## Concrete Mix Calculation

Concrete Hub application (which can be downloaded for free) is now providing a new concrete mix design tool which allows you to design your new concrete mix in an easy and rapid way. No need to have the ACI standard in hand, the application provides all guidelines and performs the calculations for you.

### What is a concrete mix?

A concrete mix is a blend of different materials which are proportionate in a way to create a concrete of a certain strength, durability and workability for structural applications. A concrete mix contains 5 major elements: cement, water, coarse aggregates, fine aggregates (sand) and air in different proportion. Additional elements such as pozzolanic materials and chemical admixtures can also be incorporated to the mix to increase its properties.

### How to design a concrete mix?

In general, the concrete mix is designed to follow the guidelines provided by ACI Committee 211 Standard Practice for Selecting Proportions for Normal, Heavyweight and Mass Concrete (ACI 211.1-91). A concrete mix can be designed by using the tables and calculation provided in the standard. The designing process can be time consuming and challenging because all concrete mixes are unique in their properties. However the challenge of creating a unique concrete mix has been solved.

### Concrete Hub -Concrete Tools- Concrete Mix Design

The Concrete Hub application now provides an easy and fast way to do a preliminary mix design. The Concrete Hub provides a free concrete mix design tool. The add-on allows you to create proportions for your mix design based on either absolute volume or weight method. The application performs all the calculations in either SI or Imperial units according to the ACI 211.1-91 standard and provides guidelines from the standard at each steps through the help icon.The application generates a summary file that can be easily share once your concrete mix design is completed. In order to create your unique concrete mix there are 8 steps to be taken.

#### The application is divided in 8 steps:

#### Step 1: Slump Flow

The concrete slump represents the flowability/ workability of a concrete mix. For example a higher slump allows for better placement in congested reinforced elements. The first step of the application requires you to define the maximum and minimum slump for the fresh mix properties. If the flow dimensions are unknown the help icon allows you to define the type of element which outputs the associated slump requirements.

*The help guideline is based on Table 6.3.1 (Table A1.5.3.1) of the ACI standard. *

#### Step 2: Aggregate size

You will need to define the aggregate size required for the mix design. In general, coarse aggregate maximal dimension is governed by the limitations of the structure cross section and reinforcement design. Increasing the aggregate size is usually more economical as it reduces the amount of cement per unit of volume, however it can potentially affect the workability of the mix. In contrary, reducing the maximal size of the coarse aggregate allows to reach higher strength at equivalent water-cement ratio.

* The help icon available on this page proposes the different aggregate sizes based on the limitation of Tables 6.3.3 (A1.5.3.3) *

#### Step 3: Mixing Water and Air Content

Step 3 provides the first estimation of the amount of water required to obtain the appropriate workability based on the slump flow and the aggregate size. It also suggestions the amount of entrapped air required for the non-air entrained or an air-entrained concrete. The entrapped air is an important parameter when the concrete structure is exposed to freezing or deicing salts. In such conditions, increasing the air content will increase the durability because it allows the water to expend in the entrapped air when it freezes. This reduces the internal pressure caused by the formation of ice.

Using the help menu on in this step automatically calculate the water weight and the amount of entrapped air required based on the aggregate size, slump a level of exposure based on the recommended values of ACI committee Tables 6.3.3/ A1.5.3.3.

#### Step 4: Concrete Strength and Water Cement Ratio

Step 4 requires you to enter the required compressive strength and associated water cement ratio. The water cement ratio (w/c ratio) is the most important parameter of the concrete mix design. The w/c ratio governs the strength, durability and workability of the concrete mix. For example, reducing the water-cement ratio will increase the strength of the concrete and provide a better durability. However, decreasing the w/c can importantly reduce the workability of the concrete, potential solution such as adding water reducer can be implemented (refer to Step 7). In the help option you can select the wanted compressive strength and the associated water cement ratio will be displayed based on Table 6.3.4(a) A1.5.3.4(A)). Additionally, the help section provides guidelines for the maximum permissible w/c based on the structure exposition(Tabl6.3.4(b)/ A1.5.3.4(b)). With the values entered the application calculated the amount of cement required. The amount of cement can be reduced by introducing pozzolanic materials to the mix.

*Step 4.1- Pozzolanic materials*

On this page you will also have the alternative of including pozzolanic materials such as fly ash, silica fumes or slag to the mix. Using pozzolanic material as a replacement for a quantity of the cement is more ecological and economical. It generally slows down the curing mechanism and provide enhance properties to the concrete. You can select the preferred method of calculation. Based on the specific gravity of the pozzolanic material a new adjusted water-cementitious material ratio, amount of pozzolanic material and adjusted cement weight will be calculated.

#### Step 5: Coarse aggregate

Unit weight of coarse aggregate, finesse modulus, volume of coarse aggregate per volume of concrete are the required fields for step 5. The application will output the quantity of coarse aggregate required. The help option lets you select the coarse aggregate size and modulus of finesse of fine aggregates and outputs the volume of oven-dry-rodded coarse aggregate, calculation is based on Table 6.3.6/ A1.5.3.6 values. This table is based on the workability of the concrete.

#### Step 6: Fine aggregate

Step 6 calculates the quantity of fine aggregate required for the proposed concrete mix. Depending on the method of calculation (per weight or per volume) the amount of fine aggregate is calculated differently. For volume calculation method, the fine aggregate is calculated based on a 1m3 (1 yd3) of concrete while the weight method calculated the amount of fine aggregate based on the estimation of concrete weight. Depending on the type of concrete (non-entrained or air entrained) the first estimate of concrete weight can be calculated based on ACI Table 6.3.7.1/ A1.5.3.7.1 which is provided in the help section of Step 6.

#### Step 7: Adjustment for Moisture in Aggregates

Step 7, the last step in the calculations, is to adjust the amount of water in the mix design based on the input of the moisture content and degree of moisture absorption of coarse and fine aggregates. It is important to take in consideration the amount of water the aggregates give to the mix and retrieve from the mix because this causes variation in the water- cement ratio. The application computes the new quantity of water, coarse aggregate and fine aggregates based on the input values. The amount of water can further be reduced by using water reducer (chemical admixtures).

*Step 7.1- chemical admixtures*

You have the option of incorporating water reducer or other chemical admixture such as air entrained to the mix composition. Incorporating water reducer allows you to keep a constant water-cement ratio for a smaller cement ratio with compromising the strength and increasing the workability. Air entrained admixtures can be very useful at increasing the durability and workability of a mix.

#### Step 8- Summary Design

In Step 8, you can enter the volume of the concrete batch required. The application will display the concrete mix information and the quantity of each material required for the specified volume of concrete. The summary report of the mix calculation can now be share with coworker via email.