Concrete Mix Design Proportioned by Trial Mixes
Concrete Mix Design Proportioned by Trial Mixes
(OP)
What documentation do you expect to see in a concrete mix submittal that is designed with trial mixes per ACI 318 rather than field experience? I am accustomed to submittals with field experience where a summary of the test result are provided and the statistical calculations justifying the concrete strength. For trial mixes, do you expect the submittal to include the all of the trial mix designs or just the final design with satisfactory f'cr. Should all compression test results be included for all of the cylinders tested, or just the average for each trial mix?






RE: Concrete Mix Design Proportioned by Trial Mixes
RE: Concrete Mix Design Proportioned by Trial Mixes
Thank you for the information. When a mix design has no historical records, would you expect to see the actual compression test report from a testing agency, or will a simple statement from the mix design engineer stating the average compression test result be sufficient (the required f'cr is 1000+psi over f'c per ACI 318 table 5.3.2.2 or similar table in ACI 301)? At a minimum, I want to know the date of the test(s) since aggregates can change over time.
By the way, we have started to see trial mixes rather than historical data for typical concrete mix submittals.
RE: Concrete Mix Design Proportioned by Trial Mixes
Stick to your guns on what you want to see. I don't do mix design review routinely anymore, but when I did the producers in our area could spot my requirements for mix design submittals. They knew they would have to comply strictly with ACI requirements and provide me with all the aggregate info I typically requested. Those submittals became known by my name, though the comments were not necessarily endearing! More like....Oh $hit...another "Ron" mix design submittal....but they complied and my clients were better protected both functionally and legally. One of the 3 or 4 local producers actually took pride in the fact that his submittals could pass my scrutiny.
RE: Concrete Mix Design Proportioned by Trial Mixes
I appreciate the encouragement. Since I can be excessively detail oriented, I really make an effort to approve submittals as noted rather than have them revised and resubmitted. I am amazed at some of the simple things that are missing or wrong in submittals. I'd better stop typing before I get up on a soap box and start whining about poor quality submittals.
RE: Concrete Mix Design Proportioned by Trial Mixes
CCS 1: Approximate compressive strength (N/mm2) of concrete mixes made with a free-water/cement ratio of 0.5
etc.
Thanks in advance.
RE: Concrete Mix Design Proportioned by Trial Mixes
RE: Concrete Mix Design Proportioned by Trial Mixes
On the projects in which I have been associated, we have not experienced any problems with this method for strength (we are normally out in the boonies and not in a city where there are ready mix plants at hand). Also, as aggregate (or cement, fly ash) sources may vary, any change of a source would require a new trial mix design. For instance on one project the contractor had a back-up cement source in case his nominated source went down or was unable to produce sufficient cement. This can be particularly important when fly ash is used as its properties are dependent on the source of coal used in the burning. As statistics become available, the stdev of 5 MPa can be modified based on the history - I have found contractors, though, reluctant to do so especially if their unit rate is based on m3 of concrete placed - likely as they feel the owner will want a reduction in price if he can reduce his cement content . . . or that "if it ain't broke, don't fix it."