Due to recent partial failures of the wearing surfaces at porous concrete pavement BMPs in and around the Denver metropolitan area, I am asking for a temporary moratorium on this BMP until my investigation determines what is causing the failures. 

Sites that have experienced rapid deterioration of the porous concrete wearing surface include:

• Safeway Grocery Store, SE corner of 13^th Ave. and Krameria St., Denver, constructed in 2005.
  Deterioration to the point that usability is impaired.

• Vitamin Cottage, NW corner of Colorado Blvd. and Evans Ave., Denver, constructed in 2007.
  Deterioration to the point that usability is impaired.

• Wal-Mart Super Center, NW corner Tower Rd. and I-70, constructed in 2006.
  Deterioration minimal at this time, but similar to the Safeway site in 2007.

• The demonstration site monitored by UDFCD at the Lakewood City maintenance facility (constructed by UDFCD in 2005) has experienced no deterioration yet.

Speculation as to the cause of the failures includes chemical interaction with magnesium chloride, mechanical shearing and/or abrasion by torsional motion of tires, freeze/thaw conditions, improper concrete mix design, and improper placement and/or curing techniques.

I am in contact with a forensic engineering firm specializing in material failures and hope to have an answer soon.  In the meantime, it would be imprudent to construct new porous concrete pavement BMP facilities in this region using the existing specifications for the wearing course.

 

Ken A. MacKenzie, P.E.
Manager, Master Planning Program
Urban Drainage and Flood Control District
2480 W. 26th Ave. Denver, CO 80211
Voice 303.455.6277   Fax 303.455.7880
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