Fiber Cement Composites Research Articles

Behaviour of cracked fibre composites under limited cyclic loading

Using the well-established ACK theory as a basis, the paper develops general equations to describe the loading/ unloading/reloading behaviour of a cracked fibre cement composite. In particular, the theoretical relationships between the unloading strain and the resulting residual strain at zero load and subsequent reloading modulus are examined. The theory describes with reasonable accuracy the experimental behaviour of test specimens of a cement composite reinforced with continuous fibrillated polypropylene networks.

An evaluation of theories and a design method of fibre cement composites

The paper briefly presents the existing theories of fibre cement composites based on spacing and composite material concepts. The mathematical equations giving the tensile and the flexural strength are restated using a common set of notations. These equations are used to predict the first crack and ultimate stresses in tension and flexure, and compared with experimental values. Based on the comparison, a set of equations are identified and a design method of fibre cement composite is proposed.

Experimental test results for flexure and direct tension of fibre cement composites

The effectiveness of random fibre reinforcement in a cement-based matrix subjected to tension can vary enormously. At one extreme there is no increase in ultimate tensile strength and an increase in toughness which is barely perceptible. At the other extreme, for the same 1.5% volume fraction of fibres, the ultimate load is almost doubled and the toughness is increased by a factor of more than twenty. The main conditions for the different tensile tests are outlined and the probable major factors contributing to the very diverse behaviour are examined with particular reference to results obtained at Birmingham.

Influence of slow crack growth on the fracture resistance of fibre cement composites: R. N. Swamy International Journal of Cement Composites Vol 2 No 1 (February 1980) pp 43–53

Influence of slow crack growth on the fracture resistance of fibre cement composites: R. N. Swamy International Journal of Cement Composites Vol 2 No 1 (February 1980) pp 43–53

Fibre cement composites: research at BRE

Research on the prospects for fibre cement composites began at the Building Research Establishment more than a decade ago with the pioneering development of an alkali-resistant glass fibre. A very considerable amount of work has been carried out on glass fibre-reinforced cement. BRE has also been concerned in assessing the potential of other fibres such as carbon, polypropylene and Kevlar for cement reinforcement; other matrices such as gypsum plaster and autoclaved calcium silicates have also been examined. The principal achievements of the work are reviewed.

Some properties of fibre-polymer concrete systems

In fibre cement composites, the properties of the matrix have a significant control over the properties of the composite. This paper investigates the possibilities of using polymer dispersions to overcome the difficulties of low elongation at break and possibly of the high stiffness of the cement matrix. Five different types of polymer dispersions have been studied and their influence on the strength, stiffness and shrinkage characteristics of polymer modified plain and fibre concretes has been investigated. The effects of dry, wet and dry-wet curing on these properties have been studied. It is shown that with proper selection of the type of polymer, modification of water content, and possible use of a defoaming agent, polymer dispersions can be used to advantage to improve the properties of fibre cement composites.

The interfacial bond stress in steel fiber cement composites

In fiber cement composites most fibers are in a state of partial bond due to internal stresses arising from moisture migration during fabrication and subsequent volume changes in the matrix. A wide variation in the computed interfacial bond strength therefore occurs depending upon the type of test or when derived from phenomena such as crack spacing. In practice debonding of the fibers occurs in flexural tension in the presence of a strain gradient. This paper presents further data on steel fiber mortar and concrete to confirm the validity of the composite mechanics approach to predict the composite flexural strength. It is shown that the composition of the matrix and its strength properties influence the fiber-matrix interfacial bond stress and the relative contributions of the matrix and the fibers to the composite flexural strength.

RILEM Symposium 1975 Fibre Reinforced Cement and Concrete

The RILEM Symposium on Fibre Reinforced Cement and Concrete held in London in September 1975 was organised by the RILEM Technical Committee 19-FRC in conjunction with the Building Research Establishment, the Cement and Concrete Association and the Concrete Society. This paper reviews some of the more important factors presented at the symposium and highlights some of the conclusions drawn from it. The symposium established further that fibre cement composites are a new class of construction material in their own right. The limitations of their performance have to be just as well understood as the freedom they offer to designers if the material is to be used wisely.

Chemical interactions between glass fibres and cement

The rate of removal of ions from a zircono-silicate glass fibre by aqueous extracts of Portland cement has been experimentally determined. To accelerate the reaction, digestions have been carried out at elevated temperatures. The reaction rate for the glass composition investigated favours a log-time dependence. The reacted fibres show a relative enrichment of Zr on the surface, although no definite zirconia-containing phase has been identified. Soda-lime and borosilicate glass fibres which have been similarly examined for comparison purposes, required considerably shorter periods of digestion to produce suitable concentrations of glass breakdown products. The reaction rate for soda-lime glass appears to be largely controlled by Na + diffusion. With borosilicate glass, no simple interpretation can be applied to the breakdown mechanism because of the complex nature of the reaction products. The significance of these results in the interpretation of the durability of zircono-silicate glass fibre cement composites is discussed.

Fibre reinforcement of cement and concrete

The concept of reinforcing materials weak in tension is delight-fully simple. Asbestos fibres are known to have been used almost 4,500 years ago to strengthen clay post. The use of continuous reinforcement is as old as reinforced concrete; the use of short, discrete reinforcing elements is relatively new, although the significance of the fibre geometry and the need to improve the fibre shape to obtain adequate fibre-matrix bond was recognised more than fifty years ago. In spite of these early attempts to apply the ideas of composite action to building materials, the development and practical usage of fibre-reinforced cement composites, like reinforced earth, is barely two decades old. The world-wide interest, however, in the potentialities of these new construction materials has resulted in many meetings in the last five years, and the RILEM International Symposium on Fibre Cement Composites to be held in London from 17–17 September, 1975 is another step forward in consolidating the future prospects of these composites. This paper presents a preview of the achievements to date in this area.