【正文】 e efficiently and safely.At Elk Creek Dam, the aggregate was produced from an andesitebasalt(安山玄武巖) outcrop（露頭） about 3000 ft (910 m) upstream and to the right of the dam. Rock was hauled to the primary jaw crusher, located in the quarry(采石場(chǎng)), using 85ton {77metricton} end dump trucks（后卸式卡車(chē)）. Rock was crushed to 9in (230mm) maximum sizes. The aggregate was transported from the quarry down a 12 percent slope by a 56inwide, 2085ftlong ( x 635 m) conveyor belt rated at 1000 tons/h (907t/h) and stored in a surge pile using a radial stacker(棧式料倉(cāng)). A series of cone crushers and screens then produced 3in (75mm), 1in (38(mm), and 3/4in (19mm) aggregate sizes. The aggregate was transferred from these stockpiles by three 7yd3 ( m3) frontend loaders into movable hoppers discharging onto five conveyors which fed the batch plant surge piles. From there, the material was loaded from reclaim tunnels onto 36inwide (910mm) conveyor belts and transported to the RCC and conventional concrete batch plant aggregate bins(貯料倉(cāng)). The Elk Creek layout is shown in Fig. 。Three concrete mixing plants about 300 ft (90 m) upstream of the dam were used to produce the bedding grout, conventonal concrete, and RCC for Elk Creek. Conveyors were used to move the mix from the plants to the dam and deposit it on either side of a regulating outlet structure.The concrete plant layout and location should be selected to minimize energy requirements whether the RCC is transported to the dam by conveyor or haul vehicles. The intent should be to minimize haul distances, vertical lift, and exposure of the RCC to sun, wind, or rain. If trucks or other vehicles are used for hauling, the plant should be located on a raised, freedraining area. This avoids making mud and helps to prevent tracking of foreign material onto the dam.Fueling and field maintenance of equipment should not be done on the RCC surface because of the likelihood of contamination(污染) and consequent problems in establishing a secure bond between lifts at that point. Fuel spills were a problem at Monksville Dam because the contractor was allowed to refuel on the dam. That potential problem was addressed at Elk Creek Dam by specifying that the contractor use a movable refueling pad （墊）on the surface of the dam to collect and contain fuel spillage. The contractor chose instead to refuel equipment and perform maintenance off the surface of the dam. Mixing RCCIn most cases, the methods used for transporting, spreading, and pacting RCC will not affect production as much as the speed and efficiency of mixing. Thus, the mixing plant capacity should exceed the laydown capacity(設(shè)計(jì)容量).Achieving the desired product consistency and quality at continuous, high production rates requires good concrete plant design and rigorous maintenance. RCC mixes are relatively harsh and sticky, and the lean, dry material has no fluid properties. The design of misers, transfers, and hoppers must take these characteristics into consideration in order to avoid caking（結(jié)塊）and loss of capacity.The mixing method must produce a homogeneous mixture of the ingredients. This factor determines the mixing time and, to a large extent, the production rate. Tests should be done to determine retention times（拌合時(shí)間）required for each mix. The variablespeed pugmill mixers （葉片式攪拌機(jī)）used during 1987 at Elk Creek Dam required 38s of mixing for 6yd3 () batches. At Willow Creek Dam, the retention time in the 9yd3 ( m3) drum misers was 75 s.The trend in design is to use one RCC mix for the body of the dam. For large projects that require a variety of mixes, the plant chosen for the job must be able to change mix designs quickly and little or no mechanical or manual manipulation to plant ponents. On most projects, different plants are used to produce conventional concrete and RCC.For major projects the weights of all ingredients should be digitally recorded as a function of time, date, and mix design. Because of the sensitivity of RCC to excess water, the plant should be equipped with instrumentation to determine the fine aggregate moisture content. In Japan, automatic waterbatching systems are adjusted according to results of continuous monitoring of the moisture content of sand in the sand storage piles. This System has been used on most Japanese RCD projects and has resulted in precise control of moistllre colltent. In the United States most contractors feel continuous visual inspection of the RCC placement or a Vebe test is a more reliable control of water content than moisture meters in the aggregate piles.Proper blending or ribboning of the aggregates and cementitious material on the charging belt as they are fed into the miser will help to speed mixing time and avoid buildup of the sticky material. Achieving the proper timing and angle of introduction of water into batehed mixtures is also important. The proper sandwiching of material to achieve best results with RCC often is different from conventional mass concrete mixes. Each plant and mix bination has its own quirks（特點(diǎn)）, so the exact method of ribboning mix constituents（要素） can only be determined by trial and error(反復(fù)試驗(yàn)).Highspeed batching and mixing can best be achieved with individual weigh systems for aggregate. Accumulative weigh systems make it more difficult to finetune the ribboning of constituents on the belt. Mixing plantsVarious binations of batch and continuous concrete plants using drum and pugmill mixers have been used to produce RCC. Continuousmix plants can provide higher output capability than batch plants, and the most sophisticated continuous mixers can produce the same degree of control as batch plants. Land use and labor requirements are generally less for continuous plants.Drum mixers have the advantage of using less energy than pugmills and provide good control of batch proportions. Pugmills are faster and are generally more portable than drum mixers. Pugmills have been used on all RCC da