In this PDH or CE course student will learn concrete repairing mainly includes removing unsound concrete and replacing it with repair or overlay materials. One of the key requirements for any kind of repair system is to have adequate bond strength between the existing concrete substrate and overlay throughout the service life. When a repair is performed, the differences in the properties of two materials will affect bond strength and stress distribution. Of particular relevance are differences in shrinkage, elastic modulus and thermal movement.
The repair system can be considered as a three phase composite system: substrate, overlay and bond zone. Bond zone here refers to the interface and vicinity of bond plane. The bond zone must be capable of withstanding the stresses imposed on the system. Different factors have effects on the bond strength and its integrity.
The quality assurance of bond strength requires test methods that can quantify the bond strength as well as identify the failure mode. There have been numerous investigations led to development of different test methods. The forces which are applied in each test and the failure mode are important in order to choose the proper test. Tests are defined both in laboratory and field. An interpretive study on test methods is presented which classifies and compares the tests based on the applied force, failure mode and practical importance of each test.
As the failure modes are either in tension or in shear, two test methods are more applicable; first one is “Pull off test” which is a tensile test and it can be performed both in situ and in the lab. The simplicity and accuracy of the test has made it the most popular test method in projects. The second one is “slant shear test”, which has the shear failure mode and it can be done only in the lab. The so called Twist off test is a relatively new test method to appraise the bond strength in the interface. The advantage of the test is the possibility to perform it in the construction site. The test still needs further developments.
In this PDH or CE course the learning objective are:
Franco F. Davati, P.E.Review the quiz before studying the course.
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