Study On Evaluation Methodology And Influencing Factors Of Carbonation Of Concrete With High Content Mineral Admixture

Nowadays, the use of mineral admixture is becoming more and more widespreadin our country. In practice, in order to save energy, protect the environment and raisethe economic efficiency, it is hoped that the content of mineral admixture in theconcrete should be as high as possible. However, when clinker content is low in theconcrete and the mineral admixture reacts with Ca(OH)2to play its activity, theconcrete mixed with “binder with poor clinker content” is easier to be carbonatedunder the condition of little akali reserve. Once the concrete begins to carbonate, thesteel rusts and the load capacity of structural element decreases, which leads to a badinfluence to the reliability. Once the anti-carbonation property of concrete structurecannot be guaranteed, serious accidents will probably happen. So it is an importantsubject to be highly focused. Therefore, the analysis of concrete carbonation is asignificant part of evaluating the durability of the reinforced concrete.The subject investigated in this paper is concrete with high content mineraladmixture. The main contents include the following:(1) the distinguishment andrelation of the concrete anti-carbonation properties between accelerated carbonationmethod and natural carbonation method;(2) to determine the carbonation reactiondegree of concrete under various conditions (water-binder ratio, content of mineraladmixture, total amount of cementitious materials and fly ash-slag ratio);(3) to studycombined influence of different curing times and conditions to concretes withdifferent fly ash contents and under the same strength.The results show that the accelerated carbonation method is able to reflect thepractical situation of concrete carbonation in most cases. But when it comes toevaluate the long-term carbonation properties of concrete with high content mineraladmixture, the results from accelerated carbonation method cannot be applied directly,especially for concretes with the same strength grade. In the matter of influencingfactors for carbonation, the shorter the curing time is, the bigger the water-binderratio is and the higher the content of mineral admixture is, the concrete will be easier to be carbonated. The influence of total amount of cementitious materials and flyash-slag ratio are tiny to carbonation depth of concrete. But under the same conditionconcretes mixed with slag only have a better anti-carbonation ability than that withfly ash only.In order to investigate the microscopic mechanism for the macroscopicappearance of concrete carbonation, TGA test of complex binder was also conducted.The rationality of the explanation for the results of macroscopic test could be furtherverified.At the end of the paper some conclusions are made on test methods and testprocedure, and also some suggestions about research work in the future are given.