Chapter 2 Construction Materials Concrete

Concrete is a mixture of,

• cement

• fine and course aggregate

• water​

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Concrete and cement are not the same thing.

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Where in a house will you find concrete?

​Concrete

Cement is an ingredient in concrete.

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Cement is a mixture of shells, limestone, clay silica, marble, shale, sand, and other materials that are ground, blended, fused, and crushed into a powder. ​

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When water is added, ​a chemical reaction takes place to harden the concrete.

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Cement can be thought of as the "adhesive or glue" in concrete. ​

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Cement

Aggregate is composed of fine sand and course gravel

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It is mixed with cement and water to provide structure and strength in concrete.

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Aggregate can be thought of as the "filler".

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​Aggregate

The proportions of a cenrete mixture affect the properties of the final result.​

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A typical ratio of 1:2:4 indicates​,

• 1 part cement

• 2 parts sand

• 4 parts gravel​

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Proportions

Forms are used to 'form up' the concrete into the desired shape.

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Concrete "sets up" in several hours, but isn't fully cured at it's maximum strength for nearly 28 days. ​

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Forms

An admixture is a substance other than water, aggregate, or cement that is added to concrete to modify it's chemical properties. ​

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• Air-retraining-provides greater resistance to freezing and high early strength properties

• Superplasticizer-significantly reduces the amount of water needed

• Retarder-delays the setting and hardening of concrete

• Accelerator-shortens the setting time and increases early strength​

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Admixture

Footings bear the load of the foundation walls and the building, including its contents, and are designed according to the load and the type of soil on which they bear.

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Discuss different symbols and what a house sits on here. ​

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Footings

Concrete can withstand great compressive strength, but relatively poor in counteracting bending or tension forces. ​

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Rebar (steel reinforcing bars) are placed in footings and foundation walls to provide tensile strength and to tie together adjacent parts of concrete structures. ​

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​Rebar

Some buildings and structures utilize pre casted components including beams, columns, walls, pipes, that are manufactured off site and then transported to the construction size and placed into place. ​

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Precast Components