CONCRETE SHRINKAGE AND ITS TYPES

Concrete Shrinkage

The volumetric changes of concrete structures due to the loss of moisture by evaporation is known as concrete shrinkage.Concrete shrinkage is the change in length per unit length and is, therefore  a dimensional number expressed as percent.It is a time dependent deformation which reduces the volume of concrete without the impact of external forces and is usually quantified in term of micro strain which is equal to 1x10^-6 in/in or 1x10^-6 m/m.

Types of Concrete Shrinkage

1. Plastic Shrinkage
2. Drying Shrinkage
3. Carbonation Shrinkage
4. Autogenous Shrinkage

1. Plastic Shrinkage

Plastic shrinkage occur very soon after pouring the concrete in the forms.The hydration of cement result in a reduction in the volume of concrete due to evaporation from the surface of concrete, which leads to cracking.

2. Drying Shrinkage

The shrinkage that appears after the setting and hardening of the concrete mixture due to loss of capillary water is know as drying shrinkage.Drying shrinkage generally occurs in the first few months and decreases with time.

3. Carbonation Shrinkage

Carbonation shrinkage occurs due to the reaction of carbon dioxide (CO2) with the hydrated cement minerals, carbonating Ca(oh)2 to CaCo3.The carbonation slowly penetrates the outer surface of the concrete.This type of shrinkage mainly occurs at medium humidity and results increased strength and reduced permeability.

4. Autogenous Shrinkage

Autogenous shrinkage occurs due to no moisture movement from concrete paste under constant temperature.It is a minor problem of concrete and can be ignored.

Factors Affecting Shrinkage

The shrinkage of concrete depends on several factors which are

1. Water-Cement Ratio

Shrinkage is mostly influenced by the water-cement ratio of concrete.It increases with the increases in the water-cement ratio.

2. Environmental Condition

It is one of the major factor that affect the total volume of shrinkage.Shrinkage is mostly occurred due to the drying condition of the atmosphere.It increases with the decrease in the humidity.

3. Time 

The rate of shrinkage rapidly decreases with time.It is found that 14-34% of the 20 years shrinkage occurs in two weeks, 40-80% shrinkage occurs in three months and the rest 66-85% shrinkage occurs in one year.

4. Types of Aggregate

Aggregate with moisture movement and low elastic modulus cause large shrinkage.The rate of shrinkage generally decreases with the increase of the size of aggregates.It is found that concrete made from sandstone shrinks twice than the concrete of limestone.

5. Admixtures

The shrinkage increases with the addition of accelerating admixtures due to the presence of calcium chloride (CaCl2) in it and it can be reduced by lime replacement.  

Other Factors

• The method of curing.
• The strength of concrete.
• The dimension of elements
• The type and quantity of cement.
• Granular and microbiological composition of aggregate.

FIBER REINFORCED CONCRETE - TYPES, APPLICATIONS AND ADVANTAGES

Fiber Reinforced Concrete

Fiber reinforced concrete is a type of concrete containing fibrous materials which increases its structural integrity.It contains short discrete fibers that are uniformly distributed and randomly oriented.Fibers include steel fibers, glass fibers, synthetic fibers and natural fibers.Within these different types of fibers each of them lend varying properties to the concretes, fiber materials, geometries, distribution, orientation and densities.

Effect of Fibers in Concrete

Fibers are usually used in concrete to control cracking due to plastic shrinkage and drying shrinkage.They also reduce the permeability of concrete and thus reduce bleeding of water.Some types of fibers produce greater impact, abrasion and shatter resistance in concrete.Large steeel or synthetic fibers can replace rebar or steel completely in certain situations.Fiber reinforced concrete has all but completely replaced bar in underground construction industry such as tunnel segments where almost all tunnel lining are fiber reinforced in lieu of using rebar.Indeed, some fiber reduce the compressive strength of concrete.

The amount of fiber added to a concrete mix is measured as a percentage of the total volume of the composite (concrete and fibres) termed volume fraction (Vf). Vf typically ranges from 0.1 - 3%.Aspect ratio (l/d) is calculated by dividing fibre length (l) by its diameter (d).Fibers with a non-circular cross section use an equivalent diameter for the calculation of aspect ratio.

Types of Fiber Reinforced Concrete

1. Steel Fiber Reinforced Concrete
2. Glass Fiber Reinforced Concrete - GFRC 
3. Polypropylene Fiber Reinforced Cement Mortar & Concrete
4. Asbestos Fibers
5. Carbon Fibers
6. Organic Fibers

1. Steel Fiber Reinforced Concrete

Steel fiber reinforced concrete has gradually advanced in recent years, rather unproven material to one which has now attained acknowledgement in numerous engineering applications.Lately it has become more frequent to substitute steel reinforcement with steel fiber reinforced concrete.A numbers of steel fiber types are available as reinforcement.Round steel fiber the commonly used type are produced by cutting round wire into short length.The typical diameter lies in the range of 0.25 to 0.75 mm.Rectangular steel fiber are usually 0.25 mm thick, although 0.3 to 0.5 mm wire have been used.

Round steel fibers are produced by cutting or chopping the wire, flat sheet fibers having a typical c/s ranging from 0.15 to 0.41 mm in thickness and 0.25 to 0.90 mm in width are produced by silting flat sheets.Deformed fiber, which are loosely bounded with water-soluble glue in the form of a bundle are also available.

2. Glass Fiber Reinforced Concrete (GFRP)

Glass fiber reinforced concrete consists of high-strength, alkali-resistant glass fiber embedded in a concrete matrix.Glass fiber is made up from 200 to 400 individual filaments that are lightly bounded to make up a stand glass fiber is made and these stands can be combined to make cloth mat or tape or can be chopped into various lengths.It is not possible to mix more than about 2% by volume of fibers of a length of 25mm by using the conventional mixing techniques for normal concrete.

The major appliance of glass fiber has been in reinforcing the cement or mortar matrices used in the production of thin sheet products.The commonly used verities of glass fibers are e-glass used.In the reinforced of plastics & AR glass E-glass has inadequate resistance to alkalis present in Portland cement where AR-glass has improved alkali resistant characteristics.

3. Polypropylene Fiber Reinforced Cement Mortar and Concrete

Polypropylene is one of the cheapest & abundantly available polymers polypropylene fibers are resistant to most chemical & it would be cementitious matrix which would deteriorate first under aggressive chemical attack.Its melting point is high (about 165℃).So that a working temp.

Polypropylene fibers being hydrophobic can be easily mixed as they do not need lengthy contact during mixing and only need to be evenly distressed in the mix.Polypropylene short fibers in small volume fractions between 0.5-15 commercially used in concrete.

4. Asbestos Fibers

Asbestos fibers are naturally available inexpensive mineral fiber,has been successfully combined with Portland cement paste to form a widely used product called asbestos cement.Asbestos fibers are thermal-mechanical & chemical resistance and for sheet product pipes, tiles and corrugated roofing elements these are suitable.The fiber has low impact strength due to a relatively short length of about 10 mm. 

5. Carbon Fiber

Carbon fiber are about 5-10 micrometer in diameter and composed mostly of carbon atoms.Carbon fibers have several advantages including high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and low thermal expansion.These properties have made carbon fiber very popular.Carbon fiber are expensive and strength and stiffness characteristics have been found to be superior to those of steel.But they are more vulnerable to damage then even glass fiber, and hence are generally treated with resign coating. 

6. Organic Fibers

Organic fiber such as polypropylene or natural fiber may be chemically more inert than steel or glass fibers.They are also cheaper, especially if natural.A large volume of vegetable fiber may be used to obtained a multiple cracking composite.The problem of mixing and uniform dispersion may be solved by adding a superplasticizer.

Application of Fiber Reinforced Concrete

• Pre-cast application
• Fiber shotcrete
• Slope stabilization
• Manholes, roof tiles, panels 
• Dams and hydraulic structures
• Highway and airfield payments
• Impact resisting structures

Advantages of Fiber Reinforced Concrete

• Increase ductility.
• Decrease permeability.
• Increase fire resistance.
• Less prone to corrosion.
• Decrease mix water bleed rate.
• Improve toughness of concrete.
• Greater resistance to crack formation.
• Resistance to thermal and moisture stress.
• Fiber increases the shear capacity of reinforced concrete beam upto 100%.

Disadvantages of Fiber Reinforced Concrete

• Material cost is high.
• Greater reduction of workability.
• Lower compressive strength than steel.
• Cost of forms and artisanry is relatively high.
• Cracks can develop due to shrinkage and live loads.
• Very low tensile power 1/10 of its compressive potency.

WHAT IS POLYMER CONCRETE - TYPES, APPLICATIONS AND ADVANTAGES

Polymer Concrete

Polymer concrete is a type of concrete that uses polymer to replace lime-type cement as binder.It is a conventional concrete made with Ordinary Portland cement wet cured, and impregnated with a liquid/gaseous monomer (Methyl methacrylate) and polymerized by gamma radiation or chemically initiated means i.e. by using thermal catalytic method (adding 3% by weight Benzoyl peroxide) to the monomer as a catalyst.The impregnation is helped by drying the concrete at an extreme temperature by evacuations and absorbing the monomer under limited pressure.

Polymer concrete have been overseen by Committee 548 of the American Concrete Institute since 1971.It is not like traditional concrete , although it uses some of the same type of materials.It is also used for construction projects in the same manner, but the polymer compounds give the concrete several characteristics that tends to make it safer or more durable than regular concrete.

Types of Polymer Concrete

1. Polymer Concrete (PC).
2. Polymer Cement Concrete (PCC).
3. Polymer Impregnated Concrete (PIC).

Properties of Polymer Concrete

• It has good resistance against corrosion.
• The binder is more expansive than cement.
• Low permeability to water and aggressive solution.
• It is lighter in weight compared to traditional concrete.
• It has long term durability with respect to freeze and thaw cycles.
• It has good adhesion to most surfaces, including to reinforcements.

Advantages of Polymer Concrete

• It has high tensile strength.
• It has high impact resistance.
• It has high compressive strength.
• It has more resistance to chemical attacks.

Applications of Polymer Concrete

• Road.
• Kerbstones.
• Marine works.
• Irrigation works.
• Prestressed concrete.
• Nuclear power plants.
• Food processing buildings.
• Prefabricated structural elements.
• Sewage works and desalination plants.
• Waterproofing of structures and numerous indistrial applications.

WHAT IS PRE-STRESSED CONCRETE - TYPES AND ADVANTAGES

Pre-stressed Concrete

Pre-stressed concrete is a combination of high strength concrete and steel strands.Prestressing is generally a way to overcome concrete weakness in tension.Generally the concrete undergoes compression on top flange and tension at bottom flange.In prestressing the tendons are stretched along the axis and cement is poured, later when the tendons and released the compression is generated at the botttom which tries to counter-balance the compression due to loading at the top part of the beam.The upward force along the length of the beam counteracts the service loads applied to the member.

Pre-stressed concrete was invented and patented in 1886 by Henry Jackson, an engineer from San Francisco USA.Pre-stressed concrete makes a strong structural materials that is used in the building of roof slabs, bridges girders and railroad ties.The walnut Lane Memorial Bridge built in 1951 in Philadelphia, Pennsylvania become the first structure in USA made of this type.

Pre-stressed concrete can be created using two different methods, they are as fallows:

1. Pre-tension 
2. Post-tension

1. Pretensioning 

The pretensioning method involves in stretching high tensile steel stands between abutments located at both ends of the concrete casting bed.After the stands are taught, concrete is poured into beds, where it surrounded and adheres to the stands.Once the concrete is dry it will have bonded to the steel.After the concrete has reached the desired strength the strands are released, resulting in the concrete developing a slight arch that makes it more resistant to heavy loads.

2. Post Tensioning

In post tensioning the steel is prestressed only after the beam is cast, cured and attain strength to take the prestress.Within the sheathing, the concrete is cast.For the passage of steel, ducts are formed in the concrete.

Once the casted concrete hardens completely, the tendons are tensioned.One end of the tendon is anchored and the other end is tensioned In same cases, the tensioning can be performed from either side and anchored subsequently.

Once the prestressing is complete, there is space between the tendons and the duct.This leads to:

1. Bounded Construction
2. Unbounded Construction

1. Bounded Construction

In bounded construction the space between the duct and the tendon is filled with cement grout.The grouting process helps the steel to resist corrosion to a large extent.The ultimate strength is increased as this method increases the resistance to live loads acting.The grout is a mixture of cement and water without admixtures.In this grout sand is not used.

2. Unbounded Construction

In unbounded construction no grout is used to fill the space between the duct and tendon.Here steel is galvanized to protect from corrosion.A waterproofing material is used for galvanizing.

Advantages of Pre-stressed Concrete

• It has high compressive strength.
• It is a best for construction of sleek and slender structures.
• It is more durable than reinforced concrete.
• The prestressing system works for a span greater than 35m.
• Prestresseing helps to reduce the dead load of the concrete structure.
• Prestressed concrete are free from cracks.
• Prestressing enhance shear strength and fatigue resistance of concrete.

Disadvantages of Pre-stressed Concrete

• It has higher material cost.
• Prestressing is an additional cost.
• High skilled labor is required.
• Advanced technical knowledge and strict supervision is very important.

WHAT IS CONCRETE - TYPES AND ADVANTAGES

Concrete

Concrete is a composite material and is a mixture of cement, sand, aggregate, water and sometimes admixtures in required proportion.It is one of the most important and useful materials for construction work.When all the ingredients (cement, sand, aggregate,water) are mixed in the required proportions the cement and water start a reaction with each other to bind themselves into a hardens mass.The hardens rock like mass is known as concrete.

Properties of Concrete

• It has high compressive strength.
• It has low tensile strength.
• It is more economical than steel.
• It has low coefficient of low thermal expansion.
• It is free from corrosion and there is a no appreciable effect of atmospheric agents on it.

Types of Concrete

1. Waterproofing Cement Concrete
2. Coloured  Concrete
3. Lightweight  Concrete
4. Pre-cast  Concrete
5. Ready-mix  Concrete
6. Transit-mix  Concrete
7. No Fines  Concrete

1. Waterproofing Cement  Concrete

For certain types of works like water storage tanks, reservoir, basement wall, roofs swimming pool, sewage units etc, the impermeability of concrete is absolutely essential.Normally it can be started that if the concrete is made dense and free from cracks this is watertight.

2. Colored Concrete

Colored concrete is a type of concrete that has pigment mixed through, so that color is distributed entirely throughout.

Colored concrete can be made by following ways:

• By adding of suitable coloring pigments to the extend of about 8-10% of the weight of the cement.
• By using colored cement for the preparation of concrete.
• By selecting aggregates possessing the required colored.

3. Lightweight Concrete

Light weight concrete mixture is made with a lightweight coarse aggregate and sometimes a portion or entire fine aggregate may be lightweight instead of normal aggregate.The light weight concrete having bulk density between 5-18 KN/m3.

4. Pre-cast Concrete

Precast concrete is refers to any type of concrete structure that is manufactured at a plant and transported to the construction site.In general, regular concrete structures are normally molded, poured and cured on-site.Precast concrete is used in a variety of construction projects ranging from home, landscaping. buildings, bridges etc.It is being used more in residential projects because it is more readily available than even before and provides quality and uniformity that may be lacking in on-site concrete work.

5. Ready-mix Concrete

Ready-mix concrete is a type of concrete that is manufactured in a factory or batching plant, according to set recipe, and then delivered to worksite by trucks mounted transit mixers.

6. Transit-mix Concrete

The concrete that is mixed either wet or dry en route to a job site is known as Transit-mix concrete.A transit-mix truck carries a mixer and a water tank from which the driver can, at the proper time, introduce the required amount of water into the mix.

7. No Fines Concrete

The no-fines concrete consists of cement, course aggregate and water.Thus the fine aggregate or sand is eliminated and such concrete has been adopted for cast-in-situ external load bearing wall of single and multi-storey houses, small retaining walls, damp-proofing sub-base materials etc.

Advantages of Concrete

• The compressive strength of concrete is very high.
• It is very strong in compression.
• It can be cast easily into any desired shapes.
• It can be pumped and sprayed in difficult positions.
• It possesses a minimum corrosive and weathering effects.
• It is economical than any other building materials.
• It is fire resistant.

TYPES OF CONCRETE JOINTS

Concrete Joints

Concrete joints are placed in the concrete to compensate for the expansion and contraction of the materials due to weather conditions.In order to avoid cracks, concrete installers will predict where the concrete will cracks and how it will expand based on there assessment they will create forming, saw, tool and place joint formers at different locations.

Concrete joints can be classified in following categories:

1. Construction Joints
2. Expansion Joints
3. Contraction Joints
4. Warping Joints

1. Construction Joints

Construction joints are made before and after interruptions in the placement of concrete or through the positioning of precast units.Concreting operation should be so planned that the work is completed in one operation.Location are usually predetermined so as to limit the work that can be done at one time to a convenient size,with least impairment of the finished structure,through they may also be necessitated by unforeseen interruptions in concrete operations.Construction joints may run horizontally or vertically depending on the placing sequence prescribed by the design of the structure.

Best location of thee construction joints are as follows:

• Beam: Joint may be located at mid-span or center of the column in direction at right angles to the length of the beam.

• Column: Joint should be located a few centimeter below its junction with the beam.

• Slab: Joints may be placed at mid span or directly over the center of the beam, at right angle to the slab.

2. Expansion Joints

Expansion joints are designed to allow for expansion of the concrete, due to the rise in the temperature above the temperature during construction.Expansion joints also permit the contraction of the element.They are commonly found between sections of building, bridges, sidewalks, railway tracks, piping system, ships and other structures.The open gap of expansion joints varies between 2 cm to 2.5 cm. In case of transfer the load from one slab to the adjacent slab, dowel bars are used at suitable intervals at these joints.Expansion joint movement may be high upto 30% of joint width.

3. Contraction Joints

Contraction joints are provided to permit contraction of the concrete.These joints are spaced closer than expansion joints.These joints are purposely designed to regulate cracking that might otherwise occur due to the unavoidable, often unpredictable, contraction of concrete.These joints are often called controlled joints because they are intended to control crack locations.Contraction joint movement is supposed to be small.

4. Warping Joint

Warping joints are designed to relieve stresses induced due to warping effect.These joints are also known as hinged joints.

TYPES OF CONCRETE CRACKS

Concrete Cracks

Concrete cracks are occur due to several reason like due to constructional movement, shrinkage etc.After hardening, cracks occur due to chemical reactions and thermal changes. 

The main reason of concrete cracks are as fallows:

1. Excess water in  water-concrete mixture

Due to the adding of excess amount of water in concrete mix it increases the w/c ratio, the strength of the concrete also will reduce.During summer the extra water present in the concrete evaporates which causes shrinkage.Due to the shrinkage cracking can take place in concrete.

2. Rapid Drying Concrete

The actual amount of water is required to be added in the concrete mix to complete the chemical reaction.If the concrete dries before completion of the reaction  it causes cracking.

3. Lack of Control Joints

Lack of control joint leads cracking in the concrete if the area is large.Some time it is also seen that if the dimension of the control joint i.e, thickness of joint is not proper causes cracking.

4. Freezing and Thawing

When excess amount of water freezes in winter, the volume expands and cracking occurs.

Types of Cracks in Concrete

1. Shrinkage Cracks

When concrete is in plastic state, it is full of water.When that water leaves the concrete, it leaves behind large large voids between the solid particles.These empty spaces make the concrete weaker and more prone to cracking.This type of cracking happens frequently and is referred to as "shrinkage cracking".

Shrinkage cracks can happen anywhere in a slab or wall.In a poured concrete cracks can be diagonal or vertical and are usually uniform in width.Sometimes these cracks have a V-shape with top portion of cracks are large and the lower portion of cracks are smaller.

2. Vertical Cracks

Vertical cracks often appear in multiples (multiple cracks in one or more areas). Vertical foundation cracks in poured concrete foundations that tend to appear nearly straight or to wander,normally even in width, intermittent or more often straight is caused by shrinkage/thermal and are usually low risk.

When there is significant vertical dislocation or signs of ongoing movement, you should consult a structural engineer.If the cause is shrinkage, it is probably less of a concern that if due to settlement.

A vertical foundation cracks because of earth loading, or frost could be unusual.A more massive vertical cracks may occur when the construction contractors incorrectly prepare a concrete foooting,and when the wall had poor steel reinforcement as the workers poured the concret to the wall. Cracks may also occur during the footing settlement.

3. Diagonal Cracks

Settlement usually causes diagonal cracks that are almost the full height of foundation wall.When there's a settlement problem with the footing on one side of the wall, this settlement can also cause a diagonal crack.In this type of case, a structural engineer should be consulted.If the diagonal cracks is wider at the top than at the bottom,then it may be caused by expansion clay soil or frost damage.If the crack is wider at the bottom than the top, there is likely a problem with the settlement beneath. 

Some uniform diagonal cracks are merely caused by shrinkage and will only cause water leakage problems.

4. Horizontal Cracks

Horizontal cracks found in the center of the wall are most likely caused by an applied load such as backfill around foundation compacted improperlyor too soon, earth compacting as it settles, hydrostatic pressure against foundation due to high water table and poor drainage against the foundation wall, or heavy equipment operated too soon or too close to the foundation wall.Horizontal cracks found high up on the wall are most likely caused by frost damage.Sometimes these fine cracks are not noticed for years.In a case like this, a structural engineer should be consulted.

5. Structural Cracks

Structural cracks in residential foundations usually result from horizontal loading or settlement.Most structural cracks resulting from an applied load are nearly horizontal and appear 16" to 48" from the top of the wall.They are more common in block foundation walls.

6. Floor Cracks

Floor cracks in concrete slabs are relatively common and usually not worrisome on a structural level.They should be repaired to prevent common issues like moisture, insects and damage from seeping through.When floor cracks leak, it is usually caused by hydrostatic pressure or a high water table.Therefore, sealing the crack will  redirect those issue elsewhere, so fixing the source of those problems beforehand is recommended.

7. Hairline Cracks

Hairline cracks may develop in concrete foundations as the concrete cures.Hairline cracks do not cause problem with the stability of the foundation but do cause leakage problems.If the cracks appear shortly after pouring the concrete foundation, concrete may have been mixed poorly or poured too quickly.In poured concrete foundations, hairline crack frequently appear in the centre of the walls because the wall corners have greater stability.

8. Temperature and Shrinkage Cracks

Horizontal cracks found in the center of the wall are most likely caused by an load such backfill around foundation compacted improperly or too soon, earth compacting as it settles, hydrostatic pressure against foundation due to high water table and poor drainage against the foundation wall, or heavy equipment operated too soon or too close to the foundation wall.Horizontal cracks found high up on the wall are most likely caused by frost damage.Sometimes these fine cracks are notr noticed for years.In a case like this, a structural engineer should be consulted.

9. Settlement Cracks

Settlement cracks may appear when the underlaying ground has not been compacted or appropriately prepared or if the subsoil was not was of the proper consistency.A settlement crack may also appear as a random crack above area where the soil of the subgrade was uneven after the concrete was poured.Settlement cracks are usually more extensive at the top of the crack than the bottom as the foundation "bend" over a single point, allowing differential settlement.This type of cracks is usually continous and may occur multiple times in a wall.

WHAT IS SELF CONSOLIDATING CONCRETE - PROPERTIES, ADVANTAGES AND DISADVANTAGES

Self Consolidating Concrete

Self consolidating concrete is a concrete mix which has a low yield strees, high deformability, good segregation resistance and moderate viscosity.It is a highly flowable type of concrete that spreads into the form without the need of mechanical vibration.Self compacting concrete is highly flowable, non-segregating concrete with a slump flow of 20 - 30 inches that can spread into place fill the formwork and encapsulate the reinforcement without any mechanical consolidation.

In self consolidating concrete sometimes superplasticizers and viscosity modifier are added in the mix to minimize bleeding and segregation in the concrete mix.A well designed SCC has high deformability and excellent stability against segregation.

Self consolidating concrete has similar water-cement ratio or cement binder ratio as compared to the ordinary concrete mix.It give slightly higher strength because without the use of the vibrator at the time of concrete pouring, it will improve the bond between the concrete hardened paste and aggregates.

In self consolidating concrete the SCC mix must be placed at a higher velocity than that of regular concrete.It has been poured into the slab or in columns more than the hight of 5 m without segregation of aggregate because of SCC design. 

Materials Used For Self Consolidating Concrete

1. Cement

Ordinary Portland cement of grade 43 or 53 is used in self consolidating concrete.

2. Aggregates

The aggregates which can used in SCC is limited to 16 mm.The aggregates are well graded either round or cubical in shape.The fine aggregates used in SCC must have 4.75 mm maximum in size.

3. Water

The quality of water is same as used in reinforced concrete and pre-stressed concrete construction.

4. Mineral Admixtures

The admixtures used in SCC are as fallows:

• Fly Ash: It improves the quality and durability of self consolidating concrete structures.

• Silica Fumes: It increase the mechanical properties of  self consolidating concrete structures.

• Stone Powder: It improves the powder content of  self consolidating concrete structures.

• GGBS: Ground granulated blast furnace slag helps to improve the rheological properties of  self consolidating concrete.

Properties of Self Consolidating Concrete

1. Filling Ability 

This property of the concrete is the ability to flow under its own weight without any vibration provided intentionally.

2. Passing Ability

This property is the ability of the concrete to maintain its homogeneity.

3. Segregation Resistance

This is the resistance of the concrete not to undergo segregation when it flows during the self compaction process.

Advantage of Self Consolidating Concrete

• The quality of the construction is high.
• It improves the structure integrity.
• It provide high strength to the structures.
• It reduces labour cost.
• It reduces time during placing of concrete.
• It reduces the noise level of mechanical vibrators.
• It allows innovative architectural features.
• It provides wide variety of placement techniques.
• It has excellent flow even around heavy reinforcement areas.
• The durability of concrete structure is high compared to normal concrete structure.

Disadvantage of Self Consolidating Concrete

• Low density.
• Low fire resistance.
• It is more costly than conventional concrete.
• Highly skilled workers are required for the production of SCC.
• Lack of globally accepted test standard to undergo SCC mix design.
• Increased plastic shrinkage potential.

WHAT IS FERROCEMENT CONSTRUCTION - PROPERTIES, ADVANTAGE AND DISADVANTAGE

Ferrocement Construction

Ferro-cement construction is a type of construction in which reinforced mortar or plaster is applied over an "armature" of metal mesh,woven expanded-metal and closely spaced thin steel rods such as rebar.The metal commonly used is of iron or steel.The cement is typically a very rich mix of cement and sand in a ratio of 3:1. Ferro-cement is made with mesh of diameter 0.5 mm to 1 mm reinforced between cement mortar of ratio.

Materials Required for Ferrocement Construction

1.Cement Mortar Mix

The cement mortar is the mixture of cement,sand,admixture and water.Generally the mix used in the construction of ferrocement has cement-sand ratio of 1:2 to 1:3 with water cement ratio 0.4 to 0.45.

• Cement

In ferrocement construction Ordinary Portland Cement is used in mortar while in cold climate generally rapid hardening cement is used.The recommended quantity of cement is 500-600 kg/m3.

• Sand

In ferrocement, sand which we used should be clean and well graded.To attain a high grade impervious mortar ordinary river sand can be used.The maximum allowable grain size of the sand is 2.36mm and fineness modulus should lie within the range of 2.5 - 3.0.

• Admixture

Admixtures is used in ferrocement  to improve the workability of the mortar and can reduce the water cement ratio.A varities of admixtures are available in market.

2. Skeleton Steel

The skeleton steel forms the skeleton of the structure and consists of steel roads and staples and wire fabric.The basic function of the skeleton steel is to support the steel wire mesh that plays a major role in imparting structural strength especially in boats,bags etc.

The steel roads used are 3 to 8 mm thick and their thickness varies according to location from 6mm to 20mm.They are spaced at a distance of 7.5 cm to 12cm from each other.In skeleton steel mainly Fe-415 or Fe-500 bars are used.

3. Steel Mesh Reinforcement 

The steel mesh reinforcement is generally made of galvanized steel wires with diameter ranging from 0.5 mm to 1.5 mm and spaced out at a center to center distance of 6mm to 20 mm.The wires are either weaving or welded together to form a mesh. The woven mesh has a square opening,whereas the welded wire mesh has a rectangular or hexagonal openings.

Properties of Ferrocement

• It is very durable and versatile material.
• High tensile strength and stiffness.
• Less shrinkage and low weight.
• Better impact and punching shear resistance. 
• Undergo large deformation before cracking or high deflection.
• It is inexpensive.

Advantage of Ferrocement

• High resistance to cracking width.
• It has good impermeability.
• It has better resistance against earthquake.
• It has good fire resistance property.
• Suitable for pre-casting.
• Low maintenance cost.
• It is more suitable for structure like shells, roof, water tanks etc, because it can be fabricated in many desired shape.

Disadvantage of Ferrocement

• Corrosion of the reinforcing materials due to the incomplete coverage of metal by mortar.
• It has low shear strength.
• Much time consumed during tying rods and mesh.
• Large number of labours required.
• Low ductility.
• Susceptibility to stress rapture failure.
• It is difficult to fasten to ferrocement with bolts,screw,welding and nails etc.

REINFORCED CONCRETE- ADVANTAGES AND USES

Reinforced Concrete

Reinforced concrete is a composite material, is a combination of cement concrete with reinforcements (Steel bar).In reinforced concrete steel is embedded in such a manner that the two materials act together in resisting forces.The reinforcing steel absorbs the tensile, shear and compressive stresses in a concrete structure.Plain concrete is not suitable for most construction projects because it cannot easily withstand the stresses created by vibrations, earthquakes, wind and other forces.In reinforced concrete, the tensile strength of steel and compressive strength of concrete work together to allow the member to sustain these stresses over considerable spans.

Reinforced concrete is a popular building material because it is very strong, easy to work, adaptable, versatile and affordable.Now a days it is widely used in the construction of precast structure, irrigation canals, drains, hydro-power tunnel etc.

Advantages of Reinforced Concrete

1. Strength

Reinforced concrete posses very good strength in tension as well as in compression.

2. Durability

Reinforced concrete structure are durable if properly designed.The reinforced concrete has low permeability, concrete can resist chemicals dissolved in water such as sulfates, chloride and carbon dioxide which may cause corresion in concrete.

Reinforced concrete structures is not affected by weather that is why is ideal for underwater and submerged applications like dams, canals, lining and waterfront etc.

3. Versatility

Concrete has a property of versatility because fresh concrete is in liquid limit.When concrete can be placed on formwork or shuttering it is in a flowable state.

4. Fire Resistance

Reinforced concrete structure are more fire resistant than other commonly used construction materials like steel and wood.It can withstand to fire about 3-4 hours if proper cover is provided in the structure  member.

5. Rigidity

Reinforced concrete member are good in rigidity due to stiffness.

6. Economical

Concrete are widely used worldwide because it is inexpensive when compared with other materials like steel structure.The production cost of reinforced concrete is very low and also its maintenance cost is also low because of its long lasting nature.

7. Seismic Resistance

During the time of designing reinforced concrete structure all types of load which acts on the structure are designed as per Is Ccode guideline therefore these types of structure are extremely resistant to earthquakes.

8. Multiple Application

One of the major advantages of concrete is its ability to be used in different application methodologies.Concrete is hand applied, poured, pumped, sprayed, grouted and also use as shotcrete.

Disadvantages of Reinforced Concrete

• Reinforced concrete structure are heavier than other structures like steel, wood and glass.
• It required massive formwork and shuttering and for that it requires lots of site space and labor work.
• The cost of the form used for casting RC is relatively higher.

Uses of Reinforced Concrete

• It is used in Building construction
• It is used in Foundation
• It is used in Water tank conctruction
• It is used in Road construction
• It is used in Bridge construction
• It is used in Flyovers construction 
• It is used in Marine construction
• It is used in Retaining wall construction
• It is used in construction of Bunkers and Silos

GREEN CEMENT - TYPES, APPLICATION AND ADVANTAGES

Green Cement

Green cement is a form of cement produced with the help of a carbon-negative manufacturing process.This cement is environmentally friendly product that minimizes carbon footprint of cement production.The concept of green cement emerged with the discovery of geopolymer cement in 1950s.Geopolymer cement is manufactured by using aluminosilicates instead of calcium oxide which damaging the environmental badely. The silicates can be obtained from industrial waste materials such as fly ash and blast furnace slag.

Green cement manufacturing reduces the cement intake.This cement reduces the carbon footprint upto 40%. Apart from reducing carbon dioxide emissions, the green cement manufacturing process also helps to maintain cement strength.It is composed of calcined clay and powdered limestone,it has desired characteristics such as reduced porosity and enhanced mechanical strength.

Benefits of Green Cement

1. Make Use of Industrial Waste

Fly ash a by-product of thermal power plant is produced in a large quantity which requires large area to disposed it.Green cement not only makes use of the fly ash waste but also protects the land from harmful environmental effects.

2. Requires Less Energy

The materials used in the traditional cement manufacturing process requires large amount of natural gas/coal for heating purposes.In green cement manufacturing industrial by-products are used as raw material which requires less energy. Green cement is more resistant to changes in temperature, therefore reducing the costs associated with both heating and cooling.

3. Lower Carbon Dioxide Emission

Clay, sand and pulverized limestone are some of the ingredients used in traditional cement.These ingredients requires heat releasing approx 5% to 8% of the total carbon dioxide.Green cement on the other hand does not requires as much heat during its production releasing upto 80% less carbon dioxide.

4. Long Lasting

Green concrete has a lower shrinkage rate and also becomes stronger far more quickly than concrete made with traditional cement.And since green concrete can withstand temperature as high as 2400℉, it makes building significantly more fire resistant.

Types of Green Cement

1. Ekkomaxx Cement

It is a type of green cement produced by Ceratech company in the USA.It is composed of 95% fly ash and 5% of renewable liquid additives.

The main characteristics of Ekkomaxx cement are high early strength, resilience, crack resistance, low chloride permeability, sulphate attack resistance, durability, corrosion resistance which is more than three times of conventional cement and the resistance to freezing and thawing is greater than that of normal cement.

2. Geopolymer Cement

Geopolymer, cement is a binding system that hardens at room temperature.It is also known as alkali-activated cement,is produced from aluminosilicates instead of the more environmentally damaging calcium oxide.The aluminosilicates are obtained from industrial by-product like fly ash.

3. Magnesium Oxychloride Cement

Magnesium oxychloride cement is also known as Solar cement.It is an environment friendly and carbon neutral cement.It is produced from magnesium oxide powder and concentrated solution of magnesium chloride.

The magnesium oxychloride cement has high compressive strength and set quickly and magnesium oxide absorb carbon dioxide from the atmosphere, but water can reduce its strength.However this weakness of MOC can be tackled to certain extent by introducing 15% of fly ash and the same amount of silica fume.The additives fill the pore structure in MOC which makes the concrete denser.Both strength and durability of concrete is improved considerably.

4. Ferrocrete

The ferrocrete cement is manufactured by mixing silica and iron which are waste byproduct from steel and glass industry.This material mixture is then cured with CO2, and consequently, it potentially becomes carbon negative materials.

5. Calcium Sulfoaluminate Cement

The calcium sulfoaluminate cement is a specially used in many applications where high early strength and fast setting development are necessary such as bridge decks, airport runways, patching roadways, tunneling etc.The calcium sulfoaluminate cement is produced of a kiln that requires a temperature of 2250℉ rather than 2500℉ of conventional cement.The calcium sulfoaluminate cement sets rapidely gain 28day strength of conventional concrete in 24 hours.

6. Cement Produced Using Superheated Steam

The superheated steam cycle will be used to modify the cement particles and render them more sensitive.The CO2 generated may be detected through this phase after it has been extracted.

7. Cement Produced With Reactive Hydrothermal Liquid Phase Densification

This form of cement is manufactured using the same raw materials as Ordinary Portland cement but at lower temperatures and through specific chemical reactions which generate less CO2 compared to convention Portland cement production processes.

Advantages of Green Cement

• Reduces the emission of CO2 as it does not requires as much heat during production, releasing upto 80% less carbon dioxide.
• Make use of industrial waste such as fly ash, silica fume and last furnace that may require several acres of land to dispose it.
• Requires less energy.

WHAT IS MORTAR - PROPERTIES, TYPES AND USES

What is Mortar

Mortar is a paste made by cement and water or by lime, surkhi and water. Lime and cement is a binding material in the mortar.Sand and surkhi give the strength to the mortar.It is a material used in masonry construction to fill the gaps between the bricks and blocks used in construction.

Properties of Good Mortar 

• It should be durable.
• It should be cheap.
• It should be easily workable.
• It should possess high durability.
• It should set quickly so that speed in construction may be achived.
• It should be capable of developing good adhesion with the building units such as bricks,stone etc. 
• The joints formed  by mortar should not develop cracks and should be able to maintain their appearance for a sufficiently long period.

Types of Mortar Used In Masonry Construction

1. Based on Applications
2. Based on Binding Materials
3. Based on Strength 
4. Based on Bulk Density
5. Based on Special Purpose of Mortars

Based on Application

1. Brick Laying Mortar

This type of mortar used to bind bricks in masonry construction.The ratio of the ingredients of brick laying mortar is decided based on kind of binding material used. 

2. Finishing Mortar

Finishing mortar is used for pointing and plastering works.It should have great strength,mobility and resistance against atmospheric action.This mortar is also used for ornamental finishing.

Based on Building Materials

1. Cement Mortar

Cement mortar is a homogenous paste of cement, sand and water.Different cement mortars are obtained by mixing different proportion of cement and sand.Cement mortar will give strength and resistance against water.The ratio of cement mortar is varies to 1:2 to 1:6.

2. Lime Mortar

Lime is used as a binding material, lime mortar is composed of lime and an aggregate such as sand, mixed with water.There are two types of lime fat lime and hydraulic lime.Lime mortar are flexible, allowing for movement in the building and thus preventing cracks in the masonry.

3. Gypsum Mortar

Gypsum mortar is made up from gypsum, which requires a lower firing temperature.Gypsum mortar is not durable as other mortars in damp conditions.

4. Surkhi Mortar

Surkhi is made by grinding brunt brick,brick-bats or burnt clay. Surkhi mortar is a mixture of lime, surkhi and water. Surkhi is finely-powdered brunt clay which provides more strength than sand and it is cheaply available in the market.

5. Mud Mortar

Mud mortar is a type of mortar where mud is used as binding materials.In mud mortar rice-husk, cow dung and sawdust is used as fine aggregate.Mud mortar is used where lime or cement is not available.

6. Gauged Mortar

Gauged mortar is a type of mortar where cement and lime both are used as binding materials and sand is used as fine aggregate. In gauged mortar cement is added to enhance the strength of the mortar.It economical than cement mortar.The cement to the lime propertion varies from 1:6 to 1:9.

Based on Bulk Density

1. Light Weight Mortar

When the mortar having bulk density less than 15 KN/m3 then it is called as light mortar.It is prepared by mixing rice-husk, jute fibers, saw dust, coirs or asbestos fibers along with sand and lime or cement as binder.It is generally used in the soundproof and heat proof constructions.

2. Heavy Weight Mortar

When the mortar having bulk density of 15KN/m3 or more then it is called as heavy mortar.

Based on Strength

1. Type M Mortar

Type M mortar is considered to be the strongest mortar.It is the highest strength mortar minimum 17.2 Mpa.It is used for exterior masonry work.This type of mortar is used where lateral load or substantial gravity are exerted.Load bearing wall retaining wall, footings etc its example.

2. Type S Mortar

Type S mortar is considered to be the medium strength mortar minimum 12.4 MPa with high bonding ability.It is used for grade application with normal to moderate loading. Type S mortar has great durability that is why it is highly suitable for locations where the masonry is in contact with the ground, such as shallow retaining wall.

3. Type N Mortar

It is medium strength mortar with 5.2 MPa and most common type of mortar.Type N mortar used for reinforced interior and above grade exterior load-bearing walls on which normal loads are imposed.

4. Type O Mortar

Type O mortar is considered to be a low strength mortar with minimum 2.5 MPa. Type O mortar is used for interior non load bearing applications with very limited exterior use.

Based On Special Purpose of Mortars

1. Fire Resistant Mortar

Fire resistant mortar is prepared by mixing aluminous cement to the fine powder of fire bricks.If there are any fire warnings to the structures in a particular zone, then fire resistant mortar will be used which acts as fireproof shield.

2. Packing Mortar

The constituents of packing mortars are generally cement-sand, cement-loam or sometimes cement-sand-loam.This type of mortar is used to pack the oil wells. Packing mortar should be of high homogeneity, water resistance and high strength.

3. Sound Absorbing Mortar

In sound absorbing mortar cement, lime, gypsum or slag is used as a binding materials while pumice and cinder as fine aggregate.It is used to reduce the level of noice and acts as sound proof layer.

4. X-ray Shielding Mortar

X-ray shielding mortar is used in the x-ray room.To provide protection against x-rays the room walls and ceilings are plastered with  X-ray shielding mortar.This mortar is of heavy type with bulk density around 22KN/m3.Fine aggregates from heavy rock and suitable admixture are used to prepare this type of mortar.

5. Chemical Resistant Mortar

Chemical resistant mortar is made of by the combination of liquid and powder, it should be mixed in proportion from workable mortar which after setting and curing of liquid get solid.

The additives added may not resist all the chemical attacks.For example silicate type chemical mortar resists nitric, chromic, sulphuric or any acidic damage but it cannot prevent the structure against damage by alkalies of any concentration.

Uses of Mortar in Masonry Construction

• It is used to bind the bricks and stones with each other.
• It is used for plastering.
• It is used to hide the openjoints of brickwork and stonework.
• It is used to repair cracks in structure.
• It is used to distribute uniform load over the lower brick.
• It is use to improve the general appearance of the structure.