Reliability of AMBT and CPT in testing the effectiveness of SCM to mitigate alkali–silica reaction of field concrete

Abstract

This paper examines the reliability of the Australian Standards accelerated mortar bar test (AMBT) and concrete prism test (CPT), AS 1141.60.1 and 60.2, respectively, and the potential for extending these standard test methods to the determination of the type and dosage of supplementary cementitious materials (SCMs) required to mitigate deleterious alkali-silica reaction(ASR) in a similar manner to the corresponding ASTMC1567 and CSAA23.2-28A. Both AMBT and CPT have their strengths and limitations, however, their overwhelming value is in the availability of laboratory test results and their correlation with long-term performance (up to 20 years) of large concrete blocks and structural elements. Since Australia has no existing field exposure site, this paper uses reported data from CANMET’s and Ontario Hydro’s outdoor exposure sites in Ottawa and Kingston, respectively, in Canada and the 18-year exposure site data from the BRE site in the UK to demonstrate the efficacy of the AMBT and CPT approaches to evaluation of ASR reactivity and ASR mitigation using SCM blended cements. Good correlations are observed for moderately–reactive and highly reactive aggregates used with low-alkali cement and cement with alkali contents up to 0.9 % Na2Oeq. The assessment of reported research demonstrates that both AMBT and CPT have the capacity to predict the long–term performance of structural concrete. In addition, AMBT and 2-year CPT test results for eight Australian reactive aggregates are reported showing the influence of SCMs (fly ash and slag) on mitigation of expansion. Whilst both AMBT and CPT demonstrated their potential for assessing SCMs in mitigation of ASR, AMBT was found to be more conservative than CPT and higher SCM dosages were required to achieve a non-reactive classification. The accelerated test data reported coupled with the correlation of AMBT and CPT to the prediction of long term performance of concretes strongly supports the extension of the Australian test methods AS1141.60.1 and 60.2 for the assessment of ASR mitigation using SCMs.