International Concrete Abstracts Portal

The background to the development of two types of thin, fabric-reinforced, portland cement concrete sheets is described and range of properties given. Both normal weight and lightweight mortars (including cellular mortars) were used as a matrix. Glass or synthetic fiber continuous reinforcement in the form of fabric scrims and/or nonwoven three-dimensional fabric were used. The materials developed are potential substitutes for plywood, cement asbestos, and other types of sheet material that require the properties of weather resistance, incombustibility, nonbiodegradability, and economy. The test results also suggest that the matrix and reinforcement concepts developed will lead to applications in other reinforced concrete uses. The thin sheet materials lend themselves to easy manufacture in a comparatively simple plant.

Thin-section fiber reinforced concrete (FRC) panels may be subjected to localized impact. In this study, thin sheet FRC materials, made with asbestos fibers in different matrixes, were tested under impact loading, using a drop-weight instrumented impact machine. The impact properties were characterized in terms of the peak bending load and the fracture energy (computed as the area under the load-deflection curve). Companion specimens were tested under static loading. The specimen dimensions were about 200 mm wide, 600 mm long, and 6 to 12.7 mm thick. In all cases, the peak bending loads were considerably higher under impact loading than under static loading; however, the fracture energies were always higher under static loading. These effects can be explained in terms of the porosity of the interfacial matrix, and the degree of bundle separation of the asbestos fibers.

Precast thin ferrocement planks have replaced wood for a variety of applications. Present knowledge about joining them using steel bolts or similar means is very limited. While bolted connections are commonly employed in steel construction, their suitability for connecting precast reinforced concrete or ferrocement elements is yet to be fully investigated, particularly when subjected to both bending and direct tension. A series of tests were carried out at the Structural Engineering Research Centre, Madras, India, on precast ferrocement planks connected together using steel bolts for transferring tension and flexural moment

Presents comprehensive test data on the tensile behavior of 12.5 cm thick ferrocement plates. The main variables investigated were mesh geometry, specific surface, volume fraction, mesh yield strength and skeletal bars. The specimens were specially designed to insure failure in the gage length. The matrix was proportioned for high strength, high workability, and high durability with low water-to-binder ratio, and 50 percent fly ash replacement. Cracking and deformation were monitored throughout the loading range. The results showed that the composite properties of elastic modulus and ultimate tensile strength could be satisfactorily predicted. However, the cracking behavior for a wide range of mesh geometry could not be satisfactorily predicted by a single unique relationship. There was, however, good correlation between the composite properties of ultimate tensile strength and ultimate flexural strength. The results show that by suitable design of the matrix and the reinforcement, high-strength, ferrocement sheets with high crack resistance can be developed for a variety of structural applications.

Presents comprehensive test data on the flexural strength, deflection, and cracking behavior of thin sheets of 6 to 13 mm thickness reinforced with a wide range of reinforcing elements. Two different sizes of sheets were generally tested under four-point loading, and in the case of glass fibers, a further small laboratory scale test specimen was also tested. Five different types of reinforcing elements were used: steel fibers, welded steel mesh without and with steel fibers, two types of woven polypropylene fabrics and glass fibers. The matrix was designed for durability and high workability with low water-binder ratio and a superplasticizer. In addition, 50 to 70 percent of the portland cement was replaced by fly ash. Extensive test data are presented and compared in terms of limit proportionality, modulus of rupture and cracking. It is shown that a wide range of reinforcement elements can be successfully used for thin sheet applications, and that the performance characteristics of thin sheets are very much a function of the type, geometry, and volume fraction of the reinforcement.

A simplified analytical procedure is proposed to predict stress-strain diagram of ferrocement composites under tension. A fracture mechanics approach is used to predict the load at first cracking. Results of a limited experimental investigation are also shown and used to evaluate the analytical model. The influence of curing is also demonstrated experimentally.

Reports on the performance of semi-full scale pavement and overlay slabs under static loads. The test results of 60 mm SFRC pavement slabs having 0.5 percent fibers by volume have been presented under different loading and subgrade conditions. The test results of 100 mm PCC (plain cement concrete) pavement slab resting over a well-compacted subgrade have also been presented. The performance of 201 mm ferro-fibro overlay cast over 60mm cracked SFRC pavement has been reported and compared with a 40 mm SFRC overlay slab cast over 60 mm SFRC pavement. The experimental results of semi-full scale overlay and pavement slabs have been validated by infinite element analysis, a numerical technique developed for the analysis of unlimited domain of a layered system consisting of an overlay, pavement and subgrade of known properties. A comparative study has been presented with respect to Ferro-fibro and SFRC overlays.

Flexural behavior of sandwich beams reinforced with thin layers of steel-fiber reinforced mortar was studied in this investigation. The effect of variations in thickness of the reinforced layer on the modulus of rupture, Young's modulus, and toughness of the member was investigated. This investigation considered one single specimen size with fiber reinforced mortar using one fiber geometry and content. Steel fibers with 0.6 x 0.3 mm cross section and 18 mm long were used. The specimens were cast in 100 x 100 x 350 mm molds. Eight series of sandwich beams with different thicknesses of the reinforced layer were tested. Experimental results indicated that sandwich beams can have strength and toughness comparable to fully fiber reinforced beams. The minimum thickness of the fiber reinforced layer required to impart ductile behavior to the sandwich beam was found to be about one-sixth of the beam depth.

Strength properties of steel fiber reinforced concrete and plain concrete specimens subjected to normal atmospheric exposure and accelerated cyclic testing in marine environment were examined. The concrete mix design consisted of cement:sand:aggregate in ratio of 1:1.96:3.01 with water-cement ratio of 0.6. The steel fibers, 10 mm in length, were added in volume of 0.0, 0.6, and 1.2 percent of the mix. Strength properties--compressive, flexural, and tensile strength of the concrete specimens containing steel fibers--showed considerable improvement over those obtained in the plain concrete exposed to the normal atmospheric condition. Both steel fiber reinforced and plain concrete specimens subjected to accelerated cyclic testing at 60 C, 24-hr cycle in marine environment, showed that the addition of fibers provided considerable improvement in strength properties. However, corrosion of the fibers was observed at or near the surface, and continued to worsen after 20 cycles. Specimens with 1.2 volume percent of steel fibers exhibited the largest increase in compressive and flexural strength in both test conditions, normal atmospheric and accelerated cyclic testing.

The inherent light weight, toughness, low permeability, smooth surface finish and resistance to shrinkage cracking have all contributed to GFRC being an attractive alternative to traditional materials in the following areas of mining: 1) stabilization of rock tunnels by in situ spraying of thin skins; 2) construction of ventilation stopping walls both by a surface bonding technique and as a direct substitute for simple lime and sand mortars; 3) fire protection of timber packs by lightweight GFRC renders with improved adhesion and impact strength; 4) manufacture of drainage channels which are lighter in weight than their concrete counterparts and tougher than the asbestos cement alternatives; and 5) production of permanent formwork, which is lighter in weight and has a better surface finish than concrete and is much more efficient than the use of temporary shuttering.