Impact of Fly Ash and Metakaoline on the Crack Resistance and Shrinkage of Concrete

Drying shrinkage is one of the important durability properties that poses a direct impact on the other properties such as permeability, chloride diffusivity, expansion of crack width, strength. The onset of shrinkage cracks and its propagation with time are the key issues which have to be investigated. The formation and expansion of cracks weakens the interior structure of the concrete as it paves the way for the major reactive chemicals to diffuse inside the core structure. A detailed and comparative study is being done where first set of specimens were prepared with replacement levels of 0%, 15%, 20%, 25% and 30% fly ash (FA) for cement and second set of specimens were prepared with 0%, 4.5%, 9%, 13.5%, 18% of metakaoline (MK) replaced with cement. The specimens were tested for drying shrinkage, restrained shrinkage cracks and compressive strength. The results obtained from testing first, second set of specimens were discussed and compared with the results obtained from testing of third set of specimens prepared by the combined mix of FA + MK with replacements levels of 15%FA + 4.5%MK, 20%FA + 9%MK, 25%FA + 13.5%MK, 30%FA + 18%MK. It is seen that the combined mix of 25%FA + 13.5%MK significantly improved the strength, drying shrinkage and resistance to crack width formation than individual substitutions of MK and FA.

Automated summary

Drying shrinkage is an important durability property of concrete that directly affects other properties. This study compared the effects of replacing cement with fly ash (FA) and metakaoline (MK) on drying shrinkage and strength. The results showed that a combination of 25% FA and 13.5% MK significantly improved the strength, drying shrinkage, and resistance to crack width formation in concrete.