This investigation concerns the discovery of weak concrete in a portion of the deck of the Elkhorn City bridge, APD 640(4), within a year after it was opened to traffic. The deck concrete was placed between April 14 and June 14, 1968. The bridge serves heavy coal-trucks traffic. Failures occurred in the eastern-most span (No. 5) in April or May of 1969, Undoubtedly, the heavy loading contributed to early disclosure of defective concrete.
A preliminary investigation was made in May 1969, and reported by memorandum May 21, 1969. The bottom third or half of concrete in the affected portion, Span 5, was found to be atypical. The color was light tan -- contradistinctive from a greenish gray prevailing elsewhere.
The bridge is pictured in Fig. 1. Span 5 is at the far end. A coal-truck is shown on Span 2. Fig. 2 shows the failure zone from underneath, Fig. 3 is a diagram showing the approximate limits of the affected area of Span 5 and the location of cores is pictured in Fig. 4.
During the May 1969 investigation, rebound readings were made with a Swiss Hammer, on top of the deck, in the failed area, Low readings were obtained near the hole in the deck and along some transverse cracks. However, in general, the readings were not extremely low nor did the top surface of the deck appear abnormal. The cause of the high rebound readings is revealed by the cores (Nos. 1, 2, and 3). Obviously, the lower portions were not strong enough to withstand coring. Remnants of the bottoms of cores and spells from the deck appeared to be crumbly and light in weight. From microscopic examination, it appeared to contain sufficient -- if not excessive -- cement and also appeared to contain excessive air bubbles. It was hypothesized, in the original report, that either the cement had come from an alien source or was "spent" or "poisoned". The defective concrete was the first poured (April 24, 1968) on the deck and was, possibly, the first hatched in the season. It was spread rather uniformly and covered with normal concrete.
The defective concrete was removed and replaced with new concrete by the contractor later in 1969.
By letter of September 5, 1969, the Bureau of Public Roads urged further inquiry into the matter -- from the standpoint of discerning or defining cause of the trouble.
Digital Object Identifier
Havens, James H., "An Investigation of Low-Strength Concrete and Resulting Structural Failure in a Bridge Deck" (1970). Kentucky Transportation Center Research Report. 958.