Unit 7. Concrete

 

Vocabulary.

Aggregate – заполнитель

Diluted – разбавленный

Cure – затвердевать

Imperviousness – герметичность

Mouldability – способность к формованию

Concrete is a building material made by mixing cement (portland cement and water) with aggregate (sand and stone). The cement is the ‘glue’ that binds the particles in the aggregate together. The strength of the cement depends on the relative proportions of water and cement, with a more diluted paste being weaker. In addition, the relative proportions of cement and aggregate affect the strength, with a higher proportion of making stronger concrete. The concrete hardens through the chemical reaction between water and cement, without the need for air. Once the initial set has taken place, concrete cures well under water. Strength is gained gradually, depending on the speed of the chemical reaction. Admixtures are sometimes included in the concrete mix to achieve certain properties. Reinforcement steel is used for added strength, particularly for tensile stresses. Concrete is normally mixed at the building site and poured into formwork of the desired shape, in the position that the unit will occupy in the finished structure. Units can also be precast, either at the building site or at a factory.

Concrete is associated with high strength, hardness, durability, imperviousness and mouldability. It is a poor thermal insulator, but has high thermal capacity. Concrete is not flammable and has good fire resistance, but there is a serious loss of strength at high temperatures. Concrete made with ordinary portland cement has low resistance to acids and sulphates but good resistance to alkalis.

Answer the questions:

1. What does the strength of the cement depend on?

2. What is required for curing of concrete?

3. What kind of admixtures can be used in the concrete mix?

4. What are the properties of concrete?

5. How does high temperature affect concrete?

 

Exercises:

1) Decide whether the following statements are true or false:

1. Concrete is a building material made of cement and aggregate.

2. Air is needed for the concrete to harden.

3. Reinforcement steel is added to better mouldability.

4. Precast concrete can be made at a factory only.

5. Concrete is not fire resistant.

2) Match the combinations from the left with their Russian equivalents:

 

1. Precast concrete 2. Reinforced steel 3. Tensile stress 4. Thermal insulator 5. Fire resistance

a) Напряжение при растяжении b) Сборный бетон c) Огнеупорность d) Арматурная сталь e) Теплоизоляция

 

3) Guess the word by its definition:

1. Pieces of broken or crushed stone or gravel

2. Any alien element or ingredient

3. Easily set on fire

4. A tine portion or fragment of something

5. The ability to withstand wear, pressure or damage

4) Open the brackets and put the verbs in a correct form:

1. The particles in the aggregate (bind) by the cement.

2. The strength of concrete (depend) on the proportions of cement and aggregate.

3. Certain properties (achieve) by including admixtures.

4. Concrete (characterize) by high strength.

5. High temperature (affect) the strength of concrete.

 

 

References: http: //www.fao.org/docrep/s1250e/s1250e08.htm