TYPE OF CONCRETE HARDENED TEST

TYPE OF CONCRETE HARDENED TEST

1. Compressive Strength Test

The compressive strength test measure the compressive strenth of concrete. Refer IS 516(1959) Page No. 11.

2. Split Tension Test

The split-tension test measures the tensile strength of concrete. Refer IS 5816 (1999).

3. Flexure Strength Test

The flexure strength test (ASTM C78) is important for design and construction of road and airport concrete pavements. It's used to measure the flexure strength of concret.
Refer IS 516(1959).

4. Rebond Hammer Test

The rebound hammer test, also known as the Schmidt hammer test, is a nondestructive test performed on hardened concrete to determine the hardness of the surface (Figure 1). The hardness of the surface can be correlated, to some extent, with the concrete strength. The rebound hammer is commonly used to get an indication of the concrete strength. The device is about 0.3 m (1 ft) long and encloses a mass and a spring.

The spring-loaded mass is released to hit the surface of the concrete. The mass rebounds, and the amount of rebound is read on a scale attached to the device. The larger the rebound, the harder is the concrete surface and, therefore, the greater is the strength. The device usually comes with graphs prepared by the manufacturer to relate rebound to strength. The test can also be used to check uniformity of the concrete surface.

Fig 1. Rebound hammer for nondestructive evaluation of hardened concrete.

The test is very simple to run, and is standardized by ASTM C805. To perform the test, the hammer must be perpendicular to a clean, smooth concrete surface. In some cases, it would be hard to satisfy this condition. Therefore, correlations, usually provided by the manufacturer, can be used to relate the strength to the amount of rebound at different angles. Rebound hammer results are also affected by several other factors, such as local vibrations, the existence of coarse aggregate particles at the surface, and the existence of voids near the surface. To reduce the effect of these factors, it is desirable to average 10 to 12 readings from different points in the test area.

Refer IS 13311-1 (1992)

5. Penetration Resistance Test

The penetration resistance test, also known as the Windsor Probe test, is standardized by ASTM C803. The instrument (Figure 2) is a gunlike device that shoots probes into the concrete surface in order to determine its strength. The amount of penetration of the probe in the concrete is inversely related to the strength of concrete. The test is almost nondestructive since it creates small holes in the concrete surface.

The device is equipped with a special template with three holes, which is placed on the concrete surface. The test is performed in each of the holes. The average of the penetrations of the three probes through these holes is determined, using a scale and a special plate. Care should be exercised in handling the device to avoid injury. As a way of improving safety, the device cannot be operated without pushing hard on the concrete surface to prevent accidental shooting. The penetration resistance test is expected to provide better strength estimation than the rebound hammer, since the penetration resistance measurement is made not just at the surface but also in the depth of the sample.

Fig. 2 Windsor probe test device.

6. Ultrasonic pulse Velocity Test

The ultrasonic pulse velocity test (ASTM C597) measures the velocity of an ultrasonic wave passing through the concrete (Figure 7.39). In this test, the path length between transducers is divided by the travel time to determine the average velocity of wave propagation. Attempts have been made to correlate pulse velocity data with concrete strength parameters. No good correlations were found, since the relationship between pulse velocity and strength data is affected by a number of variables, such as age of concrete, aggregate–cement ratio, aggregate type, moisture condition, and location of reinforcement (Mehta and Moneiro, 2005). This test is used to detect cracks, discontinuities, or internal deterioration in the structure of concrete.

Fig. 3 Ultrasonic pulse velocity test 

7. Maturity Test

Maturity of a concrete mixture is defined as the degree of cement hydration, which varies as a function of both time and temperature. Therefore, it is assumed that, fora particular concrete mixture, strength is a function of maturity. Maturity meters (Figure 5) have been developed to provide an estimate of concrete strength by monitoring the temperature of concrete with time. This test (ASTM C1074) is performed on fresh concrete and continued for several days. The maturity meter must be calibrated for each concrete mix.

Fig. 4 Ultrasonic pulse velocity apparatus

Fig. 5 Checking the maturity of fresh concrete using the maturity meter.