Flexural Performance of Cement-Treated Sand Reinforced with Geogrids for Use as Sub-Bases of Pavement and Railway Structures

Cement-treated sand (CTS) exhibits undesirable brittle behavior after the applied stress reaches its peak strength. This research investigates the flexural behavior of CTS that is reinforced with uniaxial geogrid (CTSG). A total of 6% cement content was mixed with sand. Uniaxial geogrids with three different strengths were utilized to create the CTSG samples. The number of reinforcement layers, including single and double reinforcements, was studied. The image processing method was applied to analyze the surface cracks in the specimens. The results show that the geogrid type and the number of reinforcement layers affect the flexural behavior of the CTSG. Geogrid reinforcement changed the behavior of the CTS from a brittle material to a semi-brittle or ductile material because the residual tensile stresses were carried by the geogrids. The high-strength geogrid with a double reinforcement layer proved to be most effective in enhancing the peak strength and toughness with improvement ratios of 1.80 and 11.7, respectively. Single and double reinforcement layers with all geogrid types can reduce surface cracks with average crack reduction ratios of 64% and 83%, respectively. The CTSG can be successfully used as a sub-base layer to increase flexural performance and the lifetime of pavement and railway structures.     

Geotechnical Engineering Properties of Cement Fly Ash Gravel Mixtures for Application as Column-Supported Highway and Railway Embankments

Our study investigates the geotechnical engineering properties of cement fly ash gravel mixtures in the laboratory. Gravels with three different size ranges were blended with cement and fly ash. The mixture properties were investigated, including the porosity, density, permeability, unconfined compressive and splitting tensile strengths, cohesion, and friction angle after curing for 28, 50, and 90 days, respectively. The experimental results revealed that the gravel sizes and fly ash contents significantly influenced the strength characteristics. The permeability coefficients of the cement fly ash gravel mixtures were 0.9 to 1.7 cm/s, much higher than a soil-cement column. The unconfined compressive strengths and splitting tensile strengths were found to be from 3.75 to 18.5 MPa and from 0.5 to 2.5 MPa, respectively. The cohesion and friction angle values ranged from 2.2 to 5.3 MPa and 30 to 40 degrees. The mixture strength was 6 to 30 times higher than a soil-cement column. The 15% fly ash provided the best strength characteristics as it exhibited the most significant calcium silicate hydrate contents. Thus, using cement fly ash gravel column-supported embankments is more productive than using a soil-cement column and granular pile to increase the column-bearing capacity and overall stability and accelerate the consolidation process.