Research On The Efects Of Concrete Durability Due To Thermal Sulfate Corrosion

The thesis explored sulfate corrosion on the strength and durability of concrete structures,under the complicated geological environment, in the construction and operation process of the railway Bridges and tunnels,with high temperature groundwater,sulfate and dry-wet cycle inside the concrete working together. Grouping by orthogonal test, respectively from sulfate after soaking the cube compressive strength, chloride ion electric flux, frost resistance, considering temperature, sulfate concentration, soaking way in its effects. Grouping by orthogonal test, considering their effects of temperature, sulfate concentration, soaking ways, respectively from cube compressive strength, chloride ion electric flux, frost resistance after sulfate soaking.(1)Cube compressive strengthBy grouping 9 orthogonal set of text, carried out compressive strength test after 28d, 56d,84d,112d,140d sulfate soaking, and come to the following conclusions:①From the perspective of the five ages of soaking test, the temperature has a significant effect on the compressive strength, the higher the temperature, the more serious sulfate corrosion of concrete, the lower cube compressive strength. In the phase of cube compressive strength reducing after sulfate erosion, the higher the temperature, the greater the rate of change, the greater the strength reduction.② In five ages, each group test, compressive strength has a first increases and then process. In an increase in the severity of phase, Sulfate solution concentration had no obvious effect on the strength; With the increase of soaking age, the compressive strength reduce stage, with the increase of concentration, the compressive strength significantly lower.③ From three methods for soaking, comparing with fully soaking, dry-wet alternate soaking, sulfate corrosion of half soaking is more apparent, the compressive strength of half soaking is lower than the other two types of soaking, but the effect is limited.④ FFrom range analysis of the three factors,soaking temperature, concentration of sulfate, soaking ways, the temperature is the biggest factors influencing the compressive strength of concrete cube, followed by sulfate concentration and soaking ways, the two are close.⑤ As the temperature increases, the effect of sulfate concentration on the compressive strength after sulfate corrosion become more obvious.In other words,the high temperature can promote effect of concentration on compressive strength.(2) Chlorine ion electric fluxBy grouping 9 orthogonal set of test, carried out electric flux test after 28d,56d,84d, 112d,140d sulfate soaking, and come to the following conclusions:① Temperature can obviously influence the electric flux of concrete, the test within 5 ages, the higher the temperature, the greater the electric flux. In the increasing phase of electric flux after sulfate erosion, its rate of change is greatest at 50℃, followed by 20℃ and 80℃ is minimal. Therefore the most serious sulfate corrosion is at 50℃.② The higher the soaking solution concentration of sodium sulfate, the sulfate corrosion of concrete more serious, the greater the electric flux value; By the three soaking ways, half soaking, compared with other two kinds of soaking, significantly more can promote the sulfate corrosion of concrete, increase the concrete electric flux; followed by fully soaking, dry-wet alternate soaking is smallest.③ From range analysis of the three factors, the temperature is the biggest factors influencing the concrete electric flux, followed by sulfate concentration and soaking, the two are close.④ With the increase of temperature, the effect of sulfate concentration on electric flux increase; But when the temperature increases to a certain, with the increase of temperature, the effect of sulfate concentration on electric flux decreases. In other words, As temperatures increases, the effect of concentration on electric flux, first increases then restrains.(3) Freeze-thaw cycleThrough two temperature (20℃,50℃) and three kinds of sulfate concentration(0, 2.5%,5%),140-day fully soaking and then 50 times of freeze-thaw cycling test, come to the following conclusions:① Concrete soaked in high temperature (50℃) Sulfate, the relative dynamic elastic modulus is less than which soaked in normal temperature(20℃) after the freeze-thaw cycle, in other words, the frost resistance of concrete in high temperature less than in normal temperature after sulfate corrosion.②The higher sulfate solution soaking concentration is, the more serious the sulfate corrosion of concrete, after the freeze-thaw cycle, the lower the relative dynamic elastic modulus.③ Sulfate corrosion under the condition of high temperature (50℃), the relationship between mass loss and the change of the relative dynamic elastic modulus is roughly linear after freeze-thaw cycle; and 20℃, the mass loss and the change of the relative dynamic elastic modulus has no obvious relation.