Effect of conveyance and storage methods on the quality of concrete aggregates

Abstract

The necessity frequently arises during the construction of large hydraulic structures to transport concrete ag= gregates over long distances. The quality of these materials and of the mixed concrete depends on a well=thoughtout method of transport from the source of the material to the place of use.The sand=gravel quarry at the construction site of the Krasnoyarsk hydroelectric plant is 70 km downstream of the dam. The gravel screening plant ( Fig. 1) is located at the quarry. The plant has an output of 600 tons/h of screened gravel (washed in summer) in four sizes: 0=5, 5=20, 20=40, and 40=80 mm.The gravel is discharged into intake hoppers. Aggregates of different sizes are delivered by conveyors from a height reaching 15 m to aggregate storage cones 9.. An underground shaft 3 with two conveyor lines is used for the delivery of materials to wharves for loading into barges. Additionally, the material may be delivered by the con= veyors to stock piles in standby storage 4, and further along shaft 5, beneath the stockpiles, to wharves 6. 9 In summer the aggregates are conveyed in barges. The barges are unloaded by means of gantry-cran e clam= shells to handling storage 7 (at the wharf), then through shaft 8 the aggregates are carried by conveyors into pile= stackers of main storage 9, and the aggregates are stockpiled to a height of 10 m. The materials drop from a height of 5 to 10 m into the barges during loading operations. The aggregates are delivered from the main storage through underground shafts 10 and 11 to delivery bins 12 of the concrete mixing plant, where the material is stockpiled to a height of 10 m. From the batching bins the aggregates are transported by conveyors to delivery bins 13 of the concrete mixing plant, and further, through hatching conveyor 14 to the continuous concrete mixer. Thus, the mated= al, while moving from the screening facility to the concrete plant is dumped 6 to 7 times into high heaps of coni= cal shape. When moving along the conveyors the material is handled 28 to 46 times with a total length of conveyor lines of 4714 to 4980 m.