Thursday, 2 June 2016

Assessment of concrete strength in existing structures: Why

Hi everyone. Today I will present an introductory overview of my research project. My research is related to the assessment of concrete strength in existing structures. My today's discussion will be based on answering the question why assessment is required. I will also add how the concept grew and developed over time. 

Concrete is the most widely used construction materials all over the world, we all aware of that. But concrete properties varies from sample to sample. Concrete is generally composed of aggregate, cement, and water. Properties of constituting materials along with their mixing ratio play important role in determining final mechanical properties of concrete. Placement of concrete, environmental condition, and quality control during each operation also contribute to final property of concrete. All of these factors lead to the variability in concrete property. 

We sometimes hear about the collapse of different structures. These collapses result tragic loss of lives as well as economy. Most of these collapse occurs during construction and operation of the structures. Again, earthquake is continuously threatening in many parts of the world. Most of the old structures were not built considering the threats of earthquake. With the advancement of knowledge and technology, earthquake and other environmental loading is more clear to us. On the other hand, existing structures sometimes undergo structural modification. A structure can be subjected to changed loading condition. All these factors lead to the assessment of capacity evaluation of the structures. Moreover, with the progress of time, people are  focusing on how to make the most use of limited resources. So, extending life time of existing structure has gained special attention in recent years. It is now preferred to retrofit the old structures rather than demolishing and rebuilding. So, assessment becomes necessary to evaluate the performance of existing structures. Strength of concrete plays important role in carrying out accurate assessment of the structures. 

Testing in concrete structures is a century old practice. The testing began with the implementation of Brinell hardness method for concrete and cement paste. Later on several testing methods has been developed over time. These tests is carried out in existing structures without damaging original structures. That is why they are known as non-destructive tests. Non-destructive tests (NDTs) for compressive strength estimation of concrete allows the concrete to be tested without any damaged or creating any adverse effect on the structural integrity in concrete structure. 

With the help of NDTs, measurement can be performed directly on the structural concrete. Among the commonly used NDTs, some tests are completely non-destructive and some are partially destructive. Partially destructive tests offer some damage on the surface of concrete but they do not affect the structural integrity. Rebound hammer test, ultrasonic pulse velocity (UPV) test, resonance frequency test, and maturity test are completely non-destructive. Partially destructive tests include pull out test, cut and pull out (CAPO) test, penetration resistance test, break off test, and pull off test. All of these tests are generally classified as non-destructive tests.

NDTs are influenced by different properties of concrete and its constituting materials, and several factors related to the environment. NDTs provide indirect approach for compressive strength estimation of concrete. NDTs generally assess the easily measureable properties of concrete. Measured value is then related to uniaxial compressive strength. Efficiency and quality of strength estimation depend on the sensitivity of strength to the tests, measurement error and range of variation of test results as compared to the variation of strength. Being influenced by several factors, NDTs provide compressive strength of concrete within their own limitations which result in high degree of uncertainty. This uncertainty in strength estimation in turn results in poor evaluation of existing concrete structure.

We do not want to live in dark in present time especially in time of science and technology. So, the project focuses on the reduction in uncertainty in assessing the strength concrete. Hope, this clears the query. See you soon with more insights.

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