ABSTRACT
ABSTRACT: When certain aggregates containing silica react with a highly alkaline solution, an alkali-silica gel may form, e.g., ‘Alkali-Silica Reaction (ASR)’. This gel may subsequently expand in the presence of moisture, causing wide-spread cracking in structures composed of these materials. Although the mechanisms and manifestation of ASR in portland cement concrete pavements and structures has been extensively documented over the past several decades, the possibility of ASR formation in asphalt concrete mixtures has received little attention until recently. In this study, asphalt mixtures were tested to determine whether alkali-silica reaction occurs in asphalt containing reactive aggregate and calcium hydroxide when exposed to potassium acetate deicing solution. Two aggregates: ottawa sand (non-reactive aggregate) and fused silica (reactive aggregate) were investigated. Various soaking solutions were studied, including: water, sodium hydroxide solution, and potassium acetate solution saturated with calcium hydroxide. Samples were conditioned at 80°C for 7 days. Compelling evidence of alkali-silica reaction in mixtures containing the fused silica was observed, including: 1) gel formation in mixtures conditioned in the potassium acetate plus calcium hydroxide solution; 2) expansion and surface cracking in mixtures conditioned in the sodium hydroxide solution, and; 3) decreased fracture energy of mixtures conditioned in a sodium hydroxide or potassium acetate plus calcium hydroxide solution. Additional testing and field validation is still needed to fully understand the practical implications of ASR formation in asphalt mixtures and, if needed, to develop appropriate material specifications to avoid problems associated with ASR formation.
