PROPERTIES OF MATERIALS (INTRODUCTION)

PROPERTIES OF MATERIALS

INTRODUCTION

The aim of this course is to provide student architects with a fair knowledge of building materials in common use. Knowing the building materials available is not sufficient enough to aid one in making a good choice in the event of building specification, one needs to know the chemical and physical structure of such building materials and the functional requirements they proffer in order to make good choices.

Physical materials exist basically in three states: solids, liquids and gases. An object is to be a solid when it maintains its shape and size. Solids exhibit a regular arrangement of atomic, ionic, or molecular particles, this is to say that solids objects have crystalline structure.

Building materials could either be stone, wood, metal, ceramics, rubber, polymer, clay glass etc.

HISTORY OF MATERIALS DEVELOPMENT

People have constructed buildings and other structures since prehistoric times, including bridges, amphitheatres, dams, roads and canals. Contemporary building materials have a long history and some of the structures built thousands of years ago are regarded as remarkable. To understand why things were constructed the way they were in prehistory, we need to rely on archaeology to record the form of the parts that survive and the tools used; and other branches of history and architecture to investigate how the builders lived and recorded their accomplishments.

The history of building is marked by a number of trends, which are as follows:

·         The need for increasing durability of the materials used. Early building materials were perishable, such as leaves, branches, and animal hides. Later, more durable natural materials such as clay, stone, and timber, and, finally, synthetic materials, such as brick, concrete, metals, and plastics were used.

·         Another need was the quest for buildings of ever greater height and span; this was made possible by the development of stronger materials and by knowledge of how materials behave and how to exploit them to greater advantage.

·         A third major drive was the need to exercise greater over the interior environment of buildings: increasingly precise regulation of air temperature, light and sound levels, humidity, odours, air speed, and other factors that affect human comfort has been possible. Yet another trend is the change in energy available to the construction process, starting with human muscle power and developing toward the powerful machinery used today.

The history of building materials development can be traced through the following periods:

a.   Neolithic period

Neolithic, also known as the New Stone Age, was a time period roughly from 9000 BC to 5000 BC named because it was the last period of the age before wood working began. The tools available were made from natural materials including bone, antler, hide, stone, wood, grasses, animal fibers, and the use of water. These tools were used by people to cut such as with the hand axe, chopper, adze, and celt. Also to scrape, chop such as with a flake tool, pound, pierce, roll, pull, leaver, and carry. Building materials included bones such as mammoth ribs, hide, stone, metal, bark, bamboo, clay, lime plaster, and more. For example, the first bridges made by humans were probably just wooden logs placed across a stream and later timber track ways. In addition to living in caves and rock shelters, the first buildings were simple shelters, tents like the Inuit's tupek, and huts sometimes built as pit-houses meant to suit the basic needs of protection from the elements and sometimes as fortifications for safety such as the crannog. These buildings were built self-sufficiently by their inhabitants rather than by specialist builders, using locally available materials and traditional designs and methods which together are called vernacular architecture.

Picture showing Neolithic crannog

b.   The Copper Age and Bronze Age

The Copper Age is the early part of the Bronze Age. Bronze is made when tin is added to copper and brass is copper with zinc. Copper came into use before 5,000 BC and bronze around 3,100 BC, although the times vary by region. Copper and bronze were used for the same types of tools as stone such as axes and chisels, but the new, less brittle, more durable material cut better. Bronze was cast into desired shapes and if damaged could be recast. A new tool developed in the copper age is the saw. Other uses of copper and bronze were to "harden" the cutting edge of tools such as the Egyptians using copper and bronze points for working soft stone including quarrying blocks and making rock-cut architecture.

c.   The Iron Age

The Iron Age is a cultural period from roughly 1200 BC to 50 BC with the widespread use of iron for tools and weapons in several regions in the world prime of which include Ancient Mesopotamia, Ancient Egypt, Ancient Greece, Roman Empire and China. Iron is not much harder than bronze but by adding carbon iron becomes steel which was being produced after about 300 BC. Steel can be hardened and tempered producing a sharp, durable cutting edge.

Ancient Mesopotamia

The earliest large-scale buildings for which evidence survives have been found in ancient Mesopotamia. The smaller dwellings only survive in traces of foundations, but the later civilizations built very sizeable structures in the forms of palaces, temples and ziggurats and took particular care to build them out of materials that last, which has ensured that very considerable parts have remained intact. The chief building material was the mud-brick, formed in wooden moulds similar to those used to make adobe bricks. Bricks varied widely in size and format from small bricks that could be lifted in one hand to ones as big as large paving slabs. Rectangular and square bricks were both common. They were laid in virtually every bonding pattern imaginable and used with considerable sophistication. Drawings survive on clay tablets from later periods showing that buildings were set out on brick modules. By 3500 BC, fired bricks came into use and surviving records show a very complex division of labour into separate tasks and trades. Fired bricks and stone were used for pavement.

Picture showing stacked dried bricks ready for firing

Ancient Egypt

As opposed to the cultures of ancient Mesopotamia which built in brick, the pharaohs of Egypt built huge structures like the ziggurats in stone. The arid climate has preserved much of the ancient buildings. Adobe (sun-baked mud brick) construction was used for ancillary buildings and normal houses in ancient times and is still commonly used in rural Egypt. The hot, dry climate was ideal for mud-brick, which tends to wash away in the rain. The Ramesseum in Thebes, Egypt (Luxor) provides one of the finest examples of mud brick construction. Extensive storehouses with mud-brick vaults also survive, all constructed with sloping courses to avoid the need for formwork.

The grandest buildings were constructed in stone, often from massive masonry blocks. The techniques used to move massive blocks used in pyramids and temples have been subject to extensive debate. Some authors have suggested that the larger may not be cut stone but fabricated with concrete.

Picture showing aerial view of the Ramesseum in Thebes

The Egyptian pyramids were chiefly impressive for their enormous size and the staggering manpower that must have been employed in their construction. The largest is the Great Pyramid of Giza which remained the tallest structure in the world for 3800 years. The engineering problems involved were chiefly to do with the transport of blocks, sometimes over long distances, their movement into location and exact alignment. It is now generally agreed that the skilled building workers were respected and well treated, but undoubtedly very large numbers of labourers were necessary to provide the brute force.

Picture showing the Pyramid at Giza

Ancient Greece

The ancient Greeks, like the Egyptians and the Mesopotamians, tended to build most of their common buildings out of mud brick, leaving no record behind them. However very many structures do survive, some of which are in a very good state of repair, although some have been partly reconstructed or re-erected in the modern era. The most dramatic are the Greek Temples. The Greeks made many advances in technology including plumbing, the spiral staircase, central heating, urban planning, the water wheel, the crane, and more.

No timber structures survive (roofs, floors etc.), so our knowledge of how these were put together is limited. The spans are, in the main, limited and suggest very simple beam and post structures spanning stone walls. For the longer spans it is uncertain if the Greeks or Romans invented the truss but the Romans certainly used timber roof trusses. Before 650 B.C.E. the now famous ancient Greek temples were built of wood, but after this date began to be built of stone. The process of a timber structure being repeated in stone is called petrification or "petrified carpentry".

Fired clay was mainly restricted to roofing tiles and associated decorations, but these were quite elaborate. The roof tiles allow a low roof pitch characteristic of ancient Greek architecture. Fired bricks began to be employed with lime mortar. Very prominent buildings were roofed in stone tiles, which mimicked the form of their terracotta counterparts. While later cultures tended to construct their stone buildings with thin skins of finished stones over rubble cores, the Greeks tended to build out of large cut blocks, joined with metal cramps. This was a slow, expensive and laborious process which limited the number of buildings that could be constructed. The metal cramps often failed through corrosion.

Picture showing masonry techniques of ancient Greece and Rome

Roman Empire

In striking contrast to previous cultures, an enormous amount is known about Roman building construction. A very large amount survives, including complete intact buildings like the Pantheon, Rome and very well preserved ruins at Pompeii and Herculaneum. We also have the first surviving treatise on architecture by Vitruvius which includes extensive passages on construction techniques.

The great Roman development in building materials was the use of hydraulic lime mortar called Roman cement. Previous cultures had used lime mortars but by adding volcanic ash called a pozzolana the mortar would harden under water. This provided them with a strong material for bulk walling. They used brick or stone to build the outer skins of the wall and then filled the cavity with massive amounts of concrete, effectively using the brickwork as permanent shuttering (formwork). Later they used wooden shuttering which was removed for the concrete to cure. An example of a temple made of Roman concrete in the 1st century BC is the Temple of Vesta in Tivoli, Italy. The concrete was made of nothing more than rubble and mortar it was cheap and very easy to produce and required relatively unskilled labour to use, enabling the Romans to build on an unprecedented scale. They not only used it for walls but also to form arches, barrel vaults and domes, which they built over huge spans. The Romans developed systems of hollow pots for making their domes and sophisticated heating and ventilation systems for their thermal baths.

The Romans substituted bronze for wood in the roof truss(s) of the Pantheon's portico which was commissioned between 27 BC and 14 AD. The bronze trusses were unique but in 1625 Pope Urban VIII had the trusses replaced with wood and melted the bronze down for other uses. The Romans also made bronze roof tiles.

Lead was used for roof covering material and water supply and waste pipes. The Latin name for lead is plumbum thus plumbing. Romans also made use of glass in construction with colored glass in mosaics and clear glass for windows. Glass came to be fairly commonly used in windows of public buildings.

China

China is a cultural hearth area of eastern Asia, many Far East building methods and styles evolved from China. A famous example of Chinese construction is the Great Wall of China built between the 7th and 2nd centuries BC. The Great Wall was built with rammed earth, stones, and wood and later bricks and tiles with lime mortar. Wooden gates blocked passageways. The oldest archaeological examples of mortise and tenon type woodworking joints were found in China dating to about 5000 BC.

Chinese temples were typically wooden timber frames on an earth and stone base. The oldest wooden building is the Nanchan Temple (Wutai) dating from 782 CE. However, Chinese temple builders regularly rebuilt the wooden temples so some parts of these ancient buildings are of different ages. Traditional Chinese timber frames do not use trusses but rely only on post and lintel construction.


Middle Ages
The Middle Ages of Europe span from the 5th to 15th centuries AD from the fall of the Western Roman Empire to the Renaissance and is divided into Pre-Romanesque and Romanesque periods.
Fortifications, castles and cathedrals were the greatest construction projects. The Middle Ages began with the end of the Roman era and many Roman building techniques were lost. But some Roman techniques, including the use of iron ring-beams, appear to have been used in the Palatine Chapel at Aachen, c. 800 AD, where it is believed builders from the Langobard Kingdom in northern Italy contributed to the work. A revival of stone buildings in the 9th century and the Romanesque style of architecture began in the late 11th century. Also notable are the stave churches in Scandinavia.

Picture showing Villard de Honnecourt's Flying Buttresses

Materials

Most buildings in Northern Europe were constructed of timber until 1000 AD. In Southern Europe adobe remained predominant. Brick continued to be manufactured in Italy throughout the period 600–1000 AD but elsewhere the craft of brick-making had largely disappeared and with it the methods for burning tiles. Roofs were largely thatched. Houses were small and gathered around a large communal hall. Monasticism spread more sophisticated building techniques. The Cistercians may have been responsible for reintroducing brick-making to the area from the Netherlands, through Denmark and Northern Germany to Poland leading to Backsteingotik. Brick remained the most popular prestige material in these areas throughout the period. Elsewhere buildings were typically in timber or where it could be afforded, stone. Medieval stone walls were constructed using cut blocks on the outside of the walls and rubble infill, with weak lime mortars. The poor hardening properties of these mortars were a continual problem, and the settlement of the rubble filling of Romanesque and Gothic walls and piers is still a major cause for concern.

Romanesque buildings of the period 600–1100 AD were entirely roofed in timber or had stone barrel vaults covered by timber roofs. The Gothic style of architecture with its vaults, flying buttresses and pointed gothic arches developed in the twelfth century, and in the centuries that followed ever more incredible feats of constructional daring were achieved in stone. Thin stone vaults and towering buildings were constructed using rules derived by trial and error.

The Renaissance

The Renaissance in Italy, the invention of moveable type and the Reformation changed the character of building. The rediscovery of Vitruvius had a strong influence. During the Middle Ages buildings were designed by the people that built them. The master mason and master carpenters learnt their trades by word of mouth and relied on experience, models and rules of thumb to determine the sizes of building elements. Vitruvius however describes in detail the education of the perfect architect who, he said, must be skilled in all the arts and sciences. Filippo Brunelleschi was one of the first of the new style of architects. He started life as a goldsmith and educated himself in Roman architecture by studying ruins. He went on to engineer the dome of Santa Maria del Fiore in Florence.

Materials

The major breakthroughs in this period were to do with the technology of conversion. Water mills in most of western Europe were used to saw timber and convert trees into planks. Bricks were used in ever increasing quantities. In Italy the brickmakers were organised into guilds although the kilns were mostly in rural areas because of the risk of fire and easy availability of firewood and brickearth. Brickmakers were typically paid by the brick, which gave them an incentive to make them too small. As a result, legislation was laid down regulating the minimum sizes and each town kept measures against which bricks had to be compared. An increasing amount of ironwork was used in roof carpentry for straps and tension members. The iron was fixed using forelock bolts. The screw-threaded bolt (and nut) could be made and are found in clockmaking in this period, but they were labour-intensive and thus not used on large structures. Roofing was typically of terracotta roof tiles. In Italy they followed Roman precedents. In northern Europe plain tiles were used. Stone, where available, remained the material of choice for prestige buildings.

17th Century

The seventeenth century saw the birth of modern science which would have profound effects on building construction in the centuries to come. The major breakthroughs were towards the end of the century when architect-engineers began to use experimental science to inform the form of their buildings. However it was not until the eighteenth century that engineering theory developed sufficiently to allow sizes of members to be calculated. Seventeenth-century structures relied strongly on experience, rules of thumb and the use of scale models.

Materials and tools

The major breakthrough in this period was in the manufacture of glass, with the first cast plate glass being developed in France. Iron was increasingly employed in structures. Christopher Wren used iron hangers to suspend floor beams at Hampton Court Palace, and iron rods to repair Salisbury Cathedral and strengthen the dome of St Paul's Cathedral. Most buildings had stone ashlar surfaces covering rubble cores, held together with lime mortar. Experiments were made mixing lime with other materials to provide a hydraulic mortar, but there was still no equivalent of the Roman concrete. In England, France and the Dutch Republic, cut and gauged brickwork was used to provide detailed and ornate facades. The triangulated roof truss was introduced to England and used by Inigo Jones and Christopher Wren.

Many tools have been made obsolete by modern technology, but the line gauge, plumb-line, the carpenter's square, the spirit level, and the drafting compass are still in regular use.

Picture showing the great Hampton Court Palace

Picture showing the Salisbury Cathedral

The 18th Century

The eighteenth century saw the development of many the ideas that had been born in the late seventeenth century. The architects and engineers became increasingly professionalised. Experimental science and mathematical methods became increasingly sophisticated and employed in buildings. At the same time the birth of the industrial revolution saw an increase in the size of cities and increase in the pace and quantity of construction.

Materials

The major breakthroughs in this period were in the use of iron (both cast and wrought). Iron columns had been used in Wren's designs for the House of Commons and were used in several early eighteenth-century churches in London, but these supported only galleries. In the second half of the eighteenth century the decreasing costs of iron production allowed the construction of major pieces of iron engineering. The Iron Bridge at Coalbrookdale (1779) is a particularly notable example. Large-scale mill construction required fire-proof buildings and cast iron became increasingly used for columns and beams to carry brick vaults for floors. The Louvre in Paris boasted an early example of a wrought-iron roof. Steel was used in the manufacture of tools but could not be made in sufficient quantities to be used for building.

Brick production increased markedly during this period. Many buildings throughout Europe were built of brick, but they were often coated in lime render, sometimes patterned to look like stone. Brick production itself changed little. Bricks were moulded by hand and fired in kilns no different to those used for centuries before.

The 19th Century

The industrial revolution was manifested in new kinds of transportation installations, such as railways, canals and macadam roads. These required large amounts of investment. New construction devices included steam engines, machine tools, explosives and optical surveying. The steam engine combined with two other technologies which blossomed in the nineteenth century, the circular saw and machine cut nails, lead to the use of balloon framing and the decline of traditional timber framing.

As steel was mass-produced from the mid-19th century, it was used, in form of I-beams and reinforced concrete. Glass panes also went into mass production, and changed from luxury to every man's property.

Plumbing appeared, and gave common access to drinking water and sewage collection. Building codes have been applied since the 19th century, with special respect to fire safety.

The 20th Century

With the Second Industrial Revolution in the early 20th century, elevators and cranes made high rise buildings and skyscrapers possible, while heavy equipment and power tools decreased the workforce needed. Other new technologies were prefabrication and computer-aided design.

Trade unions were formed to protect construction workers' interests. Personal protective equipment such as hard hats and earmuffs also came into use.

From the 20th century, governmental construction projects were used as a part of macroeconomic stimulation policies, especially during the Great depression (see New Deal). For economy of scale, whole suburbs, towns and cities, including infrastructure, are often planned and constructed within the same project (called megaproject if the cost exceeds US$1 billion), such as Brasília in Brazil, and the Million Programme in Sweden.

In the end of the 20th century, ecology, energy conservation and sustainable development have become more important issues of construction.

Picture showing Woolworth building under construction in 1912

CHAPTER 2: STONE

In geology, rock or stone is a naturally occurring solid aggregate of one or more minerals. For example, the common rock granite is a combination of the quartz, feldspar and biotite minerals. The Earth's outer solid layer, the lithosphere, is made of rock. Rocks have been used by mankind throughout history. From the Stone Age, rocks have been used for tools. The minerals and metals found in rocks have been essential to human civilization. The familiar stone types that are used today are identified through four categories: Sedimentary, Metamorphic, Igneous and Man-made stone.

I.          SEDIMENTARY STONE

These come from organic elements such as glaciers, rivers, wind, oceans, and plants. Tiny sedimentary pieces broke off from these elements and accumulate to form rock beds. They bond through millions of years of heat and pressure. Stones found under this category are limestone and sandstone.

Picture Showing large deposit of sedimentary rock.

 a)Limestone (CaCO₃): Mainly consists of calcite. It does not show such graining or crystalline structure. It has a smooth granular surface and varies in hardness. Some dense limestone can be polished. Common colors are black, grey, and white. It is more likely to stain than marble. Limestone is known to contain lime from sea water. Limestone is an important building stone in many parts of the world. It is normally quarried from surface outcrops. Limestone is used as cut stone for building, and is common throughout Europe in cathedrals and palaces where the relatively soft nature of the stone allows decorative carving. Limestone is widely used as crushed stone, or aggregate, for general building purposes. When heated, the calcium carbonate in limestone decomposes to lime, or calcium oxide, and is important as a flux in smelting copper and lead ores and in making iron and steel. Lime is a key ingredient in the manufacture of cement and concrete.

b)Sandstone: These are coarse-grained, sedimentary rock consisting of consolidated masses of sand deposited by moving water or by wind. The chemical constitution of sandstone is the same as that of sand; the rock is thus composed essentially of quartz. The cementing material that binds together the grains of sand is usually composed of silica, calcium carbonate, or iron oxide. The color of the rock is often determined largely by the cementing material, iron oxides causing a red or reddish-brown sandstone, and the other materials producing white, yellowish, or grayish sandstone. When sandstone breaks, the cement is fractured and the individual grains remain whole, thus giving the surfaces a granular appearance.

II. Metamorphic stones originate from a natural form of one type of stone to another type through the mixture of heat, pressure, and minerals. The change may be a development of a crystalline formation, a texture change, or a color change. Stones termed as metamorphic stones are Marble, Slate, Serpentine and laterite.

a)Marble: Marble is a crystalline, compact variety of metamorphosed limestone, consisting primarily of calcite (CaCO₃), dolomite (CaMg (CO₃)₂), or a combination of both minerals. Pure calcite is white, but mineral impurities add color in variegated patterns. Hematite, for example, adds red; limonite, yellow; and diopside, blue. Marble is capable of taking a high polish and is used principally for statuary and for building purposes. Extensive deposits are located in Italy, Great Britain, and in the United States in Georgia, Tennessee, Vermont, Alabama, and Colorado. Commercially the term marble is extended to include any rock composed of calcium carbonate that takes a polish, and it includes some ordinary limestones.

Picture showing Marble

Marble is classified into three categories:

1.     Dolomite: If it has more than 40% magnesium carbonates.

2.    Magnesium: If it has between 5% and 40% magnesium

3.    Calcite: If it has less than 5% magnesium carbonate.

b)Slate: Slate, dense, fine-grained, fissile rock, formed by the metamorphism of shale or clay, or more rarely of igneous rocks. The process of metamorphism results in consolidation of the original rock and in formation of new cleavage planes along which slate characteristically splits into thin, broad sheets. Many rocks that show “slaty cleavage” are by extension loosely called slate. True slate is hard and compact and does not undergo appreciable weathering. The basic minerals comprising slate are quartz and muscovite, a kind of mica; biotite, chlorite, and hematite are often present as accessory minerals, and apatite, graphite, kaolin, magnetite, tourmaline, and zircon may occur as minor accessory minerals. Slate is commonly bluish-black or gray-black in color, but red, green, purple, and variegated varieties are known. Slate is quarried usually in open pits and rarely in underground workings. The stone splits best when it is “green,” or freshly taken from the quarry. Slate is used for floors, roofs, electrical panels, window and door sills, baseboards, stair treads, paving stones, laboratory table tops and sinks. It is widely used for structural and industrial purposes. Though some blackboards may still be made of slate, most blackboards have been replaced with synthetic materials as have most roofing materials. Polished slate is used in some interior designs.

Picture showing Slate

c)Serpentine: Serpentine, common, widely distributed mineral, composed of hydrated magnesium silicate, Mg₃Si₂O₅(OH)₄, so called because of serpentlike bands of green color occurring in massive varieties. The massive variety has a greasy, waxy luster, and the fibrous variety is silky. Both varieties are colored light and dark green, which in massive formations of antigorite produce a beautiful, variegated coloring. The hardness of the mineral ranges from 2 to 5, and the specific gravity ranges from 2.2 for chrysotile to 2.65 for antigorite. Chrysotile is the mineral from which asbestos is made.

Picture showing serpentine

d). Laterite is a metamorphic rock. It has a porous and sponge-like structure. It contains high percentage of iron oxide. Its colour may be brownish, red, yellow, brown and grey. Its specific gravity is 1.85 and compressive strength varies from 1.9 to 2.3 N/mm2. It can be easily quarried in blocks. With seasoning it gains strength. When used as building stone, its outer surface should be plastered.

III. Igneous stones are mainly formed through volcanic material such as magma. Underneath the Earth's surface, liquid magma cooled and solidified. Mineral gases and liquids penetrated into the stone and created new crystalline formations with various colors. The major form of Igneous rock is the Granite.

a)Granite: Granites are primarily made of Quartz (35%), Feldspar (45%) and Potassium. Granite are usually whitish or gray with a speckled appearance caused by the darker crystals. Potash feldspar imparts a red or flesh color to the rock. Granite crystallizes from magma that cools slowly, deep below the earth's surface. Exceptionally slow rates of cooling give rise to a very coarse-grained variety called pegmatite. Granite, along with other crystalline rocks, constitutes the foundation of the continental masses, and it is the most common intrusive rock exposed at the earth's surface.

The specific gravity of granite ranges from 2.63 to 2.75. Its crushing strength is from 1050 to 14,000 kg per sq cm (15,000 to 20,000 lb per sq in). Granite has greater strength than sandstone, limestone, and marble and is correspondingly more difficult to quarry. It is an important building stone, the best grades being extremely resistant to weathering. Black granite is known as an Anorthosite. It contains very little quartz and feldspar and has a different composition than true granite.

IV. Man Made Stones are stones derived from synthetic mixtures such as resin or cement with the additive of stone chips.

a)Terrazzo: Marble and granite chips embedded in a cement composition.

b)Agglomerate or conglomerate: Marble chips embedded in a colored resin composition.

c)Cultured or Faux Marble: A mix of resins that are painted or mixed with a paint to looks like marble.

PROPERTIES OF STONE

Strength & Durability:

The more compact grained and heavier a stone the harder it is. Due to alternate wetting and drying the resulting crushing strength can be reduced even up to 30-40%. Being dry stones allow more crushing strength than when wet. It is the ability of a stone to endure and maintain its essential and distinctive characteristics i.e. resistance to decay, strength and appearance. Physical properties such as density, compressive strength and porosity are measured in order to determine its durability. Durability is based upon the stones natural physical properties, characteristics and the environmental conditions to which it will be or is subjected too. Another factor of stones durability is its Aesthetic Durability or Dimensional Stability. Cosmetic changes may occur. This has to do with the Color Stability of certain stones. These changes can take place in two ways.

SUNLIGHT:

When some stones are used in exterior applications and exposed to direct sunlight they fade or change color. Dark colored stones and those that contain organic matter will generally fade to a much lighter color. The Coral stone being of a biogenic origin contains organic material that will be affected by ultraviolet exposure.

MOISTURE:

Some stones have moisture sensitive mineral contents that will cause the stone to develop rust spots, or other color variations, or contain moisture sensitive substances that will cause blotchy and streaking discolorations. Certain lime stones contain bituminous materials that are soluble when exposed to moisture. Some marbles are also moisture sensitive when in high moisture areas, showers and those with steam features; these stones have a tendency to develop dark botches.

Porosity & Permeability:

Porosity is the ratio of pores (micro-voids) in the stone, to its total solid volume. Pores and the capillary structure develop differently in each of the three stone groups. Dense and compact stones have very few or no pores in them. An important feature of sedimentary rocks is their porosity. Pores are natural holes in the stones which allow fluids like rainwater to enter and leave the fabric. Some free fluid flow through a rock is necessary to maintain the rock's durability, and it is not always advisable to block such flow by using incorrect mortar mixes or by injecting unsuitable synthetic fluids.

Very high porosities, however, may allow excessive volumes of corrosive fluids such as acid rainwater to enter and cause severe damage to the rock. Thin section rock analysis can identify where such problems are likely to occur. Most durable sedimentary building stones commonly have moderate porosity.

Associated with stones porosity is its permeability. This is the extent to which the pores and capillary structures are interconnected throughout the stone. These networks, their size, structure and orientation affect the degree and depth to which moisture, vapors and liquids can be absorb into the interior of the stone or migrate from the substrate by capillary action through the stone.

Permeability is increased when a stone is highly fractured or the veining material is soft or grainy. A particular variety of stone may be highly permeable (a well defined interconnected network of pores), although its porosity is low (a low percentage of voids).

The size and shapes of pores and the capillary structure differs in stones and is an important factor in relation to stone decay.

 

Hardness & weathering:

Hardness is the property of a material to avoid and resist scratching. It is determined by comparison with the standard minerals of the Moh’s scale. The objective of the MOH Scale is to measure stones resistance to hardness.

Measurement of Hardness:

1. Talc
2. Gypsum
3. Calcite (Most Marbles)
4. Fluorite
5. Apatite
6. Feldspar (Granite)
7. Quartz (Granite)
8. Topaz
9. Corundum
10. Diamond

Weathering

It is a complex interaction of physical, chemical and biological processes that alters the stone in some general or specific way. The physical properties of stone differs widely between stone groups and even within the same stone type.

The mineral composition, textural differences, varying degrees of hardness and pore/capillary structure are the main reasons why stone nor all the surface of the same stone shows signs of alteration the same and evenly. These minerals can be broken down, dissolved or converted to new minerals by a variety of processes which are grouped as Mechanical and Chemical. Intensity and duration are two key elements that govern to what extent weathering reactions will have on stone.

Water absorption and frost resistance:

Moisture from rain, snow or other environmental conditions penetrates the wall leading to cracks, efflorescence, rust staining, wood rotting, paint peeling, darkening of masonry and spalling. The perfect sealing of a masonry wall surface is almost impossible since fine cracks and joints will allow the passage of water into the wall.

 

 

Absorbency:

It is the result of these two properties (permeability and porosity). Absorbency is an important determining factor in stones sensitivity to stains. The size of the pores, their orientation, how well they are networked and the type of finish the stone has are important contributing factors to a stones overall absorbency. In relation to cleanability this factor is more important than how porous a stone is. Honed and textured surfaces are more susceptible to soiling and staining due to the fact that there are more open pores at the surface than a highly polished finish.

The polishing process has a tendency to close off pores leaving fewer ones exposed, resulting in a low absorbent surface. However, some varieties of stone have large pores and capillary structures and even when these stones are polished they still remain very absorbent. Most common oils can be easily absorbed into all types of stone.

Frost action or commonly called freeze/thaw cycles occur when water within the pore structure or cracks freezes to ice. It has been estimated when water freezes it expands between 8 to 11 percent, with a force of 2,000 pounds per square inch to 150 tons per square foot. This increase of internal pressure combined with repeated freeze/thaw cycles produces micro-fissures, cracks, flaking.

STONE TEST

Acid Test:

Here, a sample of stone weighing about 50 to 100 gm is taken. It is placed in a solution of hydrophobic acid having strength of one percent and is kept there for seven days. Solution is agitated at intervals. A good building stone maintains its sharp edges and keeps its surface free from powder at the end of this period. If the edges are broken and powder is formed on the surface, it indicates the presence of calcium carbonate and such a stone will have poor weathering quality. This test is usually carried out on sandstones.

Attrition Test:

This test is done to find out the rate of wear of stones, which are used in road construction. The results of the test indicate the resisting power of stones against the grinding action under traffic. The following procedure is adopted:

i. Samples of stones is broken into pieces about 60mm size.

ii. Such pieces, weighing 5kg are put in both the cylinders of Devil’s attrition test machine. Diameter and length of cylinder are respectively 20cm and 34 cm.

iii. Cylinders are closed. Their axes make an angle of 30 degree with the horizontal.

iv. Cylinders are rotated about the horizontal axis for 5 hours at the rate of 30 rpm.

v. After this period, the contents are taken out from the cylinders and they are passed through a sieve of 1.5mm mesh.

vi. Quality of material which is retained on the sieve is weighed.

vii. Percentage wear worked out as follows:

Percentage wear = loss in weight/initial weight X 100

Crushing Test:

Samples of stone is cut into cubes of size 40x40x40 mm. sizes of cubes are finely dressed and finished. Maximum number of specimen to be tested is three. Such specimen should be placed in water for about 72 hours prior to test and therefore tested in saturated condition.

Load bearing surface is then covered with plaster of paris of about 5mm thick plywood. Load is applied axially on the cube in a crushing test machine. Rate of loading is 140 kg/sq.cm per minute. Crushing strength of the stone per unit area is the maximum load at which the sample crushes or fails divided by the area of the bearing face of the specimen.

Crystalline Test:

At least four cubes of stone with side as 40mm are taken. They are dried for 72 hrs and weighed. They are then immersed in 14% solution of Na2SO4 for 2 hours. They are dried at 100 degree C and weighed. Difference in weight is noted. This procedure of drying, weighing, immersion and reweighing is repeated atleast 5 times. Each time, change in weight is noted and it is expressed as a percentage of original weight.

Crystallization of CaSO4 in pores of stone causes decay of stone due to weathering. But as CaSO4 has low solubility in water, it is not adopted in this test.

Freezing and thawing test:

Stone specimen is kept immersed in water for 24 hours. It is then placed in a freezing machine at -12 degC for 24 hours. Then it is thawed or warmed at atmospheric temperature. This should be done in shade to prevent any effect due to wind, sun rays, rain etc. this procedure is repeated several times and the behaviour of stone is carefully observed.

Hardness Test:

For determining the hardness of a stone, the test is carried out as follows:

i. A cylinder of diameter 25mm and height 25mm is taken out from the sample of stone.

ii. It is weighed.

iii. The sample is placed in Dorry’s testing machine and it is subjected to a pressure of 1250 gm.

iv. Annular steel disc machine is then rotated at a speed of 28 rpm.

v. During the rotation of the disc, coarse sand of standard specification is sprinkled on the top of disc.

vi. After 1000 revolutions, specimen is taken out and weighed.

vii. The coefficient of hardness is found out from the following equation:

Coefficient of hardness = 

Impact Test:

For determining the toughness of stone, it is subjected to impact test in a Page Impact Test Machine as followed:

i. A cylinder of diameter 25mm and height 25mm is taken out from the sample of stones.

ii. It is then placed on cast iron anvil of machine.

iii. A steel hammer of weight 2kg is allowed to fall axially in a vertical direction over the specimen.

iv. Height of first blow is 1 cm, that of second blow is 2cm, that of third blow is 3 cm and so on.

v. Blow at which specimen breaks is noted. If it is nth blow, ‘n’ represents the toughness index of stone

REFERENCES

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Alfred Swenson and Pao-Chi Chang, "History of Building"

Hunt, Norman. Living in ancient Greece. New York, N.Y.: Chelsea House Publishers, 2009. 24. ISBN 0816063397

Strickland, Carol, and Amy Handy. The Annotated Arch: A Crash Course in the History of Architecture. Kansas City, MO: Andrews McMeel Pub., 2001. 12. ISBN 0740710249

https://en.wikipedia.org/wiki/History_of_construction

Stephany, Erich Der Dom zu Aachen (Aachen Cathedral) Arend und Ortmann, Aachen, 1972

Stephany, Erich Der Dom zu Aachen (Aachen Cathedral) Arend und Ortmann, Aachen, 1972

 Upton, Dell. Architecture in the United States. Oxford: Oxford University Press, 1998. 153. ISBN 019284217X

Bill Addis. Building: 3000 years of Design Engineering and Construction. Phaidon. 2007. p. 632

A.Becchi, M.Corradi, F.Foce & O. Pedemonte (eds.). Construction History: Research Perspectives in Europe. Associazione Eduardo Benvenuto. 2004

http://www.modernmarble.net/Typeofstone.html

https://en.wikipedia.org/wiki/Rock_%28geology%29

Roberts, Dar. "Rocks and classifications". Department of Geography, University of California, Santa Barbara. Retrieved 11 November 2012.

"Limestone (mineral)." Microsoft® Encarta® 2009 [DVD]. Redmond, WA: Microsoft Corporation, 2008

"Stone." Microsoft® Encarta® 2009 [DVD]. Redmond, WA: Microsoft Corporation, 2008.

Bateman, Alan M. "Slate." Microsoft® Encarta® 2009 [DVD]. Redmond, WA: Microsoft Corporation, 2008

"Granite." Microsoft® Encarta® 2009 [DVD]. Redmond, WA: Microsoft Corporation, 2008. 

http://www.aboutcivil.org/Stone-properties-and-tests.html

http://theconstructor.org/building/tests-on-building-stones/5552/