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Which of the following materials is NOT typically used in fibre reinforced concrete?

Glass

Nylon

Wood (correct)

Steel

What is the typical range of fibre content by volume in fibre reinforced concrete?

5 to 10 per cent

0.5 to 2.5 per cent (correct)

2 to 4 per cent

1 to 3 per cent

Which application is NOT commonly associated with fibre reinforced concrete?

Explosive resistant structures

Road pavements

Bridge decks

Wooden furniture (correct)

What is the maximum aggregate size recommended for fibre reinforced concrete?

10 mm Signup and view all the answers

What characterizes high-strength concrete?

Compressive strength greater than 40 MPa Signup and view all the answers

Which admixture is commonly used to aid in the placement of high-strength concrete?

Superplasticizers Signup and view all the answers

How does an increase in the aspect ratio of fibres affect mixing of fibre reinforced concrete?

It intensifies mixing difficulties Signup and view all the answers

In fibre reinforced concrete, which of the following is a common issue when the steel fibre content exceeds 2 per cent?

Difficulty in mixing Signup and view all the answers

What contributes to achieving high tensile strength in RPC?

Addition of small-sized steel fibers Signup and view all the answers

Why is the compressive strength of RPC typically higher than that of normal concrete?

It utilizes pozzolanic materials like silica fume. Signup and view all the answers

What is a major advantage of using RPC in construction?

It can structurally compete with steel. Signup and view all the answers

Which characteristic is NOT a property of RPC?

High porosity Signup and view all the answers

What is a limitation of RPC mentioned in the content?

Expensive components compared to conventional concrete. Signup and view all the answers

Which application is most suitable for RPC due to its properties?

Structures that need high tensile strength and ductility Signup and view all the answers

How does the use of steel fibers affect RPC?

It enhances its flexural strength Signup and view all the answers

What is the maximum compressive strength of RPC approximately?

200 MPa Signup and view all the answers

What is a characteristic feature of high performance concrete (HPC) concerning its resistance?

High resistance to chemical attack Signup and view all the answers

How does high strength concrete (HSC) affect the design of columns in high-rise buildings?

It allows for larger floor areas due to decreased column size. Signup and view all the answers

What is one of the main benefits of using vacuum concrete?

It improves the strength by removing excess water. Signup and view all the answers

Which component is essential for increasing the inherent qualities expected in high performance concrete when aiming for strengths above 80 MPa?

Silica fume Signup and view all the answers

What is an important consideration for the shape of aggregates used in high performance concrete?

Aggregates should be cubic to ensure high strength and workability. Signup and view all the answers

What is the primary reason for reducing the water-to-cement (w/c) ratio in high strength concrete?

To improve the strength and durability of the concrete. Signup and view all the answers

What significant benefit does the use of high strength concrete (HSC) provide in the construction of bridges?

It decreases the amount of steel required for support beams. Signup and view all the answers

Which of the following characteristics is NOT typically associated with high performance concrete?

Low density Signup and view all the answers

Study Notes

Special Concretes

Special concretes are various types of concrete, each with specific characteristics and applications.

Syllabus

Polymer concrete
Sulphur infiltrated concrete
Fiber reinforced concrete
High strength concrete
High performance concrete
Vacuum concrete
Self-compacting concrete
Geopolymer concrete
Reactive powder concrete
Concrete made with industrial wastes

Polymer Concrete

Concrete is porous, due to air voids, water voids, or inherent gel porosity.
Porosity reduces strength.
Reducing porosity increases concrete strength.
Vibration, pressure, or spinning methods do not effectively reduce water or inherent gel porosity (estimated at ~28%).
Impregnation of monomer and subsequent polymerization is a technique to reduce inherent porosity and improve concrete strength and other properties.
Types include Polymer Impregnated Concrete (PIC), Polymer Cement Concrete (PCC), Polymer Concrete (PC), and Partially Impregnated and surface coated polymer concrete.

Polymer Impregnated Concrete (PIC)

A precast conventional concrete cured and dried in an oven or by dielectric heating, from which air in open cells is removed by vacuum.
A low-viscosity monomer is diffused through the open cells and polymerized using radiation, heat, or chemical initiation.
Knowing water and air void concentration in the system is necessary to determine monomer penetration rate.
Obtaining maximum monomer loading is possible by removing water and air from the concrete using vacuum or thermal drying (thermal drying is faster).
This prevents air entrapment in the specimen during soaking, enabling total or maximum monomer loading.
Applying pressure is a technique to reduce monomer loading time.
Monomers used include Methylmethacrylate (MMA), Styrene, Acrylonitrile, t-butyl styrene, and other thermoplastic monomers.

Polymer Cement Concrete (PCC)

Made by mixing cement, aggregates, water, and a monomer-based plastic mixture.
The mixture is cast into molds, cured, dried, and polymerized.
Used monomers include Polyester-styrene, Epoxy-styrene, Furans and Vinylidene Chloride.

Polymer Concrete (PC)

Aggregate bound with polymer binder instead of Portland cement.
Graded aggregates are prepacked and vibrated in a mold.
Monomer is diffused through the aggregates and polymerization is initiated by radiation or chemical means.
Silane coupling agent is added to the monomer to improve bond strength between polymer and aggregate.
Polyester resins do not require polymerization.

Partially Impregnated (or Coated in Depth CID) and Surface Coated (SC) Concrete

Partial impregnation can suffice for situations requiring surface resistance to chemical and mechanical attack along with increased strength.
Even with partial impregnation, significant increases in original concrete strength have been obtained.
Production can involve initially soaking dried specimens in liquid monomer (like methyl methacrylate), then sealing them in hot water (70°C) to prevent evaporation loss.

Polymerization

Polymerization can be done thermally by adding 3% benzoyl peroxide to the monomer as a catalyst.
Monomer penetration depth depends on the hardened/dried concrete's pore structure, soaking duration, and monomer viscosity.

Applications of Polymer Impregnated Concrete

Prefabricated structural elements
Prestressed concrete,
Marine works
Desalination plants
Nuclear power plants
Sewage works/pipes, and disposal works
Ferrocement products
Waterproofing of structures
Industrial applications

Sulphur-Infiltrated Concrete

Sulphur, sand, and coarse aggregates are the primary ingredients.
Molten sulphur is added to preheated aggregates.
The hot mix is immediately transferred to moulds.
No curing is required; moulds can be stripped quickly after sulphur solidifies.
Products can be remoulded, and concrete reused with low wastage.
Strength up to 44 MPa has been achieved with 30% sulphur, 50% sand, and 20% coarse aggregate.
Versatile for precast slab elements, canal linings, and tunnel linings.
Two procedures exist: -Procedure A: 24 hours moist curing, then drying at 1210C for 24 hours, then placed in molten sulphur at 1210C for 3 hours. -Procedure B: Drying, vacuum pressure (2mm Hg) for 2 hours, then soaking in molten sulphur at atmospheric pressure for 30 minutes, cooling to room temperature, and weighing.

Fibre Reinforced Concrete

A composite material combining cement/mortar/concrete with discontinuous, discrete, and uniformly dispersed fibres.
Common fibres include steel, polypropylene, nylon, asbestos, coir, glass, and carbon.
Fibres are typically circular or flat, described by aspect ratio (ratio of length to diameter).
Typical aspect ratio ranges from 30 to 150.
Steel fibre is a common type.
Round fibres are generally used.
Steel fibre diameter usually ranges from 0.25 to 0.75 mm. Steel fibres may rust and lose strength.
Polypropylene and nylon fibres commonly increase impact strength, but have low modulus of elasticity.
Asbestos, a mineral fibre, is successful because it mixes with Portland cement and has tensile strength between 560 to 980 N/mm2.
Alkali-resistant glass fibre ("CEMFIL") exists due to issues with alkaline conditions.
Carbon fiber shows high tensile strength (2110 to 2815 N/mm2) and Young's modulus. Cement composites with carbon fiber reinforcement have high modulus of elasticity and flexural strength.

Factors Affecting Fibre Reinforced Concrete

Fibre type
Fibre geometry
Fibre content
Orientation
Fibre distribution
Concrete mixing/compaction techniques
Aggregate size/shape

High Strength Concrete

Compressive strength greater than 40 MPa.
Made by lowering water-cement ratio (w/c) to 0.35 or less.
Low w/c ratio necessitates a superplasticizer for good placement.

Ingredients for High Strength Concrete

Common cement type (almost any ASTM Portland cement).
Aggregates play a vital role. Low water-cement ratio densifies the matrix and interfacial transition zone; the aggregate may become the weak link in mechanical strength development.

Guidelines for Selecting Materials (High Strength Concrete)

Higher targeted compressive strength usually means smaller maximum coarse aggregate size.
Up to 70 MPa, use coarse aggregate with maximum size from 20-28 mm.
For 100 MPa, use aggregate with a maximum size of 10-20 mm.

Special Methods of Making High Strength Concrete

Seeding (adding finely ground, hydrated Portland cement).
Revibration (controlled vibration to remove defects like bleeding, plastic shrinkage, and continuous capillary channels).
High-speed slurry mixing (prepares cement-water mixture and blends with aggregates).
Water reducing admixtures to improve compressive strength.

Inhibition of Cracks (High Strength Concrete)

Inhibiting crack propagation increases strength.
Concrete cubes made this way have strength up to 105 MPa.
Impregnating low strength porous concrete with sulphur can make satisfactory high strength concrete (up to 58 MPa).
Cement fondu (clinker) with slag as aggregate can achieve strength up to 250 MPa at water-cement ratio 0.32.

Fire Resistance (High Strength Concrete)

Axial deformation of HSC columns exhibits better fire resistance compared to NSC columns.

Strength-weight ratio (High Strength Concrete)

Strength-weight ratio of lightweight HSC is comparable with structural steel.

Differences between NSC and HSC

Microcracks form at 40% of strength in NSC, and interconnect at 80-90%
Fracture surface in NSC is rough and along the transition zone.
Fracture surface in HSC is smooth.
There are lower numbers of broken aggregate particles.

Applications (High Strength Concrete)

Column size reduction
Decreased steel amount in columns
Increased floor space in high-rise buildings
Fewer beams in bridges supporting slabs

High Performance Concrete (HPC)

Concrete with special characteristics developed for particular applications and environments.
Characteristics include high workability, high strength, high modulus of elasticity, high density, high dimensional stability, low permeability, and high resistance to chemical attack.
Characteristics associated with HPC include ease of placement, compaction (without segregation), early-age strength, long-term mechanical properties, permeability, durability, heat of hydration, toughness, volume stability, sustained life in severe environments, high resistance to frost and deicer scaling, and toughness and impact resistance.

HPC (Steps to create HPC)

Reduce mixing water significantly
Reduce w/c ratio to get higher strength
Reduce w/c ratio to less than 0.3 increases transition zone properties
Silica fume to improve transition zone qualities
Silica fume is vital for strength beyond 80 MPa
Best fly ash and GGBS yield further improvements

HPC (Aggregates)

Shape and sizes of aggregates are important in HPC.
Crushed aggregates can be used.
Care should be taken to ensure aggregates are mainly cubic, with minimal flaky or elongated particles.
Flaky/elongated particles negatively impact workability.

Vacuum Concrete

Removes excess water to improve concrete strength.
First invented by Billner in the US in 1935.
Reduces the final water-cement ratio before setting to control strength and other concrete properties.
Vacuum concrete overcomes the contradictory requirements of workability and high strength.

Vacuum Concrete Equipment

Vacuum pump with hose pipe
Water separator
Filtering pad
Screed board vibrator
Power floater
Power trowel

Vacuum Concrete Applications

Industrial floor sheds/cold storage
Hydropower plants
Bridges
Ports and harbour
Cooling towers

Vacuum Concrete Advantages

Increased final concrete strength (~25%)
Reduced concrete permeability
Higher concrete density
Increased bond strength (~20%)
Reduced final finishing time
Early wall form removal
Increased durability

Vacuum Concrete Disadvantages

High initial cost
Need for trained labor
Need for specific equipment
Power consumption
Porosity potential for water, oil, and grease seepage, consequently weakening the concrete.

Self-Compacting Concrete (SCC)

Can make concrete structures without vibration (e.g., placing concrete underwater using a tremie).
Mass concrete and shaft concrete are commonly placed without vibration.
Lower strength and challenging to consistently produce quality.
Focuses on high performance, better, more reliable, and uniform quality.

SCC Materials

Cement (43 or 53 grade)
Aggregates (limited to 20 mm, well-graded, cubic or rounded)
Good quality mixing water
Chemical admixtures (superplasticizers – polycarboxylated ethers)
Mineral admixtures (fly ash, GGBS, silica fume, stone powder, fibres)

SCC Requirements

Filling ability
Passing ability
Segregation resistance
Workability of SCC is higher than "very high" in common tests.

SCC Tests

Slump flow (using Abrams cone)
50 cm slump flow
J-ring
V-funnel (at 5 minutes)
L-box
U-box
Fill box
Orimet.

Viscosity Modifying Agent (VMA)

VMAs typically contain polysaccharides as active ingredients.
Starches can also control viscosity.
Diutan gum and welan gum can be part of VMAs.
VMAs are compatible with most superplasticizers.
VMAs must be added after superplasticizers and mixed with cement particles.

Geo Polymer Concrete (GPC)

Alternative binder to Portland cement.
Activates source materials (fly ash, rich in Silicon [Si] and Aluminum [Al]) by alkaline liquids to form the concrete binder.

GPC Environmental Benefits

Reduces CO2 emissions.
An environmentally friendly concrete alternative to ordinary Portland cement (OPC).

GPC Objectives

Produce a carbon dioxide emission-free cementious material.
Develop environmentally friendly construction materials
Study the compressive strength using fly ash and GGBS.
Eliminate the necessity for heat curing of concrete.

GPC Materials

GGBS (as per IS 12089-1987)
Fly ash (as per IS 3812-2003)
Superplasticizer (e.g., C1plast SP430)
Distilled water
Alkaline solutions (e.g., Sodium Hydroxide, Sodium Silicate)
Aggregates

GPC Mixing

Mix cement, fine/coarse aggregates, superplasticizer, and water in a concrete mixer for ~3 minutes.

GPC Curing

Conventional concrete cubes are cured in water for approximately 28 days.
GPC curing often includes hot-air drying and delayed ambient curing.

GPC Advantages

Reduced CO2 emissions
Price of fly ash is low
Better compressive strength properties
Fireproof
Low permeability
Eco-friendly nature
Excellent qualities in acid and salt environments

GPC Applications

Pre-cast concrete products (railroad sleepers, electric poles)
Marine structures
Waste containment

Reactive Powder Concrete (RPC)

Ultra high strength, high ductility, cementitious composite with advanced mechanical and chemical properties.
Leads to achievable maximum compressive strength (120-150 MPa).
Coarse aggregate removal is key to further strength increase.

RPC Composition

Cement (Low C3A content)
Silica fume (absence of aggregates)
Sand (good hardness, readily available)
Quartz powder (crystalline particle size)
Steel fibres (good aspect ratio for improved ductility)
Clean water (no contaminants)
Superplasticizers (e.g. acrylate copolymers, naphthalene sulfonates, or melamine sulfonates)

RPC Objectives

Remove coarse aggregates for homogeneity
Use pozzolanic silica fume
Optimal superplasticizer usage reduces w/c and improves compaction.
Post-setting heat treatment improves microstructure
Fiber addition improves ductility

RPC Properties

Compressive strength (above normal concrete levels, approximately 200 MPa).
Durability factor (linked to compressive strength)
High flexural strength (with steel fibers)

RPC Advantages

Structural potential comparable to steel
Significant dead load reduction
Improvement in seismic performance with lighter members
Lower interconnected porosity diminishes liquid/gas transfer (non-existent penetration)

RPC Limitations

Least costly components are replaced by higher-cost elements
Long-term properties are not yet fully understood or known.

Concrete Made with Industrial Wastes

Construction and demolition wastes
Lathe waste
E-waste
Rubber tyre waste
Coconut shell waste
Egg shell powder
Fly ash
GGBS
RHA
Silica fume
Barchips
Alcofine

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