Brick is a traditional building material in China, the total output of bricks in 1996 amounted to 760 billion. At present, brick is still the most common walling material in China. The raw material for brick making – clay - can be easily obtained everywhere, while the brick making process is comparatively simple and the plant investment is low. Brick is very flexible in laying for all sorts of masonry structures. Despite its low efficiency in building construction, its manufacture is labor intensive, thus providing advantageous to any developing country. 

Above all, brick buildings are cheap to build, comfortable to live in, and easy to maintain and repair. It is also durable, heath protected and energy saved. For example, the market price for the standard brick (240x115x53mm) is about USD0.01-0.02/pc. We do believe that to promote China brick technology will be helpful for the developing countries to build low cost houses with masonry structure.

Characteristics of clay bricks

1.  Types

     (1) Common bricks (solid bricks)
     (2) Perforated bricks – vertically cored for bearing walls
     (3) Hollow blocks – horizontally cored for non-bearing walls
     (4) Bricks for decoration, such as lattice brick, glazed wall tiles, floor tiles, split tile, etc

2. Uses of clay bricks

   (1) Structural
   Clay bricks are used for load bearing walls up to 18 or 28 meters high (according to wind load).

   (2) Architectural
   Split tiles for outside wall decoration and lattice bricks are used for architectural purposes.

   (3) Functional
   Horizontally cored hollow bricks are used for laying fill-in brickwork (or in fill) or curtain walls of reinforced concreted concrete skeleton structures.

3. Strength properties of clay bricks

Design engineers traditionally used clay bricks of compressive strength greater than 100kg/cm2 for the construction of load bearing walls of five to six story buildings. Bricks of inferior quality are used for non-load-bearing walls, diaphragm walls or less important structures.

As far as load-bearing strength is concerned, the compressive strength of clay bricks is far more than sufficient. Actually, it is durability, which is the main considerations, since under fired bricks undoubtedly have low compressive strength and are not durable.

4. Durability, stability and appearance of clay bricks

Those are governed by clay brick standard specifications, clay bricks of good quality should meet the requirement of the specifications.


Raw materials

1. Prospecting procedures

As soon as a clay brickworks is planned, a feasibility study is undertaken. The first thing to do is to have a chartered geological team to investigate the raw material (clay) supply, to locate the clay resource, to find out the size of the clay reserve, followed by various tests to determine the clay's properties.

2. Sizing the reserves

By means of drilling and pit exploration, the clay distribution in a certain area is investigated as requested. As a result of the exploration, a preliminary estimate of the amount of available clay reserve is made.

3. Requirements of clay for brick making

Due to the variety of clays, the raw material study and test, such as physical analysis, mineral and chemical compositions analysis, drying and firing properties, and so on, is very important to determine the production process and select the proper equipment list accordingly. However, we might provide a assumed properties as below, which can only be taken as base-line references.

• Volume weight : 1.3kg/m3 

• Atterberg plasticity index : 8-14 %

• Drying linear shrinkage : ≤5%

• Firing linear shrinkage : ≤3%

• Coefficient of drying sensitivity : ＜1.2

Quartz with diameter over 2mm, limestone, conch, weed, root, etc are not allowed, otherwise additional pretreatment equipment shall be added. 


Quarrying methods

1. Organization

The appropriate method and equipment are selected according to the properties of clays (e.g. types of clay, its hardness, cohesiveness, etc), topography features of the quarry and the distance of transportation to the preparation plant. 

2. Quarry operations

Clays of different properties are divided into separate regions, each of which is designated for making certain products. Clays with lime-nodules in lumps should be removed to assure safe production. Safe operations in steep banks, in pits with underground drainage system and in abandoned underground mining tunnels are to be carried out with special attention. 

Drainage around the quarry pit should be done before extraction starts, otherwise quarry operation is not possible after rainy days. High underground water level would increase the moisture content of the natural clay. Drainage helps to lower it.

3. Clay extraction

In clay extraction, overburden consisting of grass, tuffs, slags, gravels etc should be cleared first. The quarrying area must be free of any obstacle (trees, fences, piping, tombs, etc). 

4. Handing and transportation of clay

In China, extraction sites are usually not more than 200 or 300 meters from the preparation plants since transporting clay in trucks would increase the cost of production. Bulldozers are commonly used to bring the clay to the plants.


Preparation of clay

The production of quality bricks is largely dependent on the proper preparation of raw material. Usually the preparation includes: ageing, cleaning, crushing, grinding, screening, proportioning, mixing, wetting and tempering, etc. 

For your information, proportioning of two or more raw materials is seldom used in China's brick industry.  It involves a lot of technological questions and often leads to the increase of production cost. To find and locate one appropriate quarry and plant site would reduce the investment cost. 

	Ageing bed		Clay taker

Shaping of clay bricks

Plastic extrusion is mostly used in the production of clay bricks.

Handing of shaped products (green bricks)

The extruded column of clay is initially cut into segment, and then cut into green bricks by a wire cutter.  The cut green bricks are transported on a belt conveyor, from which they are removed manually and set into a dry car. An alternative method is to have the cut green bricks on the belt assembled and set with an automatic setting machine into a dryer car or onto pellets.

	Box feeder		Segment Cutter		Wire Cutter

Dry of bricks

There are two drying methods, natural drying & artificial drying. 

• Natural drying uses the sun's heat, which is an economic source of energy. But it needs a large area for its drying yards. 

• Artificial drying has the advantage of constant production all-year-round, but requires higher capital investment.

	Drying Chamber		Drying Car		Setting machine

Firing of bricks

Usually the adobe will be set on to a kiln car manually with less investment cost. An alternative method is to discharge the adobe onto the belt conveyor and set with an automatic setting machine onto a kiln car, but it has higher requirement in uniform size of adobes and requires higher capital investment.

Bricks are fired in different kinds of kilns up to the temperature of 950°C-1050°C. After a series of physical-chemical reactions, the desired strength and physical as well as chemical properties are finally obtained. 

The fuel used is usually coal, gas and oil. 

The most generally used kilns are annular (Hoffmann) kiln and tunnel kiln. Annular kiln is an elongated circular kiln with fire-holes on its longitudinal arch roof. Owing to the poor control capacity of firing temperature, it has been replaced by tunnel kiln. 

The tunnel kiln has a long tunnel with loaded kiln cars on rails moving along the tunnel. The firing zone is stable somewhere near the middle of the tunnel. In contrast to the annular kiln, the preheating, firing, cooling zones are stable while the stacks of bricks loaded on kiln cars are moving. Cooling air coming in through the kiln exit, passes through the cooling zone, is heated in the firing zone thus heating the bricks and is extracted near the kiln entrance by means of fans. Fuel (oil or gas, coal will be generated into coal gas first) is generally added automatically manually through the burners.

	Tunnel Kiln		Control Room		Transferring Car

Handling methods

For tunnel kiln, the equipment mentioned above is used for handling purposes. For annular kiln, wheelbarrows are used for transporting the bricks into the kiln and a special wheelbarrow unloads the whole stack as one stack in the yard.

The fired bricks out of tunnel kiln are unloaded from kiln cars onto a special wheelbarrow manually by a simple tool "brick clamp" which can clamp four standard bricks easily and quickly at a time, and stored in yard around the kiln in stacks. each. Then they are transported to the construction site by customers. 

Loading the trucks in brickworks and unloading in the construction site are also done manually by "brick clamp".