Research Project C-22 is an investigation of the geologic aspects of limestone aggregate that might cause failure if used in highway construction. This represents work being carried on at the Highway Materials Research Laboratory in Lexington. The end point of this work is to determine the cause or causes of failure and provide a test that will delete faulty materials from construction work.

In order to evaluate the engineering aspect of the author's work, a study ef the physical tests of these same aggregates is to be made. A correlation between Laboratory Analysis and performance Surveys of these same aggregates in roads should be sufficient to make pertinent observations.

Limestone varies in any and all proportions of its basic constituents, with the introduction of some new minerals from time to time. As defined, limestone should be composed of calcium carbonate plus some small amount of impurities. The variation in amount and types of impurity give a limestone its characteristics and this variation is so unique that very rarely will two limestones be identical. The variation in minerals is complex, inasmuch as two different minerals having the same elements, may have entirely different reactions to any influence brought upon them. As to the limits set on the name "limestone", the presence of 50% carbonate material should assign a rock as limestone. A chemical analysis, although helpful, will not be a positive criterion as the analysis tells only the compounds present and not the way in which they are combined.

It seems a reasonable hypothesis that the impurities present are the dominant agents in any failure of limestone aggregate and a careful comparative study of these impurities should show whether the premise is well founded. This, then, is the main objective of the study.

Report Date


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No. 28

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