【文章內(nèi)容簡介】 ms in Japan. Pugmills need to be carefully designed to avoid maintenance problems and excessive wear on paddles and plates, particularly for mixes with large aggregates. In drum mixes, excessive buildup of the sticky material can occur, reducing capacity and mixing efficiency. Redesign of fins（鰭狀物） has helped to avoid this problem in some cases. Considerable cleanup of the drums on a daily basis is often required.For highvolume production, largerthanaveragecapacity drum mixers may be necessary to cope with problems encountered when mixing noslump RCC. Blending a zeroslump (塌落度)mixture with a high proportion of fines often causes long mix and discharge times. At Willow Creek, a fourbin Noble 600 plant with two 9yd3() Erie Strayer drums was used. The plant had been proven on an earlier highway job at 600 to 750 yd3(460 to 570m3) times were 30 s longer than for the fluid highway paving mix, and the drums had to be derated（降級(jí)為）to between 7 l/2 and 8 yd3 ( and 6 m3) because the diameter of the discharge end was increased to speed dumping. On average, the plant produced 400 yd3/h (310 m3/h) of RCC and peaked during one shift at 438 yd3/h (335 m3/h).Four 250yd3/h (190 m3/h) IHIHydam pugmills made by Ishikawajima Construction Machinery were used by the Japanese contractor for mixing batched RCC at Elk Creek Dam. The doubleshaft(雙軸) pugmills were hydraulically driven and allowed for variable rotation speeds during the charging(進(jìn)料), mixing, and discharging processes .The coarse aggregate was crushed basalt sized from 3/4 to 3 in (19 to 75mm) maximum. Batching was puterized using ErieStrayer controls. The maximum output of the four 6yd3 () mixers was 1014yd3/h (775 m3/h). That was achieved on October 29, 1988.Two different batchtype mixing plants were used to produce RCC at Upper Stillwater. The first plant built at the site was a Noble 600 with two 8yd3 (6m3) tilting drum mixers. A second plant, a Noble 600 modified to accept two 4yd3(3 m3) Nikko highintensity, spiralflow pugmill mixers, was added later. Each plant achieved peak production rates of about 420 yd3/h (320 m3/h) in 1986. Abrasive quartzite sandstone aggregate with a silica content of about 80 percent created extraordinary maintenance problems. Problems were greater with the Nikko bottomdischarge pugmill mixers, which suffered from high wear rates on the paddles and breakage of the liner plates(襯砌板).For the drum mixers, rubberized plastic liners were installed and these worked well. The highwear steel liner plates on the Nikko mixers had to be replaced five times during the 1986 season, however. That was due mainly to breakage caused by the shock of loading and mixing RCC. Initially, the contractor switched to milder steel liner plates. They broke at about the same rate as the highwear plates but they cost less and were more readily available.For the 1987 season, a beltdrive system was installed on the Nikko mixers to allow a 10 percent reduction in paddle（攪拌） speed. Retention times were kept the same so that wear was reduced somewhat. In addition, a 3/8inthick () layer of 11,000lb/in2 (76MPa) epoxysilica（環(huán)氧硅石） grout was troweled onto the backs of the liner plates before the sixth set of plates was bolted to the mixer wall. The grout is monly used as a coating for nuclear reactor containments and has the beneficial characteristics of being durable but relatively soft. Placing it between the plates and the mixer wall solved the breakage problem.RCC production peaked in 1987 during the first week in June at an average of 548 yd3/h (419 m3/h) during two production shifts per day. Production from both plants during the entire month averaged 515 yd3/h (394 m3/h) over 59 shifts. The RCC batching and delivery system produced 266,000 yd3 (203,000 m3) in June 1987. The dam was topped out (達(dá)到壩頂高程)on August 8, 1987.Two ARAN ASR200 continuousmix pugmill plants were used successfully to produce 183,000 yd3 (140,000 m3) of RCC placed over 17 weeks at Copperfield Dam in Australia. Crushed alluvial gravel with a maximum size of in (63 mm) was used as aggregate. Each plant produced a different mix, one with cement and fly ash for interior concrete and one with only cement for the exterior faces. Slow progress in jumpforming the 330ftlong (100m), central overflow spillway controlled RCC production rates on much of the dam. Hence, neither of the selfcontained, mobile mixing plants was used to capacity although both were needed in order to produce the different mixes simultaneously. The average hourly output was 290 yd3 (220 m3) for the first plant and 234 yd3 (179 m3) for the other.A contractordesigned continuousmix plant produced consistent, highquality RCC at Monksville Dam. Mixer proficiency test results are shown in Fig. . The plant consisted of three 8yd3 (6m3) feed bins with adjustablespeed belts straddling a 36inwide (914mm) main feed belt。 a 75ton (68t) cement silo(筒倉) with aerators and one vane feeder（螺旋進(jìn)料器）。 a Davis pugmill with a capacity of 500 yd3/h(382 m3/h)。 a stacker belt。 and an 18yd3 (14 m3) twostage surge bin.The plant could be operated manually or by a puter programmed to initiate the production sequence starting at the surge hopper(涌浪式加料斗). Sensing devices included a feedbelt scale（帶稱）。 tilt gages on each feed bin。 an electronic water flow meter。 and a revolution counter（旋轉(zhuǎn)式稱量臺(tái)） for metering cement through the ital display was available for realtime measurement of aggregate feed. For aggregate, cement, and water, the system provided cumulative data every 5 min. Transporting RCC Transport of RCC can be by scraper(鏟土機(jī)) conveyor, bottomand reardump trucks, large frontend loaders or a bination of these. Continuous, highspeed conveyors appear to be the most desirable method for large RCC jobs. Scrapers have worked well on most mediumsize projects, and rear dumps have been used successfully on a variety of jobs. Segregation(分離) of the larger aggregate, usually