Non-Destructive Methods Of Testing Concrete Strength
Over the years non-destructive test methods have been developed to determine an estimated the strength of concrete.
4 Non-Destructive Methods Of Testing The Strength Of Concrete
Pull Out Test
The pull-out test is generally used for early diagnosis of possible strength issues. However, it can be used as a valuation method to test the strength of concrete in existing erections. Pull out testing is done by attaching a small piece of equipment to the exterior screw, nut, bolt or fixing after which it is pulled to the designated stress load point to ascertain how secure and robust the structure is.
- The Advantage of pull-out testing – If the relationship to strength is determined, the method can deliver stout test results.
- The Disadvantage of pull-out testing – It involves the squashing and damaging of concrete.
The idea is to measure the rebound of a spring driven hammer mass after it impacted with concrete. This test has been used extensively since 1948. It is a popular method due to the simplicity and the convenient use for field applications. Rebound hammer is applied to evaluate surface hardness. This test method is standardized through ASTM C 805 and to use it for estimating strength it is required to establish a relationship between strength and rebound number for the given apparatus and concrete. The relationship can be found by correlating rebound numbers which are measured on the structure with the measured strengths of cores taken from the subsequent locations.
- The Advantage of rebound hammer testing – It is suitable to use for most field applications and the test can be applied to evaluate the uniformity of concrete.
- The disadvantage of rebound hammer testing – The method is biased as surface condition; presence of sub-surface voids and the presence of rebar can influence test results.
Ultrasonic Pulse Velocity (UPV)
Ultrasonic Pulse Velocity is a preferred method for detecting impairments in structural components and quality control of concrete materials. Due to modern progression in transducer technology, the test has been extensively accepted in testing of concrete materials. The concept involves measuring of the travel time of acoustic waves in an agent and comparing them to density and elastic properties of the material. Travel time of ultrasonic waves is a reflection of the internal condition of the test area.
- The Advantage of UPV testing – It can be used for detection of sub-surface deficiencies.
- The Disadvantage of UPV testing – The method is subjective to the presence of voids, cracks, and rebar and there are not enough results to establish the reliability of this method in the field.
Combined methods include a combination of the above-mentioned methods for estimating the on-site strength of concrete. Several researchers have evaluated the combination of Rebound hammer and UPV. The mixed concrete methods can often deliver more thorough results. To improve the accuracy of strength estimation is by considering these factors:
- Type of cement
- Cement content
- Petrologic aggregate type
- Fine aggregate fraction
- Aggregate maximum size
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