ASR often caused from using bad aggregate composed of disorganized silica-chain rocks, like what you'd find in volcanics like obsidian. Or from microcrystalline quartz like chert or opal, or strained quartz like quartzite. Not many volcanics in local quarries around Austin so potential bad aggregate could be from a microcrystalline form like chert.
Anyone figure out the source quarry yet?
The additives (or lack of additives in this case) are also a factor, and based on article above, sounds like that is a big factor. Fly ash, silica fume, and slag all additives that help mitigate against ASR formation.
With all the construction occuring in central Texas these days, I wonder if the ASR problem will extend beyond pools due to general lack of availability of additives like article suggests. Or maybe it's isolated to the pool subcontractor using bad aggregate and/or saving money not adding the additives.