1) Concrete is made from three different materials.
2) Coarse aggregate ranges in size from 20 mm to 40 mm.
3)When the minimum thickness of the finished concrete is 100 mm, the maximum size of aggregate should not be greater than 25 mm.
4) When the reinforcing rods are close together, the maximum size of aggregate used should
be 10mm.
5) Cover is the thickness of concrete between the reinforcing rods.
6) The reinforcing rods are placed near the bottom of the rib of a concrete beam.
7) Spalling can occur in a solid concrete slab when the cover to the reinforcement is greater than
the maximum size of the coarse aggregate.
8) When the minimum horizontal distance between reinforcing rods is 15 mm, the maximum size
of aggregate should be less than 12 mm.
IX. Read the text:
Building materials in the hot climate zones
Cane and leaves are available in the warm-humid zones and grass in the intermediate and subtropical zones. Vine, bamboo and palm-fronds are used for buildings in the warm-humid zones. Because these materials are light, do not store heat, and allow the free passage of air, they are frequently used for making roofs. However, they have a relatively short life span because they deteriorate rapidly due to termite attack. They are also highly combustible.
Both hardwoods and softwoods are found in most tropical and subtropical areas with the exception of the hot dry zones. On external woodwork preservative stains should be used rather than paints which tend to deteriorate fairly rapidly in the hot zones. Extremes of climatic conditions cause dimensional changes producing cracks, splits and warping. Wind-blown sand and grit gradually erode exposed timber. In warm-humid zones timber is liable to wet and dry rot and to attack by termites and beetles.
Earth is one of the most widely used traditional building materials in hot-dry lands. Earth is used not only for walls but also for roofs; mud brick vaults and domes are common in countries like Iran and Egypt. Because mud has less strength than most other construction materials, mud walls are built thicker. Partly due to the thickness of mud walls and partly due to its low thermal conductivity, rooms built of mud are much cooler in hot climates than those of any other material. Mud bricks are brittle and do not withstand tension well. For this reason the vault and the dome were evolved in the East. There is a high risk of termite damage in some areas. Walls exposed to weathering and rain require frequent repair work.
Concrete and reinforced concrete are widely used throughout the non-temperate zones. Cement is manufactured locally in many places. Sand is found almost everywhere but it may be contaminated with soluble salts. Suitable aggregate may be difficult to find. Concrete is most frequently used for the structure, foundations and floor slabs of buildings. Care must be taken when using concrete for walls and roofs. Heat builds up on the exterior of concrete walls and roofs due to solar radiation and surface temperatures usually exceed air temperatures. Then, because concrete walls tend to be thin and concrete has a low resistance to the passage of heat, heat is conducted into the interior. Salts in aggregates and water can cause corrosion of the reinforcement and subsequent spelling of the concrete cover. In hot-dry areas the rapid evaporation and shortage of water can result in low strength, cracking and high permeability.
|
|
|
Complete this table with notes about all the materials described above;
| Material | Availability | Use | Properties | Problems/ Durability |
| Cane, leaves, vine, bamboo, palm-fronds | warm-humid zones | |||
| Grass | ||||
| Hardwoods and softwoods | ||||
| Earth | ||||
| Concrete |
X. Work in groups of three. Make a list of the building materials found in your country. Write 100-120 words comparing these materials from the point of view of their cost, strength and appearance. Share your ideas with other students.
XI. a) Some building materials are not environmentally friendly, plastics are among them. Their storage and recycling can cause damage to the environment. Are there any ways to reduce their negative impact on the environment? Share your ideas with other students.
