COMMENTS: The water requirement for various tests of cement depends on the normal consistency of the cement, which itself depends upon the compound composition and fineness of the cement. THEORY: In actual construction dealing with cement, mortar or concrete, certain time is required for mixing, transporting and placing. During this time cement paste, mortar, or concrete should be in plastic condition. The time interval for which the cement products remain in plastic condition is known as the setting time.
Initial setting time is regarded as the time elapsed between the moments that the water is added to the cement to the time that the paste starts losing its plasticity.
The final setting time is the time elapsed between the moment the water is added to the cement, and the time when the paste has completely lost its plasticity and has attained sufficient firmness to resist certain pressure. The former defines the limit of handling and the latter defines the beginning of development of mechanical strength.
The constituents and fineness of cement is maintained in such a way that the concrete remains in plastic condition for certain minimum time. Once the concrete is placed in the final position, compacted and finished it should lose its plasticity in the earliest possible time so that it is least vulnerable to damages from external destructive agencies. This time should not be more than 10 hours which is referred to as final setting time.
Initial setting time should not be less than 30 minutes. The cement block thus prepared in the mould is the test block. Determination of initial setting time: 1 Place the test blocks confined in the mould and rests it on the non-porous plate, under the rod bearing initial setting needle, lower the needle gently in contact with the surface of the test block and quickly release, allowing it to penetrate into the test block.
Determination of final setting time: 1 Replace the needle of the Vicat apparatus by the needle with an annular attachment. All the apparatus shall be free from vibration during the test. Care shall be taken to keep the needle straight. COMMENTS: The factors influencing the setting properties of cement are its composition, the percentage of retardant, degree of calcination, fineness of grinding, aeration subsequent to grinding clinker, percentage of water used to make cement paste, the temperature of the mixing water, cement and the atmosphere where the cement paste is placed, and the amount of manipulation the paste receives.
Standard Sand: The standard sand to be used in the test shall conform to IS: or sand passing percent through 2 mm sieve and retained percent on 90 micron IS sieve. THEORY: The compressive strength of cement mortars is determined in order to verify whether the cement conforms to IS specifications and whether it will be able to develop the required compressive strength of concrete.
Strength test are not done on neat cement paste because of difficulties of excessive shrinkage and subsequent cracking of neat cement. Strength of cement is indirectly found on cement — sand mortar in specific proportion.
The average compressive strength of at least three mortar cubes area of the face 50 cm2 composed of one part of cement and three parts of standard stand should satisfy IS code specifications. The cubes are prepared for this purpose. Testing: 1 Take the cube out of water at the end of 3 days with dry cloth. Measure the dimensions of the surface in which the load is to be applied. For 3 days strength: Sl. For 28 days strength: Sl. COMMENTS: In addition to the effect of composition, the strength of cement is greatly influenced by the degree of burning, the fineness of grinding, and the aeration it receives subsequent to final grinding.
Under-burnt cement is likely to be deficient in strength. Compressive strength is the basic data required for mix design. By this test, the quality and the quantity of concrete can be controlled and the degree of adulteration can be checked. THEORY: The specific gravity of an aggregate is generally required for calculations in connection with cement concrete design work for determination of moisture content and for the calculations of volume yield of concrete. The specific gravity also gives information on the quality and properties of aggregate.
The specific gravity of an aggregate is considered to be a measure of strength of quality of the material. Stones having low specific gravity are generally weaker than those with higher specific gravity values. The bulk density of an aggregate is used for judging its quality by comparison with normal density for that type of aggregate.
It is required for converting proportions by weight into proportions by volume and is used in calculating the percentage of voices in the aggregate. Find its weight W3. Find its weight W4 6 Repeat the same process for another trail by taking the aggregate up to the full of the container and by filling the water up to same point. Description Trial 1 Trial 2 No. Weight of empty container W1 2. Weight of container with material W2 3.
Take ml of dry sand V1 ml in clean measuring jar of ml capacity. Add a measured quantity of ml clean water to the above sample V2 ml i. Shake the jar thoroughly till all air bubbles are expelled. Moisture forms a film around each particle and this film of moisture exerts surface tension which keeps the neighbouring particles away from it.
Therefore, when no point contact is possible between the particles, this causes bulking of sand. Thus increase in volume of sand due to presence of moisture is known as bulking of sand. When more water is added sand particles get submerged and volume again becomes equal to dry volume of sand. Fine sands show greater percentage of bulking than coarse sands with equal percentage of moisture.
The points on the graph should be linked as a smooth curve. Then from the graph, maximum percentage of bulking and the corresponding moisture content is determined. COMMENTS: The bulking of the volume depends on the extent of surface tension and consequently how far the adjacent particles are kept away which in turn depends upon the percentage of moisture content and the particle size of the fine aggregate.
It is interesting to note that the bulking increases with the increase in moisture content up to a certain limit and beyond that the further increase in the moisture content results in the decrease in the volume and at a moisture content representing saturation point, the fine aggregate shows no bulking.
Due to the bulking, fine aggregate shows completely idealistic volume. Therefore, it is absolutely necessary that consideration must be given to the effect of bulking in proportioning the concrete by volume.
If the effect of bulking is overlooked, in case of volume batching, the resulting concrete is likely to be under-sanded and harsh. It will also affect the yield of concrete for the given cement content. Weighing balance Sensitivity 0. Coarse aggregate is broken stone used in concrete.
The size of the fine aggregate is limited to maximum 4. Fineness modulus is only a numerical index of fineness, giving some idea about, the mean size of the particles in the entire body of concrete. Determination of fineness modulus is considered as a method of standardization of grading of aggregates i. It is obtained by sieving known weight of given aggregate in a set of standard sieves and by adding the percent weight of material retained on all the sieves and dividing the total percentage by Carry out sieving by hand, shake each sieve in order 75mm , 40mm, 20mm, 10mm, and 4.
Cumulative Sl. Retained Retained Passing retained 1. The slump cone is a hollow frustum made of thin steel sheet with internal dimensions, as the top diameter 10 cms.
The bottom diameter 20 cms, and height 30cms. It stands on a plane nonporous surface. To facilitate vertical lifting from moulded concrete it is provided with a suitable guide attachment and suitable foot pieces and handles. The tamping rod is 16mm. This vertical settlement is called slump. Slump is a measure of workability. There are four types of slump- i. True slump refers to general drop of the concrete mass evenly all around without disintegration.
Zero slump concrete is defined in the same document, as concrete of stiff or extremely dry consistency showing no measurable slump after removal of the slump cone. Collapse slump indicates that concrete mix is too wet and the mix is regarded as harsh and lean.
Shear slump indicates that the concrete lacks cohesion. It may undergo segregation and bleeding and thus is undesirable for the durability of concrete.
For each mix take 2. Cement, 5 Kg. Tamp each layer 25 times with tamping rod. Note: Slump test is adopted in the Laboratory or during the progress of the work in the field for determining consistency of concrete where nominal max. Any slump specimen which collapses or shears off laterally gives incorrect results and at this juncture the test is repeated only true slump should be measured.
For example, a harsh coarse mix cannot be said to have same workability as one with a large portion of sand even though they have the same slump.
The upper mould has internal dimensions as top dia 25 cm D1 bottom dia. The lower hopper has internal dimensions, top The cylinder has internal dimensions as 15 cm dia. D5 and 30cm height H3. The dimensions between bottom of the upper hopper and top of the lower hopper, bottom of the lower hopper and top of cylinder are 20 cm h1 and h2 , each case.
The lower ends of the hoppers are filled with quick release trap doors. THEORY: This test is adopted to determine workability of concrete where nominal size of aggregate does not exceed 40 mm. It is based on the definition, that workability is that property of concrete, which determines the amount of work required to produce full compaction.
The test consists essentially of applying a standard amount of work to standard quantity of concrete and measuring the resulting compaction.
The compaction factor is defined as the ratio of the weight of partially compacted concrete to the weight of fully compacted concrete. It shall be stated to the nearest second decimal place. Remove the excess concrete above the top of the cylinder by a trowel.
A single steady penetration will usually affect release. The ages shall be calculated from the time of the addition of water to the dry ingredients. Number of Specimens: At least three specimens, preferably from different batches, shall be made for testing at each selected age. Specimen 6 cubes of 15 cm size. M15 or above Mixing Mix the concrete either by hand or in a laboratory batch mixer Hand Mixing 1 Mix the cement and fine aggregate on a water tight none-absorbent platform until the mixture is thoroughly blended and is of uniform color 2 Add the coarse aggregate and mix with cement and fine aggregate until the coarse aggregate is uniformly distributed throughout the batch 3 Add water and mix it until the concrete appears to be homogeneous and of the desired consistency Sampling Clean the mounds and apply oil Department of Civil Engineering Supreme Knowledge Foundation Group of Institutions Page.
Note:Minimum three specimens should be tested at each selected age. If strength of any specimen varies by more than 15 per cent of average strength, results of such specimen should be rejected. Load P Type of Compressive No. Otherwise, repeat tests shall be made. COMMENTS: Factors affecting the strength of concrete can be broadly grouped into those depending upon the testing methods and the others independent of the testing methods. Factors depending on testing methods are size of test specimen, size of specimen relative to maximum size of aggregate, moisture condition of specimen, rate of loading adopted, and type of testing machine used; and those independent of testing method are type of cement and age of cement, type and size of aggregates, degree of compaction, water-cement ratio, aggregate- cement ratio, air voids, curing method and curing temperature Department of Civil Engineering Supreme Knowledge Foundation Group of Institutions Page.
Tests at any other age at which the tensile strength is desired may be made, if so required. It is found that when the diameter is decreased, the strength of glass fiber is significantly increased. Suitable treatment is also required to utilize the glass fibers as micro reinforcement because it gets corroded due to the effect of alkali present in the portland cement.
Fiber reinforced concrete is mostly used for manufacturing precast products such as spun pipes, wall cladding etc. A workable concrete should possess following two requirements. The concrete should be compacted with minimum efforts. The concrete should not form bleeding and segregation. Workability of concrete mainly depends on the mix proportion and the properties of concreting materials water, cement, aggregates. The shape, size, and grades of aggregates also play a great role in the variation of workability.
For better workability fine and coarse aggregates should be well graded. It has been found that concrete made of round grain sand is more workable than the concrete of crushed sand. If air entraining admixture is used in the mix, it will also increase the workability and decrease segregation and bleeding.
Proportion Of Coarse And Fine Aggregates: Workability can be increased by decreasing the amount of coarse aggregates in the mix. Fine aggregates produce more wore workable concrete. Shape Of aggregates: Round shaped aggregates give better workability than angular shaped aggregates. By expanding the cement content in the mix. By including admixtures in the mix.
Apparently, the necessity of workability differs as per the nature of the job and blockage in the full stream of concrete due to the spacing and nature of the reinforcement. The workability of concrete is generally measured by one of the following three tests. Slump Test. Compaction Factor Test. Vee-Bee Test. To produce high quality concrete we must take some precautions to avoid those common problems during concreting.
In this article, we will discuss common concrete problems and how to prevent them. Due to bleeding some measure of water with sand particles and other cementing materials appears at the surface of the concrete. Following precautions should be taken to reduce bleeding in concrete. Design the mix appropriately. Include least water content in the mix. Use greater amount of cement content. Use greater amount of fine particles.
Utilize a little measure of air entraining admixture. It is generally seen in the plastic stage of concrete. As a result honeycomb, laitance, scaling, porous layer, bond failure etc. Following precautions should be adopted to prevent segregation in concrete.
Never use excessive water content. Take care of handling, placing, and proper compaction of concrete. Do not allow the concrete to be dropped from more heights. Use air entraining admixture. Keep the formwork to be watertight. It is mainly occurred due to the bad effect of bleeding and segregation of concrete. The bond between subsequent layers of concrete becomes weaker and as a result, laitance is developed.
Clay, dust, silt content etc should be removed before mixing the concrete. Water-cement ratio should be maintained properly. Water should not be sprayed on the concrete surface during finishing work. Use well graded fine aggregates in the mix. Add little amount of water reducing admixture in the concrete mix. Due to this effect concrete surface becomes worse. Scaling can be prevented by taking same precautions adopted for laitance. Basically, this type of cracks occurs in very hot climate.
Utilize dust free aggregates in the mix. Guarantee appropriate hydration of concrete. Avoid early surface finishing of concrete. Hence the concrete strength differs from one batch to another batch over a time period. The variation in concrete strength depends on several factors such as variation in the materials quality, mix proportion, batching, mixing techniques, handling, and workmanship. These variations are unavoidable during concrete production.
Therefore it is essential to control these variations to reduce the contrast between the minimum strength and characteristic mean strength of the concrete mix and consequently diminishing the quantity of cement substance. The method which controls this distinction is known as quality control of concrete. Quality control ensures the logical use of the available materials after testing their properties and reducing the cost. Without quality control, there is no guarantee that the weakness of one area will be compensated in another by over spending in that area.
In that case, quality control offers the best solution. Quality control helps to minimize the risks of overdesign that reduces the overall cost. Quality control promotes the completion of a project by checking the concrete production and rectifying the faults at every stage. It reduces the repair and maintenance cost. Compaction Factor Machine, Weighing Machine, 3. Steel Trowel Or Mechanical Vibrator. Fill the upper hopper by pouring the concrete sample in it. Open the hinged door at the lower end of the upper hopper allowing the concrete to fall into the lower hopper.
Immediately open the gate of at the bottom of the lower hopper to allow the concrete to fall into the cylindrical mould. Remove the excess concrete above the top level of the mould by using a trowel. Take the weight of the cylindrical mould with concrete partially compacted concrete and find out the weight of the concrete W1.
Now remove the concrete from the mould and refill it with the same concrete sample in 5 cm layers. Compact the each layer of the concrete fully by using a steel rod or mechanical vibrator. There should be no air voids present in the concrete 7. Now take the weight of the cylinder with concrete Fully compacted concrete and find out the weight of the concrete W2. Calculate the compaction factor by below given formula. The uses of waterproofing agents should be kept away as much as possible for working in ordinary situations.
A thick concrete with least conceivable air voids should accordingly be the essential thought in making of dampproof concrete. The accompanying conditions should be fulfilled to accomplish the waterproofing of concrete. Utilize the best accessible material. Proportionate the aggregates by using fineness modulus strategy. Utilize just as much amount of water is required to get the desired workability. Mix the concrete completely. Proper supervision amid laying and compaction. Finish the curing of concrete.
However, in specific cases such as water retaining structures, structures that are to be constructed in water-logged soil, or in soggy climate, it might be important to adopt additional precautions to assure water-tightness. This incorporates the expansion of certain waterproofing materials such as permo, sika, pudlo etc in the concrete mix at the time of mixing. This is named as integral waterproofing. Different causes of cracks in concrete are described below. In drying shrinkage, the volume of concrete is gradually decreased and if the component is restrained against free movement, tensile stresses are developed which causes cracks.
When the tensile strain capacity of concrete exceeds due to the differential volume change, it will crack. The deformation of concrete depends on the type of building materials used in the construction such as bricks, cement concrete blocks etc. This unusual deformation of concrete results in cracking. Hence the volume is increased and cracks. The physical properties of concrete totally depend on the hydration of cement.
If curing is not done properly concrete will be failed to acquire its full strength. Improper concrete curing may also lead the concrete to crack. It also protects the surface from heat, wind etc. In cold climates, it prevents the concrete from freezing by preserving heat of hydration of cement. This method gives satisfactory results for curing of concrete slabs and pavements. This method is not so effective due to the difficulty of keeping the concrete surface be moist all the time. In this method, concrete surface is first covered with moist wrapper for 24 hours.
After that, the covers are then removed and small amount of clay puddles are constructed around all the area. Then water is filled for final curing. The membrane protects the water loss from concrete. It is seen membrane curing for 28 days give equivalent strength to two weeks moist curing. This method allows the concrete to achieve its full strength within a short time, thus curing is also finished within short time. Steam curing is mostly adopted for the production of precast members. The mortar gives the mass and the wire mesh contributes tensile strength and ductility of the material.
As a result, the concrete shows a high tensile strength to weight ratio and excellent cracking performance. It is also known as ferroconcrete. Mortar mix. Sand fine aggregates. Wire mesh. Skeleton steel. It can be fabricated into any desired shape. The tensile strength of ferro-cement is very high than conventional concrete. The structures made with ferro-cement are thin and lightweight.
Construction procedure is easy, quick and no skilled labours are required. Formwork is also not required in such construction. Precast members can be suitably manufactured by using this type of concrete. Maintenance cost is very low, almost nil. It is fire, corrosion, and earthquake resistance. It is economical. The application of ferrocement are as follows: 1. Mobile home, 2. Modular housing, 3.
Water tank, 4. Swimming pool, 5. Wind tunnel, Marine work, etc. Water has a great role on the strength and workability of concrete. After lots of experiments it has been found that for a specific proportion of materials in a concrete mix, there is a certain amount of water that gives maximum strength. A slight change in the amount of water causes much more differences in the strength of concrete. If less water is used, the resultant concrete will be nearly dry, hard to place in the form and may create difficulties in compaction.
Besides this, with less water proper setting will not be guaranteed and thus the strength of concrete get reduced considerably.
On the other hand, if water is used more, it may develop larger voids and honey- combing in the set concrete, in this way decreasing its density, durability, and strength. Hence, water cement ratio attends an important role in producing concrete of required strength. The lower the ratio, the greater is the strength of concrete. In this article, I will discuss the basic differences between concrete and mortar. Concrete is a mixture of cement, sand, aggregates and water, on the other hand, mortar is made from cement, sand, and water.
Concrete is much stronger than mortar. Mortar is less durable than concrete. The water-cement ratio is higher in mortar, but the main aim of concrete is to keep the water-cement ratio as minimum as possible. Mortar is a good binding material and it is mostly used to bind the bricks together. Due to greater strength and durability concrete is used in all type of construction works such as buildings, bridges, roads etc.
Concrete gives a long outcome but mortar has to be replaced in every 20 — 30 years. Mix design can be divided into following two categories 1. Design mix concrete and 2. Nominal mix concrete. In design mix concrete, it is assumed that compressive strength of concrete is totally dependent on the water-cement ratio. This method is generally used when the quality control requirement for design mixes are difficult to execute. As we have explained for normal work, nominal mix concrete can be designed by taking cement, fine aggregate and coarse aggregate in the ratio of 1 : n : 2n.
Following requirements should be considered to produce the best quality concrete: 1. Use well graded, hard and durable aggregates. Use sufficient quantity of cement to achieve required water tightness and strength. Mix the concrete thoroughly for getting better homogeneity. Keep the water-cement ratio as minimum as possible. Compact the freshly placed concrete to remove air bubbles and voids. Cure the concrete properly at least for 28 days. Maintain the concrete temperature above the freezing point until it becomes hard enough.
If we fulfill all the above requirements then we can easily produce a good quality concrete. Generally, a long term pressure changes the shape of concrete structure and the deformation occurs along the direction of the applied load. When the continuous load is removed, the strain is decreased immediately. The amount of the decreased strain is equal to the elastic strain at the given age.
This quick recovery is then followed by a continuous decrease in strain, known as creep recovery that is a part of total creep strain suffered by the concrete. The time taken by a concrete structure to attained creep is 5 years. The rate of creep generally decreases with the increase of the size of aggregates. Types of cement. Entrained air. Concrete strength. Improper curing etc. The tendency of separating coarse aggregate particles from the concrete mix is known as segregation.
Generally, it is observed in the plastic stage of concrete. Segregation mostly occurs in very lean and wet concrete. Honeycomb, sand streaks, porous layers, rock pockets etc are the results of segregation in hardened concrete.
Excessive water content in the mix. Use of poor graded aggregates. Improper design of the mix. Poor compaction of concrete. Over vibration of concrete. The design of the concrete mix should be done properly.
Water content should not be added more than the desired amount. Handling, placing, and compaction of freshly mixed concrete should be done carefully.
A proper vibration also reduces the chances of segregation. Concrete should not be dropped from more heights. Air entraining admixtures can be used to enhance the viscosity of concrete.
Formwork should be always watertight to prevent leakages. In its original form, the finely ground cement is very sensitive to water.
Out of the four main ingredients C3A, C3S and C2S quickly react with water which finally produces a jelly- like paste that starts solidifying. The activity of changing from a fluid state to a solid state is known as setting. The setting action stays more predominant in first few minutes but after sometimes it becomes dominant. Practically this solidifying action is required to be delayed because enough time is needed for mixing, transporting and finally placing the concrete into final location before losing the plasticity of the mixture.
For plastic concrete, it is necessary to be placed and consolidated before the initial setting and it should remain undisturbed until the paste becomes a hardened mass. The concrete gains its strength as rapidly as possible after initial stiffening. The formwork should be removed after a permissible interval of time and further construction should be then started. Thus the frost action in cold climate is minimized. As per IS specification, the minimum initial setting time is 30 minutes for ordinary portland cement and 60 minutes for low heat cement.
As per IS specification, The maximum final setting time for all type of cement is 10 hours. It is another form of segregation where some amount of water comes to the concrete surface after placing and compacting, before setting.
The water content carries Sometimes bleeding helps to reduce the plastic shrinkage cracks in concrete. Concrete loses its homogeneity which results in weak and porous concrete.
It makes the concrete permeable. It delays the surface finishing in pavement construction. Bleeding of concrete causes high water-cement ratio at the top surface. The bond between two concrete layers become weaker. Pumping ability of concrete is significantly reduced. Design the concrete mix properly. Add minimum water content in the concrete mix. Add more cement in the mix. Increase the amount of fine particles in the sand. Use a little amount of air entraining admixture.
Use more finely ground cement. The test is performed to check the consistency of freshly mixed concrete in a specific batch. Consistency refers to the ease and homogeneity with which the concrete can be mixed, placed, compacted and finished.
This test is most widely used due to the simplicity of apparatus and simple test procedure. The slump test gives satisfactory results for the concrete mix of medium to high workability and unfortunately, it does not give the correct indication of low workability, which may give zero slumps. This test is also known as slump cone test. Mould or slump cone with a height of mm, bottom diameter mm, and top diameter mm. Standard tamping rod. Non-porous base plate. Measuring scale.
First, clean the inner surface of the empty mould and then apply oil to it. Set the mould on a horizontal non-porous and non-absorbent base plate. Fill the mould fully by pouring freshly mixed concrete in three equal layers. Stroke each layer 25 times with the standard tamping rod over the cross-section. After stroking 25 times the top layer is struck off level, now lift the mould slowly in the vertical direction without disturbing the concrete cone.
Use the measuring scale to measure the difference level between the height of the mould and the concrete sample. The subsidence of concrete is known as the slump and the value of slump is measured in mm. Shear Slump: When one-half of the concrete mass slide down the other is called the shear slump. This type of slump is obtained in a lean concrete mix. Collapse Slump: When the sample is collapsed due to adding excessive water, it is known as collapse slump.
Zero Slump: For very stiff or dry mixes it does not show any changes of the slump after removing the slump cone. The procedure of slump test is simple and easy than any other workability test. Inexpensive and portable apparatus is required for this test.
Slump test can be performed at the construction site as well as in the laboratory. The slump test is limited to concretes with the maximum size of aggregate less than 38 mm. The test is suitable only for concretes of medium or high workabilities i. For very stiff mixes having zero slumps, the slump test does not show any difference in concretes of different workabilities. Heavy mass construction 2. Pavements 3. Bridge deck 4.
Beams and slabs 5. Columns, retaining walls and thin vertical members etc. Prestressed concrete members are free from cracks and the resistance to the effect of impact, shock, and stresses are higher than rcc structures. Longevity of prestressed structure is greater than rcc structure because the reinforcement stays unaffected from outer agencies.
High compressive strength of concrete and high tensile strength of steel are used for prestressing that makes it more economical. Smaller sections can be used for longer span by reducing the section of members. Prestressed members are lighter in weight and easily transportable. It requires a smaller amount of construction materials.
The shear resistance of members can be increased by using curved tendons. Prestressing also reduces the diagonal tension in concrete. The main disadvantage of prestressing is that it requires some special equipment like jacks, anchorage etc, which pretends the use of prestressing. High tensile steel is required for prestressing that is very difficult to procure.
It requires highly skilled workers and should be prepared under expert supervision. It is costlier than other rcc structures.
It is a time- dependent deformation which reduces the volume of concrete without the impact of external forces. The hydration of cement results in a reduction in the volume of concrete due to evaporation from the surface of concrete, which leads to cracking. Drying shrinkage generally occurs in the first few months and decreases with time.
The carbonation slowly penetrates the outer surface of the concrete. This type of shrinkage mainly occurs at medium humidities and results increased strength and reduced permeability. It is a minor problem of concrete and can be ignored. It increases with the increases in the water-cement ratio. Shrinkage is mostly occurred due to the drying condition of the atmosphere. It increases with the decrease in the humidity. TIME: The rate of shrinkage rapidly decreases with time.
The rate of shrinkage generally decreases with the increase of the size of aggregates. It is found that concrete made from sandstone shrinks twice than the concrete of limestone.
It contains higher c3s content and finer grinding. Therefore it gives greater strength development at an early stage than OPC. The strength of this cement at the age of 3 days is almost same as the 7 days strength of OPC with the same water-cement ratio.
The main advantage of using rapid hardening cement is that the formwork can be removed earlier and reused in other areas which save the cost of formwork.
This cement can be used in prefabricated concrete construction, road works, etc. This cement is less reactive and its initial setting time is greater than OPC. This cement is mostly used in mass concrete construction.
Cement with such composition has excellent resistance to sulfate attack. This type of cement is used in the construction of foundation in soil where subsoil contains very high proportions of sulfate. To obtain the white color The raw materials used in this cement are limestone and china clay.
This cement, due to its white color, is mainly used for interior and exterior decorative work like external renderings of buildings, facing slabs, floorings, ornamental concrete products, paths of gardens, swimming pools etc. It produces lower heat of hydration and has greater resistance to attack of chemical agencies than OPC. Concrete made with PPC is thus considered particularly suitable for construction in sea water, hydraulic works and for mass concrete works.
Hence the cement stored does not spoiled even during monsoon. This cement is claimed to remain unaffected when transported during rains also. Hydrophobic cement is mainly used for the construction of water structures such dams, water tanks, spillways, water retaining structures etc. Due to the various color combinations, this cement is mainly used for interior and exterior decorative works.
This cement is used for the construction of water-retaining structure like tanks, reservoirs, retaining walls, swimming pools, dams, bridges, piers etc.
This type of cement can be used with advantage in mass concrete work such as dams, foundations, and abutments of bridges, retaining walls , construction in sea water. This cement is also known as calcium aluminum cement CAC. The compressive strength of this cement is very high and more workable than ordinary portland cement. This type of cement is mainly used for grouting anchor bolts and prestressed concrete ducts.
Batching can be done in two different ways. Volume Batching 2. Weight Batching. MIXING: In this process, all the materials are thoroughly mixed in required proportions until the paste shows uniform color and consistency. Hand mixing and machine mixing are the two different methods of mixing. After that, the concrete is correctly placed on the formworks. Concrete can be transported to the site location in two ways 1. Manual Transportation. Mechanical Transportation.
It is required to increase the ultimate strength of concrete by enhancing the bond with reinforcement. CURING: Curing is the process in which the concrete keeps its moisture for a certain time period to complete the hydration process. Curing should be done properly to increase the strength of concrete. Low Heat Cement — 14 Days.
It is also known as super workable concrete. As the name suggests, this concrete compacts by itself without the use of external vibrators. Faster construction and requires less manpower reduce the overall cost of production. SCC can be placed easily in complicated formwork and dense reinforcement. It is super workable due to its low water-cement ratio, which gives rapid strength development, more durability, and best quality. As it is self-compacted there is no need to use any vibrator.
Bleeding and segregation problems are almost nil. It produces a smooth and well-finished surface at the end of concreting. Thinner concrete slabs can be cast easily. Working procedure is totally safe. It is environment-friendly. SCC requires high fluidity in tight joints formwork, which slow downs the casting rate. Due to its low water-cement ratio, plastic shrinkage cracks may occur. But this can be avoided by curing properly.
Highly skilled and experienced workers are required for the production of SCC. It is more costly than any other conventional concrete. This cement is very suitable for under sea applications and sewer infrastructures. It can be used in cold area where rapid strength development is required. HAC is also used in refractory concretes where it requires more strength at very high temperature.
High alumina cement is very reactive and has very high compressive strength. It is more workable than ordinary portland cement. The initial setting time of HAC is about to 3. It is extremely resistant to chemical attack. It induces more heat during the setting time, so it can not be affected by frost. The manufacturing cost of HAC is very high. It loses relative strength in humid condition and high temperature. The whole system is also known as spraycrete.
Dry-mix process and 2. Wet-mix process. Excellent bonding in nature makes the concrete layers very strong. It is more economical than conventional concrete and requires less formwork. The Concrete can be applied by a nozzle from a safe distance. The production cost is very high. Dusting problems. So many wastages of concrete. Thin overhead vertical or horizontal surfaces. Curved or folded sections like tunnels, canals, reservoirs, or swimming pools, and pre-stressed tanks.
Stabilized rock slopes. Restoration and repairing of old building and fire-damaged structure. Waterproofing walls etc. It is produced by cement, water, and air pores no need of coarse aggregates. It is also known as foamed concrete, porous concrete, aerated concrete, lightweight concrete etc. This type of concrete is self-leveling, self-compacting, and can be easily pumped.
Foam concrete can be used in 1. Insulating lightweight concrete production. Lightweight blocks and panels. Partitions wall. Prefabricated buildings.
Heat and sound insulating. Pipelines etc. Foam concrete is very economical, it can be produced at very low cost. This type of concrete has thermal insulation properties.
Transportation is very easy and can be pumped. Michelle Daigle Dec. They know how to do an amazing essay, research papers or dissertations. Asma Sammy Jun. Total views.
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