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ACI method of concrete mix design is based on the estimated weight of the concrete per unit volume. This method takes into consideration the requirements for consistency, workability, strength and durability. This article presents ACI method of concrete mix design.ACI Method of Concrete Mix Design
Required Data:
Before starting concrete mix design, basic information on raw materials shall be prepared which include:- Sieve analyses of fine and coarse aggregates.
- Unit weight (dry rodded density) of coarse aggregate.
- Bulk specific gravities and absorptions or moisture content of aggregates.
- Mixing-water requirements of concrete developed from experience with available aggregates.
- Specific gravities of Portland cement and other cementitious materials, if used.
- Relationships between strength and water-cement ratio or ratio of water-to-cement plus other cementitious materials, for available combinations of cements, other cementitious materials if considered, and aggregates.
Procedure forÂ ACI Method of Concrete Mix Design
1. Choice of slump
If slump is not specified, a value appropriate for the work can be selected from Table 1. The values provided in table can be used only when vibration is used to consolidate concrete. To read more about slump, Please click here. Table 1 Recommended slumps for various types of constructionConstruction type | Slump value, mm | |
Minimum | Maximum* | |
Reinforced foundation walls and footings | 25 | 75 |
Plain footings, caissons, and substructure walls | 25 | 75 |
Beams and reinforced walls | 25 | 100 |
Building columns | 25 | 100 |
Pavements and slabs | 25 | 75 |
Mass concrete | 25 | 50 |
*May increased 25mm for methods of consolidation other than vibration |
2. Choice of maximum size of aggregate
commonly, maximum aggregate size should be the largest that is economically available and consistent with dimensions of structural element. ACI 211.1-91 specify that, maximum aggregate size shall not surpass:- One-fifth of the narrowest dimension between sides of forms.
- one-third the depth of slabs
- 3/4-ths of the minimum clear spacing between individual reinforcing bars, bundles of bars, or pre-tensioning strands.
3. Estimation of mixing water and air content
The quantity of water per unit volume of concrete required to produce a given slump is dependent on:- nominal maximum size
- particle shape
- grading of the aggregates
- concrete temperature
- amount of entrained air
- use of chemical admixtures.
Slump, mm | Water, Kg/m^{3} of concrete for indicated nominal maximum sizes of aggregate | |||||||
9.5 mm | 12.5 mm | 19 mm | 25 mm | 37.5 mm | 50 mm | 75 mm | 150 mm | |
25-50 | 207 | 199 | 190 | 179 | 166 | 154 | 130 | 113 |
75-100 | 228 | 216 | 205 | 193 | 181 | 169 | 145 | 124 |
150-175 | 243 | 228 | 216 | 202 | 190 | 178 | 160 | ---- |
Approximate Air content quantity, % | 3 | 2.5 | 2 | 1.5 | 1 | 0.5 | 0.3 | 0.2 |
Slump, mm | Water, Kg/m^{3} of concrete for indicated nominal maximum sizes of aggregate | |||||||
9.5 mm | 12.5 mm | 19 mm | 25 mm | 37.5 mm | 50 mm | 75 mm | 150 mm | |
25-50 | 181 | 175 | 168 | 160 | 150 | 142 | 122 | 107 |
75-100 | 202 | 193 | 184 | 175 | 165 | 157 | 133 | 119 |
150-175 | 216 | 205 | 197 | 184 | 174 | 166 | 154 | ---- |
Recommended average total air content (%) for different level of exposure | ||||||||
Mild exposure | 4.5 | 4 | 3.5 | 3 | 2.5 | 2 | 1.5 | 1 |
Moderate exposure | 6 | 5.5 | 5 | 4.5 | 4.5 | 4 | 3.5 | 3 |
Severe exposure | 7.5 | 7 | 6 | 6 | 5.5 | 5 | 4.5 | 4 |
4. Selection of water-cement or water-cementitious material ratio
Strength, durability, and determine water to cement ratio:Without strength vs. w/c ratio data for a certain material, a conservative estimate can be made for the accepted 28-day compressive strength from Table 4. Additionally, if there are severe exposure conditions, such as freezing and thawing, exposure to seawater, or sulfates, the w/c ratio can be obtained from table 5. Table 4 Relationship between water-cement or water-cementitious materials ratio and compressive strength of concrete28-days compressive strength in MPa (psi) | Water cement ratio by weight | |
Non-air entrained | Air entrained | |
41.4 (6000) | 0.41 | --- |
34.5 (5000) | 0.48 | 0.40 |
27.6 (4000) | 0.57 | 0.48 |
20.7 (3000) | 0.68 | 0.59 |
13.8 (2000) | 0.82 | 0.74 |
Types of structure | Structure wet continuously of frequently exposed to freezing and thawing | Structure exposed to seawater |
Thin sections (railings, curbs, sills, ledges, ornamental work) and sections with less than 25mm cover over steel | 0.45 | 0.40 |
All other structures | 0.50 | 0.45 |
5. Calculation of cement content
The amount of cement is fixed by the determinations made in Steps 3 and 4 above.6. Estimation of coarse aggregate content
The most economical concrete will have as much as possible space occupied by coarse aggregate since it will require no cement in the space filled by coarse aggregate. The percent of coarse aggregate to concrete for a given maximum size and fineness modulus is given by Table 6. Coarse aggregate volumes are based on oven-dry rodded weights obtained in accordance with ASTM C 29. Table 6: Volume of coarse aggregate per unit of volume of concreteMaximum aggregate size, mm | fineness moduli of fine aggregate | |||
2.40 | 2.60 | 2.80 | 3 | |
9.5 | 0.50 | 0.48 | 0.46 | 0.44 |
12.5 | 0.59 | 0.57 | 0.55 | 0.53 |
19 | 0.66 | 0.64 | 0.62 | 0.60 |
25 | 0.71 | 0.69 | 0.67 | 0.65 |
37.5 | 0.75 | 0.73 | 0.71 | 0.69 |
50 | 0.78 | 0.76 | 0.74 | 0.72 |