Search

In this study, the effect of polypropylene (PP) fibres on both the dynamic mechanical properties of CGCB and the mechanism of reinforcement and toughening was explored. Impact compression tests were conducted on CGCB specimens via pendulum impact-loaded split Hopkinson pressure bar (SHPB) testing, and the dynamic stress strain curves, dynamic compressive strength (DCS), dynamic increase factor (DIF), energy consumption characteristics, fractal dimensions of crushing, and reinforcing toughening mechanism of CGCB were investigated at different PP fibre lengths and strain rates. Furthermore, the microstructures of the CGCB specimens were tested by using scanning electron microscopy (SEM). The research results show that with the addition of PP fibres, the peak stress, peak strain, and residual strength of the CGCB specimens are significantly improved, and their ductility and toughness is enhanced. The DCS of CGCB is significantly positively correlated with strain rate. The addition of fibres can effectively improve the DCS and DIF of CGCB, and the improvement effect gradually weakens and tends to stabilise with increasing fibre length. The absorption energy per unit volume of the CGCB specimens increases with increasing fibre length and strain rate. At different strain rates, the addition of fibres significantly reduces the fractal dimension of the failure mode of the CGCB specimens. Moreover, 12 mm long fibres can not only more effectively decrease specimen cracking but also improve impact resistance. Moreover, the three-dimensional network structure formed by fibre dispersion can absorb and disperse impact energy and reduce the damage caused by impact to the matrix, thereby enhancing the dynamic mechanical properties of CGCB and improving its crack resistance. This research provides a scientific reference for enhancing the mechanical properties of cemented mine backfills under dynamic disturbance environments. [Display omitted] • Studied the effect of PP fibre on the dynamic mechanical properties of CGCB. • Analyzed the failure modes and energy dissipation of CGCB under dynamic loads. • Quantitative evaluation of CGCB fragmentation degree using fractal dimension. • Revealed the reinforcement and toughening mechanism of PP fibres on CGCB. • Anchoring and bridging effect of PP fibres on the microstructure of CGCB. [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 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]

Economic and environmentally friendly polypropylene (PP) fibre and polyvinyl alcohol (PVA) fibre were found to be beneficial to the strength of recycled coarse aggregate concrete (RCAC), but the effects in the fracture properties of the RCAC has been overlooked. This study added PP fibre and PVA fibre to enhance the ability of the RCAC to resist crack instability expansion. The three-point bending tests were performed to compare the fracture properties of the RCAC with fibres and without fibre. The reinforcement mechanism of fibres was analyzed by the single-fibre pullout tests and scanning electron microscopy tests. The experimental results indicated that fibres could not effectively increase the compressive strength of RCAC but the splitting tensile strength of RCAC was significantly improved with the increase of the volume fraction of fibres and the optimal volume fraction of fibre was 1.5% PP fibre. The PP fibre and PVA fibre both effectively improved the fracture properties of RCAC but acted in the post-cracking stage and the linear loading stage, respectively. As a concrete manifestation of the PP fibre was more effective in increasing the peak load, unstable toughness, and fracture energy of RCAC than the PVA fibre while the PVA fibre was more effective in increasing the initial cracking load and the initial toughness. The 1.0% PP fibre had the best effect on the fracture properties, which increased peak load, unstable toughness, and fracture energy by 47.2%, 42.3%, and 5500%, respectively. The 0.2% PVA has the best effect on the fracture properties of RCAC at the stage before the cracks developed which increased initial cracking load and initial toughness by 25.2% and 43.7%, respectively. In addition, the development of cracks of RCAC with PP fibre was more tortuous than that of RCAC with PVA fibre. A reinforcement mechanism analysis showed that there were obvious diamond-shaped depressions on the surface of PP fibre which provided mechanical interlock to enhance the RCAC. The hydrogen bonds of PVA fibre also enhanced the RCAC through the hydration products attached to the surface of the PVA but it is weaker than diamond-shaped depressions. These results provided theoretical and experimental support for the research gap of PP fibre and PVA fibre in RCAC. • Roles of PP fibre and PVA fibre in the fracture properties of RCAC were explored. • The crack propagation of RCAC with PP and PVA fibre was observed based on the DIC technique. • The fracture mechanism of RCAC with PP and PVA fibre was discussed. [ABSTRACT FROM AUTHOR]

Highlights • Impact behaviour of Hybrid Fibrous Geopolymer Composite (HFGC) is tested and investigated. • Influences of impact strength and fibre content on HFGC are addressed. • Scattered experimental impact test results of HFGC is analysed using Weibull distribution. • Impact energy of HFGC is analysed and modelled. Abstract The latest research data indicates that geopolymer concrete reinforced with mono fibre has a remarkable enhancement in its impact strength and fracture toughness, which is well documented. Nevertheless, many aspects of impact behaviour of Hybrid Fibrous Geopolymer Composites (HFGC) are still unexplored, which are of primary importance for defense projects in the world. For the first time, the impact behaviour under falling weight collision of HFGC were evaluated and further analysed. The HFGC mixtures were fabricated using three different fibres viz., 5D hooked end steel, polypropylene and glass. The main parameters studied were the fibre dosage and amalgamations of different fibres. Totally seven mixes were prepared and further investigations were conducted in two phases. In the first phase, five cylindrical specimens were fabricated for each mix and tested as per the ACI committee 544 falling weight collision test recommendations. Subsequently, a comprehensive two-parameter Weibull distribution was executed to scrutinise the scattered experimental test results of cylindrical specimens and presented in terms of reliability function. In the second phase, prism specimens were fabricated and tested under the same falling weight collision. Then, an analytical model was formulated for evaluating the impact energy at failure of HFGC prism specimens and comparisons were made with experimental data. The hybridisation of the above three fibres at a certain dosage and incorporation in geopolymer composites led to an enhanced impact performance and ductility properties. Further, the obtained impact energy at failure from modelling well agrees with the experimental results. Henceforth, it is a successful research data that is presented herein which will be eminently valuable for understanding the performance of new fibrous geopolymer composites (FGC) made with hybrid fibres that which are available all over the world. [ABSTRACT FROM AUTHOR]

Abstract The effect of recycled tyre polymer fibre (RTPF) on mechanical and durability performance of concrete has been increasingly studied in recent years, primarily because of the economic and sustainable feasibility of RTPF's application in construction industry. This paper presents an experimental study on workability, static compressive strength and dynamic compressive properties of concrete reinforced with RTPF with various fibre dosages (i.e. 1.2, 2.4, 4.8 and 9.6 kg/m3) that have not been extensively investigated. Results indicate that the dynamic compressive properties including dynamic compressive strength, energy absorption capacity, ultimate strain and dynamic increase factor of all mixtures were highly sensitive to the strain rate. The optimal RTPF content was found to be 2.4 kg/m3 (i.e. 0.2% fibre volume fraction (V f)) considering fresh and hardened properties, as adding this content into concrete induced the most development in dynamic compressive strength (with the highest increase of 12.9%), fracture energy (with the highest improvement of 54.4%) and total energy absorption (with the largest enhancement of 26.4%). It was found from scanning electron microscope (SEM) image analysis that RTPF exhibits bridging performance with no obvious fracture on its surface, and 0.1% V f of PPF could be replaced by 0.2% V f of RTPF for concrete. [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]

• Properties of alkali-excited fly ash aerogel foam concrete were studied. • The microstructure of alkali-excited fly ash aerogel foamed concrete was analyzed. • Test variable included aerogel particles, fly ash, foam and polypropylene fiber. • Developed concrete exhibited excellent thermal performance and mechanical strength. • Aerogel used in concrete had excellent thermal insulation performance. With increasing focus on low-carbon energy conservation and environmental protection, there is a need to consider all aspects of life in future developments. To meet the concept and requirements of energy conservation and environmental protection in the building industry, we have developed alkali-excited aerogel-foamed concrete that exhibits excellent thermal insulation performance and mechanical strength. The variables involved in its production include fly ash, foam, aerogels, and polypropylene fibres. In this study, the microstructure and mechanical and thermal properties of alkali-excited fly ash aerogel foam concrete was analysed. The results indicated that fly ash can replace a portion of the cement, resulting in a reduction in the thermal conductivity of the concrete. The addition of aerogels and foams to the concrete can significantly decrease its thermal conductivity. Specifically, when the aerogel content reaches 12 % and the foam content reaches 75 %, the thermal conductivity of the concrete decreases from 0.498 W/m·K to 0.183 W/m·K and 0.19 W/m·K, respectively. However, this decrease in thermal conductivity comes at a cost of approximately 50 % reduction in the flexural and compressive strengths of the concrete. The findings reveal that the aerogel has excellent thermal insulation performance similar to that of the foam, but it has little influence on the mechanical properties of the concrete. Additionally, an increase in the polypropylene fibre content significantly improves the mechanical properties of alkali-excited fly ash aerogel concrete, but the thermal properties of the concrete remain mostly unaffected. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • PP fibre can improve the UCS, stiffness, ductility and stability of CPB. • Best fibre parameter levels are a fibre content of 0.15% and a fibre length of 6 mm. • PP fibre bring much more improvement to the early strength of CPB. • Fibre can bridge the cracks of CPB. Abstract This experimental study was carried out to investigate the influence of polypropylene (PP) fibre on the compressive behavior and microstructural properties of tailings (classified as CL – lean clay) cemented paste backfill (CPB). The compressive behavior was determined by the unconfined compressive strength (UCS), and structural changes in CPB were evaluated by macrostructural failure analysis and microstructural tests with scanning electron microscopy (SEM) analysis. Orthogonal tests were designed to research the influences and significance of the cement content, solid mass concentration, fibre content and fibre length on CPB. The results indicate that although the fibre parameters are not as significant as the cement content and solid mass concentration for CPB strength, they are also important factors for improving the UCS of CPB, and the effect of PP fibre on the early (3 days curing time) and later (28 days curing time) stage strength of the backfill is much more obvious than that on the medium stage (7 days curing time) strength. And fibre can enhance the stiffness and ductility of CPB with increasing strain and E 50. In addition, the fibre content is much more important than the fibre length, there is no linear relationship between UCS and the fibre parameters (fibre content and fibre length), and the best fibre parameter levels are a fibre content of 0.15% and a fibre length of 6 mm in this study. Moreover, macrostructural failure analysis and SEM microstructural tests indicated that PP fibre tend to bridge the cracks, which can reduce the porosity of the CPB matrix and improve its compactness, integrity and residual strength with some calcium silicate hydrate (C-S-H) gelling trapped on its surface. [ABSTRACT FROM AUTHOR]

Highlights • Fibre reinforcement helps in controlling the width and length of the cracks. • Fibre reinforcement improves the compressive and tensile strength of soil blocks. • Fibre reinforced blocks show higher resistance to wearing and erosion. • Fibre reinforcement does not adversely affect the cost of the soil blocks. • Reinforced soil blocks offer a sustainable solution toward low cost construction. Abstract Soil as a construction material offers the most economic and effective alternative toward solving the huge demand for low cost housing units, as it imposes the least demand on resources, particularly in tropical regions. But the strength and durability of soil blocks is a major concern. Therefore, an investigation was carried out to reinforce soil blocks with natural and synthetic fibres in an attempt to offer an economic and sustainable alternative without compromising the strength and function. A comparison on the performance of soil blocks reinforced with four different fibres – alkali resistant glass, polypropylene, banana and jute were studied. The effect of fibre reinforcement on the physical, mechanical and durability properties were examined for the fibre contents of 0.25%, 0.50%, 0.75% and 1% by weight of soil. The optimum percentage of fibre reinforcement for each type of fibre was determined. The study shows that fibre reinforcement augments the performance of the soil blocks significantly. It improves the strength & resistance to erosion and wearing of the soil blocks and deters its susceptibility to shrinking and cracking. Reinforcement with jute fibre yielded the maximum strength and was also observed to be the most durable option of the selected fibres. Natural fibre reinforced soil blocks were also the most economic option among the fibres studied. [ABSTRACT FROM AUTHOR]

Highlights • Influence of polypropylene (PP) fibres on the performance of RAC is studied. • The optimum fibres content is obtained as 0.5% volume fraction. • Influence of PP fibres on tensile strength is more pronounced compare to compressive strength. • Fibres play a major role in crack bridging. Abstract The present experimental investigation examined the influence of incorporation of microfilament type polypropylene fibres into low strength recycled aggregate concrete on the basis of number of parameters such as compressive strength, split tensile strength, flexural strength, modulus of elasticity and non-destructive parameters. Experimental studies are carried out with addition of 0.5%, 0.75% and 1% polypropylene fibres in both natural aggregate concrete (NAC) and recycled aggregate concrete (RAC). The recycled aggregate concrete is prepared with 100% replacement of recycled coarse aggregates with natural coarse aggregates. The present study reveals that the fibre content has negligible effects on compressive strength. However, the fibres play an important role in determining the split tensile and flexural strength of concrete for both NAC and RAC. The maximum increments for RAC are 12.01% and 17.15% for split and flexural strength values respectively over unreinforced RAC. Based on the results obtained for each series, it can be inferred that optimum fiber content is 0.5%. The variations of axial and lateral strain with axial stress are also determined using strain gauges. It can be observed that the effect of fibres on strain enhancement is more prominent in case of NAC compare to RAC. [ABSTRACT FROM AUTHOR]

Abstract A comprehensive experimental program was undertaken to analyse the structural and material characteristics of synthetic fibre reinforced geopolymer concrete. This study focused on the effect of monofilament and fibrillated polypropylene fibres and monofilament structural polyolefin fibres on mechanical and flexural performance of fly ash based geopolymer concrete. Five types of synthetic fibres at a 0.5% volume fraction were added to geopolymer concretes. The specimens’ compressive strength, indirect tensile strength, modulus of elasticity, modulus of rupture, flexural toughness and fracture energy were determined. Where possible, comparative analyses where conducted to assess the performance of fibre reinforced geopolymer concrete against conventional Portland cement based systems. The flexural toughness parameters were obtained using procedure laid down in ASTM C1018, JCI-SF4 and ASTM C1609. The results indicated that the macro polyolefin fibres exhibited the largest fracture energy which is likely due to high mechanical bonding and low fibre aspect ratio. Relationships are established to predict the compressive and tensile strengths, modulus of elasticity, compressive stress–strain curve and relation between the deflection and CMOD of synthetic fibre reinforced geopolymer concrete. [ABSTRACT FROM AUTHOR]

Abstract For plain mortar without fibres, it has been found that its fresh properties are governed mainly by the water film thickness (WFT). For fibre reinforced mortar with fibres added, it has been suggested that the effects of the fibres may be evaluated in terms of a fibre factor (FF) combining the fibre volume and aspect ratio together. In two previous studies on the workability of polypropylene (PP) fibre reinforced mortar, the combined effects of WFT and fibre volume and the combined effects of WFT and fibre length have been separately studied. Herein, additional tests with both the fibre volume and fibre length varying simultaneously have been carried out to generate more data for evaluating the combined effects of WFT, fibre volume and fibre length. Based on the test results, a new model is developed whereby the workability attributes are each expressed as a single-variable function of the product of a linear function of WFT and an exponential function of FF. By this model, the roles of WFT and FF are revealed and the workability may be estimated for preliminary design of PP fibre reinforced mortar. [ABSTRACT FROM AUTHOR]

Abstract The impact-resistance behaviour of basalt‒polypropylene fibre-reinforced concrete containing the mineral admixture (BPFRC) was experimentally investigated under impact loading using a ϕ 75 mm split-Hopkinson pressure bar. The results showed that the dynamic compressive strength, dynamic elastic modulus and critical strain of BPFRC increased with increasing strain rate. The addition of basalt fibre (BF) and polypropylene fibre (PF) yielded significant increases in the strain rate effect of the dynamic compressive strength and dynamic elastic modulus of concrete and improved the deformation capacity of concrete. The influence of PF on the strain rate effect of dynamic compressive strength of concrete was greater than that of BF. However, there was no clear difference between the influences of BF and PF on the strain rate effect of the dynamic elastic modulus of concrete. There was a significant positive correlation between the hybrid volume of fibre and the strain rate effect of the dynamic compressive mechanical behaviour of BPFRC. The proposed viscoelastic damage constitutive model in this study can be used to accurately describe the dynamic mechanical behaviour of BPFRC. [ABSTRACT FROM AUTHOR]

Fire or high temperature is a big challenge to ultra-high performance concrete (UHPC). Strength loss of UHPCs can reach up to 80% after exposure to 800 °C. In this study, a total of six UHPC mixtures were designed and tested after subjected to elevated temperatures up to 1000 °C. The effects of aggregate type, fibre type and heating rate were investigated. Residual compressive strengths and stress-strain relationships were studied. Besides, attention was paid to explosive spalling since UHPCs are usually of compact structure and thus more vulnerable to explosive spalling than other concretes. Scanning electron microscope (SEM) analysis was conducted to help understand the mechanism of variation of internal structure under different temperatures. It was found the mixture containing steel slag and hybrid fibre had excellent fire resistance. After being subjected to 1000 °C, this mixture retained a residual compressive strength of 112.8 MPa or a relative value of 69%. [ABSTRACT FROM AUTHOR]

The use of recycled concrete aggregates in structural concrete is a sustainable solution to reduce the extraction of natural resources and the detrimental impacts of waste concrete to the environment. The present study aimed to assess the compressive and flexural behaviour of recycled aggregate concrete (RAC) and normal concrete (NC) modified with silica fume and steel fibres or polypropylene fibres (PPFs). The coupling effects of the silica fume and fibres on the compressive strength, fracture toughness, modulus of elasticity, and failure mode of the RAC and NC were analysed following a series of axial compression and three-point bending tests. The results show that the thick steel fibre exhibited worse interfacial bonding with the cement paste than the PPF, but the addition of silica fume enhanced these interfacial bonds, resulting in an improvement in the compressive and flexural behaviour of the fibre-reinforced RAC. Additionally, the coupling effect of silica fume and steel fibre was better than that of the silica fume and PPF. Based on the synthetical consideration of the performance improvement and economic cost, 10% silica fume content by the equal quantity substitution of cement is optimal for the compressive and flexural strength of steel-fibre reinforced RAC. [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]

• A coupled hygro-thermal–mechanical model is proposed for UHPPFRC in fire. • The failure of PP fibre and porosity change of the UHPPFRC panel are considered. • The new model can predict internal stress within the UHPPFRC panel. • The tensile strength of UHPPFRC is regarded as a fluctuation. • Analysis for failure probability of the UHPPFRC panel is carried out. To date, many buildings are prone to fire from non-structure systems like high-pressure laminates and insulated cladding systems. Ultra-high-performance concrete (UHPC) has been applied to the cladding systems due to its excellent mechanical properties at room temperature and non-flammable characteristic. To improve its mechanical properties under fire condition, different fibres like PP fibre have been employed to reinforce UHPC. The tensile strengths of these ultra-high-performance PP fibre reinforced concrete (UHPPFRC) panels vary due to the different orientations of internal PP fibres. However, few studies have been carried out on the internal stress and fire resistance of these claddings. Study on understanding the fire behaviours and failure process of the UHPPFRC panel is essential for developing claddings with better fire resistance and durability. In this study, a coupled hygro-thermal–mechanical model is developed to predict the internal stress and temperature distribution within the UHPPFRC panel. The microscopic failure process of PP fibre and porosity change within the panel during heating are all embodied in the model, and its accuracy has been validated. The initial and the residual tensile strengths of the UHPPFRC panel are considered to fluctuate between two extrema due to the random fiber orientation. Based on this, Program Evaluation and Review Technique (PERT) is applied to investigate the effects of fibre dosage and heating rate on retarding crack propagation and failure of the UHPPFRC panel under high temperature. Results from the numerical investigation indicate that 0.55% dosage of PP fibre can effectively postpone crack occurrence and propagation within the UHPPFRC panel at linear elastic phase, and faster heating rate can accelerate the pore pressure generation process. Also, internal fibre orientation is a significant factor affecting the fire endurance of the UHPPFRC panel subjected to elevated temperature, which should be considered for safety and reliability evaluation of the structure. [ABSTRACT FROM AUTHOR]

• Experimental study to quantify the static and dynamic tensile properties of geopolymer concrete (GPC) and fibre reinforced GPC (FR-GRC). • The influences of steel fibre and polypropylene (PP) fibre on GPC tensile properties are quantified. • The tensile strength of both plain GPC and FR-GPC are sensitive to strain rate effect. • Fibres are found to improve the impact resistance and deformation capacities of GPC with better energy absorption capacities. • Micro-structure analysis reveals that steel fibre has better bonding with GPC than PP fibre. Geopolymer concrete (GPC) has attracted much attention over the past decades because it utilizes industry wastes and has outstanding mechanical properties. To improve its ductility and energy absorption capabilities, various types of fibres have been incorporated into GPC. This paper carries out an experimental study to quantify the dynamic tensile properties of GPC and fibre reinforced GPC (FR-GRC) with hooked-end steel fibre and polypropylene (PP) fibre. Both quasi-static and dynamic split-tensile tests are performed on plain GPC and FR-GPC covering strain rates of 10-5s−1 to 16 s−1. The addition of 0.5% volume content of steel and PP fibres is found to effectively improve the ductility of GPC at both static and dynamic states. Under quasi-static loading, the crack opening displacements reach about 0.15 mm for GPC, 9 mm for SGPC and 8 mm for PPGPC upon failure, and when subjected to impact loading, the crack-opening rate of GPC is higher than that of FR-GPC. Fibre stretching process after concrete crack till pull-out/fracture is observed which considerably contributes to the reduction of crack expansion and the enhancement of energy dissipation capacity of GPC, with enhancements reaching up to 33% for PPGPC and 94% for SGPC. The split-tensile properties of both plain GPC and FR-GPC are found to be sensitive to strain rate, while geopolymer with PP fibre shows a similar behaviour as plain geopolymer, and GPC with steel fibres appears to be less sensitive to strain rate effect. Empirical relations are proposed to correlate the dynamic increase factor (DIF) of tensile strength for GPC and FR-GPC with strain rate. Comparison between plain GPC and FR-GPC shows that fibres can absorb additional energy to improve the impact resistance and deformation capacities. [ABSTRACT FROM AUTHOR]

The current version of the European standard for concrete structures gives tabulated data for the evolution of the mechanical properties of normal strength concrete subjected to elevated temperatures. However, the standard acknowledges the lack of sufficient data for the case of high strength concrete with limestone aggregate and there are no provisions for fibre reinforced concrete at high temperatures. This paper presents the experimental results obtained on six batches of normal and high strength fibre reinforced concrete made with limestone aggregates and tested after exposure to high temperatures. These results gave a good correlation with previous researches and equations were obtained to describe the evolution of the compressive strength and the flexural strength at elevated temperatures. Ductility was also measured in the flexural strength tests and results suggested that the use of steel fibres with higher aspect ratio may lead to lower ductility after exposure to temperatures higher than 650 °C. [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]

Tracer analysis was used to investigate the durability of concrete exposed to fire and then soaked in salt water. Two types of concrete specimens—high-strength concrete (HSC) and HSC with polypropylene (PP) fibres—were heated to different temperatures before being soaked for 30 days in a 10% NaCl solution. The chloride penetration depth was then measured with electron probe microanalysis, and the apparent chloride diffusion coefficients were estimated. The apparent chloride penetration was deeper in specimens exposed to higher temperatures. HSC with PP fibres exhibited greater penetration because the fibres melted. The chloride diffusion coefficient increased with the exposure temperature. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study to examine the hardened and fresh properties of self-compacting concrete (SCC) containing nano-CuO (NC) and polypropylene (PP) fibres. Slump-flow, T 50 and V-funnel tests were carried out on fresh SCCs. The hardened properties of SCCs included compressive strength, flexural strength, tensile strength, water absorption and electrical resistivity were studied. Moreover, Scanning Electron Microscope (SEM) was employed in order to investigate the microstructure of the cement matrix. Results revealed that NC had a significant influence on compressive strength, water absorption and electrical resistivity of SCCs. The replacement of cement with a combination of 3% NC and 0.3% PP fibre gave better mechanical and durability performances than the other samples. However, the compressive strength reduced slightly when PP fibres were added to the concrete. SEM images illustrated that NC refined the pores of cement matrix and thus resulting in low permeability. Also, it is evident from the SEM images that PP fibres would improve the properties of SCCs by bridging across the cracks. Apparently, the inclusion of 3% NC and 0.3% PP can be considered as an appropriate combination regarding the fresh and hardened properties of concrete. Furthermore, three support vector machine (SVM) approaches were used to predict the compressive strength based on the mix proportions. The results demonstrated that the Wavelet Weighted Least Square SVM (WWLSSVM) and Least Square SVM (LSSVM) models gave more accurate prediction than standard Support Vector Machine (SVM). [ABSTRACT FROM AUTHOR]

This study intends to investigate the impact of high temperature, melting and burnout of Polypropylene Fibre (PP fibre) on mechanical properties, pore size distribution and air permeability of high strength concrete. The specimens were high-strength concrete with 120 MPa strength produced with a water-binder ratio of 20%. To examine the effects of melting and burnout of the PP fibre, the experiment was conducted using two mixtures. One mixture contained 1.5 kg/m 3 of PP fibre, while the other did not contain any PP fibre. Heating temperatures were set to room temperature (RT), 120, 200, 300 and 400 °C, considering the temperatures for the melting and burnout of the PP fibre. After heating and cooling, compression tests were carried out on the concrete specimens to measure the modulus of elasticity and Poisson's ratio. Pore size distribution was measured using the fragments created by the compression tests. Air permeability was estimated by measuring the pore size distribution. It was found that melting and burnout of the fibre did not affect the compressive strength and modulus of elasticity but the Poisson's ratio of the specimens containing fibres increased at 400 °C. The effect of melting and burnout of fibre on pore volume and air permeability is quite small. If it is assumed that micro-cracks affected the air permeability, it is expected that high strength concrete with a large fibre content should create many micro-cracks at high temperature, leading to an increase of air permeability. [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]

The paper focuses on studying experimentally the potential benefits (in terms of stiffness, strength, ductility) stemming from the use of different fibres on the flexural behaviour of concrete beam specimens. Different types of steel and polypropylene fibres were added into the concrete mix at volumetric contents of 0.5% and 1.0% either individually or in different combinations. Three-point bending tests were carried out to establish the behaviour exhibited by the fibre reinforced concrete specimens produced up to failure and determine the associated mechanical properties of the subject material. The residual mechanical properties of the same specimens were also established after exposing them to temperatures of 280 °C. From the test data obtained it was observed that even though the use of hybrid fibres can result in the development of higher residual tensile strength and improved toughness, at elevated temperatures, the use of steel fibres appears to provide optimum post-cracking behaviour. [ABSTRACT FROM AUTHOR]

Highway transportation is the most preferred transportation system as compared to other modes due to its high accessibility. Flexible highway pavement consists of mainly aggregate and bitumen, besides, in order to improve performance, some organic and/or inorganic additives are also utilized as additional constituents in the hot mix asphalt (HMA). By improving performance, positive characteristics can be gained to the HMA such as high strength, durability, toughness, suitable flexibility and resistance to impact. In this study, an attempt has been made to minimize deterioration due to the damage given by different aggressive environmental conditions. For that purpose, polypropylene fibers were added in varying ratios (0, 5, 7.5 and 10% by weight of binder) into the HMA, then these mixtures were maintained in the freeze-thaw cycling cabinet, CaCl 2 , NaCl and Na 2 SO 4 solutions for a certain period. The results showed that stability increased continuously by mixtures with a content of up to 7.5% of polypropylene fibre, and then a drop was observed by 10% fibre reinforced mixtures. In addition, exposure to freeze-thaw cycles and Na 2 SO 4 solution was found as the most harmless and harmful conditions, respectively among other environments in the investigation. [ABSTRACT FROM AUTHOR]

Fracture mechanics is widely used to analyze the material behaviour in a structure. The paper reports the results of an experimental programme focused on the effect of various synthetic fibres on the fracture properties of concrete investigated in Mode I conditions. The changes in concrete properties were analysed on the basis of the critical stress intensity factor K Ic , the critical value of crack tip opening displacement (CTOD c ) and the fracture energy G F . The addition of the synthetic fibres had a slight effect on the strength properties of concrete but, at the same time, it had a significant influence on the fracture mechanics parameters by the modification of pre-cracking and particularly post-cracking behaviour of the concrete. Results of measuring the toughness and energy-absorption characteristics showed that the specimens reinforced with synthetic fibres acquired a great ductile behaviour and energy absorption capacity, compared to ordinary concrete specimens. [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]

This paper presents the effects of nano silica (NS), micro silica (MS) and combined NS and MS on bond behaviour of steel and polypropylene (PP) fibres in high volume fly ash (HVFA) mortar. Three types of bend configuration of hook-end steel fibre commercially available are considered, while the PP fibre was crimped shape. Three different fly ash contents of 40%, 50% and 60% (by wt) as partial replacement of ordinary Portland cement (OPC) are considered in HVFA mortar, while a control mortar containing 100% OPC was also considered. The NS and the MS was added as 2% and 10% (by wt), respectively as partial replacement of OPC in HVFA mortar containing 40% fly ash. In the case of combined NS and MS, 2% NS and 10% MS was used as partial replacement of OPC in HVFA mortar. However, in the case of HVFA mortars containing 40% fly ash and different NS and MS, total OPC content of 60% was kept constant in all HVFA mixes containing NS, MS and NS + MS. This was considered to compare these mixes with HVFA mortar containing 40% fly ash. Results indicate that maximum pull-out force of both steel and PP fibres decreases with increase in fly ash contents in HVFA mortars at both 7 and 28 days. The addition of 2% NS and 10% MS showed almost similar improvement in the maximum pull-out force of steel and PP fibres at both ages in HVFA mortar containing 40% fly ash. The combined use of 2%NS + 10%MS also improved the maximum pull-out force and higher than 2% NS and 10% MS. The reduction in large capillary pores in HVFA mortars containing nano and micro silica observed in Mercury Intrusion Porosity test improved the bond of steel and PP fibres in those mortar due to formation of additional calcium silicate hydrate (C-S-H) gel is believed to be the reason behind this improvement. The maximum pull-out force also increased with increase in number of bends in the hook-end of steel fibre in all mortars in this study at both 7 and 28 days. Extra energy absorbed by the higher number of bends is the reason of such improvement in maximum pull-out force. However, in the case of absorbed energy mixed results are observed in the case of different number of bends in steel fibre ends. Good correlations also exist between the maximum pull-out forces of all three types of steel fibres with compressive strength of mortars showing strong influence on the bond behaviour. [ABSTRACT FROM AUTHOR]

Highlights: [•] Optimum combination of hybrid fibres is 0.9% steel and 0.1% polypropylene fibres. [•] The fibres improved flexural deflection and toughness properties significantly. [•] The addition of steel fibres enhanced the flexural ductility as high as 26%. [•] Flexural toughness and residual strength improved upon the addition of fibres. [Copyright &y& Elsevier]

• Failure of fibre reinforced SSRAC was obviously affected by coarse aggregate type. • The concrete stress–strain curve varied with the variation in mix component. • The change of concrete deformation distribution was negligible after adopting fibres. • The crack propagation significantly changed with the variations in fibre type and content. This study investigates the mechanical properties of fibre reinforced seawater sea-sand recycled aggregate concrete (SSRAC). A total of 360 concrete specimens, considering four different variables—the type of concrete (SSRAC, recycled aggregate concrete and ordinary concrete), age (day 7, 14 and 28), fibre type (polypropylene and stainless steel fibres) and content—were fabricated. The macro properties and mechanical mechanism of discrete fibre reinforced SSRAC were systematically studied through a novel experimental system involving axial compression test and digital speckle correlation method (DSCM). The failure pattern, strength, ductility, stress–strain curve, deformation filed, crack initiation and propagation of fibre reinforced SSRAC were analysed. The major research findings indicate that the stainless steel fibres (SSF) could effectively offset the effects of seawater, sea-sand and recycled aggregates on the mechanical properties of concrete compared to polypropylene fibres (PF). The failure pattern of specimen slightly changed with the fibre type used. The compressive and splitting tensile strengths of SSRAC increased with an increase in PF content, while the optimal SSF content for SSRAC was 1.0% by volume content of concrete. Moreover, the typical influence of PF on the elastic modulus of SSRAC was negative but SSF could greatly improve that of specimen. The axial stress–strain curve of fibre reinforced SSRAC consisted of elastic, elastic–plastic ascending and declining stages. Increasing SSF and PF contents decreased the curve curvature while increased the ductility and peak strain, and the descending branch of curve tended to be smooth. Generally, the effects of fibres on the crack initiation of SSRAC and the distributions of deformation field and cracks were negligible compared to coarse aggregates, while the crack propagation of SSRAC significantly changed with the variations in fibre type and content. The cracks and high-value strain of SSF reinforced SSRAC developed slowly compared to plain SSRAC and PF reinforced SSRAC. Finally, an analytical stress–strain model of fibre reinforced SSRAC considering the coupled effects of various variables were proposed, which can be used to conduct a theoretical evaluation and design of the marine structures. [ABSTRACT FROM AUTHOR]

Abstract: This experimental study investigates the effect of specimen shape on residual mechanical properties of polypropylene (PP) fibre self-compacting concrete (SCC) exposed to elevated temperatures from 200 to 600°C. Various shaping regimes were used including cylindrical and cubical shapes for a series of durations of 2 and 4h, and air cooling to the room temperature before testing. The temperature determination results prove that the shaping regimes caused an action of “thermal shock” to SCC under elevated temperatures, characterized by a high temperature at fixed time of exposure. The experimental results indicate that, compared cylindrical specimen with cubical one, thermal shock induced by cylindrical shape air cooling caused more severe damage to concrete in terms of greater losses in compressive strength than those with cubical shapes. The fact that the impact of shapes on mechanical properties indicates that shaping could cause thermal shock to specimens, which is in good agreement with the results of the temperature determination. PP fibre can enhance residual strength and fracture energy of concrete subjected to thermal shock induced by air cooling from high temperatures up to 600°C to room temperature. [Copyright &y& Elsevier]

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]

Abstract: In the realization of sustainable construction using structural lightweight concrete, the development of oil palm shell concrete (OPSC) faced the density bottleneck of 2000kg/m3. This study aims to compare the effect of polypropylene (PP) and nylon fibres in enhancing the mechanical properties of oil palm shell fibre-reinforced concrete (OPSFRC). The volume fractions (V f) of 0.25%, 0.50% and 0.75% were studied for each fibre. As multi-filament PP fibres were added into OPSFRC, the marginal density reduction was reported without any change in the mechanical properties. Although mixes reinforced with nylon fibres showed an increment in density of 80–120kg/m3 and the highest enhancement in both compressive and tensile strengths, these were accompanied by a decrease in the modulus of elasticity (MOE). The optimum density reduction and MOE were obtained in OPSFRC containing fibrillated PP fibres along with a reduction in the compressive and tensile strengths. An increase in the post-failure compressive toughness of OPSFRC of up to 14% was reported in mixes reinforced with this fibre. The ultrasonic pulse velocity (UPV) was examined and the results showed that OPSC produced had attained good condition at the age of 7-days. [Copyright &y& Elsevier]

Abstract: The seismic rehabilitation of stone masonry buildings requires a quantitative understanding of the constituent materials under variable rates of loading. The stress-rate sensitivity of cementitious composites and rock has been intensively investigated. However, the literature on the impact resistance of masonry joints is scarce, particularly with regard to the bond behaviour using fibre reinforced mortars. This paper describes the stress-rate sensitivity of masonry units bound with fibre reinforced Type S mortars. A drop-weight impact machine was used to generate stress rates in the range of 1kPa/s–108 kPa/s. The dynamic impact factor and stress-rate sensitivity were evaluated for the flexural strength of the mortar and the bond strength and further, the pattern of failure was noted for each mix and loading rate. Polypropylene micro-fibres were incorporated as discrete reinforcement at 0%, 0.25% and 0.5% volume fraction into the mortar. Results show that the impact resistance of the masonry units increased in the presence of fibres. However, the stress-rate sensitivity of the bond strength decreased with an increase in the fibre content. Also, where as the mode of failure in those masonry units bound with plain mortars was through fracture at the mortar-block interface, the addition of fibres transferred the failure plane to within the masonry block. [Copyright &y& Elsevier]

Abstract: A polypropylene fibre was added to lime-based mortars in order to check whether they were improved by this admixture. Different properties of lime-based mortars were evaluated: fresh state behaviour through water retention, air content and setting time; hardened state properties such as density, shrinkage, water absorption through capillarity, water vapour permeability, long-term flexural and compressive strengths, pore structure through mercury intrusion porosimetry, and durability assessed by means of freezing–thawing cycles. An improvement in some properties of aerial lime-based mortars – such as permeability, mechanical strengths, reduction in macroscopic cracks or durability in the face of freezing–thawing cycles – was achieved when fibre was added at a low dosage. When a larger amount of additive was used, only the reduction in cracks and the durability of the material were improved. [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]

Investigations of the structure of polypropylene fibres coloured with a mixture of quinacridone and phthalocyanine pigments were carried out. The structure of the fibres, evaluated by wide-angle X-ray scattering and small-angle X-ray scattering methods, was compared to the structure of noncoloured fibres and the fibres coloured with particular pigments. It was stated, that pigments participate in the nucleation process at low take-up velocity. In the presence of pigments, nuclei of two polymorphic forms α and β are formed. In fibres coloured with the mixture of pigments the competition between formation of the α and β nuclei occurs. The β nuclei formed on the crystals of the quinacridone pigment dominate. The high number of the β nuclei, together with the higher growth rate of the β crystals, leads to the formation of a structure containing a large amount of the β form, only slightly lower in comparison to the fibres coloured with the quinacridone pigment. At higher take-up velocities under higher molecular orientation in the cooled stream of the fibre, the very effective row nuclei are produced. In the presence of such nuclei, pigments do not participate in the nucleation process and do not affect the fibre structure. [Copyright &y& Elsevier]

The scanning electron microscopy investigations of the morphology of the polypropylene fibes were carried out. The studies were performed for gravity spun fibres as well for fibres taken at different take-up velocities in the range from 100 to 1350 m/min. The noncoloured fibres and fibres coloured with quinacridone and phthalocyanine pigments were investigated.The studies revealed that the morphology of fibres is strongly influenced by take-up velocity and the presence of pigments.At low take-up velocity the spherulitic structure is observed. While in noncoloured fibres the big spherulites are formed in coloured fibres fine spherulites occur. In fibres coloured with quinacridone pigment spherulites possess a sheaf-like structure. The wide angle X-ray scattering measurements showed that spherulites occurred in noncoloured fibres consist of the α modification, whereas the sheaf-like spherulites in fibres coloured with quinacridone pigment of the β modification.At higher velocities the spherulitic structure transforms into a fibrillar one. The fibrils possess a hierarchical structure and consist of microfibrils formed from a bundle of nanofibrils.The change of the fibres morphology was interpreted by a change of the nucleation mechanism. [Copyright &y& Elsevier]

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]

• The addition of basalt fibre and polypropylene fibre increases the dynamic compressive behaviour of concrete. • Increasing the matrix strength and improving the strain rate exhibited a similar impact on the damage pattern of basalt fibre and polypropylene fibre. • Basalt fibre mainly contributes to the strength of concrete, and polypropylene fibre mainly contributes to the energy consumption. • A dynamic damage constitutive model was established. In this study, the dynamic compressive behaviour of concrete reinforced with hybrid basalt-polypropylene fibres (HBPRC) and different matrix strengths was investigated using a split Hopkinson pressure bar. The results indicated that the differences between the highest dynamic strength and the dynamic strength of the reference concrete for each matrix strength grade increased from 6.63 MPa, 3.77 MPa, and 4.80 MPa under the minimum strain rates to 7.16 MPa, 9.04 MPa, and 12.08 MPa under the maximum strain rates. The strain rate effect of dynamic compressive strength of HBPRC was increased by increasing the volume of hybrid basalt fibre (BF) and polypropylene fibre (PF) from 0.1% to 0.2%, but was decreased with increasing matrix strength. The toughness was increased with increasing strain rate, hybrid BF and PF volume, and matrix strength. A microscopic test indicated that an increase in the matrix strength and strain rate exhibited a similar impact on the damage patterns of BF and PF. The primary effect of BF on the dynamic mechanical properties of HBPRC was to increase the strength and that of the PF was to improve the energy dissipation. A dynamic damage constitutive model for HBPRC was established based on the continuum media and statistical damage theories, and its validity was verified. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The objective of this paper is to analyse the mechanical behaviour of polypropylene fibre reinforced concrete subjected to load cycles and propose a model to predict the crack-opening increase and mechanical performance evolution over the cycles. Fatigue tests were performed in pre-cracked specimens with two fibre types and contents to assess the evolution of the crack-opening for prescribed numbers of load cycles. The residual flexural tensile strength was assessed before and after these tests to estimate the impact of the cycles in the remaining resistant capacity of the specimens. Results suggest that the mechanism of crack propagation is independent of the fibre type and content. The accumulated damage due to the cycles produces an offset in the quasi-static residual tensile strength curve. These findings underpin the proposal of a model to predict the evolution of the crack-opening and the remaining resistant capacity. An optimisation procedure is proposed to derive the model parameters using a limited number of initial load cycles. [ABSTRACT FROM AUTHOR]

Recycled tyre polymer (RTP) fibre has recently been gaining ever-increasing attention from the scientific community as a promising substitute to synthetic fibres for cementitious composites to improve sustainability. This paper, for the first time, investigates the behaviour of RTP fibre reinforced concrete (FRC) under dynamic splitting tension, focusing on the effects of fibre content (0.1, 0.2, 0.4 and 0.8 vol%) and strain rate (0.88–3.54 s−1) and the feasibility of replacing polypropylene (PP) fibre with RTP fibre for FRC. Results indicate that the inclusion of RTP fibres is favourable in enhancing the splitting tensile properties of concrete under various strain rates (10−1 to 101 s−1), where the dynamic splitting tensile strength and dissipated energy of concrete mixture containing 0.2 vol% RTP fibre are improved by 5.5%–14.2% and 24.9%–36.7% respectively compared to the plain mixture as a result of fibre bridging effect. Fibre pull-out process considerably contributes to the enhancement of energy dissipation capacity. The splitting tensile properties of all mixtures are sensitive to strain rate, where the developed empirical equations well describing the relationship between dynamic increase factor (DIF) and strain rate provide insight into this rate sensitivity. A comparison between RTP-FRC and PP-FRC confirms that RTP fibre can be used as a sustainable and cost-effective alternative to PP fibre for cementitious materials considering engineering properties and potential economic benefit of the composites. [ABSTRACT FROM AUTHOR]

• Dosage of 0.15% PP fibre can prevent 115–135 MPa UHSC from spalling. • No spalling on UHSC encased columns with 0.15% PP fibre under axial force. • Steel fibres can delay but cannot prevent UHSC from spalling. • Slight effects of low porosity and specimen size on the spalling of UHSC. High strength construction materials are now attractive owing to their economic and architectural advantages. The higher the material strength, the smaller member size is required. Ultra-high strength concrete (UHSC) encased columns are being developed for the erection of high-rise buildings due to their higher load bearing capacity and smaller cross section size compared to normal strength concrete encased columns. When the UHSC is subject to elevated temperature, explosive fire-induced spalling is more often observed than in normal strength concrete. The consequence of spalling could cause serious life loss and damage to the close key infrastructure. Spalling is mostly due to the UHSC increased density, lower permeability and brittleness. Most of the previous studies show that polypropylene fibres have been found effective in preventing fire spalling. The aim of this experimental study is to discover the minimum polypropylene fibre dosage to control the fire spalling of steel fibre reinforced concrete of 115–135 MPa strength. The experimental study was carried out on 15 concrete specimens with different parameters and two fibre-reinforced concrete encased columns exposed to ISO 834 fire. The study indicates that a polypropylene fibre dosage of 1.365 kg/m3 can prevent the 115–135 MPa ultra-high strength concrete from explosive fire spalling. This polypropylene fibre dosage is lower than that proposed in Eurocode 2, which is 2 kg/m3. The proposed lower polypropylene fibre dosage can potentially bring sustainability (use less polypropylene fibres that are made of crude oil) and economy, as well as improve constructability by improving the workability of fresh concrete. It is also found steel fibres may relieve the fire spalling but not adequate to prevent spalling. Moreover, there is no significant effect of the size and inner temperature of the centre of the concrete specimen on spalling. [ABSTRACT FROM AUTHOR]

• Electrical resistance of cement-based sensor was considerably decreased with addition of PP fibre. • CB nanoparticles attached PP fibre surface have high aspect ratio and can form conductive paths. • Piezoresistivity of cementitious composite was significantly improved by addition of PP fibre. • Oriented distribution of CB along PP fibre provides enough networking in cement-based sensors. The cement-based sensors have a great potential for structural health monitoring, especially functional sensors filled with nano-carbon black (NCB) particles. To improve the sensing efficiency of NCB filled cementitious composite, polypropylene (PP) fibres were premixed with NCB during the manufacturing of cement-based sensor. Although the compressive strength is slightly decreased, the electrical conductivity and piezoresistivity of the NCB filled cementitious composite are improved by PP fibres. Microstructural characterization indicated that NCB attached to the surface of PP fibres significantly promotes the generation of conductive paths and contact points in cement-based sensors. The results can provide a new insight into the application of nonconductive fibres to enhance the conductivity and piezoresistivity of spherical conductors filled cement-based sensor. [ABSTRACT FROM AUTHOR]

The pore characteristics of hybrid basalt–polypropylene fibre-reinforced concrete (HBPRC) are investigated using mercury intrusion porosimetry. The research results indicate that the cumulative pore volume of concrete increases with fibre addition. The pore surface fractal dimension (D S) of HBPRC in gel, capillary, and large pore regions decreases sequentially although it has no physical characteristics in a transition pore region. The incorporation of fibres has an insignificant effect on D S in gel and capillary pore regions; however, it has a reducing effect on D S in the large pore region. Furthermore, the greater the concrete strength, the larger D S becomes and the greater the reducing effect of fibres on D S in the large pore region. Through microscopic and mesoscopic analyses, it has been suggested that bubbles introduced by fibres and the weak dispersion of such fibres are the main reasons for the deterioration of the large pore structure of HBPRC. [ABSTRACT FROM AUTHOR]

Intermingled fractal unit (IFU), composed of many fractal units with different fractal characteristics and geometries, is used to reconstruct the pore fractal characteristics of porous materials. In this paper, a three-dimensional (3D)-IFU model for characterising the pore structure of hybrid basalt-polypropylene fibre-reinforced concrete (HBPRC) was developed, and the applicability of this model was verified by test results. The results indicated that the volume fraction of the macropore (≥100 nm) of HBPRC increases with the addition of fibres. The higher fibre content causes a larger volume fraction of the macropore. Moreover, the lower matrix strength of concrete causes a more significant effect of fibres on the macropore of HBPRC. Compared with other fractal models, the 3D-IFU model not only has excellent simulation capability for cumulative porosity distribution and pore size distribution but also has high fitting accuracy for the total porosity, critical pore size and threshold porosity of HBPRC. Furthermore, the fractal dimension of the pore size distribution, derived from the 3D-IFU model, well reflects the effect of fibres on the pore structure characteristics of HBPRC. Unlabelled Image • The addition of basalt fibre and polypropylene fibre increases the volume fraction of the macropore (≥100 nm) of hybrid basalt-polypropylene fibre-reinforced concrete, and this effect increases with the decreasing concrete matrix strength. • According to the construction process of Menger sponge and in the light of the construction principle of intermingled fractal unit, a 3D-IFU model is established to characterise the pore fractal characteristics of concrete. • The developed 3D-IFU model has excellent simulation capability for the cumulative porosity distribution, pore size distribution, total porosity, critical pore size and threshold porosity of HBPRC. • The pore size distribution fractal dimension derived from the 3D-IFU model well reflects the effect of fibres on the pore structure characteristics of hybrid basalt-polypropylene fibre-reinforced concrete. [ABSTRACT FROM AUTHOR]