Properties of concrete Topic MIX DESIGN OF CONCRETE

Properties of concrete Topic : MIX DESIGN OF CONCRETE

Properties of concrete Submitted To: DR. AYUB ELAHI Submitted By: SOHAIB NASEER M. ZAEEM FAKHAR ISRAR–UL–HAQ AWAIS ULLAH BILAL RIAZ 2 K 9 -scet-29/CIVIL 2 K 9 -scet-03/CIVIL 2 K 9 -scet-30/CIVIL 2 K 9 -scet-31/CIVIL 2 K 9 -scet-59/CIVIL

INTRODUCTION Concrete 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.

INTRODUCTION The 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 Mixtures Factors 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. Ø American method Ø British method

Steps For Mix Designing ACI 1. 2. 3. 4. 5. 6. 7. 8. METHOD Choice of slump Choice of max. Size of aggregates Estimate of water and air contents Selection of water cement ratio Calculation of cement contents Estimate of coarse aggregates content Estimate of fine aggregates content Adjustments to mix proportion

Steps For Mix Designing BRITISH 1. 2. 3. 4. 5. METHOD Determining the Free Water/ Cement Ratio Determining the Free-water Content Determining the Cement Content Determining the Total Aggregate Content 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 <3/4 C Spacing between bars, S: Dmax <3/4 S 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 Content The 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 Slump Maximum 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 Ø Range of w/c= 0. 45 to 0. 65 Ø For mix design of Ø 1: 2: 4 Ø The w/c is standardized as 0. 5

Water Content Water demand is influenced by: Ø Slump requirement Ø Aggregate size Ø Aggregate shape Ø Air content Ø Cementing materials content Ø Temp Ø Admixtures

Water Contents Slump mm Water. Kg/m 3 of concrete for idicated nominal maximum size of aggregate 9. 5 12. 5 19 25 37. 5 50 75 150 25 to 50 207 199 190 179 166 154 130 113 75 to 1 oo 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 Non-air entrained concret

Cement Content Cement Material Content= Water Content W/CM Minimum cement content may be specified for the purpose of: –Durability –Finishability –Wear resistance –Appearance Excessively high cementitious contents should be avoided for: –Economy –Avoid adverse effects Workability Shrinkage Heat of hydration