Microscopic analysis of paste and aggregate distresses in pervious concrete in a wet, hard freeze climate

In a recent survey, the durability and condition of 29 in service pervious concrete pavements built in a wet, hard freeze environment were assessed, and 33 core samples were collected. Following up on this survey, this paper identifies some of the common subsurface distresses observed in the core samples with optical microscopy instruments. In the distressed samples, cracks went through the aggregate, paste, and interfacial transition zone (ITZ). The cracks were similar to cracks in conventional concretes that formed due to known freeze/thaw damage. In addition to cracking patterns, it was discovered that none of the 33 pervious concrete samples contained the recommended quantity or spacing of entrained air bubbles. There was a lack of entrained air bubbles despite the addition of air-entraining admixtures to all of the pervious concrete mixtures. It is unknown if the lack of entrained air bubbles contributed to the cracks in the pervious concretes.

► Pervious concrete is not consistently durable in wet, hard freeze climate zones.
► Distressed pervious concrete pavements showed subsurface crack patterns.
► Crack patterns similar to cracks caused by known freeze/thaw damage.
► Pervious concrete paste does not entrain air bubbles despite addition of AEA.