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151 10/25/2017 Dr.Ahmad Alfraihat

CHAPTER-5 BONDING MATERIALS

-Cement -Introduction

Manufacture of portland cement Chemistry of cement

Bogues equation Properties of cement compounds

Tests of cement Aggregates

Geological classifications Aggregates classificatins by

Size, Shape, Textures, Specific gravity Physical and Mechanical properties


Introduction

• Ancient Romans were first to use concrete - word of Latin origin- based on hydraulic cement, that is a material which hardens under water.

• Only in 1824 modern cement “Portland Cement” was patented by Joseph Aspdin.


Portland Cement

• Portland Cement: Name given to a cement obtained by intimately mixing together: – Calcareous materials (Lime stone CaO, chalk) – Argillaceous materials (Silica (SiO2) from sand, alumina

(Al2O3) from clay or shale) – and iron oxide (Fe2O3) burning them at a clinkering temperature, and grinding the

resulting clinker. • No materials other than Gypsum (CaSO4.4H2O), water, and

grinding aids may be added after burning.


Manufacture of Portland Cement

• Crushing the raw material. • Grinding raw materials into a very fine powder. • proportioning. • Mixing. • Burning in a large rotary kiln (7m diameter and 230 m long,

slightly inclined) at temperature of 1400oC. • Product is called clinker which is cooled down and ground to a

very fine powder (1.1X1012 particles/kg). • Some gypsum added (to prevent flash-setting of cement) and

the resulting product is the commercial Portland cement.


Cement Microstructure


Chemistry of Cement

• Main Compounds in Portland Cement Compound Oxide Composition Abbreviation

Tricalcium Silicate 3CaO.SiO2 C3S

Dicalcium Silicate 2CaO.SiO2 C2S

Tricalcium Aluminate 3CaO.Al2O3 C3A

Tetracalcium Aluminoferrite

4CaO.Al2O3. Fe2O3 C4AF

C= CaO S= SiO2 A = Al2O3, F = Fe2O3

H = H2O,

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Bogue’s Equation

• Bogue’s equations are used to find the percentage of main compounds in cement.

C3S= 4.07(CaO) – 7.60(SiO2) – 6.72(Al2O3) -1.43(Fe2O3) – 2.85(SO 3)

C2S= 2.87(SiO2) – 0.754(3CaO.SiO2)

C3A= 2.65(Al2O3) -1.69(Fe2O3)

C4AF= 3.04(Fe2O3)

The terms in brackets represent the percentage of the given oxide in the total mass of the cement.

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Example: Bogue’s Equation

C3S= 4.07C – 7.60 S – 6.72 A -1.43 F – 2.85(SO 3)

C2S= 2.87 S – 0.754 C3S

C3A= 2.65 A -1.69 F

C4AF= 3.04 F

Find the oxide composition for the cement with percentage of main compounds of C3S = 60%, C2S = 18%, C3A = 6%, C4AF = 60%, and SO3 = 3%

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General Properties of Cement Compounds

• C3S and C2S are the most important compounds which are responsible for the strength of hydrated cement paste.

• C3S Hydrates & harden rapidly & is largely responsible for initial setting & early

strength.

• C2S Hydrates & harden slowly and contribute largely to strength increase at ages

beyond one week.

• C3A Undesirable, it contribute slightly to early strength, liberate large amount of heat

which helps in the hydration of C3S and C2S. C3A is beneficial in the manufacture of cement in that it facilitate the

combination of lime and silica. • C4AF Doesn’t affect the behavior significantly, its presence may accelerate the

hydration of the silicates, it reacts with gypsum.


Minor Cement Compounds • In addition to the major compound, there exist minor

compounds such as : MgO, TiO2, MnO3, K2O, and Na2O Their amount is not more than few % of the mass of cement.

• Oxide of Sodium (Na2O) & Potassium (K2O) (Known as Alkalis) are of interest since they react with some aggregates (Alkali-Aggregate reaction) that cause disintegration of concrete and affect the rate of gain of strength of cement.

• Minor compounds refer to their quantity and not necessarily their importance.


Hydration of Cement

• Both silicates require approximately the same amount of water for hydration, but C3S produce more than twice as much as Ca(OH)2 as is formed by the hydration of C2S.

• The reaction of C3A with water is very rapid and would lead to a flash set, which is prevented by the addition of Gypsum to the cement clinker.

• C3A requires more water for hydration than the silicates.

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Heat of Hydration & Strength • Heat of hydration: the quantity of heat (in joules) per

gram of cement evolved upon complete hydration at a given temperature.

• About one-half of the total heat is liberated between 1 & 3 days.

• About 3/4 of total heat is liberated in 7 days.

• Nearly 90% of total heat is liberated in 6 months.


Heat of Hydration & Strength

• Rate of heat of hydration depends on: 1. Mixtures added 2. Temperature 3. Degree of fineness 4. Amount of water 5. Cement type


Tests on Cement • Quality of cement is vital for production of good concrete. • Quality control is achieved by performing some tests in the

cement plant LAB. • Tests are also needed to conform to requirements of national

standards. • Cement tests are also necessary for periodic acceptance tests. • Tests for chemical composition will not be covered in this

course. • Fineness tests, setting times, soundness tests, an • strength tests will be briefly covered.


Fineness of Cement

• Hydration starts at the surface of cement particle, thus the total surface area of cement represent the material available for hydration.

• Rate of hydration depends of the fineness of cement particle. Thus for rapid development of strength a high fineness is necessary.

• Test: Determination of Specific Surface (m2/kg) .


Consistence of Standard Paste

• To determine the initial and final setting times and soundness tests, cement paste of standard consistence has to be used.

• It is necessary to determine for any given cement the water content which will produce a paste of standard consistence Normal Consistency.

• Normal Consistency is determined by the Vicat apparatus: • Vicat apparatus: Measures the depth of penetration of a

10mm diameter plunger under its own weight.


Vicat Consistency Apparatus


Setting Time • Term used to describe the stiffness of the cement paste.

• Setting refers to a change from liquid to rigid state.

• Initial set (corresponds to rapid rise) & final set (correspond

to the peak temperature). • False set: Some times occurs within few minutes of mixing

with water. No heat is evolved and concrete can be remixed with no addition of water.

• Flash set: Occurs when C3A reacts with water rapidly which would lead to a flash set. Characterized by the liberation of heat.


Initial Setting Time • Initial setting time: Time required for the paste to change

from liquid state to plastic state. • Using Vicat apparatus

The time in which a1mm diameter needle acting under prescribed weight on Normal consistency paste penetrates to a point (5mm) from the bottom of special mold.

(BS: Min. of 45 min. and higher for lower strength class) • Using ASTM C191-92

The time in which a1mm diameter needle acting under prescribed weight on Normal consistency paste penetrates (25mm).

(smaller depth of penetration than Vicat in BS) (ASTM: Min. of 60 min.)


Final Setting Time

• It occurs when the paste harden. • Final setting = time when the needle doesn’t

sink visibly in the paste or when the needle makes an impression on the paste surface.

• BS: Max of 10 hrs Final time (min.) = 90 + 1.2 [Initial time (min)]


Setting Time using Gillmore Test

• Gillmore Test (ASTM C266-89) • The initial setting time is the time required for the

test specimen to bear the initial Gillmore needle (113.4 g and a tip diameter of 2.126 mm) without appreciable indentation, while the time required for the test specimen to bear the final Gillmore needle (453.6 g and a tip diameter of 1.066 mm) without appreciable indentation is the final setting time.


Gillmore Test Apparatus


Factors Affecting Setting

• Fineness of the cement: finer cement accelerates setting.

• Chemical composition of cement: Tricalcium Aluminate (C3A) and tricalcium silicate (C3S) decrease the setting time.

• Amount of Water: High water content increase the setting time

• Ambient Temperature: High ambient temperature decreases the setting time.


Soundness Test • Cement Paste after setting may under go a large change in

volume (expansion) which cause disruption of the hardened concrete.

• Expansion can be due to reaction of CaO, MgO, & Ca(SO4) • Cements exhibit this type of expansion are classified as

unsound. • Le Chatelier accelerated test (BS EN 196-3:1995) for

detecting unsoundness due to free lime • Autoclave test (ASTM C151-89) for detecting unsoundness

due to Magnesia (MgO) and lime. • No test is available to detect soundness due to excess of

Calcium Sulphate but may be done by chemical analysis.


Le Chatelier accelerated test • Cement paste of normal consistency is stored in water for

24hrs. • Expansion after boiling in water for 1hr and cooling to room

temp is determined. • If expansion exceed a specified value (10mm), further test is

made after cement has been spread and aerated for 7 days. • At the end of the 7 days lime may be hydrated or carbonated. • A second expansion test should fall within 50% of the original

specified value. • A cement failing to satisfy one of these tests should not be

used. • Unsoundness due to lime is rare.


Autoclave test (ASTM C151-89)

• Normal consistency cement paste specimen of known length is cured in humid air for 24hrs. then heated by high pressure steam for 1hr so the temperature of 216oC is attained.

• Attain temp. & pressure for further 3hrs, then the pressure is reduced within 1.5 hrs, and specimen is cooled in water for 15 min. to reach 23oC.

• after another 15 minutes, Length of specimen is measured.

• Expansion due to autoclaving must not exceed 0.8% of the original length


Strength of Cement • Strength tests are not conducted on neat cement

paste because its difficult to obtain good specimen and the variability in test results due to that.

• Cement-sand mortar (cement + sand + water) specimens are used to determine the strength of cement.

• Strength tests: – Direct tension – Compression – Flexural


Compressive Strength of Cement

• BS EN 196-1:1995 Mortar prism test. – Strength classes

• N: Normal • R: Rapid hardening properties

• ASTM C109-92 (Compressive Strength of Hydraulic Cement Mortars using 2-in. or [50-mm] Cube Specimens) – Cement-sand mix (1: 2.75) – Water/cement ratio = 0.485 – 50 mm cubes – Cube samples are cured in saturated lime water at 23oC – Compressive strength = load @ failure/ cross section area.

• ASTM C349-82 (Compressive Strength of Hydraulic-Cement Mortars using Portions of Prisms Broken in Flexure).


Flexural Test

• ASTM C348-93 (Flexural Strength of Hydraulic-Cement Mortars). – Mortar prism (40 x 40 x 160 mm) loaded at mid span. – Mix proportions, storage, and curing are same as compressive strength

test.

Sf = 0.0028 P where: S f = flexural strength, MPa, and P = total maximum load, N.

– Sf = (M/I) y ………. Y =h/2, M=Pl/4, I= bh3/12


Cube & Prism Molds


Direct tension

• Briquette mold samples of cement mortar. • Fixed and pulled apart at specified rate. • Tensile strength = T/A • A = 1 in2


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