Bridge Deck Overlays
I. Flexibilized Epoxy Systems

A. There have been a number of flexibilized epoxy formulations available on the market with flexibility ranging from 10% to 50%.

• Tensile strength:  4,000 psi to 1,000 psi.

• Comprehensive Strength: 10,000 psi to 5,000 psi. 

B. No data is available on these systems in reference to low-temperature flexibility.  Caltrans test labs have studied some flexible epoxy formulations for flexural creep measurement as per California Test Method 419.  These results were disappointing and in their conclusion, flexibilized epoxies tested will be poor candidates for bridge deck overlayments.

C. The data available from the field installation indicate that with epoxies having higher flexibility (at room temperature), the following problems are observed.

• i.A decline in bond strength with age takes place resulting in lower skid numbers. 

• ii.Aggregate retention declines with aging.

• iii.Delamination of the overlay follows due to steady loss of flexibility and increased differences in coefficient of expansion. 

D. With a higher strength low flexibility material, reflective cracking is quickly apparent.  Furthermore, delamination takes place due to differential in coefficient of expansion. 

E. From the standpoint of waterproofing of the bridge deck, most of the flexibilized epoxy application have failed to supply a reliable waterproofing system.  However from the skidproofing standpoint, these applications have medium to good success for a limited period of time.

F. Epoxy formulations controlled by ASTM Test Methods such as ASTM-C881-87 in its various grades, classifications and types calls for very limited properties which do not control the overall quality of the products performance.  There are many mediocre and low grade products which will easily pass those requirements, but would not perform in the field.  Although it is in an excellent attempts to provide a generic standard specification, from a performance standpoint, a much more detailed specification is required to ensure quality field performance for an extended period (five to ten years). 

II.Epoxy – Urethane Co-Polymer System (FLEXOGRID)

A. POLY-CARB’s FLEXOGRID is the only epoxy-urethane co-polymer that we were able to find that has been used as a bridge deck overlay with any traceable success. 

B. Long-term flexibility.  Test results on installations more than five years old indicate that over 80-90% of it original flexibility was maintained in the system.  Its low temperature flexibility was verified by the tests performed by the California Department of Transportation under their Test 419 for the flexural creep measurements at low temperatures.

C. Effectiveness of waterproofing.  Some six to seven year old bridges were flooded with water and seepage of water was expected through the visible cracks at the bottom of the deck.  The absence of moisture coming through these cracks was conclusive evidence that the FLEXOGRID overlay was effectively waterproofing the bridge deck. Wiss, Janney & Elstner has performed tests on FLEXOGRID

MARK – 163 system based on accelerated weathering as per NCHRP-244 method and concluded complete stoppage of corrosion of rebars present in the concrete saturated with chloride ions.

D. Skid numbers.  FLEXOGRID applications made with silica aggregate have not done very well in maintaining the skid numbers whereas the FLEXOGRID application done with Washington stone have maintained their skid numbers in excess of 55 after four years of its application thus far studied.

E. Long term adhesion to the pavement.  FLEXOGRID applications have been made with manual mixing as well as automated positive displacement equipment.  Isolated bond failure has been traced to hand application done on either a very warm day or a very cold day (below 50^oF).  Machine applications have been successful even at temperatures ranging from 40^oF to 100^oF with one exception where in the very early stages of machine usage, a machine had malfunctioned and produced disproportionate mixing materials in Wisconsin.

F. Performance over patched concrete.  Epoxy-based patching material has not done well due to the coefficient of expansion differential and excessive heat generated in mass use of epoxy-based patching materials (used in early 80’s. 

A total non-compatibility is observed in patches based on magnesium phosphate type of system (SET-45). Satisfactory results were obtained with non-shrink cementitious based patching systems with high strength rapid set properties.  The most successful systems have been found to be rapid setting silica fumed based patching system with extremely high density and high resistance to chloride ion penetration. 

G. From a satisfactory standpoint, applications made by the FLEXOGRID machine also address E.P.A. issues as measuring, mixing and dispensing avoids human contact and eliminates the hazardous waste and handling of empty containers.