Calcined Clay Pozzolan as an Admixture to Mitigate the Alkali-Silica Reaction in Concrete

James Sarfo-Ansah,Eugene Atiemo,Kwabena Appiah Boakye,Albert A Adjaottor,Delali Adjei

doi:10.4236/msce.2014.25004

Abstract

Calcined clay pozzolan has been used to replace varying portions of high alkali Portland limestone cement in order to study its effect on the alkali-silica reaction (ASR). Portland limestone cement used for the study had a total Na2Oeq of 4.32. Mortar-bar expansion decreased as pozzolan content in the cement increased. The highest expansion was recorded for reference bars with no pozzolan, reaching a maximum of 0.35% at 42 days whilst the expansion was reduced by between 42.5% and 107.8% at 14 days and between 9.4% and 16.4% at 84 days with increasing calcined clay pozzolan content. Mortar bars with 25% pozzolan were the least expansive recording expansion less than 0.1% at all test ages. X-ray diffractometry of the hydrated blended cement paste powders showed the formation of stable calcium silicates in increasing quantities whilst the presence of expansive alkali-silica gel, responsible for ASR expansion, decreased as pozzolan content increased. The study confirms that calcined clay pozzolan has an influence on ASR in mortar bars and causes a significant reduction in expansion at a replacement level of 25%.

Highlights

Materials and MethodsCalcined clay pozzolan, produced by CSIR-BRRI, class 32.5R Portland limestone cement (PLC) manufactured by Ghana Cement Company Limited (GHACEM) were used for the research
How to cite this paper: Sarfo-Ansah, J., et al (2014) Calcined Clay Pozzolan as an Admixture to Mitigate the Alkali-Silica Reaction in Concrete
Calcined clay pozzolan has been shown in the study to have an influence on the alkali-silica reaction

Summary

Materials and Methods

Calcined clay pozzolan, produced by CSIR-BRRI, class 32.5R Portland limestone cement (PLC) manufactured by Ghana Cement Company Limited (GHACEM) were used for the research. Total cement to aggregate ratio of 1:3 was used in forming mortar bars of size 25 mm × 25 mm × 285 mm using water to cement ratio of 0.5 instead of the specified 0.47 to cater for workability of the pozzolan cement mortar. After initial length readings were taken, the specimens were further cured for 27 days in water at 20 ̊C to enable the pozzolanic reaction proceed to an appreciable rate. The bars were further cured in water at 80 ̊C for 24 h after which zero readings of the bars were measured using a length comparator recommended in ASTM C 490 [25]. After taking the initial lengths, the bars were placed in 1N NaOH solution at 80 ̊C and subsequent lengths measurements were taken at 14, 42, 56 and 84 days. The morphology of the hydrated samples was studied with an Olympus BX 41 TF optical microscope

Physical and Chemical Evaluation

Mortar Bar Expansion

Hydration Products and Surface Examination

Conclusions