shakeelahsan
Civil/Environmental
We have to go about obtaining cores from RCC Slabs. I'd request to guide me for obtaining cores and interpreting compressive strength results.
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Guide for Obtaining Cores and Interpreting Compressive Strength Result 4
- Thread starter shakeelahsan
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Yes. The beam looks good from pic. However, it looks like the concrete cover wasn't adequate to begin with. Anyway, if the exposed area coluldn't be fixed locally, knock out the remaining covers and re build as suggested with adequate concrete clear cover.
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1
- #22
bridgebuster
Active member
The visual examination of the core is important as well. You can download
Petrographic Methods of Examining Hardened Concrete: A Petrographic Manual; Publication No. FHWA-HRT-04-150
July 2006
at
It's a large file 26 MB
Petrographic Methods of Examining Hardened Concrete: A Petrographic Manual; Publication No. FHWA-HRT-04-150
July 2006
at
It's a large file 26 MB
Shakeel,
Have you measured the thickness of the existing roof slab? Also the cover that was provided originally. And lastly, can you describe the reinforcement? It seems to be some type of fabric or ladder reinforcement.
Operations like sandblasting, shotcreting etc. would probably require removal of the equipment below. Because the beams/joists appear to be in good condition, I would try to find a way to work from above. If you have the details of the original structure, you could analyze the joists to see if they can carry a new slab on top to span the short distance between the joists. You would still have to find a way to stabilize the spalling, which can't be doing either the equipment or the operators any good.
This spalling is a vivid example of failure to provide or maintain an adequate waterproofing membrane.
Have you measured the thickness of the existing roof slab? Also the cover that was provided originally. And lastly, can you describe the reinforcement? It seems to be some type of fabric or ladder reinforcement.
Operations like sandblasting, shotcreting etc. would probably require removal of the equipment below. Because the beams/joists appear to be in good condition, I would try to find a way to work from above. If you have the details of the original structure, you could analyze the joists to see if they can carry a new slab on top to span the short distance between the joists. You would still have to find a way to stabilize the spalling, which can't be doing either the equipment or the operators any good.
This spalling is a vivid example of failure to provide or maintain an adequate waterproofing membrane.
- Thread starter
- #24
shakeelahsan
Civil/Environmental
Thickness of slab is 6" and clear cover to reinforcement steel is 0.75".
Could you please explain how sandblasting to this slab would be done, the procedure I may recommend to my client, if approved?
Engr. Shakeel Ahsan
Director Engineering
CMEC - Pakistan
Could you please explain how sandblasting to this slab would be done, the procedure I may recommend to my client, if approved?
Engr. Shakeel Ahsan
Director Engineering
CMEC - Pakistan
Sandblasting may be done in several ways...
1. You can use actual sand...usually for this application a 20-30 sandblasting sand is used. Lots of cleanup and protection of equipment below is required.
2. You can use an abrasive grit, such as carborundum or other abrasive grit,like sand...same cleanup required.
3. You can use dry ice. Almost not cleanup other than the blast residue from the slab.
1. You can use actual sand...usually for this application a 20-30 sandblasting sand is used. Lots of cleanup and protection of equipment below is required.
2. You can use an abrasive grit, such as carborundum or other abrasive grit,like sand...same cleanup required.
3. You can use dry ice. Almost not cleanup other than the blast residue from the slab.
I have used hydroblasting on a couple of projects to remove poor concrete and with a reasonable operator it works very well. Like using dry ice, it can be used in environmentally sensitive areas with fewer problems. With higher pressures, hydroblasting can remove sound 40 MPa concrete.
I don't have any manuals, except for a couple of 'advertising publications, but a search of the net should bring up a pile of information. A matter of discussing this with someone that undertakes this work. It's been around for a decade, maybe more, but I first used it about 10 years back.
Sandblasting may be the least costly and is more common.
Dik
I don't have any manuals, except for a couple of 'advertising publications, but a search of the net should bring up a pile of information. A matter of discussing this with someone that undertakes this work. It's been around for a decade, maybe more, but I first used it about 10 years back.
Sandblasting may be the least costly and is more common.
Dik
From Wiki... and there's more.
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Hydrodemolition (also known as hydro demolition, hydroblasting, hydro blasting, hydromilling, waterblasting, and waterjetting) is a concrete removal technique which utilizes high-pressure water to remove deteriorated and sound concrete as well as asphalt and grout. This process provides an excellent bonding surface for repair material and new coating applications. First developed in Europe in the 1970s, this technology has become widely accepted for concrete removal and surface preparation throughout Europe and North America.
Hydrodemolition is not used as much for demolition as it is for surface restoration and protection projects. When concrete has deteriorated or the reinforcing steel has begun to corrode, it is necessary to remove any unsound concrete and reinforcing bars (rebar) in order to replace it with new concrete and maintain the integrity of the structure. This process has also been used to remove sound concrete that is not compromised in any way. This may be done to install a preventive cathodic protection system, or to remove concrete in structures in which vibration is a concern. Unlike jackhammers, hydrodemolition does not produce vibrations throughout a structure and therefore does not introduce micro fractures.
Dik
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Hydrodemolition (also known as hydro demolition, hydroblasting, hydro blasting, hydromilling, waterblasting, and waterjetting) is a concrete removal technique which utilizes high-pressure water to remove deteriorated and sound concrete as well as asphalt and grout. This process provides an excellent bonding surface for repair material and new coating applications. First developed in Europe in the 1970s, this technology has become widely accepted for concrete removal and surface preparation throughout Europe and North America.
Hydrodemolition is not used as much for demolition as it is for surface restoration and protection projects. When concrete has deteriorated or the reinforcing steel has begun to corrode, it is necessary to remove any unsound concrete and reinforcing bars (rebar) in order to replace it with new concrete and maintain the integrity of the structure. This process has also been used to remove sound concrete that is not compromised in any way. This may be done to install a preventive cathodic protection system, or to remove concrete in structures in which vibration is a concern. Unlike jackhammers, hydrodemolition does not produce vibrations throughout a structure and therefore does not introduce micro fractures.
Dik
I figured that the stuff would have to be protected anyway and it was just offered as another alternative.
Hydroblasting seems to remove loose material that regular sandblasting doesn't seem to get at... in particular with corrosion byproducts; they may find the slab and rebar is in worse condition than the photos show.
kslee:
For corrosion related work, I like hydroblasting if you have a good applicator. If you have an overzealous cowboy (my apologies to any Texans in the forum) he can do some serious damage if he's not careful. Regular sandblasting is more common and generally less costly. For environmentally sensitive stuff I think dry ice is maybe a little better. In support of Ron's comment, the less aggressive nature of it generally makes containment of the byproducts more containable.
Dik
Hydroblasting seems to remove loose material that regular sandblasting doesn't seem to get at... in particular with corrosion byproducts; they may find the slab and rebar is in worse condition than the photos show.
kslee:
For corrosion related work, I like hydroblasting if you have a good applicator. If you have an overzealous cowboy (my apologies to any Texans in the forum) he can do some serious damage if he's not careful. Regular sandblasting is more common and generally less costly. For environmentally sensitive stuff I think dry ice is maybe a little better. In support of Ron's comment, the less aggressive nature of it generally makes containment of the byproducts more containable.
Dik
- Thread starter
- #34
shakeelahsan
Civil/Environmental
What is the unit cost for Hydro blasting, Sand blasting and Dry Ice?
You can give the unit cost for your area, I'd just like to interpret it for Pakistan.
You can give the unit cost for your area, I'd just like to interpret it for Pakistan.
- Thread starter
- #36
shakeelahsan
Civil/Environmental
Dear All,
I have these results for Concrete Cores from laboratory now.
I'd request comments from all of you.
Sample L/d Correction Load Strength Corrected Strength
No. Ratio Factor N (N/mm2) Strength (lb/in2)
1 1.25 0.94 139250 17.72 16.63 2416
2 1.25 0.94 138360 17.61 16.55 2400
1 0.70 0.74 98913 12.59 9.32 1351
2 0.70 0.74 112640 14.34 10.61 1538
1 1.00 0.87 85607 10.90 9.43 1374
2 0.75 0.80 115980 14.76 11.81 1712
1 1.25 0.94 138450 17.62 16.56 2402
2 1.00 0.87 137840 17.54 16.26 2213
1 0.75 0.80 123150 15.67 12.54 1818
2 0.75 0.80 123811 15.73 12.59 1825
1 0.87 0.82 137315 17.48 14.33 2078
2 1.00 0.87 139260 17.72 15.42 2236
I need recommendations on existing condition of concrete.
Tests on three samples of steel reinforcement resulted Yield Strength of 490000 Psi, 42909 Psi & 50708 Psi and Ultimate strength of 69997 Psi, 60440 Psi & 71421 Psi respectively. Elongation was 12%, 10% & 11% respectively.
What are your recommendations?
Engr. Shakeel Ahsan
Director Engineering
CMEC - Pakistan
I have these results for Concrete Cores from laboratory now.
I'd request comments from all of you.
Sample L/d Correction Load Strength Corrected Strength
No. Ratio Factor N (N/mm2) Strength (lb/in2)
1 1.25 0.94 139250 17.72 16.63 2416
2 1.25 0.94 138360 17.61 16.55 2400
1 0.70 0.74 98913 12.59 9.32 1351
2 0.70 0.74 112640 14.34 10.61 1538
1 1.00 0.87 85607 10.90 9.43 1374
2 0.75 0.80 115980 14.76 11.81 1712
1 1.25 0.94 138450 17.62 16.56 2402
2 1.00 0.87 137840 17.54 16.26 2213
1 0.75 0.80 123150 15.67 12.54 1818
2 0.75 0.80 123811 15.73 12.59 1825
1 0.87 0.82 137315 17.48 14.33 2078
2 1.00 0.87 139260 17.72 15.42 2236
I need recommendations on existing condition of concrete.
Tests on three samples of steel reinforcement resulted Yield Strength of 490000 Psi, 42909 Psi & 50708 Psi and Ultimate strength of 69997 Psi, 60440 Psi & 71421 Psi respectively. Elongation was 12%, 10% & 11% respectively.
What are your recommendations?
Engr. Shakeel Ahsan
Director Engineering
CMEC - Pakistan
I would not consider any of these results as structural grade concrete. Concrete strength is a good indicator of durability, and it is apparent from the core results that the concrete is of very poor quality. Demolition and reconstruction is looking like the answer.
I would suggest that reconstruction be considered; the material is not durable. What is the area above the slab used for and what type of salt exposure did it have?
On a positive note, and to re-iterate, unless shear is an issue, the strength of the concrete has little effect on the flexural strength for the amount of reinforcing shown in the photos.
Dik
On a positive note, and to re-iterate, unless shear is an issue, the strength of the concrete has little effect on the flexural strength for the amount of reinforcing shown in the photos.
Dik
- Thread starter
- #40
shakeelahsan
Civil/Environmental
These are single storey structures, with no roof water/ heat proofing at all.
During my inspection visit to site, it was revealed that the structures never had any roof drainage system, leaving the area exposed to rains and extensive sun light.
Temperature in this area goes up to 50C and water table changes during seasons, water is saline, and perhaps the atmospheric conditions over 35 to 40 years time span have resulted this damage to the structure.
Engr. Shakeel Ahsan
Director Engineering
CMEC - Pakistan
During my inspection visit to site, it was revealed that the structures never had any roof drainage system, leaving the area exposed to rains and extensive sun light.
Temperature in this area goes up to 50C and water table changes during seasons, water is saline, and perhaps the atmospheric conditions over 35 to 40 years time span have resulted this damage to the structure.
Engr. Shakeel Ahsan
Director Engineering
CMEC - Pakistan
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