An Experimental Study On The Mechanical Properties Of Leached Cement Paste

Cementitious materials are widely used in civil engineering,hydraulic engineering,and nuclear engineering.Leaching of concrete structures located in water environmrnts is a durability issue to be solved urgently.To evaluate the degradation of mechanical properties of leached cement paste,the water/cement ratio and leaching time are taken as the design variables and the effects of these variables on the mechnical indexes of cement paste are studied through experiment.By measuring the leaching depth,water absorption in saturated surface-dried condition,mass loss rate,damage,porosity,and variations in pore structure,the leaching degree of cement paste is evaluated.It is found that the leaching depth of cement paste with high water/cement rations increases approximately linearly with the increase of leaching time,while that with low water/cement ratios gradually decreases.As leaching time increases,the density of cement paste decreases,the prosity gradually increases and tends to be stable,and the number of large pores obviously increases.To study the uniaxial mechanical properties of leached cement paste,the strength,peak strain,and stress-strain curve are measured and the failure characteristics of cement paste are analyzed through splitting tension test,axial tension test,and axial compression test.It is found that the splitting tensile strength decreases approximately linearly with leaching depth.The decrease rates of axial tensile strength and axial compressive strength decrease gradually with leaching time and the relationship between strength and leaching time is quadratic.However,the peak strain increases with leaching time.Based on the leaching characteristics on the cross section of cement paste,a strength degradation model of cement paste is proposed.To study the mechanical properties of leached cement under multi-axial stresses,a triaxial compression test of leached and partially leached cement paste is conducted.The compressive strengths of leached cement paste under different confining pressures are compared,the cause for the sensitivity of leached cement paste to confining pressure is analyzed,and the reference shear strength of leached cement paste is calculated.It is also found that the peak strain first decreases and then increases with confining pressure.