compressive strength of concrete
compressive strength of concrete
(OP)
I know that concrete needs some time to hydrate; therefore (compressive strength test specimens or cubes) are placed in water for 28 days (at that time concrete reaches 90% of its total comp. strength) and then tested and the results are usually used in design, BUT the structure itself cannot be placed in water! So does anyone know if there is any scientific reasoning for that, or why we place the cubes in water while we cannot place the structure in water as well?
RE: compressive strength of concrete
RE: compressive strength of concrete
RE: compressive strength of concrete
To try and test for all the variable conditions encountered in the field using a few cast cylinders of limited area and mass would be ludicrous.
There are many correlatable ways to estimate the in-place strength of concrete. All are approximations, not actual. Some methods are nondestructive, while others are destructive...but again, they are estimates.
RE: compressive strength of concrete
RE: compressive strength of concrete
RE: compressive strength of concrete
The testing of concrete specimens is undertaken to ensure what was delivered was correct and the correct mix (Quality Assurance/QA). Anything which can reduce the strength of the concrete (workmanship, hydration etc...) should be taken into account within the factors of safety, partial factors of safety at the design stage. The testing is there as a QA check, so needs to follow a standardised procedure for routine testing. If however you want to know something else, i.e. what is the actual strength for the actual concrete under the actual conditions, then you should design a sampling, curing and testing program to suit outside of the routine QA process. There is a big difference between QA checks on what was delivered to site (cured samples, tested at 7 and 28 days etc...) to investigative testing.
Concrete companies are very sensitive to how samples are taken, cured and tested and at any opportunity will disregard anyone elses testing , especially when it 'suggests' a failure (e.g. all the correction factors applied to cores to return an equiavlent cube strength!)
RE: compressive strength of concrete
RE: compressive strength of concrete
RE: compressive strength of concrete
RE: compressive strength of concrete
I'm from the UK and working in Asia, so what advantage would there be for me to have an American Concrete Institute field certification?
RE: compressive strength of concrete
my point was......you should have applicable training. good luck
RE: compressive strength of concrete
I enjoyed Zambo's comment. This is an international forum, but many US contributors do not seem to realize it.
RE: compressive strength of concrete
RE: compressive strength of concrete
In the class, we learned the basic principals for gradations, mix designs, sample preparation and testing procedures. The professor had a hint of mischievousness and encouraged variations in sample preparation withing the specified limits (no rebar in the the cylinders, etc.), but allowed the use of "admixtures" like sugar to recognize the effects on compressive strengths. He also explained the effects of "short stroking" and non-vertical rodding when entering OR retracting and the effects of tapping the exterior of the cylinder before finishing and putting into curing. We also got into the problems of properly handling and transporting cylinders before lab curing. It is easy for a technician to add or reduce the cylinder strength by 300 psi and still be withing the required procedures. That is why it is important to have the same technician preparing the samples (so get sloppy).
When working as a concrete technician for the DOT, it was amazing to see the abuses that were no different than what we learned as tricks and jokes.
ACI is very good, but it must be adopted by a code or referenced in a specification, enforced and recognized for what it is and how it can be legally abused. In many international locations, the standards are adopted, but rarely but into force with controlled results because the structures are not critical or high-performance.
RE: compressive strength of concrete
RE: compressive strength of concrete
EM 1110-2-2000 Standard Practice for Concrete for Civil Works Structures Change 2 01 Feb 94(original)
http://1
RE: compressive strength of concrete
RE: compressive strength of concrete
You have raised a simple, yey good question, many of us have learned/refreshed with you together. I, for one, long forgot a lot of those basics.
RE: compressive strength of concrete
RE: compressive strength of concrete
RE: compressive strength of concrete
RE: compressive strength of concrete
There are many ways to evaluate the strength of concrete in the field, almost all of which must be properly correlated to standardized sampling and testing.
There are too many variables in the field to assume the concrete sampled in the field and tested in a lab represents the in-place conditions.
RE: compressive strength of concrete
RE: compressive strength of concrete
With regard to the curing environment: The near 100% humidy (moist/mist room) is an acceptable method. Usually when a laboratory is set up this way, this curing environment is segregated from general work-space so as not to pose the health risks identified to employees.
The materials used to construct the moist cure room determine how much maintenance is required to keep it functional (i.e. wood shelves need replacing often, mold needs to be given attention...etc.)
Having worked with both environments, the moist room is more convenient for the technicians, where as it more costly in initial setup and maintanence. There are companies that manufacture pre-built cure-rooms.
The cure tanks pose ergonomic issues for the technicians that have to retrieve cylinders on a daily basis. If you're pulling 50+ cylinders out of tanks a day, you can feel the strain on your back - they make tools for that as well.
There are pros and cons to both environments.
RE: compressive strength of concrete
iandig...I can't imagine why anyone would propose having the entire lab area at 100% humidity...that would be a miserable working environment and would cause problems for the equipment that wasn't designed for it (compressive strength testing machine for instance). As for legionella and other humidity related maladies, if curing tanks are kept with lime saturated water as required, you're not likely to get any of that. As for the surrounding area, reasonable ventilation will prevent the room's humidity from reaching intolerable values.
RE: compressive strength of concrete
RE: compressive strength of concrete
RE: compressive strength of concrete
RE: compressive strength of concrete
You can find these at www.ndtjames.com
IN regards to ACI certification, it is actually a very large organization with chapters all over the world, I personally am aware of many asian chapters, with certification being acceptable in Hong Kong as well as Kuala Lumpur