MODULE 4 Special Concrete (1).ppt

Light Weight Concrete - LWC
• It is a type of concrete which
– includes an expanding agent
– increases volume of mixture
– Gives additional qualities such as nailability and
lessened the dead weight.
• It is lighter than conventional concrete
• Has a dry density of 300 kg/m3-1840 kg/m3;
87 to 23% lighter.

Light Weight Concrete
• LWC is produced by using LWA.
• LWC weigh 300 kg/m3-1840 kg/m3,
depending on type of LWA used or method
of production.
• Lightness depends on inorganic aggregates
which are light in weight.

Light Weight Concrete
• LWC has been used in USA for more than 50
years.
• Its strength is roughly proportional to its
weight.
• Its resistance to weathering is same as that
of ordinary concrete.

Light Weight Concrete - Advantage
• Reduction in dead loads
• Decreased foundation sizes because of
decreased loads
• Savings in transporting & handling precast
units on site.
• Reduction in formwork and supports.

Light Weight Concrete - Advantage
• Savings in structural steel supports –
light weight
• Improved fire resistance.
• Better insulation against heat and
sound.

Light Weight Concrete - Disadvantages
• greater COST (30-50%)
• Need for more care in placing
• Greater POROSITY
• More drying shrinkage

Light Weight Concrete - Use
• Construction of under-beds for floors and
roof slabs, where huge savings are made by
decreasing dead load.
• Insulated sections of floors and walls

High Density Concrete
• HD or HW concrete: density >
2600kg/m3 or range between 30KN/m3-
64KN/m3.
• HDC is made from natural heavyweight
aggregates such as magnetite which
give densities of 3900kg/m3.

• Made using iron or lead as a
replacement for a portion of the
aggregate.
• These give even greater densities of
– 5900kg/m3 for iron or
– 8900kg/m3 for lead.

• It is designed in same way as NWC, but
additional self weight is taken into account.
• Transported and Placed in the same way as
NWC, but additional density means that
smaller volumes can be transported &
placed.
• Unit weight of HDC is > 25% higher than that
of NWC (24KN/m3).

• Construction of
– Nuclear radiation shield walls: selection of
concrete for radiation shielding is based on space
requirements, & on type & intensity of radiation.
– Ballast blocks
– Counterweights
– Sea walls

• Except for density, physical properties of HDC are
SIMILAR to Normal weight concrete.
• Desirable Properties of HDC: high modulus of rigidity,
low thermal expansion, low elastic & creep deformations
• HDC containing higher cement show HIGH creep &
shrinkage.
• HDC having - Cement-CA ratio as 1:5 – 1:9; w/c ratio as
0.5 to 0.65 produce dense & crack-free concrete.

• Care must be taken to avoid overloading the
mixer especially
• Batch size should be reduced to 50% of
mixer capacity.
• Formwork: stronger to withstand higher load.

• To prevent segregation of heavier aggregates
from the rest of the aggregates, better
workability help in reducing the segregation.
• Pre-placed aggregate method of concreting is
used for placing HDC in confined areas to
minimize segregation of scrap steel.

Vacuum Concrete
• Excessive w/c ratio is detrimental for concrete.
• Restrict w/c ratio in order to achieve higher strength.
• Chemical reaction of cement with water requires a w/c
ratio of < 0.38, whereas the adopted w/c ratio is
generally much more than that mainly because of the
requirement of workability.
• Workability is also important for concrete, so that it can
be placed in the formwork easily without honeycombing.

Vacuum Concrete
• After the requirement of workability is over, this
excess water will eventually evaporate leaving
capillary pores in the concrete.
• These pores result into high permeability & less
strength in concrete.
• Therefore, workability and high strength don’t go
together as their requirements are contradictory to
each other.

Vacuum Concrete
• Vacuum concreting is the effective technique
used to overcome this contradiction of
opposite requirements of workability & high
strength.
• With this technique both these are possible
at the same time.

Vacuum Concrete
• In this technique, excess water after placement and
compaction of concrete is sucked out with the help of
vacuum pumps.
• This technique is effectively used in industrial floors, parking
lots and deck slabs of bridges etc.
• Magnitude of applied vacuum is 0.08 MPa & water content
is reduced by 20-25%.
• Reduction is effective up to a depth of 100-150mm only.

Advantages of vacuum concreting
• Due to dewatering through vacuum, both
workability and high strength are achieved
simultaneously.
• Reduction in w/c ratio increase the compressive
strength by 10-50% & lowers the permeability.
• It enhances the wear resistance of concrete
surface.

Advantages of vacuum concreting
• Surface obtained after vacuum dewatering is
plain and smooth due to reduced shrinkage.
• Formwork can be removed early and surface
can be put to use early.

Shotcrete
• Shotcrete is concrete (or mortar) conveyed through a hose
and pneumatically projected at high velocity onto a surface,
as a construction technique.
• Shotcrete is usually an all-inclusive term that can be used
for both wet-mix & dry-mix versions.
• The term "shotcrete" refers to wet-mix and "gunite" refers to
dry-mix.
• Shotcrete undergoes placement and compaction at the
same time due to the force with which it is projected from
the nozzle.

Shotcrete
• It can be impacted onto any type or shape of surface,
including vertical or overhead areas.
• Shortcreting has proved to be the best method for
construction of curved surfaces.
• Domes are now much easier to construct with the advent
of shotcrete technology.
• Tunnel linings are also becoming easy with this technology.

Shotcrete
• Usually patented polypropylene fibers are included
in the shotcrete which increases the cohesive nature
of shotcrete through mechanically binding the
Cementitious materials together.
• This mechanism reduces the rebound waste that
occurs through the shotcreting process and these
fibers also resist plastic shrinkage and cracking
through their ability to enhance the early stage
tensile strength of concrete.

Shotcrete
• Shotcrete also gives better surface finishes and
reduces surface tearing on non-linear sections.
• Cementitious material containing the polypropylene
fibers resist cycles of freezing and thawing and also
reduces the chances of water and chemical
penetrations.

SHOTCRETE VERSUS CONVENTIONAL CONCRETE
• Unlike conventional concrete, which is first placed
and then compacted in the second operation,
shotcrete undergoes placement & compacted at the
same time due to force with which it is projected
from the nozzle.
• Shotcrete is MORE dense, homogeneous, strong,
and waterproof.

SHOTCRETE VERSUS CONVENTIONAL CONCRETE
• Shotcrete needs less repair & suffers little
deteriorations.
• Shotcrete is not placed or contained by forms.
• It can be impacted onto any type or shape of
surface, including vertical or overhead areas.
• It forms an excellent bond and can be given a
variety of surface finishes.

Functions of Shotcrete
• Seal Surface, curved or folded sections, canal, reservoir & tunnel lining
• Preserve Ground Strength
• Support of Individual Blocks
• Form a Structural Arch
• Bridges / Dams
• Sewer
– Sanitary
– Storm (Culverts / Basins)
– Headwalls / Wing Walls
• Piers / Docks
• Ditches
• Retaining Walls – Waterproofing
• Slope Stabilization

Types of Shotcrete
• Dry Mix Process
• Wet Mix Process

Dry Mix Process
• Mixture of cement & damp sand is conveyed
through a delivery hose pipe to a mechanical
feeder or gun.
• Mixture is carried by compressed air through the
delivery hose to a special nozzle.
• Nozzle is fitted with a perforated through which
water is introduced under pressure & intimately
mixed with other ingredients.

Dry Mix Process
• Mortar is jetted from the nozzle at high velocity on
to the surface to be shotcreted.
• Amount of water should be so adjusted that
wastage of material by rebounding is minimum.
• w/c ratio: 0.33-0.5. Lower w/c ratio leads to – higher
strength, less creep & drying shrinkage & higher
durability.
• Preferred for LWC.

Wet Mix Process
• In this process, all ingredients (cement, sand, small-
sized CA & water) are mixed before entering the
chamber of delivery equipment.
• RMC is conveyed by compressed air at a pressure to a
nozzle.
• Additional air is injected at the nozzle to increase the
velocity & improve the gunning pattern.
• w/c ratio is very accurately controlled.
• Does not cause dust problem

Wet Mix Process
• Rebounding of jetted concrete depends on
– w/c ratio: decreases with higher w/c ratio
– Nature & position of surface treated: higher rebounding for vertical &
overhead surfaces
• Hz Slab: 5-15% rebound; Sloping & VR Surface: 15-30%
rebound; Overhead surface: 20-50%
• Higher durability is achieved by using air-entraining agents.
• Larger capacity available in wet mix results in higher rates of
placing of concrete.

Advantage of Shotcrete
• Formwork is used only on 1 side of the work
• Suitable for thin section & for sites where
accessibility is difficult
• Bonds perfectly well with the existing old
concrete masonry, exposed rocks, etc.
• Very effective in repair of structures.

Disadvantage of Shotcrete
• Dusting problem from sand & cement (dry
mix)
• High cost
• Wastage due to rebound

Fibre Reinforced Concrete
• Presence of micro-cracks at mortar-aggregate interface is
responsible for the inherent weakness of plain concrete.
• This weakness can be removed by inclusion of fibres in the
mix which transfer loads at the internal micro-cracks.

Discreet Fibre Reinforced Concrete
• In this system, concrete is reinforced by random
dispersal of short, discontinuous & discreet fine
fibres of specific geometry.
• Fibres interlock & entangle around aggregate
particles which leads to
– Reduced workability
– More cohesive mix
– Mix less prone to segregation
– Restrain shrinkage

• Fibres are produced from – Steel, Glass &
Organic polymers.
• Naturally occurring asbestos fibres &
vegetable fibres (jute) are also used for
reinforcement.

• Fibres are classified into 2 categories:
– Hard Intrusion: have higher elastic modulus;
Steel, Carbon & Glass; it improves Flexural &
Impact resistances.
– Soft Intrusion: have lower elastic modulus;
Polypropylene & Vegetable Fibres; it improves
Impact resistance of concrete but do not
contribute much to flexural strength.

Fibre Reinforced Concrete
• Major factors affecting characteristics of FRC
– w/c ratio
– % of fibres
– Diameter & Length of fibres
• Location & extent of cracking depends on
– Orientation of fibres
– Number of fibres

Fibre Reinforced Concrete - Disadvantage
• Reinforcement bars in RCC are continuous &
carefully placed in the structure to have optimize
performance;
• Fibres are discontinuous & randomly distributed
throughout the concrete which leads to its inferior
performance.
• Fibres are more expensive than reinforcement
bars.

Fibre Reinforced Concrete - Advantage
• Fibre act as Crack arrestor restricting the
development of cracks & thus transforming a
brittle matrix (portland cement with its low
tensile & impact resistances) into a strong
composite with
– superior crack resistance
– Improved ductility
– Distinctive post-cracking behaviour before failure

Preplaced or Slurry Infiltrated Fibre Concrete
(SIFCON)

(SIFCON)
• For achieving high fibre volume, dry fibres are pre-
placed in the formwork & cement slurry is made to
infiltrate the bed of fibres. This composite is called
SIFCON.
• Another form SIFCON has recently been developed
is known as SIMCON (Slurry Infiltrated MAT
Concrete).

(SIFCON)
• SIMCON is a new generation of high performance
fibre reinforced concrete (HPFRC), made by
infiltrating sheet of stainless steel fibres with a
specially designed cement-based slurry.
• Fibre mats are shaped & wrapped around existing
columns & beams; & injected with concrete slurry to
strengthen them.

Advantage of SIMCON
• Add tensile strength & ductility to concrete
• Smaller fibre volume fraction is required to achieve
substantial increase in mechanical properties
• At failure, mass of fibres & concrete crumbles into small
harmless flakes which pose little danger
• Steel fibre mats provides inherent strength & utilize fibres
with much higher aspect ratio (length/dia)
• SIMCON is easier to handle & construct than with SIFCON
• It exhibit better mechanical properties with lower fibre
volume fraction.

Steel-fibre Reinforced Concrete
• Round steel fibres: cutting round wires into short
lengths (dia 0.25-0.75mm); 0.3-0.5 mm - India.
• Rectangular steel fibres are produced by cutting the
sheets about 0.25mm thick.
• For improving the bond between fibre & matrix,
fibres are – Indented, Crimped, Machined & Hook-
ended.
• Aspect ratio (length/dia) of fibres: 30-250.

Properties of Steel-fibre Reinforced Concrete
• Slump test & Compacting Factor is a poor
indicator of workability for steel-fibre concretes.
• This is because internal structure & flow
characteristics are different due to presence of
fibre; which form a stable system due to
interlocking of fibres thus resisting the flow of
fresh concrete.

Properties of Steel-fibre Reinforced Concrete
• Vee-bee test which incorporates the effects of
vibration give a realistic assessment of workability of
fibre concretes.
• Workability decreases with an increase in fibre
concentration & aspect ratio.
• There is a critical fibre content for each aspect ratio
beyond which response to vibration decreases
rapidly.

Application of Steel-fibre Reinforced Concrete
• Highway & Airfield Pavements: higher flexural
strength results in reduction in thickness; resistance
to impact & repeated loading is increased; smooth
riding surface without irregular depressions.
• Hydraulic Structures: resistance to cavitations &
erosion damage by high velocity flow
• Fibre Shotcrete: used in rock slope stabilization,
tunnel lining & bridge repair

Application of Steel-fibre Reinforced Concrete
• Refractory Concrete: more durable when exposed
to high thermal stress, thermal cycling, thermal
shock.
• Precast Applications: include manhole covers,
concrete pipes, machine bases & frames.
• Structural Applications: increased impact resistance,
inhibit crack growth & crack widening, more ductile
& shear strength.

Polypropylene Fibre-Reinforced Concrete
• Polypropylene fibres are used in small volume
fractions between 0.5-1% in concrete to improve
impact strength of hardened concrete.
• Low modulus of elasticity.
• These fibres being hydrophobic can be easily mixed
as they do not need lengthy contact during mixing &
only need to evenly dispersed in the mix.

Polypropylene Fibre-Reinforced Concrete
• Hence these are added shortly before the end of
mixing normal constituents.
• Inclusion of these fibres reduces workability.
• Highly air-entrained concretes can be stabilized by
fibres.
• They deteriorate under attack from ultraviolet
radiation.

POLYMER CONCRETE COMPOSITE
• PCC are obtained by combined processing of polymeric
materials with some or all ingredients of cement concrete
composite.
• Depending upon the process by which the polymeric
materials are incorporated, polymer concrete are classified
as:
– Polymer-impregnated Concrete (PIC)
– Resin or Polymer concrete
– Polymer Modified Concrete

Polymer-impregnated Concrete (PIC)
• In PIC, low viscosity liquid monomers or pre-
polymers are partially or completely impregnated
into the pore systems of hardened cement
composite & are then polymerised.
• It improves the durability & chemical resistance.
• Modest improvement in structural properties.

Polymer-impregnated Concrete (PIC)
• Total or in-depth impregnation improves
structural properties considerably.
• It is used as surface impregnation of bridge
decks to make them impervious to intrusion
of moisture, chemicals & chloride ions.
• It is used repairing cavitations & erosion in
dams.

Resin or Polymer concrete
• It is composite wherein the polymer replaces the
cement-water matrix in cement concrete.
• It is manufactured in a manner similar to cement
concrete.
• Monomers or pre-polymers are added to the graded
aggregates & mixture is thoroughly mixed by hand
or machine; which is then cast in moulds of wood,
steel or aluminium to the required shape or form.

Resin or Polymer concrete
• Mould releasing agents can be added for easy
demoulding.
• This is then polymerized either at room temperature
or at an elevated temperature.
• The polymer phase binds the aggregate to give
strong composite.
• PC pipes are used for transporting a variety of
chemicals, for carrying effluents & wastewater, etc.

Polymer Modified Concrete
• It is a composite obtained by incorporating a
polymeric material into concrete during mixing
stage.
• But this polymer should not interfere with the
hydration process.
• The composite is then cast into required shape &
cured in conventional manner.

Polymer Modified Concrete
• Hydrated cement & polymer film formed due
to curing of polymeric material constitute an
inter-penetrating matrix that binds the
aggregate.
• PMC is also called as Polymer Cement
Concrete (PCC)

Ferrocement
• In ancient India, construction was done using mud walls with
woven bamboo mats.
• In present form, in a thin reinforced concrete construction,
cement mortar matrix is reinforced with many layers of
continuous & small diameter wire meshes over the entire
surface.
• In Ferrocement, mortar provides the mass & wire mesh
imparts tensile strength & ductility to the material.
• Ferrocement provide very high tensile strength-weight ratio &
superior cracking performance.

Ferrocement
• FC improves following properties
–High resistance against cracking
–Toughness
–Fatigue resistance
–Impermeability

Advantages of Ferro-Cement
• FC structures are thin & light.
• A 30% reduction in self-weight of structure,
15% reduction in steel consumption & 10% in
roof cost can be achieved.
• FC is suitable for manufacturing precast units
which can be easily transported.

Advantages of Ferro-Cement
• Construction technique is simple & hence does not
require highly skilled labour.
• Partial or complete elimination of formwork is
possible.
• FC construction can be easily repaired in case of
local damage due to abnormal loads.

Properties of Ferro-cement
• Its strength per unit mass is high
• It has the capacity to resist shock load.
• It can be given attractive finish like that of teak and
rose wood.
• FC elements can be constructed without using
formwork.
• It is impervious.

Uses of Ferro-cement
• It can be used for making:
– Partition walls
– Window frames, chajjas and drops
– Shelf of cupboards
– Door and window shutters
– Domestic water tanks
– Precast roof elements
– Reapers and rafters required for supporting roof tiles.
– Pipes
– Silos
– Furnitures
– Manhole covers
– Boats.

Applications of Ferrocement
• FC behaves as Steel Plates due to very high % of well
distributed & continuously running steel reinforcement.
• FC can be easily moulded to any desired shape, lightness,
firmness & toughness of steel plates.
• Due to very high tensile strength-weight ratio & superior
cracking behaviour, FC is an attractive material for light &
water-tight structure & other portable structures such as
mobile homes.

Ferrocement In Building Industry
• FC planks, panels can be used for construction of
beams, columns, floor, roofs, walls, chajjas and lintels.
• It can be used in combination with PCC or RCC.
• FC being a thin material single piece panel of size up to
4.5m x 4.5m or more can be manufactured as floors &
walls. Large span beams, roofs can also be
constructed.
• FC being crack resistant and anti-corrosive material
lasts much more than R.C.C.

• Dead load of FC building is reduced by at least 50%.
Consequently the foundation cost gets reduced.
• FC membrane lining is used for water proofing of terraces,
basements, tanks.
• FC water proofing is the only treatment where reinforcement
is used in the form of wire mesh layers .
• Therefore FC water proofing treatment should generally last
longer than conventional.

• FC is a good material for elevation treatment. Since it is
constructed in thin sections, it contributes negligible dead
weight, and at the same time it is crack resistant, water proof
and strong.
• FC is a very good fire resistant material having capacity to
resist fire up to 750°C for long period of 48 hours & even
more. FC can be modified to resist even high temperatures,
1200°C to 1500°C.
• FC building are better pollution and fire resistant as
compared to RCC. Therefore, FC building are preferable to
RCC for functional VIP and strategic buildings.

High Performance Concrete
• Definition by American Concrete Institute (ACI)
• HPC was defined as ‘concrete, which meets special
performance & uniformity requirements that cannot
be achieved routinely by using only conventional
materials & normal mixing, placing & curing
practices.’

• REQUIREMENTS may involve
– enhancement of placement & compaction without
segregation
– long-term mechanical properties
– Early age strength
– volume stability or increased service-life in
severe environments.

• A HPC element is that which is designed to
– give optimized performance characteristics for a
given set of load, usage and exposure conditions,
consistent with requirement of cost, service life
and durability.

• HPC has
– Very low porosity through a tight & refined pore structure
of cement paste.
– Very low permeability of the concrete
– High resistance to chemical attack.
– Low heat of hydration
– High early strength and continued strength development
– High workability and control of slump
– Low w/c ratio, Low bleeding and plastic shrinkage

Salient Features of HPC
• Compressive strength > 80 Mpa, even upto 800 Mpa
• w/c ratio: 0.25-0.35 ,therefore very little free water
• Reduced flocculation of cement grains
• Wide range of grain sizes
• Densified cement paste
• No bleeding - homogeneous mix
• Less capillary - porosity
• Discontinuous pores
• Stronger transition zone at interface between cement paste
& aggregate
• Low free lime content

Salient Features of HPC
• Powerful confinement of aggregates
• Little micro-cracking until about 65-70% of fck
• Smooth fracture surface
• High degree of impermeability to prevent ingress of
water/moisture/CO2 /SO4 /air /oxygen /chloride
• High resistance to sulphate attack, abrasion, erosion, &
cavitation
• Absence of micro-cracking, High level of corrosion
resistance, High electrical & chemical resistivity

Advantages of Using HPC
• Reduction in member size, resulting in
increase in plinth area/useable area & direct
savings in the concrete volume.
• Reduction in the self-weight and super-
imposed DL with the accompanying saving
due to smaller foundations.

• Reduction in form-work area and cost with
the accompanying reduction in shoring &
stripping time due to high early-age gain in
strength.
• Construction of High–rise buildings with the
accompanying savings in real-estate costs in
congested areas.

• Longer spans & fewer beams for same magnitude
of loading.
• Reduction in the number of supports and the
supporting foundations due to the increase in
spans.
• Reduction in thickness of floor slabs and supporting
beam sections-which are a major component of the
weight and cost of the majority of structures.

• Superior long-term service performance under static,
dynamic and fatigue loading.
• Low creep and shrinkage.
• Greater stiffness as a result of a higher modulus, Ec
• Higher resistance to freezing & thawing; chemical attack
• Improved long-term durability & crack propagation.
• Reduced maintenance & repairs.
• Smaller depreciation as a fixed cost.

Application of High Performance Concrete
• Major applications of HPC have been in
the areas of
–Pavements
–Long-span bridges
–High-rise buildings.

• Pavements
– early strength gain of HPC
– its reduced permeability
– increased wear or abrasion resistance
– improved freeze-thaw durability.

• While the conventional normal strength concrete
continue to be used in most cases of pavement
construction, different types of HPC are being
considered for pavement repairs for early opening
to traffic, bridge deck overlays, & special
applications in rehabilitation of structures & other
developments.

• Bridges
– Use of HPC would result in smaller loss pre-
stress & consequently larger permissible stress
and smaller cross-section being achieved, i.e. it
would enable the standard pre-stressed concrete
girders to span longer distances or to carry
heavier loads.

• Bridges
– Enhanced durability allow extended service life of the
structure.
– Precast girders: due to reduced weight transportation &
handling will be economical.
– Concrete structures are preferable for railway bridges to
eliminate noise & vibration problems and minimize the
maintenance cost.

• High-rise Buildings
– The reasons for using the high strength concrete
in high-rise buildings are to REDUCE
• Dead load,
• Deflection
• Vibration & noise
• Maintenance cost.

Ingredients of HPC
• Cement
– Physical & chemical characteristics of cement
play a vital role in developing strength &
controlling rheology of fresh concrete.
– Fineness affects water requirements for
consistency.

Ingredients of HPC
• Cement
– When looking for cement to be used in HPC, one
should choose cement containing as little C3A as
possible because lower amount of C3A, the easier
to control the rheology & lesser the problems of
cement-super plasticizer compatibility.
– Finally from strength point of view, cement should
be finely ground & contain a fair amount of C3S.

Ingredients of HPC
• Fine aggregate
– Both river sand & crushed stones may be used.
– Coarser sand may be preferred as finer sand
increases water demand of concrete
– Sand particles should also pack to give MIN void
ratio as test results show that higher void content
leads to requirement of more mixing water.

Ingredients of HPC
• Coarse aggregate
– By usage of mineral admixtures, the cement
concrete becomes more homogeneous and there
is marked enhancement in strength properties as
well as durability characteristics of concrete.
– Strength of HPC is controlled by strength of CA.

Ingredients of HPC
• Water
– It is an important ingredient of concrete as it actively
participates in the chemical reactions with cement.
– The strength of cement concrete comes mainly from the
binding action of the hydrated cement gel.
– The requirement of water should be reduced to that required
for chemical reaction of unhydrated cement as the excess
water would end up in only formation of undesirable voids in
the hardened cement paste in concrete.
– From HPC mix design considerations, it is important to have
the compatibility between the given cement & chemical/
mineral admixtures along with the water used for mixing.

Ingredients of HPC
• Chemical Admixtures
– These are essential ingredients in the concrete mix, as
they increase efficiency of cement paste by improving
workability of mix & there by resulting in considerable
decrease of water requirement.
– Different types of chemical admixtures are
• Plasticizers
• Super plasticizers
• Retarders
• Air entraining agents

Ingredients of HPC
• Chemical Admixtures
– Placticizers & super-placticizers help to disperse cement
particles in the mix & promote mobility of concrete mix.
– Retarders help in reduction of initial rate of hydration of
cement, so that fresh concrete retains its workability for a
longer time.
– Air entraining agents artificially introduce air bubbles that
increase workability of the mix & enhance resistance to
deterioration due to freezing & thawing actions.

Ingredients of HPC
• Mineral admixtures
– The major difference between CCC & HPC is the
use of mineral admixtures in HPC.
– Some of the mineral admixtures are
• Fly ash
• Silica fumes
• Carbon black powder
• Anhydrous gypsum based mineral additives

Ingredients of HPC
• Mineral admixtures
– MA like fly ash & silica fume act as puzzolonic materials &
fine fillers, thereby the microstructure of hardened cement
matrix becomes denser & stronger.
– Use of silica fume fills the space between cement
particles & between aggregate & cement particles.
– Note: addition of silica fume to the concrete mix does not
impart any strength to it, but acts as a rapid catalyst to
gain the early age strength.

Self Compacting Concrete
• Concrete that is able to
– flow & consolidate under its own weight,
– completely fill the formwork of any shape, even in
presence of dense reinforcement, while
– maintaining homogeneity &
– without the need for any additional compaction.

• Origin
– Introduced to the concrete industry, in Japan,
primarily, through the work of Prof. Okamura in
the late 1980’s.
– Motivation behind this was gradual reduction of
skilled labor, which led to reduction in quality of
construction work, affecting adversely, the
durability of concrete due to poor compaction.

• SCC has more powder content & less CA.
• Fillers used can be – flyash, ground GBFS,
condensed silica fume, rice husk ash, lime powder,
chalk powder & quarry dust
• SCC incorporates
– high range water reducers (HRWR, Super plasticizers) &
– viscosity modifying agent in small amount.

Potential Benefits of SCC
• Contractor
– Reduced labor requirement & cost
– Reduced plant requirement
– Reduced remedial work
– Reduced noise, improved site health & safety
– No vibrating equipment required, Reduces
placing costs

Potential Benefits of SCC
• Designer / client
– Used in more complex design & heavy
reinforcement
– Improved aesthetics & durability
– Quicker construction time
– Less variation in the production of concrete &
more homogeneous concrete
– Better surface finish

SCC Potentials beyond conventional concrete
• Improved efficiency
• Use with close meshed reinforcement
• For complex geometric shapes
• For slender components
• Generally where compaction is difficult
• Fast installation rates
• Noise reduction
• Reduced damage to health

Fresh SCC Properties
• Filling ability: “The ability of SCC to flow into
& fill completely all spaces within the
formwork, under its own weight.”

• Passing ability: “The ability of SCC to flow
through tight openings such as spaces
between steel reinforcing bars without
segregation or blocking.”

• Segregation resistance: “The ability of SCC to
remain homogeneous in composition during
transport and placing.”

Test Methods for Determining Fresh SCC Properties
• FILLING ABILITY
– Slump flow & T50CM slump flow
– V- Funnel
• PASSING ABILITY
– L-Box
– U-box
– J-ring
– Fill Box
• SEGREGATION RESISTANCE
– V-Funnel at T5 Minutes
– GTM Screen stability test

• Slump flow (spread)
– Secondary measurement of T50 cm can be made
– Represents time taken in seconds to reach
horizontal diameter of 50 cm.
– Recommended limits are 2-5 sec

• V-Funnel Test
– To assess the FLOWABILITY of fresh concrete
– Time taken for concrete to flow through the narrow end is
measured
– Measures VISCOSITY of concrete
– Recommended value for V-funnel flow < 12sec

• L-Box Test
– PASSING ABILITY of fresh concrete.
– T20 cm & T40 cm marks of horizontal section of L – box
are the indications of ease of flow of concrete.
– Recommended values of flow time are: T20 cm = 1 ± 0.5
sec & T40 cm = 2 ± 0.5 sec
– Height of the concrete at the end of horizontal section is
expressed as a % of that of remaining in the vertical
section (H2/H1).

• L-Box Test
– Recommended value for blocking ratio: H2/H1 ≥ 0.80.

• U-Box Test (Box-shaped)
– Measures the FILLING ABILITY of concrete.
– Difference in height of two sections is measured.
– Recommended value: difference in height of the limbs <
30 mm

• J-Ring Test
– Measures PASSING ABILITY of concrete, Simple test
– Can be used in conjunction with Slump flow test,
combination can test filling ability & passing ability
– Difference in height, in between the concrete inside & that
just outside the J-ring is measured

• J-Ring Test
– Difference in height of MAX of 10 mm is considered
appropriate
– Bars can be of different diameters and also varied
spacing: Preferably three times the MAX aggregate size
– Used in conjunction with slump flow test

• V5min flow time
– This is secondary parameter of the V-funnel test
– Measures time of flow of concrete after time gap of 5min
– Indicates the tendency for segregation
– Recommended value is: < +3 sec of time at zero hours

• Acceptance of SCC
– Combinations may be:
• Slump flow, V-funnel and U-box tests (Japan)
• Slump flow and L-Box (Sweden)
• J-ring and U-box
• Slump flow, U-Box/L-Box, V-funnel (at 5min.)

Types of Crack/Failure
• Structural causes of distress of concrete
– Externally applied & environmental loads
exceeding the design stipulations
– Accidents & Subsidence
– Poor construction practices
– Error in design & detailing

• Structural causes of distress of concrete
–Construction Overloads
–Drying Shrinkage
–Thermal stress
–Weathering
–Chemical reactions
–Corrosion of Reinforcement

• Plastic concrete suffer damage due to
– Plastic Shrinkage
– Settlement Cracking
• Honeycombing, bolt-holes can be avoided by
providing a watertight & rigid framework.
• Blowholes develop during concreting operations
due to improper design of formwork

• Blowholes are formed on the surface of concrete
by trapped air & water bubbles against the face
of formwork.
• These can be REDUCED if the form face is
slightly absorbent & adequate compaction is
provided.
• Large blowholes must be filled with 1:1 or 1:2
cement-sand mortar.

• Honeycombing consists of groups of interconnected
deep voids due to inadequate compaction or loss of
grout through joints in formwork or between
formwork & previously cast-concrete.
• Unsound material is chipped out to solid concrete
• After surface has been prepared, a bonding coat
should be applied to all exposed surfaces, & new
concrete is placed against the prepared surface.

• Cracks in horizontal surface as concrete stiffens
due to plastic shrinkage (rapid drying of surface)
• Cracks formed above ties, reinforcement, etc., due
to plastic settlement or concrete continues to settle
after starting to stiffen
• Cracks in thick sections, as concrete cools due to
restrained thermal contraction.

• Voids in concrete due to honeycombing or
inadequate compaction.
• Colour variation due to variations in mix
proportions, curing conditions, materials,
characteristics of form face, vibration.
Leakage of water from formwork.

• Powdery formed surface due to surface retardation, caused
by sugars in certain timbers.
• Rust-strains due to pyrites in aggregates ; rubbish in
formwork.
• Plucked surface due to insufficient release agent; careless
removal of formwork.
• Lack of cover of reinforcement due to movement of
reinforcement during placing of concrete; badly fixed
reinforcement.

Diagnosis of Distress in Concrete
• Following information helps in diagnosing the
cracks:
– Whether the crack is new or old
– Type of crack: active or dormant
– Whether it appears on opposite face of member
also
– Pattern of cracks

Diagnosis of Distress in Concrete
• Following information helps in diagnosing the
cracks:
– Soil condition, type of foundation used, sign of movement
of ground
– Observations on similar structures in same locality
– Study of specifications, method of construction used &
test results at site
– Views of the designer, builder, occupants of the buildings
– Weather during which the structure has been constructed

Crack Control or Repair
• It involves 3 processes:
– Preparation of surface
– Selection of Materials
– Application of materials

• Preparation of surface
– Cracked & deteriorated areas are cut or chipped
out of the solid concrete.
– All the loose material should be cleaned &
surface is washed off before actual patching is
started.

• Preparation of surface
– Care should be taken to remove excess water
from the cavity.
– To obtain a good bond, the surface of concrete
should be coated with a thin layer of cement
grout before placing the patching material.

• Selection of Materials
– Mechanical properties of repair material should be
similar to those of structure to be repaired
– For conventional repairs, cement-based material
– mortar or concrete are used depending on the
extent of repair.

• Application of materials
– Methods used for filling the material are
• Drypacking
• Concrete replacement
• Mortar replacement
• Grouting
• Large volume prepacking of concrete
• Shotcrete or guniting

Repair by Jacketing
• Process of fastening a durable material over the
existing concrete & filling the gap with a grout that
improves the performance by strengthening.
• Jacketing restores or increases the section of an
existing member by encasement in a new concrete.
• It is applicable for protecting the member against
further deterioration.

Repair by Jacketing
• This method is useful the compression
members like columns & piles.

Repair by Jacketing
• REINFORCED CONCRETE JACKET
– Size of jacket & number & diameter of steel bars used in
jacketing process depend on the structural analysis that
was made to the column.
– In some cases, before this technique is carried out, we
need to reduce or even eliminate temporarily the loads
applied to the column; this is done by the following steps:
• Putting mechanical jacks between floors.
• Putting additional props between floors.

MODULE 4 Special Concrete (1).ppt

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