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Concrete: mix, strength classes and proper curing
Construction

Concrete: mix, strength classes and proper curing

ISAR GROUP7 November 20265 min read

Concrete is the backbone of construction. Its strength depends not only on the mix but also on how it is placed and cured.

What concrete is made of

Concrete is a mix of cement, water, sand and gravel or crushed stone. Cement reacts with water, hardens and binds the aggregates together. Where needed, admixtures are added for workability, frost resistance or water tightness.

Water-cement ratio and strength

The biggest single factor in strength is the ratio of water to cement. Extra water makes concrete easier to work with but lowers its strength. Concrete is graded into strength classes, and the design sets the class needed for the loads on the structure.

Placing and compaction

Concrete is poured into the formwork without breaks and compacted with vibrators so no air pockets remain. It must not be dropped from a great height, or the mix will separate.

Curing and care

Concrete usually reaches its design strength in 28 days. In the first days it must be kept moist, protected from drying out in hot weather and from freezing in cold weather. Test samples are taken from each pour and checked in the laboratory.

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