Reinforced cement concrete (mortar + aggregate)
Concrete is a product obtained artificially by hardening of the mixture of cement. sand, gravel and water in predetermined proportions. When these ingredients are mixed,they form a plastic mass which can be poured in suitable moulds, called forms, and set on standing into hard solid mass. The chemical reaction of cement and water, in the mix,is relatively slow and requires time and favourable temperature for its completion. This time, known as setting time may be divided into three distinct phases. The first phase.designated as time of inilial sel. requires from 30 minutes to about 60 minutes for completion.During this phase, the mixed concrete decreases its plasticity and develops pronounced resistance to flow. The second phase, known as final set, may vary ·between 5 to 6 hours after the mixing operation. During this phase, concrete appears to be relatively soft solid without surface hardness. The third phase consists of progressive hardening and increase in strength. The process is rapid in the initial stage, until about one month after mixing, at which time the concrete almost attains the major portion of its potential hardness and strength.
Depending on the quality and proportions of the ingredients used in the mix, the properties of concrete vary almost as widely as different kinds of stones. Concrete has enough strength in compression, but has little strength in tension. Due to this, concrete as such is weak in bending, shear and torsion. Hence the use of plain concrete. described above, is limited to applications where great compressive strength and weight are the principal requirements and where tensile stresses are either totally absent or are extremely low. However,to use cement concrete for common structures such as beams, slabs, retaining structures etc, steel bars may be placed at tensile zones of the structure which may then be concreted.The steel bars, known as steel reinforcement, embedded in the concrete. take the tensile stresses. The concrete so obtained is termed as reinforced cement concrete. commonly abbreviated as R.C.C.
Cement
Concrete
Aggregate
Steel
inside strength of concrete
plain and reinforced concrete
Type of cement
33 grade, 43 grade, 53 grade
Cement may be classified into five groups : (1) Portland Cement. (2 ) High Alumina
Cement, (3) Super Sulphated Cement, (4) Natural Cements and (5) Special Cements. with the following subdivisions :
1. Portland Cements
(a) Ordinary Portland Cement
(b) Rapid Hardening Cement
(c) Extra Rapid Hardening Cement
(d) Low Heat Portland Cement
(e) Portland Blast furnace Slag Cement
(t) Portland-Puzzolana Cement
(g) Sulphate Resisting Portland Cement
(h) White Portland Cement
(i) Coloured Portland Cement
2. High Alumina Cement
3. Super Sulphated Cement
4. Natural Cements
5. Special Cements
(a) Masonry Cement
(b) Trief Cement
(c) Expansive Cement
(d) Oil Well Cement
Aggregate
Aggregates is a general term applied to those inert or chemically inactive materials which, when bonded together by cement, form concrete. Most of the aggregates used are naturally occurring aggregates such as crushed rock, gravel and sand. Artificial and processed aggregates may be broken brick of crushed air-cooled blast furnace slag. Light weight aggregates, such as pumice, furnace clinker, coke, breeze , sawdust. foamed slag. expanded slates. expanded vermiculite etc. are also used for the production of concrete of low density
Aggregates may be divided into two groups :
(a) Coarse aggregates-those more than 4.75 mm in size are known as coarse aggregate.
(b) Fine aggregate- Aggregates less than 4.75 mm are known as fine aggregates
Some of the important characteristics of aggregates are :
(1) strength
(2) size
(3)particle shape
(4) surface texture
(5) grading
(6) impermeability
(7) cleanliness
(8) chemical inertness
(8) physical and chemical stability at high temperatures
(10) coefficient of thermal expansion, and
(11) cost.
Generally 20 mm aggregates is used
Light wt structure (Lintel,Small slab etc)- 10 mm
Mass Concreting (Dam,Retaining Wall & Above)- 40 mm
Water
Water acts as lubricant for the fine and coarse aggregates and acts chemically with cement to form the binding paste for the aggregate and reinforcement. Water is also used for curing the concrete after it has been cast into the forms.
Water used for mixing and curing shall be clean and free from injurious amountof oils, acids, alkalis, salts, sugar, organic materials or other substances that may be deleterious to concrete or steel. Potable water is generally considered satisfactory for mixing concrete.
PH value should vary between 6-9
Fresh Concrete PH-13
Old Concrete PH-8
fresh concrete
old concrete
PH value of cement
permissible level
Admixture
Accelerator
Retarder
Plasticizer
air entraining
generally TMT bar available in market
mild steel
hysd Bar
TMT bar
CRS
wire mesh
rolled Steel section
duty of engineer
characteristic strength
Represent
elastic modulus
cranked bar
Shrinkage
Fatigue
Workability
how to measure workability
durability of concrete
for costal area
for normal weather condition
Compaction
placing and height
Curing
Formwork
under water concreting