Q Bank for Civil Engineer LDCE Exam - Write short notes on. (4)

Q.No.3. Write short notes on. 

1. Honey combing of concrete & its prevention. 

3. Design of concrete mix. 

4. Optimum moisture content & maximum dry density. 

5. Contour & contour interval. 

1.Honey combed

For laying roofs slab , loose centering should not be permitted where vibraters are used otherwise the bottom of the slab will be honeycombed .

• Preventions 

1. Centring should be made of steel or strong wood of which joints should be water tight. 

2. Steel form have advantage over wooden form work, it is easy assembled and dismantled. 

3. The surface of timber shuttering should be well wetted or a coat of lime wash or soap water coat before pouring the concrete. 

4. In steel shuttering oiling shall be done immediately before the pouring the concrete.

3. Design of concrete mix: 

The aim of concrete mix design is to determine the proportions in which cement, fine aggregate, coarse and water should be mixed to produce concrete of required strength, workability and durability with minimum cost. The design of concrete mix can be done following methods. 

i. Normal mix: 

When the proportions of cements, aggregate and water are adopted based on arbitrary standard, the concrete produced is termed as nominal mix concrete. ii. Design mix: Design mix can be defined is the process of selecting the ingredient of concrete and determine their relative proportions with the object of producing concrete of certain minimum strength and durability as economically as possible .The purpose of designing as can be seen from the about definitions is two-fold .The first object is to achieve the stipulated minimum strength and durability. The second object is make to the concrete the most economical manner. 

Variables in Proportioning

With the given materials, the four variable factors to be considered in correction with specifying a concrete mix are : 

a) Water cement ratio 

b) Cement content or cement aggregate raito 

c) Gradation of the aggregates 

d) Consistency

In general all four these inter related variables can not be chosen or manipulated arbitrarily. Usually two, three factors are specified and the others are adjusted to give optimum values of strength, workability and economy. 

4.Optimum moisture cement:- 

the maximum moisture content in the soil after which the addition of water creates hindrance in bringing the particles closer is called optimum moisture content. If the moisture content of the soil is more than the optimum moisture content, no compaction of the soil is possible because of too wetness. 

Maximum Dry Density:- 

The weight of dry solid matters contain in a unit volume of soil divide by total volume of soil is known as Dry density. It can be determined after water has been dried out without changing its bulk volume. 

5. Contour & Contour Distance:- 

A contour is an imaginary line on the ground joining the points of equal elevation. The elevation and depression on the map are shown by means of contour. All the points on the same contour have same elevation above datum surface. The line joining those points on map is called contour line. Contour interval is the difference in levels of two successive contour line, It may be 5 mitrs, 10 mitrs, or 50 mitrs or even 100 mitrs depending upon the purpose and scale of the map.