Mix Design Of Concrete 1s2253
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PROPERTIES OF CONCRETE
A good concrete should have three basic qualities : a) Strength b) Workability c) Durability
Table 1: Nominal Mixes As Per IS: 456-2000 (Fine Aggregate of Zone II As Per IS: 383- 1970) Grade of As per Mix ratio by wt concrete IS:383-1970 Cement Fine Coarse Max size of aggregat aggregat graded e e coarse aggregate M20 M20 M20
10 20 40
1 1 1
: : :
1.8 1.5 1.3
: : :
2.7 3.0 3.2
Max Max W/C cement ratio aggregate ratio by mass 0.60 0.60 0.60
Proportions by weight can be converted to proportions by volume, by dividing with the bulk density of the materials available for use at site. The bulk density of sand may be taken 1.44 Kg/lit
1:5 1:5 1:5
Table 2: Grades Of Concrete As Per IS:456-2000 Group
Grade Designation
Specified characteristic compressive strength of 150mm cube at 28 days N/mm²
Ordinary Concrete
M10 M15 M20
10 15 20
Standard Concrete
M25 M30 M35 M40 M45 M50 M55
25 30 35 40 45 50 55
High Strength Concrete
M60 M65 M70 M75 M80
60 65 70 75 80
DURABILITY OF CONCRETE •
A durable concrete is one that performs satisfactorily in the working environment under its anticipated exposure conditions during service.
•
Main characteristics influencing the durability of concrete is its permeability to ingress of water, oxygen, carbon dioxide, chloride, sulphate and other potentially deleterious materials.
•
Factors influencing durability include a) b) c) d) e) f)
The environment The cover to embedded steel The type and quality of constituent materials The cement content and water/cement ratio of the concrete Workmanship, to obtain full compaction and efficient curing The shape and size of the member
STATISTICAL PRINCIPLE For assessing the acceptance criteria of concrete on statistical principles a large number of cube test results are needed. At a given stage of construction, let the cube strength of ‘n’ samples be available. The strength of each sample is the average strength of 3 samples. The sampling is also done in a random manner. If the strength of ith sample Mean strength, fm Deviation of each sample from mean Standard deviation
= fi = Σ fi / n = (fm –fi ) = √Σ (fm –fi )2/(n-1)
The value of standard deviation will be low in case of good control and high in case of lax control. The acceptability of concrete depends upon achieving a desired mean strength and keeping the deviation small.
Acceptance criteria as per old code a)
b)
c)
The grade of concrete is specified. M25 concrete means concrete with a characteristic strength of 25 MPa at 28 days curing. A target mean strength is fixed. ft = fck + k x s ( The value of k for calculating ft is taken as 1.65, which gives a probability of not more than 5% of the samples tested will fall below fck) Each sample is checked for acceptability. Test strength of each sample will be the average of three specimen with individual variation being not more than ±15% of the average.
Clause 15.1 of IS: 456-1978 a) Accept all samples with fi ≥ fck b) For samples with strength less than fck two checks are applied. Both checks must be satisfied • First check : fi should not be less than the larger of two values. (i) fck – 1.35 x s (ii) 0.8 x fck
•
Second check : Average strength of all the samples is not less than fck + 1.65 [ 1-√(1/n)] s Clause 15.2 of IS: 456-1978 a) Reject the concrete if fi is less than the greater of (i) fck – 1.35 x s (ii) 0.8 x fck
b) Reject the concrete also if fi < fck + [1.65 – (3/√n)] s Note : concrete which does not meet the requirement of Clause 15.1 but has a strength greater than required by clause 15.2 can be accepted at the discretion of the designer.
Acceptance criteria as per new code The acceptance criteria as per new code is : a) fm ≥ fck + 0.825 x s or (fck +4) MPa , whichever is greater AND b) fi ≥ (fck – 4) MPa Where, fm = Mean of four results in a group fi = Strength of any individual sample s = Established standard deviation rounded off to nearest 0.5 MPa Note :- When sufficient number of samples have not accumulated, a standard deviation of 4.0 MPa is assumed for M20 & M25 concrete. While 5.0 MPa is taken for M30 to M50. The calculated value of ‘s’ is used as soon as 30 results are available.
( BASED ON IS:456 – 2000)
METHOD OF CONCRETE MIX DESIGN Step 1 :-
Work out the Target mean strength of concrete from the relation:
fck = fck +t x s Where,
fck = fck =
Target average compressive strength at 28 days characteristic compressive strength at 28 days
s
= Standard Deviation
t
= 1.65 (as per IS:456-2000 clause 9.2.2 )
Table 3: Assumed Standard Deviation For Three Strength Groups Grade of Concrete
Assumed standard deviation MPa
M10 M15
3.50
M20 M25
4.00
M30 M35 M40 M45 M50
5.00
The above values correspond to the site control having proper storage of cement; Weigh batching of all materials; controlled addition of water; regular checking of all materials, aggregate grading and moisture content; and periodic checking of workability and strength. Where there is deviation from the above, the values given in the above table shall be increased by 1 N/mm²
Step 2 :Find out the value of W/C ratio against the target mean strength from the curves available for the purpose. Select the appropriate curve for the type of coarse aggregate and the type of cement being used. Step 3 :For durability consideration check the obtained free watercement ratio from appropriate table of IS:456-2000. If required use lower value of water cement ratio. Step 4 :As per clause 7 page 17 of IS:456-2000 find out the degree of workability required for the job. Step 5 :From table 4, find out the quantity of free water in Kg/m³ for the type and maximum size of aggregate being used and for the required workability and normal- air entrained concrete.
Step 6 :Find out the cement content in Kg/m³ from the information of step 2 and step 5. Cement content =
Free water content Water cement ratio
For durability consideration, check the minimum cement content , if required take higher value. Step 7 :Find out the density of concrete in Kg/m³ for different maximum sizes of coarse aggregate corresponding to particular value of combined specific gravity of aggregates from the given tables 5,6 &7. Step 8 :Find out the aggregates content per cum of concrete. Total aggre = conc density – Free water – cement content (Kg/m³ )
(Kg/m³ )
(Kg/m³ )
(Kg/m³ )
Step 9 :Find out the proportions of sand (percent) of the total aggregate from table 8 for particular maximum size of coarse aggregate, required workability, zone of sand and water- cement ratio. Find out the quantity of fine aggregates in Kg/m³ from total aggregate calculated in step 8 above. Step 10 :Find out the quantity of coarse aggregate in Kg/m³ by subtracting the quantity of fine aggregate from total aggregates. Step 11 :If the coarse aggregates are in more than one fraction , they shall be combined in a suitable proportion to get a graded coarse aggregate as per IS: 383-1970. In general, if the coarse aggregates are in single size as per IS: 383-1970, they shall be combined as follows for obtaining a combined graded aggregate. (a) 10 & 20 mm aggregate in ratio 1:2 (b) 10, 20 & 40 mm aggregate in ratio 1:1.5:3
IMPORTANT NOTE THE CALCULATED MIX PROPORTIONS MUST BE CHECKED BY TRIAL MIXES FOR REQUIRED SPECIFICATIONS, AND AS PER REQUIREMENTS SUITABLE ADJUSTMENT IN THE MIX PROPORTION SHOULD BE DONE.
COMPRESSIVE STR VS W/C RATIO (Uncrushed coarse aggregate) 80.0
A=21.6 – 25.0 N/mm² B=25.0 – 29.8 N/mm² C=29.8 – 35.0 N/mm² D=35.0 – 41.5 N/mm²
70.0 28 – DAY COMPR STR OF CONCRETE (N/mm²)
E=41.5 – 48.0 N/mm² F=48.0 – 53.4 N/mm²
60.0 50.0 40.0
F E
(Values given above correspond to the 7- day strength of cement tested according to IS: 4031-1968)
D C B A
30.0 20.0 10.0 0.0 0.30
0.35
0.40
0.45
0.50
WATER – CEMENT RATIO
0.55
0.60
0.65
0.70
COMPRESSIVE STR VS W/C RATIO (Crushed coarse aggregate) 80.0
28 – DAY COMPR STR OF CONCRETE (N/mm²)
70.0 60.0 50.0 40.0
A=21.6 – 25.0 N/mm² B=25.0 – 29.8 N/mm²
F
C=29.8 – 35.0 N/mm² D=35.0 – 41.5 N/mm² E
E=41.5 – 48.0 N/mm² F=48.0 – 53.4 N/mm²
D
(Values given above correspond to the 7- day strength of cement tested according to
C
IS: 4031-1968)
B A
30.0 20.0 10.0 0.0 0.30
0.35
0.40
0.45
0.50
WATER – CEMENT RATIO
0.55
0.60
0.65
0.70
Water cement ratio & cement contents for Durability Type of Exposure
Plain Cement Concrete
Reinforced Cement Concrete
Min cement Kg/m³
Max Free W/C
Min grade of concrete
Min cement Kg/m³
Max Free W/C
Min grade of concrete
Mild
220
0.6
-
300
0.55
M20
Moderate
240
0.6
M15
300
0.5
M25
Severe
250
0.5
M20
320
0.45
M30
Very Severe
260
0.45
M20
340
0.45
M35
Extremely Severe
280
0.40
M25
360
0.4
M40
Note :- Min cement content value applies to 20mm max size of agg
Adjustments to minimum cement content for aggregates (other than 20mm max size of agg) Sl No.
Nominal max aggregate size
Adjustments to minimum cement content
1.
10
+40
2.
20
0
3.
40
-30
Note :a) b)
Cement content prescribed in the table is irrespective of the grades of cement and is inclusive of mineral ixtures like fly ash, silica fume etc. The additions such as fly ash or ground granulated blast furnace slag may be taken into in the concrete composition with respect to the cement content and water cement ratio if the suitability is established and as long as the maximum amounts taken into do not exceed the limit of pozzolona and slag specified in IS 1489(Part I) and IS 455 respectively.
Table 4:Approx Free water content(kg/m³) With non air- entrained concrete (Normal entrapped air) Maximum size of aggregate (mm)
10
20
40
Type of aggregate
Slump (mm)
-
25-75
50-100
100-180
Compacting factor
0.75-0.80
-
-
-
Degree of workability
Very low
Low
Medium
High
Uncrushed
150
205
220
240
Crushed
180
235
250
265
Uncrushed
140
180
195
210
Crushed
170
210
225
245
Uncrushed
120
160
175
190
Crushed
155
190
205
220
When coarse and fine aggregates of different types are used, the free water content is estimated by the expression : 2 W f + 1 W c , where, 3
3
Wf = Free water content appropriate to type of fine aggregate Wc = Free water content appropriate to type of coarse aggregate
Table 5:Estimated wet density of fully compacted concrete(kg/m³) (Max size of saturated & surface dry aggregate 10 mm for first trial) Free water content (Kg/m³)
Specific gravity for combined aggregates 2.4
2.5
2.6
2.7
2.8
2.9
130
2250
2320
2390
2460
2530
2600
140
2235
2305
2375
2445
2515
2585
150
2220
2290
2360
2430
2500
2570
160
2205
2275
2345
2415
2485
2555
170
2190
2260
2330
2400
2470
2540
180
2175
2245
2315
2385
2455
2525
190
2160
2230
2300
2370
2440
2510
200
2145
2215
2285
2355
2425
2495
210
2130
2200
2270
2340
2410
2480
220
2115
2185
2255
2325
2395
2465
230
2100
2170
2240
2310
2380
2450
240
2085
2155
2225
2295
2365
2435
250
2070
2140
2210
2280
2350
2420
The table is worked out for cement content 330 kg/m³. For each 20 Kg difference in cement content from 330 Kg correct the weight per m³, 3 Kg in the same direction.
Table 6:Estimated wet density of fully compacted concrete(kg/m³) (Max size of saturated & surface dry aggregate 20 mm for first trial) Free water content (Kg/m³)
Specific gravity for combined aggregates 2.4
2.5
2.6
2.7
2.8
2.9
120
2285
2355
2425
2495
2565
2635
130
2270
2340
2410
2480
2550
2620
140
2255
2325
2395
2465
2535
2605
150
2240
2310
2380
2450
2520
2590
160
2225
2295
2365
2435
2505
2525
170
2210
2280
2350
2420
2490
2560
180
2195
2265
2335
2405
2475
2545
190
2180
2250
2320
2390
2460
2530
200
2165
2235
2305
2375
2445
2515
210
2150
2220
2290
2360
2430
2500
220
2135
2205
2275
2345
2415
2485
230
2120
2190
2260
2330
2400
2470
The table is worked out for cement content 330 kg/m³. For each 20 Kg difference in cement content from 330 Kg correct the weight per m³, 3 Kg in the same direction.
Table 7:Estimated wet density of fully compacted concrete(kg/m³) (Max size of saturated & surface dry aggregate 40 mm for first trial) Free water content (Kg/m³)
Specific gravity for combined aggregates 2.4
2.5
2.6
2.7
2.8
2.9
100
2335
2405
2475
2545
2615
2685
110
2320
2390
2460
2530
2600
2670
120
2305
2325
2445
2515
2585
2655
130
2290
2360
2430
2500
2570
2640
140
2275
2315
2415
2485
2555
2625
150
2260
2330
2400
2470
2540
2610
160
2245
2315
2385
2455
2525
2595
170
2230
2300
2370
2440
2510
2580
180
2215
2285
2355
2425
2495
2565
190
2200
2270
2340
2410
2480
2550
200
2185
2255
2325
2395
2465
2535
210
2170
2240
2310
2380
2450
2520
The table is worked out for cement content 330 kg/m³. For each 20 Kg difference in cement content from 330 Kg correct the weight per m³, 3 Kg in the same direction.
Table 8: Proportion of fine aggregate with different workability Zone of FA
I
II
III
IV
W/C ratio
10mm aggregate
20 mm aggregate
40 mm aggregate
VL
L
M
H
VL
L
M
H
VL
L
M
H
0.3
43-53
46-56
49-60
54-67
32-39
35-42
39-47
44-53
27-33
29-35
33-39
38-46
0.4
46-56
48-58
51-62
57-69
34-42
37-45
41-49
46-56
29-35
31-38
35-42
41-49
0.5
48-58
50-61
53-65
59-72
37-45
39-47
43-52
48-59
31-38
33-41
37-44
43-52
0.6
50-61
52-63
56-68
62-75
39-47
41-50
45-54
50-61
33-41
36-43
39-47
45-54
0.7
52-64
55-66
58-70
64-77
41-50
44-53
47-57
53-64
36-44
38-46
42-50
47-57
0.3
36-43
37-46
40-49
44-54
27-32
28-35
32-39
35-44
22-27
23-29
27-33
31-38
0.4
37-46
39-48
42-51
46-57
28-34
30-37
33-41
37-46
24-29
25-31
28-35
32-41
0.5
39-48
41-50
44-53
47-59
30-37
32-39
35-43
39-48
25-31
27-33
30-37
34-43
0.6
41-50
42-52
45-56
49-62
32-39
34-41
36-45
41-50
27-33
29-36
32-39
36-45
0.7
42-52
44-55
47-58
51-64
34-41
36-44
38-47
43-53
29-36
31-38
34-42
38-47
0.3
29-36
32-37
33-40
37-44
23-27
24-28
27-32
30-35
18-22
20-23
22-27
26-31
0.4
31-37
33-39
35-42
38-46
24-28
26-30
28-33
31-37
20-24
21-25
24-28
27-32
0.5
32-39
34-41
36-44
40-47
25-30
27-32
29-35
33-39
21-25
23-27
25-30
29-34
0.6
34-41
36-42
38-45
42-49
27-32
29-34
31-36
35-41
23-27
24-29
27-32
30-36
0.7
35-42
37-44
39-47
43-51
28-34
30-36
32-38
36-43
24-29
26-31
29-34
32-38
0.3
26-29
27-32
29-33
32-37
19-23
21-24
23-27
26-30
16-18
18-20
19-22
22-26
0.4
27-31
29-33
30-35
34-38
21-24
22-26
24-28
28-31
17-20
19-21
20-24
24-27
0.5
28-32
30-34
32-36
35-40
22-25
24-27
26-29
29-33
18-21
20-23
22-25
25-29
0.6
30-34
31-36
33-38
36-42
23-27
25-29
27-31
30-35
20-23
22-24
23-27
26-30
0.7
31-35
32-37
35-39
37-43
25-28
26-30
28-32
32-36
21-24
23-26
25-29
28-32
Table 9: Grading requirements of Coarse aggregates (IS:383-1970) IS Sieve Designation
Percentage ing for Single Sized Aggregate of Nominal Size
Percentage ing for Graded Aggregate of Nominal Size
63mm
40mm
20mm
16mm
12.5mm
10mm
40mm
20mm
16mm
12.5mm
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
80mm
100
-
-
-
-
-
100
-
-
-
63mm
85-100
100
-
-
-
-
-
-
-
-
40mm
0-30
85-100
100
-
-
-
95-100
100
-
-
20mm
0-5
0-20
85-100
100
-
-
30-70
100
-
-
16mm
-
-
-
85-100
100
-
-
-
90-100
-
12.5mm
-
-
-
-
85-100
100
-
-
-
90-100
0-5
0-5
0-20
0-30
0-15
85-100
10-35
25-55
30-70
40-85
4.75mm
-
-
0-5
0-5
0-10
0-20
0-5
0-10
0-10
0-10
2.36mm
-
-
-
-
-
0-5
-
-
-
-
(1)
10mm
Table 10 : Grading Requirements For Fine Aggregates (IS :383-1970) IS Sieve Designation
I
II
III
IV
100
100
100
100
4.75 mm
90-100
90-100
90-100
90-100
2.36 mm
60-95
75-100
85-100
95-100
1.18 mm
30-70
55-90
75-100
90-100
600 micron
15-34
35-59
60-79
80-100
300 micron
05-20
08-30
12-40
15-50
150 micron
00-10
00-10
00-10
00-15
10 mm
Percentage ing For Grading Zone
For crushed stone sands, the permissible limit on 150 micron IS sieve is increased by 20 %. Fine aggregate complying with the requirements of any of the grading zone in this table is suitable for concrete. It is recommended not to use the fine aggregate conforming to the grading zone IV in reinforced concrete unless tests prove it suitable for the purpose. Where concrete of high strength and good durability is required, fine aggregate conforming to any of the four zones can be used, but the concrete mix should be properly designed. As the fine aggregate grading becomes progressively finer, the ratio of fine aggregate to coarse aggregate should be progressively reduced.
Exposure Conditions Sl Exposure No. condition
Description
1.
Mild
Concrete surfaces protected against weather or aggressive conditions, except those situated in coastal areas.
2.
Moderate
Concrete surfaces sheltered from severe rain or freezing whilst wet Concrete exposed to condensation and rain Concrete continuously under water Concrete in or buried under non aggressive soil / ground water Concrete surfaces sheltered from saturated salt air in coastal area
Sl Exposure No. condition
Description
3.
Severe
Concrete surfaces exposed to severe rain, alternate wetting and drying or occasional freezing whilst wet or severe condensation Concrete completely immersed in sea water Concrete exposed to coastal environment
4.
Very Severe
Concrete surfaces exposed to sea water spray, corrosive fumes or severe freezing conditions whilst wet Concrete in with or buried under aggressive sub- soil/ ground water
5.
Extreme
Surface of in tidal zone in direct with liquid/ solid aggressive chemicals
Workability of Concrete Sl No.
Placing conditions
Degree of workability
Slump (mm)
1.
Blinding Concrete Shallow Sections Pavements using pavers
Very low
0.75-0.80 (CF)
2.
Mass Concrete Lightly reinforced sections in slabs, beams, walls, columns Floors Hand placed pavements Canal linings Strip footings
Low
25-75
3.
Heavily reinforced sections in slabs, beams, walls, columns Slipform work Pumped concrete
Medium
50-100 to 75- 100
4.
Trench fill In-situ piling
High
100- 150
5.
Tremie Concrete
Very High
By flow determination
Example 1:A mix is required to be designed for M20 grade of concrete which is to used in lightly reinforced slab. Other details are as given below : Standard deviation from previous relevant work Required workability Exposure Maximum free W/C ratio Minimum cement content Maximum size of aggregate Type of sand Cement Other Details
: 4.0 N/mm² : (low) slump (25-75 mm) : mild : 0.55 : 300 Kg/ m³ : 20mm (uncrushed) : River sand : OPC 43 Grade : The sand and aggregate has been used in the construction since the last 40 years and they are found to be quite good.
Test results of materials : Cement 7 days compressive strength
: 39.5 N/mm²
Sand grading
: Zone II
Aggregate grading
: 20- 05 mm graded
Specific Gravity of Sand
: 2.7
Specific Gravity of Aggregate
: 2.7
Water absorption of sand
: 1.4%
Water absorption of aggregate
: 0.9%
Bulk density of room dry sand
: 1.52 Kg/lit
Bulk density of room dry aggregate
: 1.47 Kg/lit
Solution :Step 1 :Target mean strength of concrete, _
f
ck
=
f ck + 1 . 65 s
= 20 + 1.65 x 4.0 = 26.6 N/mm² Step 2 :- Selection of free w/c ratio 7- day compressive strength of cement = 39.5 N/mm² Type of aggregate = Uncrushed (River gravel) Therefore, from the appropriate curve, the w/c ratio for target strength of 26.6 N/mm² is 0.51. The value is selected as the same is less than specified max w/c ratio of 0.55
Step 3 :- Selection of free water content From table, for 20mm uncrushed aggregate and river sand, for required workability of 25-75 mm slump, free water content is found to be 180 kg/m³ Step 4 :- Determination of cement content w/c ratio = 0.51 Water = 180 kg/m³ Cement = 180/0.51 = 353 kg/m³ The value of cement content is higher than the specified minimum cement content of 300 kg/m³, hence accepted Step 5 :- Determination of concrete density Specific gravity of combined aggregates Maximum size of aggregate Free water content Density of concrete ( from table )
= 2.7 = 20mm = 180 kg/m³ = 2408 kg/m³
Step 6 :- Determination of aggregate quantity Concrete density = 2408 kg/m³ Cement content = 353 kg/m³ Water content = 180 kg/m³ Total aggregates = (2408 – 353 – 180) kg/m³ = 1875 kg/m³ Step 7 :- Determination of sand content Workability = Low Max size of aggregate = 20mm Zone of sand = II w/c ratio = 0.51 From table the proportion of sand = 33- 39% = 36% (say) Sand = 1875x0.36 = 675 kg/m³ Step 8 :- Determination of coarse aggregate Coarse aggregate = (1875- 675) kg/m³ = 1200 kg/m³
FINAL PROPORTIONS : Thus the quantity of materials per cum of concrete on the basis of saturated and surface dry aggregates: Water = 180 kg/m³ Cement = 353 kg/m³ Sand = 675 kg/m³ Coarse agg = 1200 kg/m³ Mix ratio by weight on the basis of saturated and surface dry aggregates: Cement : Sand : C/aggregate = 1 : 1.91 : 3.40 Water cement rati0 = 0.51
CONVERSION OF PROPORTION BY WEIGHT TO PROPORTION BY VOLUME Proportion by weight can be converted into proportion by volume, by dividing it with the bulk density of site aggregates. Bulk density of cement = 1.44 x 103 kg/m³ Bulk density of sand = 1.52 x 103 kg/m³ Bulk density of c/ aggregate = 1.47 x 103 kg/m³ Therefore, mix ratio by volume = 1 : 1.81 : 3.33 Free water cement ratio = 0.51 Working out volume of aggregate for one bag of cement Cement = 50 kg = 35000cc Dry sand = 1.81x35000 = 2x(33cm x 33cm x 29cm) Room dry agg = 3.33x35000 = 4x(32cm x 32cm x 28.5cm) Free water = 25.5 liter NOTE : The bulking of sand and adjustment in mixing water should be taken into consideration as per actual moisture content of site aggregates.
MIX DESIGN WITH USE OF PLASTICIZER In Example 1 above , it is proposed to use superplasticizer for reduction in mixing water. It is found that 3cc/kg of superplasticizer reduces 10% of water. Accordingly, water reqmt = (180-18) Kg/ m³ = 162 Kg/ m³ Cement reqmt = (162/0.51) Kg/ m³ = 318 Kg/ m³ Density of wet concrete = 2430 Kg/ m³ Total aggregate = (2430 – 162 – 318) Kg = 1950 Kg/ m³ Therefore, Sand = 1950x0.36 = 683 Kg/ m³ C/ aggregate = 1950 – 683 = 1267 Kg/ m³ Superplasticizer = 318x3 = 954 cc/ m³
Quantity of material by volume per bag of cement Cement = One bag (50 Kg) Dry sand = 2x( 33cm x 33cm x 32.6cm) Dry aggregate = 4x( 32cm x 32cm x 33.3cm) Water = 25.5 lit Superplasticizer = 150 cc Saving in cost/cum of concrete Saving in cement = 353 – 318 = 35 Kg cost of cement saved = 35x3 = Rs.105 Cost of superplast = Rs. 50 (One liter)
Overall saving
= Rs.(105-50)
= Rs. 55
(Per cum of concrete)
Thus use of superplasticizer results in saving in cost and other benefits such as reduction in mixing water & well compacted better finished concrete.
A good concrete should have three basic qualities : a) Strength b) Workability c) Durability
Table 1: Nominal Mixes As Per IS: 456-2000 (Fine Aggregate of Zone II As Per IS: 383- 1970) Grade of As per Mix ratio by wt concrete IS:383-1970 Cement Fine Coarse Max size of aggregat aggregat graded e e coarse aggregate M20 M20 M20
10 20 40
1 1 1
: : :
1.8 1.5 1.3
: : :
2.7 3.0 3.2
Max Max W/C cement ratio aggregate ratio by mass 0.60 0.60 0.60
Proportions by weight can be converted to proportions by volume, by dividing with the bulk density of the materials available for use at site. The bulk density of sand may be taken 1.44 Kg/lit
1:5 1:5 1:5
Table 2: Grades Of Concrete As Per IS:456-2000 Group
Grade Designation
Specified characteristic compressive strength of 150mm cube at 28 days N/mm²
Ordinary Concrete
M10 M15 M20
10 15 20
Standard Concrete
M25 M30 M35 M40 M45 M50 M55
25 30 35 40 45 50 55
High Strength Concrete
M60 M65 M70 M75 M80
60 65 70 75 80
DURABILITY OF CONCRETE •
A durable concrete is one that performs satisfactorily in the working environment under its anticipated exposure conditions during service.
•
Main characteristics influencing the durability of concrete is its permeability to ingress of water, oxygen, carbon dioxide, chloride, sulphate and other potentially deleterious materials.
•
Factors influencing durability include a) b) c) d) e) f)
The environment The cover to embedded steel The type and quality of constituent materials The cement content and water/cement ratio of the concrete Workmanship, to obtain full compaction and efficient curing The shape and size of the member
STATISTICAL PRINCIPLE For assessing the acceptance criteria of concrete on statistical principles a large number of cube test results are needed. At a given stage of construction, let the cube strength of ‘n’ samples be available. The strength of each sample is the average strength of 3 samples. The sampling is also done in a random manner. If the strength of ith sample Mean strength, fm Deviation of each sample from mean Standard deviation
= fi = Σ fi / n = (fm –fi ) = √Σ (fm –fi )2/(n-1)
The value of standard deviation will be low in case of good control and high in case of lax control. The acceptability of concrete depends upon achieving a desired mean strength and keeping the deviation small.
Acceptance criteria as per old code a)
b)
c)
The grade of concrete is specified. M25 concrete means concrete with a characteristic strength of 25 MPa at 28 days curing. A target mean strength is fixed. ft = fck + k x s ( The value of k for calculating ft is taken as 1.65, which gives a probability of not more than 5% of the samples tested will fall below fck) Each sample is checked for acceptability. Test strength of each sample will be the average of three specimen with individual variation being not more than ±15% of the average.
Clause 15.1 of IS: 456-1978 a) Accept all samples with fi ≥ fck b) For samples with strength less than fck two checks are applied. Both checks must be satisfied • First check : fi should not be less than the larger of two values. (i) fck – 1.35 x s (ii) 0.8 x fck
•
Second check : Average strength of all the samples is not less than fck + 1.65 [ 1-√(1/n)] s Clause 15.2 of IS: 456-1978 a) Reject the concrete if fi is less than the greater of (i) fck – 1.35 x s (ii) 0.8 x fck
b) Reject the concrete also if fi < fck + [1.65 – (3/√n)] s Note : concrete which does not meet the requirement of Clause 15.1 but has a strength greater than required by clause 15.2 can be accepted at the discretion of the designer.
Acceptance criteria as per new code The acceptance criteria as per new code is : a) fm ≥ fck + 0.825 x s or (fck +4) MPa , whichever is greater AND b) fi ≥ (fck – 4) MPa Where, fm = Mean of four results in a group fi = Strength of any individual sample s = Established standard deviation rounded off to nearest 0.5 MPa Note :- When sufficient number of samples have not accumulated, a standard deviation of 4.0 MPa is assumed for M20 & M25 concrete. While 5.0 MPa is taken for M30 to M50. The calculated value of ‘s’ is used as soon as 30 results are available.
( BASED ON IS:456 – 2000)
METHOD OF CONCRETE MIX DESIGN Step 1 :-
Work out the Target mean strength of concrete from the relation:
fck = fck +t x s Where,
fck = fck =
Target average compressive strength at 28 days characteristic compressive strength at 28 days
s
= Standard Deviation
t
= 1.65 (as per IS:456-2000 clause 9.2.2 )
Table 3: Assumed Standard Deviation For Three Strength Groups Grade of Concrete
Assumed standard deviation MPa
M10 M15
3.50
M20 M25
4.00
M30 M35 M40 M45 M50
5.00
The above values correspond to the site control having proper storage of cement; Weigh batching of all materials; controlled addition of water; regular checking of all materials, aggregate grading and moisture content; and periodic checking of workability and strength. Where there is deviation from the above, the values given in the above table shall be increased by 1 N/mm²
Step 2 :Find out the value of W/C ratio against the target mean strength from the curves available for the purpose. Select the appropriate curve for the type of coarse aggregate and the type of cement being used. Step 3 :For durability consideration check the obtained free watercement ratio from appropriate table of IS:456-2000. If required use lower value of water cement ratio. Step 4 :As per clause 7 page 17 of IS:456-2000 find out the degree of workability required for the job. Step 5 :From table 4, find out the quantity of free water in Kg/m³ for the type and maximum size of aggregate being used and for the required workability and normal- air entrained concrete.
Step 6 :Find out the cement content in Kg/m³ from the information of step 2 and step 5. Cement content =
Free water content Water cement ratio
For durability consideration, check the minimum cement content , if required take higher value. Step 7 :Find out the density of concrete in Kg/m³ for different maximum sizes of coarse aggregate corresponding to particular value of combined specific gravity of aggregates from the given tables 5,6 &7. Step 8 :Find out the aggregates content per cum of concrete. Total aggre = conc density – Free water – cement content (Kg/m³ )
(Kg/m³ )
(Kg/m³ )
(Kg/m³ )
Step 9 :Find out the proportions of sand (percent) of the total aggregate from table 8 for particular maximum size of coarse aggregate, required workability, zone of sand and water- cement ratio. Find out the quantity of fine aggregates in Kg/m³ from total aggregate calculated in step 8 above. Step 10 :Find out the quantity of coarse aggregate in Kg/m³ by subtracting the quantity of fine aggregate from total aggregates. Step 11 :If the coarse aggregates are in more than one fraction , they shall be combined in a suitable proportion to get a graded coarse aggregate as per IS: 383-1970. In general, if the coarse aggregates are in single size as per IS: 383-1970, they shall be combined as follows for obtaining a combined graded aggregate. (a) 10 & 20 mm aggregate in ratio 1:2 (b) 10, 20 & 40 mm aggregate in ratio 1:1.5:3
IMPORTANT NOTE THE CALCULATED MIX PROPORTIONS MUST BE CHECKED BY TRIAL MIXES FOR REQUIRED SPECIFICATIONS, AND AS PER REQUIREMENTS SUITABLE ADJUSTMENT IN THE MIX PROPORTION SHOULD BE DONE.
COMPRESSIVE STR VS W/C RATIO (Uncrushed coarse aggregate) 80.0
A=21.6 – 25.0 N/mm² B=25.0 – 29.8 N/mm² C=29.8 – 35.0 N/mm² D=35.0 – 41.5 N/mm²
70.0 28 – DAY COMPR STR OF CONCRETE (N/mm²)
E=41.5 – 48.0 N/mm² F=48.0 – 53.4 N/mm²
60.0 50.0 40.0
F E
(Values given above correspond to the 7- day strength of cement tested according to IS: 4031-1968)
D C B A
30.0 20.0 10.0 0.0 0.30
0.35
0.40
0.45
0.50
WATER – CEMENT RATIO
0.55
0.60
0.65
0.70
COMPRESSIVE STR VS W/C RATIO (Crushed coarse aggregate) 80.0
28 – DAY COMPR STR OF CONCRETE (N/mm²)
70.0 60.0 50.0 40.0
A=21.6 – 25.0 N/mm² B=25.0 – 29.8 N/mm²
F
C=29.8 – 35.0 N/mm² D=35.0 – 41.5 N/mm² E
E=41.5 – 48.0 N/mm² F=48.0 – 53.4 N/mm²
D
(Values given above correspond to the 7- day strength of cement tested according to
C
IS: 4031-1968)
B A
30.0 20.0 10.0 0.0 0.30
0.35
0.40
0.45
0.50
WATER – CEMENT RATIO
0.55
0.60
0.65
0.70
Water cement ratio & cement contents for Durability Type of Exposure
Plain Cement Concrete
Reinforced Cement Concrete
Min cement Kg/m³
Max Free W/C
Min grade of concrete
Min cement Kg/m³
Max Free W/C
Min grade of concrete
Mild
220
0.6
-
300
0.55
M20
Moderate
240
0.6
M15
300
0.5
M25
Severe
250
0.5
M20
320
0.45
M30
Very Severe
260
0.45
M20
340
0.45
M35
Extremely Severe
280
0.40
M25
360
0.4
M40
Note :- Min cement content value applies to 20mm max size of agg
Adjustments to minimum cement content for aggregates (other than 20mm max size of agg) Sl No.
Nominal max aggregate size
Adjustments to minimum cement content
1.
10
+40
2.
20
0
3.
40
-30
Note :a) b)
Cement content prescribed in the table is irrespective of the grades of cement and is inclusive of mineral ixtures like fly ash, silica fume etc. The additions such as fly ash or ground granulated blast furnace slag may be taken into in the concrete composition with respect to the cement content and water cement ratio if the suitability is established and as long as the maximum amounts taken into do not exceed the limit of pozzolona and slag specified in IS 1489(Part I) and IS 455 respectively.
Table 4:Approx Free water content(kg/m³) With non air- entrained concrete (Normal entrapped air) Maximum size of aggregate (mm)
10
20
40
Type of aggregate
Slump (mm)
-
25-75
50-100
100-180
Compacting factor
0.75-0.80
-
-
-
Degree of workability
Very low
Low
Medium
High
Uncrushed
150
205
220
240
Crushed
180
235
250
265
Uncrushed
140
180
195
210
Crushed
170
210
225
245
Uncrushed
120
160
175
190
Crushed
155
190
205
220
When coarse and fine aggregates of different types are used, the free water content is estimated by the expression : 2 W f + 1 W c , where, 3
3
Wf = Free water content appropriate to type of fine aggregate Wc = Free water content appropriate to type of coarse aggregate
Table 5:Estimated wet density of fully compacted concrete(kg/m³) (Max size of saturated & surface dry aggregate 10 mm for first trial) Free water content (Kg/m³)
Specific gravity for combined aggregates 2.4
2.5
2.6
2.7
2.8
2.9
130
2250
2320
2390
2460
2530
2600
140
2235
2305
2375
2445
2515
2585
150
2220
2290
2360
2430
2500
2570
160
2205
2275
2345
2415
2485
2555
170
2190
2260
2330
2400
2470
2540
180
2175
2245
2315
2385
2455
2525
190
2160
2230
2300
2370
2440
2510
200
2145
2215
2285
2355
2425
2495
210
2130
2200
2270
2340
2410
2480
220
2115
2185
2255
2325
2395
2465
230
2100
2170
2240
2310
2380
2450
240
2085
2155
2225
2295
2365
2435
250
2070
2140
2210
2280
2350
2420
The table is worked out for cement content 330 kg/m³. For each 20 Kg difference in cement content from 330 Kg correct the weight per m³, 3 Kg in the same direction.
Table 6:Estimated wet density of fully compacted concrete(kg/m³) (Max size of saturated & surface dry aggregate 20 mm for first trial) Free water content (Kg/m³)
Specific gravity for combined aggregates 2.4
2.5
2.6
2.7
2.8
2.9
120
2285
2355
2425
2495
2565
2635
130
2270
2340
2410
2480
2550
2620
140
2255
2325
2395
2465
2535
2605
150
2240
2310
2380
2450
2520
2590
160
2225
2295
2365
2435
2505
2525
170
2210
2280
2350
2420
2490
2560
180
2195
2265
2335
2405
2475
2545
190
2180
2250
2320
2390
2460
2530
200
2165
2235
2305
2375
2445
2515
210
2150
2220
2290
2360
2430
2500
220
2135
2205
2275
2345
2415
2485
230
2120
2190
2260
2330
2400
2470
The table is worked out for cement content 330 kg/m³. For each 20 Kg difference in cement content from 330 Kg correct the weight per m³, 3 Kg in the same direction.
Table 7:Estimated wet density of fully compacted concrete(kg/m³) (Max size of saturated & surface dry aggregate 40 mm for first trial) Free water content (Kg/m³)
Specific gravity for combined aggregates 2.4
2.5
2.6
2.7
2.8
2.9
100
2335
2405
2475
2545
2615
2685
110
2320
2390
2460
2530
2600
2670
120
2305
2325
2445
2515
2585
2655
130
2290
2360
2430
2500
2570
2640
140
2275
2315
2415
2485
2555
2625
150
2260
2330
2400
2470
2540
2610
160
2245
2315
2385
2455
2525
2595
170
2230
2300
2370
2440
2510
2580
180
2215
2285
2355
2425
2495
2565
190
2200
2270
2340
2410
2480
2550
200
2185
2255
2325
2395
2465
2535
210
2170
2240
2310
2380
2450
2520
The table is worked out for cement content 330 kg/m³. For each 20 Kg difference in cement content from 330 Kg correct the weight per m³, 3 Kg in the same direction.
Table 8: Proportion of fine aggregate with different workability Zone of FA
I
II
III
IV
W/C ratio
10mm aggregate
20 mm aggregate
40 mm aggregate
VL
L
M
H
VL
L
M
H
VL
L
M
H
0.3
43-53
46-56
49-60
54-67
32-39
35-42
39-47
44-53
27-33
29-35
33-39
38-46
0.4
46-56
48-58
51-62
57-69
34-42
37-45
41-49
46-56
29-35
31-38
35-42
41-49
0.5
48-58
50-61
53-65
59-72
37-45
39-47
43-52
48-59
31-38
33-41
37-44
43-52
0.6
50-61
52-63
56-68
62-75
39-47
41-50
45-54
50-61
33-41
36-43
39-47
45-54
0.7
52-64
55-66
58-70
64-77
41-50
44-53
47-57
53-64
36-44
38-46
42-50
47-57
0.3
36-43
37-46
40-49
44-54
27-32
28-35
32-39
35-44
22-27
23-29
27-33
31-38
0.4
37-46
39-48
42-51
46-57
28-34
30-37
33-41
37-46
24-29
25-31
28-35
32-41
0.5
39-48
41-50
44-53
47-59
30-37
32-39
35-43
39-48
25-31
27-33
30-37
34-43
0.6
41-50
42-52
45-56
49-62
32-39
34-41
36-45
41-50
27-33
29-36
32-39
36-45
0.7
42-52
44-55
47-58
51-64
34-41
36-44
38-47
43-53
29-36
31-38
34-42
38-47
0.3
29-36
32-37
33-40
37-44
23-27
24-28
27-32
30-35
18-22
20-23
22-27
26-31
0.4
31-37
33-39
35-42
38-46
24-28
26-30
28-33
31-37
20-24
21-25
24-28
27-32
0.5
32-39
34-41
36-44
40-47
25-30
27-32
29-35
33-39
21-25
23-27
25-30
29-34
0.6
34-41
36-42
38-45
42-49
27-32
29-34
31-36
35-41
23-27
24-29
27-32
30-36
0.7
35-42
37-44
39-47
43-51
28-34
30-36
32-38
36-43
24-29
26-31
29-34
32-38
0.3
26-29
27-32
29-33
32-37
19-23
21-24
23-27
26-30
16-18
18-20
19-22
22-26
0.4
27-31
29-33
30-35
34-38
21-24
22-26
24-28
28-31
17-20
19-21
20-24
24-27
0.5
28-32
30-34
32-36
35-40
22-25
24-27
26-29
29-33
18-21
20-23
22-25
25-29
0.6
30-34
31-36
33-38
36-42
23-27
25-29
27-31
30-35
20-23
22-24
23-27
26-30
0.7
31-35
32-37
35-39
37-43
25-28
26-30
28-32
32-36
21-24
23-26
25-29
28-32
Table 9: Grading requirements of Coarse aggregates (IS:383-1970) IS Sieve Designation
Percentage ing for Single Sized Aggregate of Nominal Size
Percentage ing for Graded Aggregate of Nominal Size
63mm
40mm
20mm
16mm
12.5mm
10mm
40mm
20mm
16mm
12.5mm
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
80mm
100
-
-
-
-
-
100
-
-
-
63mm
85-100
100
-
-
-
-
-
-
-
-
40mm
0-30
85-100
100
-
-
-
95-100
100
-
-
20mm
0-5
0-20
85-100
100
-
-
30-70
100
-
-
16mm
-
-
-
85-100
100
-
-
-
90-100
-
12.5mm
-
-
-
-
85-100
100
-
-
-
90-100
0-5
0-5
0-20
0-30
0-15
85-100
10-35
25-55
30-70
40-85
4.75mm
-
-
0-5
0-5
0-10
0-20
0-5
0-10
0-10
0-10
2.36mm
-
-
-
-
-
0-5
-
-
-
-
(1)
10mm
Table 10 : Grading Requirements For Fine Aggregates (IS :383-1970) IS Sieve Designation
I
II
III
IV
100
100
100
100
4.75 mm
90-100
90-100
90-100
90-100
2.36 mm
60-95
75-100
85-100
95-100
1.18 mm
30-70
55-90
75-100
90-100
600 micron
15-34
35-59
60-79
80-100
300 micron
05-20
08-30
12-40
15-50
150 micron
00-10
00-10
00-10
00-15
10 mm
Percentage ing For Grading Zone
For crushed stone sands, the permissible limit on 150 micron IS sieve is increased by 20 %. Fine aggregate complying with the requirements of any of the grading zone in this table is suitable for concrete. It is recommended not to use the fine aggregate conforming to the grading zone IV in reinforced concrete unless tests prove it suitable for the purpose. Where concrete of high strength and good durability is required, fine aggregate conforming to any of the four zones can be used, but the concrete mix should be properly designed. As the fine aggregate grading becomes progressively finer, the ratio of fine aggregate to coarse aggregate should be progressively reduced.
Exposure Conditions Sl Exposure No. condition
Description
1.
Mild
Concrete surfaces protected against weather or aggressive conditions, except those situated in coastal areas.
2.
Moderate
Concrete surfaces sheltered from severe rain or freezing whilst wet Concrete exposed to condensation and rain Concrete continuously under water Concrete in or buried under non aggressive soil / ground water Concrete surfaces sheltered from saturated salt air in coastal area
Sl Exposure No. condition
Description
3.
Severe
Concrete surfaces exposed to severe rain, alternate wetting and drying or occasional freezing whilst wet or severe condensation Concrete completely immersed in sea water Concrete exposed to coastal environment
4.
Very Severe
Concrete surfaces exposed to sea water spray, corrosive fumes or severe freezing conditions whilst wet Concrete in with or buried under aggressive sub- soil/ ground water
5.
Extreme
Surface of in tidal zone in direct with liquid/ solid aggressive chemicals
Workability of Concrete Sl No.
Placing conditions
Degree of workability
Slump (mm)
1.
Blinding Concrete Shallow Sections Pavements using pavers
Very low
0.75-0.80 (CF)
2.
Mass Concrete Lightly reinforced sections in slabs, beams, walls, columns Floors Hand placed pavements Canal linings Strip footings
Low
25-75
3.
Heavily reinforced sections in slabs, beams, walls, columns Slipform work Pumped concrete
Medium
50-100 to 75- 100
4.
Trench fill In-situ piling
High
100- 150
5.
Tremie Concrete
Very High
By flow determination
Example 1:A mix is required to be designed for M20 grade of concrete which is to used in lightly reinforced slab. Other details are as given below : Standard deviation from previous relevant work Required workability Exposure Maximum free W/C ratio Minimum cement content Maximum size of aggregate Type of sand Cement Other Details
: 4.0 N/mm² : (low) slump (25-75 mm) : mild : 0.55 : 300 Kg/ m³ : 20mm (uncrushed) : River sand : OPC 43 Grade : The sand and aggregate has been used in the construction since the last 40 years and they are found to be quite good.
Test results of materials : Cement 7 days compressive strength
: 39.5 N/mm²
Sand grading
: Zone II
Aggregate grading
: 20- 05 mm graded
Specific Gravity of Sand
: 2.7
Specific Gravity of Aggregate
: 2.7
Water absorption of sand
: 1.4%
Water absorption of aggregate
: 0.9%
Bulk density of room dry sand
: 1.52 Kg/lit
Bulk density of room dry aggregate
: 1.47 Kg/lit
Solution :Step 1 :Target mean strength of concrete, _
f
ck
=
f ck + 1 . 65 s
= 20 + 1.65 x 4.0 = 26.6 N/mm² Step 2 :- Selection of free w/c ratio 7- day compressive strength of cement = 39.5 N/mm² Type of aggregate = Uncrushed (River gravel) Therefore, from the appropriate curve, the w/c ratio for target strength of 26.6 N/mm² is 0.51. The value is selected as the same is less than specified max w/c ratio of 0.55
Step 3 :- Selection of free water content From table, for 20mm uncrushed aggregate and river sand, for required workability of 25-75 mm slump, free water content is found to be 180 kg/m³ Step 4 :- Determination of cement content w/c ratio = 0.51 Water = 180 kg/m³ Cement = 180/0.51 = 353 kg/m³ The value of cement content is higher than the specified minimum cement content of 300 kg/m³, hence accepted Step 5 :- Determination of concrete density Specific gravity of combined aggregates Maximum size of aggregate Free water content Density of concrete ( from table )
= 2.7 = 20mm = 180 kg/m³ = 2408 kg/m³
Step 6 :- Determination of aggregate quantity Concrete density = 2408 kg/m³ Cement content = 353 kg/m³ Water content = 180 kg/m³ Total aggregates = (2408 – 353 – 180) kg/m³ = 1875 kg/m³ Step 7 :- Determination of sand content Workability = Low Max size of aggregate = 20mm Zone of sand = II w/c ratio = 0.51 From table the proportion of sand = 33- 39% = 36% (say) Sand = 1875x0.36 = 675 kg/m³ Step 8 :- Determination of coarse aggregate Coarse aggregate = (1875- 675) kg/m³ = 1200 kg/m³
FINAL PROPORTIONS : Thus the quantity of materials per cum of concrete on the basis of saturated and surface dry aggregates: Water = 180 kg/m³ Cement = 353 kg/m³ Sand = 675 kg/m³ Coarse agg = 1200 kg/m³ Mix ratio by weight on the basis of saturated and surface dry aggregates: Cement : Sand : C/aggregate = 1 : 1.91 : 3.40 Water cement rati0 = 0.51
CONVERSION OF PROPORTION BY WEIGHT TO PROPORTION BY VOLUME Proportion by weight can be converted into proportion by volume, by dividing it with the bulk density of site aggregates. Bulk density of cement = 1.44 x 103 kg/m³ Bulk density of sand = 1.52 x 103 kg/m³ Bulk density of c/ aggregate = 1.47 x 103 kg/m³ Therefore, mix ratio by volume = 1 : 1.81 : 3.33 Free water cement ratio = 0.51 Working out volume of aggregate for one bag of cement Cement = 50 kg = 35000cc Dry sand = 1.81x35000 = 2x(33cm x 33cm x 29cm) Room dry agg = 3.33x35000 = 4x(32cm x 32cm x 28.5cm) Free water = 25.5 liter NOTE : The bulking of sand and adjustment in mixing water should be taken into consideration as per actual moisture content of site aggregates.
MIX DESIGN WITH USE OF PLASTICIZER In Example 1 above , it is proposed to use superplasticizer for reduction in mixing water. It is found that 3cc/kg of superplasticizer reduces 10% of water. Accordingly, water reqmt = (180-18) Kg/ m³ = 162 Kg/ m³ Cement reqmt = (162/0.51) Kg/ m³ = 318 Kg/ m³ Density of wet concrete = 2430 Kg/ m³ Total aggregate = (2430 – 162 – 318) Kg = 1950 Kg/ m³ Therefore, Sand = 1950x0.36 = 683 Kg/ m³ C/ aggregate = 1950 – 683 = 1267 Kg/ m³ Superplasticizer = 318x3 = 954 cc/ m³
Quantity of material by volume per bag of cement Cement = One bag (50 Kg) Dry sand = 2x( 33cm x 33cm x 32.6cm) Dry aggregate = 4x( 32cm x 32cm x 33.3cm) Water = 25.5 lit Superplasticizer = 150 cc Saving in cost/cum of concrete Saving in cement = 353 – 318 = 35 Kg cost of cement saved = 35x3 = Rs.105 Cost of superplast = Rs. 50 (One liter)
Overall saving
= Rs.(105-50)
= Rs. 55
(Per cum of concrete)
Thus use of superplasticizer results in saving in cost and other benefits such as reduction in mixing water & well compacted better finished concrete.
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