In order to predict potential aggregate alkali-silica reactivity, there was development and assessment of an ultra-accelerated testing method using advanced nonlinear ultrasonic techniques. There was observation of the nonlinear interaction of propagating acoustic waves being affected by very early alkali-silica reaction (ASR) gel formation during standard accelerated mortar bar exposure (ASTM C1260 or AASHTO T 303). There was observation, furthermore, of a clear distinction of varying reactivity in the nonlinearity parameter for three different aggregates. Compared to a 14-day standard accelerated mortar bar test method test period, aggregate reactivity could be distinguished in as early as four days through the spectroscopic technique. Study results suggests that further development of this method could result in very rapid screening of aggregates for alkali reactivity and very early detection of ASR damage in the laboratory.