1994-01-31_INSPECTION - M1977378

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f L. Perino Page 2 uary 31, 1994 concrete mix was as specified except that the maximum aggregate size was reduced to 3/8-inch from the original 3/4-inch to facilitate placement through the slick-line. A pre-measured and bagged plasticizer ("SupercizerTMI,) was added to each batch of concrete to further facilitate placement through the slick-line. The specified 16 percent of fly ash was included in each pre- mixed and pre-measured bag. Additional cement was added to maintain the specified strength, which was verified by testing before the formulation was accepted for purchase and placement. The remote controlled fill hose permitted complete filling of the bulkhead to within 1-foot of the back of the tunnel. The fill pipe used for filling the final foot of the bulkhead restricted flow of concrete into the bulkhead form. This did not cause a problem except when the injected concrete engulfed the fill pipe. It may be possible to use a slightly larger diameter final fill pipe and larger bulkhead openings at the top of the form. The placement of the extremely low slump and low water/cement ratio concrete was facilitated by the ingenious remote controlled vibrator set-up. Filling to the back of the bulkhead would be speeded-up by developing a method of stiffening the vibrator hose, possibly by tapping the hose to a 1 x 1-inch angle iron. It appears that the speed of filling future bulkheads can be facilitated by inserting a smaller screen over the concrete pump feed bin to screen out the occasional coarse lump of pre-set concrete that had somehow formed during transport and storage of the pre-mixed concrete. The cement content of the pre-mixed concrete appeared to be more variable than anticipated. Some of the batches in the concrete mixers were obviously dryer than others and in those cases the water/cement ratio was increased to 0.46. The water/cement was increased to 0.49 for a very limited number of batches to permit pumping through the slick-line. The higher water/cement ratio was used when filling the top of the form to facilitate complete filling of the bulkhead form. All-in-all the bulkhead filling proceeded with a minimum of problems, certainly fewer than I anticipated. The bulkhead filling produced a bulkhead that should exceed all specifications. The 28-day strength tests should verify that the first F-Level/Brenneman bulkhead exceeds all design strength specifications. I hope this review of filling the first bulkhead meets your requirements. Sincerely, -4 , d14S .. John F. Abel, Jr. Colorado P.E. 5642