# ACI Method of Concrete Mix Design – Procedure and Calculations

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 for 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 construction
 Construction 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

Fig. 1: Measuring slump

### 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.
These limitations may be ignored provided that workability and methods of consolidation are such that the concrete can be placed without honeycomb or void.

Fig. 2: Coarse aggregate

### 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
• concrete temperature
• amount of entrained air
Table 2 and Table 3 provide estimates of required mixing water for concrete made with various maximum sizes of aggregate, for non-air  and air-entrainment concrete, respectively. Table 2 Approximate mixing water (Kg/m3) and air content for different slumps and nominal maximum sizes of aggregates for non-air content concrete
 Slump, mm Water, Kg/m3 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
Table 3 Approximate mixing water (Kg/m3) and air content for different slumps and nominal maximum sizes of aggregates for air content concrete
 Slump, mm Water, Kg/m3 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

Fig. 3: mixing water

### 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 concrete
 28-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
Table 5 maximum permissible water/cement ratios for concrete in severe exposure
 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

Fig. 4:water to cement ratio

### 5. Calculation of cement content

The amount of cement is fixed by the determinations made in Steps 3 and 4 above.

Fig.5: Cement

### 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 concrete
 Maximum 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

Fig. 6:Coarse aggregate

### 7. Estimation of fine aggregate content

At the completion of Step 6, all ingredients of the concrete have been estimated except the fine aggregate. There are two standard methods to establish the fine aggregate content, the mass method and the volume method. the "volume" method will be used because it is a somewhat more exact procedure. The volume of fine aggregates is found by subtracting the volume of cement, water, air, and coarse aggregate from the total concrete volume. Then once the volumes known the weights of each ingredient can be calculated from the specific gravities. The volume occupied in concrete by any ingredient is equal to its weight divided by the density of that material (the latter being the product of the unit weight of water and the specific gravity of the material).

Fig.7: Fine aggregate

### 8. Adjustments for aggregate moisture

#### Aggregate weights

Aggregate volumes are computed based on oven dry unit weights, but aggregate is typically batched based on actual weight. Therefore, any moisture in the aggregate will increase its weight and stockpiled aggregates almost always contain some moisture. Without correcting for this, the batched aggregate volumes will be incorrect.

#### Amount of mixing water

If the batched aggregate is anything but saturated surface dry it will absorb water (if oven dry or air dry) or give up water (if wet) to the cement paste. This causes a net change in the amount of water available in the mix and must be compensated for by adjusting the amount of mixing water added.

Fig.8:aggregate water content