1) What is bleeding and how you avoid it? 2) Types of cement and their usage. 3)
ID: 1765292 • Letter: 1
Question
1) What is bleeding and how you avoid it? 2) Types of cement and their usage. 3) What is cement water ratio and how it effect and draw it 4) What is segregation and how you avoid it? 5) Concrete allowable temperature and why? 6) Draw BMD and SHD for simple and continues beam 7) Draw simple, continues, cantilever beams reinforcement. 8) Slab reinforcement. 9) Concrete elements allowable cover 10) Types of slabs and their usage. 11) Types of support? 12) Sort of street layer. 13) Horizontal and vertical curve in roads. 14) What are specifications of coarse layer? 15) What is surface water drainage? 16) What is storm water drainage? 17) Types of foundations and uses. 18) Types of settlement 19) How we can determine the soil bearing capacity? 20) What is depth of foundation and how we calculate it? 21) How water table effect foundation depth? How you avoid it? 22) Where is Saudi Arabia benchmark? 23) Water channel cross road?Explanation / Answer
Bleeding is the tendency of the water to rise to the surface of freshly laid concrete. This results from inability of the solid material of concrete to hold the all the water mixed fro preparation of concrete and during the process of material downward settling. If we resort to surface finish in presence of bleeding it would weaken the top surface.
Ways to reduce bleeding in concrete include:
1. RAPID HARDENING CEMENT:
Rapid hardening cement is very similar to ordinary Portland cement (OPC). It contains higher c3s content and finer grinding. Therefore it gives greater strength development at an early stage than OPC. The strength of this cement at the age of 3 days is almost same as the 7 days strength of OPC with the same water-cement ratio.
The main advantage of using rapid hardening cement is that the formwork can be removed earlier and reused in other areas which save the cost of formwork. This cement can be used in prefabricated concrete construction, road works, etc.
2. LOW HEAT CEMENT:
Low heat cement is manufactured by increasing the proportion of C2S and by decreasing the C3S and C3A content. This cement is less reactive and its initial setting time is greater than OPC. This cement is mostly used in mass concrete construction.
3. SULFATE RESISTING CEMENT:
Sulfate resisting cement is made by reducing C3A and C4AF content. Cement with such composition has excellent resistance to sulfate attack. This type of cement is used in the construction of foundation in soil where subsoil contains very high proportions of sulfate.
4. WHITE CEMENT:
White cement is a type of ordinary Portland cement which is pure white in color and has practically the same composition and same strength as OPC. To obtain the white color the iron oxide content is considerably reduced. The raw materials used in this cement are limestone and china clay.
This cement, due to its white color, is mainly used for interior and exterior decorative work like external renderings of buildings, facing slabs, floorings, ornamental concrete products, paths of gardens, swimming pools etc.
5. PORTLAND POZZOLANA CEMENT:
Portland pozzolana cement is produced either by grinding together, Portland cement clinkers and pozzolana with the addition of gypsum or calcium sulfate or by intimately and uniformly blending Portland cement and fine pozzolana.
It produces lower heat of hydration and has greater resistance to attack of chemical agencies than OPC. Concrete made with PPC is thus considered particularly suitable for construction in sea water, hydraulic works and for mass concrete works.
6. HYDROPHOBIC CEMENT:
Hydrophobic cement is manufactured by adding water repellant chemicals to ordinary Portland cement in the process of grinding. Hence the cement stored does not spoiled even during monsoon. This cement is claimed to remain unaffected when transported during rains also. Hydrophobic cement is mainly used for the construction of water structures such dams, water tanks, spillways, water retaining structures etc.
7. COLORED CEMENT:
This Cement is produced by adding 5- 10% mineral pigments with Portland cement during the time of grinding. Due to the various color combinations, this cement is mainly used for interior and exterior decorative works.
8. WATERPROOF PORTLAND CEMENT:
Waterproof cement is prepared by mixing with ordinary or rapid hardening cement, a small percentage of some metal steerages (Ca, Al, etc) at the time of grinding. This cement is used for the construction of water-retaining structure like tanks, reservoirs, retaining walls, swimming pools, dams, bridges, piers etc.
9. PORTLAND BLAST FURNACE CEMENT:
In this case, the normal cement clinkers are mixed with up to 65% of the blast furnace slag for the final grinding. This type of cement can be used with advantage in mass concrete work such as dams, foundations, and abutments of bridges, retaining walls , construction in sea water.
10. AIR ENTRAINING CEMENT:
It is produced by air entraining agents such as resins, glues, sodium salts of sulfate with ordinary Portland cement.
11. HIGH ALUMINA CEMENT:
High alumina cement (HAC) is a special cement, manufactured by mixing of bauxite (aluminum ore) and lime at a certain temperature. This cement is also known as calcium aluminum cement (CAC). The compressive strength of this cement is very high and more workable than ordinary Portland cement.
12. EXPANSIVE CEMENT:
The cement which does not shrink during and after the time of hardening but expands slightly with time is called expansive cement. This type of cement is mainly used for grouting anchor bolts and prestressed concrete ducts.
It is the ratio of amount of water to cement/cementations material added in a mix. it affects the strength of mix obtained. Generally, higher the water cement ratio, lesser the strength achieved
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.
During handling, transporting and placing, due to jerks and vibrations the paste of cement and sands gets separated from coarse aggregate. If concrete segregates during transit it should be remixed properly before depositing. However a concrete where initial setting time is over, should not be used.
Prevention of Segregation of Concrete:
Wherever depth of concreting is more than 1.5 meters it should be placed through temporary inclined chutes. The angle of inclination may be kept between 1:3 and 1:2 so that concrete from top of chutes travels smoothly to bottom, use of small quantity of free water from top at intervals helps in lubricating the path of flow of concrete to bottom smoothly. The delivery end of chute should be as close as possible to the point of deposit.
Segregation in deep foundations and rafts of thickness more than 1 meter, there is every possibility of presence of segregated concrete near bottom or in center if proper supervision is not there. Such segregation can be detected by advanced method of testing like ultrasonic testing. In case of doubt random ultrasonic testing should be conducted and if it is present, designer’s opinion should be taken. This type of segregation can be rectified by pressure grounding with special chemical compounds.
After any defect rectified by pressure grouting core test has to be performed to ensure that the strength of concrete has reached to the desired level.
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