(6.)
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Sl. No.
|
Age of Loading
|
Creep Coefficient
|
|
1
|
7 Days
|
2.2
|
|
2
|
28 Days
|
1.6
|
|
3
|
1 Year
|
1.1
|
(7.) A value of compacting factor of 0.75 to 0.80 is suggested.
(8.) The life of the structure can be lengthened by providing extra cover to steel, by chamfering the corners or by using circular cross-sections or by using surface coating which prevent or reduce the ingress of water, CO2 or aggressive chemicals.
(9.) Environmental Exposure Conditions-
(i) Mild
(ii) Moderate
(iii) Severe
(iv) Very Severe
(v) Extreme
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(10.) Concrete in sea-water or exposed directly along the sea-coast shall be at least M-20 grade in the case of plain concrete and M-30 in case of reinforced concrete.
(11.) Design mix concrete is preferred to nominal mix. If design mix concrete cannot be used for any reason or the work for grades of M-20 or lower, nominal mixes may be used with the permission of engineer-in-charge.
(12.) The target mean strength of concrete mix should be equal to the characteristic strength plus 1.65 times the standard deviation.
(13.) Nominal mix concrete may be used for grade of M-20 or lower.
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(14.) In batching concrete, the quantity of both cement and aggregate shall be determined by mass.Admixture, if solid by mass. Liquid admixture may however be measured in volume or mass.Water shall be weighed or measured by volume in a calibrated tank.(15.) For guidance, the mixing time shall be at least 2 minutes.
(!6.) Spacers or chairs should be placed at a maximum spacing of 1m.
(17.)As a general guidance, the maximum permissible free fall of concrete may be taken as 1.5 m.
(18.) Joints are a common source of weakness and therefore, it is desirable to avoid them.If this is not possible, their number shall be minimized.
Also Read:Important terms/points of civil engineering
(19.) Fresh concrete should be thoroughly vibrated near construction joints so that mortar from the new concrete flows between large aggregates and develop proper bond with old concrete.
(20.) Curing is the process of preventing the loss of moisture from the concrete whilst maintaining a satisfactory temperature regime.
(21.) Supersulphated cement concrete is seriously affected by inadequate curing and the surface has to be kept moist for atleast 7 days.
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(22.) Exposed surfaces of concrete shall be kept continuously in a damp or wet condition by ponding or by covering with a layer of sacking, canvas, hessian or similar materials and kept constantly wet for at least sever days from the date of placing concrete in case of OPC and at least 10 days where mineral admixtures or blended cements are used.The period of curing shall not be less than 10 days for concrete exposed to dry and hot weather conditions. (23.) In the case of concrete where mineral admixture or blended cements are used, it is recommended that above minimum periods may be extended to 14 days.
(24.) The individual variation should not be more than +-15% of the average.If more, the test results of the sample are invalid.
(25.) The minimum frequency of sampling of concrete of each grade shall be in accordance with the followings:-
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|
Sl.
No.
|
Quantity
of concrete in the work (in cum)
|
Number
of samples
|
|
1
|
1 to 5
|
1
|
|
2
|
6 to 15
|
2
|
|
3
|
16 to 30
|
3
|
|
4
|
31 to 50
|
4
|
|
5
|
51 and above
|
4 plus one additional sample for
each additional 50 cum or part thereof
|
Also Read:Important one liner questions with their answers, Part-11
(26.) Dead loads shall be calculated on the basis of unit weights:-
PCC-24 KN/cum
RCC-25 KN/cum
(27.) Wind and seismic loading shall be treated as imposed loading.
(28.) Span to depth ratio:-
Basic values of span to effective depth ratios for spans up to 10 m:-
Cantilever-7
Simply supported-20
Continuous -26
(29.) The maximum area of tension reinforcement in beam, shall not exceed 0.04bD.
(30.) The maximum area of compression reinforcement shall not exceed 0.04bD.
(31.) The maximum spacing of shear reinforcement measured along the axis of the member shall not exceed 0.75d for vertical stirrups and 'd' for inclined stirrups at 450
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Also Read:Important one liner questions with their answers, Part-10(32.) The diameter of reinforcing bars shall not exceed one-eight of the total thickness of the slab.(33.) The minimum no. of longitudinal bars provided in a column shall be 4 in rectangular columns and 6 in circular columns.
(34.) The bars shall not be less than 12 mm in diameter.
(35.) A reinforcement concrete columns having helical reinforcement shall have at least six bars of longitudinal reinforcement within the helical reinforcement.
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(36.) Spacing of longitudinal bars measured along the periphery of the column shall not exceed 300 mm.(37.) Normally structures exceeding 45 m in length are designed with one or more expansion joints.
(38.) The partial safety factor of steel-1.15
(39.) The partial safety factor of concrete-1.5
(40.) The limiting values of the depth of neutral axis for different grades of steel based on the assumptions:-
|
Sl. No.
|
fy
|
xu max/d
|
|
1
|
250
|
0.53
|
|
2
|
415
|
0.48
|
|
3
|
500
|
0.46
|
(41.) The maximum compressive strain in concrete in axial compression is taken as 0.002
(42.) The nominal shear stress in beams of uniform depth shall be obtained by the following equation-Tv=Vu/bd
(43.) Equation shear, Ve shall be calculated from the formula, Ve=V+1.6T/b
(44.) Cement has cohesive and adhesive properties in the presence of water.
Also Read:Thermal Power Plant Description
(45.) Cement comprises of two types of components:-
(i) Calcareous Compound (Lime)
(ii) Argillaceous Compoung (Silica/Clay)
(46.) Lime, magnesia and sulpher are the three compounds which affects the soundness of cement.
(47.) Tricalcium Silicate (C3S)-Develops on early strength
Di calcium Silicate (C2S)-Ultimate strength
Tri calcium Aluminate (C3A)-Flash-set
Tetra calcium alumino ferrite (C4AF)-Flash-set
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(48.) Field test of cement:-
(i) Colour Test
(ii) Physical properties Test
(iii) Lump Test
(iv) Strength Test
(49.) Physical laboratory test of cement-
(i) Consistency Test
(ii) Initial setting time test
(iii) Final setting time test
(iv) Soundness Test-(a.) Le-chatelier's test
(b.) Autoclave test
(v) Strength Test- (a.) Compressive strength test
(b.) Tensile strength test
(vi) Specific gravity test
(vii) Finenss test- (a.) Sieve method
(b.) Air permeability test
(c.) Sedimentation method
(viii) Heat of hydration test
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(50.) Fineness modulus of the sand should be in the range of 2 to 3.5(51.) Sand helps in increasing the volume of mortar.
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Written By-
Ritesh Raj
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