Top 40 Typical Interview Questions and Answers for Civil Site Engineer | Civil Site Inspector | QA QC Engineer | QC Civil Inspector
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| Concrete Placement |
Well oriented Questions and Answers Topic wise
Technical Interview Questions Asked by Interviewer to a Civil Engineer, Civil Quality Control Engineer in Interview
CHAPTER 2 – FRESH CONCRETE INSPECTION AT POURING LOCATION
What are the essential elements of Concrete placement?
A. The maximum height of the concrete drop is less than or equal to 1.5 meters.
B. Segregation must be prevented by ensuring transit mixture is approved, has operating revolution counter, no adding water after batching, and concrete is placed in such a manner to prevent segregation (only shovels can be used to move concrete around inside the forms no raking allowed. Vibrators should not be used for that purpose.
C. Proper vibration must be implemented (proper vibrating – dropping the vibrator under its own weight until it gets to the desired drop height, then leaving it there for 3-7 seconds then pulling at the count of 3 to 4 seconds. When vibrating subsequent layers, the vibrator must penetrate a centimeter into the older layer.
D. Some laborers must be continuously watching the forms in case a wall is being poured, proper height of each concrete lift must be observed, such as the usual 600mm stated normally in project specifications. Also, tamping on the wall is necessary to assist in the consolidation process.
E. The concrete temperature and the slumps are two strong indicators of the inspector’s knowledge. A slump between 75mm and 125mm is normal for normal pours. The maximum allowed temperature for concrete when arriving at the project site is 32 degrees celsius.
QUE 1 – How will trucks be checked on-site when receiving concrete?
ANS 1 – A. Revolution Counter
B. Ticket Checked for Concrete Batching time and Slump Value at the plant.
D. Temperature Test (32 C maximum @ Site).
E. Assure Lab Technician is present at the site and performs testing.
F. 6 Cubes or 4 Cylinders should be taken per 50cum or recommended in the project specification.
QUE 2 – What is the purpose of the slump test?
ANS 2 – To determine the consistency of the workability of the concrete mix and to check for the required slumps.
QUE 3 – What are allowable slumps?
ANS 3 – 2.5cm to 7.5cm (for vibrated structure and without admixture ) and If with admixture and plasticizer, Slump depends upon the design mix. Slump shall be checked as per design mix.
QUE 4 – What is a plasticizer?
ANS 4 – Usually applied at a low water-cement ratio concrete to make it workable.
QUE 5 – What is the maximum temperature of concrete that can be poured into a concrete structure?
ANS 5 – 32 Degrees C.
QUE 6 – Min and Max atmospheric (ambient) temperature prior to paving?
ANS 6 – Min is 5 Degree C in cold weather and 45 degrees C max for hot weather.
QUE 7 – Min and Maximum temperature of concrete at the site prior to pouring?
ANS 7 – Min Concrete temp is 10 degrees, and Max is 32 degrees C
ANS 8 – 1. To maintain the amount of water in the concrete mix.
2. To minimize hairline cracks
QUE 9 – Types of Curing?
ANS 9 –
Water Curing – as in ponding, spraying, wet sand and wet earth
Membrane Curing – as in plastic film, liquid membrane curing compound, and reinforced paper
Steam Curing.
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| Curing Membrane |
QUE 10 – When will you apply the curing of the concrete?
ANS 10 – After the concrete has initially set (35 to 40 minutes is the initial setting time of concrete)
QUE 11 – For how many days are you going to cure a structure?
ANS 11 – Seven days (in some cases like PPC types of cement, 14 days of curing are recommended)
QUE 12 – What is hydration?
ANS 12 – It is the formation of a compound by the combination of water and other substances or in concrete; it is the chemical reaction between water and cement.
QUE 13 – How many times do you apply the curing membrane?
ANS 13 – At least two times. The second application is perpendicular to the first and applied after the first application has set.
QUE 14 – Concrete Curing Water shall not have more than …………….. Of total dissolved solids (TDS).
ANS 14 – 1000 ppm
QUE 15 – Concrete can be dropped freely at a height of …………
ANS 15 – 1.5 meter
QUE 16 – Max and min slope of chutes used in pouring concrete?
ANS 16 – Max slope is 1:2 (Vertical to Horizontal), Min slope is 1:3
QUE 17 – Advantages of reducing the water-cement ratio of concrete mix?
ANS 17 – Increased strength, Increase water tightness, Lower absorption, Increased resistance to weathering, a better bond between concrete and reinforcement.
QUE 18 – What are the two basic types of concrete?
ANS 18– Structural and nonstructural concrete.
QUE 19 – How would you compare 7 days and 28 days compressive strength of concrete?
ANS 19 – 70 to 75 % of that of 28 days strength.
QUE 20 – What is a composite structure?
ANS 20 -It is a structure composed of two materials as in steel and concrete.
QUE 21 – What is a non-composite structure?
ANS 21 – It is a structure made of either concrete or steel.
QUE 22 – What are the reasons behind the cracks?
ANS 22 – Poor Curing Practice, Poor design, Poor Vibration which results in segregation, less rebar covering, poor quality of concrete, movement of falsework or forms, higher water-cement ratio, Severe atmospheric attack which shows the effect on the heat of hydration with water initially
QUE 23 – What are the concrete samples?
ANS 23 – The cylinder and the cubes for the compressive strength test.
QUE 24 – Within how many hours should concrete mix be discharged after leaving the batching plant or after all the aggregates, cement, and water are in the mixer?
ANS 24 – Within one hour if the mixer is an agitated mixer (Also depends on the design mix) And Within 30 minutes if the mixer is a non-agitated mixer.
QUE 25 – What is the initial setting time of Concrete Mix?
ANS 25 – 35 to 40 minutes.
QUE 26 – What is the mixing time of a stationary or central batching plant (concrete)?
ANS 26 – 50 to 90 seconds
QUE 27 – What is the agitating speed of the mixer?
ANS 27 – 2 to 6 revolutions per minute (rpm)
QUE 28 – What is the mixing speed of the mixer?
ANS 28 – 6 to 18 rpm
QUE 29 – What is concrete fatigue?
ANS 29 – It is the weakening of a material caused by repeated loads.
QUE 30 – What is creep?
ANS 30 – It is deformation due to the sustained load.
QUE 31 – How would you know if the concrete has gained its initial set?
ANS 31 – If there is no more water seen (brightness) on the surface of the concrete, or if there is no water on the surface of the concrete.
QUE 32 – If agitated concrete is discharged after more than one hour, what will happen?
ANS 32 – The concrete is over mixed, becomes hot, and the strength is reduced
QUE 33 – How many layers are in the concrete cube?
ANS 33 – Concrete Cube is cast in 3 layers.
QUE 34 – How many strokes are done in one layer in a concrete cube?
ANS 34 – 35 Strokes in one layer.
QUE 35 – What is the size of rode used in concrete cube casting and slump test?
ANS 35 – Dia – 16mm and 600mm length.
QUE 36 – What is the size of a concrete cube?
ANS 36 – 150mm X 150mm X 150mm.
QUE 37 – What is the size of slump cones?
ANS 37 – Height – 30cm, Top of Cone – 10cm, and Bottom of cone – 20cm.
QUE 38 – How many layers are in the slump test??
ANS 38 – 3 Layers in ASTM and BS but 4 Layers in Indian standard.
QUE 39 – How many strokes are done in one layer in a slump test?
ANS 39 – 25 Strokes
QUE 40 – What are the essential elements of Concrete placement?
ANS 40 – See Answer on the top of the page.
ANS 40 – See Answer on the top of the page.
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