Study On Anti-sulfate Erosion Performance Of Concrete In Saline Soil Area In Northwest China

In recent years,the“One Belt,One Road”strategic policy has brought a large amount of infrastructure investment to the vast northwest region,and has built a large number of large structures such as bridges and highways.The climatic conditions in the northwest region are complex,and the saline soil is widely distributed.The most common high-content salt in soil is sulfate.Concrete structures constructed in this environment are highly vulnerable to sulfate attack.Therefore,solving the problem of sulfate erosion can improve the durability of concrete structures in saline soil.In view of the specific situation of the Jingxin Highway-Baiming highway section,the atmospheric environment simulation box is used to simulate the sulfate erosion process of the indoor accelerated simulation concrete.In macroscopic,the anti-corrosion coefficient of flexural strength,the anti-corrosion coefficient of compressive strength,relative dynamic elastic modulus and mass loss rate are used to evaluate the sulfate resistance of concrete.In microscopic,the pore structure characteristics,SEM image,EDS spectrum diagram and XRD diffraction pattern are used to analyze the sulfate attack mechanism of concrete.The performance of concrete sulfate resistance in saline soil is studied from the following aspects.?1?Under the condition of 20°C erosion temperature,10mm×10mm×60mm size mortar test pieces,40mm×40mm×160mm size mortar test pieces and 100mm×100mm×300mm size concrete test pieces were tested,then the effect of size effect on concrete sulfate attack analyzed.?2?The whole immersion erosion is used to simulate all the structures immersed in the erosive environment,and the structures buried in the erosive environment are simulated by the dry-wet cycle erosion.Under the condition of 20°C erosion temperature,the mortar specimens are used for full immersion and dry-wet cycle erosion,thereby the impact of erosion systems on concrete sulfate attack analyzed.?3?The ambient temperature was simulated by the laboratory atmospheric simulation box,and the temperature was controlled at 20°C,10°C and 5°C.The mortar specimens were used for sulfate attack at different temperatures to analyze the effect of erosion temperature on concrete sulfate attack.?4?At different erosion temperatures,the medium sulfur-resistant cement and ordinary Portland cement mortar specimens were used for sulfate attack under the conditions of full immersion and dry-wet cycles,and the influence of cement varieties on the sulfate resistance of concrete was analyzed.?5?At different erosion temperatures,the mortar specimens with mineral admixture were used for sulfate attack under full immersion and dry-wet cycles to analyze the effect of mineral admixture on the sulfate resistance of concrete.The macroscopic evaluation index and microscopic test are used to compare and analyze the sulfate attack law of concrete under different conditions.The research shows that:?1?The 10mm×10mm×60mm size mortar test piece has poor resistance to sulfate attack and the erosion speed is fast;the 40mm×40mm×160mm size mortar test piece and the100mm×100mm×300mm size concrete test piece,having basically the same resistance to sulfate attack,have better sulfate attack resistance,while the corrosion test time of the concrete specimen is longer.Therefore,mortar test pieces can be used to study the sulfate attack performance of concrete.?2?The erosion of mortar specimens under full immersion is mainly chemical corrosion,while the erosion of mortar specimens under the action of dry and wet cycles is a process in which chemical erosion and physical erosion coexist;Compared with the full immersion,the mortar samples have poor resistance to sulfate attack under the action of dry and wet cycles;Different erosion systems have different mechanisms of sulfate attack.Especially in the dry and wet cycle,the erosion rate is faster.?3?The flexural resistance coefficient,compressive resist coefficient and relative dynamic elastic modulus of mortar specimens all showed a decreasing trend with the decrease of erosion temperature.Moreover,the lower the erosion temperature,the shorter the strengthening period of the mortar specimen and the lower the strengthening value.The mass loss rate of mortar specimens increases with the decrease of erosion temperature.The lower the erosion temperature,the shorter the period of negative growth.It can be seen from the microscopic test analysis that the erosion temperature is different and the erosion products are different.Moreover,as the temperature decreases,the content of the thaumasite increases gradually,and the erosion damage is more serious.?4?The medium sulfur-resistant cement mainly reduces the formation of ettringite by limiting the content of C₃A to improve the sulfate attack resistance of the mortar specimen.Under the condition of full immersion,the medium sulfur-resistant cement can improve the sulfate attack resistance of the mortar specimen under three kinds of erosion temperatures,but under the action of dry and wet circulation,the medium sulfur-resistant cement has no obvious improvement under three kinds of erosion temperatures for sulfate corrosion resistance of mortar specimens.The improvement of sulfate attack performance of medium sulfur-resistant cement is related to erosion products,so it has certain limitations.?5?The mineral admixture mainly improves the pore characteristics of the mortar specimen through its micro-aggregate effect and pozzolanic effect,and improves the impermeability of the mortar specimen,thereby improving the sulfate attack resistance of the mortar specimen by reducing the intrusion amount of sulfate.Under the condition of full immersion or dry-wet cycle,the mineral admixture can improve the sulfate attack resistance of the mortar specimen under three kinds of erosion temperatures.Compared with the medium sulfur-resistant cement,the mineral admixture improves the sulfate attack resistance of the mortar specimens in a wider range;the low temperature affects the activity of the mineral admixture,so the dosage must be reasonably controlled at low temperatures.