SAND

SAND 

It consists of small grains of silica and is formed by the disintegration of rocks caused by weather.

Classification of Sands

The classifications of sand are;

Fine sand,

medium sand,

 and coarse sand

Fine sand = 0.075 to 0.425 MM

Medium sand = 0.425 to 2 MM

Coarse Sand = 2.0 to 4.75 MM

Various type of sand

Depending upon the source from which sand is obtained it is classified as

1)      Pit sand (coarse sand)

2)      River sand 

3)      Sea sand  

1)    Pit Sand (coarse sand)     

It is found as deposits in soil and has to be excavated out. It consists of sharp angular grain which is free from salt. It is coarse sand, reddish yellow in color, and is used in concreting normally

2)    River Sand                      

This is obtained from the bank and bed of rivers. It usually consists of fine rounded grains.it may be fine or coarse sand. It is normally white and grayish in color. It is widely used for plastering and is available in clean condition

3)    Sea Sand  

This is obtained from sea shores. It is brown in color and it also has the fine rounded grain. As it is obtained from sea it contains salt, which is used in attracting moisture from atmosphere. Such absorption causes dampness and disintegration of work. It is generally not used for engineering purpose due to its retards setting action of cement. It is normally used for non-structural purposes

Bulking Of Sand

It is the property of sand by virtue of which its apparent volume increases when some water is added to it. It happens mainly due to surface tension.

This increase in volume will not take place when the sand is either dry or fully saturated.

The bulking depends both on moisture content as well as particle size Bulking increases gradually with the increase in moisture content.at 4% increase in moisture content by weight, the increase in volume is about 25 percent.it then decreases with the increase in moisture content till it become zero when the water is more than 20%.

 Bulking is more in fine sand than in coarser one.

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CONCRETE

CONCRETE

Concrete is made by mixing: Cement, water, fine aggregates, coarse aggregates and admixtures (if required).

Properties of concrete

Properties of Fresh Concrete are

a) Workability

b) Consistency

c) Segregation

d) Bleeding

e) Setting Time

a) Workability

The concrete mix should be workable, so that it can be placed and consolidated properly by the workmen.

 b) Consistency

Consistency is the fluidity or degree of wetness of concrete. It is a major factor in indicating the workability of freshly mixed concrete.

c) Segregation

Segregation refers to a separation of the components of fresh concrete, resulting in a non-uniform mix. The primary causes of segregation are differences in specific gravity and size of constituents of concrete. Moreover, improper mixing, improper placing and improper consolidation also lead to segregation.

 d) Bleeding

Bleeding is the tendency of water to rise to the surface of freshly placed concrete. It is caused by the inability of solid constituents of the mix to hold all of the mixing water as they settle down. It is special case of segregation

e) Setting Time

The transition process of changing of concrete from plastic state to hardened state. Setting of concrete is based or related to the setting of cement paste. Thus cement properties greatly affect the setting time. 

f) Temperature

The higher the temperature of the concrete at placement the greater the initial rate of strength development, but the lower long-term strength. This is why important to reduce the temperature of 

fresh concrete when concreting in hot climate.

Properties of Hardened Concrete

a) Strength

b) Permeability & durability

c) Durability

d) creep deformations

a) Strength 

The strength of concrete is basically referred to compressive strength.

Strength of Concrete depends on

–Strength of cement paste

 –Strength of aggregate

– Interface between cement paste and aggregates

 b) Permeability & durability

The permeability of concrete is controlled by capillary pores. The permeability depends mostly on w/c, age, degree of hydration. In general the higher the strength of cement paste, the higher is the durability & the lower is the permeability.

c) Durability

Concrete should be strong and durable.

Durability increases with density of concrete.

 d)  Creep Deformations   

Creep in concrete can reduce the pre-stress and possibly lead to cracking

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AGGREGATES

AGGREGATES

 Aggregates are materials mixed with binding materials like cement, lime or mud in the preparation of mortar or concrete. These shall consist of naturally occurring stones, gravels, and sand and shall be hard, strong and durable. Natural aggregates are formed by the process of weathering and abrasion, or by artificial crushing of larger parent mass. The aggregates occupy 7080% of the volume of concrete, their impact on various characteristics and properties of concrete is considerable.to know more about the concrete one should know more about the aggregates which constitute more volume of the concrete

PROPERTIES OF AGGREGATES

 Physical Properties

The physical properties of aggregates are those that refer to the physical structure of the particles that make up the aggregate. 

a) Absorption, Porosity, And Permeability

 Absorption relates to the particle's ability to take in a liquid.

Porosity is a ratio of the volume of the pores to the total volume of the particle. Permeability refers to the particle's ability to allow liquids to pass through it.

 The porosity, permeability and absorption of an aggregate particle may affect the strength of the aggregate, abrasion resistance, surface texture, specific gravity, bonding capabilities, and resistance to freezing and thawing action. 

b) Surface Texture

Surface texture is the pattern and the relative roughness or smoothness of the aggregate particle.

 A rough surface texture gives the cementing material something to grip, producing a stronger bond, and thus creating a stronger hot mix asphalt or Portland cement concrete.

c) Aggregate Voids

 Aggregate particle voids influence the specific gravity and absorption of the Aggregate materials.

d) Strength And Elasticity

High strength and elasticity are desirable in aggregate base and surface courses. These qualities minimize the rate of disintegration and maximize the stability of the compacted material.

e) Density And Specific Gravity

The density and the specific gravity of an aggregate particle is dependent upon the density and specific gravity of the minerals making up the particle and upon 

f) Hardness

Hard aggregates have good cementation and are more resistant to abrasion and degradation.

 Whereas soft aggregates have poor cementation and are not resistant to abrasion and degradation.

 g) Particle Shape

The shape of the aggregate particles affects such things as:

1) The asphalt demands of hot mix asphalt

2) The workability and the strength of both Portland cement concrete and asphalt pavements irregular and angular aggregates give more strength as compared to round aggregates but are less workable than round aggregates

TESTS FOR AGGREGATES LOS ANGELES ABRASION TEST

Objective

 To determine the resistance to degradation of small size coarse aggregate in Los Angeles machine.  Several mechanical properties of aggregates are of interest, especially when the aggregates are to be used in road construction or are to be subjected to high wear. Strength, toughness, hardness or resistance to wear is an important property of concrete used in roads and floor surfaces subjected to heavy traffic. 

Los Angeles abrasion test studies all possible reasons causing wear.in the Los Angeles abrasion machine attrition, abrasion, and crushing are all present as follows

 Attrition: by the friction between the aggregate particles.

Abrasion: by the friction between the steel balls and the aggregates

 Crushing: by hitting the walls of the testing machine Los Angeles test is suitable for coarse aggregates of different sizes and is not used for fine aggregates

Apparatuses

 Los Angeles machine,

 Sieves,

Balance,

Steel balls,

 Scoop,

 Sample trays,

 Oven,

 Wire brush

Procedure

Prepare the sample according to gradation

Ø  Place the test specimen and abrasive charge in the Los Angeles Abrasive Testing Machine and close the opening with the dust-tight cover. 

Ø  Start the testing machine and allow operating for the required number of revolutions at a speed of 30 to 33 rpm. 

Ø  When the testing machine has completed rotating the required number of revolutions, remove the cover and carefully empty the entire contents into a pan. Remove the abrasive charge from the pan.

Ø  Separate the test specimen on the 4.75-mm sieve, and then sieve the passing 4.75-mm material on the 1.70-mm sieve. Combine the material retained on the 4.75 and 1.70-mm sieves. Weigh and record these values to the nearest 1 g.  

Ø  Wash the aggregates retained on sieve no 12.n the Place these aggregates in oven for drying and then weighed.

Now find the abrasion value in percentage by the formula as given below

Abrasion value= (W1˗ W2\ W1) ×100                                  

Where  W1=weight of material before test

W2=weight of material after test

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Qualities of Good Bricks

Qualities of Good Bricks

 The qualities of good bricks are as listed below:

Colour

Colour should be uniform and bright. Shape          

 Bricks should have plane faces.

 They should have sharp and truly right angled corners.

Texture

Bricks should have fine, dense and uniform texture.

 A fractured surface should not show fissures, cavities, loose grit and unborn lime.

Size  

Bricks should be of standard size as prescribed by the standard code.

 Soundness

 Bricks should give a metallic sound when struck with a hammer or with another brick.

Strength

Crushing strength of bricks should be as high as possible. The Indian Standard code does not permit the use of any brick with crushing strength of less than 55kg/cm2. A field test for strength is that when dropped flat from a height of 0.9m to 1m on a hard ground, the brick should not break into pieces

Water absorption

 After immersing bricks in cold water for 24 hours, water absorption of bricks should not be more than 20 per cent by weight. For class-I work; this limit is 15 per cent.

 Efflorescence

 Bricks should not show white patches when soaked in water for 24 hours and then allowed to dry in shade. White patches are due to the presence of sulphates of calcium, magnesium, sodium and potassium, and they keep the masonry permanently in a damp and wet condition.

Thermal conductivity

Bricks should have low thermal conductivity so that buildings built with them are cool in summer and warm in winter. 

Sound insulation

Heavier bricks are poor insulators of sound while light weight and hollow bricks provide good sound insulation. The strength and sound insulation properties of bricks contradict each other. Hence, bricks with unnecessarily too high strength (heavy bricks) need not be used.       

Fire resistance

Fire resistance of bricks is usually good. In fact sometimes bricks are used to encase steel columns as a measure of fire protection.

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Functions of various ingredients of brick earth

Functions of various ingredients of brick earth

Silica:

It enables the brick to retain its shape and imparts durability, prevents shrinkage and warping. Excess of silica makes the brick brittle and weak on burning. A large percentage of sand or uncombined silica in clay is undesirable. However, it is added to decrease shrinkage in burning and to increase the refractoriness of low alumina clays

Alumina: 

Alumina absorbs water and renders the clay plastic. If alumina is present in excess of the specified quantity, it produces cracks in brick on drying. Clays having exceedingly high alumina content are likely to be very refractory.

Lime:

lime normally constitutes less than 10 per cent of clay.

Lime in brick clay has the following effects:

1. Reduces the shrinkage on drying.

2. Causes silica in clay to melt on burning and thus helps to bind it.

3. In carbonated form, lime lowers the fusion point.

 4. Excess of lime causes the brick to melt and the brick loses its shape.

 5. Red bricks are obtained on burning at considerably high temperature (more than 800°C) and buff-burning bricks are made by increasing the lime content.

Magnesia:

 magnesia rarely exceeding 1 per cent affects the color and makes the brick yellow, in burning; it causes the clay to soften at slower rate than in most case is lime and reduces warping. Iron oxide:   Iron oxide constituting less than 7 per cent of clay, imparts the following properties:

1. Gives red color on burning when excess of oxygen is available and dark brown or even black color when oxygen available is insufficient; however, excess of ferric oxide makes the brick dark blue.

 2. Improves impermeability and durability.

 3. Tends to lower the fusion point of the clay, especially if present as ferrous oxide.

4. Gives strength and hardness.

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Defects In Bricks ,Brick Earth Composition:

Defects in bricks

Over burning of bricks:

Bricks should be burned at temperatures at which incipient complete and viscous verification occur. However, if the bricks are over burnt, a soft molten mass is produced and the bricks lose their shape. Such bricks are not used for construction works.

Under burning of bricks:

 When bricks are not burnt to cause complete verification, the clay is not softened because of insufficient heat and the pores are not closed. These results in higher degree of water absorption and less compressive strength  . Such bricks are not recommended for construction works.

Bloating:

 This defect observed as spongy swollen mass over the surface of burned bricks is Caused due to the presence of excess carbonaceous matter and sulphur in brick-clay

Black core:

 When brick-clay contains bituminous matter or carbon and they are not completely removed by oxidation, the brick results in black core mainly because of improper burning.

Efflorescence:

 This defect is caused because of alkalis present in bricks. When bricks come in contact with moisture, water is absorbed and the alkalis crystalize. On drying grey or white powder patches appear on the brick surface.

Chuffs:

 The deformation of the shape of bricks caused by the rain water falling on hot bricks is known as chuffs

Spots:

 Iron sulphide, if present in the brick clay, results in dark surface spots on the brick surfaces. Such bricks though not harmful are unsuitable for exposed masonry work.

Blisters:

 Broken blisters are generally caused on the surface of sewer pipes and drain tiles due to air imprisoned during their moulding.

Brick Earth Composition:

For the preparation of bricks, clay or other suitable earth is moulded to the desired shape after subjecting it to several processes. After drying, it should not shrink and no crack should develop. The clay used for brick making consists mainly of silica and alumina mixed in such a proportion that the clay becomes plastic when water is added to it. It also consists of small proportions of lime, iron, manganese, sulphur, etc

The proportions of various ingredients are as follows:

Silica	50 to 60%
Alumina	20  to 30%
Lime	10%
Magnesia	less than 1%
Ferric oxide	less than 7%
Alkalis	less than 10%

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