Topic : MIX DESIGN OF

CONCRETE

Properties of concreteSubmitted To:

DR. AYUB ELAHI Submitted By:

SOHAIB NASEER 2K9-scet-29/CIVILM.ZAEEM FAKHAR 2K9-scet-03/CIVILISRAR–UL–HAQ 2K9-scet-30/CIVILAWAIS ULLAH 2K9-scet-31/CIVILBILAL RIAZ

2K9-scet-59/CIVIL

INTRODUCTIONConcrete is the second largest material consumed by human beings after food and water as per WHO. It is obtained by mixing cement, fine aggregate, coarse aggregate and water in required proportions. The mixture when placed in forms and allowed to cure becomes hard like stone. The hardening is caused by chemical action between water and the cement due to which concrete grows stronger with age.

INTRODUCTIONThe strength, durability and other characteristics of concrete depend upon the properties of its ingredients, proportion of the mix, the method of compaction and other controls during placing, compaction and curing.

Definition

the process of selecting suitable ingredients of concrete and determining their relative proportions with the object of producing concrete of certain minimum strength and durability as economically as possible

Objective In Designing Concrete Mixtures

To determine the most economical & practical combination of readily available materials to produce a concrete that will satisfy the performance requirements under particular conditions of use

Designing Concrete MixturesFactors to be considered

•Workability•Placement conditions•Strength•Durability•Appearance•Economy

Factors to be considered

• Strength – important to the design engineer • Durability – important to the owner • Workability – important to the contractor • Economy – important to the owner

Proportioning concrete is the art of optimizing the mixture to meet these requirements

Methods Of Selection Of Mix Proportions

There are two main methods for the selection of mix proportions of concrete.

American methodBritish method

Steps For Mix DesigningACI METHOD

1. Choice of slump2. Choice of max. Size of aggregates3. Estimate of water and air contents4. Selection of water cement ratio5. Calculation of cement contents6. Estimate of coarse aggregates content7. Estimate of fine aggregates content8. Adjustments to mix proportion

Steps For Mix DesigningBRITISH METHOD

1. Determining the Free Water/ Cement Ratio

2. Determining the Free-water Content3. Determining the Cement Content4. Determining the Total Aggregate

Content5. Determining of The Fine and Coarse

Aggregate Contents

Coarse Aggregate Requirement

Grading

•Nature of particles–Shape–Porosity–Surface texture

Max Aggregate Size

Cover between steel & form, C: Dmax <3/4C

Spacing between bars, S: Dmax <3/4S

Depth of slab, D: Dmax <D/3

Max Aggregate Size(For pumped concrete)

Dmax < 1/3 diameter of hose or 1-1/2 inch, whichever is smaller

Fineness Modulus of Sand

•The FM is calculated from particle size distribution of the sand

•Values should range between 2.3 to 3.1

•Coarse sand has a higher FM than fine sand

•FM influences the bulk volume of coarse aggregate

Air ContentThe amount needed depends on:

Max aggregate size –Less paste as size increases

Workability Requirements

Concrete must always be made with a workability,consistency and plasticity suitable for job placement

Workability Requirements

Concrete Construction SlumpMaximum

Slump Minimum

Reinforced walls & footings 3 1

Plain footings, caissons, and Substructure walls

3 1

Beams & reinforced walls 4 1

Columns 4 1

Pavements and slabs 3 1

Mass concrete 3 1

Water cement ratio

Range of w/c= 0.45 to 0.65For mix design of1:2:4The w/c is standardized as 0.5

Water ContentWater demand is influenced by:

Slump requirementAggregate sizeAggregate shapeAir contentCementing materials contentTempAdmixtures

Slump mm

Water. Kg/m3 of concrete for idicated nominal maximum size of aggregate

9.5 12.5 19 25 37.5 50 75 150

Non-air entrained concret

25 to 50 207 199 190 179 166 154 130 113

75 to 1oo 228 216 205 193 181 169 145 124

150 to 175

243 228 216 202 190 178 160 -

Amount of air entrapped %

3 2.5 2 1.5 1 0.5 0.3 0.2

Water Contents

Cement ContentCement Material Content= Water Content W/CM

Minimum cement content may bespecified for the purpose of: –Durability –Finishability –Wear resistance –Appearance

Excessively high cementitious contents should be avoided for: –Economy –Avoid adverse effects

WorkabilityShrinkageHeat of hydration