Effect Of Large Amount Of Mineral Blending Compound On Carbonization Resistance Of Concrete

The large amount of mineral admixture in modern concrete will degrade the carbonization resistance of concrete.Therefore,it is of great practical significance and economic benefit to explore the development and change law and microscopic mechanism of carbonization depth of large-amount mineral-doped concrete under the action of different influencing factors,and to provide theoretical support and design suggestions for the design and industrial development of green concrete mix ratio.In this paper,fly ash and slag were selected as alternative cementitious materials,and based on the orthogonal test method,through mechanical test and rapid carbonization test,four influencing factors were set up:single-doped fly ash dosage（20%,40%,60%）,double-doped fly ash+slag powder total doping（40%,60%,80%）,water-to-glue ratio（0.35,0.425,0.5）,particle size matching（Class I S95,Grade I S105,Grade II S95,Grade II S105）,and Particle Size Matching（I Class S95,Grade II S105）.The influence of different parameters on the evolution of the carbonization depth of concrete with large amount of mineral blending was explored,the linear relationship between the flexural resistance,compressive strength and carbonization depth of concrete was obtained by linear regression equation,and the microscopic morphology,types and contents of hydration products before and after carbonization of hardened pure slurry samples were analyzed by microscopic analysis methods such as scanning electron microscopy-energy spectroscopy（SEM-EDS）,X-ray diffraction（XRD）,differential scanning heat-thermogravimetric（DSC-TG）,etc.Explore the causes and micro-mechanisms of macroscopic experiments.The study found that the anti-carbonization performance of concrete deteriorates with the improvement of mineral admixture,when the water-to-glue ratio is 0.35,the amount of single-doped fly ash should not exceed 40%,the total amount of double-doped fly ash and slag（of which the quality ratio of fly ash and slag is 1:1）should not exceed 60%;when the amount of mixing is 60%,the compound doping II.fly ash and S95 slag can maximize the anti-carbonization performance of concrete;the anti-carbonization performance of concrete is improved with the reduction of the water-to-glue ratio.When designing the mix ratio in the project,a low water-to-glue ratio should be selected as much as possible.Through the fitting of the linear regression equation,it can be known that there is a high linear correlation between the bending resistance and compressive resistance of concrete and the carbonization resistance of concrete;the degree of correlation between the four influencing factors and the carbonization resistance of concrete is obtained through the gray correlation degree calculation,from high to low:water-glue ratio>double-doped fly ash,total slag>single-doped fly ash>particle size matching.The content of Ca（OH）₂crystals in each group of specimens was explored by DSC-TG and XRD experiments,and it was found that with the increase of mineral blending and material doping,the content of Ca（OH）₂crystals inside the concrete was significantly reduced,which was due to the fact that the mineral admixture would consume a large amount of Ca（OH）₂in the concrete pore liquid when the secondary volcanic ash reaction occurred,which although it could compact the microstructure of the concrete to a certain extent and increase its impermeability,it degraded the anti-carburization performance of the concrete.