Consolidation Experiment On Mechanism Of Loess By Hydroxylapatite

Based on researching malan loess taken from Lanzhou,Gansu,compacted remodeling samples under the optimum moisture content(OMC)with hammer,improved its compressive strength.And using various concentration solution of diammonium phosphate(DAP)as consolidation agent,which reacted with calcium carbonate generate network of nanometer hydroxyapatite(nano-HAP)reinforce internal structure of loess.We also test using calcium chloride(CaCl2)solution as external source of calcium,to improve consolidation effect of DAP.cement modified groups was set as the control group.Consolidated sapmles was cured to different age,then dried out and made uniaxial compressive experiments,to study the change of each sample's compressive strength.By using scanning electron microscope/Energy Dispersive X-ray Detector(SEM/EDX)and X-ray diffraction spectrum(XRD)to investigate micro morphology,element distribution and crystal composition of samples,and studied consolidation effect and mechanism of DAP for loess.The results of test show that:(1)Through the hydration reaction of certain components in cement and loess,it is proves that cement stabilization can improve strength and properties of loess.8%of Cement content produce the best reinforcement effect of cement stabilized loess.But early strength of cement stabilized loess is low,and excessive addition of cement leads to plastic deformation appear in soil,then resulting in cracks,which limited the application of cement stabilized.loess in engineering;(2)In the uniaxial compressive strength test of loess added with mere DAP solution,compressive strength of samples gradually grew with the increase of the concentration of DAP solution added.The result of test proves that adding 3.0mol/L DAP solution produce the best effect of on consolidating loess,which making the compressive strengths of consolidated loess samples respectively increased by 290%,350%,420%,and 460%at curing 3 days,7 days,14 days,and 28 days.The early strength of consolidated loess sample grew rapidly,and slowed down gradually after curing 14 days.while the later strength still has considerable growth.(3)The SEM microscopic characterization tests showed that the microscopic morphology of the loess is significantly changed after adding DAP solution in loess samples.EDX and XRD tests confirmed the complex reaction between calcite and DAP to generate phosphorus-containing hydroxyapatite(HAP)in loess.The amount and the degree of crystallinity of HAP generated increase with the increase of the concentration of DAP solution.The generation amount and degree of crystallinity of HAP reached a maximum,when adding 3.0 mol/L DAP solution.(4)Using microscopic analysis to obtain the micro-mechanism of DAP consolidated loess:after adding DAP solution,the hydroxyapatite precipitates of the network nanostructure generated in the loess,Hydroxyapatite has stronger cementation than calcium carbonate and can bind adjacent loess particles which promote the connect and degree of roughness on the surface of loess particles,increases the internal friction angle of loess and filled the pores in loess,then improve the compressive strength of consolidated loess.(5)Because of the high content of calcium in loess,adding CaCl2 as a supplemental calcium source has limited enhancement of loess strength and even lower consolidation effect of adding DAP solution at the same concentration.Due to the limited binding between HAP and loess particles produced by reaction between CaCl2 and DAP,may could not effectively cement the loess,strengthen the loess structure.To sum up,DAP as a new loess consolidation agent,can effectively improve the uniaxial compressive strength of loess.and reduce consumption of cement and lime to modified grouting,avoiding energy consumption and pollution in the process of producting cement and lime to achieve the purpose of saving energy and reducing emissions.