Prevention of Alkali-Silica Reaction in massive concrete structures: Laboratory and field correlation

Abstract

Due to the current concerns about the reliability of laboratory test methods used to assess the long-term potential alkali-reactivity of slow or moderately reactive aggregates, as well as the long-term effectiveness of preventive measures against the deleterious development of ASR, in 2008, EDP in collaboration with LNEC initiated a comparative field and laboratory research program to obtain a better understanding on the reliability of laboratory test procedures in representing and forecasting field performance. To accomplish this, in addition to a laboratory test campaign, an in-situ outdoor exposure testing site was created, in 2016, at the Foz Tua dam (Portugal). The hydroelectric scheme was built between 2011 and 2017. The laboratory testing campaign to assess the effectiveness of fly ash in preventing deleterious development of ASR in the dam concrete included petrographic examination of the aggregates, chemical analysis of the cement and fly ash, and expansion tests on mortar and concrete prisms produced with materials of the same provenance as those used in the dam construction. The in-situ testing campaign, involving large concrete specimens cast both in the laboratory and in-situ, includes monitoring of expansion, periodic measurement of cracks, periodic determination of the velocity of propagation of pulses of ultrasonic longitudinal waves, stiffness damage testing, determination of concrete compressive strength, and determination of concrete alkali content. Up to this moment, no expansion was detected in the field specimens. As expected, so far, no structural or visual evidences of ASR development were detected in the dam.