Page 38 - PH_Masonry_Final_Ver 1_July 2020

Water Cement Ratio

The water–cement ratio is the ratio of the weight of water to the weight of cement used in a con-
crete mix and has an important influence on the quality of concrete produced. A lower water-

cement ratio leads to higher strength and durability, but may make the mix more difficult to place.
Placement difficulties can be resolved by using plasticizers or super-plasticizers.

Concrete hardens as a result of the chemical reaction between cement and water. For every kilo-

gram of cement, about 0.25 kg of water is needed to fully complete the hydration reactions. This
requires a water-cement ratio of 1:4 often given as a proportion 0.25. However, a mix with a w/c

ratio of 0.25 may not mix thoroughly, and may not flow well enough to be placed, so more water
is used than is technically necessary to react with the cement. More typical water-cement rati-

os of 0.4 to 0.6 are used. For higher-strength concrete, lower water, cement ratios are used,
along with a plasticizer to increase workability.

Too much water will result in segregation of the sand and aggregate components from the ce-

ment paste. Also, water that is not consumed by the hydration reaction may leave the concrete
as it hardens, resulting in microscopic pores that will reduce the final strength of the concrete. A

mix with too much water will experience more shrinkage as the excess water leaves, resulting in
internal cracks and visible fractures (particularly around inside corners) which again will reduce

the final strength.

Cement Aggregate Ratio

When making concrete it's important to use the correct concrete mixing ratios to produce a
strong, durable concrete mix. To make concrete there are four basic materials you need: Portland

cement, sand, aggregate (stone), and water. The ratio of aggregate to sand to cement is an im-
portant factor in determining the compressive strength of the concrete mixture.

A concrete mixture ratio of 1 part cement, 3 parts sand, and 6 parts aggregate will produce a M10

Concrete.

M10 - 1:3:6, M15 - 1:2:4, M20 - 1:1.5:3, M25 - 1:1:2

Participant Handbook : Masonry 38