What is low-chert aggregate and what benefits do they provide?
Chert, which is found to some degree in most aggregate deposits used to produce concrete in Southeastern Wisconsin, is porous aggregate (sand, gravel, or crushed stone) with low-resistance to weathering. Chert can cause surface defects, known as “pop outs,” in exterior concrete flatwork applications. Pop outs are indentations in a concrete slab surface created when porous aggregate picks up moisture, freezes, expands, and fractures, taking a portion of the concrete slab surface mortar with it. Pop outs can be minimized by using low-chert aggregates, which contains a specified maximum percentage limit of porous aggregates. Generally this percentage ranges from 95-98% chert-free.
