What is the workability of concrete | test, definition, improvement and meaning | what is the workability of concrete। workability of concrete definition। workability of concrete measured by। Types of workability। Workability of concrete test and improvement
Workability is the property of fresh concrete mixtures by the the virtue of which can be easily mixed, transported, compacted and finished with minimum loss of homogeneity that is directly impacts strength, quality, appearance and even the cost of labour for placement and finishing,
It is also described in simple words, workability means the ease of placement, compacted and workable concrete means the ability of concrete chich can be placed and can be compected easily without any bleeding and segregation.
Relatively it’s provide enough strength and long durability for concrete structure, workability is relevant towster cement ratio, workability increases and strength decreases.
Workability of concrete is a broad term that is widely used and influence by various factors as etc W/C ratio, A/C ratio, size and shape of aggregate.
All types of concrete in different work as road construction, light foundation ,poll, heavy mass construction, bridge deck, beams, slab, column and retaining wall for desired workability is not same which is depend on two factor sectionsize, amount and spacing of reinforcement and process of compaction.
What is the workability of concrete?
Regarding this, “what is the workability of concrete “, the workability of concrete is a property of freshly mixed concrete that is performing easily placement and compacted with minimum loss of homogeneity, according to good workability or desired workability is higher strength and good bond with reinforcing steel in concrete design and that can be easily moved, placed and consolidated efficiently, results in a quality concrete design with long service life.
Workability of concrete definition
Regarding this “workability of concrete definition”, the workability of concrete is defined as amount of useful internal work required to be done by the concrete in order to activate full compaction.
Basic facts and definition about workability of concrete according to two standard laboratory test which follows the specific guidelines-
According to ASTM -C125-93 – workability of concrete is manipulate a freshly mixed quantity of concrete with minimum loss of homogeneity.
According to ACI-116R-90 – workability of concrete is the property of freshly mixed concrete which determines the ease and homogeneity with which it can be mixed, placed, consolidated and finished.
What are the types of workability of concrete?
Workability of concrete is three types on the basis of handle, placement and compacted that is 1) unworkable concrete, 2) medium workacble concrete, and 3) highly workable concrete.
What is the unworkabl concrete?
Unworkable concrete is define as those concrete which is harsh, difficult to hand mixing, having water cement ratio is below 0.4, difficult to maintain the homogeneity with which it can be mixed, placed, consolidated and compaction due to fact high segregation of aggregate as cement paste is not stick property to the aggregate.
What is the medium workable concrete?
Medium workable concrete is relatively easy to placement and compaction without segregation and loss of homogeneity, this type of concrete Is used in light construction concrete work having W/C ratio is 0.4 to 0.55.
What is the highly workable concrete?
Highly workable concrete is freshly mixed concrete by the vertue of which can be easily handled, mixed, placed and compacted. This type of concrete flow easily and settle down without much effort, W/C ratio is more than 0.55, this concrete compact itself therefore is self compacting concrete, so very easy to handle, mixing, placement and consolidated.
What are the factors that affecting the workability of concrete?
Workability is relevant to water cement ratio, it increases as water cement ratio increases and strength decreases. Workability of concrete is directly proportional to water cement ratio as water to cement ratio increases there is gradually increased in workability. Workability of concrete is inversely proportional to strength, as workability increases that’s leads to gradually decrease in strength.
Factors affecting workability are following:-
1. water content- the higher the water content per cubic meter of concrete, the higher will be the workability. Only addition of water is concrete does no effect it’s workability, it reduces it strength. In order to increase the workability cement contain is also required to be increased in the same proportion of water.
2. aggregate/ cement ratio- higher the aggregate/cement ratio, the leaner the concrete and lower the workability, and lower aggregate/cement ratio gives better workability.
3. size of aggregate- the bigger the size of aggregate, higher will be the workability, and small size aggregate results in the formation of less workable concrete.
4. shape of aggregate- rounded or cubical aggregate makes the strong concrete mix compared to angular, elongated or flaky aggregate. It means angular and rough aggregate reduces workability, flakiness and elongation also reduces workability and rounded, smooth aggregate increases the workability.
5. well graded aggregates with less wide content, it gives higher workability
6. admixures- admixtures may increases workability
7. Rough aggregate surface requires more cement to produce a workable concrete mix and provide a better bond then the aggregate with a smooth surface
8. decreses bleeding and segregation is more workable of concrete, also durability increase but decrease strength.
9. Time transit is inversely proportional to workability of concrete.
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Workability of concrete measured by which test
Workability of concrete measured by three test methods which are the following – 1) slump test in concrete, 2) Compaction factor test, and 3) Vee-bee consistometer test.
What is the slump test in concrete?
What is the slump in concrete?:- the concrete slump test is a field method that it measures the workability of concrete. It is test on site. This test is performed to test is performed to check the the consistency of freshly mixed concrete in specific batch. This test does not give direct measures of workability.
Concrete slump test or slump cone test is is widely used because of the simplicity of apparatus required and the test procedure. The slump test is to determine the consistency of freshly concrete mix prepared at the the laboratory or the construction site during the the progress of the work, not shows directly workability.
What are the apparatus required for concrete slump test?
Apparatus for concrete slump test are follows:-
1. Slump cone or mould with top diameter 100mm, bottom diameter 200mm and height 300mm
2. Standard tamping rod with diameter 16cm and length 60cm.
3. Nonporous base plate
4. Measuring scale
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What is the procedure of concrete slump test?
Procedure of concrete slump test- concrete slump test is very simple to procedure.
1. First kill in the inner surface of the empty mould and then apply oil to it.
2. Set the mould on a horizontal non porous base plate
3. Fill the slump cone with concrete in in 4 approx equal layer
4. Compact each layer with 25 stroke bye standard temping road
5. Remove the the excess concrete and level the top
6. Clean the water leaved between base plate and mould
7. Raise the mould from concrete immediately and slowly remove it completely
8. Measures the difference between height of the the slump cone and the height of the specimen being slump value.
What are the types of concrete slump?
Types of slump test- Initially slump cone raised, than its sample shape depend to water cement ratio. Due to fact that slump of test considered collapse, shear type of slump, true slump and zero slump.
Slump value for concrete
Slump Value for concrete is the the gap between top of slump cone and and subsided concrete. Measures the difference between height of the slump cone and height of the specimen wing tested is slump value. Slump test recommended values of slumps for different concrete mixes.
Types of concrete Slumps value in mm
● Heavy mass construction : 25-50 mm
● Pavements : 20-30 mm
● Bridge decks : 25-75 mm
● lightly reinforced : 25-75 mm
● floors : 25-75 mm
● canal lining. : 25-75 mm
● strip footings : 25-75 mm
● Heavily reinforced sections. : 50-100 mm
● Beams : 50-100 mm
● slabs. : 50-100 mm
● column : 50-100 mm
● Pumped concrete. : 50-100 mm
● slip form work. : 50-100 mm
● retaining walls : 75-150 mm
● Thin vertical member : 75-150 mm
What is the ideal value of slump?
What is the ideal value of slump? Slump value of concrete is suitable for medium to high workability having slump value 25 mm to 125 mm and we consider two sample dry case and wet case, ideal value of slump will be 25-50 mm (1-2 inch) in case of dry sample and 150-175 mm (6-7inch) in case of wet sample.
What is Compaction factor test for workability of concrete?
Regarding this, compaction factor test is the measurement of workability test for concrete conduct in laboratory developed by road research laboratory in United Kingdom and used to determine the workability of concrete.
This test is used for concrete concrete which have low workable for which slump test is not perform that is sufficiently sensitive to enable as a result the compaction factor value ranges from 0.7 to 0.95.
What are Apparatus required for compaction factor test of workability of concrete?
Compaction factor test required following apparatus which are as follows:- 1) Trowls (15.2 cm long), 2) A rod of steel (1.6cm diameter and 61 cm long), and 3) Balance.
Procedure of compaction factor test
1. The concrete sample is placed in the upper hopper
2. Upper hopper is opened, the sample drops into lower hopper filling it to overflowing.
3. The sample falls into the cylinder and surplus cement is removed from the top of the cylinder with the help of trowel
4. Then clean the outside surface of cylinder, the cylinder is weighted and it is recorded as weight of partially compacted concrete.
5. The cylinder is again filled with concrete in layers.each layer is fully compacted with tapping rod.
6. The cylinder is again weighed after wiping and cleaning the outside surface of cylinder.
7. The compacting factor is calculated from the formula
Compacting factor= weight of partially compacted conc/ weight of fully compacted conc.
Relation between workability and compacting factor
Workability of concrete and compacting factor close to each other and give the idea of strength
1. Compacting factor:- 0.75 to 0.80 degree of workability – very low
2. Compacting factor:- 0.87 degree of workability – low
3. Compacting factor:- 0.935 degree of workability- medium
4. Compacting factor:- 0.96. degree of workability – high
What is the Vee bee consistometer test?
Regarding this, Vee bee consistometer test, this is a good laboratory test which is used particularly for good dry mixes, it is also used for the low conc having low workability for slump is limited to value 50mm. This test is performs the compactibility of the freshly mixed concrete and relative effort measurement to change the mass of the concrete from a definite shape to the other.
What are the Apparatus for vee-bee test?
1. Vee bee consistometer, vibrating table having length 380 mm, width 260 mm and height of 260 mm.
2. Metal slump cone, weighing balnce Cylindrical container
3. Standard iron tamping rod and trowels
4. Funnel and guide sleeve
Procedure of Vee bee test of measurement of workability
1. Concrete is filled in sheet metal cone.
2. Rider of glass plate brought into position, it is touching the top of the concrete
3. Vibrating actions is subjected to the concrete cone by starting the vibrator
4. The vibration is untill the concrete surface becoms horizontal, the time taken to attain horizontal surface is noted, the degree of workability perform the time in seconds.
Value of degree of workability
Degree of of workability with respect to Vee bee consistometer gives the value of range time which is required in seconds as follows
1. Degree of Workability-: very low, time in seconds – 20-40 seconds
2. Degree of Workability-: low, time in seconds – 10-20 seconds
3. Degree of Workability-: medium, time in seconds – 7-10 seconds
4. Degree of Workability-: high,. time in seconds – 3-7 seconds
5. Degree of Workability-: very high, time in seconds- 1-3 seconds
Workability of concrete can be improved by
Regarding this, “what are the factors that improve the workability of concrete”?, improvement of workability of concrete is depend on various factors, workability of concrete improved by following factors which are as follows:-
1. To use the aggregate rounded cubical and smooth shape of aggregate, improve the workability of concrete.
2. Elongated and flaky shape of aggregate is not used in construction structure.
3. To use the bigger size of aggregate
4. Increasing the water / cement ratio improve the Workability of concrete
5. Use the admixtures
6. Lower the aggregate/cement ratio
7. Adding the admixtures improve the Workability of concrete
8. Addition of non porous aggregate
9. Use the air entraining mixtures
10. To use well graded aggregates.
Workability of concrete is directly proportional to
Regarding this, workability of concrete is directly proportional to water cement ratio, as a relatively increases the water cement ratio that increase the workability in same proportion and decreses the water cement ratio that decrease the workability of concrete.
Workability of concrete is inversely proportional to
Regarding this, workability of concrete is inversely proportional to time transit, as a long time transit affect the workability of concrete and also workability of concrete inversely proportional to strength of concrete, as workability increases leads to decrease in strength and reduced in workability increase the strength.
Strength of concrete and workability relationship
Regarding this, strength of concrete and workability relationship, strength of concrete is the vital property of workability for construction structure, ability of fresh concrete to contain the more density or compaction to maximum density is possible with a reasonable amount of construction structure of work.strength of concrete is depend on water cement ratio, an increase of water cement ratio indicates a decrease the compressive strength of concrete and increase of workability of concrete.
In other fact the compressive strength of concrete is directly proportional to time transit, longer the time taken of construction structure increses the strength of concrete and inversly affect the workability of concrete.