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High Strength Concrete Mix design

Written by Haseeb Jamal

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The type of concrete generally with compressive strength of 6000psi (40MPa) or greater is called a

- W e need high strength concrete in our modern infrastructures in order to pu

Now what is mix design? Although the American Concrete Institute (ACI) doesn't use the term, pref

Proportioning Concrete

Part of mix design is to develop mix ratios that lead to high compression stresses at failure.

The two criteria for a successful mix ratio are:

1. High compressive stress

2. Adequate workability

Once a mix ratio is selected, we need to compute the Amounts of cement, water, and aggregates

required. The amount of these ingredients and the processing depend on weather the concrete

prepare in laboratory or in field. Beside Proportioning HSC designing require study of the

following aspects.

// Selecting Maximum Aggregate Size

Remember that while discussing mix-design of High strength concrete the term cement isuse to describe all the cementious materials in the concrete and not just the Portland cement. In

general, smaller size

aggregates

have been shown to produce higher strength concretes, for a fixed w/(c+p) ratio. However, the

use of the largest possible coarse aggregate may be an important consideration in terms of

optimizing modulus of elasticity, creep, and drying shrinkage of the concrete.

ACI 318 recommends that the maximum aggregate size not exceed one-fifth of the

narrowest dimension between the sides of the forms, one-third of the depth of slabs, nor

three-quarters of the minimum clear spacing between individual reinforcing bars or prestressing

tendons.

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8/3/2019 High Strength Concrete Mix Design

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High Strength Concrete Mix design

Written by Haseeb Jamal

Particularly for a high-strength concrete, a coarse aggregate should be chosen that is

sufficiently hard, clean, and free of surface coatings.

Fineness Modulus of Fine Aggregates for High-Strength

Concrete

If a fineness modulus less than 2.5 is used, the resultant mixture may be "sticky",

resulting in poor workability and a higher water demand. In general, because of the increased

cement (fines) content of a high-strength mixture, the volume of sand is kept to the minimum

necessary to achieve workability and compatibility.

Pozzolan Addition in High Strength Concrete

A Pozzolan Is Defined as a siliceous and aluminous material which in itself possesses little or

no cementitious value but in concrete its give strength in two ways, physically and chemically.

Physically its finely divided particles fills pores and chemically it react with calcium hydroxide at

ordinary temperatures to form compounds possessing cementitious properties.

Generally, a first trial mixture using only cement (no pozzolans) should be prepared and

evaluated. So that we could compare strength of high strength concrete with conventional

concrete

// Moisture Conditions of Aggregate

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High Strength Concrete Mix design

Written by Haseeb Jamal

The moisture content and aggregate absorption values are used in adjusting the amounts

(mass) of aggregates and water to be included in batch proportions. The measured moisture

content is used to adjust the mass of aggregate to achieve thenecessary mass of saturated surface dry (SSD)

aggregates

. Absorbed water doesn't become part of the mixing water, so the mass of water is adjusted

based on the difference between the moisture contents and absorptions of the coarse and fine

aggregates

, weighted by their dry masses in the mixture.

Testing Age

Because high-strength concrete can gain considerable strength after the normally specified

28-day curing age, many specifications utilize testing ages of 56 or 91 days. This guide attempts

to adjust mixture proportions to produce the desired strength at the specified testing age.

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