Walker Consultants performed a condition assessment of three below ground glycol retention tanks at the Des Moines International Airport. These tanks are used to temporarily hold runoff from airplane de-icing paving during colder months.
Assessment of the tanks required Walker’s specialty-trained confined space entrants and attendants to perform the investigation. Two tanks were cast-in-place, three-bay barrel tanks and one was a large tank with cast-in-place walls and floor with precast, pre-stressed concrete columns, inverted tee beams, and field-topped double tee cap. The assessment was comprised of visual observations with limited elastic wave testing (dragging chains on floor surfaces) and tapping vertical and overhead surfaces.
Regular maintenance items, such as leaking construction joints, were observed at the barrel tanks. During the observation of the large tank, concrete aggregate and paste deterioration were recorded and elastic wave testing was found to be ineffective. Walker recommended additional testing services and performed testing consisting of petrography and infrared analysis of concrete samples. The petrographic analysis revealed chemical attack, secondary ettringite, poor air entrainment of the concrete matrix, and microcracking at the cap from improper curing. Infrared analysis also revealed chemical attack and identified the presence of a sealer product that was likely applied to cast-in-place concrete at the time of construction. The restoration phase of the large tank is being planned at this time and will likely occur over a few years due budget constraints.