Homework SourseQUESTION 4 20 marks i For large scale offshore concrete stru
Solution
FRIST PART
Requirement of the concrete mix should be known erlier so that it can be do calculation for mix design.Mix design are tested in the laboratory for the confirmation of the result but before calculation of mix design the informaton about the site conditon ,strength ,workability required and available material should be known-
Some information are required under such conditon as follows
A-characterstic strength of the concrete used :As in the question the 7 days chasracterstic strength given .But here we need 28 days characterstic strength .Since characterstic strength is the compressive strength of the cube of the concrete block of size 150*150*150 after curing 28 days and the test result are not to be failed by 5%.
B-Workability of the concrete: Here since the case is of the offshore structure so workabilty is very sensitve chatarterstic which is required and in the queston it is given that the concrete has to be pump for a horizontal distance of the 100 meter so this measure also will come into existence while designing the concrete mix
C-Conditon of Weather:Weather affect the setting time of the concrete ,in hot weather it get set rapidly and in cool weather it plrolong its setting time .Acoordng to the weather at the site admixture and cooling agent required to make the concrete workable aquiring the full strenth at the site .
D-Exposer Condition of the concrete:Exposer conditon will play an important role in the offshore structure.The exposer conditon such as chemical action coastel region .There will change in the mix design for different type of exposer conditon such as moderate ,severe ,very severe and at the different case of exposer the design method are different gven in the code book.
E-Material Quality:Type of material used in the concrete should be tested earlier such as it physical property chemical property also the test should conducted in laboratory for durablity ,moisture content ,size of the materal.And apart from this type of cement to be used in the concrete play a very imortant role in the mix design or strength of the concrete .
F-Batch Mixing and Volume mixing:These two method of mixing are to be known for the design mix.Manual mxing machine mixing ready mix concrete have their different quality of the concrete .
G-Control of quality at the site:This is the most important thing the strength of the concrete as well as the durability of the concrete depend on the how it is operating at the site during the constructon work.During the mix design it is nessesary to understand the method that how it will be operated at the site
SECOND PART
In case of the fire damage of the reinforced column we can use the sprayed concrete.this is the method of the concreting where we don not pour or place concrete into the framework.The spray concrete sometime also nown as the Gunite,Shot Concrete or Shotcrete.Sprayed concrete used for fire damages, under ground structure ,retainng wall,pile facing wall and for the existng structure repaire.
There are mailny two way of the applicaton of the sprayed concrete
A-Dry Process Sprayed Concrete: Dry mix of cement and aggregate which is predetermined is propelled via spraying nozzle.where a finely atomised water which is added in the material stream to hydrate the cement .
B-Wet Process Sprayed Concrete:It used the wet concrete of the batch and proppeled through pipe to the discharge nozzle where becase of the high pressure concrete reaches at the positon .
Above both method use to high velocity of the air for propulson of the concrete.Thus in the our case of the fire damage we wll require the sprayed concrete using the wet method of the applicaton becuase concrete mixed with water wll be eaisly used at the damage portion and we require also concrete which stuck at the damage.
