Concrete

Concrete Cement Sand Gravel Water

Portland Cement A dry powder made from limestone and is usually packaged in bags containing 1 cubic foot and weighs 94 pounds

Portland Cement When mixed with water, it forms the “glue” to hold the aggregate together

Fine Aggregate Sand It should be clean of clay, silt, and organic matter

Course Aggregate Gravel and rocks over ¼” in diameter

Water Should be clean

Concrete Trucks Most concrete is delivered by trucks to the construction site as ready-mixed concrete

Mortar Does not contain coarse aggregates and is used to join bricks or blocks

Cement Although many people call concrete “cement”, cement is the powdered material and concrete is the mixture of ingredients

Weight lbs. per cubic foot

Slump Stronger concrete requires less slump The consistency or wetness of the mixture

Slump If concrete has too much slump (is too wet), adding aggregate such as sand and gravel will correct the problem

Uniformity Is thoroughly mixing all ingredients so that the “glue” which is wet cement will be around all sand and gravel particles (aggregates)

Workability Refers to the ease with which concrete can be placed and shaped

Ratio Expressed as a three digit number Example: 1,2,3

Ratio The first number is parts of cement Second number is parts of fine aggregate (sand)

Ratio The third number is parts of large aggregate (gravel) Parts may be shovels full, pounds, cubic feet, etc.

Ratio Less sand, gravel, and water are used for the same amount of water to make concrete stronger

Fuller’s Rule The mixing of a total of 42 volumes of cement, sand, and gravel will produce 27 volumes of concrete

1 2 1/ Volumes Concrete =+ + cement sand gravel = 42 volumes

Hand Mixing May be done in a wheelbarrow or mixing box (mortar box) by using a shovel or hoe

Hand Mixing Add sand and then cement and mix thoroughly Then add and mix gravel

Hand Mixing Last thing to add is water and mix well

Machine Mixing Uses a concrete or mortar mixer

Machine Mixing First, add about 10% of water needed so that ingredients will not stick to mixer

Concrete