Top 10 interview Questions for civil engineering students

1.What are the steps involved in the concreting process, explain?

The major steps involved in the process of concreting are as follows:
1. Batching
2. Mixing
3. Transporting and placing of concrete
4. Compacting.

> 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. In case of volume batching the measurement is done in the form of volume whereas in the case of weight batching it is done by the weight.
> Mixing: In order to create good concrete the mixing of the materials should be first done in dry condition and after it wet condition. The two general methods of mixing are: hand mixing and machine mixing.
> Transportation and placing of concrete: Once the concrete mixture is created it must be transported to its final location. The concrete is placed on form works and should always be dropped on its final location as closely as possible.
> Compaction of concrete: When concrete is placed it can have air bubbles entrapped in it which can lead to the reduction of the strength by 30%. In order to reduce the air bubbles the process of compaction is performed. Compaction is generally performed in two ways: by hand or by the use of vibrators.

2. Describe briefly the various methods of concrete curing.

Curing is the process of maintaining the moisture and temperature conditions for freshly deployed concrete. This is done for small duration of time to allow the hardening of concrete. The methods that are involved in saving the shrinkage of the concrete includes:
(a) Spraying of water: on walls, and columns can be cured by sprinkling water.
(b) Wet covering of surface: can be cured by using the surface with wet gunny bags or straw
(c) Ponding: the horizontal surfaces including the slab and floors can be cured by stagnating the water.
(d) Steam curing: of pre-fabricated concrete units steam can be cured by passing it over the units that are under closed chambers. It allows faster curing process and results in faster recovery.
(e) Application of curing compounds: compounds having calcium chloride can be applied on curing surface. This keeps the surface wet for a very long time.

3. What do you understand by “preset” during the installation process of bridge bearings?

During the installation of bridge bearings the size of the upper plates is reduced to save the material costs. This process is known as preset. Generally the upper bearing plate comprises of the following components:
> Length of bearing
> 2 x irreversible movement.
> 2 x reversible movement.
The bearing initially is placed right in the middle point of the upper bearing plate. No directional effects of irreversible movement is considered. But since the irreversible movement usually takes place in one direction only the displaced direction is placed away from the midpoint. In such cases the length of the upper plate is equal to the length of the length of the bearing + irreversible movement + 2 x reversible movement.

4. Why are steel plates inserted inside bearings in elastomeric bearings?

In order to make a elastomeric bearing act/ function as a soft spring it should be made to allow it to bulge laterally and also the stiffness compression can be increased by simply increasing the limiting amount of the lateral bulging. In many cases in order to increase the compression stiffness of the bearing the usage of metal plates is made. Once steel plates are included in the bearings the freedom of the bulge is restricted dramatically, also the deflection of the bearing is reduced as compared to a bearing without the presence of steel plates. The tensile stresses of the bearings are induced into the steel plates. But the presence of the metal plates does not affect the shear stiffness of the bearings.

5. What reinforcements are used in the process of prestressing?

The major types of reinforcements used in prestressing are:
> Spalling Reinforcement: The spalling stresses leads to stress behind the loaded area of the anchor blocks. This results in the breaking off of the surface concrete. The most likely causes of such types of stresses are Poisson`s effects strain interoperability or by the stress trajectory shapes.
> Equilibrium reinforcements: This type of reinforcements are required where several anchorages exist where the prestressing loads are applied in a sequential manner.
> Bursting Reinforcements: These kinds of stresses occur in cases where the stress trajectories are concave towards the line of action of load. In order to reduce such stresses reinforcements in the form of bursting is required.

6. In the design of bridge arguments what considerations should be made to select the orientation of the wing walls?

Some of the most common arrangements of wing walls in cases of bridge arguments are as follows:
> Wing walls parallel to abutments: This method is considered to take least amount of time to build and is simple as well. But on the downside this method is not the most economical. The advantage of this type of design being that they cause the least amount of disturbance to the slope embankment.
> Wing walls at an angle to abutments: This design method is considered to be the most economical in terms of material cost.
> Wing walls perpendicular to abutments: The characteristic of this design is it provides an alignment continuous with the bridge decks lending a support to the parapets.

7. In case if concrete box girder bridges how is the number of cells determined?

When the depth of a box girder bridge exceed 1/6th or 1/5th of the bridge width then the design recommended is that of a single cell box girder bridge. But in case the depth of the bridge is lower than 1/6th of the bridge width then a twin-cell or in some cases multiple cell is the preferred choice. One should also note that even in the cases of wider bridges where there depths are comparatively low the number of cells should be minimized. This is so as there is noticeably not much improvement in the transverse load distribution when the number of cells of the box girder is higher than three or more.

8. Under what circumstances should pot bearings be used instead of elastomeric bearings?

Pot bearings are preferred over elastomeric bearings in situations where there are chances of high vertical loads in combinations of very large angle of rotations. Elastomeric bearings always require a large bearing surface so that a compression is maintained between the contact surfaces in between the piers and the bearings. This is not possible to maintained in high load and rotation environment. Also the usage of elastomeric bearings leads to the uneven distribution of stress on the piers. This results in some highly induced stresses to be targeted at the piers henceforth damaging them. Due to the above reasons pot bearings are preferred over elastomeric bearings in such cases.

9. Why should pumping be not used in case of concreting works?

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 head when the concrete is placed above the pumps. Since only water is pump able, all the pressure generated is by the water that is present in the concrete. The major problem due to pumping are segregation effects and bleeding. In order to rectify and reduce these effects, generally the proportion of the cement is increased in order to increase the cohesion , which leads to the reduction of segregation and bleeding. Also if a proper selection of the aggregate grading can vastly improve the concrete pump ability.

10. Why should curing not be done by ponding and polythene sheets?

The primary purpose of curing is to reduce the heat loss of concrete that is freshly placed to the atmosphere and in order to reduce the temperature gradient across the cross-section of the concrete. Ponding is not preferred for curing as this method of thermal curing is greatly affected by cold winds. In addition to that in ponding large amounts of water is used and has to be disposed off from the construction sites. Polythene sheets are used on the basis that it creates an airtight environment around the concrete surface henceforth reducing the chances of evaporation over fresh concrete surfaces. But the usage of polythene can be a drawback as it can be easily blown away by winds and also the water lost by self-desiccation cannot be replenished.