Study On Performance Degradation Of Reactive Powder Cement-based Materials In Sulfate Environment

Sulfate erosion is one of the factors leading to durability damage of concrete.In China,the widespread distribution of sulfate causes serious damage to concrete structures constructed in saline-alkali soil environment.As a new type of high-performance cement-based composites,the compactness,strength and durability of reactive powder cement-based materials are much better than those of traditional cement-based materials,and are more and more widely used in practical engineering.Therefore,the durability of reactive powder cement-based materials in sulfate environment was studied in this paper,and the results have reference value for the design and evaluation of high durability of reactive powder cement-based materials.In this paper,the durability of reactive powder cement-based materials suffered from dry-wet cycles in sulfate solution was studied by combinnation of macroscopic and microscopic test.The deterioration law of reactive powder cement-based materials under the influence of silica fume content,water-binder ratio and sulfate solution concentration was clarified and related mathematic models were established.The microscopic testing methods such as XED,SEM and TGA-DTG were used to analyze the change of internal structure of cement-based materials and the characteristics and morphology of corrosion products.Based on the pore structure parameters,the fractal dimension model of pore surface was used to study the effect of erosion on the pore structure.The main research contents are as follows:?1?The compressive and flexural strength of reactive powder cement-based materials increases first and then decreases with the increase of silica fume content,and increases with the decrease of water-binder ratio.Reactive powder cement-based material with 15% silica fume has good hydration degree;and it has low internal porosity and good homogeneity of paste at low water-binder ratio.?2?To carry out the durability test of reactive powder cement-based materials under the combined action of sulfate erosion and dry-wet cycle.After dry-wet cycles 30,the macroscopical properties of reactive powder cement-based specimens with 15% silica fume content deteriorated slightly,and the corrosion degree of 5% Na₂SO₄ solution is serious.The attenuation model of mass and compressive strength under the influence of multiple factors is established.?3?Considering the three factors of silica fume content,wet-dry cycle times and sulfate solution concentration,the micro-structure changes,the growth characteristics of main hydration products and the content changes of corrosion products of reactive powder cement-based materials after sulfate and wet-dry cycle were analyzed by means of SEM,XRD and TGA-DTG.After dry-wet cycles 30,the corrosion products with 15% silica fume content increased less,and the corrosion products exposed to 5% Na₂SO₄ solution increased more,and the damage deteriorated more seriously.?4?By MIP testing technology to study the effect of the amount of silica fume,the number of dry-wet cycles and the concentration of sulfate solution on pore structure of reactive powder cement-based materials under sulfate attack environment.After dry-wet cycles 30,the porosity of silica fume 15% is lower,and the porosity of gel hole is relatively high.The porosity of 5% Na₂SO₄ solution is higher,the harmful pore occupied a higher proportion,and the pore surface structure is more complicated.The results indicate that 15% silica fume has less corrosion products and low pore surface complexity;the specimens has more corrosion products and the pore surface is more complex under 5% Na₂SO₄ solution.