used to handle bulk cement. Bulk cement  is measured in tons (2,000 lb) and smaller quantities are bagged in cloth  or  paper  sacks,  each  containing  94  pounds  of cement. A 94-pound sack of cement is equal to 1 cubic foot  by  loose  volume. Cement bags should not be stored on damp floors, but should rest on pallets. The bags should be stacked against each other to prevent circulation of air between them, but not stacked against outside walls. If the stacks of cement are to be stored undisturbed for long periods, they  should  be  covered  with  tarpaulins. Cement bags that have been stacked in storage for long  periods  sometimes  acquire  a  hardness  called WAREHOUSEPACK.  This can usually be loosened by rolling the sack around. Cement that has lumps or is not free flowing should not be used. AGGREGATE separately-the fine aggregates on sieves with openings 1/4 inch or smaller and the coarse aggregate on sieves with  square  openings  from  about  1/4  inch  and  larger. The fine sieves are numbered—the larger the number, the smaller the sieve opening; for instance, the No. 100 sieve has 100 openings per inch, and the No. 4 sieve has 4 openings per inch. The grading of both coarse and fine aggregate and the relative proportions of each in the mix can greatly affect the properties of the fresh concrete. Concrete made with coarse sand or not enough sand is hard to pump and will be harsh and difficult to trowel. Also, aggregates can segregate or separate from the cement paste   during   placement,   producing   nonuniform concrete.   Air-entraining   will   help   in   overcoming grading problems of this kind. Coarse aggregates should be round or subround in shape. This thape allows the cement  paste  to  coat  the  particles  more  easily  during mixing. The aggregates used in concrete must be strong, HANDLING AND STORAGE OF durable, and chemically inert and generally occupy 60 AGGREGATES to 75 percent of the concrete mix in volumc (70 to 85 percent by weight). Natural aggregate deposits are Aggregates  containing  particles  of  different  sizes excavated from pits, rivers, lakes, or seabeds. These have a natural  tendency  to  segregate  whenever  loaded, natural deposits consist of gravel and sand that can be transported,  or  otherwise  disturbed.  Aggregates  should readily  used  in  concrete  after  minimal  processing. always  be  handled  and  stored  by  a  method  that Crushed aggregates are produced by crushing quary minimizes   segregation. rock, boulders, cobbles, or large-size gravel. Crushed Stockpiles should not be built up in cone shapes, aggregates  are  usually  washed  and  graded  before  being formed by dropping successive loads at the same spot. used in concrete. The most commonly used aggregates This  process  causes  larger  aggregate  particles  to are  sand  and  gravel  and  when  combined  with  cement produce  a  strong,  durable  mass  that  is  practically segregate  and  roll  down  the  sides,  leaving  the  pile  with without  voids. a large amount of fine aggregate at the top and a large amount of coarse aggregate at the bottom. A stockpile The coarse aggregates used in a mix usually consist should be built up in layers, each made by dumping of gravel or crushed stone up to 1 1/2 inches in size. successive loads alongside each other. Course  aggregates  are  primarily  used  as  filler.  These If  aggregate  is  dropped  in  a  free  fall  from  a aggregates can pass through a 3-inch sieve and are retained on a No. 4 sieve. In massive structures like clamshell,  loader,  or  a  conveyor,  some  of  the  fine dams, the coarse aggregates may include natural stones material may be blown aside, causing segregation of fines on the lee side of the pile. Clamshells, loaders, and or rocks, ranging up to 6 inches or more in size. conveyors should be discharged in contact with the Fine aggregates are those materials that can pass pile. through a No. 4 sieve but are retained on a No. 100 sieve. The fine aggregates and sand in concrete are used to fill the  voids  between  the  large  aggregates.  Care  should  be taken to prevent dirt and othcr debris from getting mixed into the sand. The foreign material affects the bonding quality of the sand. The gradation of the aggregate is a major factor in the workability, water requirements, and strength of concrete. Fine and coarse aggregates are usually sieved The bottom of an overhead charging bin should always slope at least 50 degrees towards the center outlet. If the slope is less than 50 degrees, segregation will occur as the material is discharged. When a bin is being charged, the material should be dropped from a point directly over the outlet. Material dropped in at an angle or discharged against the sides of the bin will segregate. Since a long drop causes both segregation and the breakage  of aggregate particles, the length of a drop 7-2