Air Pollution

Every smoking chimney turns out to be a source of air pollu­tion. Home furnaces tended to burn soft coal incompletely, thus add­ing unburned carbon particles to the air.

The use of natural gas or oil that have a negligible mineral content is of great help in reducing pollution, but has the disadvan­tage of rapidly consuming materials which could better be con­served for future generation as raw materials for the manufacture, for example, chemicals and plastics.

It has been found that some chemical processes, such as the manufacture of lime, Portland cement, steel, tend to give off much dust.

Lead, bromide and chloride emitted from the exhaust of automobiles which burn lead-containing gasoline produce a lead-chloride-bromide aerosol which is considered to be a common air contaminant in urban areas, it being toxic to people. The chief at­mospheric gaseous pollutants originating from the earth's surface appeared to be oxides of sulphur, oxides of nitrogen, incompletely burned hydrocarbons, and carbon monoxide.

These gases are known to react with energy from sunlight to produce photochemical smog. Smog not only can be highly irritating to eyes and lungs, but it can also cause extensive damage to vege­tation.

There are many problems to be solved concerning the pollu­tion of air.

Water Pollution

Some cities simply run their raw sewage directly into nearby natural waters. This is one of the worst types of water pollution.

Another type of pollution of sea and ocean water is petro­leum oil, it taking place in connection with off-shore drilling opera­tions. It should be also noted that unfortunately there is as yet no satisfactory method of overcoming the effects of oil spills, although many methods have been tried.

Earth Pollution

In addition to air and water, the solid part of the earth is also in danger from pollution. Solid wastes include such things as: metal cans, glass bottles, plastic containers, ashes from the combustion of coal and wood, and radioactive isotopes. The problems created by pollution are very difficult, but fortunately great progress is being made in their solution.

Russia plans to protect the land, its mineral and water re­sources, plants and animals. The atmosphere over cities is the ob­ject of constant care and attention on the part of the government. Each year steps are taken to improve the protection of the atmos­phere from harmful factory pollution.

Hundreds of new devices to trap and neutralize the harmful substances contained in discharged gases go into service. As a re­sult, in more than 70 per cent of cities where the air monitored, dis­charges of dust, sulphur gases and hydrogen sulphide were either stabilized or reduced altogether, harmful industrial pollution of the air of cities and industrial centres having been greatly diminished throughout the country.

Extensive measures are being taken to set up reservations and carry through biotechnical measures for the protection and re­production of species of animals, birds and valuable fish.

Much money is being spent, but it should be noted that money alone is not enough to protect the environment. The attitude of people is vital and much depends on the people.

There will never be complete success unless human beings are taught to use nature with care.

Text 2 Plastics - The Newer Applications In Building

Plastics have now been developed to such an extent that they can be applied to almost every branch of building, from the lay­ing of foundations to the final coat of paint

Plastics products offer many advantages over the materials they replace, such as ease of hancing, iower maintenance costs and rapidity of assembly.

The large range of decorative plastics laminates now avail­able to the architect and builder has brought about a revolution in interior and exterior design. These materials are no longer for deco­ration only, but are made to withstand severe outdoor conditions for varying periods of time and are sufficiently rigid to stand on their own in certain cases without support. They can be worked by all the methods commonly employed by the builder. Many disadvantages have had to be overcome in the development of decorative lami­nates before they could be put on the market, particularly with re­spect to their weathering properties.

A laminate has been developed which is suitable for both inside and outside use. This consists of a paper filler impregnated with thermosetting resins, on top of which is laid similarly impreg­nated paper. The paper itself is topped with a melamine resin treated skin which gives a tough surface, this sandwich being then pressed and subjected to heat. The laminate formed is 5/8 in. thick, and it is claimed to stand up to severe exterior conditions for at least ten years without serious fading. As a complete structural material in itself, it is recommended for exterior work on shopfronts, walls, en­trances, doors, windows. Its chief advantage is that it needs no maintenance other than an occasional wipe down with a damp cloth, and another important property is that curved surfaces can be intro­duced and sharp corners eliminated in areas where hygiene is an essential consideration. For interior use it is recommended for sur­facing - or sometimes as a structural material for kitchens, bath­rooms and lavatory walls, for doors, staircase walls, window sills, etc.

Text 3 Silent Metals

A hundred years ago noise on the main streets of the world's biggest cities did not exceed 61 decibels. Today it is 100 and more. Industrial noise is at very high level at many factories, and in some it reaches 90 to 110 decibels.

Noise is an ever growing inconvenience of modern life, and much of й is generated by vibrations of metals. These vibrations not only cause noise but can also lead to "fatigue" and consequent fai­lure of a structure.

Research into methods which can minimize vibrations in structures is therefore of considerable importance. There are two methods to reduce vibration in an engineering design; either we make the structure so stiff and heavy that it cannot vibrate signifi­cantly, or we introduce "damping" into the structure, that is, we have to introduce some mechanism for the absorption of energy within the system.

To apply damping coating is standard practice today. The damping coatings are usually made of plastics and are applied to sheet-metal shells such as car bodies. This method is often cheap and has the advantage that the coating can be applied precisely where damping is required. But these damping coatings may be ef­ficient for certain sound frequencies and temperatures.

So, metallurgists were interested in the possibility of metals that are strong and tough enough to be used in structures. But they must also possess a high inherent damping capacity that is inde­pendent of frequency and less temperature-dependent than that of plastics.

Scientists want to combine some of the properties which characterize steel; with high damping capacity of lead and to pro­duce a material that could be used to minimize noise and vibration. This can, in fact, be done with several materials, the most out­standing of which are alloys of manganese and copper. These al­loys can be stronger than ordinary steel, with similar toughness and hardness, yet they have a damping capacity nearly 50 times greater than that of steel.

However, noise and vibration are problems to be faced by engineers. It is seldom sufficient merely to replace a troublesome component with one of a high-damping alloy. The particular charac­teristics of these "high-damping" structural alloys should be property« employed. As a result, perhaps, the future will be a little quieter - in some respects at least!

Text 4 Mortars

Mortar is the matrix used in the beds and side joints of brickwork and for plastering walls and floors. Its functions are as follows:

• to distribute the pressure throughout the brickwork;

• to adhere and bind together the bricks;

• to act as a non-conductor and prevent the transmission, of heat, sound, and moisture from one side of wall to the other.

The factors governing the choice of mortars for various pur­poses are:

• strength as being a main factor determining the strength of the wall;

• porosity and capillary characteristics as affecting the rain-excluding properties and durability of the wall;

• content of soluble salts which determines the possibility to destruction of the masonry or brickwork.

Mortar, consists of an inert aggregate bound by a cementing material. The cementing material is most important in determining the characteristics of the mortar. The usual cementing materials used for constructional work are hydraulic limes or Portland cement.

Clean, sharp pit sand is the best aggregate. Old bricks, burnt ballast or stones ground in a mortar mill may be used as substitutes for sand.

Mortars may be classified as follows:

1. Cement mortars.

2. Cement-lime mortars.

3. Lime mortars.

Lime mortar. This is a mixture of quick lime and sand in the proportion of 1 part lime to 2 or 3 parts sand in addition to water. It is the principal material used for bedding and jointing bricks, stones, etc. The slaked lime is mixed with the sand and water either by hand or in a mortar mill. The period of slaking, composition and strength of mortar depends upon the class of lime used.

Non-hydraulic lime mortars must be well slaked before use. This type can be stored in a heap for several days after mixing, pro­vided the surface is smoothed over with a shovel to minimize car-bonation by the exclusion of as much air as possible. As such mor­tars can only harden when exposed to the atmosphere, a relatively large proportion of sand must be added to the lime to assist in the penetration of air. For this reason the proportion of sand may be as high as 4 parts by volume of sand to 1 part lime. These mortars are not suitable for work below ground level, especially if the ground is water-logged.

Hydraulic lime mortars should be used within an hour after being mixed. Any mortar which has stiffened and cannot be knocked up by means of a trowel to a sufficiently plastic condition should never be used. The proportion of lime to aggregate ranges from 1 part lime to from 2 to 3.5 parts sand, and common mixture being 1:3. These are excellent mortars for all purposes and are particularly suited for work below the ground level and in exposed positions.

Magnesian and dolomitic lime mortars have a slow-setting action and they should therefore be slaked for several hours before use. Their properties and uses are somewhat similar to those of hy­draulic lime mortars.

Black mortars. Ashes or clinkers from furnaces are crushed finely and ground with the lime in a mortar mill to produce a cheap and strong mortar, known as black mortar. The ashes should be free from unburnt coal and dust. A common proportion is 1 part lime to 3 parts ashes or clinker. They are hard-setting mortars and are suitable for internal walls and for brickwork and masonry where the colour is not objected to.

Cement mortars. It is stronger than lime mortar and is used in the construction of piers and load-bearing walls; it is also em­ployed for work below ground level and for external walls. Cement mortar is now extensively used during winter, owing to its relatively quick-setting property. It must be used immediately after mixing. The usual composition is 1 part cement to 3 parts sand. A dense cement mortar should not be used for bedding and jointing low-strength bricks.

Lime-cement or compo mortars. Compo is a mixture of lime, cement and sand. It is usual to mix the lime mortar and then to gauge this mixture with the necessary proportion of Portland cement immediately before the mortar is required for use. Only non-hydraulic lime should be used for this class of mortar. The addition of cement increases the hydraulicity of the mortar, besides, increas­ing its strength and the rate of hardening is therefore accelerated. The gauging also increases the workability of the mortars. The pro­portions vary from 1 part cement : 2 to 3 part lime : 9 to 12 parts sand. Eminently hydraulic and magnesian limes should not be gauged with cement.

Strength of mortar. Cement mortar produces the strongest brickwork, non-hydraulic lime mortar is approximately half the strength of that in cement mortar, and the strength of eminently hy­draulic mortars is interemediate between that of cement and non-hydraulic lime mortars. The strength of compo mortars depends upon the cement content and may be very little less than of cement mortar.

Text 5 Reinforced Concrete

Reinforced concrete is a combination of two of the strongest structural materials, concrete and steel, either of which is used separately. Consequently, the resulting materials has the advan­tages of both. *

Concrete has poor elastic and tensional properties, but it is rigid, strong in compression, extremely durable under and above ground, and in the presence or absence of air and water, it in­creases in strength with age, it is fire resistant, and suitable for any architectural or engineering forms.

Steel has great tensional, compressive and elastic properties but is not durable below ground or if exposed to moisture, it loses its strength with age or exposure to high temperature. Steel is also fragile in appearance, giving an impression of weakness rather than strength. When strength is the most important consideration great care must be taken to produce a concrete that will be homogeneous and as dense as possible. Homogeneity is not possible without through mixing. To obtain strength and density, the aggregate must be sand and gravel, or crushed rock clean and free from organic matter, and carefully graded from the smallest to the largest parti­cles.

The maximum size of the aggregate depends upon the thickness of the concrete and the closeness of the reinforcing steel.

For stabs up to three inches thick ft should pass a half inch mesh, for stabs over three inches, and for beams, columns, footings retaining walls, and other moderately heavy work, it should not be more than three quarter inch, and from one to one and a half inch for heavy work. All that passes a three-sixteenth inch mesh should be considered sand.

The sand and stone must be proportioned and mixed so that all cavities formed between the various size particles can be completely filled with smaller particles down to cavities that can be filled only with cement.

The cement should be ground extremely fine and should be stored in a water-proof shed, or otherwise well protected from atmos­pheric influence.

The water should be fresh and free from earthy and organic mat­ter. Sea water should be used for reinforced work. The sodium chloride that ft contains may oxidize the steel with resulting cracks in the concrete.

For general work the most suitable proportions of cement and aggregate are: 1 part cement, 2 parts sar\d, and 4 parts gravel or crushed rock.

Let us consider what is the effect of the addition of steel rein­forcement to a concrete.

Steel is a material which does not undergo shrinkage on dry­ing, and therefore the steel acts as a restraining medium in a rein­forced concrete member; shrinkage causes tensile stresses in the concrete which are balanced by compressive stresses in the steel. Now the steel itself deforms under the induced stresses so that there must be a resultant shrinkage moment in a reinforced con­crete member.

An economic quantity of steel, however, can be so disposed as to distribute the cracking under shrinkage stresses and thus ren­der it innocuous. This is the problem for the designer of a reinforced concrete building, and it demands careful consideration on a proper design basis, both of the quantity and of the distribution of the rein­forcement.

The method of reinforcement generally used is putting in a wire mesh or system of light rods into the concrete and that must not be done at random.