I. Advantages:
a) Economical: Concrete is the
most inexpensive and the most readily available material. The cost of
production of concrete is low compared with other engineered construction
materials. Three major components: water, aggregate and cement. Comparing with
steel, plastic and polymer, they are the most inexpensive materials and
available in every corner of the world. This enables concrete to be locally
produced anywhere in the world, thus avoiding the transportation costs necessary
for most other materials.
b)
Ambient temperature hardened material: Because cement is a low
temperature bonded inorganic material and its reaction occurs at room
temperature, concrete can gain its strength at ambient temperature.
c) Ability
to be cast: It can be formed into different desired shape and sizes right
at the construction site.
d) Energy
efficiency: Low energy consumption for production, compare with steel
especially. The energy content of plain concrete is 450-750 kWh / ton and that
of reinforced concrete is 800-3200 kWh/ton, compared with 8000 kWh/ton for
structural steel.
e) Excellent resistance to water. Unlike
wood and steel, concrete can harden in water and can withstand the action of
water without serious deterioration. This makes concrete an ideal material for
building structures to control, store, and transport water. Examples include
pipelines (such as the Central Arizona Project, which provide water from
Colorado River to central Arizona. The system contains 1560 pipe sections, each
6.7 m long and 7.5 m in outside diameter 6.4 m inside diameter), dams, and
submarine structures. Contrary to popular belief, pure water is not deleterious
to concrete, even to reinforced concrete: it is the chemicals dissolved in
water, such as chlorides, sulfates, and carbon dioxide, which cause
deterioration of concrete structures.
f)
High temperature resistance: Concrete conducts heat
slowly and is able to store considerable quantities of heat from the
environment (can stand 6-8 hours in fire) and thus can be used as protective
coating for steel structure.
g)
Ability to consume waste: Many industrial wastes can be
recycled as a substitute for cement or aggregate. Examples are fly ash, ground
tire and slag.
h)
Ability to work with reinforcing steel: Concrete and steel
possess similar coefficient of thermal expansion (steel 1.2 x 10-5;
concrete 1.0-1.5 x 10-5). Concrete also provides good protection to
steel due to existing of CH (this is for normal condition). Therefore, while
steel bars provide the necessary tensile strength, concrete provides a perfect
environment for the steel, acting as a physical barrier to the ingress of
aggressive species and preventing steel corrosion by providing a highly
alkaline environment with about 13.5 to passivate the steel.
i) Less maintenance required:
No coating or painting is needed as for steel structures.
II. Limitations
and their improvements
Quasi-brittle
failure mode: Concrete is a type of quasi-brittle
material.
Solution: Reinforced concrete
Low
tensile strength: About 1/10 of its compressive strength.
Improvements: Fiber
reinforced concrete; polymer concrete
c) Low toughness:
The ability to absorb energy is low. Improvements: Fiber reinforced concrete
d) Low strength/BSG ratio (specific strength):
Steel (300-600)/7.8. Normal concrete
(35-60) /2.3 Limited to middle-rise buildings. Improvements: Lightweight concrete;
high strength concrete
e) Formwork is needed:
Formwork fabrication is laborer intensive and time consuming, hence costly
Improvement: Precast concrete
f)
Long curing time: Full strength development needs a month.
Improvements: Steam curing
g)
Working with cracks: Most reinforced concrete structures have
cracks under service load. Improvements:
Pre-stressed concrete.
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