Test III

Select the best possible answer out of the choices from the list to the statements (multiple choice):

1. When coal burns in power plants and boilers, … .

a. it only produces a powder kind of material.

b. it does not leave any quantities of non-combustible minerals.

c. the only result is generating electricity.

d. it also leaves behind molten particles rich in silica, alumina, and calcium.

2. Fly ash, also known as pulverized ash, … .

a. gets collected at the bottom of the boiler.

b. constitutes about 80 percent of the total ash, generated by a boiler or a power plant.

c. is used in a variety of applications involving high strength requirements.

d. is a vital ingredient of all the concrete products.

3. Fly ash is supposed to be known as … .

a. the ideal cementitious material in making mass concrete and high strength mixes.

b. a material used in post-tensioned applications.

c. a material used in soil stabilization in case of adding lime.

d. a material heavier than the cement.

4. Fly ash is mainly used in places where the concrete may be … .

a. poured directly at the jobsite in large slabs called "tilt-up panels".

b. reinforced with embedded steel bars.

c. exposed to sulphate ions in ground and water.

d. stressed under tension.

5. The fine particles of fly ash can be used … .

a. in many agricultural products.

b. for manufacturing silica.

c. as a mineral filler in paints.

d. to effectively fill voids.

Test IV

Complete the sentences by filling in the correct word that fits a statement (gap fill). Choose the appropriate words from the word bank given below.

A. exhaust B. requirements C. total D. amount

E. composition F. non-combustible G. additional

H. wonder I. form J. voids K. powder L. fuel

1. A significant …… of energy is generated by burning coal in power plants throughout the world.

2. Another source of fly ash are the boilers from industrial plants that uses pulverized coal or lignite as …… .

3. These particles are collected from the …… before they fly away and are used in making concrete products.

4. These particles come together and solidify to …… glassy spherical particles which are finer than the cement particles.

5. Fly ash is used in a variety of applications involving structural and low strength ….

6. The amount of fly ash in the Portland cement will vary on the basis of chemical …… of both fly ash and Portland cement.

7. The fine aggregate in the cement should be reduced for the …… volume of fly ash.

8. The fine particles of fly ash can be used to effectively fill …… .

9. Coal is not completely carbon, it contains quantities of …… minerals.

10. When the coal burns in a power plant, it not only generates energy but also produces a …… kind of material.

UNIT 15

Concrete Mix with Fly Ash

Read, translate the following text and be ready to fulfil the tests:

Fly ash or pulverized fuel ash (pfa) is a finely divided powder thrown out as a waste material at the thermal power plants using pulverized coal for raising steam in the boilers. The fly ash is an industrial waste and great hazard for our environment. In the building industry, the use of fly ash as a part replacement of cement in mortar and concrete at the construction site has been made all over the world and is well known.

The important building materials which can be produced from fly ash are:

- Portland fly ash cement.

- Ready-mixed fly ash concrete.

- Precast fly ash concrete building units.

- Sintered fly ash lightweight aggregate for concrete.

- Lime fly ash cellular concrete.

- Fly ash building bricks.

- Fly ash stabilized high-magnesia cement.

- Oil-well cementing composition.

- Hydraulic binders.

- Bituminous products.

The advantages of fly ash concrete over the corresponding plain cement concrete are:

- Improved workability.

- Lower heat of hydration.

- The increase in creep with fly ash content up to 15% is negligible.

- Increases the modulus of elasticity of concrete when concretes of the same strength with and without fly ash are compared.

- Superior resistance to freezing and thawing.

- Improved sulphate resistance.

- Lower water and air permeability.

- Lower leaching of lime liberated during hydrating of cement.

- Reduced alkali-aggregate reactions.

- Greater resistance to attack of aggressive waters.

Since a huge quantity of cement is used in mass concrete construction and the cost of fly ash is negligible as compared to that of the cement, the use of fly ash concrete brings about a substantial saving in cement consumption and overall construction cost. Fly ash concrete may be used in concrete structures including high strength concrete without any risk of steel corrosion. Researchers have proved that concrete with approved quality fly ash does not induce corrosion of reinforcing steel even in marine and industrial aggressive environments. With proper mix design the 7 and 28-days strength of fly ash concrete may be equal or even more than plain concrete. The 90 days strength of fly ash concrete may be more than 140% of plain concrete.

Read, listen to the pronunciation and memorize the active vocabulary to the text: