Construction Technologu and. Building Materials Learning Limit º. º Training Module for Barefoot Technicians. Page 2. Page 3. Construction Technologu. The Book Building Materials By S.K. Duggal is considerably modified version of the edition. In thrid edition of the book extensive revisions have been made . 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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Building Materials & Construction Planning Textbook free. Pages·· MB·19, books. 1 A Text Book of Building Materials, C.J. Modulepdf. Item 1 - 6 Building materials in civil. engineering Editor-in-Chief: Haimei Zhang Translator: This book is suitable for students majoring in “Civil Engineering”. The book is considerably modified version of the edition. The second edition of this book deals with properties of building materials and techniques for.
When the cumulative screen residue of artificial sand of 0. And desiccation cracks will appear. A set of square-hole sieves whose diameters are 4. Notify me of new posts by email. In the light of Composite Portland Cement GB , the national standard, the content of magnesium oxide in cement clinker should be no more than 5. Classification of Concrete ' 1 By cementing materials, there are:
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Statics and Dynamics By R. Hibbeler Book April Punmia, Ashok Kumar Jain, Arun April 8. April 7. Popular Files. January June 2. February 6. June 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. Thus, the volume will expand 1.
The national standards require: The so-called boiling method includes Pat test and Le Chatelier test. Pat test is to make the cement paste of normal consistency into cement cake, boil it for 3h, and then observe it by naked eyes. If there is no crack and no bending by ruler inspection, it is called qualified soundness. Le Chatelier test is to measure the expansion value after the cement paste is boiled and get hardened on Le Chatelier needles. I f the expansion value is within the required value, its stability is qualified.
If there is contradictory between the results mcasured by Pat test and Le Chatelier test, Le Chaterlier test should prevail. The hydration of free magnesium oxide is slower than that of free calcium oxide. Therefore, its harm can be inspected only by autoclave test. The harm of gypsum will be found by immersing in room-temperature water for a long time. Then the poor dimensional stability caused by magnesium dioxide and gypsum is inconvenient to be tested rapidly.
Thus, they should be controlled strictly in the production of cement. Strength and Strength Grade Strength is an important technical index to indicate the quality of cement and also is the basis for the division of strength grade. This method is to produce a set of plastic gel sand specimens of 40mmx40mmxl60mm by mixing a portion of cement by weight and three portions of China's I S 0 standard sand with water in the ratio of 0.
According to the test results, the strength grade of Portland cement can be determined in the light of the requirements in Table 4. Portland Cemenf and Ordinary Portland Cement GB requires that every strength grade value should not be lower than the provisions in the Table 4.
R-apid I 28d Alkali Content The alkali content refers to the content of Na20 and K 2 0 in cement. The condition for concrete to conduct the alkali-aggregate reaction is that the cement must contain alkali. When the active aggregate material is used, the cement with low alkali content should be used. The national standard requires: The national standard still prescribes that the product is waste as long as one of the four items, magnesium, sulfur trioxide, stability, and the initial time, does not meet the requirements.
Any product whose fineness, final setting time, and strength are under the required indexes is unqualified. Off-grade cement is prohibited in engineering.
If only the strength of cement is below the stipulated index, the use of cement can be demoted. The main reasons for corrosion are: Soft-water Corrosion Dissolution Corrosion Rain, snow, distilled water, industrial condensate water, and the river water and lake water with low bicarbonate content, all of them belong to soft water.
When hardened cement paste has contacted with these kinds of water for a long time, calcium hydroxide in the cement paste dissolves first per litre water can dissolve calcium hydroxide of 1. Under the role of still water or zero-pressure water, the dissolution will stop because the surrounding water is easy to get saturated due to the dissolved calcium hydroxide, and dissolution only occur on the surface, little impact.
But if the cement paste is in fluid water or pressure water, the dissolved calcium hydroxide is easy to be washed away, the density of gypsum keeps decreasing, and even other hydrates will dissolve.
The corrosion gets to the inner part to enlarge the cement pores and lower the strength, which will destroy the structures of cement paste to totally collapse. When the environmental water contains bicarbonate, bicarbonate will react with the calcium hydroxide in cement paste and generate the insoluble calcium carbonate: In practical projects, the cement structures which will contact with soft water should get hardened in the air at first to form a layer of calcium carbonate, which may protect the structures from dissolution corrosion.
Acid Corrosion 1 Carbonate Corrosion There is quite a little carbon dioxide dissolving in industrial effluent and groundwater. The carbon dioxide in water reacts with calcium hydroxide in 4 Cement 59 cement paste and generates calcium carbonate. If continuing to react with phenolated water, it will change into soluble calcium bicarbonate. The structure of cement paste will be destroyed because of the dissolution of calcium bicarbonate and the decomposition of the other products in cement paste.
Its chemical reaction is as follows: If there is too much carbonate in water which exceeds the equilibrium concentration, the above reactive mode should occur From right to left.
In addition, the decreasing of calcium hydroxide concentration will lead to the dissolution of the other hydrates in cement paste, thus intensifying the corrosive effect. Various acids have different degrees of corrosive effect on cement paste.
They react with calcium hydroxide in cement paste and generate chemical compounds which can dissolve in water or can expand in volume, leading to the damage of cement paste. Among all these acids, the ones with the fastest corrosive effect are hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid which are inorganic acids and acetic acid, formic acid and lactic acid which are organic acids.
For example, hydrochloric acid reacts with calcium hydroxide in cement paste: Sulfuric acid reacts with calcium hydroxide: Salt Corrosion 1 Sulfate Corrosion When the environmental water contains sodium sulfate, potassium sulfate, ammonium sulfate and other kinds of sulfate, they can conduct substitution reaction with calcium hydroxide, generating calcium sulfate.
Calcium sulfate reacts with solid calcium aluminate hydrate in cement paste and generates the high-sparse calcium sul foaluminate hydrate whose volume is 1. Figure 4. To sum up, the nature of sulfate corrosion is expansible chemical corrosion.
Calcium chloride is soluble in water. And dihydrate gypsum causes the 4 Cement 61 damaging effects of sulfate. Therefore, magnesium sulfate plays double corrosive roles of magnesium salts and sulfate in cement paste. Alkali Corrosion Alkali solution is generally harmless if its concentration is low.
But the Portland cement with high aluminate content will be destroyed by contacting with strong base. For example, sodium hydroxide can react with the unhydrated alumniate in cement paste and generate the soluble sodium aluminate: There is carbohydrate, animal fat and others except the above corrosive types.
In fact, cement paste corrosion is a very complex physical and chemical process. There is seldom one kind of corrosion existing in the environment where cement paste suffers corrosion and there are often several kinds of corrosion, co-existing and mutually impacting. The hndamental reason for the cement corrosion is: The total process of corrosion is: The content of clinker in Portland cement and that of calcium hydroxide and calcium aluminate hydrate in hydrated products are high, so the anti-erosion of cement paste is bad, inappropriate to be used in the environment with erosive media.
The Prevention of Corrosion According to the above analysis of corrosion reasons, the corrosion of cement paste occurs because chemical reaction can happen between its external 62 Building materials in civil engineering environment and internal environment. The corrosive compound must be the solution with a certain concentration, such as high temperature, proper humidity, fast flow, and the corrosion of steel bar.
Thus, the following measures can be adopted in the use of cement: The amount of mixing water for Portland cement should be strictly controlled in order to reduce the pore space. The mix proportion should be designed reasonably in order to improve the compactness of cement concrete.
Low water-cement ratio and the best construction method should be adopted as much as possible. In addition, the insoluble calcium carbonate shell or calcium fluoride and thin silica gel film generated by conducting carbonization or fluosilicic acid treatment on the surface of concrete and mortar can increase the compactness of the surface and decrease the infiltration of erosive media.
The resistant stone, ceramic, plastic, and waterproof material are covered on the surface of cement paste, forming a impermeable layer for protection, to prevent the corrosion media contacting with cement paste directly. The attention should be paid to water-resistance and moisture-resistance in transport and storage of cement. Thcre should be a specific place for cement storage at the construction site and the storeroom should be dry.
Cement should be stored separately according to different varieties, strength grades and date of production, and the cement in bulk should be stored in different 4 Cement 63 rooms; and the cement in bags should be stored on the backing plate 30cm higher above the floor and 30cm away from the surrounding walls with a stacking height below 10 bags; in the storage of cement, the one which is stored first should be used first, and cement should not be stored for a long time.
The storage period generally should be less than 3 months and the cement stored for over 6 months can be used only through test. Agglomeration often appears in wet cement. And minor caking can be crumbed by fingers or ground in proper way. Then the activity of wet cement can be restored partly. It can be used in minor projects after re-determining its strength grade.
The mixture of blended materials can change the performance of cement, adjust the strength, diversify the varieties, increase yields, decrease costs, expand the application, and utilize industrial wastes and local materials comprehensively. According to different amounts and varieties of blended cement, they are: Active Blended Materials The Portland cement mixed with active blended material can react with calcium hydroxide, the hydrated product of cement, and generate hydraulic binding material which can possess certain strength and change some properties of Portland cement a fter setting and hardening.
The commonly used materials are blast furnace granular slag, pozzolana blended material, and fly ash. The fused blast furnace slag is quenched into granules by water, which prevents the fused mass transferring into crystalline structure. The fused mass changes into vitreous body with high potential chemical energy and high activity.
The alkaline slag with a lot of calcium oxide has weak hydraulicity due to the content of dicalcium silicate. The blended materials with hydrous silicic acid are: The Al-Si vitreous materials are: The blended materials with artificial calcined clay are: Inactive Blended Materials This kind of material includes: Inactive blended materials themselves are not or slightly of hydraulicity or pozzolana and cannot produce chemical reaction with mineral components in cement that is, no chemical activity or can produce small chemical effect.
The addition of such materials in cement clinker can only improve the cement quality, decrease the strength grades, and reduce the heat of hydration.
Ca ON 2, hydrate in cement clinker, and gypsum can trigger the activity of the active blended materials. In other words, calcium hydroxide and gypsum can agitate hydration and accelerate the hardening of cement, known as activator.
The common activators include alkali activator and sulfate activator. The catalysis of sulfate activator can be brought into full play only under the condition of alkali activator. According to Portland Cement, Ordinary Portland Cement GB , the national standard, the strength grades of ordinary cement can be divided into: The initial setting time of ordinary cement should not be earlier than 45min, and final setting time should not be later than 10h.
The screenings left on the square-hole sieve of 0. And boiling stability must be qualified. The ignition loss of cement should be less than 5. One of the blended materials, limestone, kiln dust, fly ash and volcanic ash, is allowed to replace the slag. According to Portland blast furnace slag Cement, Portland Pozzolana Cement, and Portlandfly-ash Cement GB , the national standard, the content of magnesium oxide in clinker should not exceed 5.
If the stability of cement tested by autoclave method is qualified, the content of magnesium oxide can be extended to 6. The content of sulfur trioxide should not exceed 4. The strength grades of slag cement can be divided into The requirements for fineness, setting time and soundness of slag cement are the same to those of ordinary cement.
The regulated density of slag cement is usually 2. Slow Setting and Hardening The hydration process of slag cement is more complicated than Portland cement. At first, the minerals in cement clinker react with water and generate calcium silicate hydrate, calcium aluminate hydrate, calcium ferrite hydrate and calcium hydroxide.
Calcium hydroxide and gypsum mixed in cement are the alkali activator and the sulfate activator for slag respectively which react with active silicon oxide and aluminum oxide again to generate calcium carbonate hydrate, calcium aluminate hydrate, and calcium sulphoaluminate.
The setting and hardening is slow because the content of clinker minerals in slag cement is small and the hydration happens at two steps. Low Early Strength, and Rapid Growth of Later Strength Because the setting and hardening of slag cement is very slow, the early strength 3d and 7d is low.
The calcium silicate gel increases after the second hydration, so the later strength 28d grows rapidly, which may keep pace with or even exceed Portland cement see Figure 4. Low Heat of Hydration The decrease of slag cement in clinker can cause the reduction of C3S content and C3A content which will release much heat at the hydration of cement. Therefore, it has priority in the mass concrete projects due to the low heat of hydration.
Portland Cement; 2. Slag Cemcnt; 3. Granular Slag 4. Poor Carbonization Resistance Among the hydrates of slag cement, the content of calcium hydroxide is small and alkalinity is low, so the carbonization resistance is poor. But the resistance to the dissolution corrosion and sulfate corrosion is strong. Poor Water Retention and Good Water Segregation The hydrophilicity of slag vitreous particles is low, so the water retention of slag cement is poor and its water segregation.
It is easy to form capillary channels and water packets inside concrete. There are pores after water evaporates, which decreases the intensity and evenness of concrete. Thus, the dry shrinkage performance of slag cement is high, but its water resistance, frost resistance and the resistance to the alternation between wetness and dryness are poor.
Slag cement should not be used in the concrete projects of which the impermeability is very important. Good Heat Durability Slag cement has good heat durability that can be used to prepare heat-resistant concrete because it contains a little calcium hydroxide after hardening and it is also the fire-resistant additive. High Sensitiveness to Moist Heat at Hardening The setting and hardening of slag cement is very slow at the low temperature, so insulation measures should be strengthened in the winter construction.
But its strength develops very fast under the condition of heat, thus conserved with vapor. The technical requirements for pozzolana cement are the same to those of blast-furnace slag cement. Pozzolana cement and blast-furnace slag cement have many common grounds in performance see Table 4.
The water demand of pozzolana cement is large. The dry shrinkage is more obvious than blast-furnace slag cement in the process of hardening. And under dry and heat conditions, dry shrinkage happens and the cement cracks. Thus, the conservation should be strengthened in use and it should be kept in the moist state for a long time.
The particles of pozzolana cement are very tiny, and the water segregation is low. Thus, its impermeability is good, favorable for the concrete projects.
The fineness, setting time, soundness and other technical requirements of fly-ash cement are the same to those of ordinary cement.
The hydration and hardening process of fly-ash cement is basically the same to that of pozzolana cement. And their performances have many similarities. The main character of fly-ash cement is its little shrinkage, even less than Portland cement and ordinary cement. Therefore, its frost resistance is good. The water demand of fly-ash cement is little and the concrete mixed by it is 70 Building materials in civil engineering workable because its particles are mostly spherical and the water absorption is low.
In the light of Composite Portland Cement GB , the national standard, the content of magnesium oxide in cement clinker should be no more than 5. If the cement is qualified through autoclave method for soundness, the content of magnesium oxide in clinker is allowed to reach 6. The content of sulfur trioxide in cement should not exceed 3.
The strength of composite Portland cement at each age in various strength grades should not be lower than the values in Table 4. R-pid The selection of common cement can be seen in Table 4.
Cement 71 4 Table 4. Pozzolana Cement, Fly-ash Cement. And its pozzolana cement, and fly-ash cement. Aluminate cement can be divided into four categories by its A content: According to Aluminate Cement GB20 , the national standard, the aluminate cement requirements are as follows: Chemical Composition The chemical composition of aluminate cement should be consistent with the requirements in Table 4.
Physical Properties Fineness: The two methods can be negotiated by the parties of supply and demand. If there is disagreement, the specific surface area should prevail. Setting time: If any of the other requirements can not be reached, the cement is unqualified.
The main characteristics and application of aluminate cement are as follows: The early strength is very high, and the later strength growth is not significant. Thus, aluminate cement is mainly used in the projects of which the construction period is urgent such as roads, bridges and salvaging such as plugging ; it still can be used for winter construction projects. It is more or less the same to high-grade Portland cement, but its heat release is very quick and concentrative.
Aluminate cement would not be appropriate for mass concrete projects. Therefore, aluminate cement would not be appropriate for the long-term load-bearing structure and the projects placed in hot and humid environment. It should be also noted that aluminate cement products can not be conserved by steam curing; aluminate cement should not be mixed with Portland cement or lime so as not to cause flash condensation and the strength decline; the aluminate cement should not contact with the Portland cement which has not gotten hardened yet.
In addition, the moisture-proof protection of aluminate cement should be paid attention to in the course of transportation and storage, or the strength will drop rapidly after absorbing moisture.
The use of expansive cement can overcome and improve some shortcomings of ordinary cement concrete commonly used cement will shrink in the hardening process, which causes the structures to crack and be permeable, inappropriate for some projects , and can enhance the density of cement concrete structures and the integrity of concrete.
The major components of expansive cement include: The expansion mechanism is the expansion of ettringite generated in cement paste. And the setting and hardening of silicate expansive cement is relatively slow; but that of the aluminate one is fast. Silicate Expansive Cement It is the expansive cement made by mixing aluminate cement and gypsum based on Portland cement.
The value of its expansion can be adjusted by changing the content of aluminate cement and gypsum. If the aluminate cement in silicate expansive cement is replaced by alunite, it is known as alunite expansive cement.
The addition of alunite expansive agent and aluminate expansive agent into Portland cement will also lead to the expansion of cement. Aluminate Expansive Cement Aluminate expansive cement is generated by grinding aluminate cement clinker and dihydrate gypsum or mixing their ground particles. Its self-stressing and air tightness are good. Aluminoferrite Expansive Cement It is made by anhydrous calcium sulphoaluminate and dicalcium silicate as well as gypsum. Sulphoaluminate Expansive Cement It is made by iron phase, anhydrous calcium sulphoaluminate and dicalcium silicate as well as gypsum.
By adjusting the coordinate proportion of the above four types can generate the expansive cement with different expansion ratios. The expansive cement can be divided into expansive cement and self-stressing cement according to different expansion ratios.
Thus it is also called shrinkage-compensating cement or the non-shrinkage cement. If it is the reinforced concrete, the concrete will bear compressive stress in order to achieve pre-stress.
When self-stress is more than or equals to 2. SMPa , it is called expansive cement. The self-stressing cement can be used for pressure tubes and fittings in self-stressing reinforced concrete. The expansive cement can be used for shrinkage-compensating concrete, structure. White Portland Cement White Portland cement is simply called white cement. The main difference between it and the commonly used cement is that the content of ferric oxide is less, leading to white color.
The production of white cement is basically the same to that of ordinary cement. The key is to strictly control the content of iron and ferric substance should be avoided in the production process. In addition, the manganese oxide and chromium oxide can also lead to the decrease of the whiteness, so the content must be controlled strictly. The performance of white cement is basically the same to Portland cement. According to the national standard GB, the strength grades of white Portland cement include 3.
And the cement strength of each grade in various ages should not be less than the values in Table 4. Colorful Portland Cement Based on different coloring method, there are three producing modes of colorful Portland cement: The third method is oRen adopted when the amount used in projects is not large. The colorful Portland cement includes red, yellow, blue, green, brown, black and other colors.
According to Colorful Portland Cement 78 Building materials in civil engineering JCR , the industrial standard, its strength grades can be divided into The color cement strength in various ages should not be less than the values in Table 4. What kind of influence do they bring to cement? And what about their hydrated products?
What is the structure of the cement paste after hardening? What kind of factors can cause poor dimensional stability? What is substandard product? What is waste? Analyze the impacts of various kind of corrosion to cement paste. And what are the anti-corrosion measures?
What kinds of changes will thcy cause to the Portland cement? And what about the practical significance? They cannot be used due to the misplaced labels.
Is there a simple way to identify them? Try to select the proper cement and explain the reason. Exercises The Portland cement in a certain strength grade has been stored for more than three months. Now it is tested that the compressive loading value and bending strength value of 3d are as follows, how to evaluate its strength grade? The compressive loading of 3 d kN: The bending strength o f 3 d MPa: It is one of the main building materials in projects.
The one mostly used in construction projects is the cement concrete made by mixing gel materials, aggregate sand and stone , and water, which should get through hardening process.
Cement concrete is also called ordinary concrete, which is the focus of this chapter. Concrete is widely used in industry, national defense and civil buildings. With the rapid development of China's construction projects, the concrete with different kinds of functio'ns has come into being. Classification of Concrete ' 1 By cementing materials, there are: The apparent density of concrete depends on the aggregate varieties and its own density.
Many properties of concrete are connected with apparent density. Characteristics of Concrete 1 Convenient for use: Its major shortcomings are high dead weight, low tensile strength, brittle and easy to crack. Mixed with water, cement becomes cement paste, and cement mortar not only wraps the surface of particles and fills their gaps, but also wraps stones and fills their gaps, then concrete coming into being see Figure 5.
Cement paste can function as greasing before 5 Concrete 83 hardening, which renders concrete mixture with good mobility; aAer hardening, aggregates stick together and form a hard entity, known as man-made stone-concrete.
Figure 5. In the preparation of concrete, the choice of cement varieties and strength grades are directly related with the durability and economy, of concrete.
The Choice of Cement Varieties When concrete is prepared, the rational choice should be made in light of the properties of cement varieties, according to the properties of the project, parts, construction conditions, environment and so on. The selection principles for the six common kinds of cement can be referred to in Chapter Four.
The Choice of Cement Strength Grades The cement strength grades are corresponding to the design strength grades of concrete. The standard strength grade of ordinary cement should be 1. If the cement strength is too high or too low, the cement content in concrete will be too small or too large that will have a negative impact on the technical performance and the economic effect of concrete.
The one whose diameter is more than 4. The fine aggregates used in ordinary concrete generally are the natural sand which comes into being when the natural rock excluding soft rock and weathered rock has experienced natural weathering, water transportation, sorting, and stacking and other kinds of natural conditions; the machine-made sand is made by grinding and sorting by machine, and the diameter of the rock particles is less than 4. According to different sources, natural sand can be divided into river sand, sea sand, mountain sand and desalted sea sand.
The coarse aggregates used in ordinary concrete are gravel and pebble. Category I is properly used in the concrete whose strength grade is bigger than C60; category I1 is suitable for the frost-resistant and seepage-resistant concrete whose strength grade is within CC60; category I11 is good for the concrete whose grade is lower than C