Concrete

CONCRETE

MUHAMMAD ARSLAN, DEPARTMENT OF CIVIL

ENGINEERING UET LAHORE

Introduction

Concrete and Steel are the two most commonly used Structural materials in the construction industry.



Topics Definitions Ingredients Types of cement Types of aggregate Batching & mixing of concrete Transportation of concrete Testing of concrete Pumping of concrete Curing of concrete Joints in concrete Reinforcement for concrete Additives & Admixtures for concrete Useful References



Definitions Shotcrete

It is that type of mortar or concrete which is conveyed through a hose (flexible tube) and pneumatically projected at high velocity.

Pozzolanic cement

It comes from the name of the village Pozzuoli, near Vesuvius, where the volcanic ash was first found. The Pozzolanic cement is the term used to describe the cements obtained by simple grinding of natural materials at normal temperature.

Portland cement

A cement consisting of Portland cement with not more than 5% of other inorganic materials.

Hydraulic cement

They consists mainly of silicates and aluminates of lime and can be broadly classified as natural cements, Portland cements and high Alumina cements.

Blended Cement

A cement consisting of Portland cement and two or more appropriate inorganic materials which contribute to the strength gaining properties of the cement with or without other constituents, processing additions and functional additions is called blended cement. (ASTM C 1157-94a)



Civil engineers are concerned with the calcareous cements.

Ingredients

Concrete consists of following ingredients

Cementitious material (cement or lime)

Coarse aggregate (Crush stone etc)

Fine aggregate (Sand )

Water (which is fit for drinking)



Manufacture of Portland cement

It is made of calcareous materials, such as Lime stone or chalk and from alumina and silica found as clay or shale. Marl, a mixture of calcareous and argillaceous materials is also used.

Process of manufacturing cement consists essentially of grinding the raw materials, mixing them in certain proportion and burning in a large rotary kiln at a temp of about 1450 oC. Material partially fuses in to balls called clinker. Clinker is cooled and ground to a powder form with some gypsum addition. Product obtained is called Portland cement.

Main compounds of portland cement are

Tri calcium Silicate 3CaO. SiO2 C3S

Dicalcium silicate 2CaO. SiO2 C2S

Tricalcium Aluminate 3CaO. Al2O3 C3A

Tetracalcium Aluminoferrite 4CaO.Al2O3.Fe2O3 C4AF



Bogue’s Equations The chemical composition of Portland cement is based on

the work of R.H. Bogue and others known as Bogue composition.

C3S = 4.07 (CaO)-7.6(SiO2)-6.72(Al2O3)-1.43(Fe2O3)-2.85(SO3)

C2S = 2.87(SiO2)-0.75(3CaO.SiO2)

C3A = 2.65(Al2O3)-1.69(Fe2O3)

C4AF = 3.04(Fe2O3)



Heat of Hydration

It is the quantity of heat in joules/gm of unhydrated cement evolve upon complete hydration at a given temperature

Method of determining heat of hydration is by measuring heat of solution of unhydrated and hydrated cement in a mixture of nitric and hydrofluoric acids.

Method is described in (ASTM C 186-94) and (BS 4550) section 3.8:1978

Heat of hydration of 1 gm cement is given by

136(C3S)+62(C2S)+200(C3A)+30(C4AF)



blended cement There are many ways to prepare a blended cement.

Grind cemetitious materials with clinker

Mix two or three materials in their final form

Mix Portland cement with some cementitious materials in concrete mixer.





Types of cementitious materials

As per ASTM C150-94 or C 595-94atypes of cement are given in table.



Types of Cement



Compound Composition of different type of OPC



Types of Cement

Ordinary Portland cement (Type-I)

Used in general concrete construction where there is no exposure to sulphates in soil or ground water. ENV 197-1 :1992.specific surface 300 – 400 m2/kg

Modified Cement (Type-II)

The rate of gain of strength is similar to OPC.

The rate of heat development is higher than a low heat cement.



Types of Cement Rapid hardening Portland cement (Type-III)

It is used where high early strength is required or where formwork is required for reuse or where quick construction is required.

High early strength cause high rate of heat development.

Higher C3S content (more than 55% up to 70%) and finer grinding of clinker cause increase rate of strength gaining. specific surface 450 – 600 m2/kg

It should not be used for mass construction works (Dam) or for large structural sections.

Setting time of OPC and rapid hardening cement is same i.e. not less than 45 minutes.



Types of Cement Low heat Portland cement (Type-IV)

Due to low thermal conductivity of concrete the rise in temperature in the interior of concrete mass can lead to serious cracking.

In this types of cement the rate of gain of temperature is low and limited to 250 J/g (60 cal/g) at 7 days and 290 J/g (70 cal/g) at 28 days.

Low content of C3S and C3A results in a slower development of strength.

Specific area for these cement should not be less than 320 m2/kg.

ASTM C150-94 covers the detail of low heat cements.MUHAMMAD ARSLAN, DEPARTMENT OF CIVIL


Types of Cement

Sulfate resisting Cement (Type-V) Calcium aluminates in cement can react with sulfate salt

which will increase the volume and cause disintegration of concrete.

Where Sulfate attack is suspected (i.e. shore areas, underground areas) SR cements are suitable.

C3A content must be low 3.5% as per BS 40027 : 1991

ASTM C150-94 covers the detail of Sulfate resisting Cements.



Types of Cement White cement and Pigments

These cements contain very low Iron Oxide (less than 0.3% by mass of clinker) and Manganese Oxide. China clay with Chalk o limestone is generally used.

White cement satisfy the BS 12 : 1991

Pigments used for different colours in cement like …

Iron oxides can produce Yellow, Red Brown and Black.

Chromic Oxides produces green colour

Titanium Dioxides produces White colour.

BS 1014 : 1975 for PigmentsMUHAMMAD ARSLAN, DEPARTMENT OF CIVIL


Types of Cement

Port Land Blast furnace cement It is a mixture of OPC and ggbs (ground granulated blast

furnace)

Slag is a waste product in the manufacturing of Pig Iron (300 kg slag/ton of Pig Iron)

Supersulfated Cement It is highly resistant to high concentration of sulfates

80-85 % blast furnace slag 10-15 calcium sulfate 5%portland cement clinker.

Suitable for mass concrete works (170 -190 J/g 40 -45 cal/g)



Types of Cement Anti-bacterial Cement

It’s a Portland cement interground with a antibacterial agent which prevents microbiological fermentation.

Used in food processing plants, swimming pools etc.

Hydrophobic Cement

It is a special type of cement and it can be stored for a long time under unfavorable conditions.

Hydrophobic properties are due to the formation of an water-repellent film around each particle of cement.

This cement is obtained if OPC is grinding with 0.1 to 0.4 % of Oleic acid, stearic acid or Pentachlorophenol.

Oil-well cements

It is used for grout or slurry to be pumped to depth of thousands meters (Temperature 150-300oF and 100Mpa pressure)



Types of Cement High Alumina Cement

It gain strength at a very high rate i.e 80% strength in 24 hours.

Good to resist sulfate attacks

It contains about 40% alumina and lime 15% of ferrous and ferric oxides 5% slica small amount of magnesia

Raw material are limestone and bauxite



Aggregate Aggregate is an inert material used in concrete to gain

volume stability, durability and economy.

Theoretically aggregate is not 100% inert, its physical and chemical properties effects the concrete properties.



Types of aggregate As per BS 882 : 1992 basic division between corse

aggregate and fine aggregate (sand) is 5 mm or 3/16 “ sieve

As per ASTM No.4 ASTM (4.75 MM) is the dividing line for coarse and fine aggregates.

BS 812 : Part I : 1975 explain two types of classification for aggregate.

Classification of natural aggregate

Particle shape classification



Types of aggregates

Classification of natural aggregate



Particle shape classification



Fine Aggregate Bulking of Fine Aggregate

It is defined as the increase in the volume of a given mass of sand caused by the films of water surrounding the particles and pushing them apart.



Water Water containing less than 2000 ppm dissolved solids can generally be used satisfactorily for making concrete.

Sodium carbonate in water cause rapid setting.

Bicarbonates may either accelerate or retard the setting time.

Large concentration of above two salts reduces the strength.

20,000 ppm of sodium chloride are generally tolerable.

10,000 ppm of sodium sulfate is tolerable.

Magnesium sulfate & magnesium chloride up to 40,000 ppm is tolerable.

Iron salts upto 40,000 ppm is tolerable.

Inorganic salts like (salts of manganese, tin, zink, copper & lead) up to 500 ppm are tolerable.

Sea water containing salts up to 35,000 ppm are tolerable.

Acidic water containing hydrochloric acid, sulfuric acid up to 10,000 ppm have no effect.



Water Potassium hydroxide up to 1.2% by wt. is tolerable. Industrial waste having less than 4000 ppm total solids cause up to

10% reduction in compressive strength. Raw Sewage contain up to 400 ppm of organic matter. Diluted

sewage contain up to 20 ppm, which has little effect on the strength of concrete.

Sugar in water up to 0.03%-0.15% by wt. retard the setting time of cement.

Sugar 0.15% - 0.2% accelerate the setting time. Sugar greater than 0.25% accelerate the setting time but reduce 28

days strength. Sugar in water, less than 500 ppm has no effect at all. Suspended clay or fine rock particles up to 2000 ppm can be

tolerated. Mineral (petroleum) oils greater than 2% by wt. reduces the

strength more than 20%. Algae cause large amount of air to be entrained and they also reduce

the bond between aggregate and cement paste thus cause reduction in strength.



Water Cement ratio (W/C ratio) It is the ratio of the

quantity of water to the quantity of cement.

It can be by volume or by weight.

Water cement Ratio (W/C Ratio)

Qty. of water per bag (50 kg)

W/C

ratio

W/C by Volume W/C by Weight



Batching & mixing of concrete Batching

Batching means measuring of the ingredients of concrete. It is of two types

Batching by volume

Batching by weight

Mixing

Mixing is of two type

Hand mixing

Machine mixing



Batching by volume (ASTM C 685-94) In volumetric batching, ingredients of concrete are mixed by volume.

Buckets are used to measure volume of each ingredient.

Normally volume of one cement bag is considered as standard (its volume is 1.25 ft3)

Sand volumes are computed by using bulking factors. No additional quantity is added for coarse aggregate

due to moisture. Quantity of water is effected by the moisture of fine

and coarse aggregate so minimum desirable computed net quantity of water must be added.



Bucket for measuring ingredients of concrete



Batching by weight It is more accurate method of batching.

Each ingredient of concrete is weighted and mixed.

Weighting coarse aggregate is a laborious work.

Batching plants are available now a day. They are expansive and can be recommended for large projects, where the quantity of concrete is considerable.

Batching plants are of three types.

1. Swinging hopper type.

2. Horizontal hopper type.

3. Simple weight batcher.MUHAMMAD ARSLAN, DEPARTMENT OF CIVIL


Mixing of concrete Hand mixing

Machine mixing

In hand mixing first aggregate is deposited on a platform then fine aggregate (sand) is added finally cement is spreaded on the dump of materials.

Diagonal parts of material is mixed and processes is repeated for 3 to 4 times until a uniform mixture is achieved.

Water is added preferably by shower or by making a ditch in the material.



Mixing Platform

Machine mixing

Concrete mixers used on building sites must conform BS 1305 :1974

Several types of concrete mixers are available like

1. Pan mixers or forced action mixers (P)

2. Drum mixers1. Tilting mixers (T)

2. Non tilting type mixers (NT)

3. Reversing Drum mixers

3. Specialized mixers (Colloidal mixer)



Tilting mixers (T) The mixing

chamber is called Drum.

It consists of a bowl shaped drum having vanes inside.

For discharging concrete drum can be tilted.



Tilting mixers (T)

It can be with or without hopper.



Non tilting mixer (Reversing drum mixer) Axis of mixer

is always horizontal



Truck mixers They are used

when concrete is required to transport to a long distance

They work with a central batching plant.



Specialized mixers (Colloidal mixer) They are used for shotcreting.

Colloidal mixers are used for mortar mixing.

Cement and water is mixed at a speed of 2000 rev/min then sand is added.

Pre mixing of cement and water allow better hydration



Continuous Mixers ASTM C 685-94 discuss requirements for continuous

mixing and volumetric batching.

Using a modern continuous mixer Placing, compaction and finishing can all be achieved in 15 minutes.



Segregation Segregation can be defined as the seperation of the

constituents of a hetrogeneous mixture so that their distribution is no longer uniform.

Segregation is of two types

1. Separation of coarse aggregate

2. Separation of grout

Practical rules to avoid segregation are discussed in ACI 304R-85



Bleeding Bleeding or water gain is a form of segregation.

Water rise on the surface of freshly mixed concrete.

ASTM C 232-92 describe two methods for finding bleeding.



Nominal Size of Mixer The nominal size of mixer is described by volume of

concrete after compaction (BS 1305 : 1974) it may be as low as one half of the volume of the unmixed ingredients in loose state.

Mixer sizes vary from 0.04 m3 (1-1/2 ft3) up to 13 m3(460 ft3 or 17 yd3).



Uniformity of mixing If quantity of mix less than 1/3 of the nominal capacity of mixer, the resulting mix may not be uniform.

Uniformity of mixing represents the efficiency of mixer. For truck mixer ASTM C 94-94 specify a “Rigid test” taking samples

from about 1/6 to 5/6 points of a batch, difference in properties of two samples should not exceeds the following

Density -------------------------- 16 kg/m3 1 lb/ft3

Air content ---------------------- 1 % Slump ---------------------------- 25 mm 1” %age of aggregate Retained on 3/16” sieve --- 6 % Density of air free mortar ---- 1.6 % Compressive strength ------- 7.5 %

(7 days)



Uniformity of mixing BS 3963 : 1974 (1980) suggest for two samples and

determination of the following.water content as %age of solids 0.1% Fine agg. As %age of total aggregate 0.5%W/C ratio 0.01%

Swedish investigators suggest that uniformity of cement content is the best measure of uniformity of mixing. Variation up to 6% with 20 mm slump is ok. 8 % for mixes of lower workability.

In France a radioactive tracer has been developed to determine the distribution of water or admixture.

US Army corps of Engineers test method CDR-C 55-92specifies taking samples from stationary mixers for mass concrete works and to check their uniformity.



Time of Mixing Time of mixing is infect number of revolutions of mixer !!!!!!

Generally 20 revolution with optimum speed are sufficient.

Mixing time and uniformity got a relationship (Shalon and Reinitz) shown in graph.

Strength of concrete increases with mixing time as shown by Abrams tests up to 2 minutes and after this time slight decrease in strength is observed.

Minimum time of mixing is specified by the mixer manufacturer……… min mixing time for a 0.75m3 or 1 yd3 mixer is I minute ……. Add 15 seconds for each additional 1yd3. it is given by ASTM C 94-94 and ACI 304R-89







Transportation of concrete Concrete can be transported from the mixing place

to its final placement position by following means

1. Wheel barrows

2. Chutes

3. Trucks

4. Belt conveyers.



Testing of concrete

Concrete testing can broadly classified in to two major divisions.

Green concrete Tests.

Workability tests

1. Slump test

2. Compacting factor test

3. ASTM flow test

4. Remoulding test

5. Vebe Test

6. Flow test

7. Ball penetration test

8. Nasser’s K-test

9. Two point testsMUHAMMAD ARSLAN, DEPARTMENT OF CIVIL


Testing of concrete Hardened concrete tests.

Strength in compression

Cube test (BS 1881 : Part 111 :1983)

Cylinder test (BS 1881 : Part 110 :1983) (ASTM C 192-90a

Flexural strength test

Tensile test



Testing of concrete Workability Workability determines the ease of placement and

resistance to segregation. It is the amount of useful internal work necessary to

produce full compaction. Glanville et al) ASTM C 125-93 says “ it is the property determine the

effort required to manipulate a freshly mixed quantity of concrete with minimum loss of homogeneity”

ACI 116R-90 says “it is that property of freshly mixed concrete or mortar which determines the ease and homogeneity with which it can be mixed, placed, consolidated and finished”



Slump test Slump test ASTM C 143-90a and BS 1881 : Part 102 : 1983 Slump test is performed by a frustum of cone

300 mm (12”) high 200 mm (8”) lower side diameter 100 mm (4”) upper side diameter.It is made of steel and open from both sides. Two handles are provided. It is

placed at a steel plate. Concrete of filled in three layers and compacted with (5/8”) dia steel rod. 25 blows per layer. Cone is removed and concrete settle down.

Decrement in height of concrete is called Slump measured to the nearest ½” (5 mm)

Slump is of three types1. True slump2. Shear slump3. Collapse slump



Types of Slump



Slump



Recommended Slump Values for different works Slab -----------------------1” to 2”

Narrow column sections --- 4” to 7”

Vibrating concrete ------1/2” to 1”

General RC. Works ---- 2” to 6”

Road work concrete ---- ¾” to 1-1/2”



Curing of concrete Curing means to keep the concrete moist , nearly

saturated.

Concrete surface is kept moist until the water filled pores filled by hydration products up to the desire extent.

Powers shows that hydration is greatly reduced when the relative humidity within the pores drop below 80%.

Loss from the concrete must be reduced.



Water loss



Water loss





Pumping of concrete

ACI Guide 304R-89 is the relevant document.

Pumps are mainly of three types

1. Piston type pumps or direct acting pumps

2. Squeeze pumps or peristaltic pumps

3. Special pumps

A slump of 50-150 mm is recommended for pumped concrete.

Lubrication of pipes require 0.25 m3/100 mortar for 150 mm diameter pipe.



Pumping of concrete

Pumping capacity of different types of pumps.

Type of Pump Horizontal range Vertical range

Piston type pumps 90 m 30 m

Squeeze pumps 1000 m 120 m

Special pumps 1400 m 430 m



Pumping of concrete

OUTPUT OF CONCRETE PUMPS

Type of Pump Out Put (m3 /hour)

Piston type 130

Squeeze type 20





Reinforcement for concrete Reinforcement in concrete is provided to supplement its tensile strength

deficiency. Reinforcement can be of bar, wires or welded wire fabric. Important properties of reinforcement are

MOE Yield strength Ultimate strength Grade designation Bar size (diameter)

Reinforcement can be of following types.1. Round Bars2. Deformed Bars3. Twisted Bars4. Mesh or fabric5. High tensile wires



Reinforcement for concrete MOE is taken as 29x106 psi or 200x106 MPa.

Grade is the yield strength like Grade 40 steel exhabits 40,000 psi yield strength.

Round bars are available from 3/16” to 2” and in length of 40’.

Deformed bars improves the bond strength between steel and concrete and provided with different shapes rings, projections on the surface.

Twisted bars are prepared by twisting the bars. Yielding zone of these bars are removed by twisting.

Meshes are prepared in different weights from 4-16 lbs/yd2



ASTM approved deformed bars



Types of reinforcement (ASTM)



Additives & Admixtures for concrete

Admixtures are chemicals added to concrete mix (not more than 5%) for achieving specific modifications to the normal properties of concrete.

ASTM C 494-92 classify 7 types of admixtures as follows

Type A Water reducing.

Type B Retarding.

Type C Accelerating.

Type D Water reducing and retarding.

Type E Water reducing and accelerating.

Type F Superplasticizing.

Type G Superplasticizing and retarding.



Prestressed Concrete Definition

Basic Principle

Type of Prestresing

Types of Tendons

Casting



Movement Joints Definition

Types of movement joints

Placement of joints



Concrete MIX DESIGN (PCA)



Useful Links

Concrete

Documents

pozzolanic cement

gm cement

hydraulic cement

low heat cement

joulesgm of unhydrated

final form mix portland

04fe2o3 muhammad arslan

drinking muhammad arslan