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DURABILITY of CONCRETE
STRUCTURES
Prof. Dr. Halit YAZICI
Part- I
The Cement Matrix
• Cement: – produces a crystalline structure
– binds aggregates together
• Water – causes chemical reaction to occur
– produces workability
What is Portland Cement?
• Raw limestone, clay & gypsum minerals are ground into powder & heated in kiln
(1600 ° C)
• Minerals interact at that temperature to form calcium silicates (clinker)
• Available in five types, each with varying performance characteristics and uses
• The production process for portland cement first involves grinding limestone and alumina and silica from shale or clay.
• The raw materials are proportioned, mixed, and then burned in large rotary kilns at approximately 2500°F until partially fused into marble-sized masses known as clinker.
• After the clinker cools, gypsum is added, and both materials are ground into a fine powder which is portland cement.
Source: PCA, 2003
CLINKER GYPSUM
Process of Clinker Production
Source: PCA, 2003
Source: PCA, 2003
Source: PCA, 2003
Hydration
• Portland cement becomes cementitious when mixed with water
• This reaction is referred to as
hydration. • During hydration, a crystalline
structure grows to form bonds
• Hydration begins as soon as water meets cement
• Rate of hydration increases with
increased cement fineness
Portland Cement → Gypsum+Portland Cement Clinker (pulverizing)
Portland Cement Clinker → Calcareous &
Clayey Materials (burning)
Paste → P.C. + Water
Mortar → P.C. + Water + Sand
Concrete → P.C. + Water + Sand + Gravel
Portland cement is made by mixing substances containing CaCO3 with substances containing SiO2, Al2O3, Fe2O3 and heating them to a clinker which is subsequently ground to powder and mixed with 2-6 % gypsum.
COMPOUND COMPOSITION OF P.C. (OR CLINKER)
Oxides interact with eachother in the kiln to form more complex products (compounds). Basically, the major compounds of P.C. can be listed as:
Name Chemical Formula Abbreviations
Tri Calcium Silicate 3CaO.SiO2 C3S
Di Calcium Silicate 2CaO.SiO2 C2S
Tri Calcium Aluminate 3CaO.Al2O3 C3A
Tetra Calcium Alumino
Ferrite 4CaO.Al2O3.Fe2O3 C4AF
The degree to which the potential reactions can proceed to “equilibrium” depends on:
1) Fineness of raw materials & their intermixing.
2) The temperature & time that mix is held in the critical zone of the kiln.
3) The grade of cooling of clinker may also be effective on the internal structure of major compounds.
There are also some minor compounds which constitute few %, so they are usually negligible. Moreover, portland cement compounds are rarely pure.
For example in C3S, MgO & Al2O3 replaces CaO randomly.
C3S→ALITE & C2S→BELITE
Ferrite Phase: C4AF is not a true
compound. The ferrite phase ranges from
C2AF to C6AF. *C4AF represents an
average.
Methods of Determining Compound Composition Each grain of cement consists of an intimate
mixture of these compounds. They can be determined by: 1) Microscopy 2) X-Ray Diffraction
But due to the variabilities involved the
compound composition is usually calculated using the oxide proportions.
3) Calculations (Bouge’s Equations)
Assumptions
1) The chemical reactions in the kiln proceeded to equilibrium.
2) Compounds are in pure form such as C3S & C2S
3) Presence of minor compounds are ignored.
4) Ferrite phase can be calculated as C4AF
5) All oxides in the kiln have taken part in forming the compounds.
%C3S=4.071(%C)-7.6(%S)-6.718(%A)-1.43(%F)-2.852(%Ś)
%C2S=2.867(%S)-0.7544(%C3S)
%C3A=2.650(%A)-1.692(%F)
%C4AF=3.043(%F)
Clinker Phases • Alite or 3CaO•SiO2 or C3S
– Hydrates & hardens quickly
– High early strength
– Higher heat of hydration (setting)
• Belite or 2CaO• SiO2 or C2S – Hydrates & hardens slower
than alite
– Gives off less heat
– High late strength (> 7 days)
• Modern cements are manufactured to be higher in alite for early strength
Clinker Phases • Aluminate or 3CaO• Al2O3
or C3A
– Very high heat of hydration
– Some contribution to early strength
– Low C3A for sulfate resistance
• Ferrite or 4CaO• Al2O3 •
Fe2O3 or C4AF
– Little contribution to strength
– Lowers clinkering temperature
– Controls the color of cement
Hydration of P.C.
Hydration: Chemical reactions with water.
As water comes into contact with cement particles, hydration reactions immediately starts at the surface of the particles. Although simple hydrates such as C-H are formed, process of hydration is a complex one and results in reorganization of the constituents of original compounds to form new hydrated compounds.
At any stage of hydration the hardened cement paste (hcp) consists of:
• Hydrates of various compounds referred to collectively as GEL.
• Crystals of calcium hydroxide (CH).
• Some minor compound hydrates.
• Unhydrated cement
• The residual of water filled spaces – pores.
As the hydration proceeds the deposits of hydrated products on the original cement grains makes the diffusion of water to unhydrated nucleus more & more difficult. Thus, the rate of hydration decreases with time & as a result hydration may take several years.
Major compounds start to produce:
• Calcium-silicate-hydrate gels
• Calcium hydroxide
• Calcium-alumino-sulfohydrates
At the beginning of mixing, the paste has a structure which consists of cement particles with water-filled space between them. As hydration proceeds, the gels are formed & they occupy some of this space.
1cc of cement → 2.1cc of gel
Gel Pores: 28% of the total gel volume have
diameter of 0.015-0.020 μm. (very small-loss
or gain of water is difficult)
Capillary Pores: 12.5 μm diameter, with varying sizes, shapes & randomly distributed in the paste.
Volume of capillary pores decreases as hydration takes place. Water in capillary pores is mobile, can not be lost by evaporation or water can get into the pores. They are mainly responsible for permeability.
- w/c ratio
capillary porosity
- degree of hydration
C2S & C3S: 70-80% of cement is composed of these two compounds & most of the strength giving properties of cement is controlled by these compounds.
Upon hydration both calcium-silicates result in the same products.
2C3S+6H → C3S2H3 + 3CH
2C2S+4H → C3S2H3 + CH
Calcium-Silicate-Hydrate (C-S-H gel) is similar to a mineral called “TOBERMORITE”. As a result it is named as “TOBERMORITE GEL”
Upon hydration C3S & C2S, CH also forms which becomes an integral part of hydration products. CH does not contribute very much to the strength of portland cement.
C3S having a faster rate of reaction accompanied by greater heat generation developes early strength of the paste. On the other hand, C2S hydrates & hardens slowly so results in less heat generation & developes most of the ultimate strength.
Higher C3S→higher early strength-higher heat generation (roads, cold environments)
Higher C2S→lower early strength-lower heat generation (dams)
C3A: is characteristically fast reacting with water & may lead to a rapid stiffening of the paste with a large amount of the heat generation (Flash-Set)-(Quick-Set). In order to prevent this rapid reaction gypsum is added to the clinker. Gypsum, C3A&water react to form relatively insoluble Calcium-Sulfo-Aluminates.
C3A+CŚH2+10H→C4AŚH12 (calcium- alumino-monosulfohydrate)
C3A+3CŚH2+26H→C6AŚ3H32 (calcium-alumino-trisulfohydrate “ettringite”)
When there is enough gypsum “ettringite” forms with great expansion
If there is no gypsum→flash-set
more gypsum→ettringite
formation increases
which will cause cracking
Also Calcium-Sulfo Aluminates are prone (less resistant) to sulfate attack & does not contribute much for strength. The cement to be used in making concretes that are going to be exposed to soils or waters that contain sulfates should not contain more than 5% C3A.
C4AF: The hydration of ferrite phase is not well understand. Ferrite phase has lesser role in development of strength. The hydration products are similar to C3A. Alumina & iron oxide occur interchangebly in the hydration products.
C4AŚH12 or C4FŚH12
C6AŚ3H32 or C6FŚ3H32
TYPES OF PORTLAND CEMENT
Cements of different chemical composition & physical characteristics may exhibit different properties when hydrated. It should thus be possible to select mixtures of raw materials for the production of cements with various properties.
In fact several cement types are available and most of them have been developed to ensure durability and strength properties to concrete.
It should also be mentioned that obtaining some special properties of cement may lead to undesirable properties in another respect. For this reason a balance of requirements may be necessary and economic aspects should be considered.
1) Standard Types: these cements comply with the definition of P.C., and are produced by adjusting the proportions of four major compounds.
2) Special Types: these do not necessarily couply with the definiton of P.C. & are produced by using additional raw materials.
Standard Cements (ASTM)
Type I: Ordinary Portland Cement Suitable to be used in general concrete
construction when special properties are not required.
Type II: Modified Portland Cement Suitable to be used in general concrete
construction. Main difference between Type I&II is the moderate sulfate resistance of Type II cement due to relatively low C3A content (≤%8). Since C3A is limited rate of reactions is slower and as a result heat of hydration at early ages is less. *It is suitable to be used in small scale mass concrete like retaining walls.
Type III: High Early Strength P.C. Strength development is rapid. 3 days f’c=7 days f’c of Type I It is useful for repair works, cold weather & for
early demolding. Its early strength is due to higher C3S & C3A
content. Type IV: Low Heat P.C. Generates less heat during hydration & therefore
gain of strengthis slower. In standards a maximum value of C3S&C3A& a
minimum value for C2S are placed. It is used in mass-concrete and hot-weather
concreting.
Type V: Sulfate Resistant P.C.
Used in construction where concrete will be subjected to external sulfate attack – chemical plants, marine & harbor structures.
i) During hydration C3A reacts with gypsum & water to form ettringite. In hardened cement paste calcium-alumino-hydrate can react with calcium&alumino sulfates, from external sources, to form ettringite which causes expansion & cracking.
ii) C-H and sulfates can react & form gypsum which again causes expansion & cracking.
* In Type V C3A is limited to 5%.
TS EN 197-1 NEW
CEM cements
CEM I – Portland Cement
CEM II – Portland Composite Cement
CEM III – Portland Blast Furnace Slag Cement
CEM IV – Pozzolanic Cement
CEM V – Composite Cement
TS EN 197-1
• CEM cements :
– Binding property is mainly due to hydration of calcium-silicates
– Reactive C + Reactive S > 50%
• Clinker, major and minor mineral admixtures
– Clinker + Major + Minor = 100% (mass) + Gypsum
– Major > 5% by mass
– Minor 5% by mass
TS EN 197-1 Mineral Admixtures
• K : Clinker
• D : Silica Fume
• P : Natural Pozzolan
• Q : Calcined Natural Pozzolan
• T : Calcined Shale
• W : Class – C Fly Ash
• V : Class – F Fly Ash
• L : Limestone (Organic compound < 0.5%)
• LL : Limestone (Organic compound < 0.2%)
• S : Granulated Blast Furnace Slag
TS EN 197-1 Composition
• A : Lowest amount of mineral admixture
• B : Mineral admixture amount is > A
• C : Mineral admixture amount is > B
Pozzolan
• The name Pozzolan comes from the town Pozzuoli, Italy.
• Ancient Romans (~100 B.C.) produced a hydraulic binder by mixing hydrated lime with soil (predominantly volcanic ash)
• Horasan mortar, mixing lime with finely divided burned clay, is extensively used by Ottomans
• Nowadays, the word pozzolan covers a broad range of natural and artificial materials.
Pozzolan
a material that, when used in conjunction with portland cement, contributes to the properties of the hardened concrete through hydraulic or pozzolanic activity, or both.
– Natural (Volcanic ash, volcanic tuff, pumicite)
– Artificial (fly ash, silica-fume, granulated blast furnace slag)
Pozzolan
• Siliceous or aluminous material, which in itself possesses little or no cementitious value but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide Ca(OH)2 to form compounds possessing hydraulic cementitious properties.
FACTORS THAT AFFECT THE ACTIVITY OF POZZOLANS
1) SiO2 + Al2O3 + Fe2O3 content
2) The degree of amourpheness of its structure
3) Fineness of its particles
1) SiO2 + Al2O3 + Fe2O3
The greater amount of these, the greater its activity.
ASTM C 618 & TS 25 → min “SiO2+Al2O3+Fe2O3” for natural pozzolans > 70%
Fly Ash - ASTM
Class C→ from lignitide or subbituminous coals (SiO2+Al2O3+Fe2O3>50%)
Class F→ from bituminous coals and SiO2+Al2O3+Fe2O3>70%
Silica fume → SiO2 ≈ 85-98%
Blast Furnace Slag→ SiO2 ~ 30-40%
Al2O3 ~ 7-19%
CaO ~ 30-50%
2) Amorphousness
For chemical reaction → pozzolans must be
amorphous
Volcanic ash, volcanic tuff, fly ash, silica fume
are all amorphous by nature.
Clays → contain high amounts of silica &
alumina but have a crystallic structure!
(Do not possess pozzolanic activity)
However, by heat treatment, such as calcining
~700-900°C crystallic structure is destroyed & a
quasi-amorphous structure is obtained.
2) Amorphousness
Clay → does not possess pozzolanic property
Burned clay → possess pozzolanic property
Blast furnace slag → contain high
amounts of silica, alumina & lime.
However, if molten slag is allowed to cool in air,
it gains a crystal structure. * do not possess
pozzolanic property.
However, if it is cooled very rapidly by pouring it
into water, it becomes a granular material &
gains amorpousness. * possess pozzolanic
property.
3) Fineness
Pozzolanic activity increases as fineness increases.
Volcanic ash, rice husk ash, fly ash, condensed silica fume are obtained in finely divided form.
Volcanic tuff, granulated blast furnace slag & burned clay must be ground.
ADMIXTURES
Materials added to the concrete besides
cement, water and aggregate.
To improve the properties of the concrete
required.
Admixtures can be divided in 2 groups that
is:
a) Chemical admixtures
b) Mineral admixtures
Admixtures
Air-entraining admixtures
Water-reducing admixtures
Plasticizers
Accelerating admixtures
Retarding admixtures
Hydration-control admixtures
Corrosion inhibitors
Shrinkage reducers
ASR inhibitors
Coloring admixtures
Miscellaneous admixtures
Primary admixture properties PLASTICISERS
Dispersion of cement particles increases fluidity
Water reduction increases strength
Water reduction reduces permeability, increases durability
Cement reduction reduces cost
AIR ENTRAINERS
Increase cohesion, Reduce bleed and segregation
Easier to pump
Impart freeze thaw resistance
RETARDERS
Prolong period over which concrete may be placed
Reduce problems with cold joints
ACCELERATORS
Reduce the time to reach initial set
Increase the early age strength of the concrete
FUNCTION OF ADMIXTURE
To improve workability of fresh concrete
To improve durability by entrainment of
air
To reduce the water required
To accelerate setting & hardening & thus
to produce high early strength
To aid curing
To impart water repellent / water proofing
property
To cause dispersion of the cement
particles when mixed with water
To retard setting
To improve wear resistance (hardness)
To offset / reduce shrinkage during
setting & hardening
To cause expansion of concrete and
automatic prestressing of steel
To aerate mortar / concrete to produce a
light-weight product
To impart colour to concrete
To offset or reduce some chemical
reaction
To reduce bleeding
To reduce the evolution of heat
Among the type of chemical admixture
used are:
a) Accelerator
b) Water reducing Admixture
c) Superplasticizer
d) Air Entraining Admixtures
e) Retarding Admixtures
f) Corrosion Inhibitors
g) Alkali-Aggregate Reaction Inhibiting
Admixtures
h) Shrinkage Reducing Admixtures
CONCRETE AGGREGATES
Aggregate: the inert filler
materials, such as sand or
stone, used in making
concrete
The aggregate occupies ~70-75% of the
volume of concrete, so its quality is of
great importance.
Aggregates may affect the following
properties of concrete:
Strength
Durability
Structural Performance
Economy
Aggregates have 3 main functions in
concrete:
1) To provide a mass of particles which are
suitable to resist the action of applied loads &
show better durability then cement paste alone.
2) To provide a relatively cheap filler for the
cementing material.
3) To reduce volume changes resulting from
setting & hardening process & from moisture
changes during drying.
The properties of concrete are affected by
the properties of aggregate:
1. The mineral character of aggregate affects the
strength, durability, elasticity of concrete.
2. The surface characteristics of aggregate affects
the workability of fresh mass & the bond
between the aggregate & cement paste in
hardened concrete. If it is rough, workability
decreases & bond increases.
3. The grading of aggregate affects the
workability, density & economy.
4. The amount of aggregate in unit volume of
concrete
Higher aggregate amount/unit volume of
concrete
Results in less volume changes during setting &
hardening or moisture changes. (increase in
volume stability)
Increase in strength & durability
Decrease in cost
It is a common practice to use as much
aggregate as possible in concrete
However, all aggregates are not inert:
The physical action: swelling & shrinkage
The chemical action: alkali-agg. Reaction
The thermal action: expansion & contraction
Like the other ingredients of concrete,
aggregates must also be chosen with
certain care to end up with a satisfactory
concrete.
PARTICLE SHAPE & SURFACE TEXTURE
In addition to petrological character, the external characteristics, i.e. The shape & surface texture of aggregates are of importance.
Particle Shape
Rounded: Completely water worn & fully shaped by attrition. (River Gravel)
Irregular: Partly shaped by attrition so it contains some rounded edges. (Land Gravel)
Angular: Has sharp corners, show little
evidence of wear. (Crushed Stone)
Flaky: Thickness is relatively small with
respect to two other dimensions. (Laminated
Rocks)
Elongated: Have lengths considerably larger
than two other dimensions
L
w t
FLAT ELONGATED
ROUND ANGULAR
Rounded aggregates are suitable to use in concrete because flaky & elongated particles reduce workability, increase water demand & reduce strength.
In the case of angular particles, the bond between agg. Particles is higher due to interlocking but due to higher surface area, angular particles increase water demand & therefore reduce workability. As a result, for the same cement content & same workability rounded agg. Give higher strength. ?
Surface Texture
This affects the bond to the cement paste & also influences the water demand of the mix.
Smooth: Bond b/w cement paste & agg is weak.
Rough: Bond b/w cement paste & agg. is strong.
Surface texture is not a very important property from compressive strength point of view but agg. Having rough surface texture perform better under flexural & tensile stresses.
SMOOTH ROUGH
Grading of Aggregates
―Grading is the particle-size distribution of an aggregate as determined by a sieve analysis using wire mesh sieves with square openings.
ASTM C 33
Fine aggregate―7 standard sieves with openings from 150 μm to 9.5 mm
Coarse aggregate―13 sieves with openings from 1.18 mm to 100 mm
MOISTURE CONDITION OF
AGGREGATES
DELETERIOUS MATERIALS IN
AGGREGATES
Soft particles : they are objectionable because they affect the durability adversely. They may cause pop-outs & may brake up during mixing and increase the water demand.
Salt contamination : Most important effects are: Corrosion of reinforcement
Effloresence: presence of white deposits on the surface of concrete.
SOUNDNESS OF AGGREGATES
Soundness is the ability of agg to resist
volume changes to environmental effects.
Freezing & Thawing
Alternate Wetting & Drying
Temperature Changes
SOUNDNESS OF AGGREGATES
Aggs are said to be unsound when volume
changes induced by the above, results in
deterioration of concrete. This effect may be:
Local scaling
Extensive surface cracking
Disintegration over a considerable depth
SOUNDNESS OF AGGREGATES
To detect unsound particles, aggs are treated
with Na2SO4 or MgSO4 solutions.
18 hours of immersion
Dry at 105°C+5°C to constant weight
After 5 cycles determine the loss in weight of the
agg.
SOUNDNESS OF AGGREGATES
According to TS following limits should not
be exceeded.
Na2SO4 MgSO4
Fine Agg.
Coarse Agg.
19%
22% 15%
27%
ABRASION RESISTANCE
Especially when concrete is used in roads or floor surfaces subjected to heavy traffic load.
Hardness, or resistance to wear (abrasion) is determined by Los-Angeles abrasion test.
Los Angeles Abrasion Test:
The agg with a specified grading is placed
inside the L.A. Testing Machine
Loose steel balls are placed inside the drum
The apparatus is rotated for a specified
cycles
Finally the loss in weight is determined. by
screening with #12 sieve.
Resistant → <10% for 100 revolutions
→ <50% for 500 revolutions
Alkali- Aggregate Reactivity ( AAR )
— is a reaction between the active mineral constituents of some aggregates and the sodium and potassium alkali hydroxides and calcium hydroxide in the concrete.
Alkali-Silica Reaction (ASR)
Alkali-Carbonate Reaction (ACR )
Alkali-Silica Reaction (ASR)
Visual Symptoms
Network of cracks
Closed or spalled joints
Relative displacements
Alkali-Silica Reaction (ASR)
Visual Symptoms (cont.) Fragments breaking out of
the surface (popouts)
Mechanism
1. Alkali hydroxide + reactive
silica gel reaction
product (alkali-silica gel)
2. Gel reaction product +
moisture expansion
Alkali-Silica Reaction (ASR)
Test Methods Mortar-Bar Method (ASTM 227)
Chemical Method (ASTM C 289)
Petrographic Examination (ASTM C 295)
Rapid Mortar-Bar Test (ASTM C 1260)
Concrete Prism Test (ASTM C 1293 )
Alkali-Silica Reaction (ASR)
Controlling ASR Non-reactive aggregates
Supplementary cementing materials or
blended cements
Limit alkalis in cement
Lithium-based admixtures
Limestone sweetening (~30% replacement of
reactive aggregate with crushed limestone
Effect of Supplementary Cementing
Materials on ASR
What is Concrete?
Concrete is one of the most commonly
used building materials.
Concrete is a composite material made
from several readily available constituents
(aggregates, sand, cement, water).
Concrete is a versatile material that can
easily be mixed to meet a variety of
special needs and formed to virtually any
shape.
Advantages
Ability to be cast
Economical
Durable
Fire resistant
Energy efficient
On-site fabrication
Disadvantages
Low tensile strength
Low ductility
Volume instability
Low strength to weight ratio
Hardened Concrete Properties
Strength
compressive strength 2000-8000 psi
tensile strength 200-800 psi
flexural strength
compression >> tension since concrete is notch
sensitivite
Factors Affecting Strength
Curing conditions, humidity
temperature
w/c , (inversely related) Abram’s law
air content, (inversely related), short and long term
aggregate characteristics, roughness,grading, minerological.
cement type, composition, fineness, type I vs. type III
cement content (directly related)
Strength porosity relationship
mixing water
Strength and Curing
time
in air entire time
moist cured entire time
in air after 3 days
in air after 7 days
Strength
28
100%
PERMEABILITY OF CONCRETE Permeability is important because:
1. The penetration of some aggresive solution may
result in leaching out of Ca(OH)2 which adversely
affects the durability of concrete.
2. In R/C ingress of moisture of air into concrete
causes corrosion of reinforcement and results in
the volume expansion of steel bars,
consequently causing cracks & spalling of
concrete cover.
3. The moisture penetration depends on
permeability & if concrete becomes saturated it
is more liable to frost-action.
4. In some structural members permeability itself is
of importance, such as, dams, water retaining
tanks.
PERMEABILITY OF CONCRETE
The permeability of concrete is controlled
by capillary pores. The permeability
depends mostly on w/c, age, degree of
hydration.
In general the higher the strength of
cement paste, the higher is the durability &
the lower is the permeability.
PROPORTIONING CONCRETE
MIXTURES W+C+C.Agg.+F.Agg.+Admixtures → Weights / Volumes?
There are two sets of requirements which enable the engineer to design a concrete mix.
1. The requirements of concrete in hardened state. These are specified by the structural engineer.
2. The requirements of fresh concrete such as workability, setting time. These are specified by the construction engineer (type of construction, placing methods, compacting techniques and transportation)
PROPORTIONING CONCRETE
MIXTURES Mix design is the process of selecting
suitable ingredients of concrete & determining their relative quantities with the objective of producing as economically as possible concrete of certain minimum properties such as workability, strength & durability.
So, basic considerations in a mix design is cost & min. properties.
Cost → Material + Labor
Water+Cement+Aggregate+Admixtures
Most expensive (optimize)
Using less cement causes a decrease in shrinkage and increase in volume stability.
Min.Properties →Strength has to be more
than..
Durability→Permeability has to be
Workability→Slump has to be...
In the past specifications for concrete mix
design prescribed the proportions of cement,
fine agg. & coarse agg.
1 : 2 : 4
Weight of cement
Fine Agg.
Coarse Agg.
However, modern specifications do not use these fixed ratios.
Modern specifications specify min compressive strength, grading of agg, max w/c ratio, min/max cement content, min entrained air & etc.
Most of the time job specifications dictate the following data:
Max w/c
Min cement content
Min air content
Slump
Strength
Durability
Type of cement
Admixtures
Max agg. size
PROCEDURE FOR MIX DESIGN
1. Choice of slump (Table 14.5)
PROCEDURE FOR MIX DESIGN
2. Choice of max agg. size
• 1/5 of the narrowest dimension of the mold
• 1/3 of the depth of the slab
• ¾ of the clear spacing between reinforcement
• Dmax < 40mm
PROCEDURE FOR MIX DESIGN
3. Estimation of mixing water & air content
(Table 14.6 and 14.7)
PROCEDURE FOR MIX DESIGN
4. Selection of w/c ratio (Table 14.8 or 14.9)
PROCEDURE FOR MIX DESIGN
5. Calculation of cement content with selected water
amount (step 3) and w/c (step 4)
6. Estimation of coarse agg. content (Table 14.10)
PROCEDURE FOR MIX DESIGN
7. Calculation of fine aggregate content with
known volumes of coarse aggregate, water,
cement and air
8. Adjustions for aggregate field moisture
PROCEDURE FOR MIX DESIGN
9. Trial batch adjustments
The properties of the mixes in trial batches are
checked and necessary adjustments are made to
end up with the minimum required properties of
concrete.
Moreover, a lab trial batch may not always provide
the final answer. Only the mix made and used in
the job can guarantee that all properties of concrete
are satisfactory in every detail for the particular job
at hand. That’s why we get samples from the field
mixes for testing the properties.
Example:
Slump → 75-100 mm
Dmax → 25 mm
f’c,28 = 25 MPa
Specific Gravity of cement = 3.15
Non-air entrained concrete
Coarse Agg. Fine Agg.
SSD Bulk Sp.Gravity 2.68 2.62
Absorption 0.5% 1.0%
Total Moist.Content 2.0% 5.0%
Dry rodded Unit Weight 1600 kg/m3 –
Fineness Modulus – 2.6
1. Slump is given as 75-100 mm
2. Dmax is given as 25 mm
3. Estimate the water and air content (Table 14.6)
Slump and Dmax → W=193 kg/m3
Entrapped Air → 1.5%
4. Estimate w/c ratio (Table 14.8)
f’c & non-air entrained → w/c=0.61 (by wt)
5. Calculation of cement content
W = 193 kg/m3 and w/c=0.61
C=193 / 0.61 = 316 kg/m3
6. Coarse Agg. from Table 14.10
Dmax and F.M. → VC.A=0.69 m3
Dry WC.A. = 1600*0.69 = 1104 kg/m3
SSD WC.A. = 1104*(1+0.005) = 1110 kg/m3
7. To calculate the F.Agg. content the
volumes of other ingredients have to be
determined. V = M Sp.Gr.*rw Vwater = 193
1.0*1000
= 0.193 m3
Vcement = 316 3.15*1000
= 0.100 m3
VC.Agg. = 1110 2.68*1000
= 0.414 m3
Vair = 0.015 m3 (1.5%*1)
SV = 0.722 m3 → VF.Agg = 1-0.722 = 0.278 m3
WF.Agg = 0.278*2.62*1000 = 728 kg/m3
Summary of Mix Design
Based on SSD weight of aggregates
8. Adjustment for Field Moisture of Aggregates
WSSD =WDry *(1+a) WField =WDry *(1+m)
Correction for water
From coarse aggregate: 1127-1110 = 17
From fine aggregate: 759-728 = 31
48 kg
extra
Corrected water amount : 193 – 48 = 145 kg
Summary of Mix Design
Based on field weight of aggregates
9. Trial Batch
Usually a 0.02 m3 of concrete is sufficient
to verify the slump and air content of the
mix. If the slump and air content are
different readjustments of the proportions
should be made.
Fiber Reinforced Concrete
Effect
of fiber
NEED PCC has low tensile strength, limited ductility and little
resistance to cracking
PCC develops micro-cracks, even before loading
Addition of small, closely spaced and uniformly
distributed fibres act as crack arresters.
FIBRE REINFORCED CONCRETE is a composite
material consisting of mixtures of cement, mortar or
concrete and discontinuous, discrete, uniformly
dispersed suitable fibres.
122
FACTORS AFFECTİNG THE PROPERTIES OF FRC
Relative Fibre Matrix Stiffness
Volume of Fibres
Aspect Ratio of the Fibre
Orientation of Fibres
Workability and Compaction of Concrete
Size of Coarse Aggregate
Mixing
FIB
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123
2. VOLUME OF FİBRES
124
4. ORİENTATİON OF FİBRES The effect of randomness, was tested
using mortar specimens reinforced with
0.5% volume of fibres, by orienting
them:
parallel to the direction of the load
perpendicular to the direction of the
load
in random 125
5. Workability and Compaction of
Concrete
Fibres reduce workability
6. Size of Aggregate
Size of CA is restricted to 10mm
126
7. MİXİNG Cement content : 325 to 550 kg/m3
W/C Ratio : 0.4 to 0.6
% of sand to total aggregate : 50 to 100%
Maximum Aggregate Size : 10 mm
Air-content : 6 to 9%
Fibre content : 0.5 to 2.5% by vol of mix
: Steel -1% - 78kg/m3
: Glass -1% - 25 kg/m3
: Nylon -1% - 11 kg/m3
127
FIB
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128
FIB
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INTRODUCTION OF STEEL FIBRES MODIFIES: 1. Tensile strength
2. Compressive strength
3. Flexural strength
4. Shear strength
5. Modulus of Elasticity
6. Shrinkage
7. Impact resistance
8. Strain capacity/Toughness
9. Durability
10.Fatigue
129
APPLICATIONS OF SFRC
Highway and airport pavements
Refractory linings
Canal linings
Industrial floorings and bridge-decks
Precast applications - wall and roof
panels, pipes, boats, staircase steps &
manhole covers
Structural applications
130
POLYPROPYLENE FIBER REINFORCED CONCRETE (PFRC)
Cheap, abundantly available
High chemical resistance
High melting point
Low modulus of elasticity
Applications in cladding panels and
shotcrete
131
FIB
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GLASS FIBER REINFORCED CONCRETE (GFRC)
High tensile strength, 1020 to 4080 N/mm2
Lengths of 25mm are used
Improvement in impact strengths, to the
tune of 1500%
Increased flexural strength, ductility and
resistance to thermal shock
Used in formwork, swimming pools, ducts and
roofs, sewer lining etc. 132
CARBON FIBERS Material of the future, expensive
High tensile strengths of 2110 to 2815
N/mm2
Strength and stiffness superior to that of
steel
133
Load Induced Volume Changes
Instantaneous, 1D
E
Secant modulus
Tangent modulus
c
.
concrete 'fE5133
ftcubic/lbs,concreteofweightunit
psi,strengthecompressiv'f c
Load Induced Volume Changes
Time dependant
Creep deformation Deformation
Time
Creep in Concrete
Creep in Concrete
water
Creep
Consequences of creep
Loss in pre-stress
possibility of excessive deflection
stressing of non load bearing members
Shrinkage
and Creep
140
DURABILITY of CONCRETE
STRUCTURES
Prof. Dr. Halit YAZICI
Part- I
