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.
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.
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.
What is the slab surface above used for? Parking? and why the large concentration of salt? and what about the top level of reinforcing to accommodate continuity of the slab?
Thanks, bridgebuster, for the very good link. More reading.
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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...good idea on the hydroblasting...just wasn't sure if the equipment below could take the water. You're right, dry ice is slow, but the lack of cleanup is often worth it.
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.
Any estimate would just be a WAG and not likely applicable for your environs. Once you have the equipment, the work is labour intensive and costs would not likely be applicable.
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.
It may be possible to provide new structure to encapsulate and support the existing structure. This can be done with a mesh to support it on new light steel beams/channels spanning between the existing beams.
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
