Grouting agents

Admixtures used for grouting are:

• Accelerators
• Retarders
• Gag forming agents 
• Workability agents

Workability agents

Workability is one of the most important characteristics of concrete especially under the following circumstances:

1. If the concrete is to be placed around closely placed reinforcement or in difficulty accessible sections.
2. Where special means of placement are required such as tremie, chute or pumping methods.
3. If the concrete is harsh because of aggregate characteristics or grading

The materials used as workability agents are:

1. Finely divided material
2. Water reducing agents 
3. Air entraining agents

• Common materials added as workability agents are bentonite clay, diatomaceous earth, fly ash, finely divided silica, hydrated lime and talc
• When they are added and if the quantity of water is not reduced they greatly increase the workability.

Retarders

A retarder is an admixture that slows down the chemical process of hydration so that concrete remains plastic and workable for longer time than concrete without the retarder

Retarders are used to overcome the accelerating effect effect of high temperature on setting properties of concrete in hot weather concreting.

Common materials added as retarding agents:

1. Most commonly known retarder is calcium sulphate.It is interground to retard the setting of cement.
2. Starches, cellulose products, sugars, acids or salts of acids.
3. Common sugars are one of the most effective retarding agents.
4. Other admixtures, which have been successfully used as retarding agents are Ligno sulphonic acids and their salts, hydroxylated carboxylic acids and their salts.

Accelerators

Accelerating admixtures are added to concrete to increase the rate of early strength development in concrete to

• Permit earlier removal of formwork
• reduce the required period of curing
• Advance the time that a structure can be placed in service
• Partially compensate for the retarding effect of low temperature during cold weather concreting
• In the emergency repair works

 Calcium chloride is the material very commonly used as accelerator.

The action of calcium chloride is assisting concreting at low temperature is three fold as-

• It lowers the temperature at which freezing of the wet mixture takes place
• It helps to keep the mixture warm by accelerating the generation of heat by chemical action 
• It increases the ability of the concrete to resist frost action by speeding up the rate of gain of strength

Effects of calcium chloride on concrete:

• Increases volume changes in concrete 
• Increases the alkali-aggregate reaction 
• Reduces the resistance of concrete  to sulphate attack

 

Pozzolanic admixture

Best pozzolans in optimum proportions mixed with Portland cement improves many qualities of concrete such as

1. Lower the heat of hydration and thermal shrinkage
2. Increase the water tightness
3. Reduce the alkali-aggregate reaction
4. Improves resistance to attack by sulphate soils and sea water
5. Improve extensibility
6. Lower susceptibility to dissolution and leaching
7. Improve werkability
8. Lower costs

Pzzolanic materials are-

• Clay and shales
• opaline shales 
• Diatomaceous earth
• Volcanic tuffs and pumicites

Artificial pzzolans are-

• Fly ash
• Surkhi

Air-Entraining Agents

The following types of air-entraining agents are used for making air entrained concrete:

•  Natural wood resins
• Animal and vegetable fats and oils
• Alkali salts or sulphated and sulphonated organic compounds
• Water-soluble soaps of resin acids and animal and vegetable fatty acids
• Miscellaneous materials such as the sodium salts of petroleum sulphonic acids, hydrogen peroxide and aluminum powder etc.

The most important air entraining agents which at one time enjoyed worldwide market are vinsol resin and darex.

Factors affecting air entrainment

1. The type and quantity of air entraining agents used
2. Water and cement ratio of the mix
3. Type and grading of aggregate
4. Mixing time
5. The temperature
6. Type of cement
7. Influence of compaction
8. Admixture other than air entraining agents used

The effect of air entrainment on the properties of concrete:

Air entrainment will affect directly the following three properties of concrete

• Increase resistance to freezing and thawing
• Improvement of workability
• Reduction in strength

Incidentally air entrainment also affect the following properties of concrete

1. Reduce the tendencies of segregation
2. Reduces the bleeding and laitance
3. Decreases the permeability
4. Increases the resistance to chemical attack
5. Permits reduction in sand content
6. Improves placeability and early finishing
7. Reduces the cement content, cost, and heat of hydration 
8. Reduce the unit weight
9. Permits reduction in water content
10. Reduces the alkali-aggregate reaction 
11. Reduce the modulus of elasticity

Admixture

Admixtures are those which are added to concrete to give some desired quality to the concrete.

As per the report of ACI committee 212 admixtures have been classified into 15 groups according to type of materials constituting the admixture or characteristic affect of the use. The following are 15 groups:

1.Air-entraining agents
2.Pozzalonas
3.Accelerators
4.Retarders
5.Gas forming agents
6.Air-detraining agents
7.Alkali-aggregate expansion inhibitors
8.Damp-proofing and permeability reducing agents
9.Workability agents
10.Grouting agents
11.Corrosion inhabiting agents
12.Bonding agents
13.Fungicidal, germicidal and insecticidal agents
14.Coloring agents
15.Miscellaneous agents

Types of Bricks

Bricks can be classified from different angle of view. For practical use it is often classified as

• First Class brick
• Second Class brick
• Third Class brick

 First Class Brick Characteristics

1. Burnt uniformly
2. Uniform color throughout the brick.
3. Free from cracks, flaws, stones, lime.
4. If struck with same type of brick good metallic sound can be heard.

Uses of First Class Brick

1.   Almost all kinds of construction works where bricks are necessay
2.   Load bearing walls
3.   Brick soling, pavements etc.

Second Class Brick Characteristics

1. They are well burnt or slightly over burnt.
2. Surface is smooth but some hair cracks present.
3. They might not be of equal size but their shape is equal

Uses of Second Class Brick

1. Small and less important works like load bearing works of one storied buildings.
2. Partition walls of buildings where outer surface is to be plastered.

 

 

Third Class Brick Characteristics 

1. They are slightly under burnt or over burnt
2. They do not have uniform size and shape
3. They absorb more than 25% of water when submerged in water for 24 hours.
4. Relatively soft.
5. They have some signs of efflorescence.

Uses of Third Class Brick

1. Used in structures of very low importance.
2. where structure is not exposed to rain.
3. Walls with low height.

 

Applications Of Ferrocement

1.Widely used in domestic overhead tank.This tank is light, flexible, easy to transport and cheap.

2.Different types of inlet and outlet connections can be easily done with the help of adhesive using ferrocement.

3.It can be used as "gasholder" in "gobbar gas plant".
4.With slight modification ferrocement tanks can be used as grain silos in villages to keep grains

5.Can be used as septic tank.

6.Ferrocement is ideal for boat building.This kind of boat weighs 10% less if it is made of wood.

Ferrocement

Ferrocement is a relatively new material consisting of mortar made with portland cement, water and aggregate with reinforcing mesh.
P.L. Nervi an Italian engineering and architecture developed this material in 1940.

Advantages of Hydration

1.Because of hydration cement get adhesive property and bind fine and coars aggregate.

2.Helps in joining bricks.

3.Binds rids with concrete in R.C.C(Reinforced Concrete Cement).

4.Make the cement paste rigid.

Concrete

Concrete is a rock like material, which is made by mixing cement, coarse aggregate and fine aggregate with water.

Endogeneous or endogen timber

This kind of trees increase both longitudinally and diametrically.Its diameter increase by the addition of new fibre with the old. Endogens are mostly plants like paddy, sugarcane, jute etc.

Exogeneous or exogen timber

This kind of trees increase diametrically by annual formation of layer new wood between old wood and bark of the wood which consists all the living portion of the tree.

Types of Timber

Timber is of mainly two types.
1.Exogeneous or exogen
2.Endogeneous or endogen

Relation between water cement ratio to the strength of concrete

Water has three functions in concrete

1.Wets aggregate surface
2.Imparts workability
3.Binds aggregate with cement chemically by hydration

For a given degree of compaction with the increase
of percentage of water, percentage of hydration increases.
So sufficient amount of water is necessary for hydration as well
as for increase in strength.Water also imparts workability to
concrete.but excess water cause concrete to be porous.
Hence for a certain limit strength increase with the increase of
water cement ratio.But after that strength decreases with the
increase of water cement ratio.

Why fineness of cement is necessary for rapid development of strength

The surface area of cement particles increases with the increase of fineness modulus. Hydration takes place on the surface area of cement particles.For rapid hydration surface area of cement particles should be high.Strength develops on the concrete as hydration takes place. This is why for rapid development of strength high fineness of cement is necessary.

Placing concrete underwater

Sometimes concrete needs to be placed underwater.In this case bottom dump bucket or tremie pipe is used. In this case concrete is carried through the water in water tight box by bottom dump bucket and reaching the final position there is a mechanism to open the bottom of the bucket and dispose the concrete. This will not give satisfactory result as some concrete get washed away.

Sometimes dry cement and dry coars aggregate and fine aggregate are mixed in a cement bag and disposed under water. This also do not give satisfactory result as cement bag make voids in concrete.

Among the two tremie pipe method is preferable.

Process of determining the opening area and opening length of seive

Let us consider we have to determine the opening area and opening length of #100 sieve.
#100 sieve means 100*100 openings are present in 1 square inch or 25.4*25.4= 645.16 square mm.

Hence 1 opening is present in =645.16/(100*100)
                                           =0.065 square mm
sieve openings are surrounded by threads which take some areas.Hence sieves actually get areas of around 36 to 40 percent(can vary) of its opening.
Let us assume sieve opening is 36 percentage.
Then the actual are of sieve opening is =0.065*(36/100)
                                                        =0.0234 square mm
As sieve openings are square size
Then length of the each sieve opening =square root of 0.0234
                                                       =0.153 mm

Advantages of Timber

1.Timber can be easily worked with tools of any size and can take a good polish.
2.It is comparatively stronger than any other materials in proportion to weight. That is other materials of such light weight as timber are not stronger than timber.
3.It is economic in the sense that any small piece of timber can be utilized.
4.Its use for making furniture, sports goods and decorative articles of artistic design are accepted universally without doubt.
5.Its low thermal conductivity, high resistance(electricity) and sound proofing property make it as an important building material.
6.timber structures are comparatively durable if properly treated and carefully protected from direct contact with weather and alternate change in wetting and drying.
7.Various types of timber products such as plywood, laminated board. hard board etc are nowadays used because of low weight and beauty.
8.It can be used both load bearing and non-load bearing members in structures and structural connections.
9.Its another importance is great resale value. The discard timber can be used as fuel.Even saw dust can be used by reconstructing partex board, hard boards, laminated boards etc.