Study On Pore Development And Water Migration Regularity In The Process Of Strength Formation Of Hydraulic Concrete

Nowdays,hydraulic concreter occupies an important place in the hydraulic structure,In the early performance of hydraulic concrete has become the focus of attention.At present,there are many studies on the early mechanical properties.for example,crack,creep resistance and durability of hydraulic concrete.while there are relatively few studies on the early internal structure development of hydraulic concrete,such as water migration,pore development.As the main way of water migration,the pores in hydraulic concrete not only affect the strength formation of concrete,but also have a certain impact on its durability.It’s necessary that master the development of early age performance and internal structure of hydraulic concrete.can we better ensure the quality and durability of hydraulic structures.Therefore,it’s of great theoretical and engineering significance to study the internal pore development and water migration process of hydraulic concrete.This thesis takes low heat and medium heat concrete as the research object,perform concrete compressive strength tests at different ages,one hand,analyzes the water migration law in concrete at different curing ages with the principle of nuclear magnetic resonance,meanwhile,takes industrial CT scanning to study the internal pore size and spatial distribution characteristics of hydraulic concrete at different ages.In the other hand,the same batch of low heat and medium heat concrete mentioned above are used for water saturation treatment(0h,6h,24 h,27h and 48h).The water migration law in concrete under different water saturation time is analyzed by nuclear magnetic resonance principle.Freeze-thaw cycles(0,5,10 and 15 times)were carried out on the test block after water saturation.Besides,industrial CT scanning was used to study the changes of internal pores of concrete under different freeze-thaw times.The results show that:(1)With the same mix proportion,the compressive strength of low heat cement concrete is lower than that of medium heat cement concrete in the curing age.In the early stage of curing,the strength growth rate of medium heat cement is high.At the end of curing,the growth rate of low heat cement and medium heat cement are basically the same.(2)In the curing age,the porosity of low heat and medium heat cement increases with the increase of curing age.The porosity of low heat cement is higher than that of medium heat cement,but the pore growth rate of medium heat cement concrete is higher than that of low heat cement concrete.The number of internal pores in low-heat cement concrete is significantly higher than that in medium-heat cement concrete.(3)Within the curing age,the internal small pore water(capillary water)of low heat and medium heat cement concrete decreases with theincrease of curing age,and the water consumption of medium heat cementis higher than that of low heat cement.In the early stage of curing,the internal moisture proportion of low-heat and medium-heat cement concrete isquite different,but in the later stage of curing,the internal moisture distribution of the two is basically the same.(4)After standard curing,in the process of water absorption,the large internal pore water of low-heat cement concrete accounts for the main proportion,while the small internal pore water of medium-heat cement concrete accounts for the majority in the early stage of water absorption,but after 24 h,the large internal pore water accounts for the majority.In the radius of 0-0.1um,the water ratio of medium heat cement is higher than that of low heat cement,while in 0.1-1um,1-10 um,10-25 um,25-100 um,the water ratioof medium heat cement is lower than that of low heat cement.The water absorption of low heat cement concrete is higher than that of medium heatcement.(5)After standard curing,during the freezing period,the small volume pores of lowand medium-heat cement concrete with the samemix proportion evolve to the large volume pores,It’s leading to the fragmentation of the test block.The porosity and growth rate of low heat cement concrete are significantly higher than that of medium heat cement concrete.The pore proportion of 0.01mm3,0.01-0.1mm3,0.1-1mm3 and 1-10mm3 inmedium heat cement concrete is larger than that in low heat cement concrete,while the pore proportion of 10mm3 is smaller than that in low heat cement concrete.