What are the major problems in using pumping for concreting works?

What are the major problems in using pumping for concreting works?
by

1 Answer

Answer :

In pumping operation, the force exerted by pumps must overcome the friction between concrete and the pumping pipes, the weight of concrete and the pressure head when placing concrete above the pumps. In fact, as only water is pumpable, it is the water in the concrete that transfers the pressure.
The main problems associated with pumping are the effect of segregation and bleeding. To rectify these adverse effects, the proportion of cement is increased to enhance the cohesion in order to reduce segregation and bleeding. On the other hand, a proper selection of aggregate grading helps to improve the pumpability of concrete.
by

Related questions

If on­site slump test fails, should engineers allow the contractor to continue the concreting works?

Description : If on­site slump test fails, should engineers allow the contractor to continue the concreting works?

Last Answer : This is a very classical question raised by many graduate engineers. In fact, there are two schools of thought regarding this issue. The first school of thought is rather straightforward: the contractor ... t the Engineer exercise his power to stop the contractor and save these extra time and cost?

Is it desirable to use concrete of very high strength i.e. exceeding 60MPa? What are the potential problems associated with such high strength concrete?

Description : Is it desirable to use concrete of very high strength i.e. exceeding 60MPa? What are the potential problems associated with such high strength concrete?

Last Answer : To increase the strength of concrete, say from 40MPa to 80MPa, it definitely helps in improving the structural performance of the structure by producing a denser, more durable and higher load ... Moreover, owing to a low aggregate content of high strength concrete, creep and shrinkage increases.

Can grout replace concrete in normal structure?

Description : Can grout replace concrete in normal structure?

Last Answer : The mixture of cement and water alone cannot replace concrete (Longman Scientific and Technical (1987)) because: (i) Shrinkage of grout is several times that of concrete with the same mass. (ii) ... of cement with water is more than normal concrete and this leads to the problem of severe cracking.

If a contractor proposes to increase concrete cover beyond contractual specification (i.e. 40mm to 70mm), shall engineers accept the proposal?

Description : If a contractor proposes to increase concrete cover beyond contractual specification (i.e. 40mm to 70mm), shall engineers accept the proposal?

Last Answer : In contractual aspect, based on the requirement of General Specification of Civil Engineering Works (1992 Edition), the tolerance of concrete cover is between + ... larger cover. Therefore, with an increase of concrete cover, the crack width will increase which is undesirable.

What is the function of rebate in a typical construction joint?

Description : What is the function of rebate in a typical construction joint?

Last Answer : Construction joints are created on sites to facilitate the construction process. However, if improperly constructed, the completed construction joints will leave an uneven scar on the concrete surface and affect ... After the other pour is concreted, it will hide the uneven joint inside the rebate.

In carrying out compression test for concrete, should test cubes or test cylinders be adopted?

Description : In carrying out compression test for concrete, should test cubes or test cylinders be adopted?

Last Answer : Basically, the results of compression test carried out by using cubes are higher than that by cylinders. In compression test, the failure mode is in the form of tensile splitting induced by uniaxial ... are lower than that of cubes. Reference is made to Longman Scientific and Technical (1987).

In erection of falsework, for a rectangular panel inside a falsework should it be braced along the two diagonals?

Description : In erection of falsework, for a rectangular panel inside a falsework should it be braced along the two diagonals?

Last Answer : When a rectangular panel is subject to an eccentric load or a lateral load, it tends to deform into a parallelogram with one diagonal shortening and the other elongating. Theoretically, it is sufficient to ... may come from both sides of the panel and hence it should be braced in both diagonals.

What is the indication of shear slump and collapse slump in slump tests?

Description : What is the indication of shear slump and collapse slump in slump tests?

Last Answer : There are three types of slump that may occur in slumps test, namely, true slump, shear slump and collapse slump. True slump refers to general drop of the concrete mass ... concrete. Collapse slump indicates that concrete mix is too wet ad the mix is deemed to be harsh and lean.

If concrete compression test fails, should Schmidt hammer test be adopted as an alternative test to prove the concrete strength?

Description : If concrete compression test fails, should Schmidt hammer test be adopted as an alternative test to prove the concrete strength?

Last Answer : The Scmidt hammer test is based on the elastic rebound of hammer which presses on concrete surface and it measures the surface hardness of concrete. Since the test is very sensitive to the ... strength of concrete. Therefore, it may not be considered a good substitute for concrete compression test.

What are the disadvantages of curing by ponding and polythene sheets?

Description : What are the disadvantages of curing by ponding and polythene sheets?

Last Answer : The purpose of curing is to reduce the rate of heat loss of freshly placed concrete to the atmosphere and to minimize the temperature gradient across concrete cross ... would be affected. Moreover, for water lost due to self­desiccation, this method cannot replenish these losses.

In concrete compression test, normally 150mmx150mmx150mm concrete cube samples is used for testing. Why isn’t 100mmx100mmx100mm concrete cube samples used in the test instead of 150mmx150mmx150mm concrete cube samples?

Description : In concrete compression test, normally 150mmx150mmx150mm concrete cube samples is used for testing. Why isn’t 100mmx100mmx100mm concrete cube samples used in the test instead of 150mmx150mmx150mm concrete cube samples?

Last Answer : Basically, the force supplied by a concrete compression machine is a definite value. For normal concrete strength application, say below 50MPa, the stress produced by a ... cube size of 150mmx150mmx150mm is already sufficient for the crushing strength of the machine.

In designing concrete structures, normally maximum aggregate sizes are adopted with ranges from 10mm to 20mm. Does an increase of maximum aggregate size benefit the structures?

Description : In designing concrete structures, normally maximum aggregate sizes are adopted with ranges from 10mm to 20mm. Does an increase of maximum aggregate size benefit the structures?

Last Answer : To answer this question, let's consider an example of a cube. The surface area to volume ratio of a cube is 6/b where b is the length of the cube. This implies that ... requirement can offset the disadvantages brought about by discontinuities as suggested by Longman Scientific and Technical (1987).

What is the function of shear keys in the design of retaining walls?

Description : What is the function of shear keys in the design of retaining walls?

Last Answer : In determining the external stability of retaining walls, failure modes like bearing failure, sliding and overturning are normally considered in design. In considering the criterion of sliding, the sliding ... instead of 0.8φ in the previous case and the sliding resistance can be enhanced.

What are the functions of different components of a typical expansion joint?

Description : What are the functions of different components of a typical expansion joint?

Last Answer : In a typical expansion joint, it normally contains the following components: joint sealant, joint filler, dowel bar, PVC dowel sleeve, bond breaker tape and cradle bent. Joint sealant: it seals the ... the joint . Cradle bar: It helps to uphold the dowel bar in position during construction.

Why Should Pumping Be Not Used In Case Of Concreting Works?

Description : Why Should Pumping Be Not Used In Case Of Concreting Works?

Last Answer : Answer : During the pumping operation the pump exerted pressure must overcome any friction between the pumping pipes and the concrete, also the weight of the concrete and the pressure headwhen the ... Also if a proper selection of the aggregate grading can vastly improve the concrete pump ability.

Suggest the type of cement used for the following : (i) For modular construction where form work needs to be removed early for re-use. . (ii) Mass concreting such as construction of dam. (iii) Decorative works in external surfaces of building. (iv) Cementing the oil well.

Description : Suggest the type of cement used for the following : (i) For modular construction where form work needs to be removed early for re-use. . (ii) Mass concreting such as construction of dam. (iii) Decorative works in external surfaces of building. (iv) Cementing the oil well.

Last Answer : i) For modular construction where form work needs to be removed early for reuse. – Rapid Hardening Cement ii) Mass concreting such as construction of dam. – Low heat cement. iii) Decorative works in external surfaces of building – Coloured cement. iv) Cementing the oil well. – Oil Well Cement. 

Pick up the correct statement from the following: (A) Air lift pumps are generally used for pumping water from deep wells (B) Jet pumps are generally used for pumping water from small wells (C) The hydraulic ram works on the principle of water hammer (D) All the above

Description : Pick up the correct statement from the following: (A) Air lift pumps are generally used for pumping water from deep wells (B) Jet pumps are generally used for pumping water from small wells (C) The hydraulic ram works on the principle of water hammer (D) All the above

Last Answer : (D) All the above

In case of laying gullies, siphons, intercepting traps, the cost includes (A) Setting and laying (B) Bed concreting (C) Connection to drains (D) All of these

Description : In case of laying gullies, siphons, intercepting traps, the cost includes (A) Setting and laying (B) Bed concreting (C) Connection to drains (D) All of these

Last Answer : (D) All of these

Consider the following activities in a building construction: 1. Concreting of roof slabs 2. Brick-jelly lime concrete terracing 3. Erection of form work for slab 4. Construction of parapet wall in terrace The correct sequence of these activities is (A) 1, 3, 2, 4 (B) 3, 1, 4, 2 (C) 3, 1, 2, 4 (D) 1, 3, 4, 2

Description : Consider the following activities in a building construction: 1. Concreting of roof slabs 2. Brick-jelly lime concrete terracing 3. Erection of form work for slab 4. Construction of parapet wall in terrace The correct sequence of these ... (B) 3, 1, 4, 2 (C) 3, 1, 2, 4 (D) 1, 3, 4, 2

Last Answer : (C) 3, 1, 2, 4

For concreting tunnel linings, transportation of concrete is done by (A) Pans (B) Wheel borrows (C) Containers (D) Pumps

Description : For concreting tunnel linings, transportation of concrete is done by (A) Pans (B) Wheel borrows (C) Containers (D) Pumps

Last Answer : (D) Pumps

For concreting of heavily reinforced sections without vibration, the workability of concrete expressed as compacting factor should be (A) 0.75 - 0.80 (B) 0.80 - 0.85 (C) 0.85 - 0.92 (D) Above 0.92

Description : For concreting of heavily reinforced sections without vibration, the workability of concrete expressed as compacting factor should be (A) 0.75 - 0.80 (B) 0.80 - 0.85 (C) 0.85 - 0.92 (D) Above 0.92

Last Answer : Answer: Option D

For cold weathering concreting the cement used is (a) O.P.C (b) R.H.C (c) L.H.C (d) None of these

Description : For cold weathering concreting the cement used is (a) O.P.C (b) R.H.C (c) L.H.C (d) None of these

Last Answer : (b) R.H.C

Corrosion of well pipes may not be reduced by (A) Reducing the draw down and the pumping rate (B) Reducing the flow velocity (C) Using thicker pipes (D) Using screens having larger area of openings

Description : Corrosion of well pipes may not be reduced by  (A) Reducing the draw down and the pumping rate  (B) Reducing the flow velocity  (C) Using thicker pipes  (D) Using screens having larger area of openings 

Last Answer : (D) Using screens having larger area of openings 

cement screed when concreting columns

Description : Hello, I was buying a concrete mix for concreting the fence posts and at home I noticed that the bags are written Cement screed BE 04/25. Can this be used or not? Thank you for the quick answers.

Last Answer : It can be used, but it won't have the right effect. At least add a little sharp, river sand to the pot. This mixture is too fine and even after curing it will have significantly less strength than conventional berton.

The grit and silt of the grit chambers, may not be used for A. Raising low lying areas by dumping B. Concreting C. Both A. and B. D. Neither A. nor B.

Description : The grit and silt of the grit chambers, may not be used for A. Raising low lying areas by dumping B. Concreting C. Both A. and B. D. Neither A. nor B.

Last Answer : ANS: B

What Are The Steps Involved In The Concreting Process, Explain?

Description : What Are The Steps Involved In The Concreting Process, Explain?

Last Answer : Answer : 1. Batching: The process of measurement of the different materials for the making of concrete is known as batching. batching is usually done in two ways: volume batching and weight batching ... performed. Compaction is generally performed in two ways: by hand or by the use of vibrators.

Bentonite is used in pile driving -- a) to facilitate pile driving b) to enable proper pile concreting c) to stabilize the bore hole walls* d) None of the above

Description : Bentonite is used in pile driving -- a) to facilitate pile driving b) to enable proper pile concreting c) to stabilize the bore hole walls* d) None of the above

Last Answer : c) to stabilize the bore hole walls*

Temporary staging for casting PSC Box Girder for a ROB over the Railway span shall be removed a) after hardening of concrete b) before hardening of concrete c) during concreting d) after stressing the cables

Description : Temporary staging for casting PSC Box Girder for a ROB over the Railway span shall be removed a) after hardening of concrete b) before hardening of concrete c) during concreting d) after stressing the cables

Last Answer : d) after stressing the cables

Explain the necessity of supervision for concreting operations.

Description : Explain the necessity of supervision for concreting operations.

Last Answer : Necessity of supervision for concreting operation: i. Supervision is necessary to complete all concreting operations in standard manner. ii. It is necessary to avoid any type of delay in concrete ... operations at each stage of project. vi. It found very effective in controlling bad workmanship.

A sand sample has a fineness modulus of 1.95. Whether this sand can be used for concreting? Explain the procedure to bring the fineness modulus in required permissible limits. State its importance.

Description : A sand sample has a fineness modulus of 1.95. Whether this sand can be used for concreting? Explain the procedure to bring the fineness modulus in required permissible limits. State its importance.

Last Answer : The given sand sample has a fineness modulus 1.95, which is less than prescribed limit i.e.2.2-3.2. It indicates that sand particles are finer, which is not suitable for satisfactory ... . Well graded sand is also useful for good bonding of particles and related strength criteria of concrete.

In sequence, write concreting operations.

Description : In sequence, write concreting operations.

Last Answer : i. Batching of materials ii. Mixing of materials iii. Transportation of concrete iv. Placing of concrete v. Compaction of concrete vi. Curing of concrete vii. Finishing of concrete

(i) Suggest the relevant method of water-proofing used for following construction. 1) Basement of buildings. 2) Swimming pool. 3) Water tank. (ii) Suggest the relevant method of transportation of concrete used for construction in following situation. 1) Concreting in hilly areas. 2) Concreting of high-rise building. 3) Concreting under water.

Description : (i) Suggest the relevant method of water-proofing used for following construction. 1) Basement of buildings. 2) Swimming pool. 3) Water tank. (ii) Suggest the relevant method of transportation of ... 1) Concreting in hilly areas. 2) Concreting of high-rise building. 3) Concreting under water.

Last Answer : Method of water-proofing for: 1) Basement of buildings: Waterproofing by using waterproof sealants. 2) Swimming pool: Waterproofing by spraying or grouting in cracks. 3) Water tank: Waterproofing by ... , concrete pump, slip form technique. 3) Concreting under water: Tremie pipe, grout pipe.

Write two effects and two precautions of cold weather and hot weather concreting.

Description : Write two effects and two precautions of cold weather and hot weather concreting.

Last Answer : Effects of cold weather concreting: 1. Due to cold weather, concrete shows reduced rate of hardening, which results delay in removal of formwork. 2. Water added in concrete mix gets frozen quickly, ... heat evolution. 7. High w/c ratio and ice crystals should be used to maintain workability.

Write the procedure of vaccum dewatering concreting for construction of floors.

Description : Write the procedure of vaccum dewatering concreting for construction of floors.

Last Answer : Procedure of vaccum dewatering concreting for construction of floors: The concreting using vaccum dewatering for floor construction is done as follows. 1. Concrete is places uniformly on the spread of ... Finally the floating and towelling is done to achieve better finishing of surface. 

Draw concreting operation chain in sequence.

Description : Draw concreting operation chain in sequence. 

Last Answer : Sequential chain of Concreting Operations: 

List any two precautions to be taken in cold weather concreting.

Description : List any two precautions to be taken in cold weather concreting.

Last Answer : Precautions to be taken in cold weather concreting: In extreme weather, following precautions should be taken. 1. Concreting work should be done during day time or on sunny days. 2. Warm water should ... its use. 7. Rapid hardening or quick setting cement should be used for fast setting of concrete.

In pumping stations, the type of joint generally used, is (A) Socket and spigot joint (B) Flanged joint (C) Expansion joint (D) Dresser coupling joint

Description : In pumping stations, the type of joint generally used, is (A) Socket and spigot joint (B) Flanged joint (C) Expansion joint (D) Dresser coupling joint

Last Answer : (B) Flanged joint

Check valves are installed (A) On the delivery side of the pumping set (B) At the interconnections between polluted water system and a potable water system (C) Both (a) and (b) (D) Neither (a) nor (b)

Description : Check valves are installed (A) On the delivery side of the pumping set (B) At the interconnections between polluted water system and a potable water system (C) Both (a) and (b) (D) Neither (a) nor (b)

Last Answer : (C) Both (a) and (b)

Reciprocating pumps (A) Are not suitable for variable heads (B) Are four times costlier than centrifugal pumps (C) Are not suitable for pumping water containing sediments (D) Single stroke produce pulsating flow

Description : Reciprocating pumps  (A) Are not suitable for variable heads  (B) Are four times costlier than centrifugal pumps  (C) Are not suitable for pumping water containing sediments  (D) Single stroke produce pulsating flow 

Last Answer : (A) Are not suitable for variable heads 

The efficiency of a pumping set, is generally assumed (A) 50 % (B) 55 % (C) 60 % (D) 65 %

Description : The efficiency of a pumping set, is generally assumed  (A) 50 %  (B) 55 %  (C) 60 %  (D) 65 % 

Last Answer : (D) 65 % 

Pick up the correct statement from the following: (A) Head loss in smaller size pipes at equal velocities, is less (B) Cost of pumping is less in smaller size pipes (C) Cost of smaller pipes is comparatively more (D) None of these

Description : Pick up the correct statement from the following:  (A) Head loss in smaller size pipes at equal velocities, is less  (B) Cost of pumping is less in smaller size pipes  (C) Cost of smaller pipes is comparatively more  (D) None of these 

Last Answer : (D) None of these 

When gravity and pumping systems of water distribution are adopted, the type of distribution reservoir, is (A) Elevated tank (B) Ground source reservoir (C) Intz tank (D) Stand pipe

Description : When gravity and pumping systems of water distribution are adopted, the type of distribution  reservoir, is  (A) Elevated tank  (B) Ground source reservoir  (C) Intz tank  (D) Stand pipe

Last Answer : (A) Elevated tank 

For the same draw down in two observations wells at distances r1 and r2, the times after start of pumping are t1 and t2 hours respectively. The relation which holds good is (A) t2 = r2/r1 × t1 (B) t2 = (r2/r1)² × t1 (C) t2 = (r2/r1)3 × t1 (D) t2 = (r2/r1) × t1 2

Description : For the same draw down in two observations wells at distances r1 and r2, the times after start of  pumping are t1 and t2 hours respectively. The relation which holds good is  (A) t2 = r2/r1 × t1 (B) t2 = (r2/r1)² × t1 (C) t2 = (r2/r1)3  × t1 (D) t2 = (r2/r1) × t1 2

Last Answer : (B) t2 = (r2/r1)² × t1

S1 and S2 are the draw downs in an observation well at times t1 and t2 after pumping. For discharge Q and coefficient of transmissibility T, the relationship, is (A) S2 - S1 = (2.3Q/ ) log10 (t2/t1) (B) S2 - S1 = (2.3Q/4 ) log10 (t2/t1) (C) S2 - S1 = (2.3Q/4 ) loge (t2/t1) (D) S2 - S1 = (2.3Q/4 ) loge (t1/t2

Description : S1 and S2 are the draw downs in an observation well at times t1 and t2 after pumping. For  discharge Q and coefficient of transmissibility T, the relationship, is  (A) S2 - S1 = (2.3Q/ ) log10 (t2/t1)  (B) S2 - S1 ... - S1 = (2.3Q/4 ) loge (t2/t1)  (D) S2 - S1 = (2.3Q/4 ) loge (t1/t2

Last Answer : (B) S2 - S1 = (2.3Q/4 ) log10 (t2/t1) 

The factor for the selection of pumping station site, is (A) Distance of the source of contamination or pollution (B) Height above the H.F.L. of the river (C) Future expansion (D) All the above

Description : The factor for the selection of pumping station site, is  (A) Distance of the source of contamination or pollution  (B) Height above the H.F.L. of the river  (C) Future expansion  (D) All the above

Last Answer : (D) All the above

The water level in an open well was depressed by pumping 2.5 m and recuperated 2.87 m in 3 hours and 50 minutes. The yield of the well per minute is (A) 0.0033 (B) 0.0044 (C) 0.0055 (D) 0.0066

Description : The water level in an open well was depressed by pumping 2.5 m and recuperated 2.87 m in 3  hours and 50 minutes. The yield of the well per minute is  (A) 0.0033  (B) 0.0044  (C) 0.0055  (D) 0.0066 

Last Answer : (C) 0.0055 

While determining the yield of open wells by the pumping test (A) Velocity of recharging water, increases with depression head (B) Depression head resulting at critical velocity, is called critical depression head (C) Working head is generally limited to (D) Maximum safe yield of an open well, is expected at critical depression head

Description : While determining the yield of open wells by the pumping test  (A) Velocity of recharging water, increases with depression head  (B) Depression head resulting at critical velocity, is called critical ... (D) Maximum safe yield of an open well, is expected at critical depression head 

Last Answer : (D) Maximum safe yield of an open well, is expected at critical depression head 

Pick up the correct statement from the following: (A) The water level in a still well, represents the ground water table level (B) The difference between water table level and the water level in a well after pumping, is called depression head (C) The surface of water table surrounding a well during pumping, forms a cone of depression (D) All the above

Description : Pick up the correct statement from the following:  (A) The water level in a still well, represents the ground water table level  (B) The difference between water table level and the water ... water table surrounding a well during pumping, forms a cone of depression  (D) All the above 

Last Answer : (D) All the above 

If the chosen diameter of a pipe, is less than the economical diameter (A) Cost of pipe will be less (B) Head loss will be high (C) Cost of pumping will be more than saving (D) All the above

Description : If the chosen diameter of a pipe, is less than the economical diameter  (A) Cost of pipe will be less  (B) Head loss will be high  (C) Cost of pumping will be more than saving  (D) All the above

Last Answer : (D) All the above

When the reduced level of the water source is higher than the reduced level of the consumer's place, water is generally supplied (A) By pumping system (B) By gravitational system (C) Both (a) and (b) (D) All the above

Description : When the reduced level of the water source is higher than the reduced level of the consumer's  place, water is generally supplied  (A) By pumping system  (B) By gravitational system  (C) Both (a) and (b)  (D) All the above 

Last Answer : (B) By gravitational system