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/CIVILISRARULHAQ 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.

Definitionthe 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 consideredWorkabilityPlacement conditionsStrengthDurabilityAppearanceEconomy

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

American methodBritish method

Steps For Mix DesigningACI 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 DesigningBRITISH METHODDetermining the Free Water/ Cement RatioDetermining the Free-water ContentDetermining the Cement ContentDetermining the Total Aggregate ContentDetermining of The Fine and Coarse Aggregate Contents

Coarse Aggregate RequirementGrading

Nature of particlesShapePorositySurface texture

Max Aggregate SizeCover between steel & form, C: Dmax

Max Aggregate Size(For pumped concrete)Dmax < 1/3 diameter of hose or 1-1/2 inch, whichever is smaller

Fineness Modulus of SandThe FM is calculated from particle size distribution of the sandValues should range between 2.3 to 3.1Coarse sand has a higher FM than fine sandFM influences the bulk volume of coarse aggregate

Air ContentThe amount needed depends on:Max aggregate size Less paste as size increases

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

Workability Requirements

Concrete ConstructionSlumpMaximumSlump MinimumReinforced walls & footings31Plain footings, caissons, and Substructure walls31Beams & reinforced walls41Columns41Pavements and slabs31Mass concrete31

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

Water Contents

Slump mmWater. Kg/m3 of concrete for idicated nominal maximum size of aggregate9.512.5192537.55075150Non-air entrained concret 25 to 5020719919017916615413011375 to 1oo228216205193181169145124150 to 175243228216202190178160-Amount of air entrapped %32.521.510.50.30.2

Cement ContentCement Material Content= Water Content W/CMMinimum cement content may bespecified for the purpose of: Durability Finishability Wear resistance AppearanceExcessively high cementitious contents should be avoided for: Economy Avoid adverse effectsWorkabilityShrinkageHeat of hydration