Study On Sulfate Resistance Of Semi-flexible Pavement Grouted Cement Mortar

The semi-flexible pavement is a new type of pavement that combines asphalt pavement and cement pavement.This pavement adopts their good points and avoids their shortcomings and has a good development prospect.The semi-flexible pavement is mainly composed of the porous asphalt mixture and the gro uted cement mortar.When the performance of both sides is excellent and closely combined,the semi-flexible pavement will have a good effect.However,wh en this new type of pavement is used in different environments,the durability of the material is a concern.Grouted cement mortars poured in semi-flexible pavements need to have good fluidity,certain strength and small shrinkage rate.When a large-pore aspha lt concrete pavement embedded with grouted cement mortar is applied to a sulfate-eroded area,SO₄^2-reacts with the hydration product of the grouted cement mortar to form an expansion-destructive substance,resulting in a decrease in the overall strength of the road surface.Therefore,based on the research results at domestic and foreign,this paper focuses on the durability of semi-flexible pavement grouted cement mortar in the process of sulfate attack.The main conc lusions of the paper are as follows:?1?By means of the range analysis in the orthogonal test,The influence level of the five factors?water-to-binder ratio,sand-to-binder ratio,fly ash dosa ge,silica ash dosage,water reducing agent dosage?on the basic properties bef ore the sulfate attack and the mechanical properties during the wet and dry cycle 60d of grouted cement mortar were studied.The results show that the water-binder ratio has a significant effect on the performance before and after sulfate attack.Before the sulfate attack,the fly ash has a great influence on the work performance and mechanical properties,and the sand-to-binder ratio also has a certain influence on the mechanical properties;the water reducer has a great influence on the volume stability.After sulfate attack,the fly ash has a gre ater influence on the compressive strength.The sand-cement ratio has a greater influence on the flexural strength,and the influence of silica fume on the strength is gradually enhanced.?2?Determine the mixing ratio of cement mortar with the resist coefficient as the index:the water-to-binder ratio is 0.5,the sand-to-binder ratio is 0.2%,the fly ash is 25%,the silica ash is 2.5%,and the water reducing agent is 0.3%.?3?Using the visual analysis method in the orthogonal experiment,the strength and mass changes in the process of sulfate attack were studied.When the wet and dry cycle was 20d,the turning point of the strength change appeared:the initial strength increased rapidly and increased after 20d.It tends to be slow and then begins to fall.It was also found that the mass change rate of the wet and dry cycle 20d grew faster when analyzing the quality change.?4?The combination of scanning electron microscopy and X-ray diffraction explains the cause of macroscopic performance changes.The cement mortar specimens with lower water gel?0.5?have less void distribution in the magnified 100 times SEM image,while the water gel has higher void?0.6?specimens with more void distribution,which causes SO₄^2-to enter the high water-to-bind er ratio of the specimen to cause erosion damage;In the wet and dry cycle 20d,ettringite and gypsum are present in the microscopic products,and the occurrence of both inhibits the growth of strength during this period.The growth of mass is mainly based on ettringite and gypsum.When the dry-wet cycle wa s 60d,the Ca?OH?₂ content in the grouted cement mortar specimens with high water-to-binder ratio decreased significantly,and the macroscopic performance showed that the strength of the specimens decreased or even fractured.