( total weight approx . 4,000 pounds per cubic yard ): 1 . Cement ( Type I , II , III , IV or V ) – 16 % of total volume ( approx .
600 to 660 pounds per cubic yard ). 2 . Fine aggregate ( washed concrete sand ) – 52 % of total volume ( approx . 1,650 to 2,050 pounds ). 3 . Coarse aggregate ( 3 / 8-inch pea gravel or 3 / 4 – 1 inch gravel )
– 21 % of total volume ( approx . 800 to 1,000 pounds ). 4 . Water – 11 % of total volume ( approx . 400 pounds ). 5 . Air – naturally occurring forms approx . 6 % of total volume .
Cement Types ( most common types ):
TYPE I cement , typically called white cement , and best for architectural walls and hardscape .
1 . White cement has a much brighter or higher L factor ( the amount of measured reflected light ) and has less variation in color differences between loads .
2 . White cement gives more intense colors when blended with integral colors . 3 . Contains very little iron or manganese oxides . 4 . Due to the fact that it ’ s a finer grind , white cement hydrates faster and is less user friendly than other types . 5 . White cement is more costly than types II , III , and V .
TYPE II ( High Early ) is the most commonly used cement . However , due to sulfate problems , this type has been replaced by type II / type V for most use . Type II / type V is a coarser grind and contains iron and manganese oxides that produce a gray colored product . Benefits are : lower cost than type III and type I white ; develops strength slower , which reduces rapid hydration and less cracking ; and it is more user friendly .
TYPE III is more finely ground . This cement :
1 . Is lighter in color than type II . 2 . Develops design strength typically in less than a week . 3 . Has a higher rate of hydration and therefore generally greater shrinkage can be expected . 4 . Costs between type I white and type II . 5 . Color between type I and II and is therefore a good range for architectural concrete .
TYPE IV is a low-heat cement . This type cement is no longer manufactured because mineral admixtures offer a less expensive way to achieve low-heat quality .
TYPE V cement is commonly used as type II / type V cement , which is engineered to resist severe sulfate action where soils and ground water have high sulfate content . Sulfates can rapidly deteriorate concrete mixes . As previously stated , most cement type II are type specified type II / type V .
Admixtures :
Admixtures are often used in concrete when they will affect a desired change in the properties of freshly mixed concrete . Often used admixtures are :
1 . Synthetic fibers ( reinforcing ). 2 . Retarders ( slows concrete setting ). 3 . Accelerators ( speeds concrete setting ). 4 . Fly ash , which has many benefits for concrete , e . g . aids in pumpability , finishing , and reduces ASR ( Alkali-Silica Reaction ). May promote cracking and should be avoided in mix designs unless specifying glass Lithocrete . 5 . Water reducers . 6 . Air entrainment . 7 . Color pigments used extensively in architectural concrete , either via dust-on or integral . 8 . Shrinkage reducing admixtures ( shrinkage admixtures are not effective with type III cement ).
Shaw & Sons does not recommend dust on colors . Although it can contribute to a greater color intensity , its use is usually more inconsistent among installers . The finished surface can chip , showing gray matrix , and can result in thin areas that wear through prematurely .
Concrete Material Sourcing :
It is crucial that the concrete being supplied to a project for a given paving type be consistent in material source ( cement and aggregates ) throughout the duration of the project . There are several reasons why adjacent concrete pours differ in appearance :
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