EFFECT ON UNCONFINED COMPRESSIVE STRENGTH OF SAND TEST PIECES CEMENTED WITH CALCIUM PHOSPHATE COMPOUND

Chemical grout is composed of a calcium phosphate compound (CPC) which develops to form calcium carbonate (CC) precipitation throughout the soil and leading to an increase in soil strength. In this paper, initially the condition for CPC precipitation by using different mixtures of calcium and phosphate stock solutions were investigated and analyzed. For that, Toyoura sand test pieces were cemented by CPC solutions and cured up to 28 days and carried out unconfined compressive strength (UCS) test. Moreover, Toyoura sand test pieces were cemented by CPCs with scallop shell (SS) powder and cured and these specimens also analyzed with UCS tests. The UCS of the sand test pieces cemented by CPC with SS powder was larger than that of the test pieces with no added powders. The UCS of Toyoura sand test piece cemented with the CPC-SS powder method increased to a maximum of 156.9 kPa. Moreover, the best CPC-Chem mixture for cementation is CA: DPP with the concentration of Ca/P ratio is 0.5. In addition pH concentration, scanning electron microscope (SEM), and density before and after curing were observed. The results indicate that the density and the pH concentration of the sand test pieces cemented by CPCs with SS powder were larger than that of the sand test pieces with no added powders. SEM images of test pieces cemented with CA: DPP mixture by addition of SS powders not clearly identified a crystal formation among particles of Toyoura sand.