Rapid evaluation of the threshold alkali level for alkali-reactive siliceous aggregates in concrete

A modified version of the ultra-accelerated concrete prism expansion test in alkaline solutions at 150 degrees C (testing concrete mixes at varying alkali content of concrete) was investigated in order to ascertain the reliability of this test method for evaluating the threshold alkali levels (TAL) of alkali-reactive siliceous aggregates in concrete. Five natural sands of known field performance were tested and their TAL values determined by the ultra-accelerated test were compared with those obtained from concrete prism expansion tests at 38 degrees C and 100% RH. A correlation between the threshold alkali level of the sands and their microstructural disorder coefficient, Cd, as measured by infrared spectroscopy, was also attempted. The modified ultra-accelerated concrete prism test proved to be a rapid and reliable method for evaluating the threshold alkali level of reactive siliceous aggregates in concrete, provided that an expansion limit of 0.11% at 3 weeks was taken as the reactivity judgement criterion for this test. The threshold alkali level proved to be an appropriate reactivity parameter for the selection of alkali-reactive siliceous aggregates. Also, the existence of a straight-line relationship between TAL and Cd suggested the possibility of developing a new test methodology for estimating TAL, based on Cd measurements by infrared spectroscopy. (C) 1999 Elsevier Science Ltd. All rights reserved.