Civil Quality Control Engineer Interview Question

What are the essential elements of Concrete placement?

The maximum height of the concrete drop is less than or equal to 1.5 meters.

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.

How will trucks be checked on-site when receiving concrete?

A. Revolution Counter  

B. Ticket Checked for Concrete Batching time and Slump Value at the plant.  

C. Slump Test.

  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.

What is the purpose of the slump test?

To determine the consistency of the workability of the concrete mix and to check for the required slumps.

What are allowable slumps?

In case of a dry sample, slump will be in the range of 25-50 mm. But in case of a wet concrete, the slump may vary from 150-175 mm. So the value of slump is specifically mentioned along the mix design and thus it should be checked as per local location.

Recommended slumps:

Reinforced foundation walls and footings:

a. Maximum Slump 75mm

b. Minimum Slump 25mm

Plain footings, caissons, and substructure walls:

a. Maximum Slump 75mm

b. Minimum Slump 25mm

Beams and reinforced walls:

a. Maximum Slump 100mm

b. Minimum Slump 25mm

Building columns:

a. Maximum Slump 100mm

b. Minimum Slump 25mm

Pavements and slabs:

a. Maximum Slump 75mm

b. Minimum Slump 25 mm

Mass Concrete Mix:

a. Maximum Slump 75mm

b. Minimum Slump 25mm

What is a plasticizer?

Usually applied at a low water-cement ratio concrete to make it workable.

What is the maximum temperature of concrete that can be poured into a concrete structure?

32 Degrees C.

Min and Max atmospheric (ambient) temperature prior to paving?

Min is 5 Degree C in cold weather and 45 degrees C max for hot weather. 

Min and Maximum temperature of concrete at the site prior to pouring?

Min Concrete temp is 10 degrees, and Max is 32 degrees C

Types of Curing?

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.

When will you apply the curing of the concrete?

After the concrete has initially set (35 to 40 minutes is the initial setting time of concrete)

How many times do you apply the curing membrane?

At least two times. The second application is perpendicular to the first and applied after the first application has set.

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?

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.

What is the initial setting time of Concrete Mix?

35 to 40 minutes.

What is the mixing time of a stationary or central batching plant (concrete)?

50 to 90 seconds

What is the agitating speed of the mixer?

2 to 6 revolutions per minute (rpm)

What is the mixing speed of the mixer?

6 to 18 rpm

What is concrete fatigue?

It is the weakening of a material caused by repeated loads.

What is creep?

It is deformation due to the sustained load.

How would you know if the concrete has gained its initial set?

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.

If agitated concrete is discharged after more than one hour, what will happen?
The concrete is over mixed, becomes hot, and the strength is reduced

How many layers are in the concrete cube?

Concrete Cube is cast in 3 layers.

How many strokes are done in one layer in a concrete cube?
35 Strokes in one layer. 

What is the size of rode used in concrete cube casting and slump test?
Dia – 16mm and 600mm length.

What is the size of a concrete cube?
150mm X 150mm X 150mm.

What is the size of slump cones?
Height – 30cm, Top of Cone – 10cm, and Bottom of cone – 20cm.

How many layers are in the slump test??
3 Layers in ASTM and BS but 4 Layers in Indian standard.

How many strokes are done in one layer in a slump test?
25 Strokes