Water used for making concrete should be clean. It activates the hydration of cement and forms plastic mass. As it sets completely concrete becomes hard mass.
Water gives workability to concrete which means water makes it possible to mix the concrete with ease and place it in final position. More the water better is the workability.
However excess water reduces the strength of concrete. Figure 3. To achieve required workability and at the same time good strength a water cement ratio of 0. Batching 2. Mixing 3. Transporting and placing and 4. Batching: The measurement of materials for making concrete is known as batching. The following two methods of batching is practiced: a Volume batching b Weight batching.
A gauge box is made with wooden plates, its volume being equal to that of one bag of cement. One bag of cement has volume of 35 litres. The required amount of sand and coarse aggregate is added by measuring on to the gauge box.
The quantity of water required for making concrete is found after deciding water cement ratio. For example, if water cement ratio is 0. Suitable measure is used to select required quantity of water. Volume batching is not ideal method of batching. Wet sand has higher volume for the same weight of dry sand. It is called bulking of sand. Hence it upsets the calculated volume required. A weighing platform is used in the field to pick up correct proportion of sand and coarse aggregates.
Large weigh batching plants have automatic weighing equipments. Mixing: To produce uniform and good concrete, it is necessary to mix cement, sand and coarse aggregate, first in dry condition and then in wet condition after adding water. The following methods are practiced: a Hand Mixing b Machine Mixing. Then the sand required for the batch is spread over coarse aggregate. They are mixed in dry condition by overturning the mix with shovels.
Then the cement required for the batch is spread over the dry mix and mixed by shovels. After uniform texture is observed water is added gradually and mixing is continued.
Full amount of water is added and mixing is completed when uniform colour and consistancy is observed. The process of mixing is completed in 6—8 minutes of adding water. This method of mixing is not very good but for small works it is commonly adopted. Required quantities if sand and coarse aggregates are placed in the drum of the mixer.
Water is gradually added and drum is rotated for 2 to 3 minutes during which period it makes about 50 rotations. At this stage uniform and homogeneous mix is obtained. Concrete mixer 3. Transporting and Placing of Concrete. After mixing concrete should be transported to the final position. In small works it is transported in iron pans from hand to hand of a set of workers. Wheel barrow and hand carts also may be employed.
In large scale concreting chutes and belt conveyors or pipes with pumps are employed. In transporting care should be taken to see that seggregation of aggregate from matrix of cement do not take place. Concrete is placed on form works. The form works should be cleaned and properly oiled. If concrete is to be placed for foundation, the soil bed should be compacted well and is made free from loose soil. Concrete should be dropped on its final position as closely as possible.
If it is dropped from a height, the coarse aggregates fall early and then mortar matrix. This segregation results into weaker concrete. Compaction of Concrete: In the process of placing concrete, air is entrapped.
Hence it is necessary to remove this entrapped air. This is achieved by compacting the concrete after placing it in its final position. Compaction can be carried out either by hand or with the help of vibrators.
In intricate portions a pointed steel rod of 16 mm diameter and about a metre long is used for poking the concrete. Vibration reduces the friction between the particles and set the motion of particles. As a result entrapped air is removed and the concrete is compacted. The use of vibrators reduces the compaction time. Vibration should be stopped as soon as cement paste is seen on the surface of concrete. Over vibration is not good for the concrete.
The following types of vibrators are commonly used in concreting: a Needle or immersion vibrators b Surface vibrators c Form or shutter vibrators d Vibrating tables. Needle vibrators are used in concreting beams and columns.
Surface vibrators and form vibrators are useful in concreting slabs. Vibrating tables are useful in preparing precast concrete elements. Curing of Concrete Curing may be defined as the process of maintaining satisfactory moisture and temperature conditions for freshly placed concrete for some specified time for proper hardening of concrete. Curing in the early ages of concrete is more important. Curing for 14 days is very important. Better to continue it for 7 to 14 days more.
If curing is not done properly, the strength of concrete reduces. Cracks develop due shrinkage. The durability of concrete structure reduces. The following curing methods are employed: a Spraying of water b Covering the surface with wet gunny bags, straw etc.
It accelerates curing process, resulting into the reduction of curing period. The compound shows affinity to the moisture and retains it on the surface. It keeps the concrete surface wet for a long time. Properties of Concrete Concrete has completely different properties when it is the plastic stage and when hardened. Concrete in the plastic stage is also known as green concrete.
Workability 2. Segregation 3. Bleeding 4. The properties of hardened concrete are: 1. Strength 2. Resistance to wear 3. Dimensional changes 4. Durability 5. Properties of Green Concrete 1. Workability: This is defined as the ease with which concrete can be compacted fully without seggregating and bleeding. It can also be defined as the amount of internal work required to fully compact the concrete to optimum density. The workability depends upon the quantity of water, grading, shape and the percentage of the aggregates present in the concrete.
Workability is measured by a The slump observed when the frustum of the standard cone filled with concrete is lifted and removed. The suggested values of workability for different works are as shown in Table 3. Table 3. Concreting of shallow sections with vibrations — 0. Concreting of light reinforced sections with vibrators — 0. Concreting of lightly reinforced sections without 25 — 75 mm 0.
Concreting of heavily reinforced sections without 75 — mm More than 0. Segregation: Separation of coarse particles from the green concrete is called segregation. Because of the segregation, the cohesiveness of the concrete is lost and honey combing results. Ultimately it results in the loss of strength of hardened concrete. Hence utmost care is to be taken to avoid segregation. Bleeding: This refers to the appearance of the water along with cement particles on the surface of the freshly laid concrete.
This happens when there is excessive quantity of water in the mix or due to excessive compaction. Bleeding causes the formation of pores and renders the concrete weak. Bleeding can be avoided by suitably controlling the quantity of water in the concrete and by using finer grading of aggregates.
Harshness: Harshness is the resistance offered by concrete to its surface finish. Harshness is due to presence of lesser quantity of fine aggregates, lesser cement mortar and due to use of poorely graded aggregates. It may result due to insufficient quantity of water also. With harsh concrete it is difficult to get a smooth surface finish and concrete becomes porous. Properties of Hardened Concrete 1. Strength: The characteristic strength of concrete is defined as the compressive strength of mm size cubes after 28 days of curing below which not more than 5 per cent of the test results are expected to fail.
IS grades the concrete based on its characteristic strength as shown in Table 3. But IS — specifies minimum grade of M20 to be used for reinforced concrete works. Strength of concrete depends upon the amount of cement content, quality and grading of aggregates, water cement ratio, compaction and curing. Strength of concrete is gained in the initial stages. In 7 days the strength gained is as much as 60 to 65 per cent of 28 days strength. It is customary to assume the 28 days strength as the full strength of concrete.
However concrete gains strength after 28 days also. The characteristic strength may be increased by the as factor given in Table 3.
Effect of age factor on strength of concrete Minimum age of member when design load 1 month 3 months 6 months 12 months is expected. Age factor 1. Dimensional Change: Concrete shrinks with age. The total shrinkage depends upon the constituents of concrete, size of the member and the environmental conditions.
Total shrinkage is approximately 0. The permanent dimension change due to loading over a long period is termed as creep. Its value depends upon the stress in concrete, the age of the concrete at the time of loading and the duration of the loading.
The ultimate creep strain may be estimated from the values of creep coefficient. The creep coefficient is defined as ultimate creep strain divided by the elastic strain at the age of loading. These values are listed in Table 3.
Creep coefficient based on the age of loading Age of Loading 7 days 28 days 1 year Creep Coefficient 2. The coefficient of thermal expansion depends upon the nature of cement, the type of aggregates, cement content, relative humidity and the size of the sections of the structural elements. Quartzite 1. Sand stone 0. Granite 0. Basalt 0. Durability: Environmental forces such as weathering, chemical attack, heat, freezing and thawing try to destroy concrete. The period of existance of concrete without getting adversely affected by these forces is known as durability.
Generally dense and strong concretes have better durability. The cube crushing strength alone is not a reliable guide to the durability. Concrete should have an adequate cement content and should have low water cement ratio. Impermeability: This is the resistance of concrete to the flow of water through its pores.
Excess water during concreting leaves a large number of continuous pores leading to the permeability. Since the permeability reduces the durability of concrete, it should be kept very low by using low water cement ratio, dense and well graded aggregates, good compaction and continuous curing at low temperature conditions.
The cement content used should be sufficient to provide adequate workability with low water cement ratio and the available compaction method. Slump test. Compaction factor test. Crushing strength test. Slump Test: This test is conducted to determine the workability of concrete. It needs a slump cone for test Fig. Slump cone is a vessel in the shape of a frustum of a cone with diameter at bottom mm and 50 mm at top and mm high. This cone is kept over a impervious platform and is filled with concrete in four layers.
Each layer is tamped with a 16 mm pointed rod for 25 times. After filling completely the cone is gently pulled up. The decrease in the height of the concrete is called slump.
Higher the slump, more workable is the concrete. The desired values of slumps for various works have been shown in Table 3. Slump test 2. Compaction Factor Test: This is another test to identify the workability of concrete. This test is conducted in the laboratory. The test equipment consists of two hoppers and a cylinder fixed to a stand, the dimensions and the distances between the three vessels being standardized.
Vessel A and B are having hinged bottoms whereas cylinder C is having fixed bottom. As soon as it is filled, the hinged door is opened. Concrete is collected in vessel B. Then the hinged door of B is opened to collect concrete in cylinder C. The concrete in cylinder C is weighted.
Let it be W1. Now cylinder is again filled with the sample of concrete in 50 mm layers, which is compacted by ramming and vibrating. Then the weight of compacted concrete is determined.
Let this weight be W2. The specified values of compaction factor for different works are already listed in Table 3. Compaction factor test 3. Before filling mould, it is properly oiled on its inner surfaces, so that cubes can be easily separated.
Fresh cube is filled with concrete to be tested in 3 layers and kept in the room. After 24 hours, cube is removed from the mould and kept under water for curing. After 28 days of curing cubes are tested in the compression testing machine. In this test cubes are placed over the smooth surface which is in contact with side plates of mould. Code specify the desirable strength of concrete for 3 days and 7 days for quick assessment of strength of concrete. Desirable Properties of Concrete Appropriate quality and quantity of cement, fine aggregate, coarse aggregate and water should be used so that the green concrete has the following properties: a Desired workability b No seggregation in transporting and placing c No bleeding and d No harshness.
CONCRETE 49 Hardened concrete should have a required characteristic strength b minimum dimensional changes c good durability d impermeable e good resistance to wear and tear.
Uses of Concrete 1. As bed concrete below column footings, wall footings, on wall at supports to beams 2. As sill concrete 3. Over the parapet walls as coping concrete 4. For flagging the area around buildings 5. For pavements 6. For making building blocks. However major use of concrete is as a major ingradient of reinforced and prestressed concrete. Many structural elements like footings, columns, beams, chejjas, lintels, roofs are made with R.
Cement concrete is used for making storage structures like water tanks, bins, silos, bunkers etc. Bridges, dams, retaining walls are R. Concrete is good in resisting compression but is very weak in resisting tension. Hence reinforcement is provided in the concrete wherever tensile stress is expected. The best reinforcement is steel, since tensile strength of steel is quite high and the bond between steel and concrete is good.
As the elastic modulus of steel is high, for the same extension the force resisted by steel is high compared to concrete. However in tensile zone, hair cracks in concrete are unavoidable. Reinforcements are usually in the form of mild steel or ribbed steel bars of 6 mm to 32 mm diameter. A cage of reinforcements is prepared as per the design requirements, kept in a form work and then green concrete is poured.
After the concrete hardens, the form work is removed. The composite material of steel and concrete now called R. Properties of R. It should be capable of resisting expected tensile, compressive, bending and shear forces. It should not show excessive deflection and spoil serviceability requirement. There should be proper cover to the reinforcement, so that the corrossion is prevented. The hair cracks developed should be within the permissible limit.
It is a good fire resistant material. When it is fresh, it can be moulded to any desired shape and size. Durability is very good. Uses of R. It is a widely used building material. Some of its important uses are listed below: 1. It is used for the construction of big structures like a Bridges b Retaining walls c Docks and harbours d Under water structures.
It is used for pre-casting a Railway sleepers b Electric poles 5. It is used for paving a Roads b Airports. For this purpose R. It is well known fact that concrete is very weak in tension. Hence in the slabs, lintels and beams the concrete in the portion below the neutral axis do not participate in resisting the load.
It acts as a filler material only. Hence to achieve economy the concrete in tensile zone may be replaced by bricks or tiles. Dense cement mortar is used to embed the reinforcement. The reinforcement may be steel bars, expanded mesh etc. Concrete in tension is acting as a cover to steel and helping to keep steel at desired distance. Thus in R. Prestressing the concrete is one of the method of utilizing entire concrete. The principle of prestressed concrete is to introduce calculated compressive stresses in the zones wherever tensile stresses are expected in the concrete structural elements.
When such structural element is used stresses developed due to loading has to first nullify these compressive stresses before introducing tensile stress in concrete. Thus in prestressed concrete entire concrete is utilized to resist the load. Another important advantage of PSC is hair cracks are avoided in the concrete and hence durability is high. The fatigue strength of PSC is also more.
The deflections of PSC beam is much less and hence can be used for longer spans also. PSC is commonly used in the construction of bridges, large column free slabs and roofs. PSC sleepers and electric piles are commonly used. The material used in PSC is high tensile steel and high strength steel. The tensioning of wires may be by pretensioning or by post tensioning.
Pretensioning consists in stretching the wires before concreting and then releasing the wires. In case of post tensioning, the ducts are made in concrete elements. After concrete of hardens, prestressing wires are passed through ducts. After stretching wires, they are anchored to concrete elements by special anchors.
The cracks develop even before loading. After loading micro cracks widen and propagate, exposing concrete to atmospheric actions. If closely spaced and uniformly dispered fibres are provided while mixing concrete, cracks are arrested and static and dynamic properties are improved.
Fibre reinforced concrete can be defined as a composite material of concrete or mortar with discontinuous and uniformly distributed fibres. Commonly used fibres are of steel, nylon, asbestos, coir, glass, carbon and polypropylene.
The length to lateral dimension of fibres range from 30 to The diameter of fibres vary from 0. Fibre reinforced concrete is having better tensile strength, ductility and resistance to cracking. Uses of FRC 1. For wearing coat of air fields, roads and refractory linings. For manufacturing precast products like pipes, stairs, wall panels, manhole covers and boats. Glass fibre reinforced concrete is used for manufacturing doors and window frames, park benches, bus shelters etc.
Carbon FRC is suitable for structures like cladding and shells. Asbestos FRC sheets are commonly used as roofing materials. Civil Engineering Home. Civil Engineering. Civil Engg.
Professional Ethics. Engineering Economics. Engineering Materials. Strength of materials. Building Construction. Civil Programming. Reinforced Concrete. Differential Equations. Soil Mechanics I. Past Papers. Civil Engineering Ebooks. When it intersects the horizontal plane top plane of projection , it is identified as 1H, when it intersects the frontal plane front plane of projection , it is identified as 1F, and where it intersects the profile plane right side plane of projection , it is labeled 1P.
On these planes, views of the object can be obtained as is seen from the top, front, right side, left side, bottom and rear. Consider the object and its projection in fig. In actual work, there is rarely an occasion when all six principal views are needed on one drawing.
All these views are principal views. Each of the six views shows two of the three dimensions of height, width and depth. In general, when the glass box is opened, its six sides are revolved outward so that they lie in the plane of the paper. And each image plane is perpendicular to its adjacent image plane and parallel to the image plane across from it. Before it is revolved around its hinged fold line reference line.
A fold line is the line of intersection between any hinged adjacent image planes. The left side, front, right side, and back are all elevation views. Each is vertical. The top and bottom planes are in the horizontal plane.
But in most cases the top, front, and right sides are required. Sometimes the left- side view helps to describe an object more clearly than the light side view.
Orthographic views are arranged in two techniques as a. First Quadrant Fig. When an inclined or oblique line is to be projected it is helpful to identify and draw the end points and then joining them to obtain the projection. Parallel Inclined Fig. Oblique Fig. The edges, intersections, and surface limits of these hidden parts are indicated by a discontinuous line called a dashed line or hidden line.
Particular attention should be paid to the execution of these dashed lines. If carelessly drawn, they ruin the appearance of a drawing. All the center lines are the axes of symmetry. Hidden portions of the object may project to coincide with visible portions. Center lines may occur where there is a visible or hidden out line of some part of the object. Since the physical features of the object must be represented full and dashed lines take precedence over all other lines since visible out line is more prominent by space position, full lines take precedence over dashed lines.
A full line could cover a dashed line, but a dashed line could not cover a full line. When any two lines coincide, the one that is more important to the readability of the drawing takes precedent over the other. The following line gives the order of precedence of lines. Full line 2. Dashed line 3. Careful line or cutting — plane line 4.
Break lines 5. Dimension and extension lines. Crosshatch lines. The points which are connected by lines in original object should be connected in the vertical plane. All other 5 views can be obtained in similar way. The plane of projection vertical, in case of front view should be parallel to the face for which views are being drawn.
For example, in case of top view the plane will be horizontal. In the projection there is a relationship of different views. It is usual practice to draw the front view first, then top and side views are drawn with the help of the vertical and horizontal projection lines.
This can be done using T-square, set-squares and compasses. Here only the figure C requires the use of compass in addition to T-squares and set- squares.
The spacing between views has to be determined or decided beforehand and if equal spacing is needed then fig. A can be followed and if a different spacing is needed then fig. B can be followed. Sufficient space should be provided in order to give dimensions avoiding any crowding and also excessive space should be avoided. If not mentioned or required otherwise 30mmmm spacing can be provided between two successive views.
Position of this line depends on the spacing requirement between side view and front view. If equal spacing is required then the line should originate at the corner of the front view. These lines will cut the diagonal line. It is to be noted that for 1st angle projection the lines should be projected according to position of views. For example to draw top view, vertically downward lines need to be projected from front view so that the top view is generated below the front views; for getting right side view horizontal lines from front view are to be projected toward left and so on.
The length along the third axis cannot be shown in same view. This makes it difficult to understand them and only technically trained persons can understand the meaning of these orthographic views. A layman cannot imagine the shape of the object from orthographic projections. To make the shape of an object easy to understand for both technical persons and non-technical laymen pictorial projections are used. Most commonly used pictorial drawing is Isometric drawing. When a drawing is prepared with an isometric scale or otherwise if the object is actually projected on a plane of projection, it is an isometric projection.
For this purpose the object is so placed that its principle axes are equally inclined to the plane of projection. In other words, the front view of a cube, resting on one of its corners is the isometric projection of the cube as shown in fig. But as the object is tilted all the lengths projected on the plane appears to be shortened and thus they are drawn shortened in isometric projection.
In the isometric projection of a cube shown in Fig. The extent of reduction of an isometric line can be easily found by construction of a diagram called isometric scale. For this, reproduce the triangle DPA as shown in Fig. Mark the divisions of true length on DP.
Through these divisions draw vertical lines to get the corresponding points on DA. The divisions of the line DA give dimensions to isometric scale.
The lines that are parallel on the object are parallel in the isometric projection. Vertical lines on the object appear vertical in the isometric projection. A line which is not parallel to any isometric axis is called non-isometric line and the extent of fore- shortening of non-isometric lines is different if their inclinations with the vertical planes are different.
Drawing of objects is seldom drawn in true isometric projections, as the use of an isometric scale is inconvenient. Instead, a convenient method in which the foreshortening of lengths is ignored and actual or true lengths are used to obtain the projections, is applied which is called isometric drawing or isometric view.
This is advantageous because the measurement may be made directly from a drawing. The isometric drawing is An isometric drawing is so much easier to execute and, for all practical purposes, is just as satisfactory as the isometric projection. Box method. Off-set method. In this method, the object is imagined to be enclosed in a rectangular box and both isometric and non-isometric lines are located by their respective points of contact with the surfaces and edges of the box.
It is always helpful to draw or imagine the orthographic views first and then proceed for isometric drawing. In the off-set method, the curved feature may be obtained by plotting the points on the curve, located by the measurements along isometric lines.
If there are some inclined lines in the plane it will be helpful to enclose the plane with a rectangle and then obtain the projection with reference to the sides of that rectangle.
ABCD is the required isometric projection. This can also be drawn as shown in Fig. Arrows show the direction of viewing.
Arrow at the top shows the direction of viewing. Similarly the fig. The line 3-A will intersect the line at point M. Similarly obtain the intersecting point N. With center 3 and radius 3-D draw an arc AD. Similarly the isometric views can be obtained on vertical planes as shown in fig. Then the isometric box is constructed and the orthographic views are reproduced on the respective faces of the box.
Finally by joining the points relating to the object and erasing unnecessary lines the isometric view is obtained. In a specific isometric drawing three maximum faces can be shown. Usually front view, top view and either left or right side view are selected. Use set square to make angles. Remember to cut height along vertical isometric axis.
To do this, draw 2 parallel lines of each isometric axis at the end points of other two axes. Erase the non- existing lines. Compare the orthographic views with your obtained Isometric views. If not, you are done. Step-1 b Step-2 Step-3 c d Step-4 e Fig. Draw isometric view from the orthographic views given in figures below: Md. Draw isometric view of a hexagonal prism 30mm sides and 60mm height.
Solution: Draw the orthographic views first. Following section 7. For projecting the hexagonal top view on the top face of isometric box follow section 7.
Draw isometric view of a cone with base diameter 30mm and axis 50 mm long. For projecting the circular top view on the top face of isometric box follow section 7. Exercise and Assignments: 1. Draw orthographic views of the following objects wooden objects available : 1 2 3 4 Md. Draw orthographic views for the following pictorial views Assume arbitrary dimension : 1 2 3 4 Md. Draw necessary orthographic views to represent i.
A reading table ii. Sitting chair iii. Twin seats of university bus. Laptop computer v. Wall clock. D-box of HSTU. A pentagonal pyramid. A Cylindrical pen holder. An oval shaped paper-weight. Draw isometric view of a rectangular plane having length of sides as 10 cm and 15 cm when its plane is a horizontal and b vertical. Draw isometric view of a square prism with a side of base 5cm and axis 15 cm long when the axis is a vertical and b horizontal.
Draw isometric view of a cylinder with base diameter 10cm and axis 15 cm long. A pentagonal pyramid of side of base 30mm and height 70mm is resting with its base on horizontal plane. Draw the isometric drawing of the pyramid. Draw isometric views of i. Prepare isometric drawing from the given orthographic views. Use assumed value for missing dimensions 2 1 3 4 5 6 Md. Why have you studied projection? Define projection. Why it is necessary? What do you mean by projection plane, projector and view?
Show in a sketch. Classify projection and define the types. What are the possible orthographic views of an object? Are all the orthographic views necessary to describe an object? If not, how will you choose the necessary views? Describe the glass box method. What do you mean by 1st angle and 3rd angle projection?
Which one is British and which one is American System? Which one is easier and why? Differentiate between 1st angle and 3rd angle projection. Show the arrangement of views in 1st and 3rd angle projection system.
Which lines are projected to their actual length? Which lines are not projected to their actual length? How will you obtain projection of such lines? How do you represent a hidden edge in a particular view?
How do you represent a hole in orthographic view? What is the order of precedence of line in orthographic projection? What will you do, if a solid line and a hidden line occur at the same location? What will you do, if a center line and a hidden line occur at the same location? How do you obtain views by diagonal line method? What is the standard spacing to be maintained between views? How to control space between views in diagonal line method?
What are the advantages of orthographic projection? What do you mean by pictorial projection? Classify it. What is the difference between axonometric and oblique projection? What are the different types of axonometric projection?
Why they are so named? What is the difference between isometric, diametric and trimetric projection? What is the difference between cabinet and cavalier projection? What do you mean by perspective projection? How does it differ with pictorial projection?
Why the object appears to be shortened in perspective projection? Why isometric projection is the most commonly used pictorial projection in engineering drawing? What are the advantages of isometric projection over other types of pictorial projection? In which position of object its front view becomes its isometric view? How the object is rotated to obtain its isometric view? Why are the objects appeared to be shortened in case of isometric projection?
What is the percentage of shortening? What is isometric scale? How it is constructed? Which one is advantageous and why?
What do you mean by isometric and non-isometric lines? How isometric drawing are constructed by box method. Why is it helpful to draw orthographic views before drawing the isometric view of the object?
In the box method, how will you decide the isometric axis for plotting width, length and height? Ghose, Civil Engineering Drawing and Design, , 1st ed. Amalesh Chandra Mandal, Dr. Quamrul Islam, Mechanical Engineering Drawing, , 1st ed. David L. Goetsch, John A. Nelson, William S.
Dhawan, A Textbook of Machine Drawing, , 2nd ed. Home Explore Login Signup. Successfully reported this slideshow. We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.
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