Municipal Wastewater Treatment Systems

 

The Need for Wastewater Treatment Wastewater treatment is needed so that we can use our rivers and streams for fishing, swimming and drinking water. For the first half of the 20th century, pollution in the Nation’s urban waterways resulted in frequent occurrences of low dissolved oxygen, fish kills, algal blooms and bacterial contamination.

Early efforts in water pollution control prevented human waste from reaching water supplies or reduced floating debris that obstructed shipping. Pollution problems and their control were primarily local, not national, concerns. Since then, population and industrial growth have increased demands on our natural resources, altering the situation dramatically.

Progress in abating pollution has barely kept ahead of population growth, changes in industrial processes, technological developments, changes in land use, business innovations, and many other factors. Increases in both the quantity and variety of goods produced can greatly alter the amount and complexity of industrial wastes and challenge traditional treatment technology.

The application of commercial fertilizers and pesticides, combined with sediment from growing development activities, continues to be a source of significant pollution as runoff washes off the land. Water pollution issues now dominate public concerns about national water quality and maintaining healthy ecosystems. Although a large investment in water pollution control has helped reduce the problem, many miles of streams are still impacted by a variety of different pollutants.

This, in turn, affects the ability of people to use the water for beneficial purposes. Past approaches used to control water pollution control must be modified to accommodate current and emerging issues.

Effects of Wastewater on Water Quality. The basic function of the wastewater treatment plant is to speed up the natural processes by which water purifies itself. In earlier years, the natural treatment process in streams and lakes was adequate to perform basic wastewater treatment. As our population and industry grew to their present size, increased levels of treatment prior to discharging domestic wastewater became necessary.

Collecting and Treating Wastewater. The most common form of pollution control in the United States consists of a system of sewers and wastewater treatment plants. The sewers collect municipal wastewater from homes, businesses, and industries and deliver it to facilities for treatment before it is discharged to water bodies or land, or reused.

Centralized Collection. During the early days of our nation’s history, people living in both the cities and the countryside used cesspools and privies to dispose of domestic wastewater. Cities began to install wastewater collection systems in the late nineteenth century because of an increasing awareness of waterborne disease and the popularity of indoor plumbing and flush toilets. The use of sewage collection systems brought dramatic improvements to public health, further encouraging the growth of metropolitan areas. In the year 2000 approximately 208 million people in the U.S. were served by centralized collection systems.

Many of the earliest sewer systems were combined sewers, designed to collect both sanitary wastewater and storm water runoff in a single system. These combined sewer systems were designed to provide storm drainage from streets and roofs to prevent flooding in cities. Later, lines were added to carry domestic wastewater away from homes and businesses. Early sanitarians thought that these combined systems provided adequate health protection. We now know that the overflows designed to release excess flow during rains also release pathogens and other pollutants.

 

from: Primer for Municipal Wastewater Treatment Systems. United States Environmental Protection Agency. https://www3.epa.gov/npdes/pubs/primer.pdf.

 

14. Read the text about the pollutants. Be ready to discuss the main items of the text with your group-mates:

 

Pollutants

 

Oxygen-Demanding Substances. Dissolved oxygen is a key element in water quality that is necessary to support aquatic life. A demand is placed on the natural supply of dissolved oxygen by many pollutants in wastewater. This is called biochemical oxygen demand, or BOD, and is used to measure how well a sewage treatment plant is working.

If the effluent, the treated wastewater produced by a treatment plant, has a high content of organic pollutants or ammonia, it will demand more oxygen from the water and leave the water with less oxygen to support fish and other aquatic life. Organic matter and ammonia are “oxygen-demanding” substances. Oxygen-demanding substances are contributed by domestic sewage and agricultural and industrial wastes of both plant and animal origin, such as those from food processing, paper mills, tanning, and other manufacturing processes.

These substances are usually destroyed or converted to other compounds by bacteria if there is sufficient oxygen present in the water, but the dissolved oxygen needed to sustain fish life is used up in this break down process.

Pathogens. Disinfection of wastewater and chlorination of drinking water supplies has reduced the occurrence of waterborne diseases such as typhoid fever, cholera, and dysentery, which remain problems in underdeveloped countries while they have been virtually eliminated in the U.S. Infectious micro-organisms, or pathogens, may be carried into surface and groundwater by sewage from cities and institutions, by certain kinds of industrial wastes, such as tanning and meat packing plants, and by the contamination of storm runoff with animal wastes from pets, livestock and wild animals, such as geese or deer. Humans may come in contact with these pathogens either by drinking contaminated water or through swimming, fishing, or other contact activities. Modern disinfection techniques have greatly reduced the danger of waterborne disease.

Nutrients. Carbon, nitrogen, and phosphorus are essential to living organisms and are the chief nutrients present in natural water. Large amounts of these nutrients are also present in sewage, certain industrial wastes, and drainage from fertilized land.

Conventional secondary biological treatment processes do not remove the phosphorus and nitrogen to any substantial extent - in fact, they may convert the organic forms of these substances into mineral form, making them more usable by plant life. When an excess of these nutrients overstimulates the growth of water plants, the result causes unsightly conditions, interferes with drinking water treatment processes, and causes unpleasant and disagreeable tastes and odors in drinking water.

The release of large amounts of nutrients, primarily phosphorus but occasionally nitrogen, causes nutrient enrichment which results in excessive growth of algae. Uncontrolled algae growth blocks out sunlight and chokes aquatic plants and animals by depleting dissolved oxygen in the water at night. The release of nutrients in quantities that exceed the affected water body's ability to assimilate them results in a condition called eutrophication or cultural enrichment.

Inorganic and Synthetic Organic Chemicals. A vast array of chemicals are included in this category. Examples include detergents, household cleaning aids, heavy metals, pharmaceuticals, synthetic organic pesticides and herbicides, industrial chemicals, and the wastes from their manufacture. Many of these substances are toxic to fish and aquatic life and many are harmful to humans. Some are known to be highly poisonous at very low concentrations. Others can cause taste and odor problems, and many are not effectively removed by conventional wastewater treatment.

Thermal. Heat reduces the capacity of water to retain oxygen. In some areas, water used for cooling is discharged to streams at elevated temperatures from power plants and industries. Even discharges from wastewater treatment plants and storm water retention ponds affected by summer heat can be released at temperatures above that of the receiving water, and elevate the stream temperature. Unchecked discharges of waste heat can seriously alter the ecology of a lake, a stream, or estuary.

 

SUPPLEMENTARY READING

 

Text 1

Civil Engineering

 

An overview by Joan Omoruyi,

Engineering Librarian, Northeastern University

 

Civil engineering is considered the oldest engineering discipline, since its works are traced back to the Egyptian pyramids and before. The skills of civil engineers such as building walls, bridges and roads have always been useful in warfare and civil engineers have worked on both military and civil projects. The term civil engineer was coined by British engineer John Smeaton in 1750 to distinguish those who work on civil projects from those who work on military projects.

Civil engineers are responsible for constructing large-scale projects such as roads, buildings, dams, bridges, harbors, canals, water systems and sewage systems. Civil engineering affects many daily activities: buildings in which we live and work, transportation facilities, water we drink, and drainage and sewage systems.

Structural engineering is the largest specialty within civil engineering and is concerned with the design of large buildings, bridges, tanks, towers, dams and other large structures. These engineers design and select appropriate structural components (e.g. beams, columns, and slabs) and systems to provide adequate strength, stability and durability.

Construction engineering and management: A large proportion of civil engineers work in the construction industry. The construction industry is the realization phase of the civil engineering process: building the facilities that other engineers and architects design.

Construction engineers utilize and. manage the resources of construction (the vehicles. equipment, machines, materials and skilled workers) to produce the structure or facility envisioned by the designer.

Construction is typically divided into specialty areas with each area requiring different skills, resources and knowledge to participate effectively in it. The specialty areas typically are:

· residential (single and multifamily housing);

· building (all buildings other than housing);

· heavy /highway (dams, bridges, ports, sewage treatment plants, highways);

· utility (sanitary and storm drainage, water lines, electrical and telephone lines, pumping stations);

· industrial (refineries, mills, power plants, chemical plants, heavy manufacturing facilities).

Civil engineers can be heavily involved in all of these areas of construction, however fewer are involved in residential. Due to the difference in each of these market areas most engineers specialize in only one or two areas during their careers.

 

from: http://esciencelibrary.umassmed.edu/civ_env_eng.pdf

 

Text 2

What Is Civil Engineering?

 

By Jim Lucas,

Live Science Contributor / August 28, 2014

 

Civil engineers design and build infrastructure projects, such as bridges and dams.

Civil engineering is the design and construction of public works, such as dams, bridges and other large infrastructure projects. It is one of the oldest branches of engineering, dating back to when people first started living in permanent settlements and began shaping their environments to suit their needs.

Early engineers built walls, roads, bridges, dams and levees; they dug wells, irrigation ditches and trenches. As larger groups of people began living together in towns and cities, these populations needed reliable sources of clean water, the means to dispose of waste, a network of streets and roadways for commerce and trade, and a way to defend themselves against hostile neighbors.

Ancient civil engineering projects include the roads of the Roman Empire, the Great Wall of China, the cliff dwellings at Mesa Verde and Mayan ruins at Copan, Palenque and Tikal. Many early civilizations built monuments to their rulers or gods. These may have been simple mounds or truly remarkable achievements, such as the Pyramids of Giza and Stonehenge, whose construction by pre-industrial societies remains mysterious. The names of the engineers who designed these wonders are lost to antiquity.

Today, the public is more likely to remember the names of great civil engineering projects than the names of the engineers who designed and built them. These include the Brooklyn Bridge (designed by John August Roebling and son Washington Roebling), the Hoover Dam (John L. Savage), the Panama Canal (John Frank Stevens) and the Golden Gate Bridge (Joseph Strauss and Charles Ellis). One notable exception is the Eiffel Tower, named after Gustave Eiffel, the French civil engineer whose company built it.

What does a civil engineer do? Civil engineers "design, construct, supervise, operate and maintain large construction projects and systems, including roads, buildings, airports, tunnels, dams, bridges, and systems for water supply and sewage treatment," according to the U.S. Bureau of Labour Statistics (BLS).

These engineers may also handle site preparation activities, such as excavation, earth moving and grading for large construction projects. Additionally, civil engineers may conduct or write the specifications for destructive or nondestructive testing of the performance, reliability and long-term durability of materials and structures.

Here are some recent and ongoing civil engineering projects of note:

· A team of researchers from Johns Hopkins University conducted tests to see how well buildings made of cold-formed steel can withstand earthquakes.

· Engineers at the University of Maryland are working on smart bridges that can send out warnings when they are in danger of collapsing.

· In Los Angeles, civil engineers who are experts in structural monitoring helped art conservators preserve the iconic Watts Towers monument.

What a civil engineer needs to know. Today's civil engineers need in-depth understanding of physics, mathematics, geology and hydrology. They must also know the properties of a wide range of construction materials, such as concrete and structural steel, and the types and capabilities of construction machinery. With this knowledge, engineers can design structures that meet requirements for cost, safety, reliability, durability and energy efficiency. Civil engineers also need a working knowledge of structural and mechanical engineering.

These engineers can be involved in nearly every stage of a major construction project. That can include site selection, writing specifications for processes and materials, reviewing bids from subcontractors, ensuring compliance with building codes, and supervising all phases of construction from grading and earth moving to painting and finishing.

More and more, civil engineers rely on computer-aided design (CAD) systems; therefore, proficiency with computers is essential. In addition to speeding up the drafting process for civil engineering projects, CAD systems make it easy to modify designs and generate working blueprints for construction crews.

Civil engineering jobs & salary. The BLS states, "Civil engineers generally work indoors in offices. However, many spend time outdoors at construction sites so they can monitor operations or solve problems onsite." Most civil engineers employed in the private sector work for large construction contractors or as consultants. Government institutions that employ civil engineers include state transportation departments and the military.

Most civil engineering jobs require at least a bachelor's degree in engineering. Many employers, particularly those that offer engineering consulting services, also require state certification as a professional engineer. Additionally, many employers require certification from the American Society of Civil Engineers (ASCE). A master's degree is often required for promotion to management, and ongoing education and training are needed to keep up with advances in technology, equipment, computer hardware and software, building codes, and other government regulations.

According to Salary.com, as of July 2014, the salary range for a newly graduated civil engineer with a bachelor's degree is $55,570 to $73,908. The range for a mid-level engineer with a master's degree and five to 10 years of experience is $74,007 to $108,640, and the range for a senior engineer with a master's degree or doctorate and over 15 years of experience is $97,434 to $138,296. Many experienced engineers with advanced degrees are promoted to management positions or start their own businesses where they can earn even more.

The future of civil engineering. Employment of civil engineers is projected to grow 20 percent from now to 2022, faster than the average for all occupations, according to the BLS. "As infrastructure continues to age, civil engineers will be needed to manage projects to rebuild bridges, repair roads, and upgrade levees and dams," the BLS said.

There should be many opportunities for qualified applicants, particularly those who have kept abreast of the latest developments in technology and regulations. Having good grades from a highly rated institution should give a job seeker an advantage over the competition.

 

from: http://www.livescience.com/47612-civil-engineering.html

 

 

Text 3

Classification of Buildings

 

The majority of building codes divide building into classes based upon the manner of their construction, use, or occupancy.

The following division into classes applies to the manner of construction:

1. Frame construction

2. Non-fireproof construction

a) Ordinary construction

b) Slow-burning construction

3. Fireproof construction

Frame construction embraces all buildings with exterior walls of wooden framework sheathed with wood shingles or siding; veneered with brick, stone, or terra cotta; or covered with stucco or sheet metal. Such buildings naturally have floors and partitions of wood and are considered as comprising the most inflammable type of construction.

Non-fireproof construction includes all buildings with exterior walls of masonry but with wood floor construction and partitions. Slow-burning construction designates heavy timber framing designed as far as possible to be fire resistant, the heavy beams and girders of large dimension proving far less inflammable than the slender joists of ordinary construction.

Fireproof construction includes all buildings constructed of incombustible material throughout, with floors of iron, steel, or reinforced concrete beams, filled -in between with terra cotta or other masonry arches or with concrete slabs.

Wood may be used only for under and upper floors, window and door frames, sash, doors, and interior finish. In buildings of great height the flooring must be of incombustible material and the, doors, frames, and interior finish of metal. Wire glass is used in the windows, and all structural and reinforced steel must be surrounded with fireproof material, such as hollow terra cotta and gypsum tile to protect the steel from the weakening effect of great heat.

 

Text 4

Site Investigation

 

Thebasic objective of site investigation for new works is to collect systematically and record all the necessary data which will be needed or will help in the design and construction processes of the proposed work.

The collected data should be presented in the form of fully annotated and dimensioned plans and sections. Anything on adjacent sites which may affect the proposed works or conversely anything appertaining to the proposed works which may affect an adjacent site should also be recorded.

The purpose of this work is primarily to obtain subsoil samples for identification, classification and ascertaining the subsoil's characteristics and properties. Trial pits and augered holes may also be used to establish the presence of any geological faults and the upper or lower limits of the water table.

Soil investigation is related to the subsoil beneath the site under investigation and could be part of or separate from the site investigation.

The purpose of soil investigation is to determine the suitability of the site for the proposed project, an adequate and economic foundation design, the difficulties which may arise during the construction process, the occurrence and/or cause of all changes in subsoil conditions. This purpose can usually be assessed by establishing the physical, chemical and general characteristics of the subsoil by obtaining subsoil samples which should be taken from positions on the site which are truly representative of the area but are not taken from the actual position of the proposed foundations.

Soil samples can be obtained as disturbed or as undisturbed samples.

Disturbed soil samples are obtained from boreholes and trial pits. The method of extraction disturbs the natural structure of the subsoil but such samples are suitable for visual grading, establishing the moisture content and some laboratory tests.

Undisturbed soil samples are obtained by using coring tools which preserve the natural structure and properties of the subsoil. The extracted undisturbed soil samples are tested later in a laboratory.

Setting out the building outline is usually undertaken after the site has been cleared of any obstructions and any reduced level excavation work is finished. It is usually the responsibility of the contractor to set out the building(s) using the information provided by the designer or architect. Accurate setting out is very important and should therefore only be carried out by competent persons and all their work thoroughly checked.

The first task in setting out the building is to establish a base line to which all the setting out can be related. The base line very often coincides with the building line, whose position on site is given by the local authority in front of which no development is permitted.

The objective of setting out trenches is twofold. Firstly it must establish the excavation size, shape and direction and secondly it must establish the width and position of the walls. By using the building outline profile boards can be set up to control the position, width and possibly the depth of the proposed trenches. The trench width can be marked on the profile with either nails or saw cuts and with a painted band if required for identification.

Levelling is a process of establishing height dimensions, relative to a fixed point or datum. Datum is meant sea level, which varies between different countries. For UK purposes this is established at Newlyn in Cornwall. Relative levels defined by bench marks are located throughout the country. The most common, identified as carved arrows, can be found cut into walls of stable structures.

On site it is usual to measure levels from a temporary bench mark, i.e. a manhole cover or other permanent fixture.

Instruments consist of a level (tilting or automatic) and a staff. A tilting level is basically a telescope mounted on a tripod for stability. Correcting screws establish accuracy in the horizontal plane by air bubble in a vial. Cross hairs of horizontal and vertical lines indicate image sharpness on an extending staff of 3, 4 or 5 m length. An automatic level is much simpler to use, eliminating the need for manual adjustment.

 

Text 5

Building material

 

Building material is any material which is used for a construction purpose. Many naturally occurring substances, such as clay, sand, wood and rocks, even twigs and leaves have been used to construct buildings. Apart from naturally occurring materials, many man-made products are in use, some more and some less synthetic. The manufacture of building materials is an established industry in many countries and the use of these materials is typically segmented into specific specialty trades, such as carpentry, plumbing, roofing and insulation work. This reference deals with habitats and structures including homes.

Natural materials. Building materials can be generally categorized into two sources, natural and synthetic. Natural building materials are those that are unprocessed or minimally processed by industry, such as lumber or glass. Synthetic materials are made in industrial settings after much human manipulations, such as plastics and petroleum based paints. Both have their uses.

Mud, stone, and fibrous plants are the most basic building materials, aside from tents made of flexible materials such as cloth or skins. People all over the world have used these three materials together to create homes to suit their local weather conditions. In general stone and/or brush are used as basic structural components in these buildings, while mud is used to fill in the space between, acting as a type of concrete and insulation.

A basic example is wattle and daub mostly used as permanent housing in tropical countries or as summer structures by ancient northern peoples.

Fabric. The tent used to be the home of choice among nomadic groups the world over. Two well known types include the conical teepee and the circular yurt. It has been revived as a major construction technique with the development of tensile architecture and synthetic fabrics. Modern buildings can be made of flexible material such as fabric membranes, and supported by a system of steel cables or internal (air pressure.)

Mud and clay. The amount of each material used leads to different styles of buildings. The deciding factor is usually connected with the quality of the soil being used. Larger amounts of clay usually mean using the cob / adobe style, while low clay soil is usually associated with sod building. The other main ingredients include more or less sand/gravel and straw/grasses. Rammed earth is both an old and newer take on creating walls, once made by compacting clay soils between planks by hand, now forms and mechanical pneumatic compressors are used.

Soil and especially clay is good thermal mass; it is very good at keeping temperatures at a constant level. Homes built with earth tend to be naturally cool in the summer heat and warm in cold weather. Clay holds heat or cold, releasing it over a period of time like stone. Earthen walls change temperature slowly, so artificially raising or lowering the temperature can use more resources than in say a wood built house, but the heat/coolness stays longer.

Peoples building with mostly dirt and clay, such as cob, sod, and adobe, resulted in homes that have been built for centuries in western and northern Europe as well as the rest of the world, and continue to be built, though on a smaller scale. Some of these buildings have remained habitable for hundreds of years.

Rock. Rock structures have existed for as long as history can recall. It is the longest lasting building material available, and is usually readily available. There are many types of rock throughout the world all with differing attributes that make them better or worse for particular uses. Rock is a very dense material so it gives a lot of protection too, its main draw-back as a material is its weight and awkwardness. Its energy density is also considered a big draw-back, as stone is hard to keep warm without using large amounts of heating resources.

Dry-stone walls have been built for as long as humans have put one stone on top of another. Eventually different forms of mortar were used to hold the stones together, cement being the most commonplace now.

The granite-strewn uplands of Dartmoor National Park, United Kingdom, for example, provided ample resources for early settlers. Circular huts were constructed from loose granite rocks throughout the Neolithic and early Bronze Age, and the remains of an estimated 5,000 can still be seen today. Granite continued to be used throughout the Medieval period (see Dartmoor longhouse) and into modern times. Slate is another stone type, commonly used as roofing material in the United Kingdom and other parts of the world where it is found.

Mostly stone buildings can be seen in most major cities, some civilizations built entirely with stone such as the Pyramids in Egypt, the Aztec pyramids and the remains of the Inca civilization.

Thatch. Thatch is one of the oldest of building materials known; grass is a good insulator and easily harvested. Many African tribes have lived in homes made completely of grasses year round. In Europe, thatch roofs on homes were once prevalent but the material fell out of favour as industrialization and improved transport increased the availability of other materials. Today, though, the practice is undergoing a revival. In the Netherlands, for instance, many of new builds too have thatched roofs with special ridge tiles on top.

Brush. Brush structures are built entirely from plant parts and are generally found in tropical and sub-tropical areas, such as rainforests, where very large leaves can be used in the building. Native Americans often built brush structures for resting and living in, too. These are built mostly with branches, twigs and leaves, and bark, similar to a beaver’s lodge. These were variously named wikiups, lean-tos, and so forth.

Ice. Ice was used by the Inuit for igloos, but has also been used for ice hotels as a tourist attraction in northern areas that might not otherwise see many winter tourists.

Wood. Wood is a product of trees, and sometimes other fibrous plants, used for construction purposes when cut or pressed into lumber and timber, such as boards, planks and similar materials. It is a generic building material and is used in building just about any type of structure in most climates. Wood can be very flexible under loads, keeping strength while bending, and is incredibly strong when compressed vertically. There are many differing qualities to the different types of wood, even among same tree species. This means specific species are better for various uses than others. And growing conditions are important for deciding quality.

Historically, wood for building large structures was used in its unprocessed form as logs. The trees were just cut to the needed length, sometimes stripped of bark, and then notched or lashed into place.

In earlier times, and in some parts of the world, many country homes or communities had a personal wood-lot from which the family or community would grow and harvest trees to build with. These lots would be tended to like a garden.

With the invention of mechanizing saws came the mass production of dimensional lumber. This made buildings quicker to put up and more uniform. Thus the modern western style home was made.

Brick and Block. A brick is a block made of kiln-fired material, usually clay or shale, but also may be of lower quality mud, etc. Clay bricks are formed in a moulding (the soft mud method), or in commercial manufacture more frequently by extruding clay through a die and then wire-cutting them to the proper size (the stiff mud process).

Bricks were widely used as a building material in the 1700, 1800 and 1900s. This was probably due to the fact that it was much more flame retardant than wood in the ever crowding cities, and fairly cheap to produce.

Another type of block replaced clay bricks in the late 20th century. It was the Cinder block мade mostly with concrete.

An important low-cost building material in developing countries is the Sandcrete block, which is weaker but cheaper than fired clay bricks.

Concrete. Concrete is a composite building material made from the combination of aggregate (composite) and a binder such as cement. The most common form of concrete is Portland cement concrete, which consists of mineral aggregate (generally gravel and sand), portland cement and water. After mixing, the cement hydrates and eventually hardens into a stone-like material. When used in the generic sense, this is the material referred to by the term concrete.

For a concrete construction of any size, as concrete has a rather low tensile strength, it is generally strengthened using steel rods or bars (known as rebars). This strengthened concrete is then referred to as reinforced concrete. In order to minimise any air bubbles, that would weaken the structure, a vibrator is used to eliminate any air that has been entrained when the liquid concrete mix is poured around the ironwork. Concrete has been the predominant building material in this modern age due to its longevity, formability, and ease of transport.

Metal. Metal is used as structural framework for larger buildings such as skyscrapers, or as an external surface covering. There are many types of metals used for building. Steel is a metal alloy whose major component is iron, and is the usual choice for metal structural building materials. It is strong, flexible, and if refined well and/or treated lasts a long time. Corrosion is metal’s prime enemy when it comes to longevity.

The lower density and better corrosion resistance of aluminium alloys and tin sometimes overcome their greater cost. Brass was more common in the past, but is usually restricted to specific uses or specialty items today.

Metal figures quite prominently in prefabricated structures such as the Quonset hut, and can be seen used in most cosmopolitan cities. It requires a great deal of human labor to produce metal, especially in the large amounts needed for the building industries.

Other metals used include titanium, chrome, gold, silver. Titanium can be used for structural purposes, but it is much more expensive than steel. Chrome, gold, and silver are used as decoration, because these materials are expensive and lack structural qualities such as tensile strength or hardness.

Glass. Clear windows have been used since the invention of glass to cover small openings in a building. They provided humans with the ability to both let light into rooms while at the same time keeping inclement weather outside. Glass is generally made from mixtures of sand and silicates, and is very brittle.

Modern glass “curtain walls” can be used to cover the entire facade of a building. Glass can also be used to span over a wide roof structure in a “space frame”.

Ceramics. Ceramics are such things as tiles, fixtures, etc. Ceramics are mostly used as fixtures or coverings in buildings. Ceramic floors, walls, counter-tops, even ceilings. Many countries use ceramic roofing tiles to cover many buildings.

Ceramics used to be just a specialized form of clay-pottery firing in kilns, but it has evolved into more technical areas.

Plastic. Plastic pipes penetrating a concrete floor in a Canadian highrise apartment building

The term plastics covers a range of synthetic or semi-synthetic organic condensation or polymerization products that can be molded or extruded into objects or films or fibers. Their name is derived from the fact that in their semi-liquid state they are malleable, or have the property of plasticity. Plastics vary immensely in heat tolerance, hardness, and resiliency. Combined with this adaptability, the general uniformity of composition and lightness of plastics ensures their use in almost all industrial applications today

Foam. Foamed plastic sheet to be used as backing for fire stop mortar at CIBC bank in Toronto.

More recently synthetic polystyrene or polyurethane foam has been used on a limited scale. It is light weight, easily shaped and an excellent insulator. It is usually used as part of a structural insulated panel where the foam is sandwiched between wood or cement.

Cement composites. Cement bonded composites are an important class of building materials. These products are made of hydrated cement paste that binds wood or alike particles or fibers to make pre-cast building components. Various fiberous materials including paper and fiberglass have been used as binders.

Wood and natural fibres are composed of various soluble organic compounds like carbohydrates, glycosides and phenolics. These compounds are known to retard cement setting. Therefore, before using a wood in making cement boned composites, its compatibility with cement is assessed.

Wood-cement compatibility is the ratio of a parameter related to the property of a wood-cement composite to that of a neat cement paste. The compatibility is often expressed as a percentage value. To determine wood-cement compatibility, methods based on different properties are used, such as, hydration characteristics, strength, interfacial bond and morphology.

Various methods are used by researchers such as the measurement of hydration characteristics of a cement-aggregate mix; the comparison of the mechanical properties of cement-aggregate mixes and the visual assessment of microstructural properties of the wood-cement mixes. It has been found that the hydration test by measuring the change in hydration temperature with time is the most convenient method. Recently, Karade et al. have reviewed these methods of compatibility assessment and suggested a method based on the ‘maturity concept’ i.e. taking in consideration both time and temperature of cement hydration reaction.

 

Text 6