Fiber-reinforced Cement Research Articles

Fibre toughening of MDF cement

Fibre reinforced cements are of considerable industrial importance, the production of asbestos cement amounting to about 5 m tonne per annum. The search for fibres other than asbestos has led to the investigation of glass, polypropylene, cellulose (and other fibrous materials) in a cement matrix. Whilst there has been much work on the fibrous component of cement-fibre composites little attention has been paid to the effect on the final composite properties following improvements in the cement matrix. The preparation of macro-defect-free (MDF) cements has recently been reported and the work presented here describes the preparation and the properties of fibre-reinforced MDF cement composites. The Young's modulus of elasticity and the strength of MDF cements are greatly improved and do not need fibrous reinforcement to show benefit. The main purpose of reinforcing MDF cement with fibres is to enhance toughness and impact performance. It is shown that small volume fractions of fibre (∼2%) in the MDF cement matrix produce composites with excellent toughness and impact properties.

Acrylic-polymer modified GRC

Acrylic-based polymer dispersions have a considerable and largely beneficial effect on the engineering properties of glass fibre-reinforced cement (GRC) composites. At 12 volume % polymer solid addition, improvements in bending, tensile and impact strengths over the control of up to 7%, 18% and 18% respectively have been recorded after 28 days. However, the degree of retention of these improved properties depends on the environment of use. When the composites were kept under water continuously for six years, the very good initial pseudo-ductility of the material disappeared nearly completely and the material failed in a brittle manner. Nevertheless, the stress at the limit of proportionality remained high in some cases and this may be important in design. After six years of natural weathering at Garston the modified composites were still pseudo-ductile and their LOP stress was much higher than that of the control. In this respect GRC which contained pulverized fuel ash behaved in a manner similar to that of ordinary GRC.

Erratum: “Polymer Modified Glass Fibre Reinforced Cement (PGRC) as a Protective Buffer Coating Over Thin Film Anti‐Corrosion Coatings” Presented by P. A. White at the ASCE 1983 Specialty Conference: Pipelines in Adverse Environments II, San Diego, Calif., (November 14–16, 1983)

Erratum: “Polymer Modified Glass Fibre Reinforced Cement (PGRC) as a Protective Buffer Coating Over Thin Film Anti‐Corrosion Coatings” Presented by P. A. White at the ASCE 1983 Specialty Conference: Pipelines in Adverse Environments II, San Diego, Calif., (November 14–16, 1983)

Autoclaved beaten wood fibre-reinforced cement composites

The need to beat (or refine) wood pulp fibres before using as a reinforcement in cement composites has been re-examined. In the case of Pinus radiata unbleached kraft pulp, it has been confirmed that beating the fibres does contribute to attaining optimum mechanical properties for composites fabricated from such modified fibres.

Micromechanics analysis of fibre reinforced cement composites

A three-dimensional finite-element modelling of fibre-reinforced cement composites has been adopted in this study to determine the linear elastic and non-linear properties of the composites, given the properties of the constituent materials. The micromechanics adopted for the analysis involves the formulation of constraint equations to incorporate the necessary boundary conditions. The results obtained from the numerical analysis compare favourably with the experimental results. The importance of a fully three-dimensional analysis of multi-fibre composites has been demonstrated.

Book reviews

Book reviews

Properties of glass fibre-reinforced polymer-modified cement

Several properties of glass fibre-reinforced polymer-modified cement composites, such as strength, durability, fatigue, creep, shrinkage, freeze-thaw resistance, permeability, thermal movements and fire resistance are described.

The weather and its influence on the creep of glass fibre-reinforced cement composites

This paper describes an unusual programme of long-term creep tests on glass-fibre reinforced cement (GRC) boards. The specimens were mounted out-of-doors and loaded in tension. The deformations were monitored continuously by means of special weatherproof extensometers. The recording system is shown to operate in a reliable and consistent manner. The effects of weather and of stress can be separated by comparing the responses of stressed and unstressed specimens. Humidity variations have a dominant effect on the results, but a numerical relationship between humidity and strain remains to be found. Stress causes strains which follow well-defined creep curves once the effects of weather have been allowed for. The experiments are continuing.

Future developments in fibre-reinforced cement, mortar and concrete

The current state of development of fibre-reinforced concrete is considered and the possible future of products which may arise is discussed. The various potential alternative fibres for the reinforcement of cement sheet are considered and the advantages and disadvantages compared. Possible future trends are discussed in the light of this comparison.

Toughness of fibre cement composites

The methods used to measure the toughness or impact resistance of fibre-reinforced cements and concretes are reviewed together with the failure mechanisms which determine the toughness of these materials. The importance of choosing a test which is suited to the particular mode of failure - either fibre pull-out or multiple fracture - is emphasized.

Microstructural features of interfaces in fibre cement composites

This paper briefly reviews present knowledge of microstructural characteristics of interfaces in steel fibre-reinforced concrete and glass fibre-reinforced cement. The influence of these features on the mechanism of debonding of steel fibres from a hardened cement matrix is discussed and this provides a basis for consideration of certain approaches towards the improvement of strength of steel fibre-reinforced concrete. Current ideas on the processes responsible for degradation of the strength and toughness of grc during prolonged exposure to wet environments are examined with particular reference to the role of interface microstructure.

Developments in the assessment and performance of grc over 10 years

Glass fibre-reinforced cement came into use as a construction material about 10 years ago when alkali resistant glass fibres first became available commercially. Chemical tests in alkali solution were much used in the initial stages of the development of alkali resistant fibres but increasingly these have been replaced by direct measurements of the retention of the tensile strength of fibres in a cement environment. Detailed studies of the strength of composites and of the kinetics of strength changes have led to the development of methods of accelerating the ageing of grc materials and hence predicting long term strength behaviour in different climates. New fibres with improved strength retention characteristics have recently been developed and their potential long term performance in composites and components has been assessed by means of these accelerated ageing procedures.

Creep of glass fibre-reinforced cement composites in tension

Creep of glass fibre-reinforced cement composites in tension

The air and water-vapour permeance of glass fibre-reinforced cement

The air and water-vapour permeance of glass fibre-reinforced cement

サンドイッチ構造をもつＦＲＣの衝撃曲げ挙動に及ぼす強化材の影響

The bending behavior under impact load was studied for the sandwich beam consisting of FRC (fiber reinforced cement) to give a guide for its effective use. As representative examples of FRC signifying different characteristics, GFRC (glass fiber reinforced cement) and NFRC (nylon fiber reinforced cement) were selected.In the experiments, the impact test was carried out with a three-point bending method by using a falling elastic bar. And the strain caused by the transient phenomenon in the loading elastic bar and the location where the crack occurred in the FRC were measured. Then the impact resistance of FRC was considered.Moreover, in order to interpret the behavior of the sandwich beam under impact load, a simple sandwich model with a homogeneous reinforcement was constructed for analyzing the impact test and for facilitating numerical calculation. And the effect of the span length on the dynamic flexural strain of the sandwich beam was considered.From the results obtained experimentally and numerically, it was shown that the crack occurred at the same position of the specimens, independent of the span length, and that the impact resistance of FRC improved by using it as a sandwich construction.

Wood fibre-reinforced cement composites

The use of wood fibres as reinforcement for a structural composite material has been investigated. Although wood fibres have relatively poor mechanical properties compared with synthetic fibres, they have the advantages of low density, low cost and low energy demand during manufacture. A number of possible matrix materials were considered and Portland cement was chosen for further investigation. An examination was made of the effect of the pulping technique used to prepare the fibre on the strength of the composite and on the stability of the wood fibres in the cement matrix. A chemically pretreated high-temperature thermomechanical pulp and a pulp produced by the kraft process were selected for further study. The effect of the water-cement ratio of the matrix and the weight of fibre in the composite on the strength of the composite and the rate of increase in strength and fracture energy of composite are reported for composites containing these pulps. The results indicate that the kraft pulp is suitable for applications where slurry dewatering can be employed during the forming operation and that the thermomechanical pulp is more suited to applications where low water-cement ratio slurry is used.

Flexural creep behaviour of fibre-reinforced cement composites: Swamy, R.N. and Theodorakopoulos, D.D. The International Journal of Cement Composites Vol 1 No 1 (May 1979) pp 37–47

Flexural creep behaviour of fibre-reinforced cement composites: Swamy, R.N. and Theodorakopoulos, D.D. The International Journal of Cement Composites Vol 1 No 1 (May 1979) pp 37–47

Coupling agents in wood fibre-reinforced cement composites

The effects of surface treatment of discrete wood fibres incorporated into cement have been studied by measuring the fracture energy and flexural strength of the derived composite materials. The results of this investigation confirm that the mechanical performance of a wood fibre reinforced cement composite can be altered by the use of coupling agents.

Strength and fracture properties of asbestos-cement mortar composites

The strength and fracture properties of random asbestos fibre-reinforced cement mortar composites are reported in this paper. The fibre content varies between 5% and 20% by weight. Both the ultimate tensile strength (σ t) and the modulus of rupture (σ b) increase with increasing fibre-volume fraction. These results are shown to agree satisfactorily with the law of mixtures modified for randomly oriented short fibre-reinforced composites. The critical stress intensity factor (K c) and the specific work of fracture (R) have been determined using three-point bend edge-notched beams and grooved double-cantilever-beam (DCB) specimens. There is generally good agreement between these two physical quantities estimated from the two testpiece geometries. It is shown that the fibre pull-out mechanism is dominant in the fracture of asbestos cements and that the specific work of fracture can be reasonably well predicted by considering the energies absorbed in both the pull-out and the fibre/matrix interfacial debonding processes.

The flexural strength of cement-based composites using low modulus (sisal) fibres

A model of the flexural behaviour of a cement-based composite reinforced with low modulus fibres is presented. The model predicts large increases in the flexural strength of such composites under certain conditions. An experimental programme was carried out on sisal fibre-reinforced cement; the results of this work confirmed the theoretical predictions, with increases in flexural strength - by a factor of more than three - being achieved with suitable choices of mix parameters and fibre incorporation techniques. It is suggested that the results obtained will be of considerable potential in such areas as housing construction in developing countries.