Construction Technologu and. Building Materials Learning Limit º. º Training Module for Barefoot Work Book. Exercisel: Identify the construction materials. Item 1 - 6 This book is suitable for students majoring in “Civil Engineering”, In the total cost of the construction, the cost of building materials often accounts for. Download Building Materials And Construction Books – We have compiled a list of Best & Standard Reference Books on Building Materials And Construction.
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PDF Drive is your search engine for PDF files. As of today we have Building Materials & Construction Planning Textbook free. Pages·· PDF Drive is your search engine for PDF files. As of today we have 78,, eBooks for you to download for free. No annoying ads, no download limits, enjoy . The second edition of this book deals with properties of building materials practical groundwork for students of civil, architecture and construction technology.
Thermal conductivity coefficient and specific heat should be known when thermal calculations are conducted to buildings. Serious cracks will happen sometimes. The bending strength o f 3 d MPa: Various chemical compositions result in different properties. Macro-structure The thick structure above millimeter that can be identified with magnifying glass or naked eyes is called as macro-structure. The other contents are all concerned with this focus. And materials will be destroyed gradually by the long-term and repeated actions.
Non-crystal plays the role of adhesive in products of burned clay and some natural rocks. Density Density is the dry mass per unit volume of a substance under absolute compact conditions. It is defined by: The volume under absolute compact conditions refers to the solid volume without the volume of inner pores.
Except steel, glass, asphalt and a few other materials, most materials contain some pores in natural state. In the measurement of the density of a porous material, the material is ground into powder at first; the powder is dried to fixed mass; and then the solid volume is measured by Lee's density bottle; finally the density is calculated by the above formula. The finer the powder is ground, the more real the size will be.
Thus the density value is more correct. Apparent Density Apparent density is the dry mass per unit volume of a substance under natural conditions. The volume of a substance under natural conditions refers to the solid volume and the volume of inner pores. If it is a regular shape, the volume can be directly measured; if it is in an irregular shape, the volume can be measured by the liquid drainage method after sealing pores with wax; the liquid drainage method can be directly used to measure the volume of sandstone aggregate utilized in concrete but the volume here is the solid volume plus the volume of closed pores-without the volume of the pores open to the outside.
Because the sandstone is compact with only a few pores, the volume of the pores open to the outside is little. Thus the volume measured by the liquid drainage method can be called apparent density which is called virtual density in the past.
The quality and volume change with the water content. Generally, apparent density refers to the density of a substance under dry conditions. Other moisture conditions should be specified.
Bulk Density Bulk density refers to the per unit volume of a substance under the conditions that powdery or granular materials are packed. Bulk density is measure by volumetric container.
The size of volumetric container depends on the size of particles. For example, 1L volumetric container is used to measure sand and IOL, 20L, 30L volumetric containers are used in the measurement of stone. Bulk density is the packing density of a substance under dry conditions and others should be marked.
The density, apparent density and bulk density of common building materials are listed in Table 2. Table 2. Solidity Solidity refers to the degree how the volume of a material is packed with solid substances, which is the ratio of the solid volume to the total volume. Porosity Porosity P is the percentage of the pores volume to the total volume with the volume of a substance. Porosity and characteristics of pores including size, connectivity, distribution, etc.
Generally, for the same material, the lower the porosity is, the less the connected pores are. Thus the strength will be higher, the water absorption will be smaller, and the permeability and frost resistance will be better, but the thermal conductivity will be greater.
Porosity of some common materials is listed in Table 2. Fill Rate Fill Rate D' is the degree how granules pack the granular materials in the bulk volume. Voidage Voidage P' is the percentage of the void volume among granules to the bulk volume in the bulk volume of granular materials. The relationship between fill rate and voidage can be expressed as: Hydrophilicity and Hydrophobicity When the material is exposed to water in the air, it will be hydrophilic or hydrophobic according to whether it can be wetted by water or not.
If it can be wetted by water, it is the hydrophilic material; if not, it is the hydrophobic material. When materials are exposed to water droplets in the air, there will be two cases, shown as Figure 2. In the intersection of the material, water and air, a tangent is drown along the surface of the water droplet, and the angle between the surface and the tangent is angle 8,known as wetting angle. When angle 0 is smaller than or equals to 90" O solid a Iiydroplulic rilalcrials solid b hydrophobic miiterials Figure 2.
The attractive force between material molecules and water molecules is weaker than the cohesive force between water molecules, so the material cannot be wetted by water. The hydrophobic materials are moisture-proof and waterproof, usually used for water-resistant materials or the surface treatment for the hydrophilic materials in order to reduce water absorption and improve impermeability.
The Water Absorption and Hygroscopicity 1 Water Absorption Water absorption refers to the property of absorbing water when materials are exposed to water. It is expressed by the water-absorption ratio.
And there are two types of expression: In this formula: The relationship between specific absorption of quality and that of volume is as follows: For normal materials, the higher the porosity is, the stronger the water absorption is. The more the open and connected tiny pores are, the stronger the water absorption is; it is not easy for water to be absorbed if the pores are closed; if they are large and open, water is easy to be absorbed but is hard to be hold, and thus the water absorption is weak.
The water-absorption ratios of various materials vary greatly. For example, the specific absorption of quality of granite rock is 0. If a material absorbs water, its quality will increase, its volume will expand, its thermal conductivity will increase and its strength and durability will decrease. It can be expressed by moisture content.
Moisture content is the percentage of the water quality contained in a material to its dry mass, expressed by Wh. The hygroscopic effect is reversible. Dry materials can absorb moisture in the air and wet materials can release moisture to the air.
The moisture content is called equilibrium moisture content if the content of a material equals to air humidity. The hygroscopicity of materials is related to air temperature and air humidity. The higher humility is and the lower the temperature is, the higher hygroscopicity will be; contrarily, the hygroscopicity will be low. Water Resistance Water resistance is the ability to maintain its original properties when the material is affected by water in a long-term. The water-resistant ability of different materials varies in expressing ways.
For example, the water resistance of structural materials mainly refers to the changes in intensity, and with sotlening coefficient it is defined by: KRis the softening coefficient of a material; f ,is the compressive strength of a material in water saturation state MPa ; 2 fg The basic Properties of Building Materials 17 is the compressive strength of a material in dry state MPa.
The softening coefficient of a material KRvaries between 0 clay -1 steel. The value of KR reveals the decreasing degree of the strength after the material absorbs water to saturation. The bigger KRis, the stronger the water resistance is, which indicates that the decreasing degree of the strength in saturation state is low; contrarily, the water resistance is weak.
Generally, the material whose KRis bigger than or equals to 0. KR is an important basis for selecting building materials. If the major structures are often in water or wetted seriously, the materials whose KR is bigger than or be chosen; ifthey are the minor structures or equals to 0. Impermeability Impermeability is the ability of a material to resist the pressure water or the infiltration of other liquids.
It is expressed by permeability coefficient which is defined by: Permeability coefficient K reflects the rate of water flowing in a material. The bigger K is, the faster the flow rate of water is and the weaker the impermeability is. The impermeability of some materials such as concrete and mortar can be expressed by impermeable level which is represented by the maximum water pressure resisted by materials.
OMPa, and 1. The impermeability of a material is related not only to its own hydrophilicity and hydrophobicity but also to its porosity and the characters of pores. The smaller the porosity is and the more the closed pores are, the 18 Building materials in civil engincering stronger the impermeability is.
Impermeable materials should be used in water conservancy projects and the underground projects usually affected by pressure water. Waterproof materials should be impermeable. Frost Resistance Frost resistance is the property that a material can withstand several freeze-thaw cycles without being destroyed and its strength does not decrease seriously when the material absorbs water to saturation. It is expressed by frost-resistant level.
Frost-resistant level is indicated by the biggest freeze-thaw-cycle times of a specimen that both its quality loss and strength reduction are within provisions when it is affected by freeze-thaw cycles in water saturation state, such as F25, F50, FlOO and F If this stress exceeds the tensile strength, the pore walls will crack, the porosity will increase and the strength will decrease.
The more the freeze-thaw cycles are, the greater damages there will be. And it will even cause the complete destruction of a material. There are internal and external factors affecting frost resistance of a material. The internal factors are the composition, structures, construction, porosity, the characteristics of pores, strength, water resistance, and so on. Thermal Conductivity The property of a material that indicates its ability to conduct heat is known as thermal conductivity.
It is expressed by the coefficient of thermal conductivity A ,which is defined by: The smaller the value of A is, the better insulation the material has.
The thermal conductivity of a material is related to its composition and structure, the porosity and the characteristics of its pores, the water content, temperature and other conditions. The coefficient of thermal conductivity of metallic materials is bigger than that of non-metallic materials. The bigger the porosity is, the higher the coefficient will be. Tiny and closed pores indicate low coefficient; big and open pores are easy to create convection heat, which indicates that the coefficient is high.
The thermal conductivity coefficient of a material containing water or ice increases dramatically because the coefficient of water and ice is bigger than that of air. Thermal Capacity Thermal capacity is the property of a material to absorb heat when it is heated and to release heat when it is cooled. K ]; - is the temperature difference before and after heating r, or cooling K. The specific heat, also called specific heat capacity, is the measure of the heat energy that a substance in a unit quality absorbs or releases when the temperature increases or decreases 1K.
The bigger the specific heat is, the better the stability of the indoor temperature will be. Thermal conductivity coefficient and specific heat should be known when thermal calculations are conducted to buildings. There are thermal conductivity coefficients and specific heat capacities of several common materials are listed in Table 2.
Thermal Deformation Thermal deformation is the property of a substance to expand with heat and contract with cold, customarily called temperature deformation. It is expressed by linear expansion coefficient a , which is defined by: The bigger the linear expansion coefficient a is, the greater the thermal deformation will be.
The thermal deformation is detrimental to the civil engineering. For example, in a large-area or large-volume concrete project, temperature cracks can be caused if the expansion tensile stress is beyond the tensile strength of concrete; in a large-volume construction work, expansion joints are set to prevent the cracks caused by thermal deformation; and Petroleum asphalt will have brittle factures when temperature drops to a certain extent. Flame Resistance Flame resistance is the property of a substance not to flame in case of contacting with fire in the air.
Materials can be divided into non-flammable 2 The Basic Properties of Building Materials 21 materials, fire-retardant materials and flammable materials according to their reaction to fire.
In construction, the selection of non-flammable materials or fire-retardant materials depends on fire-resistant levels of buildings and the parts where materials are used. Fire prevention should be dealt with when flammable materials are used.
Strength of Materials Strength is the greatest stress that a substance can bear under external forces loads without destruction. According to different forms of external forces, the strength includes tensile strength, compressive strength, bend strength, shear strength and others. These kinds of strength are all determined by static test, known as the static strength.
The static strength is tested by destructive experiments based on standard methods see Appendix. The stress states of a material are shown in Figure 2. The bend strength is related to the force that a material bears and the cross-section shape.
For the strip specimen with rectangular cross-section, when it is supported at both ends and a load converges in the middle, its bend strength can be calculated by: The strength of a material is related to its composition and structure.
The strength will be different if the compositions of materials are the same but the structures are different. The bigger the porosity is, the smaller the strength will be. China has provided various standard test methods of material 2 The Basic Properties of Building Materials 23 strength in order to make the results more accurate and comparable. These methods should be strictly followed when the strength is tested.
Strength Grade The strength can be divided into a number of different grades in accordance with the ultimate strength of most building materials, known as strength grade. The grades of brittle materials are mainly divided based on their compressive strength, such ordinary clay brick, stone, cement and concrete; and those of plastic materials and ductile materials depcnd on their tensile strength, such as steel.
It is significant to classify the strength grades for mastering functions and choosing proper materials. Specific Strength The specific strength is a material strength divided by its apparent density. It is an important index for measuring the high-strength and lightweight materials. The specific strength of ordinary concrete, low-carbon steel, and pine along the grain is respectively 0. The higher specific strength is, the higher strength and lighter weight the material is. Elasticity The elasticity is the property of a substance to deform with external forces and return to its original shape when the stress is removed.
The deformation fully capable of restoration is called elastic deformation. The elastic modulus is a measure of the ability to resist deformation. The bigger E is, the more difficultly the material deforms. Plasticity The plasticity describes the deformation of a material undergoing non-reversible changes of shape in response to external forces.
This non-reversible deformation is called plastic deformation. Some materials only have elastic deformation if the stress is not large, but plastic deformation will happen to them when the stress is beyond a limit, such as low-carbon steel. Under external forces, some materials will have elastic deformation and plastic deformation at the same time, but elastic deformation will disappear and plastic deformation still maintains when the stress is removed, such as concrete.
Brittleness Brittleness describes the property of a material that fractures when subjected to stress but has a little tendency to deform before rupture. Brittle materials are characterized by little deformation, poor capacity to resist impact and vibration of load, high compressive strength, and low tensile strength.
Most of inorganic non-metallic materials are brittle materials. Toughness Impacted or vibrated by stress, a material is able to absorb much energy and deform greatly without rupture, which is known as toughness, also called impact toughness. Tough materials are characterized by great deformation, high tensile strength, and high compressive strength, such as construction steel, wood and rubber. Tough materials should be used in the structures bearing impact and vibration, such as roads, bridges, cranes and beams.
Hardness Hardness refers to the property of a material to resist pressing-in or scratch of a sharp object. The materials of different kinds of hardness need various testing methods.
The hardness of steel, wood and concrete is tested by pressing-in method. For example, Brine11 Hardness HB test is expressed by the pressure loaded on the press mark per unit area. The hardness of natural minerals is often tested by scratch hardness. Mineral hardness is divided into '10 grades, and the increasing order is: Abrasive Resistance Abrasive resistance refers to the capacity of a material to resist abrasion.
It is expressed by the abrasion ratio, calculated as: N is the abrasion ratio dcm2 ; m,is the mass before abrasion g ; m2is the mass after abrasion g ; A is the abrasive area cm2. They play decorative, protective, and other specific roles such as insulation, moisture-resistance, fireproofing, sound-absorption, and sound-insulation.
And decorative effects primarily depend on colors, textures and linetypes of the decorative materials.
Color Color is an important factor for the appearance of buildings, even impacting on the environment. All the buildings are ornamented by colors. Generally, white or light-colored elevation hue often gives people a clean and fresh feeling; dark-colored elevation appears dignified and stable; people usually feel enthusiastic, excited and warm when see red, orange, yellow and other warm colors indoors; and green, blue, violet and other cold colors can enable people to be peaceful, elegant and cool.
As living conditions, climates, traditions, and customs are different, people have various feelings and evaluations on colors. Texture Texture is a comprehensive impression given by the appearance of a material, such as roughness, unevenness, grain, patterns, and color differences.
For example, the rugged surface of concrete or brick appears relatively massy and rough; and the surface of glass or aluminum alloy is smooth and delicate which seems light and vivid. Texture is connected with characteristics, 26 Building matcrials in civil engineering processing degrees, construction methods, and the types and elevation styles of buildings. Linetype Linetype mainly refers to the decorative effect of the dividing joints and the convex lines ornamented on elevations. For example, plastering, granitic plaster, pebble dash, natural stone, and aerated concrete should be all latticed or divided, which will create various elevation effects and also prevent cracking.
The size of dividing joints should be suitable for materials. Generally, the width should be mm, and the blocks of different sizes will create different decorative effects. In this process, materials are subjected to physical, chemical, biological and other natural factors besides various kinds of stress.
Physical actions include wet-and-dry, temperature, and freeze-and-thaw changes, all of which will cause expansion and contraction of materials. And materials will be destroyed gradually by the long-term and repeated actions. Chemical actions are the erosion of acid, alkali and salt aqueous solution which can change the compositions of materials and destroy them, such as the chemical erosion of cement and the corrosion of steel.
Biological action includes the destruction of fungi and insects which can molder or rot materials, such as the decomposition of wood and plant fiber. Durability is a comprehensive property of materials. Materials of different compositions and structures have different kinds of durability. For example, steel is easy to be corroded; stone, concrete, mortar, sintering ordinary clay brick, and other inorganic non-metallic materials mainly resist frost, wind, carbonization, wet-and-dry change, and other kinds of physical action; when contacting with water, some materials can be destroyed by chemical changes; and asphalt, plastic, rubber and other organic materials will be damaged due to aging.
Explain their differences. How to calculate? Is there any practical significance of the two materials in construction projects? And what are the factors influencing the water absorption? And are there any practical meanings? How to calculate various kinds of strength according to different types of stress? And how about their units? What is plasticity? What is toughness? What kinds of brittle and tough materials are often used in projects? Exercises 2. Calculate its density, apparent density, solidity and porosity.
Calculate its density. Calculate the bulk density of gravel. If water is filled into the container, the total weight 28 Building materials in civil engineering becomes Calculate the apparent density and porosity of the gravel. Calculate the amount of wet sand and wet stone respectively.
And the tension measured at the destruction is 3 1. Calculate the tensile strength of steel. In construction projects, the materials that can conglutinate granular materials such as sand and gravel or bulk materials such as bricks and stone together as a whole are called binding materials, the important materials in construction projects. And the common binding materials can be divided into: Such materials can only be hardened in the air dry conditions and their strength can maintain and develop only in the air.
And its products have many excellent characters, commonly used in construction. Varieties of gypsum will be produced when the natural dihydrate gypsum is processed with the change of heating methods and temperatures. The main production procedures are breaking, heating and grinding. The gypsum commonly used in construction projects is building gypsum, composed of p semi-hydrate gypsum. The natural dihydrate gypsum is calcined into semi-hydrate gypsum undcr the temperature of "C and then is ground into powder which is the building gypsum.
Its reactive mode is: According to GB, building gypsum can be classified into high-class, first-class and acceptable grades in light of strength, fineness and setting time, shown in Table 3. Among them, bending strength and compressive strength are measured by letting samples contact with water for 2 hours.
For example, the building gypsum of 2. Building Gypsum 2. The hydration of building gypsum technically requires that water requirements accounts for Thus, building gypsum has low strength, small apparent density, low thermal conductivity and high sound absorption after hardening.
In the process of storage and transport, building gypsum should not be exposed to moisture and mixed with sundries. Gypsum of different grades should be stored respectively and should not be mixed.
The general storage period is three months. The gypsum beyond storage period needs to be re-examined to determine the grades. And after a period of reaction, it will lose plasticity and condense into solid with certain strength. The setting and hardening of building gypsum occur because water and semi-hydrate gypsum react mutually and then restore to dihydrate gypsum: Combining with water, the semi-hydrate gypsum in the saturated solution becomes dihydrate gypsum.
The saturated solution of semi-hydrate gypsum is oversaturated for dihydrate gypsum because the solubility of dihydrate gypsum is much smaller than that of semi-hydrate gypsum. Thus, the saturated solution precipitates the dihydrate gypsum in the form of colloid particle, which accelerates the semi-hydrate gypsum to dissolve and hydrate continuously till complete dissolution.
In this process, the free water in the slurry decrease gradually because of hydration and evaporation, the colloid particles of dihydrate gypsum increase, the consistency of the slurry rises, and 32 Building materials in civil engineering friction and cohesive forces between particles grow increasingly.
Subsequently, the slurry continues getting thicker, and colloid particles gradually turn into crystals. They become bigger, symbiotic and staggered, which enable the slurry to have strength.
Such strength continues growing till complete dryness, and friction and cohesive forces between crystals stop increasing.
At this moment, the strength stops developing. In fact, setting and hardening of gypsum are continuous and complicated physical and chemical processes.
Fast Setting and Hardening The setting time of building gypsum changes with the calcination temperature, grinding rate and impurity content. Generally, mixed with water, its initial setting needs just a few minutes at room temperature, and its final setting is also within 30min.
Under the natural dry indoor conditions, total hardening needs about one week. The setting time can be adjusted according to requirements. If the time needs to be postponed, delayed coagulant can be added to reduce the solubility and the solution rate of building gypsum, such as sulfite alcohol wastewater, bone glue activated by borax or lime, hide glue, and protein glue; if it needs to be accelerated, accelerator can be added, such as sodium chloride, silicon sodium fluoride, sodium sulfate, and magnesium sulfate.
Thus, it can be used alone without any extenders, and can also be casted into construction members and decorative patterns with accurate size and smooth and compact surface. But these products have low strength and large water absorption due to big porosity. Poor Water Resistance Building gypsum has low softening coefficient about 0.
Absorbing water, it. Thus, its water resistance and frost resistance are poor, not used outdoors. When it contacts with fire, the evaporation of crystal water will absorb heat and generate anhydrous gypsum which has good thermal insulation.
The thicker its products are, the better their fire resistance will be. Large Plastic Deformation Gypsum and its products have an obvious performance of plastic deformation. Creep becomes more serious especially under bending load. Thus, it is not used for load-bearing structures normally.
If it is used, some necessary measures need to be taken. It is suitable for indoor decoration, insulation and thermal retardation, sound absorption, and fire retardation. Generally, it is made into plaster mortar, architectural and decorative products, and gypsum plank.
Indoor Plastering and Painting Mixed with water and sand, building gypsum will turn into gypsum mortar which can be used for indoor plastering. Such plastered wall is insulating, fire-resistant, sound-absorbing, comfortable, and aesthetic. The plastered wall and ceiling can be painted or pasted with wallpaper directly. The gypsum mortar can be used as indoor coating material mixed with lime.
The wall painted with this mortar is smooth, delicate, white, and beautiful. And its main technical indexes are as follows: OMPa, and that of the first-class one is 3. Decorative Products As the main raw material, gypsum will be stirred into gypsum mortar with water, added a small amount of fiber-reinforced materials and plastic materials. By its micro-expansion performance, the gypsum mortar can be made into various plaster sculptures, decorative panels and accessories. It is of mm width and mm thickness.
The length can be fixed according to needs. The thistle board is mainly used as inner wall, partition wall, and ceiling. This board has high strength which can be used as the inner wall and partition wall in residential and public buildings. And its installation does not need any keel. There are flat plates, porous plates, diamond plates, embossed plates and decorate plates which are diverse, colorful, and aesthetic, mainly used as walls and ceilings in public buildings.
With high bending strength, it can be used as inner wall and partition wall, or be used to make hmiture instead of wood. Besides, there are cellular gypsum boards, moisture-resistant gypsum boards, and compound mine-wool boards which can be used as thermal - - - - 3 Air Hardening Binding Matcrials 35 insulation panels, acoustic panels, inner walls, partition walls, ceilings, and floor basal plates.
If supported by fiber-reinforced materials and gelling agents, building gypsum can be made into gypsum coving, line board, corner pattern, lamp ring, Roman column, sculptures and other artistic gypsum products. Therefore, lime is still widely used in construction until now. Raw Materials of Lime The main raw material of lime is natural rock whose major component is calcium carbonate. The common lime includes limestone, dolomite, and chalk.
Besides the natural raw materials, another source of lime is the chemical industrial by-products. For example, the major component of the carbide slag remained in the preparation of acetylene from acetylene stone calcium carbide is calcium hydroxide, namely, hydrated lime. Lime Production After calcination, limestone generates quicklime. The reactive mode is: If the calcination temperature is too low and the calcination time is not sufficient, CaCO3 cannot dissolve completely and will generate under-burnt lime.
Under-burnt lime generates less mortar and the quality is poor, which lowers the utilization of lime; if the calcination temperature is too high, the dark-color over-burnt lime with high, density will be generated which will affect the project quality.
Quicklime is a kind of white or grey block substance whose major component is CaO. The calcinated lime contains MgO correspondingly 36 Building materials in civil engineering because its raw materials always contain some magnesium oxide components. Aging of Lime The process that quicklime CaO generates calcium hydroxide with water is known as the aging or digestion process of lime, of which the reactive mode is: The theoretical water demand needed in the aging process takes only If too much water is added, the temperature will drop and the aging process will slow down, which will extend the aging time.
There are two methods used for lime aging on construction site: Quicklime often contains over-burnt lime which is the fused mass with dark brown surface.
The aging of over-burnt lime is very slow and the over-burnt particles start to age when lime has gotten hardened. Then the volume expands, leading to uplifting and cracking. Crystallization In the use of lime mortar, Ca OH 2 solution is over-saturated and gradually precipitate crystals because the free water gradually evaporates and is absorbed by masonry. This process accelerates the hardening of lime mortar and meantime the mortar tightens and generates strength due to dryness. Carbonization With C02 in the air, Ca OH 2 generates the insoluble crystals of calcium carbonate, and the precipitated water gradually evaporates.
The reactive mode is as follows: And the precipitated CaCO3 crystals make the hardened mortar compact and enhance the strength. The content of CO2 in the air is little.
And carbonization mainly happens on the surface, contacting with the air. And the compact CaC03 film generated on the surface hinders the further infiltration of the air and prevents the inner water evaporating, which slow down the crystallization of Ca OH 2.
As time passes, the thickness of CaCO3 on the surface increases and the prevention become greater. They can be classified into three grades respectively, according to the standards of the building industry, and the corresponding indexes are listed in Table 3. The product whose various technical indexes reach a certain grade set in the tables should be targeted with this grade. If one of its technical indexes is less than the qualified grade, it should be targeted as the ineligible product.
Table 3. Good Water Retention The lime mortar generated by the aging of lime has good water retention, so it can be mixed in cement mortar to improve the water retention of mortar to facilitate construction. Slow Setting and Hardening, Low Strength Because the carbonization of lime mortar in the air is very slow, the production of calcium carbonate and calcium hydroxide is a little and quite slow.
And thus, the strength of hardened lime is low. According to tests, 1: Poor Water Resistance Calcium hydroxide is soluble in water, so if it is exposed to moisture or immerses in water for a long time, the hardened lime will scatter. If lime mortar is in humid environment before complete hardening, the water in lime cannot evaporate, and the hardening will be hindered. Therefore, lime should not be applied in humid environment. Large Shrinkage In the hardening process of lime mortar, a large amount of water evaporates, which cause the shrinkage of volume.
And desiccation cracks will appear. Thus, lime mortar should not be used alone except for the lime cream for thin painting. In use, it is often mixed with sand, hemp fiber, paper pulp, and other things to resist cracking caused by shrinkage.
And different varieties have different purposes. Lime Powder Lime powder can be made into silicate products mixed with materials containing silicon. With water, pulverized lime can be molded by being mixed with fiber materials such as glass fiber or lightweight aggregate.
Then, it can be carbonized artificially with carbon dioxide for carbonized lime board. Carbonized lime board has a good processing property, suitable for the non-load-bearing inner partition and ceiling. Mixed with a certain percentage of clay, pulverized lime can generate limestone soil.
Triple-combined soil can be generated by mixing lime powder with clay, gravel, and slag. Lime soil and 40 Building materials in civil engineering triple-combined soil are mainly used for foundation, bedding cushion, and roadbed. Lime Paste The aged lime paste or hydrated lime can turns into lime milk, diluted with water, as paint of internal and external walls and ceilings; if mixed with a certain amount of sand or cement and sand, it can be prepared into lime mortar or compound mortar for masonry or finishing; it can be used to paint inner walls or ceilings by being mixed with paper pulp and hemp fiber.
Storage of Lime Quicklime will absorb the water and carbon dioxide in the air, generate calcium carbonate powder and lose cohesive force. Thus, when stored on construction site, quicklime should not be exposed to moisture, not be more, and not stay for a long time. Moreover, the aging of lime will release a great amount of heat, so quicklime and inflammable matter should be stored separately in order to avoid fire.
Usually quicklime should be stabilized immediately and the storage period should be changed into aging period. Its major component is magnesium oxide MgO which is a kind of white or yellow powder, belonging to magnesia cement materials.
Its density is 3. Magnesia should not be exposed to moisture in transport or storage and also cannot be stored for a long time. Thus, modifier is always used to accelerate the hardening process. The most common modifier is magnesium chloride solution, and the reaction is: After adding modifier, setting and hardening will become faster, and also the strength will be improved markedly. Therefore, it is always mixed with wood chips and wood fibers to produce xylolite floor, wood-cement board, and xylolite slab.
In addition to wood chips and wood fibers, French chalk, asbestos, fine quartz sand, brick powder and other fillers are added to magnesia in order to improve the strength and wear resistance of products.
Magnesia grindstone floor will be made by using marble or rock of medium hardness as the aggregate. Magnesia floor is heat-retardate, dust-free, wear-resistant, fire-resistant, smooth, and elastic. It is a good floor material that can be colored by adding alkali-resistant mineral pigments.
Magnesia board has high tightness, high intensity, sound absorption and thermal insulation, which can be used as the inner wall, ceiling and other building materials. Reinforced magnesia has high intensity and can be used as constructional element instead of wood, such as wood pad and column. Magnesia can be made into light and porous thermal-insulating material by adding foaming agent. The water resistance of magnesia is poor, so its products should not be stored in humid places for a long time.
And its products should not be used with steel bars, for in the process of using magnesia, magnesium chloride solution is commonly used and the chloride ions can erode steel bars. In construction, it is usually used to prepare sodium silicate cement, soluble glass mortar, and soluble glass concrete. Soluble glass is widely used in the anti-acid and heat-resistant engineering.
Liquid soluble glass is alkali. Pure soluble glass solution should be clear and colorless liquid, but it often appears steel grey or yellow-green due to impurities.
In the using process, soluble glass is often heated or mixed with sodium fluosilicate Na2SiF6 as an accelerator for hardening to quicken the hardening speed. Sodium fluosilicate is added into soluble glass will react as follows, speeding up the precipitation of silicic acid gel.
Sodium fluosilicate can also improve the water resistance of soluble glass. And the number of module decides the properties and performance of soluble glass. The solid soluble glass with low module is relatively easy to dissolve in water. The bigger the number is, the higher the viscosity is and the harder it dissolves in water; the soluble glass with low module, there are many kinds of crystal composition and the cohesive force is poor, and when the module number improves, the colloid component increases and the cohesive force rises.
Different amount of water will lead to solutions of different density and viscosity. For the soluble glass solutions with the same module, the higher the density is, the stronger the cohesive force is. If urea is added into soluble glass, its cohesive force can be improved without modifying the viscosity.
Soluble glass also has strong acid corrosion that can resist the majority of inorganic acids, organic acids, and corrosive gases. The silicate gel precipitating during the hardening of soluble glass can block the capillary porosity of the material to prevent water infiltration.
Soluble glass has good heat resistance, so it does not dissolve and its strength does not decrease and even increases at a high temperature. In addition, the soluble glass can burn eyes and skin to a certain extent, so the security protection is needed. Acid-proof Material Soluble glass can be used as binding material to prepare acid-proof plaster, acid-proof mortar, and acid-proof concrete which are commonly used in anti-acid projects.
Heat-resistant Material Soluble glass has a good heat resistance that can bear a certain high temperature and its strength does not increase. Thus, it can be made into heat-resistant concrcte and mortar. Coating Soluble glass solution can be used to paint building materials or immerging porous materials. It can enhance the density and strength of materials and increase their resistance to weathering when infiltrating into the materials.
But the solution can not be used to paint or immerge gypsum products because soluble glass can react with gypsum to generate sodium sulfate crystals which will expand in pores and destroy the gypsum products. Grouting Material Soluble glass solution and calcium chloride solution are injected into soil alternately, and the two solutions will cause chemical reaction to precipitate 3 Air Hardening Binding Materials 45 silicate gel which can cement or fill the pores of soil and prevent the infiltration of water to increase the density and strength of soil.
Water-proof Plugging Material Soluble glass solution mixed with sand or cement can make setting and hardening occur quickly, for repairing or plugging structures. Moreover, mixed with various alum solutions, soluble glass can be used as water-proof agent for cement mortar or concrete.
Questions 3. What are the characteristics? Where is it used? And their characteristics. Why should lime be stabilized before use? Cement is a hydraulic mineral binding material. Blended with water, the pulverous cement can generate the plastic paste which will turn into hard cement block and bind granulated or block materials togcther after a series of physical and chemical effects. The hardening of cement paste will happen not only in the air but also in water and also can maintain and increase its strength.
Cement is one of the important materials for the construction of national economy. Also, it is the basic component for concrete, reinforced concrete, and prestressed concrete, commonly used in construction, transportation, water conservancy, electric power, national defense, and other construction projects.
According to the national cement naming standard, cement can be named based on its main hydraulic minerals as: Portland cement, aluminate cement, sulphate cement and sulpho-aluminate cement, and phosphate cement.
Among many varieties of cement, the commonly used one is the Portland cement including Portland cement, ordinary Portland cement, Portland blast furnace cement, Portland pozzolana cement, Portland fly-ash cement, and composite Portland cement.
In projects, the varieties of cement should be selected reasonably based on the specific environment. As for the property of cement, Portland cement is the basic one.
And this chapter will show a detailed exposition about the 4 Cement 47 properties of Portland cement and briefly introduce those of other kinds of commonly used cement.
There are two types of Portland cement: The sintering process of Portland cement clinker is shown in Figure 4. The process that cement raw materials is sintered in a kiln is the key to the quality of cement clinker. At lOO"C, tricalcium aluminate and tetracalcium aluminoferrite come into being. At OOaC, a large number of tricalcium aluminate and tetracalcium aluminoferrite are generated.
And the yield of calcium silicate is the most. At OO0C, tricalcium aluminate and tetracalcium aluminoferrite are in molten state and CaO and part of dicalcium silicate are dissolved in the generated liquid phase.
In this liquid phase, dicalcium silicate synthesizes tricalcium silicate by absorbing CaO which is the key to the sintering of cement. Sufficient time should be cost to make the free CaO in the raw material be absorbed, for the quality of cement clinker. After rapid cooling of the cement clinker, there comes the cement clinker block.
The Mineral Composition of Portland Cement Clinker The names and contents of the main mineral composition in Portland cement clinker are as follows: The Hydrating Capacity of Cement Clinker Minerals The building technical performance of cement mainly depends on the hydration of the several major minerals in the clinker.
Table 4. When the contents change, the property of cement will change correspondingly. For example, the increase of the content of C3S can generate the cement with high strength; the cement with low heat of hydration can be obtained by decreasing the content of C3A and C3S and increasing the content of C2S, such as cement dam.
XO 70 60 20 10 0 Age Figure 4. And the final setting is the moment when the cement begins to have strength. The process from the initial setting to the final setting is known as condensation or setting.
The setting and hardening of cement are divided by humans themselves, but in fact they are a continuous and complicated physical and chemical changing process. All these changes decide some properties of hardened cement paste, which have an important impact on the application of cement. The Hydration of Cement When water is added, the cement particles are surrounded by water, the surface of the mineral granules in clinker reacted with water immediately, a series of new compounds are generated, and a certain heat is released.
The reaction is as follows: The gypsum reacts with some of the calcium aluminate hydrate to generate insoluble needle-like crystals of calcium sulfate hydrate with significant cubical dilatation.
The Setting and Hardening of Cement Mixed with water, the surfaces of cement particles react with water immediately and the generated colloidal hydrated products gather on the 4 Cement 51 surfaces to slow down the chemical reactions and render the cement paste with plasticity.
Hydrated products can dissolve in water immediately and new surfaces of cement particles appear. Then hydration continues. The generated colloidal hydrated products increase continuously and form a loose mesh structure by contacting with some points which make the paste lose mobility and plasticity, known as setting of cement.
Hydrated products keep packing the mesh structure and begin to render cement with strength. With the extension of hardening time age , the unhydrated inner parts of cement granules continue hydrating, the crystals gradually increase, and the gel gradually become more dense, which make the bonding capacity and strength of cement paste higher and higher.
After the hardening process, the cement paste becomes a heterogeneous structure consisting of crystals, gel, unhydrated clinker particles, free water, and pores in various sizes, shown in Figure 4. Unhydrated Cement Granules; 2. Cement Gel; 3.
Capillary Pore At different ages of hardening process, the 52 Building materials in civil engineering and moisture. The higher the moisture is, the faster the hydration speed is and the quicker the setting and hardening is; otherwise, it will be slow. If the cement paste is in total dry state, the hydration cannot happen, the hardening process stops, and the strength cannot grow. Thus, watering maintenance should be strengthened after concrete structures have been casted.
When the temperature is below O"C, the hydration will nearly stop. Therefore, insulating measures should be adopted in winter construction to ensure the normal operation of the hardening process of cement. The Main Factors Affecting the Setting and Hardening of Portland Cement 1 The Impact of Cement's Composition The mineral composition of cement and their ratios are the main factors affecting the setting and hardening of cement. As mentioned above, various mineral components will reveal different characteristics when reacting with water.
For example, the increase of C3A can speed up the setting and hardening rate of cement, and the heat of hydration is high at the same time. Generally speaking, if mixed materials are added into the cement clinker, the anti-erosion will increase, and the heat of hydration and the early strength will decrease. Without gypsum, cement clinker can condense immediately by mixing with water and release heat. The major reason is that C3A in the clinker can dissolve in water quickly to generate a kind of calcium aluminate hydrate, a coagulant agent, which will destroy the normal use of cement.
If the content of gypsum is too little, the retardation affect will be unobvious. Too much gypsum will accelerate the setting of cement because gypsum can generate a coagulating agent itself. The appropriate amount of gypsum depends on the content of C3A in the cement and that of SO3in gypsum, and it also related to the fineness of cement and the content of SO3 in clinker. If the content of gypsum exceeds the limit, it will lower the strength of cement and it can even lead to poor dimensional stability, which will cause the expanded destruction of cement paste.
Thus, the national standard requires that the content of SO3 should not be more than 3. The finer the cement particles are, the larger the total surface area is and the bigger the area contacting with water is.
Thus, the hydration will be quick, the setting and hardening will be accelerated correspondingly, and the early strength will be high. However, if the cement particles are too small, it is easy for them to react with the water and the calcium dioxide in the air to destroy the storage of cement. If the cement is too fine, its shrinkage is large in the hardening process.
Thus, the finer the cement is ground, the more energy will lose and the higher the cost will be. Usually, the grain size of the cement particles is within pm 0.
If the moisture of the environment is very dry, the water in the cement will evaporate, leading to insufficient hydration and ceasing of the hardening. Serious cracks will happen sometimes.
Usually, the temperature rises at the time of curing, and the hydration of cement and the development of early strength become fast. In actual projects, the setting and hardening process of cement products is accelerated by stem curing and autoclave curing. With the increase of the hydrating degree of various clinker minerals 54 Building materials in civil engineering in cement particles, gels will grow and capillary porosities will decrease, which enables the strength to rise with the increase of age.
It is proved that cement develops rapidly within 28d and slowly after 28d. Therefore, in practical projects, the amount of water and cement will be changed without mortifying the water-cement ratio the minimum amount of cement is regulated to ensure the durability of concrete when the liquidity of cement concrete is adjusted. And all the admixtures that affect the hydration of C3S, C3A can change the performance of the hydration, the setting and hardening of Portland cement.
For example, the accelerator agents such as CaC12, Na2S04 can accelerate the hydration and the hardening of cement and improve its strength. On the contrary, the retarding agents such as calcium lignosulphonate can delay hydration and hardening of cement and affect the development of the early strength. The particle surfaces agglomerate because of hydration which seriously reduces the intensity.
Slow hydration and carbonization will happen due to the impact of the water and C 0 2 in the air, even though the storage is good. Fineness Fineness refers to the size of cement particles which directly affect the performance and the use of cement. All the products whose fineness cannot meet the requirements are sub-quality products. Sieve analysis method requires that the screenings left on the square-hole sieve of 0.
The Setting Time The setting time of cement includes the initial setting time and the final setting time. The initial time refers to the time that cement turns into paste by mixing with water and begins to lose its plasticity. And the time that cement completely loses its plasticity by mixing with water and begins to have a certain structural strength is known as the final setting time.
The national standards prescribe that the initial setting time of Portland cement should not be earlier than 45min and the final setting time should not be later than 6. All the products off-grade at the initial setting time are spoiled products and those unqualified at the final setting time are sub-quality products. The setting time of cement is measured by time determinator. Various mineral components of the cement clinker are different in the water consumption of their normal consistency.
The finer the cement is ground, the more water the normal consistency will need. The setting time of cement is very important in the construction projects. The initial setting time should not be too fast in order to ensure that there is enough time to complete every process, such as casting, before the initial setting time; and the final setting time should not be too late in order to enable the cement to complete its setting and hardening as soon as possible after pouring and tamping to make the next process occur earlier.
Soundness The soundness of cement refers to the stability of the volume change in the process of setting and hardening. If the volume change is unstable after setting and hardening, the concrete structures will crack, which can affect the quality of buildings or even cause serious accidents, known as poor dimensional stability.
The cement product whose dimensional stability is poor will be disposed as spoiled product, not used in projects. They start ageing slowly after the setting and hardening. The excessive amount of gypsum will react with the solid calcium aluminate hydrate to generate crystals of calcium sulfoaluminate hydrate. Today Updates. Statics and Dynamics By R. Hibbeler Book April Punmia, Ashok Kumar Jain, Arun April 8. April 7. Popular Files. January June February 6. Jayakumar, Dr May 1. Trending on EasyEngineering.
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