Cracking Of Concrete In The Tuscaloosa Lock
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The Tuscaloosa Lock was constructed on the Warrior River near Tuscaloosa, Alabama, between l937 and l939. It was noted in 1947 that cracks had developed in the lock walls. A board of consultants was appointed, and the members of the board examined the structure and recommended that the Concrete Research Division, Waterways Experiment Station, conduct a study to determine the cause of the cracking. The data developed by this study are summarized and discussed in this paper. It was concluded that the cracking resulted from a chemical reaction between the alkalies in the cement and unstable silica in the aggregate. It is believed that this is the first published account of cracking of concrete through cement-aggregate reaction in which chalcedonic chart is the major control responsible for the deleterious reaction. Between October 1937 and September 1939 the Mobile District of the Corps of Engineers supervised the placement of concrete in the Tuscaloosa Lock and Dam on the Warrior River near Tuscaloosa, Alabama. The cement came from two mills, the aggregates were natural sand and gravel, and the mixing water came from the Tuscaloosa city water supply. Eight years after the placement of concrete was completed, it was noted that cracks had developed in the lock walls. A board of consultants was appointed to examine the situation and make recommendations. The board met at Tuscaloosa in November 1947, reviewed the available data, examined the structure, and arrived at two conclusions: (1) cracking is more advanced in concrete made with Cement A than in that made with Cement B and (2) additional data on the condition of the structure should be obtained by drilling cores and by making a detailed crack survey. A series of cores were drilled including a 36-in.-diameter core from monolith No. 5 in the lock wall, a monolith that showed rather extensive cracking it the surface and which was so situated that internal movement might interfere with the proper functioning of the lock gates. The board met again in January 1948, examined the additional data, the cores, especially the 36-in. core hole, and concluded that: (1) the cracking in monolith No. 5 is not as serious as it had appeared from the surface and (2) an investigation should be made by the Waterways Experiment Station to determine the causes of the cracking.