Structural Brickwork

Basic info is found in Chapter 8.

Brick structures have been used in many cultures for thousands of years. In Europe it was not until the middle of the twentieth century that brick was widely replaced by concrete as a main structural material, and since then it has often been used to clad concrete structures. In addition to being more durable than concrete, brick is easier to repair by replacement with new bricks.

Brick has a low tensile strength, which means that it is best used structurally in columns, walls and vaults of a smaller scale. Its uses can be widened through reinforcement and in combination with steel, concrete or timber. Both spans and the overall size of building units can increase and brick can be used in beams and floor slabs.

In normal brickwork, brick represents approximately 70% of the volume, the rest being the mortar. A wide range of mortars are used, usually based on Portland cement, sometimes mixed with lime. The necessary strength can also be achieved using lime mortars. When lime mortars are used there is usually no need for expansion joints due to the high elasticity in the resulting brickwork. See Chapter 17 for a more thorough presentation of mortars.

Brick is a heavy material that often needs to be transported over long distances with resulting pollution and climate gas emissions. Brick production itself also seriously pollutes the environment and is very energy consuming. But bricks need low maintenance and are very durable - in the majority of cases outlasting the other materials in a building. Dieter Hoffmann-Athelm expresses this fact in his paradoxical critique of civilization: 'Brick is almost too durable to have any chance nowadays'. Bricks can withstand most chemical attacks except for the strongest acids. Drains made of the same material as bricks - fired clay - withstand acidic ground conditions, whereas concrete pipes do not (Table 13.4). It is, therefore, important that the design of brick structures is done so as to facilitate future planning of recycling. This would make brick more competitive and attractive from the environmental point of view.

Large emissions of sulphur dioxide from the brick industry can be relatively simply filtered, or else reduced by adding lime to the clay. The

13.12

Openings in stone walls.

13.12

Openings in stone walls.

Table 13.4 Use of fired bricks

Types

Firing temp (b C)

Properties

Areas of use

Vitrified bricks

1050-1300

Very hard and frost resistant

External walls, flooring, lining of concrete walls, foundations

Well-fired bricks

800-1050

Hard and frost resistant, slightly absorbent to moisture

External walls, lining of concrete

Medium-fired bricks

500-800

Medium resistance to frost, very absorbent to moisture

Internal walls, inner leaf of cavity walls, rendered external walls, moisture-buffering

Low-fired bricks

350-500

Not frost resistant, highly absorbent to moisture

Internal walls, inner leaf of cavity walls, well-rendered external walls, moisture-buffering

Cellular bricks

Approx. 1000

Moderate thermal insulation, hard and medium frost resistant, slightly absorbent to moisture

Internal walls, inner leaf of cavity walls, rendered external walls

Zytan

Approx. 12001

Good thermal insulation, very hard and frost resistant

Thermal insulation, external walls, lining of concrete

1 Fired in two rounds.

1 Fired in two rounds.

Table 13.5 Amount of work hours needed to erect 1 m2 of earth wall, according to an investigation by the Norwegian Building Research Institute in 1952, (Bjerrum et al., 1952), the gross time also including surface treatment

Method

Work hours/m2 wall, net

Work hours/m2, wall gross

Pisé by machine

3.5

5.0

Pisé by hand

5.5

7.0

Adobe by machine

3.5

5.0

Adobe by hand

5.5

7.0

The equivalent fora fully completed concrete wall with surface treatment Is 3,3 hours/m2 whereas a brick wall takes 3 hours/m2, but those figures only take Into account the amount of work carried out on the building site itself. In the case of concrete and brick a large amount of work has been done before the materials actually arrive at

The equivalent fora fully completed concrete wall with surface treatment Is 3,3 hours/m2 whereas a brick wall takes 3 hours/m2, but those figures only take Into account the amount of work carried out on the building site itself. In the case of concrete and brick a large amount of work has been done before the materials actually arrive at total energy consumption can be greatly reduced by differentiating the use of bricks into well-fired and low-fired products. Today, only well-fired bricks are produced in most countries, even though low-fired alternatives could be used for many purposes. This was common practice until around 1950.

In Northern Europe brickwork, including porous mortars and brick qualities, runs a risk of frost damage during winter if placed in exposed positions. This risk is expected to increase due to climate change in Northern Europe but to decrease farther south, which opens up for wider use of low-fired brick and lime mortars. A well-rendered brick wall can, however, cope with most situations, as demonstrated in many older buildings in parts of Northern Europe exposed to frequent frost through centuries. For more on plasters see Chapter 15.

In the completed building brick is considered a healthy material. Bricks with a high lime content as well as most low and medium-fired bricks also have good moisture regulating properties that help stabilizing indoor humidity. For maintenance, conventional washing brick walls with hydrochloric acid can cause problems in indoor climates.

13.4.1 Brick products

13.4.1 Brick products

13.13

Examples of perforated bricks.

13.13

Examples of perforated bricks.

13.14

Examples of perforated blocks.

13.14

Examples of perforated blocks.

There are three main types of structural brick: solid bricks, perforated bricks and cellular bricks. The latter two can also be produced in the form of larger block elements. In cellular bricks, various light constituents are added to increase the thermal insulation properties (see Chapter 14). Perforated bricks and blocks are widespread; they use less clay and have a slightly better insulation performance. Bricks with up to 40% perforation can have the same strength as bricks with 20% perforation. They require however additional mortar because of the many holes. Smaller holes will reduce this problem.

The size and form of bricks has varied widely, depending upon the culture and period of use. The Romans usually fired square or triangular bricks 4 cm thick and up to 60 cm in length. They also produced semicircular and ornamental bricks. The rectangular structural brick has, with very few exceptions, always been formed on the principle of its length being twice its breadth plus the breadth of a mortar joint. The British Standard brick measures 215 x 102.5 x 65 mm. The mortar joint is usually 10 mm.

On the continent the use of large hollow brick blocks for floor slabs and beams is widespread. In hollow block beams, the structure is held together by steel reinforced concrete, whilst slab units are only partly structural as they are held between beams of either hollow blocks or concrete.

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