EXHIBIT B

MIXING TIME ON MULTICOMPARTMENT PAVERS-SUMMARY AND ANALYSIS (By William Byrd Huffine, Chief, Procedures and Operations Branch, Division of Development, Office of Operations, Bureau of Public Roads, U.S. Department of Commerce, March 1961)

Reported nationwide variations in mixing time specified for multicompartment pavers are currently as delineated on the accompanying summary form No. 1. By this alphabetical listing of States under the five specific numerical specifications now in force, the apparent lack of consensus as to such requirements is clearly shown. It should be noted, however, that data for six States have been excluded from those groupings as not applicable due to little or no current activity on their part in portland cement concrete paving. Accordingly, the remaining States constitute the statistical universe whose range of variability is analyzed. Indicated variance among States in such mixing time apparently stems only partially from differences of opinion concerning requirements considered necessary to insure quality control. In other words, such variations appear secondarily ascribable and to a somewhat measurable degree-both to lack of accord with respect to the question of transfer time, and to absence of a common denominator in defining "when mixing time begins.' Respective positions of the States with respect to both of those factors are incorporated on the accompanying summaries, the first mentioned on form No. 1 and the latter on form No. 2. Fortunately, however, no corresponding lack of agreement is apparent with respect to "when mixing time ends. Consequently, and in view of a seeming consensus to the effect that current usage of modern automatic timing devices has minimized the importance of that question, it has been eliminated from this discussion. corresponding conclusion is possible, however, with respect to either transfer time or initiation of mixing time. Accordingly, both of those problems merit further consideration.

No

The accompanying summaries reflect a condensation of responses to the Commissioner's circular memorandum of January 16, 1961. They are significant, not only in portraying widespread variations among the States in specified mixing time, but also and more importantly-in pointing up or identifying areas of possible improvement. Noteworthy, from the standpoint of economy of operations, is the recent lessening-by a number of States as indicated-of previously existing restrictions precluding full realization of modern multicompartment paver capabilities. To those actions there no doubt may be attributed proportionate savings in the cost of concrete pavement. Overall potentialities of a more widespread acceptance among the States of such savings-when translated and accrued through proven economies in the highway program-are obviously tremendous. It is likewise noteworthy to witness the progress in that direction evidenced by the actions footnoted on form No. 1. A definitely favorable trend seemingly is being established.

One fundamental index of such trend is the fact more than half of the States now reportedly agree with American Association of State Highway Officials' endorsement of a 60-second mixing time overall adequacy for multicompartment pavers. In addition, five States have further extended such acceptance to realize additional benefits by authorizing a 50-second optional mixing time under circumstances outlined on summary form No. 1. By way of contrast, 10 States still cling to the once predominantly accepted requirement of 75 seconds for batch capacities in excess of 1 cubic yard. This becomes a limiting feature in view of the fact capacities of that order of magnitude are indigenous to multicompartment paver operation. To complete the spectrum, we find two States claiming distinction in each of two other uncommon groupings; namely, 65 and 90 seconds, respectively. However, one of the two States in the 90-second category reportedly is actively in the process of joining the 60-second majority consensus.

As implied by the foregoing discussion, the lack of uniformity among States with respect to mixing time is associated with lack of accord concerning inclusion or exclusion of transfer time. In addition, a corollary complication exists in the form of inconsistency in defining when mixing actually begins. Both of these aspects of the problem may be brought quite clearly into focus by examination of the background material and supporting data forwarded with the aforementioned Commissioner's memorandum of January 16. It was therein demonstrated quite conclusively that no valid reason exists for considering transfer time as a proper exclusion from mixing time in modern multicompartment paver operation. Accordingly, it is encouraging to witness the increasing accord with that conclusion. However, with respect to defining when mixing time begins, the outlook is less determinate. The complete lack of pattern disclosed by selfexplanatory summarizations on form No. 2 is indicative of a need for concerted action toward solution of that problem. However, through efforts of the Joint ARBA-AASHO Committee on Mixing Time, there have been evoked certain conclusions, the acceptance of which will no doubt be a forward step in that direction. These are now actively under consideration.

In summary, except for the subsidiary minor question of defining when mixing time actually begins, the problem of bringing into more universal acceptance mixing time criteria in consonance with modern equipment capabilities would appear well along the road to resolution.

Summary Form No. 1-Specified mixing time on Multicompartment pavers

150 seconds authorized only for automatically controlled operations.

250 seconds authorized by special provisions.

3 Revision of specifications to include transfer time under study.

4 Transfer time included only for new tribatch paver operations.

5 Specifications being revised to include transfer time.

One-half of estimated 10-second transfer time included.

7 District of Columbia and Puerto Rico counted as States.

8 75 seconds required for all batches greater than 1 cubic yard.

Transfer time included for capacities greater than 1 cubic yard.

10 Less restrictive specifications under study.

*Indicates transfer time included in mixing time.