Global and local information on distribution parameters of steel fibres in fibre reinforced concrete form essential ingredients in pursuit for further development of micromechanical, fracture mechanical or even composite modelling of such materials in the pre- and postcritical ranges. Additionally, quantitative image analysis approaches to specimens of such composites can be executed more effectively when based on proper structural models. This paper outlines first and second order stereological methods for that purpose.

Steel fibre reinforced concrete is a composite material consisting of a brittle matrix reinforced and randomly oriented fibres. The concrete matrix is brittle and the engineered steel fibres are ductile (elasto-plastic). When these two materials are mixed, the importance of the bond between the steel fibres and concrete becomes obvious.

The pull-out behavior of non-straight steel fibers cannot always be analyzed solely in terms of bonding. Rather, it is necessary to take into account the mechanical anchorage provided by the fiber geometry.

It is shown in this paper, that in the case of non-straight steel fibers a strong interaction exists between bonding and anchorage. A micro-mechanical model, based on the dissipation of energy during slipping of the fiber is proposed. In this model, bonding is included on the basis of the Coulomb friction law, without reference to a bond-slip law; mechanical anchorage is modelled from plastic deformation of the fiber.

With this model, it is possible to evaluate the significance of some physical parameters such as the water/cement ratio of the matrix, the fiber's geometry and the steel properties. Moreover, this model provides a rational basis for the optimization of the fiber-cementitious matrix interaction from an energy point of view.

In an attempt to protect steel fiber reinforcements from corrosion and improve the adherence of cement pastes to steel fiber reinforcement, we deposited a zinc phosphate (Zn-Ph) conversion coating on the surface of the fibers. At the interfacial contact zones between the cement paste and Zn.Ph, the alkali-induced dissolution caused the dissociation of abundant PO43- ions from the Zn-Ph. The interaction of PO43- ions with Ca2+ ions from the pastes led to the formation of hydroxyapatite and brushite in the vicinity of the dissolved Zn.Ph surface. Such intermediate Ca-phosphate compounds played important roles 1) in improving the cement-fiber interfacial bonds, and 2) in repairing the damage of the Zn.Ph surface dissolved by alkali. These processes protected the steel fiber from corrosion.

This research aims at a further exploration of surface treatments of carbon fibers to improve the performance of CFRC. Two approaches to treat carbon fibers were used in this study. SEM, IR, XRD were used to analyse the CFRC prepared with treated carbon fibers. Because of strong adhesion, CFRC prepared using CF with treatment has a better performance than that without treatment. Flexural strength is 30% higher, tensile strength is 48% higher, impact strength 63% higher, and deflection is increased.

In a series of preliminary experiments, the shear stiffness degradation and ’shear’ failure mechanisms of pre-cracked Slurry Infiltrated Fiber CONcrete (SIFCON) were studied. The specimens were first subjected to axial tension (in displacement control), whereafter a lateral shear was applied over the crack band. Variables in the investigation were the direction of loading with regard to the main fiber direction, and the axial crack opening before shearing. The degradation of shear stiffness resembles that of normal concrete at low crack openings, but seems governed by fiber action at larger crack openings. At low crack openings, shear failure was observed in the sense of an array of inclined tensile microcracks. At larger crack openings, inclined cracks developed through coalescence of preexisting tensile cracks.

A novel approach in tensile testing of cementitious composites using the ASCERA® hydraulic tensile tester is described. The test specimens are cylindrical bars. Steel pistons are adhesively bonded on either end of the specimens and inserted in a pressure chamber. The pressure is increased until the specimen is pulled apart by the hydraulic pressure exerted on the pistons.

Advantages of this method are: large volume under load, self-alignment to minimize externally applied bending moments, and determination of the rupture stress exactly at the fracture initiation point.

Glass reinforced cementitious composites were tested. Results are discussed with respect to curing time and fiber volume fraction. The tensile strength values obtained by hydraulic testing are compared to values obtained by traditional uniaxial tensile strength tests. A biaxial model is adopted to verify the results.

Recently there has been renewed interest in the use of alkali activation to increase the rate of strength development in blended cements. The objective of this study was to examine the advantages-disadvantages of using alkali activated blended cement materials with fiber reinforcing. There are advantages of the rapid set for certain applications.

Macro-Defect-Free (MDF) materials are cement-polymer composites exhibiting high flexural strengths and high toughness (for cement based systems). The incorporation of fibers into MDF composites has been found to offer the possibility of increasing both the ultimate flexural strength and toughness of MDF materials prepared using an ordinary portland cement-polyacrylamide matrix.

This paper examined the effect of fiber type and fine particles as a packing filler on the resulting mechanical properties. The incorporation of non-traditional materials (for MDF) into the MDF matrix is also discussed.

Portland cement was reinforced by carbon fibers (CF) with various additive materials -- silica powders, superplasticizer, polymer emulsion, fly ash, and foaming agent -- for different purposes. The variables affecting the composite properties were identified. The mechanical properties -- tensile, compressive, and flexural strengths -- were determined as a function of CF loading and length of the fibers. The bulk density of the composites decreased as the fiber loading increased. The tensile strength increased with the CF loading increase but the compressive strength decreased as the fiber content in the composite increased. Increasing difficulty in dispersing CF as the fiber loading increase and the fiber length was rectified by addition of silica aggregates. The mechanical properties were improved as the size of silica aggregate decreased which also exhibited greater effectiveness in CF dispersion. Addition of a polymer emulsion, ethyl vinyl acetate (EVA) to the composite decreased the bulk density but increased tensile and compressive strengths.

Although carbon fibers have high tensile strengths and are chemically inert, their application in cementitious composites is limited due to their brittleness. An image analysis technique employed to determine the length distribution of the reinforcing fibers before and after mixing in cement paste and mortar matrices indicates that substantial fiber breakage occurs during mixing. In paste mixtures, the average fiber length after mixing remains above the critical fiber length, but in mortar mixes the average fiber length falls below the critical fiber length resulting in no significant enhancement of composite flexural properties.

A new cementitious board reinforced with resin impregnated glass fiber screens is described. The screen are located at the top and bottom of the board and guarantee a high flexural strength and fracture energy of the material. An adequate longterm performance has been proven in field experiments.

Until now, the use of untreated polyester fibres in concrete has been delayed because these fibres are not alkali-resistant. To understand the fundamental mecanisms of degradation of such fibres in a cementitious matrix, some physico-chemical experimental techniques (SEM - EDAX - I.R. Spectrometry) associated with flexural tests were used. The degradation of polyester is caused by a saponification reaction and the toughness of the fibre-reinforced composite is quickly reduced.

To prevent such a damage and develop tougher composites, the authors modified the cementitious matrix. Adding burnt clays (kaolin and montmorillonite) to OPC enabled the polyester fibre to withstand the alkaline attack.