Building Materials

i.Adobe:Adobe is a natural building material mixed from sand, clay, and straw, dung or other fibrous materials, which is shaped into bricks using frames and dried in the sun. It is similar to cob and mudbrick. Adobe structures are extremely durable and account for the oldest extant buildings on the planet. Adobe buildings also offer significant advantages in hot, dry climates; they remain cooler as adobe stores and releases heat very slowly.

Buildings made of sun-dried earth are common in the Middle East, North Africa, and in Spain (usually in the Mudéjar style), but adobe had been in use by indigenous peoples of the Americas in the Southwestern United States, Mesoamerica, and the Andean region of South America for several thousand years, although often substantial amounts of stone are used in the walls of Pueblo buildings. This method of brickmaking was imported to Spain in the 16th century by Spaniards who had traveled to Mexico and Peru.

Bricks are made in an open frame; 25 cm (10 inches) by 36 cm (14 inches) is a reasonable size, but any convenient size is acceptable. The mixture is molded by the frame, and then the frame is removed quickly. After drying a few hours, the bricks are turned on edge to finish drying. Slow drying (shaded) avoids cracking.

The same mixture to make bricks, less the straw, is used for mortar and often for plaster on interior and exterior walls. Some ancient cultures used lime-based cement for the plaster to protect against rain damage.

The brick’s thickness is preferred partially due to its thermal capabilities (that is, adobe’s capacity to retain heat and cool temperature), and partially due to the stability of a thicker brick versus a more standard size brick. Depending on the form that the mixture is pressed into, adobe can encompass nearly any shape or size, provided drying time is even and the mixture is including of any reinforcement should the brick be too large. Reinforcement can include anything from manure, to straw, cement, rebar or wooden posts. Experience has shown that straw, cement, or manure added to a standard adobe mixture can all produce a strong brick to use in construction. A general testing is done on the soil content first. To do so, a sample of the soil is mixed into a clear container with some water, creating an almost completely saturated liquid. After the jar is sealed the test is performed by shaking the container vigorously for at least one minute. Allow the container to sit on a flat surface until the soil sediment has either collected on the bottom or remained a blended liquid. If the sediment collects on the bottom, that indicates there is a high clay content and is good for adobe. If the mixture remains a liquid, then there is little clay in the soil and using it would yield weak bricks.

The largest structure ever made from adobe (bricks) was the Bam Citadel, which suffered serious damage (up to 80%) by an earthquake on December 26, 2003. Other large adobe structures are the Huaca del Sol in Peru, built using 100 million signed bricks, the ciudellas of Chan Chan and Tambo Colorado, both also in Peru.

 

Examples of adobe mosques:

The great mosque of Jenne ,Mali.

ii. Bricks:

Bricks may be made from clay, shale, soft slate, calcium silicate, concrete, or shaped from quarried stone.

Clay is the most common material, with modern clay bricks formed in one of three processes - soft mud, dry press, or extruded.

In 2007 a new type of brick was invented, based on fly ash, a by-product of coal power plants.

Mud bricks

The soft mud method is the most common, as it is the most economical. It starts with the raw clay preferably in a mix with 25-30% sand to reduce shrinkage. The clay is first ground and mixed with water to the desired consistency for forming in a mould. The clay is pressed into steel moulds with a hydraulic press. The shaped clay is then fired ("burned") at 900-1000 °C to achieve strength.



Rail kilns

In modern brickworks, this is usually done in a continuously fired tunnel kiln, in which the bricks move slowly through the kiln on conveyors, rails, or kiln cars to achieve consistent physical characteristics for all bricks. The bricks often have added lime, ash, and organic matter to speed the burning.

 

 

Bull's Trench Kilns

In Pakistan and India, brick making is still typically a manual process. The most common type of brick kiln in use there are Bull's Trench Kiln (BTK), based on a design developed by British engineer W. Bull in the late 1800s.

An oval or circular trench, 6-9 meters wide, 2-2.5 meters deep, and 100-150 meters in circumference, is dug in a suitable location. A tall exhaust chimney is constructed in the center. Half or more of the trench is filled with "green" (unfired) bricks which are stacked in an open lattice pattern to allow airflow. The lattice is capped with a roofing layer of finished brick.

In operation, new green bricks, along with roofing bricks, are stacked at one end of the brick pile while cooled finished bricks are removed from the other end for transport. In the middle the brick workers create a firing zone by dropping fuel (coal, wood, oil, debris, etc) through access holes in the roof above the trench.

The advantage of the BTK design is a much greater energy efficiency compared with clamp or scove kilns. Sheet metal or boards are used to route the airflow through the brick lattice in such a way that fresh air flows first through the recently burned bricks, thus heating the air, then through the active burning zone. The air continues through the green brick zone (pre-heating and drying them), and finally out to the chimney exhaust where the rising gases create the suction which pulls the air through the whole system. The reuse of heated air results in a considerable savings in fuel cost.

As with the rail process above, the BTK process is a continuous one. A half dozen laborers working around the clock can fire approximately 15,000-25,000 bricks a day. However, unlike the rail process, in the BTK process the bricks themselves do not move. Instead the locations at which the bricks are loaded, fired, and unloaded gradually rotate through the trench.



Dry pressed bricks

The dry press method is similar to mud brick but starts with a much thicker clay mix, so it forms more accurate, sharper-edged bricks. The greater force in pressing and the longer burn make this method more expensive.

Extruded bricks

In extruded bricks the clay mix is 20-25% water, this is forced through a die to create a long cable of material of the demanded width and depth. This cable is then cut into bricks of the desired length by a wall of wires. The majority of structural bricks are made by this method as hard dense bricks are the result and any needed holes or other perforations can be introduced by the die. The introduction of holes reduces the needed volume of clay through the whole process, with the consequent reduction in costs per brick. The bricks are also lighter and so easier to handle and have different thermal properties compared to solid bricks. The cut bricks are hardened by drying for between 20 and 40 hours at 50-150 °C before being fired. The heat for the drying is often the waste heat from the kiln.

Fly ash bricks

In May 2007, Henry Liu, a retired civil engineer, announced that he had invented a new brick composed of fly ash and water compressed at 4,000 psi (27,939 kPa) for two weeks. Owing to the high concentration of calcium oxide in fly ash, the brick can be described as "self-cementing". The brick is toughened using an air entrainment agent, which traps microscopic bubbles inside the brick so that it resists penetration by water, allowing it to withstand up to 100 freeze-thaw cycles. Since the manufacturing method uses a waste by-product rather than clay, and solidification takes place under pressure rather than heat, it has several important environmental benefits. It saves energy, reduces mercury pollution, alleviates the need for landfill disposal of fly ash, and costs 20% less than traditional clay brick manufacture. Liu intends to license his technology to manufacturers in 2008.

(http://en.wikipedia.org/wiki/Brick).