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In the earlier symposium on mineral aggregates, Jackson (1) discussed the problem of needed research and made several statements which still apply. Possibly the most important of these statements are the ones concerning the inability of research to keep pace with the needs of construction and the need for a thorough review and digest of the available information. He commented briefly on the great demand for aggregates for use in concrete and road construction and on the time required for any comprehensive study of the fundamental characteristics of aggregates. Consequently, it was not surprising that many materials were used in construction before the real properties of these materials were known. At the present time, the same condition which existed a generation ago still prevails in that construction is using materials before research can effectively determine their properties. On the other hand, research has developed information concerning materials and their use which construction has not attempted to apply in practice. Good reasons for both of these conditions are readily available. With particular reference to aggregates, the demand for knowledge of the characteristics of materials has increased so greatly in the past few years that it has become necessary to widen to a major degree the scope of the examination of materials. Due to this expansion in the necessary studies of materials and to the fact that in some instances a considerable length of time is required for the tests, it has not been possible for research to furnish construction with all the information regarding all of the materials as fast as this information is needed. Consequently, construction has been forced to use such data as are available and to depend upon service records of materials similar and presumably of the same characteristics as those proposed for use. In the second case where research has made recommendations for changes in the use of materials which construction has not followed, the principal reason for this has been due to the expense involved. As a specific example, the improvement in the uniformity of concrete that can be obtained through the use of separated sizes of both fine and coarse aggregate might be mentioned. The cost of the construction may dictate whether changes in construction methods will be made.
Woolf, D. O.
Senior Materials Engineer, Public Roads Administration, Washington, D. C.,