into a bin should be kept to a minimum by keeping the bin as full as possible at all times. WATER The primary function of water used in a concrete mix is to start the hardening process of the concrete through hydration of the cement. A secondary function is  to  make  the  mix  workable  enough  to  satisfy  the requirements of the job. However, too much water will cause a loss of strength by upsetting the water-cement ratio. It will also cause “water gain” on the surface, a condition which leaves a surface layer of weak material called LAITANCE. Also, an excessive amount of water will impair the water tightness of the concrete. Water  used  in  mixing  concrete  must  be  clean  and free from oils, alkalis, acids, and organic materials. Most specifications recommend the mixing water be fit for drinking. This is because any water fit for drinking is usually   satisfactory   for   use   in   mixing   concrete. Seawater may be used for unreinforced concrete. ADDITIVES USED IN CONCRETE There  are  several  additives  or  admixtures  used  to change  the  composition  of  concrete  or  to  accelerate  or retard its hardening. The three commonly used are air-entraining  agents,  retarders,  and  accelerators. Additives are not recommended if the end result can be reached  more  economically  by  altering  the  mix proportions. Air-entraining  portland  cement  is a special cement that can be used with good results for a variety of  conditions.  It  was  developed  to  produce  concrete  that has a resistance to freeze-thaw action and scaling caused by  chemicals  applied  for  severe  frost  and  ice  removal, Air-entraining agents are liquids derived from natural wood resins, animal fats, vegetable fats, or various wetting  agents,  such  as  alkali  salts  and  water-soluble soaps.  Agents  are  blended  with  the  cement  during manufacturing or added at the mixing site. If done at the site,  the  agent  is  added  to  the  water  used  in  the mix. Manufactured  air-entraining  cements  are  indicated by the letter A in the type number (Types IA, IIA, IIIA, etc.).  Concrete  made  with  this  cement   contains  billions of  extremely  small,  entirely  separated  air  bubbles  per cubic  foot  of  concrete.  These  bubbles  provide  space  for water to expand due to freezing without damage to the concrete. Retarders are used to slow down the rate of setting of a concrete.    High temperatures of fresh concrete (85°F  -  90°F  and  higher)  are  often  the  cause  of  an increased rate of hardening that makes placing and finishing  difficult.  One  practical  way  to  reduce  the temperature of the concrete is by cooling the mixing water or the aggregates. Retarders do not decrease the initial  temperature  of  the  concrete.  Retarders  are sometimes  used  (o  do  the  following: 1. Offset the accelerating effect of hot weather on the  setting  of  concrete 2.  Delay the initial set of concrete when difficult or unusual conditions of placement occur, such as placing concrete in large piers and foundations 3. Delay the set for a special finishing process, such as an exposed aggregate surface Some of the materials used to retard the set of a concrete mixture are lignin, borax, sugar, tartaric acid, and salt. These materials should be added to the mixing water. CAUTION If 20 percent by volume of regarding agent is added to the mix, the effect is reversed and it then acts as an accelerator. Accelerators are  used  to  accelerate  the  strength development  of  concrete  at  an  early  age.  Calcium chloride  is  the  material  most  commonly  used  in accelerating   admixtures;   however,   in   addition   to accelerating strength gain, calcium chloride causes an increase  in  drying  shrinkage,  potential  reinforcement corrosion, discoloration, and scaling potential. Calcium chloride should be added to the concrete mix in solution form as part of the mixing water. If added to the concrete in  dry  form,  all  of  the  dry  particles  may  not  be completely   dissolved   during   mixing.   Undissolved lumps in the mix can cause pop-outs of dark spots in the hardened concrete. The amount of accelerator used should not exceed 2 percent by weight of cement. COMPUTING CONCRETE VOLUME To compute the volume of concrete required for a concrete pad, multiply the length of the pad by its width times  its  depth  to  get  cubic  feet  (L  x  W  x  D);  for example, a concrete pad is 20 feet in length by 30 feet in width and has a depth of 3 inches. First, convert the 3 inches into feet by dividing 3 by 12 to get 0.25 foot. Next, multiply the 20-foot length by the 30-foot width 7-3