Types of concrete

FAQ ON CEMENT & Concrete Types

FAQ
1 What is the Raw Material used for manufacture of cement?
Calicareous (Limestone Obtained from mines) ,argillaceous materials (Clay, Bauxite) and Iron are the commonly used raw materials in the manufacture of cement.
2 How is cement manufactured?
Manufacture of cement comprises of four stages viz.
1. Extraction of lime stone from mines.
2.Blending of ground limestone,Clay or Bauxite and iron ore or Laterite in right proportion and cintering in rotary kilns at a high temperature of 1400oC to 1500oC form Clinker.
3. Grinding of clinker with Gypsum to form cement.
4. Storing in silos, testing and despatch form the final process of manufacture.
3 What is the chemical composition of cement and the contribution of each chemical compound?

Chemical Compounds Range in *OPC% Reaction Rate Strength Attained Liberation of Heat
Tri-Calcium-silicate (C3S) 40-55 Fast
High High

Di-Calcium silicate(C2S)
25-40 Slow Lowfirst high later Low
Tri-calcium Aluminate(C3A) 8-11 Fast Low Very High
Tetracalcium Alumino ferite 13-17 Moderate Low Moderate

4 What is the role of Gypsum in cement?
Gypsum is added to control the 'setting of cement'
5 What is 'Setting of Cement'?
Setting is the stiffening of the cement paste.Broadly it refers to change of fluid to rigid state.
6 What do you mean by hardening of cement?
Hardening is the gain of strength in cement. This process of gain of strength continuous up to one year rapidly approximately and gradually after one year and up to 5 years.
7 Why should cement be 'fine'?
The rate of hydration of cement depends on the fineness of cement and for a rapid development of strength high fineness is necessary
8 What is meant by 'Soundness of Cement'?
Cements may sometimes contain free lime, which may cause expansion. Hence soundness test is conducted to see that even if uncombined lime is present in cement whether it is in prescribed limits. If it is within the prescribed limits then it is said to be sound.
9 What does, 53 grade, 43 grade and 33 grade cement indicate?
Grades 53 , 43 and 33 indicate the compressive strength of cements in Newtons for one mm2 area. i.e. 53 grade means a compressive strength of 53 N.per mm2 attained after a curing period of 28 days. Similarly 43 and 33 grades may be defined.
10 Does the colour of the cement affect it's strength?
The colour of the cement depends on the raw mateirals used. If the raw materials contain more iron resulting cements will be darker. Colour has no significance on any properties of cement. The strength of the cement is dependent on the correct proportion of raw material mix
11 What are the reasons for slow setting and quick setting of cement?
Slow setting in cement is due to Salts and chemicals in water, sand and aggregate. Cold Weather, Less cements , High % of impurities, adultrated cement, improper water cement ratio. Quick setting of Cement is due to : addition of low quantity of Gypsum, hot weather condition, high cement fineness.
12 How to store cement ?
Proper storage of cement shall permit easy access for inspection and identification.Cement shall be stored in suitable weather tight structures, to protect the cement from dampness.It shall not be piled more thah ten bags in a stack and shall be arranged in header and stretcher fashion as far as possible.while removing the bags for use,"FIRST IN FIRST OUT" rule shall be applied.
13 What is Mortar ?
Mortar is a mixture of sand, cement and water.
14 Why is concrete the most widely used construction material?
Concrete is the most versatile mouldable construction material ever known to mankind.It bears excellent fire and weather resistant properties. Most intricate shapes can be achieved with concrete . It is very good in compression though weak in tension.It is supplimented by steel to achieve tensile strength. Centuries old monuments bear testimony for its life.
15 What should be the quality of aggregate for a good concrete?
Aggregate for concrete should be inert, dense, hard durable ,structurally sound, capable of developing good bond with the cement paste, weather resistant and unaffected by water.
16 What is the sources of aggregate?
Natural sand, gravel, pebbles, rocks crushed to required size and manufactured aggregates like blast furnace slag are sources of aggregate. IS 456-2000 stipulates that the aggregates should conform to IS 383-1970.
17 What is the function of water in 'concrete'?
It is with water that the cement undergoes the process of hydration to form a gel with binding property covering the aggregates uniformly on mixing. However water for mixing shall be limited to achieve a required consistency as excess water is deterrent to concrete.
18 Can any water be used in concreting?
It is important that water used in concrete should be free from impurities Generally it should be of potable quality. Bore water would need checking before using because it often contains impurities which affect setting times and reduce the strength of concrete. Sea water is not suitable for reinforced concrete as it causes corrosion. IS456-1978 gives the maximum possible limits of solids in water.
19 What is an admixture?
An admixture is a chemical formulation generally added to concrete while mixing to induce certain desirable properties to it like better workability with water reducing admixture, delayed setting the retarders, improve the rate of hardening with accelerating admixtures, and air entertainment for better flow and lubrication.
20 What is meant by 'Reinforced Cement Concrete' (RCC)?
Concrete is strong in compression and weak in tension. A plain concrete beam when it is subjected to bending fails at the bottom side due to tension. Hence to make concrete strong in tension, steel is embedded so that it becomes strong both in tension and compression. The concrete embedded with steel is called `Reinforced Cement Concrete'
21 What are the factors affecting the workability of concrete?
The factors that are affecting the workability of concrete are water content, aggregate type and grading, aggregate/cement ratio, presence of admixtures and fineness of cement.
22 What is meant by batching?
Measurement of various ingredients of concrete like sand, metal and cement for each batch of concrete per design is called batching. Volume batching and weigh batching are the two types of batching in vogue
23 What is the process of mixing of concrete?
The different stages of `mixing of concrete' are : To locate a correct spot on a firm ground close to the concrete site, positioning the mixture machine conveniently oriented to feed the hopper , emptying the drum of concrete on the platform prepared. To stack metal,sand and cement per design mix work out per batch.to feed the drum with required quantity of water.To feed the drum with the contents of hopper and allow the mix in the rotating drum for 1 &1/2 to 2 minutes till a homogeneous mix is obtained .To empty the drum of concrete on the platform and leading it to the concreting spot.
24 What are the factors affecting the strength of concrete?
The factors that are affecting strength of concrete are : Water cement ratio Shape and size of aggregate Aggregate cement ratio ,Degree of compaction ,Age of concrete and Air entrainment and moisture in aggregate.
25 What is meant by seggregation of concrete?
Seggregation of concrete can occur in two form. In the first the coarser particles tend to separate out while concrete being conveyed along a slope(for e.g.sloped roof and staircase waist slab)or,not being homogeneous coarse aggregate settle below leaving the slurry with fine aggregate below.The second form of seggregation occurs in wet mixes by separation of grout from the mix.This happens due to over vibration of concrete and dropping of concrete from a height .
26 Why is a 'crack' developed?
A crack is developed whenever stresses in the structural component exceeds its strength .This may be due to external forces, foundation settlement, thermal changes, chemical action etc.
27 Why do 'plastering cracks' occur?
Plastering cracks appear because of evaporation of water, increased thickness, very fine sand, low quality bricks, non uniform plastering, improper seasoning of walls, use of different mix proportion , improper filling of joints, insufficient curing, more free lime/MgO.
28 Why do RCC cracks?
RCC cracks due to insufficient reinforcement and cover, corroded steel, high slump, improper vibration, volume changes, excessive coarse aggregates, expansion of concrete, lack of sufficient quantity of cement, electrical conduits not placed at sufficient depth in concrete.
29 What do you mean by M20, M30, M40 concrete?
M20, M30, M40 Grades of concrete indicates compressive strength of concrete in Newtons for one mm2 area which is called the characteristic strength of concrete after 28 days. M20 mean 20 N/mm2 similarly M30 is 30 N/mm2.
30 What is meant by water cement ratio?
The quantity of water used for mixing of concrete per unit volume related to the quantity of cement is called water cement ratio and is expressed as the ratio of the weight of water to the weight of cement used in a unit volume of concrete.
31 What is curing?
Maintenance of a favourable environment for the continuation of chemical reaction that are responsible for hardening of cement is called curing.
32 What methods are commonly employed to ensure sufficient moisture for curing?
Ponding, continuous sprinkling, covering with wet cloth, polyethylene sheets, sealing coat applied as a liquid commonly known as "Curing compounds" are some of the methods commonly employed for curing
33 What are the common mistakes which affect the quality of concrete?
Use of too much or too little water for mixing.
Incomplete mixing of aggregate with cement.
Improper grading of aggregates resulting in seggregation or blending of concrete.
Inadequate compaction of concrete.
Using concrete which has already begun to set.
Placing of concrete on a dry foundation without properly wetting it with water.
Use of aggregate containing foreign materials such as earthy matters, clay or lime. Use of water containing solids, chemicals etc
Too much trowelling of the concrete surface.
Leaving the finished concrete surface exposed to sun and wind during the first ten days after placing without curing.

Source : http://www.indiacements.co.in/asktheconcreteman.htm#

Classification
Grade
Applications

Ordinary
M10
PCC (Plain Cement Concrete) e.g. Levelling course, bedding for footing, concrete roads, etc.

M15
PCC e.g. Levelling course, bedding for footing, concrete roads, etc.

M20
RCC (Reinforced Cement Concrete) e.g. Slabs, beams, columns, footings, etc. (for mild exposure)

Standard
M25
RCC (Reinforced Cement Concrete) e.g. Slabs, beams, columns, footings, etc.

M30
RCC e.g. Slabs, beams, columns, footings, etc.

M35
RCC e.g. Slabs, beams, columns, footings, etc.

M40
RCC e.g. Pre-stressed concrete, slabs, beams, columns, footings, etc.

M45
RCC e.g. Runways,Concrete Roads (PQC), Prestressed Concrete Girders, RCC Columns, Prestressed beams

M50
RCC e.g. Runways,Concrete Roads (PQC), Prestressed Concrete Girders, RCC Columns, Prestressed beams

M55
RCC e.g..Prestressed Concrete Girders and Piers

High Strength
M60 - M80
RCC work Where high compressive strength is required such as high rise buildings, long span bridges, ultra-thin white topping etc and constructions in aggressive environment e.g. Spillways of dams, coastal construction


In addition to producing normal grade concrete ranging from M10 to M80, we produce customized special types of concrete for different applications.

Types of Special Concrete Application

High Volume Fly Ash Concrete
Mass concrete, raft foundations, roads, pavements etc.

Silica fume concrete
All high strength concrete applications in extreme environmental exposure condition like marine structure etc.

GGBS, Slag based concrete
All underground RCC application requiring high chemical resistance and enhanced durability

Ternary blend concrete
All RCC application directly in contact with aggressive soil / chemicals in marine environment and in sewage / effluent treatment plants

Light weight concrete
Repair and rehabilitation work, for thermal insulation, light weight structural fill, and light weight pre - cast panel etc

Corrosion resistant concrete
All types of RCC applications in high water table area including work near coastal areas, water tanks, etc

Polymer concrete
Repair and rehabilitation work for floorings and buildings where high early strength is required

Self Compacting Concrete
Thin sections and elements with congested reinforcements. Recently IS 456 has also included SCC with specifications in its codal provision.

Coloured Concrete
For architectural and aesthetic use

Fibre-reinforced Concrete
For concrete with higher ductility and abrasion/erosion resistance

Pervious Concrete
Concrete for parking areas, pavements, drive-ways to ensure drainage or rain-water harvesting

Water-proof Concrete
Terraces, basements, water contact structures

Temperature Controlled Concrete
Mass concrete, hot-weather concrete etc

Source
http://www.ultratechconcrete.com/concrete_smartusage.html
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