MRS Module 3
MODULE 3
1. Explain the service and exposure conditions of concrete?
Exposure Conditions Based on IS 456
There are five levels of environmental exposure of concrete upon which the durability requirements of concrete are based. Mild, moderate, severe, very severe, and extreme exposure are different exposure categories established by the Indian standards based on the environment. Table-1 explains each exposure condition along with its description of the environmental conditions.
Table-1: Environment and Exposure Conditions Based on Indian Standard
| Environment | Exposure Conditions |
| Mild | Concrete surfaces protected against weather or aggressive conditions, except those situated in coastal areas. |
| Moderate | Concrete surfaces sheltered from severe rain or freezing while wet, concrete exposed to condensation and rain, concrete in contact, or buried under non-aggressive soil/groundwater. |
| Severe | Concrete surfaces exposed to severe rain, alternate wetting and drying, or occasional freezing while wet or severe condensation. |
| Very severe | Concrete completely immersed in seawater, concrete exposed to the coastal environment, concrete surfaces exposed to seawater, corrosive fumes, or severe freeing conditions while wet. |
| Extreme | Concrete in contact with or buried under aggressive sub-soil/groundwater, the surface of members in the tidal zone, members in direct contact with liquid/solid aggressive chemicals. |
2. Elaborate the steps of condition assessment of concrete structures ?
simplified terms, structural condition assessment consists of activities of visual observation, measuring, photographing, probing and sampling, field and laboratory testing, engineering analyses, record keeping, documentation, and report preparation.a) Reviewing available information on the building. b) Conducting a condition survey of the building. c) Determining the cause and rate of progression of existing distress. d) Determining the degree of repair required.
Preliminary Condition Assessment
During the preliminary condition assessment, we can help customers with:
- Study of Documents and Existing Evidence
- Preliminary Site Assessment –Visual Inspection,Monitor and Identify Sign of Structural Damage ,Identify deterioration mechanisms ,Identify the building use and deviation from original intended use
- Preliminary numerical analysis
- Reporting
- Decision on Immediate Actions
- Recommendation for Detailed Assessment
Detailed Condition Assessment
- Detailed Document Search and Review
- Systematic and Scientific Examination of Building
- Materials Testing
- Non-Destructive Testing
- Intrusive Methods
- Structural Analysis, and Assessing Compliance with NBCC
- Report and Repair Recommendations
Non-Destructive Tests
- Ground Penetrating Radar
- Ultrasonic Pulse Velocity
- Rebound Test
- Ultrasonic Pulse Echo and Ultrasonic Tomography
- Impact-Echo Test
- Infrared Tomography
- Surface Electrical Resistivity of Concrete
- Half-Cell Corrosion Potential Mapping
- In-Place Evaluation of Concrete Strength
Intrusive Tests
- Extracting Concrete Cores and Asphalt Sawn Samples
- Determine Chloride Content and Chloride Profile
- Determine Air Void Content in Concrete
- Evaluate Concrete Compressive Strength
3. How to conduct visual inspection in concrete structures ?
A very useful tool for crack inspection is a small hand-held magnifier with a built-in measuring scale on the lens closet to the surface being viewed. With such a crack compactor the width of surface opening cracks can be measured accurately. Identification of cracks in a concrete structure is given in table
4. Explain the aspects of deciding whether to preserve, repair or demolish the concrete structures ?
First, ask yourself if you can restore it to its original integrity. Consider how deteriorated the concrete actually is. Is there spalling, which refers to exposed aggregate on a concrete structure? If so, the concrete will likely have to be replaced.
5. Elaborate the test methods for concrete evaluation.
- Penetration method –The Windsor Probe is generally considered to be one of the best means of testing penetration depth of concrete. The probe is a powder actuated gun or driver with a hardened probe and a depth gauge.
- Rebound hammer method –A rebound hammer (or a Schmidt Hammer) is a surface hardness tester consisting of a spring controlled hammer which is forced against the surface and the rebound distance is then measured on a scale.
- Pull out test method –The pull out tests involved a specially shaped steel rod which has been pre-cast into the concrete, which then uses a special ram to measure the force required to pull the rod from the concrete. This method can of course cause damage, but typically will be done to reach a threshold of minimum force before damage is caused.
- Ultrasonic pulse velocity method and Ultrasonic pulse echo technology –This technology either measures the speed of an ultrasonic pulse through concrete, using a probe on either side of the test specimen to send and receive the signal (in the pulse velocity method) or uses an echo scanner probe which is sent in and received on the same side from echo signals. Typically ultrasonic pulses will either fully reflect when a void, crack or spall is detected or at the very least change in speed considerably enough to highlight defects.
6. Explain the process of locating Delaminated concrete ?
Delamination’s can be identified when you get to hear a drummy sound or loud clack rather than the clear ringing sound when the metal hits robust concrete. If you will use the hammer to tap around this spot you will identify more hollow-sounding areas. This can be termed as surface delamination in the concrete floor.
7. Explain the Ultrasonic pulse velocity test ?
Ultrasonic pulse velocity (UPV) test means to assist the transit time of ultrasonic pulses with 50–58 kHz, created by an electroacoustical transducer and passing from one surface of the element to the other. The transit time of ultrasonic pulses depends on the density and elastic properties of the material tested.
13. Elaborate various challenges associated with concrete assessment.
Non-destructive testing methods are used to evaluate concrete properties by assessing the strength and other properties such as corrosion of reinforcement, permeability, cracking, and void structure. This type of testing is important for the evaluation of both new and old structures.
8. Explain the process of the rebound hammer test ?
When the plunger of rebound hammer is pressed against the surface of the concrete, the spring- controlled mass rebounds and the extent of such rebound depends upon the surface hardness of concrete. The surface hardness and therefore the rebound is taken to be related to the compressive strength of the concrete.
9. Explain water sorptivity test
The water sorptivity test is a unidirectional absorption test. A 68-mm-diameter core is coated around its circumference with epoxy ( 12.36) and placed in a tray with solution of water and Ca(OH)2 in order to measure the rate of water uptake into the cylinder by capillary rise. This test is performed to determine the susceptibility of an unsaturated concrete to the penetration of water. It measures the rate of absorption of water and other liquids into unsaturated concrete through capillary suction.
10. Explain methods of strength evaluation concrete structures ?
The most common method for monitoring the strength of in-situ concrete is the use of field-cured cylinders. This practice has remained generally unchanged since the early 19th century. These samples are cast and cured according to ASTM C31 and tested for compressive strength by a third-party lab at various stages.
11. Explain the microstructural assessment of concrete ?
Concrete has a heterogeneous microstructure, which consists of three components, namely, cement paste, pore structure, and interfacial transition zone between the cement paste and aggregates. Improving these three components leads to enhance mechanical strength and durability of concrete.
12. Explain the significance of non destructive testing of concrete ?
Non-destructive testing methods are used to evaluate concrete properties by assessing the strength and other properties such as corrosion of reinforcement, permeability, cracking, and void structure. This type of testing is important for the evaluation of both new and old structures.