Evaluation of alkali-silica reaction evolution in concrete using ultrasonic tests

Abstract

Concrete structures may be at risk to deteriorate by alkali-silica reaction (ASR), when they are maintained under the conditions supporting the reaction. This reaction causes the expansion of concrete and generates microcracking in the interior part and macrocracking on the surface of concrete. This transformation can lead to serious durability problems in concrete structures, which decrease their technical and economical management. The aim of this study is to monitor the damage due to ASR progression using mechanical and nondestructive tests on specimens of various scales: mortars, laboratory concrete and cores collected from a large hydraulic structure. Two Canadian crushed aggregates were used: Spratt limestone as a reactive aggregate and Limeridge limestone as a non-reactive aggregate. Two mortars and two concretes were made from these aggregates. Mortars were made according to Canadian standard CSA A23.2-25A and stored at 38[degré]C in 1 molar NaOH, solution and concretes were made and stored at 38[degré]C in humid air (R.H>90%) according to Canadian standard CSA A23.2-14A. Also two types of concrete cores containing reactive aggregates (siliceous clayey limestone and Potsdam sandstone) from two concrete locks affected by ASR were kept at 38[degré]Cin 1 molar NaOH solution. Expansion and mass variation of all specimens were measured regularly during the reaction evolution. In a first step, the properties of aggregates were characterized and their reactive silica content was measured. Non-destructive test methods were based on measurement of ultrasonic pulse velocity and resonant frequencies (longitudinal and transversal) of mortar, concrete and concrete cores. Also some other investigations were performed on the specimens: compressive and tensile strength, modulus of elasticity, non linear acoustic test, petrographic analysis by SEM and Damage Rating Index measurement. The main observations and recommendations are: (1) Measurement of elastic modulus of elasticity is the best mechanical test to assessing ASR damage in concrete. (2) The relation was observed between the expansion of mortars and the variation in its petrography features. (3) There was a good relationship between expansion and the degree of damage associated by ASR in concrete and concrete cores assessed by Damage Rating Index method. (4) Measurement of non linear parameters and resonant frequencies are the best nondestructive techniques for assessing ASR progression. A direct correlation was shown between the expansion of concrete cores and the reduction of dynamic modulus and increasing the nonlinear parameters.