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

Ans:-The Steps Involved in The Concreting Process Are Following :

➤ Batching of concrete:-It is the process of measuring concrete mix ingredients either by volume or by mass and introducing them into the mixture. Traditionally batching is done by volume but most specifications require that batching be done by mass rather than volume. 

➤Mixing of concrete:-The mixing operation consists of rotation or stirring, the objective being to coat the surface the all aggregate particles with cement paste, and to blind all the ingredients of the concrete into a uniform mass; this uniformity must not be disturbed by the process of discharging from the mixer.

➤ Transporting 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:- Once the concrete has been placed, it is ready to be compacted. The purpose of compaction is to get rid of the air voids that are trapped in loose concrete.



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

Ans:- 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.


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

Ans:- 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.



4. Describe briefly the advantages and disadvantages of using plastic and timber fenders?

 

Ans: -The advantages and disadvantages of using plastic fenders are as follows:

➨ Plastic fenders are low in strength with a relatively high resistance to abrasion.

➨Plastic fenders are resistant to chemical and biological attacks.

➨ Plastic fenders have moderate energy absorption capacity.

➨ The berthing reactions are also comparatively moderate and depends on the point of        contact.

➨Also since they are made from recycled material they are environmental friendly.

The advantages and disadvantages of using timber fenders are as follows:

➨Timber fenders are low in strength and are very susceptible to marine borer attacks and rotting.

➨The energy absorption capacity is very low.

➨The contact pressure between the vessels and the fender are Generally high.

 

5. What are the different approaches in designing the floors of the service reservoirs?

Ans:- In general there are two main approaches of designing the reservoir floors to prevent leakage of water due to seasonal and shrinkage movements:

➤  In this approach the movement joints of the reservoir floor panels are such that the free expansion and contraction of the panels takes place. Every panel is isolated from the other panels and two panels have a sliding layer between them to help in sliding.

➤ The second method does not provide any room for free movement. With seasonal and shrinkage movements, some cracks are designed to voluntarily occur on the floors of the service reservoirs. These tiny cracks are spread throughout the floor and are simply too minute to cause any leakage or corrosion of the floors. But the difference also in this method is that the amount of reinforcement used is much more than the first approach.




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


Ans:- For elastomeric bearing to function as a soft spring, the bearing should be allowed for bulging laterally and the compression stiffness can be increased by limiting the amount of lateral bulging.  

To increase the compression stiffness of elastomeric bearings, metal plates are inserted. 

After the addition of steel plates, the freedom to bulge is restricted and the deflection is reduced when compared with bearings without any steel plates under the same load.

 Tensile stresses are induced in these steel plates during their action in limiting the bulging of the elastomer. 

 This in turn would limit the thickness of the steel plates.

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


Ans:- Prestressed concrete is a method for overcoming concrete's natural weakness in tension. 

Prestressing tendons (generally of high tensile steel cable or rods) are used to provide a clamping load which produces a compressive stress that balances the tensile stress that the concrete compression member would otherwise experience due to a bending load. 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. 

➤Equilibrium reinforcements:-These types 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.


8. Describe briefly the various methods of concrete curing.

Ans:- 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:

➤Spraying of water:- on walls, and columns can be cured by sprinkling water.

➤ Wet covering of surface: can be cured by using the surface with wet gunny bags or straw.

➤ Ponding: the horizontal surfaces including the slab and floors can be cured by stagnating the water.

➤ 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.

➤ Application of curing compounds: compounds having calcium chloride can be applied on curing surface. This keeps the surface wet for a very long time.



9.Why is propping required for long structures once the formwork is removed?

Ans:- Once the process of concreting is performed the striking of the formworks should be done as soon as possible as delay in this process can lead to the discoloration of the concrete structures. In case of long structures particularly long span structures once the structures have attained enough strength to support themselves it is essential to provide them with propping as creep deflection can take place which can greatly reduce the integrity of the structure. Due to the above mentioned reasons propping should be done after the removal of formwork. Also the props should not be made to stand long as it can lead to overstress for the structures.


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

Ans:- 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.