Deterioration Process And Mechanism Of Mortars Partially Immersed In Sulfate Environment

When concrete structure exposed to a sulfate-rich environment,external sulfate ions will enter the interior of the concrete,react with cement hydration products formed erosion products such as ettringite and gypsum,resulting in cracking and spalling of the concrete and accompanying reduction in strength,making the concrete The structure breaks down before reaching the designed service life,causing great economic loss.There are a large number of concrete structures in my country's coastal and northwest inland areas that are half-soaked with sulfate ions,which may cause double destruction of cement concrete chemical erosion and physical salt crystallization.At present,mineral admixtures such as fly ash and mineral powder are already indispensable components of modern concrete.Therefore,the research on the erosion mechanism of cement-based materials containing mineral admixtures in a semi-immersed sulfate environment will help the concrete resist Development and application of sulfate attack technology.This paper mainly studies the influence of different humidity and different fly ash content on the deterioration process and erosion mechanism of mortar in semi-immersed sulfate environment,and analyzes the deterioration process and mechanism of mortar containing different mineral admixtures under different sulfate solutions,The effects of humidity,mineral admixtures and sulfate solution on the erosion mechanism in a semi-immersed sulfate environment were investigated.All the above results show that:(1)Increasing the amount of fly ash in the mortar test piece will increase the proportion of capillary pores in the range of 10-100 nm,resulting in a significant increase in capillary adsorption and transmission characteristics.Compared with the PO sample without fly ash,the 10-100 nm capillary pores of the 15%,30%,and 45% fly ash mortar specimens were increased by 11.2%,40.1%,and 73.2%,respectively.Capillary adsorption transmission of sodium sulfate solution.The rate is increased by 12.15%,26.78%,53.49%.(2)With the increasement of fly ash content,the mortar test piece increases the concentration of sulfate ions in the salt crystallization area above the liquid level of the test piece.Compared with the PO sample without fly ash,the volume-loss of 15%,30%and 45% fly ash mortar specimens after erosion increased by 82.6%,129.4% and 274.4%,and the mass loss of mortar specimens increased by 160%,533.3%,1133.3%.It showsthat the mortar specimens can further refine the pores with the increase of the fly ash content.In low humidity environment,it is more conducive to the increase of the capillary adsorption transmission rate of the sulfate solution,causing more serious physical salt crystal erosion and damage.(3)Under different humidity environments,the lower the external environment humidity,the faster the capillary absorption and transmission rate of the mortar with different fly ash content.Compared with RH = 35%,the capillary adsorption transfer rate of FA15,FA30 and FA45 decreased by 38.32%,46.96% and 28.55%,41.73% and13.88%,27.24% when RH = 65% and RH = 98%,respectively.The faster the capillary adsorption transfer rate,the more obvious the salt crystal damage of the mortar.In the medium and low humidity environment,the incorporation of fly ash will aggravate the sulfate erosion and destruction of mortar because of salt crystallization,and the incorporation of fly ash at RH = 98% can improve the corrosion resistance of the test piece to a certain extent.Under the double action of physical salt crystallization and ettringite,gypsum and other erosion products,the mortar is severely peeled off,and the RH = 98% mortar surface is basically free of salt crystal erosion and erosion of ettringite or gypsum.product.(4)The mortar partially immersed in sodium sulfate solution has serious salt crystals above the liquid surface,accompanied by the formation of ettringite and gypsum,which leads to severe exfoliation of the crystal area.The incorporation of fly ash and slag cannot improve its resistance erosion performance,but the addition of 10% silica fume can effectively reduce the capillary adsorption of the solution and reduce the erosion damage of the specimen.The surface layer above the liquid surface of the mortar half immersed in the magnesium sulfate solution is basically not damaged,but a large amount of gypsum is formed inside the mortar below the liquid surface to cause surface softening and strength reduction.A large amount of ettringite and gypsum are generated in the part above the mortar liquid surface half-immersed in the ammonium sulfate solution to cause expansion and cracking of the mortar specimen.The mortar below the liquid surface mainly produces a large amount of gypsum,which causes the mortar specimen to soften and reduce strength.