Research On Acid Resistance Of Alkali-activated Cementitious Materials

Civil engineering in acid corrosive environments requires a large amount of acid resistant cementitious materials,but Portland cement has poor corrosion resistance in acid environments.In contrast,alkali-activated slag has better acid corrosion resistance,which is related to less calcium in its composition.The calcium content in fly ash is lower than that of slag,and it can also be used to prepare alkali-activated cementitious materials.The alkali-activated slag can improve the acid resistance of fly ash,but there are few related studies.In this paper,slag and fly ash were used as raw materials to prepare different proportions of alkali-activated fly ash slag mortar,and its corrosion resistance in hydrochloric acid,nitric acid and sulfuric acid solution was studied.By observing the appearance change of the mortar specimen before and after acid corrosion,the quality loss rate,strength loss rate and corrosion depth of the mortar specimen after acid corrosion were studied to study the acid corrosion resistance of the alkali-activated fly ash slag cementitious material,and XRD and The mechanism of action was analyzed by SEM test.The main research contents and results are as follows:(1)Through the immersion test of different ages,the changes of appearance,mass loss rate,strength loss rate and corrosion depth of alkali-activated slag and alkaliactivated fly ash slag mortar in acid solution were determined.The results show that the corrosion of the three acids leads to the lightening of the surface of the test piece and the exposure of the aggregate,and the cracking of the test piece in the sulfuric acid.The mass loss rate and the strength loss rate are as follows: ordinary Portland cement mortar> alkali-activated slag mortar> alkali-activated fly ash slag mortar;and with the increase of fly ash content,the mass loss rate and strength loss rate are both gradually decreases.However,the corrosion depth of alkali-activated fly ash slag mortar is greater than that of alkali-activated slag mortar,and increases with the increase of fly ash content.(2)The corrosion law of different alkali-activated cementitious materials in hydrochloric acid,nitric acid and sulfuric acid environment was compared by immersion test at different ages.The results show that the corrosion marks of the test piece in the nitric acid solution are more obvious.The mass loss rate in the three solutions is as follows: nitric acid > hydrochloric acid > sulfuric acid.The overall strength loss also appears as: nitric acid > hydrochloric acid > sulfuric acid.However,when the fly ash content is less than 60%,the strength loss rate of the test piece in the sulfuric acid solution at the late stage of corrosion exceeds that of the test piece in the nitric acid.The corrosion depth of the three acid solutions to the alkali-activated slag mortar and the alkali-activated slag fly ash mortar was close to the initial stage,and the overall performance in the latter stage was: sulfuric acid>nitric acid>hydrochloric acid.(3)The corrosion mechanism was further analyzed by XRD and SEM.XRD analysis shows that the characteristic peaks of the original hydrated calcium silicate disappeared after the alkali-activated slag was corroded by hydrochloric acid,nitric acid and sulfuric acid solution,and the characteristic peak of silica appeared.After the alkali-activated fly ash was corroded by three acids,the original quartz and mullite characteristic peaks did not change.Characteristic peaks of gypsum also appear in alkali-activated slag and alkaliactivated fly ash which are corroded by sulfuric acid solution.The alkali-activated slag mortar is corroded by hydrochloric acid and nitric acid to cause a large number of cracks and holes,and a large amount of gypsum is formed after being corroded by sulfuric acid.There are fewer holes and gypsum formed in the alkali-activated fly ash slag mortar with 80% fly ash.