Composition Design And Durability Study Of Biomass Silicon Modified Magnesium Oxychloride Cement Protective Concrete

Qinghai is distributed with a large area of saline lakes and saline land,coupled with the harsh and harsh climate environment,which poses a serious challenge to the durability of concrete structures in the region.Most concrete structures withdraw from service early due to durability damage during service.Magnesium oxychloride cement（MOC）is an air hardening cementitious material that does not require standard maintenance.Without modification,it has excellent resistance to salt brine erosion and has broad application prospects in salt lakes and saline soil areas.However,the poor water resistance of MOC results in low salt freezing erosion resistance,which limits its further promotion and application in saline lake saline soil areas.This article is based on the practical demand for concrete durability in the Qinghai Salt Lake region and the coordinated utilization of waste resources,and designs a MOC coating protective concrete modified with biomass silicon,aiming to improve the durability of concrete structures in the salt lake region.The main research content and conclusions are as follo ws:（1）The preparation process and activity effects of highland barley straw ash（HBSA）were studied using a three-stage preparation,three-parameter design,two-dimensional analysis,and two process validation method.The results showed that based on activity index testing,respons e surface optimization design,grey entropy correlation analysis,microstructure testing and characterization,the optimal preparation conditions for active HBSA were determined as follows:the natural burned barley straw ash was calcined for 2 h at 600℃,followed by grinding for 2 h.The HBSA prepared under this condition has the highest activity,with its main component being Si O₂,with a content of up to 61.76%.（2）HBSA modified MOCM composite material（HBSA-MOCM）was prepared by adding HBSA under the optimal preparation conditions into MOC mortar（MOCM）in different mixing methods and amounts.Its early performance was tested to preliminarily determine the optimal mixing method and amount of HBSA.Through microstructure testing and characterization,combined with hydration reaction theory analysis,the mechanism by which HBSA affects the early performance of MOCM was revealed.The results indicate that the incorporation of HBSA has a significant effect on the early performance of MOCM,and is closely related to the incorporation method and content of HBSA.Incorporating HBSA into MOCM with the external mixing way can achieve better early performance.When the HBSA content is 10%,the working performance,physical properties,mechanical properties,and water resistance of MOCM are improved.The active Si O ₂ in HBSA and the hydration products of MOCM undergo secondary hydration reaction,generating a large number of M-S-H gel,filling harmful pores,refining the pore structure,and enhancing the water stability of the 5-phase crystal.（3）In order to study the salt freeze corrosion resistance of HBSA-MOCM and determine the optimal dosage of HBSA,the durability damage degradation law,morphology characteristics,and pore structure characteristics of H BSA-MOCM were studied under salt brine erosion,freeze-thaw erosion,and salt freeze coupling erosion environments.The results indicate that the content of HBSA has a significant effect on the salt,freezing,coupled erosion characteristics,and damage de gradation characteristics of MOCM.When the HBSA content is 10%,the corrosion resistance of MOCM under salt,freezing,and coupled erosion conditions is significantly improved compared to that without HBSA.With the increase of salt,freezing,and coupled erosion cycles,the specific surface area of HBSA-MOCM decreases,the most probable pore size increases,the average pore width increases,a nd the number of micro pores decreases,resulting in the deterioration of pore structure.Moreover,the damage and deterioration of HBSA-MOCM are the most severe in freeze-thaw erosion environments,followed by salt freezing coupled erosion environments,and the lightest in salt brine erosion environments.（4）By studying the interface bonding performance and corrosion resistance of HBSA-MOCM and ordinary concrete,the composition design of MOCM coating protective concrete was determined,and the reliabilit y of HBSA-MOCM and concrete synergistic work was analyzed.The results indicate that the content of HBSA,interface agent,and thickness of the bonding layer have significant effects on the interface performance between HBSA MOCM and concrete.Taking into account the early performance,salt frost resistance,and interface bonding and corrosion resistance of HBSA-MOCM with concrete,the design parameters for the composition of MOCM protective coating should be 10%HBSA added,interface agent applied,and coating thickness of 18 mm.（5）To explore the improvement effect of MOCM protective coating on the durability of concrete,durability tests and electrochemical tests were conducted on the durability damage law of MOCM protective coating on concrete and the corrosion deterioration characteristics of steel bars,in order to evaluate the protective effect of MOCM protective coating on the durability of concrete and the corrosion resistance of steel bars.The results indicate that the MOCM protective coating has a significant protective effect on the durability damage of concrete and the corrosion deterioration of steel bars.After the same erosion cycle,MOCM coated protective concrete has higher compressive strength,relative dynamic elastic modulus,and smaller specimen size deformation compared to ordinary concrete.The corrosion current density of steel bars in concrete protected by MOCM coating is lower and the corrosion rate is slower.The protective effect of MOCM coating increases the AC impedance of the steel bar corrosion process and delays the corrosion rate of the steel bar.