Sab 2112 - L9 Concrete Strength And Proportions

HARDENED CONCRETE

Concrete strength Compressive strength is the most important property of hardened concrete Concrete is used to carry compressive load Tensile strength of concrete is important to resist cracking from shrinkage and temperature changes

Cube Crushing Strength Ultimate compressive strength (N/mm2 or MPa) of concrete at failure

Characteristic Strength Strength in which not more than 5% of the cube has crushing strength lower than specified strength (fcu )

Concrete Grade A number to show the compressive strength of concrete the same as characteristic strength Example: Grade 40 – concrete has characteristic strength of 40 MPa at 28 days

CONCRETE MIX PROPORTIONS Nominal mix Prescribed/Standard mix Mix design

Nominal Mix Proportions according to the weight of the materials 1 : 2 : 4 or 1 : 1.5 : 3 Cement : Fine Agg. : Coarse Agg. Strength less than 30 MPa Need to specify w/c ratio

Example Concrete wet density = 2350 kg/m3 Mix proportions = 1 : 2 : 4 w/c ratio = 0.47 Calculate the amount of concrete constituents – Cement = ? – Fine aggregate = ? – Coarse aggregate = ? – Water = ?

Prescribed/Standard mix Concrete with specified strength has fixed mix proportions BS 5328 Clients specify: grade of concrete, workability, size of coarse aggregate Supplier: determine the actual mix proportions

Example Concrete Grade = 25 Slump = 75 mm Fine aggregate = Grading limit M Aggregate size = 20 mm Calculate the material proportions

Mix Design The purpose of the mix design is to determine the proportions of concrete constituents to produce an economical concrete with the required strength and durability.

Mix Design DoE Method ACI method Will be covered in Concrete Technology/Lab

Thank You