OPTIMIZATION OF CONCRETE MIXES – A COST SAVING WAY

Overview on Optimization of Concrete

At present, the optimization of concrete is not common in India or as a matter of fact anywhere else. There is no mention of such optimization of mix designs either in Indian Standards or codes or in British or American. Guidelines that could be considered to be acceptable by competent authorities are also not available in the public domain for the same.

Some reports/articles in the international journals related to the construction industry covering the importance of optimization are taken as a reference to study the importance of optimization.

A short History on Optimization of Concrete

The huge global demand of cement and concrete due to the large number of civil projects worldwide had many experts and industry leaders to ponder about “how to reduce the cost of the projects”. Since concrete is the common and most integral part of any civil construction, the discussion and research were centered about the minimizing the cost of concrete. This has naturally led to finding the process of reducing the cement content. This new method of designing concrete mixes with an optimum cement content without affecting the original properties of concrete is known as optimization of concrete.

What is Optimization of Concrete Mix Design

The Process of finding out a cost-effective mix design that satisfies all the required parameters of a concrete mix shall have for its optimum performance.

Optimization of concrete mixes involves the determination of the proportions of the constituents of concrete required to optimize (minimize or maximize) certain desirable properties of fresh or hardened concrete.

These are workability in the fresh (Plastic) stage and compressive strength and durability in its hardened stage.

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Factors affecting Concrete Mix.

  1. Source of Materials
  2. Properties of materials
  3. Method of preparation
  4. Method of Placing, Compaction and Curing

The selection of mix proportions is the process of choosing suitable ingredients of concrete and determining their relative quantities with the object of producing as economically as possible concrete of certain minimum properties, notably strength, durability, and a required consistency.

Concept of Optimization

Quantity of Cement paste in a given volume of concrete will be reduced through elimination of voids between the ingredients in the concrete, especially between Finer and Courser particles.

This saves the cement content and thereby cost of production.

Method to Reduce Cement Content

By reducing the void content – that normally occupies by cement – through proper packing of course and fine aggregate along with adjustments in Agg/Cement ratio.

This method is Known as Golterman Packing Model

How to Achieve Packing Method.

The coarse aggregate and fine aggregate are mixed in different proportions to arrive at maximum packing density and minimum void content. The cement paste is added in the selected mixture of aggregates to achieve desired workability and strength.

Does Optimization affect Concrete properties mainly Strength.

Studies have shown that, the compressive strength obtained by packing density approach are comparable to that of BIS code method for a given water-cement ratio.

(Ref: Concrete Mix Design By Packing Density Method by N. Raj, S. G Patil, B. Bhattacharjee)

The proposed method for optimization

The aggregates will be combined to get the optimum packing combination and respective voids in the combination of all in aggregates is calculated. The quantity of cement paste will be decided with an increase 5, 10 and 15% of that of void and mixes for the different combinations will be calculated and based on this mix will be designed. This will be compared with the conventional Method to satisfy the properties.

Different methods for optimization of mix design

Fully experimental

Fully experimental methods involve an extensive series of tests, sometimes conducted on a trial-and-error basis, and the optimization results are often applicable only to a narrow range of local materials.

1. P. L. J. Domone and M. N. Soutsos, “An approach to the proportioning of high-strength concrete mixes,” Concrete International, vol. 16, no. 10, pp. 26–31, 1994.

2. S. Ahmad, “Optimum concrete mixture design using locally available ingredients,” The Arabian Journal for Science and Engineering, vol. 32, no. 1, pp. 27–33, 2007.

Fully analytical

In order to reduce the number of trial mixtures required to obtain an optimal mixture, efforts have been made towards developing analytical methods rationalizing the initial mixture proportioning into a more logical and systematic process.

1. I.-C. Yeh, “Computer-aided design for optimum concrete mixtures,” Cement & Concrete Composites, vol. 29, no. 3, pp. 193– 202, 2007

2. J. Kasperkiewicz, “Optimization of concrete mix using a spreadsheet package,” ACI Materials Journal, vol. 91, no. 6, pp. 551–559, 1994.

Semiexperimental (half-analytical)

methods are based on combining the experimental database or experimentally developed prediction models and various analytical tools such as artificial neural network, genetic algorithm, and mathematical programming

1. I.-C. Yeh, “Optimization of concrete mix proportioning using a flattened simplex—centroid mixture design and neural networks,” Engineering with Computers, vol. 25, no. 2, pp. 179–190, 2009.

2. M. A. Jayaram, M. C. Nataraja, and C. N. Ravikumar, “Elitist genetic algorithm models: optimization of high – performance concrete mixes,” Materials and Manufacturing Processes, vol. 24, no. 2, pp. 225–229, 2009.

Statistical methods

Also termed as statistical experiment design methods or statistical factorial design methods or design of experiments methods or empirical methods, are also used frequently in obtaining the optimum concrete mixture design.

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