169. Construction Equipment. The contractor's construction equipment was as follows: The subcontractor, S. L. Robbins, in the work area between the powerplant and the cofferdam used the following equipment: 1/Where the type and size or capacity of a particular make and model of equipment were not stated in the original report, these have been obtained from current construction equipment catalogs. As specifications for a particular model may vary from year to year, some minor discrepancies may exist between the reported size or capacity and that of the equipment actually used. D. Concrete 170. General. Control of temperature and moisture content of the concrete ingredients were two major problems at Flaming Gorge Dam. The coarse aggregate surge piles were sprayed with water during the warmest part of the construction season in an attempt to lower concrete temperatures. There was no conclusive evidence that this treatment beneficiated the aggregates and it may have been detrimental because of high water temperatures. The sprays also caused flooding of the floor in the reclaim tunnel and an increase of free water in the coarse aggregates. Temperatures of the cement as received in August 1961 ranged from 90° to 130° F. The moisture content of the pozzolan remained at 0.06 percent. Three percent variation in moisture content of sand during the time it took to mix 24 cubic yards of concrete was not uncommon. This condition was especially undesirable for the first 2 or 3 hours of hauling new sand from the aggregate storage plant following a 2- or 3-hour cessation of hauling. The sand delivered to the surge piles contained more moisture than the sand stored in the surge piles at the mixing plant. When the supply of stored sand was low at the mixing plant the new wet sand was immediately transplanted to the storage bin in the mixing plant, followed by a relatively small amount of dry sand from the surge pile as the quantity of newly delivered wet sand was insufficient to fill the batching plant bin. This caused a variation in sand moisture content from batch to batch. This condition usually occurred during the latter part of a week during peak construction, as the sand hauled the first few days of the week had the benefit of additional hours of draining due to the weekend shutdown and therefore had a more stable moisture content. In April 1961 a new rock ladder was installed above the 3- to 6-inch stockpile at the aggregate plant and the rock ladder in the 6-inch bin at the batching plant was repaired, resulting in cleaner rock without excess breakage being delivered to the batching plant. This permitted a substantial reduction in the amount of wash water used over the finish screens at the plant and subsequently solved a part of the problem of free water in the storage bins. Figures 189 and 190 show aggregate stockpiles. The river water frequently exceeded a turbidity of 2,000 parts per million and when this occurred, mixing water was drawn from the domestic water system. Since this supply was limited, and treatment costly, the contractor changed the source of mixing water to the relatively clear pool between the upstream face of the dam and the upstream cofferdam. The exterior face concrete was held to a minimum thickness of from 5 to 10 feet to help temperature control. No pozzolan was used in the exterior downstream face concrete or in the upstream face above elevation 5850, nor was any pozzolan used in any exposed faces of the dam parapets, roadways or walkways or in the powerhouse or spillway concrete. The cement content of the interior mix was raised from 188 to 195 pounds per cubic yard to help the workability. Air-entraining agent was normally added by a dispenser, but the dispenser gave considerable trouble and sometimes completely failed to function. On these occasions the agent was added manually. Mixer performance tests were run on all mixers on a monthly schedule, and the charging sequence was changed and adjusted as needed to come within the specifications requirements. Occasionally it was necessary to extend the mixing time and new mixing blades were installed as needed. The scales were checked at least once a month, and the turbidity of the water was checked daily and even more frequently when questionable. The recorder charts were reviewed daily to check on the number of batches mixed and reported, and the number of exterior and interior batches were checked against the reports for each block. This gave a second check on the batches reported and also a check on the performance of the scales. The recorder was checked by the batching plant inspector as often as possible during batching operations. Figure 189. --View of the aggregate stockpiles at Henrys Fork borrow area. Aggregate sizes in the piles from left to right are 3/4 inch to 1-1/2 inches, 3/16 to 3/4 inch, 3 to 6 inches, and 1-1/2 to 3 inches. P591-421-2518, August 25, 1960. Figure 190. --Concrete aggregate surge piles near batching plant. Aggregate is separated by wooden bulkheads into (left to right) 3/4-, 1-1/2-, 3-, 6-inch aggregate and sand. Cement and pozzolan storage silos are in upper center. Batching plant is at extreme right. P591-421-2711, October 24, 1960. One percent calcium chloride was used in the batching plant as required by the specifications when the mean air temperature was below 40° F. Extensive tests were made using a water-reducing agent. However, because of the extra expense involved, the contractor used a water-reducing agent only in the deck slabs of the sidehill bridge and some of the cantilever sections of the roadway. Table 1 shows interior mix data for the mass concrete of the dam. Reduction in placing area, caused by the steel trusses used to support the gutter forms for the utility gallery, necessitated constant alternation of exterior and interior concrete mixes and prompted the contractor to request cessation of the use of concrete containing pozzolan above elevation 6007.5. This request was granted, and as soon as the pozzolan on hand was exhausted no concrete containing pozzolan was placed. The contractor requested, and was granted, permission to place the top lift of the dam in three placements with a transverse vertical construction joint at every open joint location. At the conclusion of the placements for the dam, the use of the large mixing plant was discontinued and a smaller portable plant was introduced to make the smaller placements for the finishing of the spillway, the parapet walls, walkways over the dam, elevator tower, trashracks, and penstock intake structure. This plant consisted of a 30-ton, decumulative portable plant. Cement was batched with an independent bulk cement batching plant which had a scale capacity of 5,000 pounds. Steel baffle plates were placed diagonally across the sand and coarse aggregate conveyor belts from the reclaim tunnel to the batching plant to shunt the material into metal chutes. The coarse aggregate chute led to a 4- by 12-foot finish screen with 7/8-inch openings where the aggregate was separated into the 3/4- and 1-1/2-inch nominal sizes then discharged into individual storage bins. The sand chute led directly to the storage bins, which formed a part of the portable plant. The aggregate bins of the batching plant were on a suspension scale system. The overand-under indicator was centered to adjust the tare beam. Batch weights were set on the beams and the scale beam released to act in the scale system. The bin gate was opened allowing the aggregate to spill onto a belt which elevated it into the transit mixer. When the over-and-under indicator zeroed, the gate was closed and the process repeated for the next aggregate size. The cement was delivered to the silo through an 8-inch pipe which was connected to the air slide between the cement storage silo and the main mixing plant. The transit mixers were charged as follows: (1) Ninety percent of the mixing water was placed in the mixer. (2) Aggregates were added and the air-entraining agent was added manually with the sand. (3) The transit mixer was then moved to the cement silo and cement was added. (4) The remainder of the water was added and the concrete was mixed for 40 revolutions, transported to the loading dock, and discharged into a concrete bucket. The quality of concrete produced by this plant was satisfactory, but the rate of production was rather low. 171. Preparations for Concrete Placement. (a) Dam. -- Before placing concrete on the foundation rock of the dam, all loose material was removed and the rock was thoroughly cleaned with air and water jets. In some areas it was necessary to sandblast the rock to remove objectionable coatings. Shale seams were trimmed to vertical planes flush with overlying, competent rock. The surface of the rock, with the exception of that forming nearly vertical faces, was covered with a layer of mortar prior to placement of concrete. |