Material In Civil Engineering course New Microsoft Word Document Microsoft Word
ID: 1711095 • Letter: M
Question
Material In Civil Engineering course
New Microsoft Word Document Microsoft Word ces MailingsReview View .1.1.B'L Normal | 1 No5paci Heading i Heading 2 Tite Paragraph Example 4 - What are the two factors that affect the amount of water required per cubic yards of concrete? In the mix design procedure, which property controls the w/c ratio? In the mix design procedure, which property controls the amount of cement? What is bleeding, and how is it controlled? What is segregation, and how can it be prevented? F10F1 P12 F7 FB F5 F6 F3 F4 6 E R T Y UExplanation / Answer
1. The two factors which affect the amount of water required for concrete is
a). Temparature
b). Quality of water
TEMPARATURE:- If the temparature is more then the evaporation of water is more so automatically more water is required. if temparature is low water requirement is also low.
QUALITY OF WATER:- If water is slightly alkaline then water.
2. The water to cement ratio, or w/c ratio, largely determines the strength and durability of the concrete when it is cured properly. The w/c ratio refers to the ratio of the weights of water and cement used in the concrete mix. A w/c ratio of 0.4 means that for every 100 lbs of cement used in the concrete, 40 lbs of water is added. Using a low w/c ratio is the usual way to achieve a high strength and high quality concrete, but it does not guarantee that the resulting concrete is always appropriate for countertops. Unless the aggregate gradation and proportion are balanced with the correct amount of cement paste, excessive shrinkage, cracking and curling can result. Good concrete results from good mix design, and a low w/c ratio is just one part of a good mix design.
3. The following factors which controls the amount of cement
a) Grade of concrete i.e M5,M10,M15,M20........
b) proportion of coarse aggregate and fine aggregate. i.e (1:2:4)
c) The strength of the wall required. i.e
d) The type of structure is required.
4. Bleeding is one form of segregation, where water comes out to the surface of the concrete, being lowest specific gravity among all the ingredients of concrete. Bleeding can be easily identified in the field by the appearance of a thin layer of water in the top surface of freshly mixed concrete.
Control measurs :-
a) Add minimum water content in the concrete mix, use chemical admixtures to reduce demand to water for a required workability.
b) Design the concrete mix properly.
c) Use fly ash or other supplementary cementitious materials.
d) Using air entraining admixtures is very effective in reducing the bleeding.
e) Add more cement in the mix.
f) Increase the amount of fine aggregate if sand is coarser (fineness modulus of 2.5 to 2.8 best suited) in mix and reduce aggregate proportionally.
5. Segregation of concrete is separation of ingredients of concrete from each other. In good concrete all concrete aggregates are evenly coated with sand and cement paste and forms a homogeneous mass.
Control measures
Control measures to avoid segregation during mixing:-
Control measures to avoid segregation during transit:-
a) It should be remixed properly.
b) If unmonitored, excess water is added by unskilled labours/labour contractors for increasing workability (less effort in placing and mixing) leading to higher water-cement ratio in concrete. This should be avoided. Admixtures or air entraining agents should be used to avoid segregation, that too not beyond prescribed by design/engineer in charge (usually upto 2% of cementitious material)
c) Avoid jolts and jerks during transporting concrete by mixer/millers and try to transport RMC as soon as possible to the site (before initial setting of concrete commences).