| Nitrite is the best corrosion inhibitor which used most widely and largest quantities.Generally there are two existential forms of nitrite when it is mixed into concrete,one is the free nitrite ion which can move around freely in the pores of concrete,the other is the binded nitrite ion which cannot move freely.It is generally believed that only the free nitrite ions present in the pores of the concrete can play the role of rust resistance,when it moves to the steel surface.Consequently,the concentration of free nitrite ions in concrete will directly affect the effect of corrosion inhibition.In order to improve the effect of nitrite ion corrosion resistance,the effects of mixing ratio,curing condition and external environment on the content of free nitrite ion in cement paste were studied.The main research results are as follows:In this paper,the effects of the type and dosage of nitrite,the water-cement ratio,the age,the admixture and the curing temperature on the concentration of nitrite ion in cement paste were studied.The results show as below: the concentration of free nitrite ions in cement drop along with the age,the concentration of ion in the early stage decreased rapidly,and the concentration decreased slowly after 14 days.The higher curing temperature will lead to the lower ratio of free nitrite ion and higer ratio of nitrite consolidation,but the temperature will only affect the curing rate of the nitrite ion in the early stage,and it has little effect at later stage.The larger the water-cement ratio is,the smaller the free nitrite ion concentration is,the larger the curing rate is.The curing amount of nitrite ion increased with the increase of the amount of incorporation,but the curing rate decreased with the increase of the content of the mixture.Sodium nitrite will increase the amount of C-S-H gel and increase the curing rate.Fly ash admixture will decline the ratio of nitrite consolidation and slag has the contrary effect,when mixing the fly ash and slag with the volume proportion of 1:1,the ratio of nitrite consolidation reaches the lowest.2.The effects of doped chloride ion and external chloride environment on the concentration of free nitrite ion in cement paste were studied.The results show as below: if the chloride ion and nitrite ion are doped in cement,when the amount of one doping ion increases,the concentration of another ion in cement paste will also increase,and the cement will only occur chemical solidification with chloride.The cement paste will have more free nitrite ions in the chloride solution than the one soaked in water,the main reason is due to competitive adsorption between ions rather than chemical solidification.3.Calcium nitrite will accelerate the carbonation speed of cement paste,it is harmful to the durability of concrete.In the carbonization zone of cement paste,due to the entry of CO2,the hydration products of NO2-AFm and C-S-H gel are decomposed,they release the nitrite ions which have solidified,it leads to concentration of free nitrite ion in carbonized area is higher than the Non-carbonized area,but the nitrite ions do not migrate;Silicon will immigrate into the non-carbonized area from the carbonized area,and the speed of immigration is slightly faster than the speed of carbonization,it leads to more of C-S-H gel are produced in the carbonized area,curing rate of free nitrite ions also will be improved,so the concentration of nitrite in non-carbonized area is smaller than the before of carbonation.In this paper,the effects of various factors on the content of free nitrite ion in cement paste were studied by means of quantitative analysis and micro-means.It provides a new theoretical basis and technical guidance for evaluating the effect of nitrite rust inhibitor,evaluating the age of rust and the application of engineering. |
PDF Full Text Request