Concrete testing
Concrete testing
(OP)
Have been setting spec for testing (psi and slump) concrete in sidewalks and/or curbing at mid-point per 9-yard truck load. Is this average ratio in the southeast?
Thanks
Thanks
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting GuidelinesJobs |
|
RE: Concrete testing
Also, when pumping concrete, we typically take samples from the discharge of the pump halfway through the pour. Sometimes, we take samples at both the pump discharge and the truck discharge points if there is a question regarding the difference in concrete quality as it goes through the pump.
RE: Concrete testing
RE: Concrete testing
RE: Concrete testing
regards
umitk2211
RE: Concrete testing
With the inclusion of admixtures the slump test more correctly is a measure of the fluidity of the mixture and only an indirect measure of the water. In designing concrete mixes by either the American Concrete Institute or the Portland Cement Association method, strength and durability are governed by the water-cement ratio (pounds of water per pound of cement), not by slump. It is possible to meet the same standards for concrete through a wide range of slumps – as long as cement is added in the same proportion as water is added to increase slump. Of course overly-wet mixes should be avoided, of course, because they can lead to finishing problems and problem surfaces.
RE: Concrete testing
KRS Services
www.krs-services.com
RE: Concrete testing
RE: Concrete testing
As for how many tests per pour, see the Indian MOST (Ministry of Surface Transport) - it will surprise you KRS - if I remember right, it is three samples (i.e 3 sets of tests - each set is for three cubes to be taken fro 28day strengths and additional cubes if desired for 7 day). But I will confirm. Of course, they, here take samples of even the lean (10MPa oops - that is 10MPa cube or 8MPa cylinder) concrete!!! used for mud mat!!!
Best to you all.
RE: Concrete testing
In the example I provided, all samples are taken in accordance with the procedures prescribed by ASTM standards by the representative geotechnical engineer. My understanding of the thread was mainly in reference to the standards in relation to frequency of testing. I normally specify cylinders (strength) for 7 and 28 day strengths based upon the job. Certainly, local municipal/highway standards will always apply, depending on the contract source, however I have found that in many projects, including Provincial highway projects, an end product specification places the onus of primary testing on the Contractor, with results forwarded to the geotechnical engieer for review and approval. Random testing by the owner, as a quality control and measure for payment, serves to verify the Contractor's numbers. The result is a surprising reduction of project cost to the Owner and a vastly improved product as well because the onus of responsibilty shifts from the Owner to the Contractor.
Local ordinances and regulations shall always be deemed the standard to follow, however, if other methods are desired, I am merely providing my thoughts on the subject.
I truly enjoy the responses to these forums due to the many different ways of performing the seemingly similar tasks.
Take care and all the best in the new year!
KRS Services
www.krs-services.com
RE: Concrete testing
++++++++++++++++
Confirmation of items in my earlier post – and apologies for my feeble mind!!
AASHTO (T141) specifies that sampling be a composite of two or more regularly spaced portions within a specified time frame (less than 15 minutes). The various portions are then mixed together to form a composite. For air and slump, an initial sample “may be taken after at least ¼ cubic yard or concrete has been discharged.” – not the ½ yd that I put in my earlier post – sorry.
Indian Standards (IS 1199) states “At least three approximately equal sample increments totaling 0.02m3 shall be taken from a batch during its discharge . . . Where three sample increments are taken they shall be taken at about the time when ¼, ½ and ¾ of the concrete has been discharged . . .” The samples are then made into a composite sample.
I give the IS so that we may see that different countries do have slightly different procedures. For instance, ASTM/AASTO do slumps in 3 layers; IS is in 4 layers. Normal Indian practice is to use cubes, not cylinders. Need to correct – approximately: 80% cube strength = cylinder strength (i.e., 30MPa cube = 24MPa cylinder). Ratio is somewhat higher at higher strengths (say 90% at cylinder strength >35 MPa but most here just use the 80% value. This is important to correlate specifically if you have a mixed bag as sometimes may happen in SE Asia depending on origin of contractor. One other difference is curing temps after initial 24hr – at AASHTO/ASTM it is 23degC plus or minus 1.7degC (AASHTO T23); in India it is 27degC plus or minus 2degC (IS516). This really takes into account the more typical ambient temperatures in India – probably so not so much ice or chillers are needed.
As for number of tests, MOST (Indian Ministry of Surface Transport Specs for Road and Bridge Works, 3rd Revision) states: The MINIMUM frequency of sampling of concrete of each grade shall be:
1 – 5 m3 in works: 1 sample
6 – 15 m3 in works: 2 samples
16 – 30 m3 in works: 3 samples
31 – 50 m3 in works: 4 samples
>51 m3 in works: 4 samples plus 1 sample for each added 50m3 or part thereof.
Here, the auditors would say that if you had 52 m3 in works, do 5 samples. Note, too, that this is per “works”. If contractor does three bridge parapet walls, say 11m3 each, he would be required to do 3 x 2 samples even of same class concrete.
On another international job – it was 1 sample per day of each mix used, at least 1 sample per 50m3 of concrete placed for reinforced and prestressed concrete, at least 1 sample per 100m3 for mass concrete; at least one sample from each pier cap, column and abutment, at least one set from each precast element. If same grade is used at two or more places on same structure – at least one set subject to above. For small works, say culvert headwalls and do several in day – at least 1 sample for each class. The fallacy in this particular job was that each 0.125m3 was mixed individually in portable mixers – we had, due to extreme remote locations, no ready mix!
KRS: Your 1 sample per 150m3 seems pretty liberal!!! (Point taken that your 1 per 150m3 was for client confirmation). I couldn’t find my CSA book – lent it out so can’t confirm CSA requirements.
Hope this helps – it shows that engineers/country practice/organization practice, once again, vary widely in opinions and requirements for such common and routine items as this.
p.s. (1) Can anyone tell me how I report, in accordance with AASHTO T22, a test result (7 day or 28day) to the nearest 69kPa? (viz., 0.069MPa)? I queried AASHTO and got a snide remark in return.
(2) Does anyone have a handle on maximum flakiness and elongation combined? KRS??? DirtDoc1???? This is becoming a great “audit” concern of ours: specs say 25% combined; we can’t get anything under 30 to 35% (have tried four quarry sources! – rock is not siltstone/slate, or laminated). Mixes are workable; strengths are all in accordance with spec values but worries abound about hand slaps. I have a thread in civil related on this for some details. Thanks.
RE: Concrete testing
http://www11.myflorida.com/statematerialsoffice/QualitySystems/IAProgram/IAChecklist/ASTMC-172.pdf
http://www11.myflorida.com/statematerialsoffice/QualitySystems/IAProgram/IAChecklist/ASTMC-143.pdf
http://www11.myflorida.com/statematerialsoffice/QualitySystems/IAProgram/IAChecklist/ASTMC-39.pdf
RE: Concrete testing
Thanks,
Alpharetta