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. reduced B. examples C. reinforcing D. term

E. aggregates F.manufactured G. need H. pumice I. advantages

J. ranging K. porous L. retains

1. The properties of lightweight concrete has some remarkable …… .

2.. While the …… “lightweight concrete” sounds strange, the material itself is anything but contradictory.

3. Roofing, walls, fences, ornaments, vaulted ceilings, sculptures, stairs, doors, even canoes are good …… of the usefulness of this material.

4. These expanded aggregates incorporate air into a porous structure which …… some degree of structural strength.

5. Less …… steel is required and a lower dead load of the structure can be achieved.

6. Lower construction material costs result and when using precast pieces shipping, handling, and placement costs are also …… .

7. They can also be …… by heating some types of clay, shale, slate, and obsidian in a rotary kiln.

8. Regular Portland cement concrete production consists of loading …… (gravel and sand), cement, and water.

9. When used in structural concrete, the mix has a density …… from 90 pounds per cubic foot up to about 115 pounds per cubic foot.

10. To make concrete lighter, more air and/or lighter aggregates …… to be used.

UNIT 14

What is Fly Ash Concrete?

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

A significant amount of energy is generated by burning coal in power plants throughout the world. This energy is one of the most significant sources used for generating electricity. When the coal burns in a power plant, it not only generates energy but also produces a powder kind of material, which is slowly becoming a vital ingredient of all the concrete products. This powdery material is known as fly ash.

How is Fly Ash Formed? Another source of fly ash are the boilers from industrial plants that uses pulverized coal or lignite as fuel. Coal is not completely carbon. It contains quantities of non-combustible minerals. When coal burns in power plants and boilers, it leaves behind molten particles rich in silica, alumina, and calcium. These particles come together and solidify to form glassy spherical particles which are finer than the cement particles. These particles are collected from the exhaust before they fly away and are used in making concrete products.

Fly ash, also known as pulverized ash, constitutes about 80 percent of the total ash, generated by a boiler or a power plant. The rest of the 20 percent ash, known as heavy ash, gets collected at the bottom of the boiler and can be used in structural fill applications and for manufacturing concrete blocks.

Usage. Fly ash is used in a variety of applications involving structural and low strength requirements. It is also used as a mineral filler in paints, shingles, carpet backing, and other similar products. It is an important constituent in manufacturing of mortars, stuccos and many agricultural products. But the most important usage of fly ash is in making concrete.

Classification of Fly Ash. Fly ash is classified into two types on the basis of its chemical composition. The two main types are :

Class F - This type of fly ash is produced from burning anthracite or bituminous coal. It contains a low concentration of lime and a higher concentration of silica, aluminum, and iron. It is supposed to be known as the ideal cementitious material in making mass concrete and high strength mixes. It is mainly used in places where the concrete may be exposed to sulphate ions in ground and water.

Class C - This type of fly ash is produced from burning of sub-bituminous coal and lignite. It has higher lime content and unique self hardening characteristics. It is generally used in soil stabilization as it doesn't require adding lime. It is also useful in performance mixes and pre-stressed applications.

The amount of fly ash in the Portland cement will vary on the basis of chemical composition of both fly ash and Portland cement. It is to be noted that the fine aggregate in the cement should be reduced for the additional volume of fly ash, mainly because fly ash is lighter than the cement.

Benefits of Fly Ash Concrete. When fly ash is added to the cement to generate fly ash concrete, the fly ash can do wonders to the concrete production. The fine particles of fly ash can be used to effectively fill voids. The particles are hard and round which allows the concrete to be produced using less water. Moreover, the concrete thus formed requires less energy for pumping. The type of concrete formed, makes it easier to achieve sharp, clear architectural definition without any issues of in-place integrity.

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

Active Vocabulary

1. significant значительный

2. power plant электростанция, силовая установка

3. source источник, первопричина

4. fly ash летучая зола, зольная пыль, измельченная зола, искусственный пуццолан

5. non-combustible негорючий

6. molten расплавленный, литой

7. to solidify затвердевать

8. exhaust выпускать; выпуск, выхлоп, отход

9. to constitute составлять

10. shingle кровельная дранка; гонт

11. stucco штукатурка, штукатурный гипс

12. sulphate сернокислый; сульфат, соль серной кислоты

13. cementitious цементирующий; вяжущий

14. sub-bituminous полубитуминозный

15. self hardening самозакаливание, самоотвердение

16. to reduce уменьшать, сокращать

17. additional дополнительный

18. to generate производить, вызывать

19. particle частица

20. void пустота

21. pumping накачивание

22. to achieve достигать

CONTROL TESTS

TEST I

Decide whether these statements are true or false:

1. a). When the coal burns in a power plant, it not only generates energy but also produces a great amount of exhaust.

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

c). When the coal burns in a power plant, it not only generates energy but also produces combustible minerals.

2. a). Fly ash is used in a variety of applications involving roofing, walls, fences, ornaments, vaulted ceilings.

b). Fly ash is used in a variety of applications involving fire resistance requirements.

c). Fly ash is used in a variety of applications involving structural and low strength requirements.

3. a). Fly ash is classified into two types on the basis of its chemical composition.

b). Fly ash is classified into two types on the basis of its flowability rate.

c). Fly ash is classified into two types on the basis of its compressive strength.

4. a). The amount of fly ash in the Portland cement will vary on the basis of the grade of its resistance to aggressive waters.

b). The amount of fly ash in the Portland cement will vary on the basis of its alkali-aggregate reactions.

c). The amount of fly ash in the Portland cement will vary on the basis of chemical composition of both fly ash and Portland cement.

5. a). The fine particlesof fly ash can be used to reduce water and air permeability.

b). The fine particles of fly ash can be used to effectively fill voids.

c). The fine particlesof fly ash can be used to increase the modulus of elasticity of concrete.

TEST II

Match words in columns A and B (synonym match):

A B

1. amount a). evidence b). existence

c). distinction d). quantity

2. throughout a). far b). everywhere

c). above d). abroad

3. vital a). substantial b). regular

c). brittle d). special

4. ash a). lime b). silica

c). cinder d). cement

5. additional a). supplementary b). major

c). residential d). common

6. completely a). directly b). entirely

c). formally d). perfectly

7. backing a). layer b). content

c). decking d). lining

8. to note a). to remark b). to frame

c). to involve d). to adjust

9. wonder a). affair b). work

c). miracle d). tool

10. issue a). breath b). problem

c). being d). pain

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.constitutesabout 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 tosulphate ions in ground and water.

d. stressed under tension.

5. The fine particlesof 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