BLENDED CEMENT

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BLENDED CEMENT IN Quality construction
UDAI KAFLAY PENDEN CEMENT AUTHORITY LTD.
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QUALITY OF CONCRETE
FRESH CONCRETE Workability HARDENED
CONCRETE Mechanical Strength Durability
The only parameter that can be measured with
reasonable ease and speed is the Compressive
Strength or the Mechanical Strength. Thus,
Concrete is commercially classified according to
its Compressive Strength, like M-5, M-10, M-15,
M-20, etc.
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QULAITY CONTROL OF RAW MATERIALS IN CONCRETE
PRODUCTION
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1.0 CEMENTS
PENDEN ORDINARY 1981 (33 Grade
OPC) Portland Pozzolana Cement 1985 (Calcined
Clay based) (For CHPC) PENDEN SUPREME
1996 (43 Grade OPC) PENDEN SPECIAL
1999 (For THPA) (Portland Slag
Cement) PENDEN PREMIUM (Flyash Based)
2005 (Portland Pozzolana Cement)
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PHYSICAL PROPERTIES COMPARISION
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COMPARISION OF PENDEN CEMENT PRODUCTS WITH INDIAN
STANDARDS REQUIRMENTS
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2.0 AGGREGATES Since aggregates occupy
three-quarters of the volume of Concrete, the
properties of aggregates have a major influence
on the properties of concrete.
2.1 Properties of Aggregates Sieve Analysis,
Specific Gravity, Moisture Content, Moisture
Absorption, Dry-rodded unit weights. Chemical
Reactivity, Soundness, Resistance to Abrasions
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2.2 Aggregates Quality 2.2.1 Sizes 2.2.2 Particl
e Shape 2.2.4 Texture 2.2.5 Strength
Abrasions 2.2.6 Resistance to Freezing and
Thawing (critically saturated) (porosity,
adsorption and pore structure insufficient
unfilled)) 2.2.7 Moisture Content, Absorption
Wetting Drying 2.2.8 Impurities
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Aggregates . . . Moisture Content
Absorption Lightweight Aggregate can absorb 5
29 by weight of dry Aggregate. Normalweight
Aggregate absorbs LESS than 2 Impurities Clay
swells and shrinks on wetting drying. (3
in fines, 3-10 in coarse aggregates) Excessive
quantities of silt and fine dust increase water
requirement. ORGANIC SUBSTANCE can inhibit the
hydration process thereby delaying setting time
and reducing strength. CHLORIDES, SULPHATES and
REACTIVE SILICA should be minimum.
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3.0 MIXING WATER
Water that is fit to drink is generally regarded
as acceptable for use in mixing concrete.
Water containing one thousand ppm of normally
found minerals acids can be tolerated. BUT even
small amount of various sugars and sugar
derivatives should not be used.
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4.0 ADMIXTURES Chemical Admixtures for Concrete
are used for improving various properties of
Concrete by effect of its surface
activity. 3.1 Accelerating 3.2 Retarding 3.3 W
ater Reducing, 3.4 Air-entertaining. Dosages Sol
id / Powder Maximum - 50 g/kg. of
cement Minimum - 2 g/kg. of
cement Liquid - 3 litres / m3 of
Concrete Smaller quantities are allowed only if
they are dispersed in part of the mixing
water.
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QUALITY CONTROL DURING PRODUCTION PLACEMENT AND
POST PRODUCTION OF CONCRETE
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WORKABILITY CONCRETE can be placed in the
formwork and compacted with minimum effort,
without Segregation Bleeding
CHARACTERESTICS STABILITY Should be stable
and not segregate during transportation and
placing. MOBILITY Cohesive and mobile
for placing in the PLACEABILITY form, around the
reinforcement and should be able to cast into
required shape. COMPACTABILITY Amenable to
proper and thorough Compaction. FINISHIBILITY
Possible to obtain satisfactory finish.
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Factors Affecting Workability Concerning
Mix Not Concerning Mix Water Cement
Ratio Mixing Condition Type of
Cement Temperature C3A content Time
(Workability Loss) Fineness Gypsum
content Alkali content Type of
Aggregates Maximum Size Grading Fine Particle
Content Cement Aggregate Ratio Mineral
Additions Admixtures Water Reducing Agents Air
Entrained Agents
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FACTORS EFFECTING WORKABILITY Concerning Mix For
Better Workability Minimise Particle
Interference Total Specific Area
Voids Content Aggregate Size (Larger
Better) Aggregate Shape Aggregate
Texture Fine Coarse Aggregate Mix Use of
Fine sand increases Water Demand, or For Same
Water Content, Workability Decreases. Water
Cement Ratio Cement paste around
aggregates Fill the voids Workability
increases with Water Content.
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FACTORS EFFECTING WORKABILITY Not Concerning Mix
TIME Fresh Concrete looses Workability with
Time mainly because of Loss of Moisture
Absorption by aggregates, Evaporation
Losses Consumption in Chemical Reaction
(Reduce from 12 mm to 5 mm in an
hour) TEMPERATURE Increase in Temperature,
Decreases Workability
The Choice of Workability depends upon Type of
Compacting Equipment Size of the
Section Concentration of Reinforcement
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SEGREGATION It is the ability of the concrete
mix to separate various constituents owing to the
size and specific weight difference of the
particles. Internal Segregation - Within
framework or mold External Segregation During
transportation or improper handling. Remedial
Measure Avoid the followings Maximum
aggregate size above 25 mm, Increase of coarse
aggregate fraction, Use of aggregate with
improper grading, Use of equal specific weights
of aggregates, (Coarse and Fine
Aggregate) Use of flat or elongated
aggregates, Decrease in cement content, Too
high or too low Water Cement Ratio.
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BLEEDING Bleeding is HIGHER for HIGHER
Workability , HIGHER Water Cement
Ratio, LOWER Cement content. Water reducing
admixtures containing finely divided mineral
additions REDUCE Bleeding ligno-sulphates
REDUCES bleeding rate hydrocarboxylic INCREASES
bleeding rate accelerating water reducing agents
DO NOT ENHANCE bleeding Silica fume REDUCE
bleeding rate but has CRACKING RISK.
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Bleeding Effects

• Excessive Bleeding IMPAIRS
• STRENGTH
• DURABILITY
• Excessive Bleeding RESULTS in
• Non-uniformity of Strength
• Increased Transverse Permeability
• Plastic Settlement Cracking
• Poor Bonding between cement matrix and
  underlying coarse aggregate reinforcement
• Bleeding is beneficial in hot and windy weather.
• If Evaporation exceeds the Bleeding Rate,
  Plastic Cracks develop.

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COMPRESSIVE STRENGTH It can be measured easily
and is often taken as an index of the OVERALL
Quality wherein many of the desired properties
are related Shear Strength Tensile
Strength Modulus of Elasticity Bond Impact Abr
asion Resistance Durability
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FACTORS AFFECTING COMPRESSIVE STRENGTH
Water Cement Ratio Lowering Water/Cement Ratio
Increases Strength Characteristics of
Cement Characteristics of Aggregates Proportion
of Aggregates Increasing Aggregate/Cement Ratio
Increases Strength The Degree of
Compaction Increase in Compressive Strength by
Lowering Water/Cement Ratio may be restricted if
compaction is insufficient. Efficiency of
Curing The Temperature during Curing The age of
Concrete Condition of Test
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WATER CEMENT RATIO It governs the quality of
the hardened Portland Cement binder. Strength
and Impermeability properties of Concrete are
improved by LOWERING the Water Cement
Ratio. Firstly, in general, to obtain a workable
mix, people use more water than is actually
necessary for chemical combination with the
cement. This water occupies space and when it
dries out later, it leaves behind air
voids Secondly, there is decrease in the
absolute volume of the cement paste when dried
and hardened.
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COMPRESSIVE STRENGTH AS A FUNCTION OF WATER
CEMENT RATIO
337
313
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AGGREGATES The MORE ANGULAR the sand, the
GREATER will be the WATER REQUIREMENT to produce
a given consistency, The HIGHER the percentage
of voids in a given sand, the LOWER will be the
COMPRESSIVE STRENGTH , The detrimental effects
of FREEZING and THAWING are greatly reduced when
the stone sand is processed to have LESS VOIDS
and thereby require LESS water.
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• COMPACTION
• The compactness of Hardened Concrete has a
  considerable influence on its fundamental
  properties, such as Strength, Impermeabilty and
  Durability.
• Compaction Reduces inter-particle friction
• Eliminates air pockets

Presence of 5 voids DECREASES Compressive
Strength by about 35
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CURING Curing is the process of maintaining a
satisfactory moisture content in a favourable
temperature in concrete during the hydration of
the cementitious materials so that the desired
properties of the concrete are developed. FUNCTIO
NS OF CURING To Prevent Loss of water from
Evaporation Supplement Water consumed in
Hydration Process Curing is essential in the
production of quality concrete. The potential
strength and durability of the concrete will be
fully developed if it is properly cured for an
adequate period. Loss of moisture at this stage
results in Drying, Shrinkage and Development of
Cracks.
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CURING One year Strength of continuously Moist
Cured concrete is about 50 HIGHER than that of
28 Day Moist Cured concrete. No Moist Curing can
lower the Strength by about 30 Moist Curing for
first 7 to 14 day may result in Compressive
Strength being 85 to 92 of that of 28 days Moist
Curing Minimum Curing Time 7 Days Moist
Curing (IS 456) 10 days for hot weather
(IS 7861-I)
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WATER TEMPERATURE Higher Water temperature cause
HIGHER concrete temperature, as the concrete
temperature increases the water demand increases
and STRENGTH decreases for the same
consistency. Mixing water has the greater effect
per unit of weigh of any of the ingredients on
the temperature as its specific heat is 4 5
times higher that cement and aggregates.
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CONCRETE TEMPERATURE Concrete maintained at
Higher temperature during setting and early
hardening has LOWER STRENGTH at later
ages. Avoiding High Concrete temperature during
Curing REDUCE random Cracking RESULTS GREATER
Strength at Later ages.
STREAM CURING To Develop HIGH Early Strength for
early removal of formwork specially for Precast
Concrete.
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CONCRETE TEMPERATURE The rate of reaction
between cement and water varies with temperature.
It proceeds slowly at low temperature down to
-12º C and rapidly at high temperature somewhat
below the boiling point of water.
Below 10º C are unfavourable for the development
of Early Strength Below 5º C the development of
early Strength is greatly retarded At freezing
temperature, little strength develops Curing at
temperature in excess of 70º C is not as
beneficial as prolonged curing at lower
temperature. Autoclaving at temperature above
160º C may produce strength in few hours equal to
28 days of curing at 20º C.
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DURABILITY
. . . ability of concrete to RESIST weathering
action, chemical attack, abrasion and other
conditions of service.
DURABLE CONCRETE will RETAIN its ORIGINAL FORM ,
QUALITY and SERVICEABILITY when exposed to
Environment.
DURABILITY is a function of The Choice of
Cement and its dosage The Choice of Aggregates
(form, cleanliness, stability, etc.) The Water
(quality, content and water-cement ratio) The
use of appropriate Admixtures The batching and
casting methods The curing of Concrete
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Durability . . .
Of late, the focus of construction has been
shifted from STRENGTH to DURABILITY High
Strength cements have played havoc in building
sector. These resulted in Development of
Shrinkage Cracks, Vulnerability to Severe
Environment, Reduced Life of the Structure.
DURABILITY of Concrete is impaired due to
Inability of achieving compaction leading to
honey combing Corrosion of reinforcements due
to chloride diffusion and carbonation of
concrete, cracking of concrete, Volume changes
due to sulphate attack, shrinkage, alkali
silica reaction, cracking of concrete, etc.
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DURABILITY CONCRETE FAILURES (Causes) EXTERNAL
Weathering Attack by Natural / Industrial
liquids, Bacterial Growth INTERNAL Alkali
Aggregate Reaction Volume Change due to
non-compatibility of Thermal Mechanical
properties of Aggregates Cement
paste. Presence of Sulphates Presence of
Chlorides Ingress of Moisture / Air
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RECOMMENDATION FOR DURABLE CONCRETE Limits for
Maximum Water-Cement Ratio Minimum Cement
Content Cover Thickness Type of
Cement Chloride Content in Concrete Sulphate
Content in Concrete
CONSIDERATIONS Situation of Placing Congestion
of Reinforcement Cover Thickness Workability of
Concrete Characteristics of aggregates
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HONEYCOMB It occurs when the mortar does not
fill the space between the coarse aggregates.
Its presence indicates that first stage of
consolidation has not been completed. CAUSES
- Use of improper or faulty vibrators, Poor
vibrations procedures, Unsystematic insertion
of mortar at haphazard angles, Insufficient
paste to fill the voids, Improper ratio of sand
to total aggregate, Poor aggregate
grading, Improper workability, Insufficient
clearance between the reinforcement bars.
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Entrapped Air Voids The amount of entrapped air
in concrete is depended upon Vibratory
equipment, Vibration Procedures, Properties of
concrete mix, Location in the placement. To
reduce air voids, the distance between internal
vibrator insertions should be reduced and the
time at each insertion increased.
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Pour Line These are dark lines showing on the
formed surface demarking the boundary between
adjacent batches of concrete. They indicate that
when vibrating a layer, the vibrator was not
lowered far enough to penetrate the layer below.
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SAND STREAKING CAUSES - Heavy bleeding along the
form, Character of the materials, Proportion
s of the materials, Method of depositing
concrete, Harsh and wet mix with Less
Cement and More Water, Poorly Graded
Aggregate, Dropping concrete mix through
reinforcing steel, Using Thick Lifts
without adequate Compaction, Vibrators
attached to leaking form.
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DENSE IMPERMEABLE CONCRETE MASS MORE
DURABLE Resistance to Sulphate
Attack Resistance to Acid Attack Resistance to
Chloride Ingression Carbonation
Shrinkage Alkali Silica Reaction (ASR)
Permeability of Cement Paste INCREASES
exponentially with INCREASE in Water-Cement ratio
above 0.45. Cement Content Ensure sufficient
alkalinity to provide Passive Environment To
overfill the voids between the aggregates
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DURABILITY
REDUCED PERMEABILITY RESULTS IN HIGH
RESISTANCE TO SULFATE ATTACK HIGH RESISTANCE TO
CHLORIDE INGRESSION MINIMISING THE RISK OF
ALKALI SILICA REACTION HIGH RESISTANCE TO
ACIDS AND CHEMICALS (REDUCED
LEACHING) RESISTANCE TO CARBONAGE SHRINKAGE
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Sulphate Attack
Sulphate attack causes expansion, loss of
strength and eventually transform the materials
into musky mass. The rate and depth of sulphate
attach depends upon the characteristics of
concrete strength, porosity, permeability and
chemical composition of hardened cement paste.
Combination of sulphate with Calcium ion
liberated during hydration of cement to form
gypsum, Combination of sulphate ion, gypsum and
hydrate Calcium Aluminate to form Calcium
Sulfo-aluminate hydrate (ettringite), Both these
chemical reactions result in increase in solid
volume. The formation of ettringite is the cause
of most of the expansion and disruption of
concrete by sulphate solution.
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Chloride Attack
Chloride can harmfully affect the durability of
both concrete and reinforcement. The chloride
ion content of concrete must be kept lower and
the ionic penetration from outside must be
prevented or hindered. Chloride dissolved in
water increases the rate of leaching of
portlandite thus increasing the porosity or
mortar and concrete. As a result of the attack,
the concrete swells, losses stiffness and
strength and becomes more sensitive to other
environmental attacks (sulphate, frost,
etc.) Chloride attack will result in the
corrosion of the concrete reinforcement.
Chloride attack can take place if oxygen and
moisture are present.
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Diffusion of Chloride Ions at 25º C in Cement
Paste of Water to Cement ratio 0.5
Type of Cement Diffusivity (x10-9
cm2/sec) Sulphate Resistance Portland Cement
(SRPC) 100.00 Ordinary Portland Cement
(OPC) 44.70 Portland Pozzolana Cement
(PPC) 14.70 (70 OPC 30 Flyash) Portland Slag
Cement (PSC) 4.10 (35 OPC, 65 Slag)
The rate and depth of Chloride penetration into
concrete depend upon the permeability of
concrete. It can be decreased by Decreasing the
water/cement ratio Increasing the cement
content Increasing the length of curing
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Acid Attack
The deterioration of Concrete by acids is
primarily the result of reaction between these
chemicals and Calcium Hydroxide of the hydrated
Portland Cement. In most cases, the chemical
reaction results in the formation of water
soluble calcium compounds which are then LEACHED
away by aqueous solutions.
A Dense Concrete with Low Water Cement Ratio
provides an acceptable degree of protection
against Acid Attack.
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Carbonation
Effect of Carbon Dioxide Carbon dioxide contained
in the air is potentially dangerous for concrete
durability because it can attack all of the
hydrates in the hardened cement. This alarming
prospective concerns only low strength porous
concrete.
Carbonation Shrinkage When concrete is exposed
to carbon dioxide, a reaction producing
carbonates takes place which is accompanied by
shrinkage. The source of carbon dioxide can be
either the atmosphere or water carrying dissolved
carbon dioxide.
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Alkali Silica Reaction
Although aggregates is commonly considered to be
inert filler in concrete, some aggregates may
react with alkalis present in the pore fluids of
concrete. Under such adverse conditions and in
presence of moisture, this may lead to expansion
and subsequent cracking of the Concrete.
A Dense Concrete with Low permeability and Low
Water Cement ratio provides Resistance against
Alkali Silica Reaction.
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5Cs OF DURABLE CONCRETE
CONSTITUENT MATERIALS COVER COMPACTION CURING
CARE
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COMPRESSIVE STRENGTH OF M20 CEMENT CONCRETE CUBES
PCAL Laboratory Result
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