International Journal of Civil Engineering, Volume 1, Number 1, 2009 Printed in Nigeria. All right Reserved Copyright020098/achvell Educational Books RATIONAL PROPERTIES OF STEEL FIBER - CEMENT STABILISED LATERITIC PAVEMENT MATERIAL Ekwulo E. O. and Igwe E A Department of Civil Engineering Rivers State University of Science and Technology, Port Harcourt, Rivers State, Nigeria ABSTRACT The properties of steel-fiber reinforced (SFR) cement stablized laterite were evaluated to determine the rational properties of the material. Classification test of the laterite soil was carried out to determine the physical properties of the soil. Dubic steel fibres commonly called "animal wire" with aspect ratio of 80 were used in the study. Cylindrical specimens were prepared from the soil-cement-fibre mixture using water at the optimum moisture content. The specimens were tested using the split cylinder indirect tensile test to determine the tensile strength, Poisson's ratio and modulus of elasticity of the material. The SFR cement stabilized laterite potential for crack control was also investigated. The results showed that the use of steel fibres brought as much as 50% increase in tensile strength, 21% increase in tensile modulus of elasticity, and 80.95% increase in poison's ratio. The failure mode of the SFR specimen was gradual as compared to the abrupt and brittle failure pattern of the non-SFR specimen. A conclusion was reached that the steel fibres were capable of retarding the propagation of cracks in cement stabilized laterite. It was recommended that steel reinforcement should be incorporated in the design and construction of cement stabilized flexible pavement to reduce crack propagation in the base layer. Furthermore, the values of Elastic Modulus and Poisson's ratio obtained should be used for rational design. , Keywords: Laterite, Cement, Steel Fiber Post-Cracking, And Elastic — Properties. INTRODUCTION The rational or mechanistic design of roads with cement stabilized and steel fibre-reinforced (SFR) laterite demands an adequate knowledge of the elastic properties of the material. Such information is lacking for SFR cement stabilized pavement materials, and this is to some extent responsible for non use of fibre reinforced materials in rational designs. The rational methods involve a more fundamental or analytical approach that relies on the laws of mechanics to predict critical stresses and strains by using the elastic parameters (,] . In the mechanistic design approach, the materials in each of the layers are characterized by their modulus of elasticity E and Poisson's ratio The developed tensile and compressive strains due to ' repeated application of wheel loads are then used to assess the pavement for fatigue cracking and permanent deformation (rutting) 131 . As cracking is mostly due to tensile stresses, a knowledge of tensile strength of the material is also important. This is to enable the determination of the load at which cracks would occur as to design against them. The use of elastic properties of materials as design inputs for pavement design in multi- layered elastic theory is gaining ground as it yields better performance and correlation at the end 111 . The need therefore arises to evaluate the basic properties of SFR-cement stabilized lateritic materials for use in the mechanistic approach of pavement design. This paper is aimed at using "Static Load Indirect Tensile Test" to evaluate the basic characteristics of SFR-cement stabilized lateritic soils. It is a laboratory testing programme in which SFR soil-cement mixes are treated in a way as to simulate site properties as expected during their use as pavement materials. REVIEW Fibre reinforcement is a modern technology for producing relatively inexpensive material of high strength from suitable homogenous matrix base, to which strong fibres, wires or whiskers have been added. The fibres retard the propagation of cracks and sometimes dislocation in the matrix 141 . The addition of steel fibre to cement bound material(CBM) base leads to a substantial improvement in the tensile properties of the material. The study shows that the improved tensile properties of the steel fibre reinforced CBMs can provide extra safety against longitudinal cracking 151 . The modulus of elasticity of a material, whether in tension, compression, or shear is one fundamental property that is needed for modelling mechanical behaviour in various structural applications. Nakagawa et al ( \ and Naaman 17 ', conductcd tests for tensile modulus of elasticity of fibre-reinforced cement based composites. The results indicated that the tensile 103