Each spring, I’ve noticed that the sidewalks that have been replaced in the last couple of years are in a state of disrepair. Large sections of them show flaking and crumbling. Knowing that we are scheduled to get some new sidewalks in the neighborhood this year, I asked DDOT for more information on the scaling issue and if our new sidewalks would continue to deteriorate.
I was impressed with the thoroughness of DDOT’s response, and that they have a plan for correcting the problem. What follows is DDOT’s response:
The District maintains over 1,600 centerline miles of roadway. Many of these roadways have sidewalks on both sides. We noticed that some sidewalks in the district had shown flaking and delamination. This sidewalk concrete issue is not restricted to the District and is in fact regional.
Literature review indicates the factors known to aggravate scaling in a cyclic freezing and thawing environment are:
- (a) improper construction practices (improper finishing and inadequate curing);
- (b) exposure to corrosive salts (such as magnesium or ammonium);
- (c) exposure to sodium or calcium chloride salts at an early age prior to maturity; and
- (d) exposure of an inherently poor quality and/or poorly constructed concrete to deicing salts.
Following the extensive sidewalk damage on DDOT’s Riggs Road, NE project, we took two approaches to the problem:
- (a) To protect the flaked sidewalk concrete from further damage, we applied a product to seal and resurface segments of the sidewalk and to monitor it overtime to evaluate the performance; and
- (b) Took concrete cores and performed petrographic analysis.
The resurfacing with the product to seal and resurface segments of the sidewalk was conducted in August 2014 and its performance will be evaluated this summer. The sidewalk concrete cores from Riggs Road were evaluated at the federal Turner Fairbanks Research Center in Virginia. The finding from the report indicates that the cause of scaling of the sidewalk was most likely related to poor-air void system in conjunction with improper finishing (premature finishing of the surface before bleeding was completed) of the surface. This surface was then exposed to winter conditions (freezing and thawing in presence of deicing salts, and accumulations of snow and ice), particularly the severe winter of 2013-2014.
DDOT has initiated a citywide survey of the condition of sidewalk concrete and if the trial at Riggs Road, NE, is successful, a city wide repair task will be planned and scheduled. In order to minimize such issues in the future, we have assigned an experienced engineer to vigorously inspect all constructions sites on a daily basis and enforce the Standard Specifications requirements, and any non-complying concrete, asphalt and other construction materials are rejected and replaced with approved materials. Furthermore, quality control managers of concrete producers are required to test and document concrete for slump and air content before it leaves the plants.