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The correct choice is (C) Vertical construction joint

To explain: The construction joint maybe horizontal or vertical. For an INCLINED or curved member of the joint should be at right angle to the axis of the member. It is NECESSARY to determine the LOCATION of construction joints well in advance for the viewpoint of STRUCTURAL stability.

Right CHOICE is (b) Coarse aggregate

The explanation: On the other hand, if the concrete mixture is too dry, it will be difficult to handle and place it in position. Both these CONFLICTING condition should be correlated by PROPORTIONING carefully the VARIOUS COMPONENT of concrete mixture.

The CORRECT choice is (b) Water-cement RATIO

For explanation I would say: It is found theoretically that the water REQUIRED for Function is about 0.50 to 0.60 times the weight of cement. The strength and quality of concrete PRIMARILY depend upon the water cement ratio.

Right choice is (b) Minimum VOID method

Easiest explanation: In Minimum void method, the quantity of FINE aggregate USED in the mix is about 10% more than the VOIDS in the coarse aggregate and the quantity of cement is kept at about 15% more than the voids in the fine aggregate.

Right answer is (C) Electrochemical corrosion

Easiest EXPLANATION: According to ELECTROLYTIC theory or Electrochemical corrosion, the corrosion takes place due to chemical action in combination with electrolysis. It takes place at or near the room TEMPERATURE when the metal comes into contact with moisture in contact with aqueous solution of salt, acid or BASES.

Correct answer is (a) Chlorides

Best explanation: On other HAND, the sulphates tend to retard the setting of cement and to discourage the strength of CONCRETE in early stages. It is found that the NET effect of these two CONTRADICTION reactions in the FALL in strength of concrete to the tune of about 8% to 20%.

The correct option is (c) Not recommended

Explanation: However, if REINFORCEMENT in the no-fines concrete is to be used, it is to be coated with a THIN layer of about 3 MM thickness of cement pastes so as to improve the bond characteristics and also to improve the resistance to corrosion.

The correct CHOICE is (b) T BEAM construction joint

Easiest explanation: In case of T-BEAMS, the ribs should be filled with concrete first and in the slabs forming the flanges can be filled up to the centre of the ribs. If a construction joint between slab and beam BECOMES unavoidable especially as in the case of LONG and deep beams, that T beams are used.

Right option is (c) Sea water

To explain: The MINIMUM cement content for concrete permanently under sea water should be 3 kN per metre cube and the minimum cover over there enforcement should be 75 mm. HOWEVER it is not ADVISABLE to take the RISK of corrosion of reinforcement for prestressed concrete and hence the sea water should not be used for the MAKING of the prestressed concrete.

The CORRECT choice is (c) Arbitrary method

To elaborate: In Arbitrary method of VOLUMETRIC PROPORTIONS, the proportions of cement are depending on the NATURE of work for which concrete is required. THUS the general expression for proportions of cement, sand and coarse aggregate is 1:n:2n by volume.

The CORRECT option is (c) SEA

To explain I WOULD say: HENCE, the sea WATER can be adopted for concrete structures where finishing characteristics are not important or where persistent dampness of surfaces permissible.

Right choice is (b) Slow

For explanation I WOULD say: The slow curing of concrete RESULTS in higher ultimate strength. The concrete should be cured ADEQUATELY especially when humidity is low and heat is USED to control the temperature.

The correct ANSWER is (c) Buckets

The explanation: The concrete is put up in the BUCKET and it is covered by means of Canvas to PROTECT it from water when bucket is being lowered POINT. When bucket reaches the desired depth, the bottom doors are opened out and concrete is allowed to DROP slowly.

Right answer is (c) Good

For explanation I would say: The sound ABSORPTION of light weight CONCRETE is good because of the FACT that the air borne sound energy is CONVERTED into heat in the minute CHANNELS of the concrete.

Right ANSWER is (b) Cracks

The BEST I can explain: It should HOWEVER be remembered that action of corrosion become more intensive when it is combined with adverse effects of external and internal STRESSES. Cracks USUALLY progress or advanced more rapidly where the shearing stresses are the greatest.

The correct option is (B) Joint filler

Easy EXPLANATION: The usual joint filler are built-in strips of metal, bitumen treated FELT, CANE fibre board, cork bound with rubber or resin, dehydrated cork, natural cork, softwood free from knots, etc.

Right choice is (c) Bulking of SAND

For explanation: When moisture content is increased by adding more water, the sand particles PACK NEAR each other and the amount of bulking of sand is decreased. Thus the dry sand and the sand COMPLETELY flooded with water have practically the same volume.

Correct choice is (C) WATER-cement ratio

For explanation: Similarly the higher water content increases the workability. But it is not USEFUL for chemical action. The excess water evaporates living PORES in the concrete. Thus the increase water cement ratio lowers the STRENGTH of concrete.

Correct choice is (a) Tremie

To EXPLAIN: Tremie Method consist of spreading course AGGREGATE underwater and then the salary of cement and sand its food through the pipe so as to REPLACE the water in the voids of the COARSE aggregate.

The correct answer is (a) Depth of carbonation

To explain I would say: The depth within which collision can occur under SUITABLE conditions, is nearly twice than that of normal concrete. HENCE special care will have to be taken to PROVIDE sufficient COVER to the reinforcement of LIGHTWEIGHT structure to grant protection against corrosion.

Right option is (d) WORKABILITY

To explain: The workability, as a physical property of CONCRETE alone irrespective of a PARTICULAR type of construction, can be defined as the amount of USEFUL internal work necessary to produce full COMPACTION. For instance, the workability suitable for mass concrete is not necessarily sufficient for thin, inaccessible or heavy reinforced sections.

Correct ANSWER is (a) Fineness MODULUS method

For explanation: The Tom fineness modulus is used to indicate an index number which is ROUGHLY proportional to the average size of the particle in the enter quantity of aggregates. The number of the BIS SIEVES used are from 80 mm to number 15, which are used to determine the fineness modulus.

Correct OPTION is (a) Shutter vibrators

The best I can explain: In Form or Shutter vibrators, the Vibrating action is conveyed to concrete through the formwork. A considerable ENERGY is absorbed by the formwork during TRANSMISSION of vibration. HENCE they are not GENERALLY used.

The CORRECT answer is (b) HOPPER

Easy explanation: It is NECESSARY to keep the bottom end of the Tremie sufficiently deep in the fresh concrete so as to prevent the entry of water in the Tremie. A Hopper is provided at the top to receive the concrete which GOES through the Tremie into the water.

Correct option is (B) Voids

Best EXPLANATION: The difference between voids and PORES MAY be NOTED. The pores represent the opening within the individual particles. The process of consolidation of concrete can be carried out either by hand or by means of vibrators.

Correct answer is (B) 0.45, 0.55

The best I can explain: The water CEMENT ratio for STRUCTURE which are EXPOSED to weather should be carefully decided. For structures that are CONTINUOUSLY underwater, the water cement ratio by which should be 0.55 and 0.65 for thin sections and mass concrete respectively.

The CORRECT option is (C) 3 kN/m^3

Easy explanation: HOWEVER it is not advisable to take the risk of corrosion of reinforcement for prestressed concrete and hence the SEAWATER should not be used for MAKING the prestressed concrete.

Correct choice is (a) Galvanic corrosion

To explain I would say: Whereas, the RUSTING of ferrous alloys at high temperatures from SCALES and oxides. It indicates high TEMPERATURE DRY corrosion.

Correct OPTION is (a) 30% – 40%

Easy explanation: The reduction in weight of concrete helps easy REMOVAL, transport and erection of precast PRODUCTS. The lightweight concrete does not present a special problem with RESPECT to freezing and thawing.

The correct option is (C) Shuttering

To elaborate: The shuttering, formwork or moulds is to be REMOVED when CONCRETE has Harden sufficiently to support its own weight. The formwork should be designed in such a way that it can be EASILY removed and used again.

Correct answer is (a) Steel

The best I can EXPLAIN: The steel is most LIABLE to corrosion and hence the study of Steel corrosion is of Paramount importance. To minimise the chances of development of corrosion of Steel in concrete, there should be avoiding of heavy congested reinforcement ESPECIALLY at the intersection of beams and columns.

Right option is (b) Guniting

Easy explanation: In Guniting METHOD, the surface to be treated is CLEANED and WASHED, the nozzle of gun is generally KEPT at a distance of about 750 mm to 850 mm from the surface to be treated and the velocity of nozzle varies from 120 m/sec to 160 m/sec.

Correct CHOICE is (B) Waterstops

The explanation: The function of waterstops is to seal the joint against the passage of WATER. The waterstop may ALSO be the natural and synthetic rubber or polyvinyl chloride(PVC).

Correct option is (d) Dummy JOINT

The best explanation: Above figure shows another FORM of contraction joint. It is also known as a dummy joint and in this case, a groove of 3 MM width is CREATED in the CONCRETE member to act as a joint. The groove is filled with the joint filler and its depth is about 1/3 to 1/5 of the total thickness of the member.

The correct choice is (b) SURFACE vibrators

Easy explanation: Surface vibrators are used to finish CONCRETE surface as a bridge floors, roads slabs, station PLATFORM, etc. These vibrators are found to be more effective for compacting very dry concrete MIXES because the vibration acts in the same direction of gravity and the concrete is compacted in the confined zone.

Correct option is (c) Gunite

The best I can EXPLAIN: A cement gun is used to deposit the Gunite mixture on the CONCRETE SURFACE under pressure of about 20 N/cm^2 to 30 N/cm^2. The cement is mixed with slightly moist sand and the necessary water is added as the mixture comes out from the cement gun.

Right CHOICE is (d) Sea

To explain: The minimum cement CONTENT for CONCRETE permanently under sea water should be 3 kN per m^3 and the minimum COVER over the reinforcement should be 75 mm.

Right choice is (d) Tremie

Explanation: The pipe EXTENDS from the level of working platform to the lowest point where concrete is to be DEPOSITED. The BOTTOM of the Tremie is provided with the concrete block which is FORCED out when concrete STARTS.