Determination of the Tensile Young’s Modulus
To measure the tensile modulus, the tensile force is applied to the specimen at strain intervals of 1 0 × 1 0− 6. In order to prevent failure of specimen, the maximum strain during the test is set at 6 0 × 1 0− 6. Since the plastic strain of concrete at early age may comprise a high percentage of the total strain measured, the tensile modulus is obtained from the unloading branches of the stress-strain relation as shown in Figure 4. The slope of the unloading branches after the specimen was loaded to 1 0 × 1 0− 6, 2 0 × 1 0− 6, and so forth, is determined and averaged to obtain the tensile modulus of the specimen. The force is measured twice at each strain level using a load cell with an accuracy of 0.1 kN and capacity of 200 kN. As will be discussed later, the maximum residual strain after unloading of each specimen was measured as 3 × 1 0− 6. In each case, concrete and mortar specimens were made from the same batch using the sieving procedure mentioned above.