of polypropylene fibre reinforced geopolymer to different degrees. Both the load dropping and second peak are found to improve almost instantaneously. The toughness and residual strength also increase gradually with an increase in steel fibre content. [ABSTRACT FROM AUTHOR]

The use of recycled concrete aggregates from different sources on structural concrete is a sustainable solution to minimize the extraction of natural mineral resources and the detrimental impacts of the concrete industry to the environment. The present study aimed to assess the impact of partial replacement of recycled coarse aggregate (RCA), steel (ST) and polypropylene (PP) fibres on mechanical, durability and microstructural properties of self-compacting concrete (SCC). Compressive strength, splitting tensile strength, water absorption and chloride ion penetration of the hardened composites were investigated. The microstructure and interfacial transition zone (ITZ) at the interfaces of aggregate/cement paste and fibre/cement paste of SCCs were investigated using scanning electron microscope (SEM) technique. The experimental results indicated that the addition of fibres in SCC could slightly improve the compressive strength and the resistance to water absorption. Significant improvement in splitting tensile strength was observed in SCC with increasing fibre contents, particularly when both ST and PP fibres were used. The permeability of SCC containing RCA increased with the increase of fibres. Though the strength of SCC reduced with the presence of RCA, the strengths attained were still suitable for structural applications. The SEM results showed that the crack width occurred at fibre-paste interface was smaller when compared to that at aggregate-cement interface, and the microstructure of cement paste around the fibres appeared more compact. In general, SCC mixes made of 20% RCA containing either 1% ST or 1% PP fibres, or a combination of 0.75% ST and 0.25% PP fibres were recommended regarding to the economic efficiency and hardened properties. The potential replacement of such recycled construction and demolition waste due to the technical, economic and environmental improvements it provides, would assist to the sustainability of the construction industry. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of single and hybrid FRC mixtures, with one type of steel and two types of polypropylene fibres at 0.5% and 1.0% volume fractions, is investigated through the double punch Barcelona test. Indirect tensile strength and toughness characteristics are evaluated at ambient temperature and after heating of the specimens at 280 °C. It is shown that the modified toughness estimated through Barcelona test may be a suitable index to classify FRC in terms of ductility, both for the unheated and for the heated specimens. It was also found that hybrid FRC, containing an appropriate amount of different fibre types, is superior in terms of ductility compared to the single FRC. Finally, equations are proposed for the calculation of the Total Circumferential Opening Displacement (TCOD) values by using the axial displacement measurements, considering basic characteristics of the fibres and of FRC mixture, such as fibre’s length, rupture strength and volume fraction, respectively. [ABSTRACT FROM AUTHOR]

Melon is a little popular vegetable to grow in Poland, due to high climatic requirements. Ensuring appropriate thermal conditions for plants growth is possible with relatively late planting seedlings. However, late planting does not guarantee high yield of good quality fruit. The factor enabling the earlier planting seedlings and improving the conditions of growth is the use of flat covers. The field experiment was conducted in 20082010 in central-eastern Poland. The effect of planting seedlings of melon 'Malaga F1' (15 May, 25 May and 4 June) and the length of polypropylene fibre 17 g.m-2 covering (by 4 and 8 weeks from planting, until harvest, control without covering) on the yield and economic efficiency of melon cultivation in the field was investigated. Most preferably the yield level and profitability of melon cultivation were influenced by planting seedlings on the 15 May and covering by 4 weeks. However, earlier planting decreased the share of marketable fruits in the total number of fruits. The highest share in the costs structure of melon cultivation had the costs of human labour. [ABSTRACT FROM AUTHOR]

This study examines the results from an investigation on the impact resistance of oil palm shells (OPS) concrete. The use of OPS as a substitute for regular aggregate in lightweight concrete will help reduce its negative environmental influence. There is a lack of research on the impact resistance and crack behaviour of concrete; specifically in OPS lightweight concrete reinforced by polypropylene (PP) fibre. The replication of a low-velocity projectile effect on slab samples was achieved by dropping two types of steel ball (weighing 0.380 kg and 1.25 kg), with drop height of 360 mm, through the utilization of a self-fabricated drop-weight impact test rig. A total of 12 cube specimens, with dimensions 100 × 100 × 100 mm, were used to prepare 36 slabs with various thicknesses. The 36 slabs were prepared using a concrete cutting machine to excise the three cube specimens from each mixture, into 20, 30 and 40 mm thicknesses. Impact resistance tests were then performed on them. The results demonstrate that there was a strong linear relation between volume fraction of PP fibre and impact resistance; as well as crack resistance ratio. This relation was indefeasible by changing the thickness from 20 mm to 30 mm and 40 mm. Although increasing the thickness improved the impact resistance significantly, the effect was more pronounced for ultimate failure crack resistance than for first crack resistance. [ABSTRACT FROM AUTHOR]

Conventional concrete is acknowledged to be relatively brittle material when subjected to normal stresses and impact loads. Tensile strength of concrete is approximately one tenth of its compressive strength. Concrete also possesses poor deformability and weak crack resistance in practical usage. These drawbacks limit the use of concrete. To do away brittle nature of concrete, application of discrete fibre in concrete construction has been proposed. In an attempt to increase the durability and load carrying capacity of concrete, reinforced concrete has been introduced. This study is the part of research work on evaluating the optimum use of fibre in concrete. The aim of the investigation is to determine the effect of variation of polypropylene fibre ranging from 0% to 1% with increment of 0.25%. The fibre was used as an additive in concrete with content of 0%, 0.25%, 0.50%, 0.75% and 1% for M-20 mix. Concrete mixes were produced, tested and compared with the conventional concrete mix in the terms of workability, compressive strength and splitting tensile strength. The tests were carried out after 7, 14 and 28 days of curing. The workability of concrete decreases with the increase in polypropylene fibre content. The gradual increase was seen in compressive strength and splitting tensile strength of fibre reinforced concrete up to 0.5% of fibre content for all curing ages. Beyond that there is a significant reduction in strength. The maximum compressive strength and splitting tensile strength were 28.52 N/mm[sup 2] and 3.75 N/mm[sup 2] respectively. Fibre addition was seen to enhance the physical and mechanical properties of concrete. [ABSTRACT FROM AUTHOR]

Conductive needle punched nonwoven fabrics are developed from staple polypropylene (PP) and varying weight fractions (10, 20 and 30 wt.%) of staple carbon fibres. A fibrous webs of staple PP and carbon fibres were formed at a wool-type carding machine, and these webs subsequently bonded on needle punching machine with 132 punches/cm2 and 13.5 mm needle penetration depth. The electromagnetic shielding effectiveness (EMSE), absorption and reflection characteristics of as-produced needle punched nonwoven fabrics were determined using a network analyser as specified in ASTM D4935-10 in the frequency range 15–3000 MHz. The surface resistivity measurements were carried out in accordance with ASTM D 257-07 standard. These results indicate that the EMSE values increase incrementally with frequency in the 15–3000 MHz range. The nonwoven sample with 30 wt.% carbon fibre showed the lowest surface resistivity of 3.348 kΩ and corresponding highest EMSE of ~42.1 dB in the 3000 MHz frequency range. In comparison, the highest EMSE values from 10 to 20 wt.% staple carbon fibre were found to be 15.6 and 32.2 dB in the 3000 MHz frequency, respectively. It was observed that the absorbance and reflectance curves of each nonwoven fabric move at opposite directions to each other. It was found that as the amount of carbon fibre in the nonwoven fabric increases, absorbance values decrease, but reflectance values increase. The resultant nonwoven fabric samples are expected to be used as garment interlining after thermal bonding and wall interlayer in the future. [ABSTRACT FROM AUTHOR]

Based on the detection principle regarding physical and chemical changes of the internal structure of concrete at elevated temperatures, and with the application of infrared thermal imaging technique, laboratory investigations related to infrared thermal image inspection and compressive strength test on C80 high-strength concrete (with or without polypropylene fibres) were carried out under thoroughly heated conditions. With the application of SEM and XRD analysis, the microstructure and organisational structure of the concrete could be seen. Also, data analysis could help identify their relationship in cases with polypropylene fibres added or not. The results showed that the elevated temperature through infrared images generally exhibits an upward trend with increasing temperature. Only slight damages were detected below 400°C, whereas more and more severe deterioration events were expected when the temperature was over 500°C. Meanwhile, the compressive strength kept decreasing as the temperature increased. Additionally, the addition of polypropylene fibres with appropriate length, diameter and quantity contributed to the improvement of high-temperature resistance of high-strength concrete. [ABSTRACT FROM AUTHOR]

Abstract: Surface treatments on a polypropylene (PP) fibre have contributed to the improvement of fibre/concrete adhesion in fibre-reinforced concrete. The treatments to the PP fibre were characterized by contact angle measurements, ATR-IR and XPS to analyse chemical alterations. The surface topography and fibre/concrete interaction were analysed by several microscopic techniques, namely optical petrographic, and scanning electron microscopy. Treatment modified the surface chemistry and topography of the fibre by introducing sodium moieties and created additional fibre surface roughness. Modifications in the fibre surface led to an increase in the adhesion properties between the treated fibres and concrete and an improvement in the mechanical properties of the fibre-reinforced concrete composite as compared to the concrete containing untreated PP fibres. Compatibility with the concrete and increased roughness and mineral surface was also improved by nucleated portlandite and ettringite mineral association anchored on the alkaline PP fibre surface, which is induced during treatment. [Copyright &y& Elsevier]

The most common procedure for the modification of polypropylene fibre involves adding additives, which are incorporated into polymer by physical means during fibre formation. Particles of the additives blended with polypropylene melt cause a change in the structural parameters of the fibres. The influence of flame retardants and pigments has been investigated. It was stated that the effect of additives on the fibre structure is based on two mechanisms. The first mechanism is encountered for flame retardants, which do not reveal a nucleating ability toward polypropylene crystallisation. Fibre formation flame retardants affect the melt viscosity and consequently molecular orientation. As a result, a more ordered structure is formed. Contrary to flame retardants, pigments reveal a nucleating ability toward polypropylene crystallisation. During fibre formation low extrusion velocity pigments participate in the nucleation process. Then a high crystalline structure is formed in fibres. At higher take-up velocities the crystallisation process is dominated by a high molecular orientation and the heterogeneous nucleation on pigments loses its importance. [ABSTRACT FROM AUTHOR]

The influence of two organic pigments and two flame retardants on the structure of polypropylene fibres was investigated. It was found that by spinning at low velocities in the presence of pigments a highly crystalline structure is formed. In fibres coloured with quinacridone the rarerly encountered β form of polypropylene was observed. Utilising low take-up velocities, the addition of flame retardants leads to an increase in fibre crystallinity. In the case of fibres formed at higher velocities the influence of additives on fibres structure was less visible. For all fibres, independent of additives, a similar structure containing the α form of polypropylene was obtained. [Copyright &y& Elsevier]

Abstract: In order to reduce the brittleness of soil stabilized by lime only, a recent study of a newly proposed mixture of polypropylene fibre and lime for ground improvement is described and reported in the paper. To investigate and understand the influence of the mixture of polypropylene fibre and lime on the engineering properties of a clayey soil, nine groups of treated soil specimens were prepared and tested at three different percentages of fibre content (i.e. 0.05%, 0.15%, 0.25% by weight of the parent soil) and three different percentages of lime (i.e. 2%, 5%, 8% by weight of the parent soil). These treated specimens were subjected to unconfined compression, direct shear, swelling and shrinkage tests. Through scanning electron microscopy (SEM) analysis of the specimens after shearing, the improving mechanisms of polypropylene fibre and lime in the soil were discussed and the observed test results were explained. It was found that fibre content, lime content and curing duration had significant influence on the engineering properties of the fibre–lime treated soil. An increase in lime content resulted in an initial increase followed by a slight decrease in unconfined compressive strength, cohesion and angle of internal friction of the clayey soil. On the other hand, an increase in lime content led to a reduction of swelling and shrinkage potential. However, an increase in fibre content caused an increase in strength and shrinkage potential but brought on the reduction of swelling potential. An increase in curing duration improved the unconfined compressive strength and shear strength parameters of the stabilized soil significantly. Based on the SEM analysis, it was found that the presence of fibre contributed to physical interaction between fibre and soil whereas the use of lime produced chemical reaction between lime and soil and changed soil fabric significantly. [Copyright &y& Elsevier]

This paper describes the development of so-called all-polypropylene composites, namely polypropylenes (PPs) reinforced with oriented polypropylene fibres rather than glass or natural fibres. These all-polypropylene composites have specific economic and ecological advantages since, upon recycling, a polypropylene blend is obtained that can be reused to make all-PP composites again or, alternatively, be used for other PP-based applications. One of the main challenges in the development of all-PP composites is to create a processing window that is large enough to keep the oriented PP reinforcement intact while this is combined or impregnated with PP resin. The technological breakthrough in the processing of all-PP composite that has been established is based on the hot compaction (welding) of coextruded tapes. These coextruded tapes consist of an oriented polymer core, providing strength and stiffness, and a polymer skin with a lower melting temperature than the core material forming the matrix and bonding the tapes together. Consolidation is achieved by simply 'welding' the tapes together, thus avoiding typical impregnation problems encountered in traditional thermoplastic composite manufacturing. Pilot studies have already shown the potential of a wide range of manufacturing technologies including thermoforming and filament winding. [ABSTRACT FROM AUTHOR]

Copper slag (CS) is produced during the smelting process to separate copper from copper ore. The object of the experimental research is to find the optimum percentage of CS and PPF volume fraction when CS replaces fine aggregate, and PPF volume fraction when subjected to impact loading. Copper slag was incorporated as 20%, 40%, 60%, 80% and 100% with PPF of 0.2–0.8% with 0.2% increment. The number of blows on failure of the specimen increases as the fibre volume increases. In addition, the energy absorption of composite concrete is higher than that of ordinary concrete. Concrete with up to 40% CS and 0.6% PPF volume shows a 111.72% increase in the number of blows for failure as compared to the control specimen. The impact resistance at failure was predicted by regression analysis, and very high regression coefficients of 0.93, 0.98 and 0.98 were obtained respectively at 7-, 14- and 28-days curing. In addition to regression analysis, a two-parameter Weibull distribution analysis was used to obtain reliable data on the number of blows at first cracking and eventual failure. The energy absorption at 28-day curing period is 1485.81 Nm which is 284% higher than the control mix. Based on the findings, it can be inferred that adding CS up to 60% densifies the microstructure due to its pozzolanic activity, while polypropylene fibre acts as a micro reinforcement, increasing the number of blows. [ABSTRACT FROM AUTHOR]

The four-point bending behaviour of composite sandwich panels made of corrugated steel faces and foamed concrete (FC) cores with a density of 700 kg/m3 is reported. Plain FC (PFC) core and fibre-reinforced FC (FRFC) core, reinforced with an alkaline-treated natural fibre (henequen fibre) at a volume fraction of 1%, were used. FRFC core reinforced with polypropylene fibre was also used as a reference. The results showed that panels with FRFC cores exhibited greater initial failure load, maximum load and energy absorption when compared to the PFC cored panels, which was associated with the enhancements of ductility and toughness of the FRFC cores produced by the fibres. Several energy absorbing mechanisms were observed in the panels, including the development of major tension and shear cracks in the FC core, face wrinkling and face–core debonding. The finite element simulations showed that the face–core bonding plays a crucial role in the structural performance of the panels. The findings presented herein encourage further investigations to assess the use of sandwich panels with natural-fibre reinforced cores for construction applications. • Four-point bending behaviour of composite sandwich panels with fibre-reinforced foamed concrete (FRFC) cores is studied. • FRFC core is reinforced with either natural henequen fibres or polypropylene fibres. • Sandwich panels with FRFC cores exhibit greater initial failure load and maximum load. • Improved energy absorption is observed for sandwich panels with FRFC cores. • Finite element simulations showed that face–core bonding plays a crucial role in the panels structural performance. [ABSTRACT FROM AUTHOR]