Proportioning and Mixing Concrete

The concrete must be workable and cohesive when plastic, then set and harden to give strong and
durable concrete. The mix design must consider the environment that the concrete will be in; ie exposure to sea water,trucks, cars, forklifts, foot traffic or extremes of hot and cold. Concrete is a mixture of Cement, Water, Coarse and Fine Aggregates and Admixtures. The proportions of each material in the mixture affects the properties of the final hardened concrete. These proportions are best measured by weight. Measurement by volume is not as accurate, but is suitable for minor projects.

 

 PROPORTIONING Concrete is a mixture of Cement, Water, Coarse and Fine Aggregates and
Admixtures. The proportions of each material in the mixture affects the properties of the final hardened
concrete. These proportions are best measured by weight. Measurement by volume is not as accurate, but is suitable for minor projects.

 CEMENT CONTENT As the cement content increases, so does strength and durability. Therefore to increase the strength, increase the cement content of a mix.

 

WATER CONTENT Adding MORE WATER to a mix gives a WEAKER hardened concrete. Always use as little water as possible, only enough to make the mix workable.

 

 WATER TO CEMENT RATIO As the Water to Cement ratio INCREASES, the strength and durability of hardened concrete DECREASES. To increase the strength and durability of concrete, decrease the Water-Cement ratio.

 

 AGGREGATES Too much fine aggregate gives a sticky mix. Too much coarse aggregate gives a harsh or boney mix.

  
MIXING Concrete must be mixed so the Cement, Water, Aggregates and Admixtures blend into an even mix. Concrete is normally mixed by MACHINE. Machine mixing can be done on-site or be a Pre-Mixed
concrete company. Pre-Mixed concrete is batched (proportioned) at the plant to the job requirements.