Tests of Hardened Concrete in Tension
Source: Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA
In a previous laboratory focused on concrete in compression, we observed that concrete can withstand very large stresses under uniaxial compressive forces. However, the failures observed were not compressive failures but failures along shear planes where maximum tensile forces occur. Thus, it is important to understand the behavior of concrete in tension and particularly its maximum strength as that will govern both its ultimate and service behavior. From the ultimate standpoint, combinations of tension and shear stresses will lead to cracking and immediate and catastrophic failure. For that reason, concrete is seldom if ever used in an unreinforced condition in structural applications; most concrete members will be reinforced with steel so that these cracks can be stopped and the crack widths limited. The latter is important from the serviceability standpoint because controlling crack widths and distribution is the key to durability, as this will impede deicing salts and similar chemicals from penetrating and corroding the reinforcing steel.
The objectives of this experiment are threefold: (1) to conduct tensile split cylinder tests to determine concrete tensile strength, (2) to conduct beam tests to determine concrete tensile strength, and (3) to demonstrate the influence of steel reinforcement on behavior by comparing the behavior of lightly reinforced beam with an unreinforced one.
1. Split Tension Test
- For this test, use the sample cylinders that were previously prepared (see JoVE video “Tests on fresh concrete”). Obtain two thin strips of balsa wood or similar (about 1/8” thick x 1” wide x 8’ long) to help distribute the loads on the cylinders.
- Measure the dimensions of the two cylinders. Draw a line along the diameter on each end of the specimen bisecting the c
The tensile strength for the maximum compressive load reached during the split tensile test is given by the following formula:
ft = 2Pmax/ (πDL)
where D is the diameter (inches), L is the length (inches), and Pmax is the maximum compressive load (lb.) reached during the tensile test. For these tests, the average was 388 psi with a standard deviation of 22.2 psi (Table 1).
