High strength characteristics of cement mortar reinforced with hybrid fibres

An experimental study was conducted on high strength mortar reinforced with steel fibres and hybrid fibres consisting of steel fibre, palm fibre and synthetic fibre (Barchip). The inclusion of fibres was maintained at a volumetric fraction of 2%. The compressive strength, splitting tensile strength, static modulus of elasticity, shrinkage, flexural strength, and flexural toughness were determined to study the effect of the hybrid fibres on the properties of high strength cement mortar (HSCM). The results showed that hybridization of fibres in the quantities 1.5% steel fibres + 0.25% palm fibres + 0.25% Barchip fibres, improved the compressive strength and flexural toughness significantly, and also enhanced the splitting tensile strength and flexural strength of the mortar by about 44% and 140%, respectively.     

Electrochemical studies on the performance of conductive overlay material in cathodic protection of reinforced concrete

A type of conductive overlay material made of carbon fibre filled cementitious mortar has been proposed for cathodic protection of reinforced concrete structures. It possesses advantages over many other anode materials. To evaluate its potential application in practice, the mechanical, electrical, and electrochemical properties of the material have been investigated. The addition of carbon fibres enhances the strength and toughness of the mortar, as well as the electrical performance. Accelerated anodic polarisation tests and impedance measurements were employed to study the electrochemical behaviour. Both of the fibre content and pore solution composition influence the electrochemical property and, in particular, chloride ions have been shown to have a negative effect on the material. Results indicate that the optimum fibre content should be above but in the vicinity of the percolation threshold. The work confirms the possible utilization of this type of anode material in cathodic protection of reinforced concrete.     

The investigation on the workability of fibre cocktail reinforced self-compacting high performance concrete

The workability, the strength and the toughness are the significant factors for self-compacting-high performance concrete (SCHPC). The workability is a significant precondition for application of the Fibre Reinforced SCHPC. This paper presents research results on the workability of Monofibre and Fibre Cocktail (hybrid steel-polypropylene fibre) Reinforced SCHPC. Lots of mixtures made with steel fibres, PP-fibres and fibre cocktail of various dosages have been investigated. The mixtures were tested using various new methods for evaluating the flowability, filling ability and segregation risk of the fresh mortar/concrete. Based on the results of the workability, the suitable fibre types (steel fibres, PP-fibres and fibre cocktail) and the upper level of the fibre dosages for Fibre Reinforced SCHPC have been selected for study of the mechanical behaviour and the failure patterns in the next phase.     

混杂纤维水泥砂浆的力学性能和电机敏性

通过对素砂浆、碳纤维砂浆和混杂纤维砂浆的力学性能和电机敏性能的对比 ,认为纤维的混杂具有一定的经济效益 ,有利于碳纤维水泥砂浆作为机敏材料的推广应用     

Mechanical behaviour and fibre dispersion of hybrid steel fibre reinforced self-compacting concrete

In this study, mixture design, workability, fibre dispersion/orientation, mechanical properties and fracture behaviour of hybrid steel fibre reinforced self-compacting concretes (HSFRSCCs) were investigated. Three different types of steel fibres with and/or without hooked-ends were added to the mixtures in two different volume fractions (0.75 and 1.5% of the total volume of concrete). The results of slump flow, U-box, V-funnel and J-ring tests have shown that increasing the fibre content of the concretes slightly reduced the workability of HSFRSCC, and the main influencing factor on flowability is the geometry of fibres. The addition of fibres, although did not change the final flowability, decreased the rate of flowability. The results from the experimental tests showed that the flexural strengths increased slightly with increasing strength of long fibres, whereas the splitting tensile strength remained unchanged. The concretes with high strength, long steel fibres show behaviour of enhanced toughness and ductility compared to that with normal strength steel fibres. The orientation and distribution of fibres in concrete have been investigated by image analysis and it was observed that fibres dispersed homogeneously in all concrete series without any clumping. With increasing the amount of fibres, the fibres were more vertically orientated relative to the bending loading direction, resulting in enhancement in the mechanical properties of concrete.     

Enhancing mechanical properties of concrete prepared with coarse recycled aggregates

The recycling of concrete is an important means to a sustainable material flow. The limited reuse of recycled aggregates is due to the lower quality of concrete production. Various methods have been attempted to minimise the negative effect. In this paper, the effect of adding fly ash as well as incorporating polyethylene terephthalate (PET) fibres in a concrete mix to mitigate the lower quality of recycled aggregates in concrete is presented. The study consists of two stages: in stage 1 the effects on some of the fresh and hardened concrete properties were studied and the percentage replacement of the natural coarse aggregate (NCA) by the recycled coarse aggregate (RCA) was established. From a chosen percentage of 10%, 20%, 30%, 50% and 100%, we found that the 20% replacement (RCA20) did not seem to jeopardise the compressive strength and water absorption of RCA concrete. Experimental studies were further carried out in stage 2 on the improvement on the mechanical properties of RCA20 concrete by incorporating 25% fly ash and 0.5% and 1.0% PET fibre. Beneficial effects of appropriated fly ash and PET fibre content applied on the RCA were obtained.     

Influence of recycled polyethylene terephthalate fibres on plastic shrinkage and mechanical properties of concrete

Polyethylene terephthalate bottles production has drastically increased year after year due to high versatility of polyethylene terephthalate plastics and considerable consumption of beverages. In tandem with that increase, the major concern of society has been the improper disposal of this non-biodegradable material to the environment. To deal with this concern, recycled polyethylene terephthalate bottles were incorporated in concrete as fibre reinforcements in this study. The objective of this research is to evaluate the mechanical properties of recycled polyethylene terephthalate fibre reinforced concrete (RPFRC) in comparison with control concrete without fibres. polyethylene terephthalate fibres with three different diameters (0.45, 0.65, and 1.0 mm) and two lengths (20 and 30 mm) were added at various proportions (0.5%, 1.0%, 1.5% and 2.0%) by volume of concrete in order to determine the effect of fibres initially on compressive, flexural and splitting tensile strengths of concrete. The results revealed that none of the fibres have detrimental effects up to 1% volume fraction, however further addition caused slight reductions on mechanical properties in some conditions. Plastic shrinkage resistance and impact resistance tests were also performed according to related standards. Polyethylene terephthalate fibres were observed to have marked improvements on those properties. Such a good performance could be attributed primarily to the bridging effect of fibres.     

Development and characterization of hybrid polyethylene-fibre-reinforced cement composites

The research reported here is concerned with optimizing the combined use of two different fibre types in cementitious matrices. The two fibre types were a high-modulus polyethylene fibre and a fibrillated polyethylene pulp. The effects of different volume fractions of the two fibres and their interaction on the impact resistance, flexural strength and toughness, compressive strength, bulk specific gravity, volume of permeable pores and water absorption capacity of cementitious materials manufactured with a high-performance mixer were investigated through a factorial experimental design. In the case of impact resistance, the positive effect of each fibre was pronounced in the presence of the other fibre type. For flexural strength and toughness, the combined use of polyethylene fibre and pulp produced desirable results as long as the amounts incorporated were below certain limits. The negative effects of fibres on compressive strength were less pronounced when the two fibre types were used in combination. The interactions between polyethylene fibre and pulp in deciding the specific gravity, volume of permeable pores and water absorption capacity of cementitious materials were either negligible or only moderately significant.     

Influence of steel fibres on strength and ductility of normal and lightweight high strength concrete

This paper presents the results of a series of experiments conducted to investigate the effectiveness of fibre inclusion in the improvement of mechanical performance of concrete with regard to concrete type and specimen size. Lightweight aggregate concrete and limestone aggregate concrete with and without steel fibres were used in the study. The compressive strength of the concrete mixes varied between 90 and 115 MPa and the fibre content was 1% by volume. Splitting tests on prisms and three-point bending test on notched beams were carried out on specimens of varying sizes to examine the size effect on splitting strength, flexural strength and toughness.

The experimental findings indicate that the low volume of fibre has little effect on compressive strength but improve remarkably splitting tensile strength, flexural strength and toughness. The increase in splitting tensile strength, flexural strength and toughness index for lightweight concrete seems much higher than that of normal aggregate concrete.

The size effect on prism splitting tensile strength is not significant beyond a critical (transition) size. There are apparent size effects on flexural strength and toughness index. As the specimen size increases, splitting and flexural strengths appear to decrease, and fracture behaviour tends to be more brittle.     

Effect of embedment length of untreated natural fibres on the bond behaviour in cement mortar

The present investigation is focused on studying the effects of various matrices with 1:3, 1:4 and 1:5 mortars and fibre types of sisal and coir on the bond behavior at various ages of curing, i.e., 24 h, 3 d, 7 d and 28 d. The other parameters included in the investigation are water/cement (w/c) ratio, sand gradation and embedment length of fibres. In addition, the type of failure of sisal and coir fibres for different mixes of mortars at various curing ages is also reported. From the results, it is seen that the bond strength is improving with respect to age of curing in case of sisal fibres, but decreases in case of coir fibres. The failure of fibres due to fibre fracture is observed in sisal fibres and fibre pullout is observed in coir fibres. The other varying parameters such as mortar mixes, sand gradation, w/c ratio and embedded length also showed significant effect on bond behaviour of sisal and coir fibre with the cement mortar mixes.     

Properties of cement—rice husk mixture

The properties of lightweight mortar using rice husk can benefit from pozzolanic reaction and from organic fibre reinforcement. The effect of curing and storage on 40×40×160 mm³ OPC rice husk mortar specimens is described. Two conditions are studied; one-year storage at 50% RH and at 95% RH. The final specimen properties were characterised by density, strength, SEM, EDS and XRD. It is concluded that at high humidity storage, pozzolanic reaction is well developed but husk fibres deteriorate. The mortar stored at 50% RH has a lower compressive strength and higher flexural strength, indicating inferior pozzolanic reaction and active fibre reinforcement.     

Effect of accelerated carbonation on cementitious roofing tiles reinforced with lignocellulosic fibre

The present work evaluated the effects of accelerated carbonation on mechanical and physical characteristics of cementitious roofing tiles reinforced with vegetable fibre. The maximum load and toughness of the tiles have increased approximately 25% and 80% respectively as a consequence of the accelerated carbonation. Water absorption and apparent porosity decreased with carbonation while bulk density increased as a clear indication of the densification of the composite. The improvement on the mechanical performance suggests that the fibres retained their tensile strength in the inorganic matrix. Results of specimens extracted from the tested tiles after approximately 480 days in laboratory environment and further aged indicate that soak and dry cycles promoted some leaching of hydration products and more voids and lower density when performed before carbonation. The results indicate the utilization of accelerated carbonation as an effective procedure to mitigate the degradation suffered by the cellulose fibres in the less aggressive medium.     

纤维自密实高性能混凝土工作度的试验研究

工作度、强度、韧性及耐久性是自密实高性能混凝土(SCHPC)的主要性能指标,而工作度是保证混凝土具有高性能的重要前提。本文参照目前国际上的最新发展趋势,使用流变仪(rheometer)、流动槽(flow channel)、坍落流动板(slump flow panel)、J型环(J-Ring)和L槽(L-Box)等方法研究纤维自密实高性能混凝土(FR-SCHPC)的工作度。通过大量试验分析了不同掺量的钢纤维、PP纤维及组合纤维对新拌混凝土流动性、抗离析性、流经钢筋的间隙通过性能以及自流平能力的影响;为在实际工程中应用FRSCHPC提供了依据。     

The investigation on strength and flexural toughness of fibre cocktail reinforced self-compacting high performance concrete

Based on the experimental results of the workability, the suitable fibre types (steel fibres, PP-fibres and fibre cocktail) and fibre dosages for fibre-reinforced-self-compacting-high-performance-concrete (FRSCHPC) were selected. To assess the influences of different fibres on the compressive strength, flexural toughness and failure patterns of beams and slabs, a series of experiments has been carried out and evaluated. The results show that the fibre cocktail – a combination of steel fibres and PP-fibres – can represent an optimal fibre reinforcement for self-compacting-high-performance-concrete.     

The impact resistance of masonry units bound with fibre reinforced mortars

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 1 kPa/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.     

两类合成纤维在混凝土中的作用及使用效果

按合成纤维在混凝土中所起的作用,可分为两大类别,即防裂纤维与増韧纤维。前者主要用于防止或减少混凝土的早期收缩裂缝并降低裂缝的尺度,有助于降低混凝土的渗透性与提高抗反复冻融性。后者主要用于提高混凝土的变形能力,有助于减少混凝土的干缩裂缝、增进混凝土的韧性、抗冲击性与抗疲劳性。二者均起着次要增强材的作用。作者分别论述了这两类纤维在混凝土中的作用机制,对混凝土物理、力学性能与耐久性的影响及使用效果。     

两类合成纤维在混凝土中的作用及使用效果(下)

按合成纤维在混凝土中所起的作用,可分为两大类别,即防裂纤维与増韧纤维。前者主要用于防止或减少混凝土的早期收缩裂缝并降低裂缝的尺度,有助于降低混凝土的渗透性与提高抗反复冻融性。后者主要用于提高混凝土的变形能力,有助于减少混凝土的干缩裂缝、增进混凝土的韧性、抗冲击性与抗疲劳性。二者均起着次要增强材的作用。作者分别论述了这两类纤维在混凝土中的作用机制,对混凝土物理、力学性能与耐久性的影响及使用效果。     

High temperature behaviour of polypropylene fibres reinforced mortars

The aim of this paper is primarily experimental and is intended to analyse the behaviour of two cementitious materials, before and after heat treatment: one unreinforced (i.e. without fibres) and the other reinforced (with polypropylene fibres).At room temperature and after heating up to 500 °C, the bending strength is improved by the presences of fibres. The residual young modulus is slightly higher for the fibres reinforced samples.As the temperature increases, the strength gain due to fibres inclusion is reduced. Beyond 500 °C, the bending strength is lower for the fibre reinforced cementitious material compared to those without fibres. Fracture energy is also improved for the fibre mortars at room temperature. At 400 °C this improvement decreases gradually with the introduction of polypropylene fibres. Beyond this temperature and due to the introduction of polypropylene fibres, the fracture energy is reduced.Another test is developed: rapid heating due to exposure to a flame. The temperature in the front side reaches in few seconds 1000 °C. At this temperature and after one hour of exposure, the opposite side reached 140 °C. After cooling, the punching shear strength of the fibre mortar is definitely weaker than of the mortar without fibre.     

新型纤维防水干粉砂浆性能研究

通过材料复合的方法加入不同的纤维改性干混砂浆.研究了纤维单掺和复掺对砂浆的力学性能、粘结强度、抗渗性能和吸水率的影响.以"纤维间距机理"和"复合材料机理"为基础,分析了纤维增强防水干混砂浆性能的作用机理.     

Efficiency of polypropylene and metallic fibres on control of shrinkage and cracking of recycled aggregate mortars

The use of recycled aggregates in mortar and concrete induces a large shrinkage due to the capacity of these aggregates to absorb a great quantity of water. The influence of polypropylene and metallic fibres (Fibraflex) has been studied in different proportioning to reduce shrinkage and cracking. The efficiency of polypropylene and metallic fibres to reduce restrained shrinkage cracking is evaluated by using a ring mortar cast around a stiff steel ring. By using fibres, the crack width decreases significantly. Free shrinkage results are equally investigated. Finally, crack width in reinforced fibre mortars is calculated analytically by using the model of Grzybowski and Shah. Results are compared with experimental values. The study demonstrates that theoretical values of crack widths correspond reasonably to experimental values.