Toughening of cement-based materials when reinforced with relatively high fiber volume is studied in the paper. Toughening mechanisms of composites have been experimentally studied by quantitative image analysis, laser holographic interferometry, and acoustic emission. It is found that damage localization in cement-based materials can be greatly reduced by the use of fibers. Based on fracture mechanism observed, an R-curve approach has been proposed to predict toughening of matrices due to fiber reinforcement. Theoretical predictions show good agreement with experimental results.

Three of the most important properties of fiber-reinforced concrete (FRC) are strength, toughness and resistance to cracking. The various methods of evaluating them are compared in terms of underlying rationale, ability to characterize composite material behavior in a readily understandable manner minimally affected by testing variables, and suitability for routine use in specifying and controlling concrete quality. The scope includes dynamic loading tests, slow-rate (static) loading tests, and tests to evaluate cracking induced directly by load or indirectly by restraint during shrinkage or thermal change.

Consideration of the advantages and disadvantages of the various alternatives shows that slow flexure testing in accordance with the rationale developed by the writer and incorporated into ASTM standard C1018 effectively characterizes the FRC in terms of first-crack strength, toughness, and residual strength after first crack up to any predetermined level of serviceability expressed in terms of maximum permissible deflection. Although not part of the standard, resistance to cracking under load may also be assessed by measuring crack widths at appropriate deflections.

Reinforcement of cements with very fine fibers of carbon and steel in mono- and hybrid-forms has been investigated. While both carbon and steel fibers led to considerable improvements in strength and toughness, on a comparative basis, carbon fibers bring about a better improvement in the toughness or energy absorption, and the steel fibers impart higher tensile strengths to the base cement matrices. In the hybrid-fiber systems, the improvements lie somewhere in between those of the equivalent mono-fiber systems.

The rebound number, its relationship to fundamental frequency and correlations with compressive strength and erosion - abrasion resistance are discussed. Nine mix proportions were used. The w/c ratios were varied from 0.30 to 0.65. The volumetric percentage of hooked steel fibres was varied from 0.25 to 2.0 vol.% at the w/c of 0.30; at the others the quantity of fibres was constant. In addition, mixes without fibres were made at each w/c.

The rebound number and the fundamental frequency are decreased by an increase of steel fibre content. The rebound number correlates with erosion - abrasion resistance. It does not correlate with compressive strength of concretes with constant w/c and different contents of fibres.

The application of high-strength concrete in practice is strongly limited by its more brittle behaviour than normal strength concrete.

The present study deals with an investigation of the possibilities of increasing the fracture toughness of high-strength concrete by adding fibres. Tests are made with both normal strength concrete and high-strength concrete containing different amounts of steel and polypropylene fibres. Stress-strain curves in compression are obtained by a deformation controlled test system. The toughness is described with different toughness indexes.

By using a previously proposed expression for the stress-strain curves, it is possible to make a non-linear load carrying capacity calculation for reinforced concrete beams. The results of the load carrying capacity calculation are compared with results of similar calculations made with the Danish code extrapolated to be valid for high-strength concrete.

The investigation shows that the addition of especially steel fibres is effective in increasing toughness and the non-linear load carrying capacity for high-strength concrete. It is also shown that the compression strength of high-strength concrete is increased by addition of steel fibres. The results of the load carrying capacity calculation show that the Danish code cannot be extrapolated to be valid for high-strength concrete without any modifications.

Fiber reinforced concrete was developed to improve the mechanical properties of cementitious materials. Especially by using FRC, the structural mechanical properties after the maximum load can be improved. In the present study the mechanical properties of the fiber reinforced concrete are evaluated by investigating the influence of various parameters on the complete load-deflection curve, including the descending branch.

Ceramic fiber composites (mainly with continuous fibers) are reviewed, in part, from the perspective of the pertinence of such results to cementitious construction materials. While there is a large gap in the density, stiffness, etc., of the matrices and of the types and volume fraction of fibers used in these two types of material systems, the fact that for any of these systems fiber-matrix friction/pull-out are important suggests some useful transfer of information. Fiber coatings, which can have spectacular benefits in ceramic fiber composites by controlling fiber-matrix interfaces are discussed. Matrix conformance to the fibers and fiber bending and shape are also probable factors about which less is known, but are discussed because of their potential importance. Similarly, issues of fiber size and fibermatrix property differences are briefly discussed, as are effects of matrix porosity.

A study has been carried out on cementitious composites reinforced with various synthetic fibers, focusing on their tensile behavior, toughness, and fracture mechanisms. A model is formulated to predict the tensile behavior and fracture energy of fiber reinforced cementitious composites (FRC) with short, randomly distributed fibers. The model accounts for the pull-out of fibers oblique to the fracture surfaces (including snubbing friction effect), and the variation of the fiber/matrix interfacial shear stress during pull-out. Experimental and analytical results are shown to be in close agreement for the one class of fiber reinforcement which best satisfies the assumptions of the model. Systems which violate the assumptions exhibited different failure mechanisms and were observed to show less satisfactory reinforcement performance, especially the composite fracture energy. The model is used to examine the effect of fiber properties on composite post-cracking behavior and is useful in design of such material systems with optimum performance and cost effectiveness.

The permeability of concrete to gases is of direct importance to the durability of concrete structures, because of carbon dioxide flowing through the concrete favour lime carbonation and reinforcing steel corrosion.

Mortar with and without polypropylene fibres having water/cementitious ratios of 0.30, 0.35 and 0.40 and a cement/sand ratio of 1/1 were studied. Polypropylene dosage varied from 0.1 to 0.3% by volume of cement.

The characterization of mortar permeability was made using cylindrical shaped samples (3 cm height and 15 cm diameter). These specimens were 28 days cured and then dried before the test.

The addition of fibres results in a decrease of air permeability. Variation of the water/cement ratio is of lesser importance than fiber addition.

In AR-GFRC growth of hydration products around the filaments plays a dominant role in inducing embrittlement of the fibers and loss of toughness of the composites.

The purpose of this paper is to present the way to limit the anchorage of the fibers in the matrix and to obtain a long term flexural strength of 30 MPa and an ultimate strain of 0,7 %. The improvement of the matrix is obtained by using selected metakaolinites and acrylic polymers in order to optimize the nature of the hydrates in the interface between the fibers and the matrix.

The mecanical properties and durability behaviours are reviewed using three accelerated ageing tests based on warm water, wet-dry cycles and freeze-thaw cycles. The toughness indices proposed by Shah, Ludirdja and Daniel [12] are calculated, pointing out the improvements of toughness and durability of the new V~trotex-Saint-Gobain AR-GFRC system.

Glass fiber reinforced cement pastes were prepared using a cement based on a hydraulically active glass in the system CaO-SiO2-Al2O3. The properties of such composites were compared with those made with ordinary portland cement.In all the studied materials the MOR and WOF values declined with time, however for different reasons.

Glass fiber reinforced composites made with an oxynitride analogue of alkali resistant glass were tested in tension after accelerated aging. The results were compared to composites made from oxide alkali resistant glass. The strength of the oxynitride glass reinforced composites was almost double that of the oxide glass based material. The results are related to the improved properties of oxynitride glass over oxide glass. In particular previous work has shown that surface chemistry of the oxynitride glass inhibits the formation of a strong bond between fiber and matrix. The difference in surface chemistry was examined by measuring the contact angle of aqueous solutions with respect to nitrogen content of the glass.

This paper explores the behavior of the interface of glass fiber and cementitious matrix under the effect of aging. Pull-out tests of multiple alkali resistant glass fiber strands embedded in portland cement paste matrix were conducted. Four different curing regimes of 3 and 14 days normal curing, in addition to 3 and 7 days accelerated aging were employed. A recently developed method of characterizing interfacial properties was used to identify and evaluate the important parameters at interface. The experimental data are presented on the parameter of shear stiffness of a fiber-matrix boundary layer, the shear bond strength, the frictional bond strength and the specific surface energy as a function of fiber embedded length. It was observed that aging had a larger effect on the stiffness of the interface, the shear bond strength and the specific surface energy than on the frictional bond.

Asbestos cement was the first type of FRC-material that was ever made. It consisted of neat, hardened Portland cement reinforced with asbestos fibres (Vt - 7 vol-%). The most outstanding and valuable property of a high quality asbestos cement was the highly improved durability of this composite material in comparison to what would have been the case, if no fibres had been added or the fibre reinforcement of this extremely brittle matrix had been carried out incorrectly.

This paper describes an analysis of the variation in time of the fracture energy, GF, of different types of FRC-material exposed to various climatic conditions.

The following types of fibres were examined: steel fibre, ar-glass fibre, synthetic fibre (polypropylene) and natural fibre (sisal fibre and paper pulp cellulose).

The climatic exposure conditions were natural out-door weathering or laboratory tests in a special weather-o-meter. Three test series were carried out at the Danish Building Research Institute. The results from these tests have been compared to results from five test series taken from the literature (ar-glass-, steel-, polypropylen-, sisal-fibres and neat concrete).

It is concluded that natural and glass fibres are losing strength and ductility in a cementitious matrix. This results in a drastically reduced fracture energy of the composite material over the years. In the worst cases practically no fibre effect is left after some ten years of normal out-door exposure.

For the best types of fibres examined (steel fibre, high tenacity, high bond polypropylene and combinations of these two types) the ductility and fracture energy of the composites are increasing significantly even after very long time of exposure.

Workability is measured with the LCL consistometer. The device is an open rectangular mould with an external vibrator and a removable vertical partition dividing it into two compartments. When the partition is removed, the vibrator is triggered at the same time as a chronometer. The time, t, that the concrete takes to flow to a reference line is measured.

For a matrix with a given composition (mortar and concrete), we study how workability varies when the percentage of fibres increases. The curves thus obtained take the form Ln(t)= A + B %. We show that the value of coefficient A is linked to the matrix composition while coefficient B is especially sensitive to the type of fibre used and to the gravel -fibre interaction.

Mortar and concrete compositions reinforced by fibres of very different types with different lengths and geometries (rods or ribbons) are tested and are used to validate the proposed model. The types of fibres studied are: glass fibres coated with thermoplastic, PVC fibres, steel fibres and amorphous cast iron fibres. The results can be used to optimize the geometry of very different types of fibres and thus obtain a better workability.

This research work concerns the impact behaviour of metallic fibre reinforced concrete. After a description of the experimental apparatus used, an air compressed gun, we present the main results in terms of stress–strain diagrams as a function of the strain rate. Then, we establish equations of a specific damage model which take account of the different phases of the behaviour law.

The bond between concrete and reinforcing bars under impact loading was studied for plain, polypropylene fibre reinforced, and steel fibre reinforced concretes. It was found that adding steel fibres significantly improved the bond behaviour under impact loading; polypropylene fibres had a much smaller effect.

Impact tests were carried out on post-tensioned beams, prepared both with plain concrete and fibre-reinforced concrete. It was found that post-tensioned beams might be less resistant to impact loading than were ordinary reinforced concrete beams. However, the addition of fibres to the concrete greatly increased the impact resistance of these beams.

The need to accurately predict the response of structures under impact loadings has led to an interest in the mechanical properties of component materials at high rates of loading. The mechanism of cracking and its propagation play an important role in evaluation of the response of fiber reinforced concrete structures subjected to impulsive loading. In the present study, single–edge notched beams were tested under high velocity impact loads. A computer assisted instrumented Charpy test system was employed in performing the impact tests. Development and testing of a new fiber optic sensor, for the determination of internal Crack Opening Displacements (COD) in fiber reinforced concrete is described.

Various physical phenomena are involved in the fracture process of steel fiber reinforced concrete (SFRC). Although pullout of the fiber has been the most intensively investigated parameter in studying the micromechanics of these materials, other mechanisms could be dominant, depending on the nature of the loading and the fiber orientations. Pullout tests were conducted on isolated fibers embedded in a mortar matrix with different orientations to the direction of loading.

The specimens were loaded in the chamber of a scanning electron microscope (SEM), and on an optical table with instrumentation for Laser holographic interferometry (HI). The relative contribution of the various mechanisms, such as: fiber debonding and pullout, mortar crushing, friction at comers, and plastic energy dissipation on the fibers were evaluated. When the specimens were tested in the SEM, it was observed that compressive failure with crushing of the mortar is an important physical phenomenon, in addition to plastic bending of the fiber. HI studies also indicated the crushing of mortar prior to interface debonding.

The relative amounts of energy dissipated by the various mechanisms were evaluated using experimental observations and analytical approximations. The importance of the different mechanisms at progressive stages of fiber pullout was estimated.