Study On The Properties Of Concrete Under The Coupling Action Of Carbonation And Freeze-thaw

At present,the concrete structure is prevalent in many fields,and it is the leading structure in the infrastructure of our country.With the development of society,the concrete structure is in a very complex environment.Carbonation and freeze-thaw are the two most common causes of damage,which cause very serious damage to the concrete and affect the durability and mechanical properties of the structure.Many scholars at home and abroad have studied the durability of concrete under the combined action of carbonation and freeze-thaw cycles,in this kind of test,if the carbonation time is short,there are complete carbonation zone,partial carbonation zone and non carbonation zone in the concrete.When determining the relevant performance of concrete test block,each part of carbonation zone plays its own role,and it is impossible to judge which part the performance change depends on;there are few researches on the stress-strain relationship of concrete after complete carbonation and freeze-thaw cycles.Therefore,it is of great significance to study the durability and mechanical properties of concrete under the combined action of carbonation and freeze-thaw cycles.The main contents and research results are as follows:1?234 concrete specimens of C30,C40 and C45 grades were made.2?Take 5 prisms of each strength,conduct the freeze-thaw cycle test first,set the corresponding freeze-thaw times,and then carry out the carbonation test to determine the carbonation depth at a certain carbonation age.The test results show that the freeze-thaw aggravates the carbonation of concrete,and establish the corresponding carbonation depth calculation formula.3?The rest of the specimens were carbonized first,and then put into the freeze-thaw box for freeze-thaw cycle.25 times per cycle,the specimens were taken out to determine the mass and lateral fundamental frequency.The more the freeze-thaw cycle times,the more serious the damage degree;the larger the mass loss rate value,the faster the speed;the smaller the relative dynamic modulus value,the faster the speed.Carbonation aggravates the freeze-thaw damage of concrete,and the lower the concrete strength is,the worse the frost resistance is.4?When the number of freeze-thaw cycles is reached,the concrete specimens which are completely carbonized before freeze-thaw are tested by cube compressive strength test,axial compression test,split tensile test and axial tensile test respectively.The corresponding failure forms and mechanical properties are studied,and the characteristic parameters on the stress-strain curve are analyzed.The results show that carbonation can improve the strength,but with the increase of freeze-thaw cycles,the strength decreases linearly;the peak compressive stress and the peak tensile stress decrease,the peak compressive strain and the ultimate strain increase,the peak tensile strain decreases,and the lower the strength grade of concrete,the faster the change speed.The relationship between the characteristic points and the number of freeze-thaw cycles and the average compressive strength of concrete after complete carbonation is established,and the curve is fitted respectively.