Research On Effect And Mechanism Of Inorganic Additives On Concrete Carbonation Performance

Concrete as the current widely used building materials would be damaged due to avariety of factors in a real environment. Among them, the carbonation damage is one ofthe most common problems and the loss is very serious. At present, inorganic earlystrength agent is used by many commercial concrete mixing plant and field mixingconstruction in order to shorten the curing time of concrete and improve the earlystrength quickly. However, the effect of inorganic salts on carbonization performance ofconcrete is rarely reported.This paper selects four kinds of inorganic salts which are most commonly used athome and abroad, including sulfate, chloride salt, carbonate and nitrite to systematicallystudy the effect of inorganic additives on cement mortar and concrete carbonizationperformance by the method of rapid carbonization. The results show that:(1) comparedwith the benchmark specimen, the carbonation depth of specimen mixed with four kindsof inorganic salts is reduced and the carbonation resistance of the specimens wasimproved. The carbonation resistance of the specimen mixed NaCl increases maximumand Na2CO3increases minimum.(2) With the increase of dosage of inorganic salt, thecarbonation depth of specimen mixed Na2SO4is increased, mixed NaCl and Na2CO3isdecreased, the carbonation depth of mixed NaNO2specimen of is minimum under thedosage of1.0%.(3) The carbonation depth of concrete obviously bigger than thecarbonation depth of cement mortar for four kinds of inorganic salts.(4) With thegrowth of the age, the carbonation speed gradually decreases for all specimens.The effect of inorganic salts on the density of specimen is studied by the compressive strength and the permeability resistance, and through the saturatedsolubility of calcium hydroxide for the analysis of inorganic salts on the content ofcalcium ions in the pore solution. Taking two aspects reasons in consideration, theeffects of inorganic salts on the properties of concrete carbonation resistance mechanismis studied. The results show that:(1) Adding Na2SO4can generate AFt and NaCl can generate a salt called Friedel toincrease density of specimen, thus it can improve the compressive strength andpermeability resistance and benefit the raise of the carbonation resistance of thespecimens, but the two salts cause the saturated solubility of calcium hydroxideincreases and reduce the specimen carbonation resistance. Finally, adding Na2SO4andNaCl can improve the carbonation resistance of the specimens.(2) Adding Na2CO3can generate CaCO3to increase density of specimen, thus itcan improve the compressive strength and permeability resistance. As the dosage ofNa2CO3increases, the saturated solubility of calcium hydroxide decreases sharply. Thetwo aspects reasons are beneficial to the improvement of the carbonation resistanceperformance. But the carbonation resistance of the specimen mixed Na2CO3increasesminimum, considering the compactness is the main factor that influence the inorganicsalts on the properties of concrete carbonation, the compressive strength andpermeability resistance of the specimen mixed Na2CO3increases minimum led to thecompactness increases minimum. Eventually, the carbonation resistance of the specimenmixed Na2CO3increases minimum.(3) Adding NaNO2can accelerate the formation of hydration products to increasedensity of specimen and benefits to the raise of the carbonation resistance of thespecimens. As the dosage of NaNO2increases, the saturated solubility of calciumhydroxide increases, it is not conducive to improve the performance of carbonation.Finally, adding NaNO2can improve the carbonation resistance of the specimens andunder1.0%NaNO2content has the best effect, under consideration is in the content ofpore structure have the best effect led to the highest density.