Civil and Mechanical first year syllabus for IOE, T.U. Nepal

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Characteristics strength,Grade of concrete and Nominal mixes

Characteristics strength:It is the minimum strength of concrete for which the designer has reasonable assurance. Mathematically it the compressive strength of material above which 95 percent of the test result of the 15 cm cube (after 28 days) are expected to exceed.
Grade of concrete: it is the number which denotes the characteristics strength expressed in MPa. The number is usually preceded by the letter M which refers to mix.
      Nominal mix is the fixed proportion of cement:sand:coarse aggregate(by mass or by volume).It is the approximation of grade of concrete and their nominal mix.The actual proportion for a grade of concrete can only be known from mix design method.Some grade of concrete and their respective nominal mixes are given below:
M10   -   1:3:6
M15  -    1:2:4
M20  -     1:1.5:3
M25  -     1:1:2

SOME TERMS RELATED TO MINERALS, ROCKS, STONES,CONCRETE

Cleavage: tendency of a mineral to split along a certain plane parallel to crystal face.

Hardness: it is the resistance offered to abrasion by a mineral. It is expressed in Moh’s scale. To know the hardness of the mineral, it is stretched with a series of substance of known hardness which is given below:

Talc-1   

Gypsum-2

Calcite-3

Fluorite-4

Apatite-5

Orthoclase-6

Quartz-7

Topaz-8

Sapphire,corundum-9

Diamond-10

Toughness: it measures the impact that a mineral can withstand.

Streak:It is defined as the colour of mineral in the powered form.

Lusture: it is the shine on the surface of a mineral and its appearance under reflected light.

Seasoning: it is the process of drying quarry sap. Quarry sap is the Freshly quarried stones which contain certain amount of moisture.

Dressing: it is the process of giving definite and regular shape with smooth faces to stone.

Weathering: It is the effect of atmospheric conditions on the stones, rocks. The atmospheric conditions refers to wind, rain, temperature, moisture content etc.

Texture:the feel, appearance, or consistency of a surface or a substance is called texture. It may be smooth, rough, slimy, fuzzy, honeycomb etc.

Fatigue:weakness in metal or concrete caused by repeated variation of load.

Creep:it is the permanent deformation under the influence of long term mechanical load. it can occur due to exposure with long term high stress, the stress may be below the yield strength of material.

Honeycomb: it represents the rough pitted surface resulting from incomplete filling of concrete against formwork or it represents voids in concrete resulting from incomplete filling of voids among the particles of coarse aggregate. it is caused due to the use of stiff concrete or due to insufficient vibration.