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FAQ

Approximate percentages of streangth of ordinary portland cement concrete at different ages in comparison with the streangth at 28 days

Age	1day	3 days	7 days	28 days	3 months	6 months	12 months
Strength
(Percent)	16	40	67	100	122	146	155

Strength requirement of concrete

Concrete	Equivalent	Compressive strength on 15 cm
	Controlled	Cubes, Minimum at
	Concrete	7 days	28 days
		[kg/sq.cm]	[kg/sq.cm]
01:01:02	M250	210	315
1:1/4:1/2		195	290
1:1,1/2:3	M200	175	265
1:1,3/4:3,1/2		160	240
01:02:04	M150	140	210

Allowable Stresses for Steel Conforming

Sl no	Form	Thickness or Diameter	Axial tension	Bending	Max	Shear Av.(in unstiffened web)	Bearing	Yield guaranteed	Equivalent
			Pt	Pbc/Pbt	Pq	Pq	Pb	Minimum	Pe
1	Rolled I-beams and channels	All	1500	1650					2285
2	Plates,bars universal beams and columns and	Upto and inclg 20mm	1500	1650					2285
	Sections other than above	Over 20 mm	1420	1575					2205
3	Compound girders composed of rolled I-beams or channels	Upto and inclg 20mm		1650
	With cover plates of thickness	Over 20 mm		1575
4	Plate girders with single or	Upto and inclg 20mm		1575
	Multiple webs	Over 20 mm		1500
5	Plates, Sections and bars	All			1100		1890
6	Rolled I-beams	All				945
7	Plate girders and single	Upto and inclg 20mm				945
	Channels	Over 20 mm				865
8	(A)St, 44-0 if I.S. 1977-1962
	Plates,sections and flats	6mm and over						2600
	Bars(rounds,square and hexagonal)	10mm and over						2600
	Other than rivet bars	6mm and over						2600
	(B) IS : 226-1962	Upto and inclg 20mm
	IS : 2062-1962	Over 20, upto and
	Plates, sections and flates	Incl. 40 mm						2400
		Over 40 mm						2300
	Bars(rounds,square and hexxagonal)
	Other than rivet bars	10 mm & over
		Upto & inclg.20mm						2600
		Over 20mm						2400

Reduction in strength of concrete made with stored cement

Period of storage of cement(month)	0	3	6	12	24
Approx.relative streangth at(28 days percent)	100	80	70	60	50

Removal of forms

a	Sides of foundation,Columns,beams and walls	2 days
	Under sides of slabs up to 4.5m span	7 days
c	Under sides of slabs above 4.5m span and
	Under sides of beam and arches up to 6m span	14 days
d	Under sides of beam and arches up to 6m span and upto 9m span	21 days
e	Under sides of beams and arches over 9m span	28 days

Relation between cube strength and water-cement ratio by weight for fully compacted concrete(portland cement)

Water cement ratio	Cube crushing strength
by weight	(kg./sq.cm.)
	7 days	28 days
0.35	400	530
0.4	350	470
0.45	300	420
0.5	250	370
0.55	220	320
0.6	180	280
0.65	150	250
0.7	130	220
0.75	110	200
0.8	105	180

** Volume of one bag of cement is 0.0347 cum
** Measuring box to be used at site(size 35 x 25 x 40cm)
** Voids to be deducted from stack measurements of
a   Stone metal 40mm guage and above
b   Soling stone/boulders 100mm and above
c   Excavated rocks

Permissible design stress for concrete(Kg/sq. cm.)

Grade of conc	Equivalent Concrete Mix	Como Strength at 28 days(min)		Permissible stress in compression		Permissible stress in shear	Permissible stress in bond		Perssible bearing pressure on full area
		Preliminary test	Works test	Direct	Bending	or in Tension in bending	Average	Local	(Plain CC only)

M100	1 : 3 : 6	135	100	25	30	3	4	7	20
M150	1 : 2 : 4	200	150	40	50	5	6	10	30
M200	1 : 1.5 : 3	260	200	50	70	7	8	13	40
M250	1 : 1 : 2	320	250	60	85	8	9	15	50
M300		380	300	80	100	6	10	17	60
M350		440	350	90	115	10	11	18	70
M400		500	400	100	130	11	12	19	80

Permissible design stresses in steelreinforcement( Kg/Sq.Cm)

Type of Stress	Mild steel grade 1	Medium tensile seel	Cold twisted steel
	(IS : 432-1996)	(IS : 432-1966)	(IS :1786-1966)

Tension other than in helical reinforcement in column or shear reinforcement		Half the guaranteed
Up to 40mm dia	1400	Yieldstress, sublect to a maximum of 1900	1900
Over 40 mm dia	1300

Tension in helical reinforcement in columns		1000	1300	1600
Tension in shear reinforcement in beams		1400	1400	1400

Compression in column bars		1400	1400	1400
Comparision in bar in a beam or slab when the comp		The calculated comp.stress in surrounding concrete
Resistance of the concrete is taken in to account		Multiplied by the modular ratio
Comparision in bar in a beam or slab when the comp		Half the gurantee
Resistance of the conc. Is not accounted up to 40mm dia	1400	Yield stress, subject to		1900
Resistance of the conc. Is not accounted over 40mm dia	1300	A maximum of 1900		1900

Field test for Adulteration of cement

Burn a sample of cement for 20 minutes on a steel plate heated by a stove. Adulterated sample changes colour while unadultered sample remains unchanges
Small blocks(say)2"x2"x1/2" made out of adulterated cement can be broken easily with pressure of fingures

Water assessment for building works

Brickwork, Masonary, Concrete	2250 liters/cu.m
Plastering work	85 liter/sq.m
Pointing works	60 liter/sq.m
White washing per coat	3 liter/sq.m
Road work, metalling or gravelling(6" thick)	130 liters/cum.m

Recommended mixes for various types of construction

Nature of Work	Mixture Recom-mended vol. Proport	Maximum Size of aggregate to use	Water in gallons per bag of C	Bast Consistency

Long Span R. C. Arches High Load R. C. Columns	1 : 1 : 2	1/2" to 3/4"	3.5 to 4.0	Medium

Heavily stressed members od structurers,
Small precast work such as posts and poles
: for Fencing, Telegraphs, Signals, Garden,	1 : 2 : 2	1/2" to 3/4"	4.5 to 5.0	Medium or soft
Furniture and decoratives and other
Work of very thin secion, watertight
Constructions, for high heads, long piles.

R.C. Columns and members subjected to	1 : 3 : 2
Medium loads, wall and floors of reservoir	to	3/4"	5.5	Medium
and tanks, cisterns, sewers, well kerbs and	1 .2 : 2 : 4
Platforms and other watertight constructions,
for moderate heads, non-surfaced roof slabs,
Concrete deposited under water

General R.C building work subjected to ordinary stresses	1 : 2 : 4	1/2" to 1 1/2	6.0 to 6 1/2"	Stiff for
Such as beams, Slabs, Columns, Panel walls basement and retaining		as		roads Medium
Walls, Stairs, Lintels, Sills, Roads, Pavements driveways, Side walls,		required		for others
Floors steps, Bunkers and silos, Bridge construstion dams and piers etc
Exposed to action of water and frost, Machine foundations
Subjected to vibrations, R.Cfootings, R.C piles.

Mass concrete work in culverts, Retaining walls, Compound walls	1 : 3 : 5	1" to 2"	7.5	Stiff
and ordinary machine bases, Foundation				or
Walls which need not be water-tight				Medium

Mass concrete for heavy walls foundations under column
Footings and under heavy duty floors, Concrete blocks,	1 : 4 : 8	1 1/2" to 2 1/2"	1.00 to 10.5	Medium
Hollow block construction(1/2" AGG).

Usefull notes on cement

1	Ton of portland cement = 20 Bags;
1	Cubic foot of portland cement weights 90 o 94lbs, when loodely filed. Average weight of 1 : 2 : 4 concrete; Coke breeze aggregate
	100 lbs. per cubic foot; Clinker aggregate 110 lbs. per cubic foot; brick aggregate 125 lbs. per cubic foot. Ballast aggregate 145 lbs
	per cubic foot

	Average weight 1 : 2 : 4 reinforced concrete, 150 lbs cubic foot
	4.1 cu. Ft. of concrete mixed	1 : 2 : 4	5.8 cu ft. of concrete mixed	1 : 3 : 6
	5.1 cu. Ft. of concrete mixed	1.2 1/2 : 5	7.5 cu ft. of concrete mixed	1 : 4 : 8

1	Cubic foot of loose portland cement neat as cemet paste will cover about 9.5 sq. feet,
	Inch thick
1	Cubic foot of loose portland cement to 2 of sand will cover 16.8 sq. feet, 1 inch thick
1	Cubic foot of loose portland cement to 2 of sand will cover about 29 sq. feet, 1 inch thick
1	Cubic foot of loose portland cement to 3 of sand will cover about 35.7 sq. feet, 1 inch thick