CONCRETE MIX DESIGN PROCEDURE AS PER IS:10262

A Vision To Clear Solutions.

1. Determine the mean target strength f_t from the specified characteristic compressive strength at 28-day f_ck and the level of quality control.f_t = f_ck + 1.65 S , where S is the standard deviation obtained from the Table of approximate contents given after the design mix.

2. Obtain the water cement ratio for the desired mean target using the emperical relationship between compressive strength and water cement ratio so chosen is checked against the limiting water cement ratio. The water cement ratio so chosen is checked against the limiting water cement ratio for the requirements of durability given in table and adopts the lower of the two values.

3. Estimate the amount of entrapped air for maximum nominal size of the aggregate from the table.

4. Select the water content, for the required workability and maximum size of aggregates (for aggregates in saturated surface dry condition) from table.

5. Determine the percentage of fine aggregate in total aggregate by absolute volume from table for the concrete using crushed coarse aggregate.

6. Adjust the values of water content and percentage of sand as provided in the table for any difference in workability, water cement ratio, grading of fine aggregate and for rounded aggregate the values are given in table.

7. Calculate the cement content form the water-cement ratio and the final water content as arrived after adjustment. Check the cement against the minimum cement content from the requirements of the durability, and greater of the two values is adopted.

8. From the quantities of water and cement per unit volume of concrete and the percentage of sand already determined in steps 6 and 7 above, calculate the content of coarse and fine aggregates per unit volume of concrete from the following relations:

where V = absolute volume of concrete= gross volume (1m³) minus the volume of entrapped air

S_c = specific gravity of cement

W = Mass of water per cubic metre of concrete, kg

C = mass of cement per cubic metre of concrete, kg

p = ratio of fine aggregate to total aggregate by absolute volume

f_a, C_a = total masses of fine and coarse aggregates, per cubic metre of concrete, respectively, kg, and

S_fa, S_ca = specific gravities of saturated surface dry fine and coarse aggregates, respectively

9. Determine the concrete mix proportions for the first trial mix.

10. Prepare the concrete using the calculated proportions and cast three cubes of 150 mm size and test them wet after 28-days moist curing and check for the strength.

11. Prepare trial mixes with suitable adjustments till the final mix proportions are arrived at.

I. MIX DESIGN OF CONCRETE AS PER IS: 10262.

Step 1: Design Stipulations

Table – 1

Grade of concrete	M 20	M25	M30	M35
Type of Cement	OPC/53 Grade	OPC/53 Grade	OPC/53 Grade	OPC/53 Grade
Maximum size of aggregate.	30mm	30mm	30mm	30mm
Degree of workability.	0.8	0.90	0.9	0.9
Water Cement Ratio	0.5	0.45	0.42	0.4
Cement Content kg/m3	400	400	400	400
Aggregate Cement ratio	4.3	4.8	4.8	4.9

Step 2: Test Data For Materials

Table – 2

Cement Used		OPC/53
Sp. Gravity of Cement		3.15
Sp. Gravity of 30mm Aggregate		2.8
Sp. Gravity of 10mm Aggregate		2.76
Sp. Gravity of Grit Aggregate		2.82
Sp. Gravity of Crush sand Aggregate		2.79
Chemical admixture @0.05% by wt. of cement		Superplasticizer as per IS:1093
Water Absorption (%)	30mm Aggregate	1.10
	10mm Aggregate	1.42
	Grit Aggregate	3.06
	Crush Sand Aggregate	2.80

Step 3: Sieve Analysis

Table – 3

I.S. SIEVE	COARSE AGGREGATE		FINE AGGREGATE
	CA II % Passing	CA I % Passing	Grit % Passing	Crush Sand % Passing
40mm	100.00	100.00	100.00	100.00
20mm	29.51	100.00	100.00	100.00
10mm	0.00	66.04	100.00	100.00
4.75mm	0.00	5.93	94.60	76.80
2.36mm	0.00	0.00	81.80	44.20
1.18mm	0.00	0.00	55.00	32.00
600 µ	0.00	0.00	28.80	15.60
300 µ	0.00	0.00	14.40	6.40
150µ	0.00	0.00	5.20	2.40
Fineness Modulus	7.70	6.26	3.2	4.23

Step 4: Target Strength Of Concrete

Table – 4

Grade of concrete		M20	M25	M30	M35
Target strength (N/mm2)	Fck + 1.65 S	26.60	28.25	38.25	43.25
Characteristic compressive strength (N/mm2)	3 days	12	16	21	23
	7 days	16	20	24	28
	28 days	20	25	30	35

Step 5: Selection Of Water- Cement Ratio

Grade of concrete	M20	M25	M30	M35
Water-Cement Ratio	0.5	0.45	0.42	0.4

Step 6:Proportion Of Fine Aggregate and Coarse Aggregates

Table – 6

Cement	Grit	Crush Sand	Metal II	Metal I
…	21	21	33	25

Step 7:Mix Proportions for One Cum of Concrete (SSD Condition)

Table – 7 

Grade of concrete	M20	M25	M30	M35
Mass of Cement in kg/m3	400	400	400	400
Mass of Water in kg/m3	200	180	168	160
Mass of Fine Aggregate in kg/m3	614	684	696	704
Mass of grit in kg/m3	307	342	348	352
Mass of crushed sand in kg/m3	307	342	348	352
Mass of Coarse Aggregate in kg/m3	1429	1478	1295	1271
Mass of 20 mm in kg/m3	858	887	777	763
Mass of 10 mm in kg/m3	572	591	518	508.4
Mass of Admixture in kg/m3	Nil	Nil	2	2

Step 8: Mix Proportions

Table – 8 

Grade of concrete	M20	M25	M30	M35
Cement	1	1	1	1
Water	0.5	0.45	0.42	0.4
Fine aggregate	1.53	1.71	1.75	1.76
Coarse aggregate	3.57	3.7	3.24	3.18

Conclusion

The results of mix design indicate that crushed sand can also make as good a concrete as that made of natural sand.The compressive strength obtained is same as of normal mixes.In fact use of crushed sand will become inevitable in near future because of dwindling sources of natural sand. Crushed sand particle though shaped, does not have the spherical shape of natural sand. Hence the crushed sand will have greater water demand than that of natural sand resulting in slightly higher cement consumption. However, if crushed sand is properly graded with adequate fines the mix may have lower water demand when compared to poorly graded natural sand. Besides crushed sand can afford better control on gradation when compared to natural sand. Hence crushed sand may become an economical option if good quality natural sand is not available.