Text 1. Brick loadbearing walls

Read the text more thoroughly and find out the differences between different sorts of brick and their uses.

In the text point out the introductory part and the main part.

The external wall of a house has two basic functions:

• to support the loads of suspended floors and roof

• environmental protection.

In order to satisfactorily fulfil these functions there are a number of requirements for an external loadbearing wall. These are: strength and stability, weather protection, good thermal insulation, fire protection and durability.

The two most common materials used nowadays for walling in domestic construction are brickwork and block-work. The majority of bricks are made from clay. Different clays have different characteristics and, by using special manufacturing techniques and adding a variety of additives, bricks of various colours and strengths can be produced.

Bricks can be described as:

• common bricks - these are suitable for general building work where the face of the brick will be covered with plaster, render or other finish;

• facing bricks - these come in a wide range of finishes, colours and strengths and are used where the face will be left exposed. The most common use today is for the outside walls of houses;

• engineering bricks - these are dense bricks with high compressive strength and low rates of water absorption. Although some of them may be used as facing bricks for houses they are more likely to be found in civil engineering structures such as retaining walls and bridges.

Bricks can also be classified by their resistance to frost attack. Some bricks are totally resistant to frost attack while others are quite vulnerable. Bricks suitable for severe exposure are classified F2 (the new European Standard), those suitable for moderate exposure are classified F1, and those suitable for passive exposure FO. Class F2 bricks are therefore suitable for use in any part of an external wall including situations where they may be saturated and have to undergo repeated cycles of freezing and thawing. Class F1 bricks are normally durable in the outer face of a building as long as exposure is not severe and appropriate measures have been taken in the design of the wall to prevent saturation. This generally means they are suitable above the DPC and below the eaves. Class FO bricks are generally for internal use only.

Calcium Silicate Bricks. These bricks are made from sand or crushed flint and lime together with coloured pigments. The materials are mechanically pressed into shape and then put in hardening chambers into which steam is injected under pressure. During hardening a chemical reaction occurs to produce hydrated calcium silicate. The bricks are very regular in shape and can easily be recognised by their pale colours. They are generally resistant to frost attack and virtually free from soluble sulfates.

Concrete Bricks. The majority of concrete bricks are made by blending and compacting dense aggregate with a cementitious binder under high pressure. Coloured facing bricks are manufactured by blending different aggregates or by adding special pigments. By varying the proportions of cement the bricks can be manufactured in a variety of strengths. Concrete bricks are becoming increasingly popular, particularly when mixed with crushed stone aggregate as a substitute for natural stone.

Blockwork has become very popular in the last 60 years or so because of its cost advantages over brickwork. Most blocks are equivalent in size to six bricks (three bricks high and two long) and are available in a range of widths from 50mm to 300mm. Blocks less than 75mm wide are unsuitable for loadbearing walls. Blocks are made from cement and aggregate, and by varying the quantity of cement and the nature of the aggregate, blocks with different strengths and levels of insulation can be formed.

Дата добавления: 2014-12-23