Experimental Study Of Mortar, Concrete, Corrosion Resistance Under Simulated Acid Rain Environment

With the development of industrialization, air pollution becomesmore and more serious, and the phenomenon of acid rain appears ratherfrequently in many regions of China. Acid rain corrosion of concretebegins to be one of the most important factors that influence the servicelife of concrete construction. However, there are only very few reportsabout research on acid rain corrosion of concrete in China, and manyparts of the research are still not carried on.Starting from analyzing the acid rain corrosion mechanism ofcementitious materials, this paper discussed the acid rain corrosion ofcement mortar, by corrosion experiments which simulated the conditionof acid rain in typical city of China. Then, the influence of singly addingof fly ash and the addition content, compositely adding of fly ash and slagand the addition content, sand-binder ratio of cement mortar on acid rainresistance of cement mortar was studied. Finally, acid rain corrosionexperiment of concrete was done.Experiment results show that, acid rain corrosion of cementitiousmaterials is the combined effect of H⁺ and SO₄^2-. Acid rain corrosion canresult in significantly decreasing of mechanical properties of cementmortar samples, losing of surface paste and decreasing of weight,expanding of volume, neutralization of paste surface, increasing ofporosity of internal structure etc, and ultimately make the samples losetheir workability. H⁺ in acid rain destroys hardened cement paste throughdissolved-erosion layer by layer, because H⁺ can neutralize OH^- inhardened cement paste from the outer to the inner, and dissolve Ca(OH)₂,and decrease pH value, finally make C-S-H gel decompose. Surfacedissolved-erosion by acid rain can make the compact cement mortarsurface become loose, and provide the corrosion environment of anothercorrosive SO₄^2- ion. SO₄^2- corrosion in acid rain condition is gypsum-typesulphate attacking, and it can make Ca(OH)₂ crystals transform intogypsum, and expanded destroy the internal of cementitious materials. Addition of fly ash makes the cement paste samples appear more serioussurface dissolved-erosion, and bigger addition content leads to easierneutralization by acid rain. Furthermore, fly ash has not improved themechanical properties, weight variety and volume variety. It can beconcluded that singly adding of fly ash is disadvantageous to improveacid rain resistance. In the condition of not so low pH value and relativelyhigh concentration of SO₄^2- ion, fly ash-slag-cement ternary compoundsystem can produce overstack effect, and improve the internal porestructure remarkably. Using compositely adding technique of fly ash andslag reasonably to improve the mechanical properties about acid rainresistance of cementitious materials has positive significance. It can beconcluded from experiment that, in the acid rain condition of pH=3.5, andconcentration of SO₄^2- is 0.1mol/L, the best formula is 10wt% fly ash and10wt% slag. The best sand-binder ratio of acid rain resistance of cementmortar is 2.5:1.According to the methods which were used to study the acid raincorrosion of cementitious materials, consistent conclusions are obtainedby using immersion dry-wet cycle corrosion and by using spray dry-wetcycle corrosion.