Theory regarding Standard deviation of grade wise concrete

Theory regarding standard deviation calculation

Firstly we have to know the limitation of assumed standard deviation as per coral provision IS10262

SL.Nos	GRADE OF CONCRETE	Assumed standard deviation (N/mm2) or MPA
1	M10	3.5 N/mm2
2	M-15
3	M-20	4.0 N/mm2
4	M-25
5	M-30	5.0N/mm2
6	M-35
7	M-40
8	M-45
9	M-50
10	M-55

Please be noted as per Is code we considered tolerance for standard deviation (+/- 1) N/mm2 ,with reference to the quality of building materials received at site.

While designing the Grade of concrete we consider Target mean strength in which we conform to our client that while doing testing for compressive strength of cube not more than 5% will fail or fall

Target means strength= fck ( i.e grade of concrete)+1.65 * Standard deviation

Formula to find standard deviation-√ (∑(x-x¯)²/n-1)

x =Compressive Strength of cube (average of 3 nos of cube)

x¯ =Mean of x (means total sum of strength divided by total nos of cube

N = Total number of counts

Steps to find the standard deviation :-

1. Find all the required parameter from the format of cube test report maintained on the daily basis.
2. After that put all values of parameter on the given formula for finding the standard deviation
3. Be noted take square root after calculation of inside variance value.

Definition : If we are getting less value of standard deviation as per the required value of deviation then it means we have a good and better quality control of materials used for production of concrete

Basics knowledge regarding road work

Steps sequence for filling of road with different materials:

1)Subgrade  (minimum thickness required-500mm)

2)GSB(Granular sub base -150mm thickness required)

3)WMM(wet mix macadam-150mm thickness required)

4)BM(Bituminous macadam-36mm)

5)DBM(Dense bitumen macadam-Thickness variable -50 to 100mm)

6)BC(Bituminous concrete -Thickness variable(40mm to 50mm) 

• Between WMM and BM we provide prome coat as directed by engineer-in charge with theoretical consumption of 06kg/sqm.
• After BM  in all levels of materials we provide tack coat with theoretical consumption of 0.2kg/sqm as per directed by engineer in charge.

At our present via-duct elevated flyover project in new Delhi we consider following density of each materials-

• Subgrade-1.8 gm/cc
• GSB-1.89 gm/cc
• WMM-2.1 gm/cc
• BM-2.2 gm/cc
• DBM-2.3 gm/cc
• BC-2.36 gm/cc   

Gradation chart for the materials used for road work as per the Morth:-

Sieve size	BM	DBM	BC
45 mm
37.5mm		100
26.5mm	100	90-100	100
19mm	90-100	71-95	79-100
13.2mm	56-88	56-80	59-79
9.5mm			52-72
4.5mm	16-36	38-54	35-55
2.36mm	04-19	28-42	28-44
1.18mm			20-34
600micron			15-27
300micron	02-10	07-21	10 - 20
150micron			5 - 13
75micron	0- 8	2 - 8	2 - 8
PAN

Sieve size	GSB	WMM
75 mm
53 mm
45mm
26.5mm
22.4mm
11.20 mm
9.5mm
4.75mm
2.36mm
0.85mm
0.6mm
0.425mm
0.075mm

Sieve size	WMM
	Passing limits
53mm	100
45mm	95-100
22.4mm	60-80
11.2mm	40-60
4.75mm	25-40
2.36mm	15-30
600 micron	8 - 22
75 micron	0-5
Impact value	30 max
water absorption	2 max
Los angeles abration value	40.0 max
plasticity index	6 max

GRADING FOR GRANULAR SUB-BASE MATERIALS
Is sieve Designation	Percent by weight passing the IS Sieve
	grading I	grading II	grading III	grading IV	grading V	grading VI
75	100	-	-	-	100	-
53	80-100	100	100	100	80-100	100
26.5	55-90	70-100	55-75	50-80	55-90	75-100
9.5	35-65	50-80	-	-	35-65	55-75
4.75	25-55	40-65	10- 30	15-35	25-50	30-55
2.36	20-40	30-50	-	-	10- 20	10- 25
0.85	-	-	-	-	02- 10	-
0.425	10- 15	10- 15	-	-	0-5	0-8
0.075	<5	<5	<5	<5	-	0-3

Please be noted the above mention sieve size are sufficient enough for the analysis of Gradation for all zone as per Morth (ministry of road transport and highway).

Regarding percentage passing of the materials refer the code or Morth .
Grading zone is decided by the engineer in-change as the site condition of that zone .

Regarding any query please mail me or post the comment on my blog

  Concrete Technology

a)Ingredient used to manufacture concrete-Coarse aggregate,Fine aggregate,Water,Admixture &Minerals                                                                       admixture if required.
b)Fine aggregates:

• There are four zone of fine aggregate (Zone I,II,III,IV)
• Coarse ,Medium ,Fine , Very fine (Definition of all zone of sand)
• Generally we consider 1500 kg/m3 as a bulk density of sand 
• By doing gradation of sand we can identify the zone defined for that sand.
• Sieve required for the gradation

• we check silt content of sand which in general should be less than 6% (refer IS 2386 part-3)
• Sand plays very vital role in concrete as it is pore filling materials and by combining with the cement it becomes a binding materials and while doing the trial mix we always suppose to use fresh sand and have to collect the sand after digging to 1 to 1.5 meter below the top surface of BIN from the batching plant .
• Bulking of sand is also the important factor .
• generally for the construction of Bridges and via duct elevated flyover we use Zone II sand in making the concrete.