Comparison of Non-Destructive Test Methods for Concrete Compressive Strength in Existing Structures

Estimates of in-place strength for the structural evaluation of concrete structures is a required element of a modern repair/rehabilitation project. Although in-place cores are the most direct method for determining concrete compressive strength, economy of both time and money, has lead to the development of other test methods in determining in-place concrete compressive strength . This has also allowed more tests to be taken for a significant increase in the confidence with the quality of the existing concrete.

However, different tests have different limitations and uses. These need to be fully understood before the test program starts, so that the correct test is used for the correct application. This article will review the most common test methods for in-place concrete compressive strength testing: coring, the Windsor Probe™, the Windsor Pin™, manual test hammer, and the digital test hammer

Test Method	Compressive Strength Range*	Coeeficient of Variation	Notes
Coring	Unlimited	N/A	Expensive Provides Indisputable Benchmark Data Low Number of Tests Possible Due to Sturctural and Aesthetic Integrity Issues
WindsorProbe™	17000PSI | 110 MPa	>10% Typical	Relatively Inexpensive Widest Range of Compressive Strength of Non-Destructive Test Instruments Large Number of Tests Possible for Statistical Analysis Possible Aesthetic Issues
WindsorPin™	5300 PSI | 36.9 MPa	>12% Typical	Very Inexpensive Ability to Test Wider Range of Materials No Aesthetic Issues Large Number of Tests Possible for Statistical Analysis Low Maximum Strength
Manual ReboundHammer	9000PSI | 62 MPa	>18% Typical	Least Expensive Surface Preparation May be Required Most Variable Rapid Test Ability to Take Large Amount of Data for Statistical Analysis Tedious Calculations Need to Be Done
Digital Rebound Hammer	9000PSI | 62 MPa	>18% Typical	Low Cost Surface Preparation May be Required Most Variable Rapid Test Ability to Take Large Amount of Data for Statistical Analysis Calculations are Done Automatically

* As related to 150mm ( 6 inch ) x 300mm ( 12 inch ) cores, to convert to concrete cubes multiply by 1.1

Coring:

Typical 'Destructive' test method for concrete compressive strength. Cost in both time, money and structural and aesthetic integrity of the structure hs lead to the development of 'Non Destructive' Tests.

WindsorProbe™

This is most effective Non Destructive Test, with adherents and practitioners around the globe. The wide range of concrete compressive strength that can be tested as well as the simplicity and rapidity of it's use has contributed to the test popularity. It uses a powder actuated charge to drive a pin into the concrete under test. The depth of penetration of the pin corresponds to the compressive strength of the material under test.

Windsor Pin™

Using resistance to penetration with a high tensile steel spring this test method can not only test concrete, but brick, mortar, masonry and more! A low coefficient of variation, rapid and simple to use, this test has adherents around the globe. The only limitation is the maximium compressive strength that can be tested.

ManualRebound Hammer

The most popular test method. This is very simply to use and almost no cost. Drawbacks are the high coefficient of variation and the significant amount of tests needed to be taken in order to determine the result.

DigitalRebound Hammer

This method supplements the manual test hammer by using modern digital electronics to record and manipulate the large amount of data needed to effectively use the rebound test hammer method.