Important interview Questions for QA/QC civil engineer.
Q1) How will trucks be checked on site when reciving concrete.
Ans- (1) Revolution counter
revolution counter for a concrete mixing truck which selectively records the mixing drum revolutions and also records those revolutions of the concrete mixing drum which occur Within a preset drum speed range.
The structural qualities of concrete are affected by too much or too little mixing and, as a consequence, it has become important to determine how many mixing revolutions have taken place between the time that the concrete ingredients are deposited in the mixing drum and the time that the mixed concrete is discharged
from the truck. Additionally, all revolutions of the concrete mixing drum are not mixing revolutions per se. Only those revolutions of the mixing drum which occur within a predetermined range of revolutions per minute are termed mixing revolutions. A generally accepted rate of rotation of the concrete mixing drum is from to 12 revolutions per minute but this will depend upon the particular specifications. Any rate of revolution which does not occur Within the predetermined range does not satisfactorily mix the concrete within the mixing drum and therefore such revolutions must not be counted.
(2) Ticket checked for concrete batching time and slump value at the plant .
(3) slump test
(4) temprature test (32°c maximum at site
(5) Assure lab technician is present at the site and perform testing
(6) 6 cubes or 4 cylinder should be taken per 50 cum or recommended in the project specifications.
Q2- What is purpose of slump test ?
Ans- The concrete slump test measures the consistency of fresh concrete before it sets. It is performed to check the workability of freshly made concrete, and therefore the ease with which concrete flows. It can also be used as an indicator of an improperly mixed batch.
2.5 cm to 7.5 cm ( for vibrated structure and without admixture)
And if with admixture and plasticizer ,slump depend upon the design mix slump shall be checked as per design mix.
Q3- what is plasticizer?
plasticizer is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture.
Usually applied at a low water cement ratio concrete to make it workable.
Q4- How many layers are in the concrete cube.
Ans- concrete cube is cast in 3 layers.
Q5- what is maximum temperature of concrete that can be poured into a concrete structures.
Ans- maximum 32°C
Range (10°C- 32°C)
Q6- minimum and maximum atmospheric (ambient) temprature prior to paving.
Ans- Minimum is 5°C in cold weather 45°C maximum in hot weather.
Q-7 Minimum and Maximum temprature of concrete at the site prior to pouring.
Ans- Minimum 10°C maximum 32°C.
Q8- Purpose of curing .
Ans- To maintain the amount of water in the concrete mix .To minimize hairline cracks .
Q-9 Type of Curing.
Ans- Water curing - As in ponding ,spraying ,wet sand and wet earth membrane curing as in plastic film ,liquid membrane curing compound and reinforced paper.
Q-10 What is hydration?
Ans- Hydration is the chemical reaction that occurs when water is added to cement, causing it to harden, set, and gain binding properties.
it is the formation of a compound by the combination of water and other substances or in concrete .it is the chemical reactions between water and cement.
Q-11 How many times do you apply the curing membrane.
Ans- At the least two times the second application is perpendicular to the first and applied after the first application has set .
Q-12 Concrete curing water shall not have more than of total dissolved solid (TDS)
Ans - 1000 ppm
Q-13 Concrete cnn be dropped freely at a height of
Ans- 1.5 m
Q14- Advantage of reducing the water - cement ratio of concrete mix
Ans- Increase strength,increase water tightness, lower absorption and resistance of weathering a better bond between concrete and reinforcement.
Q-15 What are the two basic type of concrete.
Ans- structural concrete and non structural concrete.
Q16- How would you compare 7 days and 28 days compressive strength of concrete.
Ans- 70-75% of that 28 days strength.
Q17- What is the composite structures?
Ans- Its a structure composed of two materials as in steel and concrete.
Q-18 What is non composite structures?
Ans- Its made of either concrete or steel.
Q- 19 What are the reason behind the cracks.
Ans- Poor concreting practice, poor design ,poor vibration, which result in the segregation ,less rebar converting, poor quality of concrete, movement of the false work or forms ,higher water cement ratio ,severe atmospheric attack, which shows the effect on the heat of hydration with water initially.
Q-20 What is rebar ?
Ans- Rebar, or reinforcing bar, is a steel bar used in concrete construction to strengthen and reinforce concrete structures:
Purpose
Rebar helps concrete withstand tensile, bending, torsion, and shearing loads, which are areas where concrete is weak.
Material
Rebar is usually made of steel because it expands with heat in a similar way to concrete, which helps reduce temperature change issues.
Installation
Rebar is placed within the concrete formwork before the concrete is poured.
Appearance
Rebar is usually not visible in concrete structures because it's buried within the concrete.
Ribs
Rebar is usually ribbed to prevent slipping within the concrete.
Q-21 What are the concrete sample.
Ans- The cylinder and cubes for compressive strength.
Q-22 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- Within one hours if the mixer is an igitated mixer ( also depend on the design mix ) and within 30 minutes. If the mixer is a non- agitated mixer.
Q- 23 What is the initial setting time of concrete ?
Ans- 35 minutes to 40 minutes.
Q24- How many strokes are done in one layer in a concrete cubes.
Ans- 35 strokes in one layer.
Q25- What is the size of concrete cube.
Ans- 150 mm x 150 mm x 150 mm .
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