Study On Effects Of Water Content On Mortar's Mechanical Properties

Mortar is a kind of building material commonly used in civil engineering.The mechanical properties of the mortar will directly affect the durability of the building and have a great impact on the safety performance of the building.The buildings in underground engineering has abundant external environment water content.The water in the external environment around the cement mortar will enter the cement mortar through infiltration and form different water content conditions,Water will degrade the mechanical properties of cement mortar.Therefore,the effect of water content on the mechanical properties of mortar must be experimentally studied.Uniaxial compression test was carried out for cement mortar specimens with different water content.The influence of water content on the mechanical properties of mortar was analyzed.The mechanism of the effect of water content on the mechanical properties of mortar was analyzed;from the viewpoint of damage mechanics,according to Weibull distribution theory,on the basis of the standard linear solid model,established the cement mortar damage model under uniaxial compression condition,compare the different moisture content of cement mortar model parameters.Using the RFPA^2D numerical simulation software was carried out on cement mortar in different moisture content simulation of uniaxial compression test,the moisture content of different state AE ring event comparison and AE energy event comparison,the influence of water content on the mechanical properties of cement mortar was further analyzed,and the results show:?1?As the moisture content increases,the mechanical properties of the mortar deteriorate.Specifically,the moisture content of the specimen increases from 0%after drying to a maximum moisture content of 10.35%,crushing strength is decreased from 13.241MPa to8.423 MP,which has a decrease of 36.39%;After 48 hours of soaking,the softening coefficient is 0.636;When not soaked,the peak strain of the specimen is 0.821%.When soaked for 48hours,the peak strain of the specimen is 0.711%,which is a decrease of 13.40%compared to not soaked;When not soaked,the Poisson's ratio of the specimen is 0.151.When soaked for 48hours,the Poisson's ratio of the specimen is 0.166,which is 9.93%higher;When not soaked,the elasticity modulus of the specimen is 17.425 GPa.When soaked for 48 hours,the elasticity modulus of the specimen is13.119 GPa,and the elasticity modulus is reduced by 24.71%;When not soaked,the residual strength of the mortar specimen is 2.375MPa.After soaking for 48hours,the residual strength is 1.339MPa,and the residual strength is reduced by 43.62%.?2?The cause of the deteriorating effect of moisture on the mechanical properties of the mortar is as followed:in the compression of cement mortar process,water will lubricate the aggregate of cement mortar;in the compression of cement mortar process,the decrease of internal pore volume causes the increase of pore water pressure and promotes the expansion of internal crack in cement mortar;due to the self-compacting effect of the cement mortar hardened colloid,the cement mortar specimen cannot fully saturate,and has moisture gradient.Forming a seepage field due to the external load.The water moves inside the mortar and creates a cracking effect on the crack.The water molecule weakens the Van der Waals force between the particles inside the mortar,reduces the cohesion between the particles and decreases the surface energy of overcoming the micro-crack.In summary,moisture has a deteriorating effect on the mechanical properties of the mortar.?3?Setting up the nonlinear elastic-damage model of cement mortar in different influence of moisture content,the numerical calculation shows that the test data and the constitutive equation are in good agreement,verifying the rationality of the theoretical model.Comparing the different moisture content of cement mortar model parameters,with the increase of moisture content,the elastic modulus of cement mortar specimen decreases,the viscous property of specimen improves and the yield stage of specimen lengthens.Microscopically,the ductility of the specimen increases.?4?By RFPA^2D numerical simulation software is carried out on the cement mortar in different moisture content simulation of uniaxial compression test,obtains the AE accumulative ringing curve and cumulative energy curve of different moisture content state,the results show that with the increase of moisture content the AE accumulative ringing count and cumulative energy decrease,but the AE accumulative ringing count curve and cumulative energy curve under different moisture content condition has the same shape and increasing trend.This is because the water come into the cement mortar,weakened the cohesion between the hydrated calcium silicate gel particles,the energy needed to make the crack initiate,develop and penetrate is reduced,so the elastic energy released during the crack expansion damaging is also reduced.In the monitoring of actual underground engineering,it is possible to master the forewarning information and the characteristics of the deformation and unstability of the tunnel gunite layer according to the acoustic emission monitoring data of the tunnel gunite layer.