5 polymer fiber

Fiber Reinforced Concrete:

“FRC is defined as a composite material consisting of concrete reinforced with discrete randomly but uniformly dispersed short length fibers.”

Fibers are generally discontinuous, randomly distributed through out the cement matrices.

Enhances flexural and tensile strength of the concrete.

Fibers may generally be classified into two: organic and inorganic.

Contd. ….

Volume fraction – measure of fiber in concrete.

Typically ranges from 0.1 to 3%.

Aspect ratio - fiber length (l) divided by its diameter (d).

Main categories of F.R.C.

SFRC - Steel Fiber Reinforced Concrete.

GFRC - Glass Fiber Reinforced Concrete.

SNFRC - Synthetic Fiber Reinforced Concrete.

NFRC - Natural Fiber Reinforced Concrete.

POLYMER FIBER REINFORCED CONCRETE (PFRC)

It comes under the category of Synthetic FRC.

Mainly preferred due to its cost effectiveness and zero corrosion risk.

This method has been recognized and approved by BIS, IRC and various national bodies.

Why PFRC for pavements?

Crack arresters-restricting the development of cracks .

Enhanced flexural strength and tensile strength of concrete.

Improved early resistance to plastic shrinkage cracking.

Improved durability and reduced surface water permeability of concrete.

Reduces the risk of plastic settlement cracking over rebar.

Cont. ….

It enables easier and smoother finishing.

Reduced bleeding of water to surface during concrete placement.

Improves the homogeneity of the concrete matrix.

Reduced water absorption.

Greater impact resistance.

The two components of PFRC

Concrete Mix

The code IRC: 44-2008 – For cement concrete mix designs for pavements with fibers.

In presence of fly ash – cement savings upto 35%.

Flexural strength- 40 MPa at 28 days.

2) Polymer fibers

Recron 3S, Polypropylene, Forta ferro, Forta econo net.

Recycled polymer waste from plastic, carpet industry, textile industry, disposed tires.

Size 12mm long and 0.045 mm diameter.

Mixed at the rate of 900gms/m3 of concrete.

Various polymers used in PFRC

PAVEMENT DESIGN

PAVING OPERATION

REQUIREMENTS FOR PAVING OPERATIONS

1) Use of microfilm or antifriction layer of 125 micron in between PFRC and DLC layers.

2) The DLC layer is to be swept clean before applying microfilm .

3) Film is nailed to the DLC layer without wrinkles and holes.

4) Concreting work in hot weather should be carried out in early or later hours.

5) The laying temperature of concrete should always be below 35 degree Celsius.

CURING

Membrane curing is used.

Texture-[censored]-curing machine performs the task.

The resin based curing compound is used at the rate of 300 ml per square meter of the slab area.

After about 1.5 hours moist Hessian cloth is spread, covered with curing compound spray.

Water curing by keeping the Hessian moist by sprinkling water is ensured for 3 days.

Completed PFRC pavement

PROTECTION AND MAINTENANCE

Insert performed neoprene sealant to protect joint groove from dirt .

Test are to be conducted on fine and coarse stone aggregates, water, cement, granular sub base, DLC etc as per standards and specification published by Indian roads congress.

No vehicular traffic until the completion of 28 days of curing, sealing of joints and completion of paved shoulder construction.

POLYESTER FIBER WASTE IN PFRC

The tests resulted in the following inferences:

1. The polyester FRC in thicknesses of 100mm or more can be used.

2. The use of polyester fibers increases the abrasion resistance of concrete by 25%.

3. The polyester fibers are resistant to the strong alkaline conditions in concrete.

4.There is no decrease in long term compressive strength or UPV of PFRC.

5. The results of this study promote effective disposal of these non bio-degradable synthetic fibers.

Advantages of PFRC

PFRC roads are highly impermeable to water.

Implementation of sensors in roads will be easier.

Environmental load of PFRC pavement was found to be significantly lower.

Maintenance activities are reduced.

Impermeable and more durable, skid resistant pavement.

Cont. ….

Fibers reduce plastic shrinkage and substance cracking.

Improved abrasion resistance and impact resistance.

Ductile and flexural toughness of concrete.

Cement saving up to 10%

Improve durability of concrete

Disadvantages of PFRC

Fibers which are too long tend to “ball” in the mix and create workability problems.

The use of PFRC, being a relatively new technology poses a threat of a high initial cost of construction.

In case the road breaks, the whole concrete slab needs to be replaced.

COMPARISONS BETWEEN PFRC AND NORMAL CONCRETE

APPLICATIONS OF PFRC

Slab On Grade.

Structural Concrete.

Water retaining Structures.

Water proofing in rooftops, sunken toilets, etc.

Kerala based projects using PFRC

CIAL Airports: Turning Pad Concrete, New Arrival Bldg, Cargo storage complex.

ICTT Vallarpadam: Jetty Construction 8000 cubic mtr slab/Simplex infra.

Cochin Port Trust: Mattancherry Warf, NCB, UTL etc.

MES: GE Air Force – Tvm Projects, DGMAPs Projects Cochin

Southern Railway: Platforms at Quilon, Kochuveli, etc.

Harbour Engineering Dept: Vipin Jetty wearing coat.

CONCLUSION

PFRC can be used advantageously over normal concrete pavement.

PFRC requires specific design considerations and construction procedures to obtain optimum performance.

Reduction in maintenance and rehabilitation operations, makes PFRC cheaper than flexible pavement by 30-35%.

Promote effective disposal of non bio-degradable synthetic fibers.

A new hope to developing and globalizing the quality and reshaping the face of the “True Indian Roads”.

Refe

4. Natural fiber

Information on mechanical properties of unprocessed natural fibers is available. In this section, a brief summary of the results of research to determine the mechanical properties of various types of unprocessed natural fibers is presented. The types of fibers for which the mechanical properties have been evaluated are given in the table below. A brief description for some of the more commonly found natural fibers is presented:

a. Coconut fiber: A mature coconut has an outer covering made of fibrous material. This part of the coconut, called the husk, consists of a hard skin and a large amount of fibers embedded in a soft material. The fibers can be extracted simply by soaking the husk in water to decompose the soft material surrounding the fibers. This process, called retting, is widely used in the less developed countries. Alternatively, a mechanical process can be used to separate the fibers. Coconut cultivation is restricted to the tropical regions of Africa, Asia, and Central America.

b. Sisal fiber: In Australia, sisal fibers have been successfully used for making gypsum plaster sheets. A considerable amount of research has been carried out in Sweden for developing good quality concrete products reinforced with sisal fibers. These fibers are stronger than most of the other natural fibers, as can be seen from the table below.

c. Sugar cane bagasse fiber. Sugar cane is cultivated in both tropical and sub-tropical regions. Sugar cane bagasse is the residue remaining after the extraction of the juice and contains about 50 percent fiber and 30 percent pith with moisture and soluble solids constituting the remaining 20 %. In order to obtain good quality fibers, the pith and other solids are removed from the fibers. The properties of bagasse fibers depend, to a very large extent, on the variety of the sugar cane, its maturity, and on the efficiency of the milling plant. The properties given in the table below are considered to be typical.

d. Bamboo fiber: Bamboo belongs to the grass family and can grow to a height of 15 m with diameters varying within the range of 25 to 100 mm. It grows naturally in tropical and sub-tropical regions. Dried bamboo stems are commonly used for building temporary structures such as scaffolding. They may also be fabricated to form a continuous reinforcing material for concrete. Bamboo fibers are strong in tension (table below) and can be used as a reinforcing material. However, they have a high water absorption capacity, low modulus of elasticity, and special equipment may be needed to extract them from the stems.

e. Jute fiber: Jute is grown mainly in India, Bangladesh, China, and Thailand. It is grown solely for its fiber, which is traditionally used for making ropes and bags to transport grains and other materials ranging from cement to sugar. Strong in tension (table below), jute fiber can also be used in a cement matrix. The process of obtaining jute fibers is very simple. Mature plants are cut and soaked in water for about four weeks, which completely decomposes the bark. The fibers thus exposed are then stripped from the stem, washed, and dried.

f. Flax: Flax is a slender and erect plant grown mainly for its fiber. Both the tensile strength and the modulus of elasticity of flax are extremely high compared to those of other natural fibers, as may be seen from the table below.

g. Other vegetable fibers: Of the various vegetable fibers, only a few have been found to be potentially suitable as reinforcing materials. The mechanical properties of the more promising fibers, namely elephant grass, water reed, plantain, and musamba, are listed. Investigations have also been carried out to explore the possibility of using other natural fibers such as palm fiber and akwara fiber as reinforcing materials for concrete. These fibers are usually removed manually from the stem of the plant.

3. Synthetic fiber

Synthetic fibers specifically engineered for concrete are manufactured from man-made materials that can withstand the long-term alkaline environment of concrete. Synthetic fibers are added to concrete before or during the mixing operation. The use of synthetic fibers at typical addition rates does not require any mix design change.

Why use?

Synthetic fibers benefit concrete in both the plastic and hardened states. Some of the benefits include:

® Reduced plastic settlement cracks

® Reduced plastic shrinkage cracks

® Lowered permeability

® Increased impact and abrasion resistance

® Increased shatter resistance

Some synthetic fibers may be used as secondary reinforcement (Hardened Concrete Performance Documentation required).

2. Glass fiber

Definition: A family of reinforcing materials for reinforced plastics based on single filaments of glass ranging in diameter from 3 to 19 micrometers (0.00012 inch to 0.00075 inch). Single filaments are produced by mechanically drawing molten glass streams. Next, the filaments are usually gathered into bundles called strands or rovings. The strands may be used in continuous form for filament winding; chopped into short lengths for incorporation into molding compounds or use in spray-up processes; or formed into fabrics and mats of various types for use in hand coatings with a material known as a coupling agent, which serves to promote adhesion of the glass to the specific resin being used. Glass fiber reinforcements are classified according to their properties. At present there are five major types of glass used to make fibers. The letter designation is taken from a characteristic property: 1) A-glass is a high-alkali glass containing 25% soda and lime, which offers very good resistance to chemicals, but lower electrical properties. 2) C-glass is chemical glass, a special mixture with extremely high chemical resistance. 3) E-glass is electrical grade with low alkali content. It manifests better electrical insulation and strongly resists attack by water. More than 50% of the glass fibers used for reinforcement is E-glass. 4) S-glass is a high-strength glass with a 33% higher tensile strength than E-glass. 5) D-glass has a low dielectric constant with superior electrical properties. However, its mechanical properties are not so good as E-or S-glass. It is available in limited quantities. Glass fibers coated with nickel, by the electron beam deposition process, are used in molding compounds and as reinforcements for electrically conductive parts. The major disadvantage of glass fiber is its unidirectional reinforcement which leads to uneven shrinkage and warpage.

1. Steel fiber details

Harde provides stainless steel and galvanized steel engineering fiber for construction in various types and sizes. For over a decade, we have been concentrating on development and manufacture of steel fiber and steel band products.

Choose from the following list to learn more about our commodities. A more complete description of these products is also available.

Steel Fiber General Description

Supplying concrete fibres, mainly Metallic fibres. Metallic fibres include low carbon cold drawing steel fibres, stainless steel fibre, and sheet steel fibres etc. We have types of Hooked Ends, Corrugation, Flat Ends and Micro steel fiber etc.

Steel Fiber

Description:

Steel fibres are filaments of wire, deformed and cut to lengths, for reinforcement of concrete, mortar and other composite materials. It is a cold drawn wire fibre with corrugated and flatted shape. It is often used to instead of Xorex steel fiber.

Applications:

- cellar walls - slabs on

vibrocompacted piles - pavements

- liquid tight floors - jointless floors

- jointless floors on - industrial floors

vibrocompacted piles - overlays

- outdoor slabs - piles

- foundation slabs - segmental linings

- suspended ground slabs

- composite slabs

Specification:

Fiber length (mm): 38 (1.5”)

Equivalent Diameter (mm): 1.0±0.03

Tensile strength: (Mpa ±5%): 850

The thickness of fiber is 0.5mm and width is 1.4mm

Fiber length (mm): 50(2”)

Equivalent Diameter (mm): 1.0±0.03

Tensile strength: (Mpa ±5%): 850

The thickness of fiber is 0.5mm and width is 1.4mm

Steel fiber specification can be made according to requirement.

================

Major Product Index:

Straight Steel Fiber

Product Description:

The cold-rolled strip steel products are made from cutting. Stainless steel fiber has high tensile strength and it can be easily dispersed, and can be easily integrated with the concrete.

Stainless steel fiber is widely used and the main parameters as follows:

Fiber length: 25-35mm

Fiber diameter: 0.3-0.7mm

Tensile strength:≥650MPa

Stainless steel fiber is made in accordance to the country standard YB/T151-1999 Standard for Steel Fibers for Concrete Uses, and the JG/T3064-1999 Standard of Steel Fiber for Concrete Building Industry.

Packing: We can provide package according to our customers’ specifications. Stainless steel fiber can be packed in one-layer of plastic and two-layer paper bags or boxes. The weight is 20kg per bag, or per customers request.

Indentation Steel Fiber

We offer steel fiber for concrete mixing to enhance the strength.

Indentation steel fiber is widely used and the main parameters as follows:

Fiber length: 25-35mm

Fiber diameter: 0.3-0.7mm

Tensile strength:≥650MPa

Steel fiber is made in accordance to the country standard YB/T151-1999 Standard for Steel Fibers for Concrete Uses, and the JG/T3064-1999 Standard of Steel Fiber for Concrete Building Industry.

--------------------------------------------------------------------------------

Hooked Ends Steel Fiber

Steel fiber with hooked ends is made using high-quality low-carbon steel wire. A kind of high-performance steel fiber, with the characteristics of the high tensile strength, good toughness, low prices, etc. The product is widely used in concrete strengthening.

Hooked ends steel fiber is made in accordance to the country standard YB/T151-1999 Standard for Steel Fibers for Concrete Uses, and the JG/T3064-1999 Standard of Steel Fiber for Concrete Building Industry.

Classify your order for hooked ends steel fiber:

Wire Diameter (mm)

Fiber Length (mm)

Tensile Strength(Mpa) of Steel Fiber

Types of fiber used in concrete

There are many types of fibers that can be used in concrete including steel fibers, glass fibers, synthetic fibers and natural fibers. The characteristics of the fiber reinforced concrete depend on the fiber material, amount, geometry, distribution, orientation, and densities of the fibers used. Fibers are added to fresh concrete during the batching and mixing process to allow them to be equally distributed throughout the concrete.

Basics Of Fiber Reinforced Concrete

What Is Fiber Reinforced Concrete

Fiber reinforced concrete is a type of concrete that includes fibrous substance that increases its structural strength and cohesion. Fiber reinforced concrete has small distinct that are homogeneously dispersed and oriented haphazardly. used are s, synthetic , glass , and natural . The characteristics of fiber reinforced concrete are changed by the alteration of quantities of concretes, fiber substances, geometric configuration, dispersal, direction and concentration.

Why Fiber Reinforced Concrete Is Used

Portland cement concrete is believed to be a comparatively brittle substance. When un-reinforced concrete is exposed to tensile stresses, it is likely to fracture and fail. Since the beginning of the nineteenth century, studies were conducted to reinforce concrete by using steel. After the reinforcement of concrete by steel, it becomes a composite group in which the steel endures the tensile stresses. When concrete is reinforced by using fiber in the mixture, it further increases the tensile strength of the composite system. Research has revealed that the strength of concrete may be improved tremendously by the addition of fiber reinforcing. Since the stretching ability under load of reinforcing fiber is greater than concrete, initially the composite system will function as un-reinforced concrete. However, with additional loading the fiber reinforcing will be activated, to hold the concrete mix together.

Characteristics Of Fiber Reinforced Concrete

The characteristics of concrete depend upon the kind of fiber utilized, volume proportion of the fiber, and the ratio of length and diameter of the fiber. These conditions will improve the mechanical properties, including toughness, ductility, tensile strength, shear resistance and loading limit of the fiber reinforced concrete. Materials used for fiber reinforcement include steel, glass, polyester, rayon, cotton, and polythene. Most commonly used materials are steel and glass that are acid resisting. Natural being vulnerable to alkali attack are not much popular. Similarly, plastic have recently been introduced in the field of reinforcement and are still in the development phase. It is considered that the contribution of plastic to increase the static strength of concrete is limited. Nylons have the characteristics of a plastic material, and presently have a limited application in the slab technology. It is generally believed that nylon possess strength that is greater than the welded wire fabric in such slabs.

Fiber Reinforced Concrete

The concrete reinforcement technology is not new and fibers have been used for reinforcement since ancient times. Popular fibers are steel and glass fibers, while plastic and nylons have a limited use. Quantities, concentration, and dispersal influence the properties of fiber reinforced concrete.

SPECIAL TYPES OF CONCRETE

PRESTRESSED CONCRETEA prestressed concrete unit is one in whichengineered stresses have been placed before it hasbeen subjected to a load. When PRETENSION-ING is used, the reinforcement (high-tensile-strength steel strands) is stretched through theform between the two end abutments or anchors.A predetermined amount of stress is applied tothe steel strands. The concrete is then poured,encasing the reinforcement. As the concrete sets,it bonds to the pretensioned steel. When it hasreached a specified strength, the tension on thereinforcement is released. This prestresses theconcrete, putting it under compression, thuscreating a built-in tensile strength.

POST-TENSIONING involves a precastmember that contains normal reinforcing inaddition to a number of channels through which the prestressing cables or rods maybe passed. Thechannels are usually formed by suspending inflated tubes through the form and casting theconcrete around them. When the concrete has set,the tubes are deflated and removed. Once theconcrete has reached a specified strength, distressing steel strands or TENDONS are pulledinto the channels and secured at one end. They are then stressed from the opposite end with aportable hydraulic jack and anchored by one of several automatic gripping devices.Post-tensioning may be done where the member is poured or at the jobsite. Each membermay be tensioned, or two or more members maybe tensioned together after erection. In general,post-tensioning is used if the unit is over 45 ft longer over 7 tons in weight. However, some typesof pretensioned roof slabs will be considerably longer and heavier than this.When a beam is prestressed, either by pre-tensioning or post-tensioning, the tensioned steelproduces a high compression in the lower part of the beam. This compression creates an upwardbow or camber in the beam (fig. 7-19). When a load is placed on the beam, the camber is forcedout, creating a level beam with no deflection.Those members that are relatively small or that can be readily precast are normally pretensioned.These include precast roof slabs, T-slabs, floorslabs, and roof joists.

SPECIAL TYPES OF Concrete Special types of concrete are essentially those with unique physical properties or those produced with unusual techniques and/or reproduction processes. Many special types of concrete are made with portland cement as a binding medium;some use binders other than Portland cement.Lightweight ConcreteConventional concrete weighs approximately150 lb per cubic foot. Lightweight concrete weighs20 to 130 lb per cubic foot, depending on its intended use. Lightweight concrete can be madeby using either gas-generating chemicals.

Roller compacted concrete

• Roller compacted concrete, sometimes called rollcrete, is a low-cement-content stiff concrete placed using techniques borrowed from earthmoving and paving work.

• The concrete is placed on the surface to be covered, and is compacted in place using large heavy rollers typically used in earthwork.

• The concrete mix achieves a high density and cures over time into a strong monolithic block.

• Roller compacted concrete is typically used for concrete pavement. Roller compacted concrete dams can also be built, as the low cement content causes less heat to be generated while curing than typical for conventionally placed massive concrete pours

Pervious concrete

• Pervious concrete contains a network of holes or voids, to allow air or water to move through the concrete. This allows water to drain naturally through it, and can both remove the normal surface water drainage infrastructure, and allow replenishment of groundwater when conventional concrete does not.

• It is formed by leaving out some or the entire fine aggregate (fines), the remaining large aggregate then is bound by a relatively small amount of Portland cement.

• When set, typically between 15% and 25% of the concrete volumes are voids, allowing water to drain.

• The majority of pervious concrete pavements function well with little or no maintenance. Maintenance of pervious concrete pavement consists primarily of prevention of clogging of the void structure.

• In preparing the site prior to construction, drainage of surrounding landscaping should be designed to prevent flow of materials onto pavement surfaces. Soil, rock, leaves, and other debris may infiltrate the voids and hinder the flow of water, decreasing the utility of the pervious concrete pavement.

Shotcrete

• Shotcrete concrete uses compressed air to shoot concrete onto (or into) a frame or structure.

• Shotcrete is mortar or (usually) concrete conveyed through a hose and pneumatically projected at through a shortcrete nozzle with high velocity onto a surface. Shotcrete undergoes placement and compaction at the same time due to the force with which it is projected from the nozzle.

• It can be impacted onto any type or shape of surface, including vertical or overhead areas.

• Shotcrete is frequently used against vertical soil or rock surfaces, as it eliminates the need for formwork.

• It is sometimes used for rock support, especially in tunneling.

• Shotcrete is also used for applications where seepage is an issue to limit the amount of water entering a construction site due to a high water table or other subterranean sources.

• This type of concrete is often used as a quick fix for weathering for loose soil types in construction zones.

SELF COMPACTING CONCRETE

The concrete where no vibration is required. The concrete is compacted due to its own weight. It is also called self consolidated concrete or flowing concrete. It can be also categorized as high performance concrete as the ingredients are the same, but in this type of concrete workability is increased. This self-consolidating concrete is characterized by:

• Extreme fluidity as measured by flow, typically between 650-750 mm on a flow table, rather than slump (height).

• No need for vibrators to compact the concrete.

• Placement being easier.

• No bleed water, or aggregate segregation.

Uses and Applications of Self Compacting Concrete:

1. It is used in location unreachable for vibrations. e.g. underground structure, deep wells or at bottom of deep sea.
2. SCC can save up to 50% in labor costs due to 80% faster pouring and reduced wear and tear on formwork.

LIGHT WEIGHT CONCRETE

• The concrete which has substantially lower mass per unit volume then the concrete made of ordinary ingredients is called lightweight concrete. The aggregates used are lighter in weight.

• Density of light weight concrete is 240 kg/m³ (15pcf) -1850 kg/m³ (115 pcf).

• Strength of light weight concrete blocks varies from 7 MPa (1000 psi) - 40 MPa (5800 psi).

• Some times Air Entrained Admixtures are also added to it giving resistance to freezing and thawing along with strength.

Uses of Light weight concrete:

• Used where extra load is not applied e.g. parapet wall, road lining etc. or to reduce dead load.

Air Entrained Concrete

• One of the greatest achievements in field of concrete technology is development of air entrained concrete. It is used where the concrete is vulnerable to freezing and thawing action.

• It is used where the concrete is vulnerable to freezing and thawing action. It is prepared by adding the air entraining admixture.

The air entrainment in concrete does the following functions:.

1. It lowers the surface tension of water and thus bubbles are created.

2. Secondly the air entraining agents prevents coalescing i.e. the combining of bubbles. The diameter of these bubbles ranges form 10 micrometer to 1000 micrometer and in entrapped air the diameter of bubble is greater than 1mm.

Air entraining agents OR air entrained admixtures are used for the purpose of making entrained air in concrete.

FREEZING AND THAWING:

There are two phenomenons regarding the freezing and thawing action on concrete.

1. when water inside concrete mass freezes it expands 9-10% due to this increase in the size it exerts pressure on its surrounding and thus creating a tensile force due to which micro cracks appear in the concrete. Due to freezing these micro cracks develop into fissures which results in disruption of concrete.

When the air entrained agents are present, extra amount of air is there as water expands these air bubble provide them thin space and the exertion of pressure is prevented.

2. Second is of osmotic pressure: In a concrete structure there are two parts, frozen and unfrozen. As the water content is higher in the frozen part, the osmotic pressure is developed and water tends to flow towards the low water concentration part. If capillaries are not available, the water develops cracks.

• Normal concrete can not sustain 3-4 cycles of freezing and thawing where as the AEA concrete can sustain 100 cycles of it.

DRAW BACKS of Air Entrained Concrete:

• It has low strength as compare to normal concrete.

  
  

High Performance Concrete

This mix has the following main properties:

• High strength.
• High workability.
• High durability.
• Ease of placement.
• Compaction without segregation.
• Early age strength.
• Long-term mechanical properties.
• Permeability.
• Density.
• Heat of hydration.
• Toughness.
• Volume stability.
• Long life in severe environments.

Preparation

High strength concrete mix can be prepared with careful selection of ingredients and optimization of mix design.

• High workability is attained by super plasticizers, they lower the water cement ratio to 0.25 which is the amount required only for hydration process.

• High durability is attributed to fly ash and silica fume which modify the e mineralogy of the cement; it enhances the compatibility of ingredients in concrete mass and reduces the CH amount. Fly ash also causes ball bearing effect increasing workability.

• The admixtures are 20-25% fly ash of partial replacement of cement and rest 70% is Ordinary Portland Cement.

• As it is not usually durable against freezing and thawing so air entrained agents can also be utilized.

Properties of high performance concrete mix

• Strength of high performance concrete ranges from 10000 psi - 15000 psi

• Water cement ratio can be reduced to 0.25

High strength concrete

• Compressive strength of high strength concrete mix is usually greater than 6,000 pounds per square inch.

• High strength concrete is made by lowering the water cement (W/C) ratio to 0.35 or lower.

• Often silica fume is added to prevent the formation of free calcium hydroxide crystals in the cement, which might reduce the strength at the cement aggregate bond.

• Low w/c ratios and the use of silica fume make concrete mixes significantly less workable, which is particularly likely to be a problem in high-strength concrete applications where dense rebar cages are likely to be used. To compensate for the reduced workability in the high strength concrete mix, superplasticizers are commonly added to high-strength mixtures.

• Aggregate must be selected carefully for high strength mixes, as weaker aggregates may not be strong enough to resist the loads imposed on the concrete and cause failure to start in the aggregate.

  
  

Properties of Normal Concrete

• Its slump varies from 1 - 4 inches.

• Density ranges from 140 pcf to 175 pcf.

• It is strong in compression and weak in tension.

• Air content 1 - 2 %.

• Normal concrete is not durable against severe conditions e.g. freezing and thawing.

NORMAL CONCRETE

1. Normal Concrete

   ---

• The concrete in which common ingredients i.e. aggregate, water, cement are used is known as normal concrete. It is also called normal weight concrete or normal strength concrete.

• It has a setting time of 30 - 90 minutes depending upon moisture in atmosphere, fineness of cement etc.

• The development of the strength starts after 7 days the common strength values is 10 MPa (1450 psi) to 40 MPa (5800 psi). At about 28 days 75 - 80% of the total strength is attained.

• Almost at 90 days 95% of the strength is achieved.

TYPES OF CONCRETE

1. Normal concrete

2. High Strength Concrete

3. High Performance Concrete

4. Air Entrained Concrete

5. Light Weight Concrete

6. Self Compacting Concrete

7. Shotcrete

8. Pervious Concrete

9. Roller Compacted Concrete

INTRODUCTION TO CONCRETE

The word "Concrete" orginates from the Latin word "Concretus", Which means to grow together. Nature of Concrete * It is a composite material * Aggregates : are 65-80% of volume Fine Aggregate - Sand Coarse aggregate - Stone * Cement : General term and applies to any bimder Portland Cement Fly ash Ground slag Silica fume * Water : Properties of quality concrete * Workability * Durabilty * Strength * Chemical Resistance * Abrasion Resistance Concrete as a material Concrete literally forms the basis of our modern life: * Roadways * Airstrips * Infrastructures * Harbour Protections * Water Distribution Advantages of Concrete * Ability to cast desired shapes. Ex: Arches, Shells, Columns, Piers,etc., * Properties can be tailored according to need (Strength, Durability, etc.,) * Ability to resist high temperture. * Does not require any protective coatings * Can be architectural and structural members at the same time.