Tensile strength of cement-fiber treated sands

Clean sand is considered as a material with no tensile strength and low shear strength. Desired properties can be attained by combining other materials with soil with the purpose of enriching soil's properties. Hence reinforcement of soil is a general improving approach of soil's characteristics. Characteristics such as shear strength, peak strength, residual strength, compressibility, dry density and hydraulic conductivity can be improved by soil reinforcement. Reinforced earth is composed of a composite material, and it alters layer's properties. For soil reinforcement, soil stability must be enriched, bearing capacity must be increased, and settlements must be alleviated, and lateral deformation must be decreased. Adding natural or synthetic fiber to soil is a reinforcement process to modify soil's properties. There are some unconventional methods of soil reinforcement achieved by the combination of randomly distributed fiber with chemical intermixtures such as cement, lime, and chemical resins. Soil stabilization has been conducted for millennia. There are numerous historic buildings throughout the world the were constructed after soil stabilization. Cement is the most frequently and successfully employed stabilizer. The addition of cement to the soil is the most widespread form of chemical stabilization in the civil engineering area. The proper range of cement that can be added to soil is from 3 to 10 percent of by dry weight of soil. It is a commonly known fact that the strength of the cemented soils increases with the curing time. Compressive strength values gained by cemented specimen after 28days curing time is nearly 90 percent of total compressive strength. The definition of the standard fiber-reinforced sand is an enhancement in the mechanical behavior of the soil composite which is combined randomly with fibers throughout the composite to increase the shear strength and give the ductility behavior to sand. Ductility behavior was gained by placing fiber in soil matrix which has high tensile strength than soil. Fiber insertion into the sandy soils changes the load distribution which is applied to a specimen. Fiber grasps and redistributes loads applied to the specimen by mobilizing a relatively wider mass of soil and enhancing the mechanical response of the material. In this series of studies effect of fiber has been evaluated by the use of yellow soil with plastic fine grains and gray sand with non-plastic fine grains, Portland cement, and fiber. There were four various tests has been conducted to illustrate the stress strain, strain number of cycles and stress deflection behavior of cemented specimens which was reinforced with fiber. Samples were prepared with optimum water content, and its dry density is close to the dry density which has been obtained from Modified Proctor test. The tests used in this study were Unconfined compression test, Unconsolidated undrained test, Flexural tensile test and quasi-static test. The results of static tests using partially saturated specimens indicate water decreased the peak stress. Nevertheless, Fiber increased the peak stress and residual strength of cemented specimen to some extent. The maximum peak stress and residual stress in non-reinforced and reinforced sands belong to specimen cured for 28days. Additionally, fiber increased the peak strength and decreased the post-peak loss of reinforced specimen in all three static tests. Two different molds with different volumes were utilized to prepare the sample to comprehend the size effect of the specimens. Size effect of the specimens was assessed by unconfined compression test. Furthermore, experiments indicate that the specimen with bigger volume had higher maximum unconfined compression strength, but after failure in 3% axial strain the residual strength of both specimens are the same where fiber has a paramount impact on the specimens. In all tests, fiber insertion altered the behavior of specimen from brittle to ductile. The last experiment was quasi-static tests. The cyclic test was carried out with conducted with stress controlled way. The cyclic loading was carried out under three peak stresses 500, 1000 and 1500 kPa. The results of cyclic tests indicate that in 500 and 1000 kPa specimen without fiber and with 0.1% fiber ratio has the same level of strain but the specimen with 0.2% fiber ratio has the highest axial strain. Nonetheless, in 1500 kpa cyclic tests specimen without fiber ratio had the highest number of cycles and the second highest was the specimen with 0.1% fiber ratio and the lowest one was the specimen with 0.2% fiber ratio.