DEVELOPING A CONCRETE MIX DESIGN MANUAL FOR NIGERIA

DEVELOPING A CONCRETE MIX DESIGN MANUAL FOR NIGERIA ANALYSIS OF TEST RESULTSMatawal Danladi S.Ojo Emeso B.Gai Friday I.Adamu Isah K.Tyoden Juliana N.Chukwuma Gerald O.

CONCRETE RESEARCH GROUPCONCRETEConcrete is one of the most widely used construction materials It is a composite building material Widespread use of concrete Effectiveness, Cost and Performance for most construction works.Its ability to exhibit such properties is a function of the constituents as well as the proportions of these constituents. Can be designed for strength ranging from 10N/mm2 to 100N/mm2, making it an extremely versatile building material. The basic constituents remain the same, but it is their relative proportions that determine the properties.

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Concrete Mix DesignThe primary objective is to select suitable constituent materials and determine their required amounts in order to produce concrete of specific characteristics and properties as economically as possible. Major Characteristics Workability, Strength and Durability. Other characteristics include density, thermal characteristics, elastic modulus etc. Performance of concrete is dependent on the required performance of concrete in two states: the fresh/plastic and hardened states. 3

Constituent Materials - CementCement is the basic constituent material in concrete. Concrete is formed when cement creates a paste with water that binds with sand and gravel to harden.Significant Properties and Quality IndicatorsStrength ClassWater to Cement ratio

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Constituent Materials - AggregatesSignificant component of concrete which constitutes 70-80% of total volumeSignificant PropertiesSize of Aggregates: Fine and CoarseParticle Size DistributionSpecific gravityMaximum size of aggregatesNature of aggregatesWater absorptionShape of aggregates.

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ObjectiveTo develop a manual which provides a step by step procedure for carrying out mix designs for the various grades of concrete by deducing the appropriate quantities of materials required for each mix. 6

MethodologyAdoption of BRE Method (British Standards) as a baselineSeries of tests were carried out on major constituents: aggregates and cement to ensure conformity with British StandardsMix Design was carried out using the British Standards to ascertain required proportions for various concrete mixesSixteen cubes were prepared for each mixWorkability was verified for each mixCompressive Strength and Density was determined at various ages of concreteComparison of charts developed with BS charts

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Scope of ProjectMaximum Aggregate Size: 10mm and 20mmStrength class of cement: 32.5, 42.5 and 52.5Slump: 30-60mm and 60-180mmCompressive strength at different ages of concrete: 3, 7, 14 and 28 daysConcrete grade: 20, 25, 30, 35, 40 and 50Type of fine aggregate: stone dust and river sand

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Properties of Aggregate UsedTestValueSpecificationAggregate Impact Value %13.7245 (BS 882 )Aggregate Crushing Value %27.2945 (BS 882 )Flakiness %21.25 40 (BS 882 )Specific Gravity (Coarse Aggregate)2.672.3 2.9Absorption % (Coarse Aggregate)0.30.2 4 Specific Gravity (Fine Aggregate)2.452.3 2.9Absorption % (Fine Aggregate)0.260.2 - 2

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Sieve Analysis of Coarse aggregates 10

Sieve Analysis of Coarse aggregates 11

Combined Gradation of AggregatesAggregate Size mmProportions %Maximum size 10mmMaximum size 20mm0 -- 450.0045.004--850.0025.008--16--24.0016--20--6.0012

Properties of Cement Used13

32.5NTEST PARAMETERRESULT STANDARDREMARKSSpecific Gravity3.1NIS 444-1:2003 2.5SatisfactoryFineness %34.2Soundness (Expansion using le chatelier mould) mm0.75 NIS 444-1:2003 10mmSatisfactorySetting time: Initial setting time (mins) final setting time (mins)127NIS 444-1:2003 60mins 600minsSatisfactory185 2 day Compressive Strength N/mm223 7 day Compressive Strength N/mm237.216Satisfactory28 day Compressive Strength N/mm247.442.5RTEST PARAMETERRESULT STANDARDREMARKSSpecific Gravity3.12NIS 444-1:2003 2.5SatisfactoryFineness %24.9Soundness (Expansion using le chatelier mould) mm1 NIS 444-1:2003 10mmSatisfactorySetting time: Initial setting time (mins) final setting time (mins)142NIS 444-1:2003 60mins 600minsSatisfactory187Satisfactory 2 day Compressive Strength N/mm230.620Satisfactory 7 day Compressive Strength N/mm241.928-day Compressive Strength N/mm247.2Mix Design ProcedureStep 1: Determination of target mean strengthStep 2: Determination of Water-cement ratioStep 3: Determination of water contentStep 4: Determination of cement contentStep 5: Determination of aggregate content

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Mix Design Procedure15

Mix Design ProcedureStep 2: Determination of Water-cement ratio

Relationship between free water cement ratio and compressive strength of concrete for different cement strength (Adopted from BRE 2009)16

Mix Design ProcedureStep 3: Determination of water content

Maximum size of aggregate mmType of aggregateWater Content kg/m3Slump 0-10Slump 10-30Slump 30-60Slump 60-18010Uncrushed150180205225Crushed18020523025020Uncrushed135160180195Crushed17019021022540Uncrushed115140160175Crushed155175190205Approximate Free water contents required to give various levels of workability (Adopted from BRE 2009)17

Mix Design Procedure18

Mix Design ProcedureStep 5: Determination of aggregate content

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Production of Concrete Cubes21

Relationship between age of concrete and compressive strength of concrete: 32.5N22

Relationship between age of concrete and compressive strength of concrete: 32.5N23

Relationship between age of concrete and compressive strength of concrete: 42.5R24

Relationship between age of concrete and compressive strength of concrete: 42.5RIncrease of compressive strength with age of concreteCharacteristic strength of concrete was achieved by 7 days in most casesThe higher the 3-day compressive strength, the higher the 28-day compressive strengthAbout 70% of 28 day strength is achieved within the first three days; about 80% is achieved by seven days and 90% is achieved by 14 days25

True Slump Attained32.542.5Max Size of Aggt10mm20mm10mm20mmDesign Slump mm30-6060-18030-6060-18030-6060-18030-6060-1802030179.55177.55014925852540179.549.582.5451725313730431753560.54315546913527.59049.528531084571401018.55050561224649.550812nilnil4063nilnil26

Relationship between compressive strength and water cement ratio: 32.5N27

Relationship between compressive strength and water cement ratio: 32.5N28

Relationship between compressive strength and water cement ratio: 42.5R29

Relationship between compressive strength and water cement ratio: 42.5R30

Proposed Relationship between compressive strength and water cement ratio31

Conclusion/ RecommendationsFurther tests would need to be conducted to verify/adjust proposed chartsAggregates: Emphasize the need for combined gradation of aggregates and discourage the use of one size aggregates for construction in NigeriaControversy of recommendations of specific applications of cement based on strength class by SON may need to be revisited.Development of Software/model to aid in the mix design process32

3233Thank you for listening