2. Decide whether the following statements are true or false according to the text.

1. The foundation is a structural component of any structure of a very limited significance. 2. Foundation, plinth, wall, column are main load bearing elements of a building.

3. Floor, slab, beam, lintel are supporting structural elements of a building.

4. Floors divide a building into different levels so that creating more accommodation on a given plot of land.

5. The stair should be constructed in such a manner that it is safe and comfortable to use and it should be so located as to prevent easy communication.

3. Answer the following questions and give examples.

1.What structural element of a building is the most important one which bears the rest of the building?

2.What is the difference between a supporting element and a load bearing element of a building?

3.What is the difference between a girder and a beam?

4.Can a slab be used as foundation?

5.Which one is the uppermost component of a building and what purpose is being used for?

TEXT 16

1. Answer the following question and read the text below to check your answer.

What are the properties of composite building materials that should be put forward?

The need for materials with properties not found in conventional materials, combined with advances in technology, has resulted in combining two or more materials to form what are called composite materials. These materials usually combine the best properties of their constituents and frequently exhibit qualities that do not even exist in their constituents. Strength, stiffness, specific weight, fracture resistance, corrosion resistance, wear resistance, attractiveness, fatigue life, temperature susceptibility, thermal insulation, thermal conductivity, and acoustical insulation can all be improved by composite materials.

Of course, not all these properties are improved in the same composite, but typically a few of these properties are improved. For example, materials needed to build aircraft and space vehicles must be light, strong, and stiff and must exhibit high resistance to abrasion, impact, and corrosion.

Fiber Reinforced Polymer (Fiber Reinforced Plastic) is an example of a composite material that is very useful for civil engineers. It is strong, stiff, and corrosion resistant, and can be used to make concrete reinforcing rebars to eliminate the corrosion problem of steel rebars. These combinations of properties are formidable and typically cannot be found in a conventional material.

Composite materials have been used throughout history, with differing levels of sophistication. For example, straw was used to strengthen the mud bricks in ancient civilizations. Swords and armor were constructed with layers of different materials to obtain unique properties. Portland cement concrete, which combines paste and aggregate with different properties to form a strong and durable construction material, has been used for many years. In recent years, fiber-reinforced concrete has been used as a building material that is strong in both tension and compression. The automobile industry has been using composite metals to build lightweight vehicles that are strong and impact resistant. Recently a new generation of composites, such as fiber-reinforced and particle-reinforced plastics, has revolutionized the material industry and opened new horizons for civil and construction engineering applications. Although several definitions of composites exist, it is generally accepted that a composite is a material that has two or more distinct constituent materials or phases.

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The properties of composite materials are affected by the component properties, volume fractions of components, type and orientation of the dispersed phase, and the bond between the dispersed phase and the matrix. The properties of the composite can be viewed as the weighted average of the properties of the components. Equations can be derived to estimate the composite properties under certain idealized material properties, loading patterns, and geometrical conditions. Assumptions that can be used to simplify the analysis include the following:

–each component has linear, elastic, and isotropic properties;

–a perfect bond exists between the dispersed and matrix phases without slipping.

2. Decide whether the following statements are true or false according to the text.

1.The need for materials with properties not found in conventional materials, has resulted in using only one material to form what are called composite materials.

2.Composite materials have been used throughout history, with differing levels of sophistication.

3.50 years ago a new generation of composites, such as fiber-reinforced and particle-reinforced plastics, revolutionized the material industry and opened new horizons for civil and construction engineering applications.

4.The properties of composite materials are affected by the component properties, volume fractions of components, type and orientation of the dispersed phase, and the bond between the dispersed phase and the matrix.

5.The properties of the composite can be viewed as the sum of the properties of the components.

3. Answer the following questions and give examples.

1.What is a composite material?

2.List some composite materials that you use in your daily life.

3.List five different advantages of composite materials over conventional materials.

TEXT 17

1. Answer the following question and read the text below to check your answer.

What are the main functions of mortar? Is it possible to make up fabric without mortar?

Mortar is a mixture of cementitious material, aggregate, and water. Mortar can be classified as cement-lime mortar, cement mortar, or masonry cement mortar. Mortar is used for the following functions:

–bonding masonry units together, either non-reinforced or reinforced;

–serving as a seating material for the units;

–leveling and seating the units;

–providing aesthetic quality of the structure.

Mortar is manufactured in four types: M, S, N and O. Mortar also needs to satisfy either proportion specifications or property specifications (ASTM C270). The proportion specifications specify the ingredient quantities, while the property specifications specify the compressive strength, water retention, air content and the aggregate ratio. Mortar can be evaluated either in the laboratory or in the field. In the laboratory evaluation, the compressive strength of mortar is tested using 50-mm (2-inch) cubes according to ASTM C109.

The minimum average compressive strengths of types M, S, N, and O at 28 days are 17,2 MPa, 12,4 MPa, 5,2 MPa and 2,4 MPa (2500 psi, 1800 psi, 750 psi, and 350 psi) (ASTM C270). The field evaluation involves the preparation of one or more trial batches before construction. These trial batches are sampled and used in establishing the plastic and hardened properties of the mixtures (ASTM C780). Mortar starts to bind masonry units when it sets. During construction, bricks and blocks should be rubbed and pressed down in order to force the mortar into the pores of the masonry units to produce maximum adhesion. It should be noted, however, that mortar is the weakest part of the masonry wall. Therefore, thin mortar layers generally produce stronger walls than do thick layers.

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Unlike concrete, the compressive strength is not the most important property of mortar. Since mortar is used as an adhesive and sealant, it is very important that it forms a complete, strong, and durable bond with the masonry units and with the rebars that might be used to reinforce masonry walls. The ability to bond individual units is measured by the tensile bond strength of mortar (ASTM C952), which is related to the force required to separate the units. The tensile bond strength affects the shear and flexural strength of masonry. The tensile bond strength is usually between 0,14 MPa and 0,55 MPa (20 psi to 80 psi) and is affected by the amount of lime in the mix.

Other properties that affect the performance of mortar are workability, tensile strength, compressive strength, resistance to freeze and thaw, and water retention. ASTM C91 defines water retention as a measure of the rate at which water is lost to the masonry units.

Grout is a high-slump concrete consisting of Portland cement, sand, fine gravel, water, and sometimes lime. Grout is used to fill the cores or voids in hollow masonry units for the purpose of:

–bonding the masonry units;

–bonding the reinforcing steel to the masonry;

–increasing the bearing area;

–increasing fire resistance;

–improving the overturning resistance by increasing the weight.

The minimum compressive strength of grout is 14 MPa (2000 psi) at 28 days, according to ASTM C476.

Plaster is a fluid mixture of Portland cement, lime, sand, and water, which is used for finishing either masonry walls or framed (wood) walls. Plaster is used for either exterior or interior walls. Stucco is plaster used to cover exterior walls. The average compressive strength of plaster is about 13.8 MPa (2000 psi) at 28 days.

Masonry is one of the oldest building technologies, dating back to use of sundried adobe blocks in ancient times. Modern masonry units are produced to high standards in the manufacturing process. While the strength of the masonry units is important for quality control, the strength of masonry construction is generally limited by the ability to bond the units together with mortar. The ability of masonry units to resist environmental degradation is an important quality consideration. This ability is closely related to the absorption of the masonry units.

Vocabulary:

Mortar — строительный раствор.

Water retention — удержание воды. Trial batches — пробные партии.

To rub — потереть.

Shear and flexural strength — прочность на сдвиг и изгиб.

Grout — раствор.

High-slump concrete — бетон с высоким осыпанием.

2.Decide whether the following statements are true or false according to the text.

1.Mortar is a mixture of cementitious material, aggregate, and water.

2.Mortar is manufactured in five types: M, S, N, O, and J.

3.During construction, bricks and blocks should be rubbed and pressed down in order to force the mortar into the pores of the masonry units to produce maximum adhesion.

4.The tensile bond strength affects the compressive and tensile strength of masonry.

5.Plaster is a fluid mixture of Portland cement, lime, sand, and water, which is used for finishing either masonry walls or framed (wood) walls.

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3. Answer the following questions and give examples.

1.Define solid and hollow masonry units according to ASTM C90.

2.What are the advantages of masonry walls over framed (wood) walls?

3.What is the mortar made of? What are the functions of the mortar?

4.What is the grout? What is the grout used for?

5.What are the ingredients of the plaster? What is it used for?

TEXT 18

1. Answer the following question and read the text below to check your answer.

What pavements do you know? What is the difference between asphalt and tarmac?

Asphalt used in pavements is produced in three forms: asphalt cement, asphalt cutback, and asphalt emulsion. Asphalt cement is a blend of hydrocarbons of different molecular weights. The characteristics of the asphalt depend on the chemical composition and the distribution of the molecular weight hydrocarbons. As the distribution shifts toward heavier molecular weights, the asphalt becomes harder and more viscous. At room temperatures, asphalt cement is a semisolid material that cannot be applied readily as a binder without being heated. Liquid asphalt products, cutbacks and emulsions, have been developed and can be used without heating . Although the liquid asphalts are convenient, they cannot produce a quality of asphalt concrete comparable to what can be produced by heating neat asphalt cement and mixing it with carefully selected aggregates.

Asphalt cement has excellent adhesive characteristics, which make it a superior binder for pavement applications. In fact, it is the most common binder material used in pavements. A cutback is produced by dissolving asphalt cement in a lighter molecular weight hydrocarbon solvent. When the cutback is sprayed on a pavement or mixed with aggregates, the solvent evaporates, leaving the asphalt residue as the binder.

In the past, cutbacks were widely used for highway construction. They were effective and could be applied easily in the field. However, three disadvantages have severely limited the use of cutbacks. First, as petroleum costs have escalated, the use of these expensive solvents as a carrying agent for the asphalt cement is no longer cost effective. Second, cutbacks are hazardous materials due to the volatility of the solvents.

Finally, application of the cutback releases environmentally unacceptable hydrocarbons into the atmosphere. In fact, many regions with air pollution problems have outlawed the use of any cutback material. An alternative to dissolving the asphalt in a solvent is dispersing the asphalt in water as emulsion. In this process the asphalt cement is physically broken down into micron-sized globules that are mixed into water containing an emulsifying agent. Emulsified asphalts typically consist of about 60 to 70 % asphalt cement, 30 to 40 % water, and a fraction of a percent of emulsifying agent. There are many types of emulsifying agents; basically they are a soap material. The emulsifying molecule has two distinct components, the head portion, which has an electrostatic charge, and the tail portion, which has a high affinity for asphalt. The charge can be either positive to produce a cationic emulsion or negative to produce an anionic emulsion. When asphalt is introduced into the water with the emulsifying agent, the tail portion of the emulsifier attaches itself to the asphalt, leaving the head exposed.

The electric charge of the emulsifier causes a repulsive force between the asphalt globules, which maintains their separation in the water. Since the specific gravity of asphalt is very near that of water, the globules have a neutral buoyancy and, therefore, do not tend to float or sink. When the emulsion is mixed with aggregates or used on a pavement, the water evaporates, allowing the asphalt globs to come together, forming the binder.

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