Experiments were conducted on specimens containing nylon or polypropylene monofilaments embedded in a precracked matrix. During pull-out tests, it was generally observed that the pulling force continued to increase after one or both sides of the filament had begun to slip out, even though one or both of the embedded filament lengths were decreasing. This indicated that the fiber/matrix shear stress increased with the fiber slippage distance. Examination of the extracted filaments under a scanning electron microscope (SEM) revealed the increased shear resistance to be the result of fiber surface abrasion. The severity of abrasion was observed to increase with the fiber slippage distance before complete pull-out. A theoretical model has been developed to predict the pull-out force versus displacement relationship based on given fiber/matrix shear strength as an increasing function of the slippage distance. The model gives good prediction in comparison with experimental results.

Fiber matrix bond characteristics can be changed by treatments of the fiber surface. The effect of such treatments on the fiber reinforced concrete (FRC) tension-softening behavior and crack resistance is studied in this paper. Various R-curve behaviors are predicted based on a simple double cantilevered beam (DCB) model using the experimentally derived tensionsoftening curves. The result suggests that fiber surface treatments can substantially alter the composite fracture resistance as measured by the R-curve.

Ductility is one of the main requirements of a reliable building material; the traditional LOP and MOR criteria do not reveal this quality. Other criteria based on deflection, energy or bond-slip relationships are presented. They are applied to four very different series of composites: very brittle, very ductile, and intermediate. The results point out that only the criteria based on the flexural test up to splitting, at a constant deflection rate, can reveal the higher ductility of the metakaoline-OPC blended matrix associated with AR glass. From this test, the bond-slip relationship can be determined. This leads to the definition of a comparative parameter which describes the mechanical interfacial compatibility of the matrix versus the fibers.

The widely held explanation for mechanical failure of silicate and silica glasses rests upon the existence of Griffith-flaw and associated free ion diffusion concepts used to model crack growth. However, this theory has consistently failed to provide complete agreement with the experimental results. This dilemma coupled with the reports of single-valued strengths in fibers cannot be rationalized by the modification of the intrinsic Griffith-flaw distribution to essentially a delta function.

It is for these reasons that the field-enhanced ion diffusion model has been introduced. The inclusion of a term for the electrostatic potential in the thin-film solution of Fick's second law has been shown to be consistent with the experimental results. Therefore, the effects on alkali ion migration as a consequence of the local variations in charge density that occur on the solution side of the glass/water interface play a direct role on the chemical corrosion mechanism. Thus chemistry which can modify the surface potential can alter the rate of aging of glass.

It has been found that the chemistry which has been used to modify the corrosion behavior of glass fibers can also alter composite properties. These modifications no doubt arise from changes in the interphase region.

We report on the effects of treatments on initial fiber strengths, aging resistance, and preliminary results of composite properties (made from our treated fibers).

Silica fume is known to improve the pore system of cementitious pastes and their adhesion capacity to fibers and other mix inclusions. This study has been mainly concerned with the effect of silica fume on the pull-out strength of randomly oriented steel fibers from concrete. Silica fume effects on the fresh mix workability and the overall flexural and compressive behavior of steel fiber reinforced and plain concretes were also assessed. The only variable in different fibrous and plain mixes was the fraction of portland cement substituted with silica fume. This fraction ranged from 0% to 20%.

The workability of plain and fibrous mixes were obtained by slump and inverted slump cone tests, respectively. In both the flexure and compression tests on fiber concrete, the complete load-deformation relationship was obtained. The pull-out strength of randomly oriented fibers was assessed through analysis of the flexural test data.

All aspects of the fresh and hardened steel fiber reinforced concrete performance considered in this study, especially the pull-out strength of randomly oriented fibers from concrete, were observed to improve with the increase in silica fume-cementitious ratio up to a certain limit, after which the trends in silica fume effects were reversed.

Very high strength castable chemically bonded ceramic (CBC) materials have been prepared which consist of finely chopped steel fibers and steel aggregate in a silica modified portland cement matrix. This paper examines the effect of metal fiber addition on compressive and flexural strengths. The overall chemistry of the matrix is held constant but the morphological form of silica used and the cure conditions are altered to examine their effect. Compressive strengths in excess of 500 MPa and flexural strengths in excess of 80 MPa can be obtained.

It is found that flexural strength increases proportionally with fiber content over the range of 0 to 10% by volume. Compressive strengths are not affected. Use of silica fume in the mixes produces higher strengths at low temperatures than mixes which contain only crystalline silica. High temperature curing/drying (400°C), which produces the highest strengths, produces equivalent properties for formulations with and without silica fume. Higher water/cement ratios are found to reduce compressive strengths but have relatively little effect on the flexural properties.

Interfacial bond properties between fibers and matrix are investigated in the present paper. A fiber pull-out test, which is commonly used to study the interfacial bond strength of fiber-matrix system, is analyzed. The bonding between fibers and matrix is assumed to be perfect before the pull-out load is applied. Griffith energy criterion is used to govern the crack propagation at the interfacial region when debonding begins. A constant frictional shear stress, which may be a result of existence of surface roughness at the interface, is assumed to exist at the wake of debonding region. Based on this mechanism, the total pull-out load can be decomposed as: resistance offered by the interfacial bond and resistance offered by the frictional stress. The proposed approach is applicable to any elastic fiber and matrix system, but only the results of steel fibers and reinforcing bar in a cementitious matrix are reported. The proposed model correctly predicts several experimental trends of bond strengths reported by other researchers. Furthermore, theoretical predictions of progressive failure of bond cracks are found to be in good agreement with a holographic interferometry study on a pull-out test.

While typical pull-out tests have been, and still are carried out extensively in materials and structural research, the results of such tests are often incapacitated by a lack of understanding of the pull-out behavior. This shortcoming is the source of numerous basic mistakes in the interpretation of pull-out curves.

The classical fiber pull-out problem has been formulated in onedimension with a view to focus on the nonlinear interfacial response. The fiber and the cocentric matrix are assumed to behave elastically. The local interfacial bond-slip characteristic has been idealized to be elastic-linear softening. This greatly simplifies the otherwise implicit governing differential equation of the debonding process. Solutions to the fiber axial force and interfacial shear stress along the embedded length of the fiber have been obtained by applying appropriate boundary and continuity conditions. The stability of the debonding process has been investigated by varying the fundamental characteristics of the fiber-matrix interface, the fiber embedment length and the fiber diameter. The analytical model has been successfully used to predict many of the characteristics experimentally observed in fibrous composites that fail by fiber pull-out.

The various “building blocks” of a computational mechanics approach to plain and steel fibre reinforced concrete (SFRC) are briefly discussed. Experimental data are incorporated, as well. Theory and experiments deal with debonding as the leading mechanism of structural loosening.

The mechanism of bond transfer between steel and concrete in a reinforced concrete member is studied in the present work. It is seen that the behavior of the interface zone can be represented by a simple generalized Mohr-Coulomb model. It is also seen that the complex relationships between the local bond stress and local slip suggested by other researchers (cubic or higher order polynomials) may be due to the geometry of the specimen and nature of stress distribution along the bar rather than intrinsic interface behavior. Behavior predicted by a generalized Mohr-Coulomb model is compared to predictions and observed behavior previously reported.

In recent years, the means of making high strength concrete are simple by adding microsilica, fly ash, or other types of additives. As the use of high strength concrete increases, the need to clearly understand its prcperties is essentially a necessity for engineering design. While much of the basic properties of high strength concrete such as compressive strength (fc), modulus of elasticity (Ec), and modulus of rupture (fr), etc., has been investigated and reported recently, many remain unavailable. This paper presents the bond strength characteristics of deformed bar, steel fibers, and normal aggregate in high strength concrete matrix. The compressive strength of concrete used in this study is 75–80 MPa (11,000-12,000 psi). Bond slip relationships of deformed bars of three different bar diameters were obtained from the pull-cut test. Two types of steel fiber reinforced high strength cemented composites were tested in a directtension, tapered specimen to observe the pulled-out behavior of steel fibers. Fiber reinforced concretes with fiber volume fraction of 0.5, 1.0, 1.5, and 2.0 % were compared to the unreinforced matrix. A direct-tension, dog boned specimen was used to study the bond between aggregate-matrix interface. The results from this study indicate that high strength concrete is generally more brittle, and in essence, allows less microcracking, less slippage, and less pulled-out deformation. This general trend is observed in both the deformed bar and fiber pulled-out as well as in aggregate-matrix interfacial debonding. The maximum slip of deformed bars in high strength concrete is about 0.15 mm.(0.006 in.) which is only one-tenth of that reported for normal concrete as 1.5 to 2.0 mm.(0.06–0.08 in.). A normalized pull-out stress-displacement relationship of high strength fiber reinforced concrete exhibits a unique behavior similar to those reported for normal fiber reinforced matrix.

The microstructures of steel reinforced ordinary Portland cement mortar samples, and those containing 40% and 70% slag as cement replacement, have been studied by electron optical techniques, after exposure to stagnant sea-water at 23°C for 320 days. Fracture surfaces along the interface with steel were examined using secondary electron imaging in the SEM. This revealed differences between the OPC and slag specimens as regards the morphology of the phases and the amounts of calcium hydroxide present. The microstructure at the interface with steel was studied by means of back scattered electron imaging combined with quantitative image analysis. Chloride concentrations at sections around the interface were determined by means of an EDXA facility linked to the SEM. Even after 320 days immersion in sea-water, there was some calcium hydroxide present in the interfacial zone.

Modern construction techniques for floor and slab systems often make use of the composite action developed between steel and concrete. Knowledge of the magnitude of adhesive force, other than mechanical bond, is necessary in the design of permanent steel formwork, which ultimately becomes an integral part of the load bearing reinforced concrete structure. To investigate the extent of adhesion at the interface between concrete and flat metal surfaces, different treatments of the metal surfaces were considered. Results are presented for six types of treated and untreated metal plates when tested in a pull-off mode with conventional concrete. The mode and the type of failures were investigated, and those parameters, which are considered to be significant in the study of this phenomenon, evaluated

There are numerous chemical agents to achieve the specified air entrainment system. Generally, these are organic chemicals which are broadly classified as soaps and detergents. One of the best known chemical agents of this type is known in the art as Vinsol resin, manufactured by Hercules, Inc., which is a wood resin salt and is the standard against which other air-entraining agents are tested under ASTM C-233.

The interfacial zone between cement paste and embedded steel is a porous one, to which the rust can easily diffuse and where it can be deposited. Strengthening the zone makes the passive oxide film more complete, and harder to rupture; the rate of corrosion decreases, the initiation stage of pitting corrosion is delayed, the effect of self-catalysis is weakened, and the acceleration of corrosion is greatly decreased. Therefore, a strengthened interfacial zone can improve the anti-corrosion properties greatly, with less cost than other methods of inhibiting corrosion.

One of the alternative ways to fabricate shaped bodies from cementious materials would be to press the loose powder of materials (in steel dies, or isostatically) and to infiltrate them with liquids using the natural capillary forces of porous bodies [1,2].

Removal of excess water from cement/sand/water mixes can be effected by electroosmosis with an efficiency of several hundred g per Watt sec, if an additive is applied which increases the absolute value of the zeta potential.

Phosphates have a long history of use as binding agents in ceramic systems. In particular the phosphate bonded alumina refractories and dental cements that employ the chemical reaction between a complex alumino-silicate glass and a buffered phosphoric acid to produce binding are among the most well known.

The work described here has been undertaken in an effort to achieve a more complete understanding of the nature of the chemical binding in these materials.

The results of a series of characterization studies on materials from the Al2O3-P2O5-H2O and SiO2-Al2O3-P2O5-H2O systems will be discussed with particular emphasis on the nature of the binding produced in these materials.

The compressive strength and water permeability of high-temperature lightweight cementing materials containing sillimanite-based hollow microspheres as a filler can be improved by treating the surfaces of the microspheres with a Ca(OH)2-saturated solution at temperatures up to 200°C. The precipitation of an epitaxial layer formed by an interaction between a hot calcium hydroxide solution and the surface of the sphere plays an essential role in developing favorable bonding characteristics at the interfaces and in promoting the hydration of the cement matrix. The properties of the composites include a slurry density of <1.2 g/cc at 25°C, a 300°C-24 hour compressive strength of >1015 psi (7.0 MPa), a water permeability of <10-4 Darcy, and a bulk density of <1.0 g/cc. It was observed that tobermoritetruscottite transformation and anorthite formation during autoclave exposure for 180 days in brine at 300°C results in slight strength reductions and increased water permeability.