Rapid Determination of Aggregate Alkali-Silica Reactivity and Threshold Alkalinity and Estimation of SCM Dosage Using Innovative Test Methods

Abstract

The prevailing practice entails a uniform, relatively modest level of alkali loading (typically 2.1–2.4 kg/m³) across all concrete mixes, disregarding the specific application. Essentially, this one-size-fits-all approach overlooks the crucial aspect of determining Aggregate Threshold Alkalinity (THA) for Alkali-Silica Reactivity (ASR). There is a pressing demand for innovative, swift, and dependable methods to gauge aggregate reactivity and THA.

To tackle these challenges, the authors have devised expeditious ASR testing techniques, including an Aggregate Chemical Test (AASHTO T364) and an Accelerated Concrete Cylinder Test (ACCT, AASHTO TP142). They have also introduced a novel performance-based method for estimating aggregate THA. Arrhenius rate theory and insights from materials science on reaction and expansion mechanisms were utilized to interpret the data and determine the Composite Activation Parameter (CAP) as an indicator of aggregate reactivity. A lower CAP signifies higher reactivity. This CAP-based approach exhibited a better comparison with ASTM C1293-based reactivity measurements and facilitated a consistent identification of aggregates belonging to false positive and negative attributes.

A procedure based on AASHTO T364 has been developed to ascertain Aggregate THA by analyzing the CAP-alkalinity relationship. The relationship between Pore Solution Alkalinity (PSA) and Aggregate THA (PSA ≤ THA) serves as the foundation for estimating Supplementary Cementitious Material (SCM) dosage to mitigate ASR in concrete. This approach facilitates rapid assessment of aggregate THA, determines appropriate concrete alkali loading, and estimates SCM dosage for effective ASR mitigation.