materials coursework

Question One

What is soundness of cement?

When referring to Portland cement, “soundness” refers to the ability of a hardened cement paste to retain its volume after setting without delayed destructive expansion (PCA, 1988). This destructive expansion is caused by excessive amounts of free lime (CaO) or magnesia (MgO)

In the soundness test a specimen of hardened cement paste is boiled for a fixed time so that any tendency to expand is speeded up and can be detected. Soundness means the ability to resist volume expansion

Procedure

1. Before commencing setting time test, do the consistency test to obtain the water required to give the paste normal consistency (P).

2. Prepare a paste by adding 0.78 times the water required to give a paste of standard consistency (i.e. 0.78P).

3. Lightly oil the Le-chatelier mould and place it on a lightly oiled glass sheet.4. Fill the mould with the prepared cement paste. In the process of filling the mould keep

the edge of the mould gently together.5. Cover the mould with another piece of lightly oiled glass sheet; place a small weight on

this covering glass sheet.6. Submerge the whole assembly in water at a temperature of 27 ± 20 C and keep there for

24 hours.7. Remove the whole assembly from water bath and measure the distance separating the

indicator points to the nearest 0.5 mm (L1).8. Again submerge the whole assembly in water bath and bring the temperature of water

bath to boiling temperature in 25 to 30 minutes. Keep it at boiling temperature for a period of 3 hours.

9. After completion of 3 hours, allow the temperature of the water bath to cool down to room temperature and remove the whole assembly from the water bath.

10. Measure the distance between the two indicator points to the nearest 0.5 mm (L2).

Calculations

Soundness/expansion of cement = L1-L2

L1=Measurement taken after 24 hours of immersion in water at a temperature of 27 ± 20 C

L2=Measurement taken after 3 hours of immersion in water at boiling temperature.

Calculate the mean of two values to the nearest 0.5 mm.

CONSTRUCTIONMATERIALSATHIYO MARTIN 1

Note::In the event of cement failing to comply with the specified requirements, a further test should be made from another portion of the same sample in manner described above, but after aeration (done by spreading out to a depth of 75 mm at a relative humidity of 50 to 80% for a total period of 7 days).

Precautions

All the measurements should be done accurately. Do not apply extra pressure while filling the moulds. During boiling water level should not fall below the height of the mould.


Question Two:

Write short descriptive notes on the following types of cement.

I. Portland blast furnace slag cementII. Portland pulverized fuel ash cement

III. Portland low heat cementIV. High alumina cementV. Super sulphate cement

VI. White cement:

SOLUTION:

1) Portland blast furnace slag cement

Portland Blast Furnace Slag Cement (P.B.F.S.C.)

By intergrinding B.F.S.+P.C. Clinker+Gypsum This cement is less reactive (rate of gain of strength & early strength is less but ultimate

strength is same) High sulfate resistance Suitable to use in mass concrete construction Unsuitable for cold weather concreting

Both P.P.C.&P.B.F.S.C. Are called blended cements. Their heat of hydration & strength development are low in early days. Because upon adding water C3S compounds start to produce C-S-Hgels & CH. The Ch & the pozzolanic material react together to produce new C-S-H gels. That’s why the early strength is low but the ultimate strength is the same when compared to O.P.C.

2) Portland pulverized fuel ash cement

Definition:

Fly ash, also known as pulverized fuel ash (pfa) is the ash resulting from the burning of pulverised coal in coal-fired electricity power stations. The ash is very fine and it is removed from the flue gases by electrostatic precipitators.

The chemical composition of pfa is somewhat different from Portland cements. It will not hydrate with water directly but needs lime and water to hydrate. In concrete the lime required arises from the hydration of the cement. Fly ash is always used in combination with Portland cement, typically in the range 80% Pc and 20% fly ash to 60% Pc and 40% fly ash, depending on the application.


The blended cement can be supplied as a pre-blended factory produced product or be prepared in the mixer by adding each material separately from its own silo. Fly ash/pc blend mixes tend to be slower to hydrate than similar Pc only mixes, but may have improved durability

3) Low Heat Cement:

Definition

It is a special cement that minimizes the amount and rate of heat generation during hydration (setting). Strength is also achieved at a slower rate. Use is limited to structures involving large masses of concrete, such as dams, where the heat generated would be excessive if normal cement were used.

● Low-heat Portland Cement, is one of hydraulic binding materials, also named Low Heat Cement, High Performance Low Heat Cement, or High Belite Cement. Code Number P·LH. ● Low Heat Cement has excellent performances such as high final strength, sulfate corrosion resistancing, good lasting properties, good resistance to rupture, etc. ● Because of its excellent performances for example lower hydration heat, high late strength, sulfate resistancing, anti-seepage and resistance to rupture etc., Low Heat Cement is widely applied in building dam, bank of river, wall of sea, and other hydraulic engineering concrete and marine concrete.● Grade: 42.5 Characteristics ● Low heat of hydration: comparing with grade 42.5 portland cement, its value of hydration heat is low about 20%, ultimate value of temperature up is low about not less than 15%, so P·LH. is very fit to apply in making mass concrete; ● Lower water requirement ● High lasting properties ● High fluidity ● Good volume stabilization ● High growth rate of final strength ● High technical strength of concrete ● Excellent impact erosion ● Excellent wear resistance ● Lower temperature upward value of heat insulation ● Super-high performance of chemical corrosion resistance: when Low-heat Portland Cement is cured in 3% solution of Na2SO4 for 6 months, its erosion resistance factor is more than 0.97, higher near 1 multiple than Ordinary Portland Cement(OPC), so it has good corrosion resistance performance especial to sulfate. To other erosion medium for example sea water and chloride, its corrosion resistance performance is obviously superior to OPC. ● Excellent resistance to drying shrinkage● Good resistance to rupture


4) High alumina cement:

High Alumina Cement (HAC) differs from Portland cement, being composed calcium aluminates rather than calcium silicates. Its rapid strength development made HAC popular from 1950 to 1970. However, mineralogical ´conversion´ sometimes caused reductions in concrete strength and increased vulnerability to chemical attack. HAC is also known as Calcium Aluminate Cement (CAC).

5) 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 & crackin

6) White Portland Cement

W.P.C. İs made from materials containing a little iron oxide & manganese oxide.

Fe2O3 + MnO ≤ 0.8%

To avoid contamination by coal ash, oil is used as fuel.

To avoid contamination by iron during grinding, instead of steel balls nickel-molybdenum alloys are used.


materials coursework

Documents