Development of Inspection Method with Partial and Small-Scale Destruction for Concrete Structures
Final Presentation
5 August 2009
Achfas ZACOEB
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1 Outline of the Presentation
1. Introduction
2. Literature Review
a. Concrete Strength Assessment
b. Concrete Damage Detection
a. Basic Theory
b. Experimental Outline
c. Results and Discussion
a. Imaging of Concrete
b. Outline and Specification
c. Performance and Verification
5. Outlook of Field Application
6. Concluding Remarks
2
Introduction
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The direct determination of the strength of concrete implies that concrete specimens must be loaded to failure and requires special specimens to be taken, shipped, and tested at laboratories. This procedure may result in the actual strength of concrete, but may cause trouble and delay in evaluating existing structures. Because of that, special techniques have been developed in which attempts were made to measure some concrete properties other than strength, and then relate them to strength, durability, or any other property.
Testing the core specimen extracted from a structure is the most
reliable method for determining the concrete strength, including that
at different distances from the surface. Cores usually have no
standard dimensions, especially in height-to-diameter ratio which
impairs the reliability of the result.5 (cont.) . #
A more direct assessment on strength can be made by core sampling and testing. Cores are usually cut by means of a rotary cutting tool with diamond bits. In this manner, a cylindrical specimen is obtained, usually with it ends being uneven, parallel and square and sometimes with embedded pieces of reinforcement. The cores are visually described and can be used for the following test such as strength and density determination, depth of carbonation, chemical analysis, water/gas permeability, petrographic analysis, and chloride permeability. Although the method consists of expensive and time consuming operations, cores give reliable and useful results since they are mechanically tested to destruction (Neville, 1981).
6
(cont.) . #
The method of core testing is very popular. In the USA the diameter
of the cores is usually 10 - 28cm, cores with a diameter of 10 -
15cm are used in Sweden and Norway. In Japan cores are used
when the maximum size of coarse aggregate is up to 50mm, but
when the maximum size is 150mm or more, the coring method
becomes inapplicable on a large scale, since the diameter of the
cores would have to be greatly increased.Typically cores will be 100mm in diameter, and should ideally be at
least three times the maximum aggregate size of G in diameter. max7 .
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2 d P
I S = where,
I S : Point load index (MPa)
P : Load (N) d
: Core diameter (mm) This figure can be used as conceptual model for derivation on Equation:
2
4 d P
I S π =
Point Load Test 7 < * " '8).
11 Basic Theory
By taking the circular area of the core into account, an argument can be
made that Equation should be written as:Basic Theory (cont.)
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12 Point Load Test
I e S
Point Load Test (cont.) Basic Theory
Considering of I variations with specimen size and shape lead to
S
introduce a reference index I which corresponds to the I of a
S(50) S
diametrically loaded rock core of 50mm diameter. A new correction function which accounts for both size and shape effects by utilizing the concept of “equivalent core diameter” (D ). This function (known
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as geometric correction factor) is given by:
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13 Point Load Test
Experimental Outline
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Point Load Test
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15 Point Load Test (cont.) Experimental Outline
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Point Load Test Experimental Outline (cont.)
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Point Load Test (cont.) Experimental Outline
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Point Loading Test Experimental Outline (cont.)
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S CV A B 'B= h/d A . ( d A 1( d/G max
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" G max
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26 Point Load Test $ (cont.)
Influence of maximum coarse aggregate size of G max I 5 5 5 "5I
S(35) I 5 5 5 "5I
S(50)
S(35)
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max
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Experimental and estimation values of I S(50)
The results were satisfied enough by showing a value of absolute relative error less than 5%. The coefficient of correlation between them also high
2
(R = 0.982) in case of core specimen diameter,
d of 35mm and maximum
coarse aggregate size,
G of 20mm is applied in max concrete structures.
28
(cont.) $ Point Load Test
Re-calculation procedure is conducted by using a new geometric factor for correcting point load index of core drilled specimen diameter of 35mm and performing linear regression analysis to propose an estimation formula for 2 each group. The coefficient of correlation, R also shows an improvement in strong relationship between point load index and compressive strength of concrete core.
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Stick Scanner Imaging of Concrete
Visual examination is the most effective qualitative method of evaluation of structure soundness and identifying the typical distress symptoms together
Experienced engineers with the associated problems. The periodic inspection covered the visual information data such as cracking, scaling, color change or stain, spalling, exposure, corrosion and rupture of steel reinforcement inside concrete
Tools and Instrument Simple tools and instrument like camera with flash, magnifying glass, binoculars and gauge for crack width measurement, chisel and hammer are usually needed. Occasionally, a light platform/scaffold tower
32 can be used for access to advantage.
Imaging of Concrete (cont.)
33 Stick Scanner
In-depth inspections are close-up, hands-on inspections, generally of a limited portion of a bridge, completed to identify deficiencies not readily detectable during routine inspections. An in-depth inspection frequently relies on special access equipment that provides the inspector better access to the structure than is available for a periodic inspection.
Another method for assisting the inspection like core drilled will gather an existing concrete condition, and investigate the inside defects, such as carbonation depth, chloride ion diffusion, cracking, void, and corrosion.
This inspection technology is developed by using a scanner (Stick Scanner) to capture internal concrete image from small diameter inspection borehole, whereas the measurement and analysis is confirmed by manipulating captured image in photograph stage.
Outline
34 Stick Scanner
old model: SS-1
new model: SS-2
Detail of Parts
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36 Stick Scanner
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Performance
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The acquisition of scanning image Image size measurement error
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Stick Scanner (cont.) Performance - 2 :
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Performance (cont.)
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Performance (cont.)
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Performance (cont.)
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45 Outlook of Field Application
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In-Situ Strength Estimation
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48 Outlook of Field Application
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50 Outlook of Field Application Interfacial debonding monitoring
Setup of four point bending test
Location of inspection borehole and point load
Outlook of Field Application (cont.) Interfacial debonding monitoring
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51 Reference image of initial stage
Concluding Remarks
Results obtained can be summarized according to the objectives of the study as follows: ' ,-
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(cont.) Concluding Remarks
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53 Suggested further study
During the investigation that had been undertaken in this study, many other alternatives and ideas have emerged. But, unfortunately within the constraints of the study, not all of these could be examined. Suggestions for further study in the field of concrete structure soundness assessment are applying the developed method and device in existing concrete structures inspection program in the different environment condition. From these differences, more data and images will collected to improve our knowledge about concrete structure degradation in order to extent the remaining service life of structure in optimum ways.
54