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Right choice is (a) Increases

Easiest EXPLANATION: The increase in volume of sand is DUE to the fact that the moisture causes film of water around sand particles and it results in the increase of volume of sand. For moisture content of about 5% to 8%, this increase of volume may be as much as 20% to 40%, depending UPON the grading of sand.

The correct CHOICE is (d) Arbitrary method

The best EXPLANATION: In Arbitrary method, there is no RIGID control over the strength of the concrete mix. However, this method is widely used for all works of SMALL magnitude because of its simplicity in the DESIGN.

The correct option is (b) Steel

Explanation: This is due to the fact that sand and PEBBLES or crushed rocks, forming the bulk of cement CONCRETE, to the extent of about 80% to 90%, usually available at moderate cost. The form work, which is of Steel or TIMBER, can be used over and over again or for other PURPOSES after it is REMOVED.

The correct option is (b) Chemical action theory

For explanation: Chemical action theory or DIRECT corrosion includes oxidation in which the OXYGEN of atmosphere COMBINES with all or PART of SURFACE of a material. In this the combined action of oxygen, carbon dioxide and moisture on steel results in corrosion or rust.

The correct option is (d) Gunite

The explanation: A cement gun is used to deposit the Gunite on the concrete surface under a pressure off about 22 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.

The correct choice is (b) Lightweight CONCRETE

To explain: The lightweight concrete is highly POROUS and hence, it leads to the CORROSION of reinforcement, if not PROPERLY protected. For lightweight concrete, the LOOSE porous materials are used as aggregates.

The correct option is (a) Consolidation

The explanation is: The main aim of consolidation of concrete is to eliminate air BUBBLES and THUS to give MAXIMUM density to the concrete. The IMPORTANCE of consolidation of concrete can be seen from the fact that a presence of 5% of voids reduces 30% STRENGTH of concrete.

The correct choice is (c) HAND

Best explanation: The mixing by hand is allowed in case of small WORKS on unimportant work were small quantity of CONCRETE is required. For important work, if hand mixing is to be adopted, it is ADVISABLE to use 10% more cement than specified.

Right answer is (c) 15°C

Explanation: At the time of PLACING, the TEMPERATURE of concrete should be between 15° CELSIUS to 25° Celsius and it should not be ALLOWED to COME into contact with water having a temperature of 35° Celsius.

Correct choice is (b) Cohesion

Explanation: No-FINES CONCRETE is highly permeable as compared to CONVENTIONAL concrete and HENCE the rendering of walls become essential. HOWEVER, in certain cases, such as the drainage layer in the soils, the advantage of quality of high permeability of no fines concrete can be taken.

The correct OPTION is (d) Electrochemical corrosion

To explain: Electrolytic theory or Electrochemical corrosion is the commonly ACCEPTED theory of corrosion. For electrochemical corrosion to occur, conditions that should be SATISFIED are- there should be an electrolyte; the CURRENT should be PASSED through the circuit and the circuit must be closed.

Correct answer is (c) SETTING, hardening

Best explanation: The water LUBRICATES the AGGREGATE and it FACILITATES the passage of cement with the voids of aggregates. This mean that water makes the CONCRETE workable.

Right answer is (c) POROUS

The best explanation: The tendency to be porous is due to the presence of voids which are FORMED during and after it’s placed. To PREVENT Porosity, there should be proper grading and consolidation of AGGREGATES. The minimum water cement ratio should be adopted.

The CORRECT answer is (a) Dowels

To explain I would say: The contraction joints are installed to allow for shrinkage movement in the structure. It MAY either be a COMPLETE contraction joint or a partial CONSTRUCTION joint. In the former case, there is complete discontinuity of both concrete and steel.

Correct answer is (c) Steel

The best EXPLANATION: 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, some preventive measures may be taken such as avoiding heavily congested reinforcement ESPECIALLY at the intersection of beams and columns, etc.

The correct CHOICE is (d) Shrinkage

Easiest explanation: The shrinkage of cement CONCRETE OCCURS as it hardens. This tendency of cement concrete can be MINIMISED by PROPER curing of concrete.

The CORRECT answer is (C) WATER tank joint

Easiest EXPLANATION: For water tanks and other STRUCTURED which store water, the strips of copper, aluminium, galvanized iron or other corrosion resistant material known as water stops or waterbars, are placed in construction joint as shown in given figure above.

Right choice is (a) Horizontal construction joint

For explanation: The construction joints are provided at locations were the construction is stopped either at the end of the DAY or for any other reason. The provisions of the construction joint become NECESSARY to ensure proper bond between the old WORK and the new work.

Correct option is (a) Concrete

For explanation I WOULD say: In this theory, when COARSE AGGREGATE is placed, voids are formed. When FINE aggregates i.e. sand is added, it occupies these voids. Further, when finely powdered cement is added, it occupies the voids of sand particles.

Correct answer is (b) Mixing

The EXPLANATION is: The materials of concrete should be mixed thoroughly so that there is a UNIFORM distribution of materials in the mass of concrete. The thorough mixing also ENSURES that WATER CEMENT paste completely covered the surface of aggregate.

The correct OPTION is (a) Compaction factor test

To explain I would say: In Compaction factor test, the concrete is allowed to fall in a lower CYLINDRICAL mould of 150 mm diameter and 300 mm height through into VERTICAL placed conical Hopper. The SURPLUS concrete appearing about the top of the mould is removed with a trowel. The weight of concrete in the mould is then found out.

Right answer is (b) M5 and M7.5

The best EXPLANATION: The LETTER M REFERS to the mix and the number indicates the specified concrete compressive strength of that makes at 28 days expressed in Newton per mm square. The GRADES of concrete lower than M15 are not to be used in RCC work.