Determination of Modulus of Elasticity Concrete


Objective: To ascertain the modulus of elasticity of concrete

Sample: Concrete calendar 15 cm diameter and 30 cm long

Process

Setting up of the Compressometer

(i) Assemble the top and base casing by keeping the spacers in position.

(ii) Put the pivot rod on the sinks and bolt them position.

(iii) Put the tightning screws of the base and top casing unscrewed (however not totally).

(iv) Place the example on a level surface.

(v) Keep the compressometer halfway on the sample so that the tightning screw of the base and top casing are at equivalent separation from the two closures.

(vi) Tighten the screws so that the compressometer is hung on the example.

(vii )Remove the spacers by unscrewing the spacer screws.

Test procedure

(I) Put the sample with compressometer in the compression testing machine and center around it.

(II)  Put the load incessantly devoid of stock at a rate of 140 kg /cm²/minute until a stress of (c+5)kg/cm² is obtained where c is the one third of standard compact strength of cubes computed to the closest 5kg /cm²(a load of 12.4T)

(III) Uphold the load at this stress for minimum of one minute and decrease steadily to an usual stress of 1.5 kg/ cm²(a load of 0.3 T)

(IV) Put the load once again at the same rate till the average stress of (c+ 1.5) kg/cm² is obtained(a load of 11.8T)

(V) Mark the compressometer reading at this load point

(VI) Lessen the load steadily and take readings at a period of 1T up to 0.3T(11.8T,10.8T,9.8T,8.8T,7.8T,…………,1.8T,0.3T)

(VII) Once again put the load for the third time and mark the compressometer readings at the time interval of 1T (0.3T,1.8T,2.8T,………….11.8T).

Note

  1. The readings have to be undertaken promptly
  2. If the in general strain witnessed on the second and third readings vary exceeding by 5%,the loading the loading has to be carried out again and again until the disparity in strain between successive readings of (c+1.5)kg/sq.cm. (11.8T) is not greater than 5%.
  3. To obtain the actual deformation, split the marked readings of the dial gauge by 2.

Graph

A load – deflection graph is then plotted for the loading and nu loading requirements. Now draw the tangents at the first segment of the loading curve and at the load matching to the working stress of the mix. Link the first point and the point on the loading curve equivalent to working stress.

Calculation

Initial tangent modulus = stress/ strain

(Take load & deflection from the initial tangent )

Tangent modulus at working stress= stress/ strain

(Take load and deflection from the tangent drawn at working stress)

Secant modulus = stress/strain

(Take load and deflection from the line joining initial point and the point at working stresses)

Report

The subsequent information has to be incorporated in the report.

(i) Identification mark

(ii) Date of test

(iii) Age of specimen

(iv)  Shape and nominal dimensions of the sample

Result

Initial tangent modulus of given concrete = ………………N / mm²

Tangent modulus at working stress =……………….N / mm²

Secant modulus (Modulus of elasticity of given concrete) = ………….. N / mm²