4.2. Prueba de hipótesis
4.2.4. Hipótesis específico 3
1. The texture of a concrete surface may indicate the possibility of a chemical attack and associated disintegration by leaching.
2. In fire damaged structure, the colour of the concrete gives an indication of maximum temperature level to which the surface had been subjected.
B. Worksheet
The visualinspection shall largely cover:
1. Recording of
l Areas of high distress ;
l Cracks & their location ;
l Excessive deflection ;
l Exposure conditions of various distressed areas ;
l Moisture, leakage/ seepage & dampness locations ;
l Abnormal vibrations in structure, if any ;
l Algae, fungus growth and/or efflorescence etc and their locations ;
l Photographic records, and
2. Identifying the areas of immediate concern.
Visual inspection would be documented in the form of Worksheets , photographic record etc for reference at a later date. Each worksheet shall : 1. Have unique identification for each of the structural members of the building
covered by it.
2. Essentially cover the following in regard to observed defects:
l Location,
l Classification, and
l The extent of spread.
LONGITUDINAL CRACKS POP-OUTS
AS CAST
DELAMINATION SPALLING RADIAL FRACTURE STRAINS
AND CRACKS INSTALLATION
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3. Have notations for recording different types of defects, which could be suitably evolved by the rehabilitation engineer before taking up the condition survey. The suggested notations used for recording the defects on Work Sheets are given in Appendix 3.2
The Worksheets (Fig. 3.5), besides being helpful in analysis for arriving at the cause of distress, would also be helpful for working out Bill of Quantities at a later date.
All the defects noticed during visual examination are required to be plotted on Work sheet for a subsequent detailed study in combination with tabulated field &
lab test results in proforma as per Appendix-3.3. This is necessary for determining the cause of deterioration.
The information obtained from visual inspection will determine whether there is need for further comprehensive investigation using more sophisticated testing techniques.
Visual inspection is, therefore, the best way of qualitative assessment of any structure.
3.1.3.4 Field/Laboratory Testing stage : Objective :
1. It may neither be feasible nor is the practice to conduct field/laboratory testing on every structural member in an existing distressed building.
2. The field/laboratory testing of structural concrete and reinforcement is to be undertaken, basically for validating the findings of visual inspection.
3. These may be undertaken on selective basis on representative structural members from each of the various groups based on exposure conditions as explained in the preceding sections.
4. The programme of such testing has to be chalked out based on the record of visual inspection.
Fig.-3.5 A Typical Work Sheet
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Table 3.4 gives the list of test methods that could be deployed for field/Laboratory testing during the course of investigations. A typical format for tabulation of the field test results/
observation is given in Appendix-3.3. NDE tests are frequently adopted during the process of condition survey
Table 3.4 : Principal Test Methods
(Source: Testing of Concrete in Structures by J H Bungey et al)
Property under Test Equipment type
investigation
Corrosion of Half Cell potential Electrochemical
embedded Steel Resistivity Electrical Concrete quality, Surface hardness Mechanical durability and Ultrasonic pulse velocity Electromechanical
deterioration Radiography Radioactive
Cement type and content Chemical/microscopic
Abrasion resistance Mechanical
Strain or crack measurement Optical/mechanical/electrical
Load test Mechanical/electronic/electrical
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3.1.4 Considerations for Repair Strategy :
In the Condition Survey Report, before arriving at the Repair Strategy, it shall include the following considerations:
1. Identification of the cause of problem and its source is the fundamental to the success or failure of the repair. A lack of attention at this point can put at risk the whole job.
2. For arriving at an effective and economical solution, systematic documentation of all observations is essential, which will greatly facilitate in diagnosing and making assessment of the extent of damage.
3. Available space and accessibility will determine the selection of repair method and repair strategy.
4. Accessibility to the areas identified for repairs needs consideration.
5. Depending upon the scope and scale of repairs, the repair strategy has to suit and dovetail the on-going activities in the building.
6. The prioritization of repairs and their sequencing are important components for deciding the repair strategy.
7. Major repair procedure may demand propping the structural members to relieve a part or full component of the load acting on the member. If the building requires extensive propping, vacating the building may become the pre-requisite.
8. Safety measures to prevent any immediate major mishap shall be prescribed without loosing further time.
9. The report should also include requirements on safety measures to be adopted during execution of repair jobs.
More experienced engineers should look in to special and peculiar distress problems For example, micro cracking or some other subtle defect could be the cause of carbonation and corrosion. Carrying out repairs to corrosion distress, missing the main cause, may simply mean that the problem recurs in a relatively short duration.
3.2 NON DESTRUCTIVE EVALUATION TESTS :
A number of non-destructive evaluation (NDE) tests for concrete members are available to determine in-situ strength and quality of concrete. Some of these tests are very useful in assessment of damage to RCC structures subjected to corrosion, chemical attack, and fire and due to other reasons. The term ‘non destructive’ is used to indicate that it does not impair the intended performance of the structural member being tested/investigated. The non-destructive evaluation have been broadly classified under two broad categories viz ‘in-situ field test’ and ‘laboratory test’. These tests have been put under five categories depending on the purpose of test as under :
1. In-situ Concrete Strength 2. Chemical Attack
3. Corrosion Activity 4. Fire Damage
5. Structural Integrity/Soundness
Various non destructive evaluation tests commonly used under each of these categories have been listed out in Table 3.5 as under :
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Table 3.5 : Commonly Used NDE Tests
Sl No Test Method Details
A. Insitu Concrete Strength:
1 Rebound Hammer Test A qualitative field test method to measure surface hardnessof concrete
2 Ultrasonic Pulse Velocity A qualitative field test by measurement of Ultrasonic Pulse Velocity (UPV)
3 Windsor Probe A qualitative field test for assessment of near surface strength of concrete
4 Capo/Pull out test
-do-5 a. Core cutting/ sampling
b. Lab Testing of Cores Field cum lab test method for assessing quality of concrete as under:
- strength - density - texture - permeability
6. Load Test A field test for assessing the load carrying capacity within the limits of elastic deformations
B. Chemical Attack
1 Carbonation Test A field/lab test for assessment of pH of concrete and depth of carbonation
2 Chloride Test A field/lab Test for assessment of total water/acid soluble chloride contents
3 Sulphate Test A Lab Test for assessment of total acid/water soluble sulphate contents of concrete
C. Corrosion Potential Assessment
1 Cover-Meter / Profo-meter A field method for measuring measurement -thickness of cover concrete (In-situ Test) -reinforcement diameter
-reinforcement spacing.
2 Half Cell Method A field method for Measuring/ plotting corrosion potential for assessing probability of corrosion
3 Resistivity Meter A field method for assessing electrical resistivity of concrete to determine its corrosion resistance
4 Permeability a. Water
b. Air A field/Lab method for assessment of in-situ permeability of concrete due to water and air.
D. Fire Damage Assessment
1 Thermo-Gravimetric A laboratory test for assessment of temperature Analysis (TGA) range to which concrete was subjected to 2 Differential Thermal A laboratory Test for assessment of qualitative
Analysis (DTA) & quantitative composition of sample of concrete 3 X-ray Diffraction (XRD) To determine the extent of deterioration in concrete
subjected to fire E. Structural Integrity/Soundness Assessment
1 Ultra-sonic Pulse velocity A field method for determination of Method discontinuities, cracks and depth of cracks
2 Radiography For taking photographs showing details of inside of a concrete member, where other NDE methods are not suitable 3 Impact Echo Test A field/laboratory test method to detect hidden damage
andits extent.
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3.2.1 Concrete Strength Assessment : A. Objective:
1. Generally, in-situ non-destructive evaluation of concrete is to have an overall idea of the quality of concrete.
2. In some cases, a sufficiently accurate estimate of quantitative value of concrete strength is required for assessment of load carrying capacity of a structural member. The need for such an estimate may arise during evaluation of change in usage of structure, modification or extension of the original structure or damage due to fire, earthquake, etc.
3. Core cutting /sampling method, as at sl no 5 in Table 3.5 above, is done by extracting the concrete cores from the beams/columns/slab or any other structural members to determine the residual insitu strength, density & porosity /permeability of concrete in laboratory. This test, being semi destructive, is also time consuming. Hence it is used selectively in combination with other NDE qualitative test results, so as to validate and calibrate such other qualitative test methods used more commonly.
B. Limitations:
The accuracy is not very high as most of the non-destructive methods of evaluation of concrete strength are based on indirect measurement of concrete strength.