Helpful Hints / Troubleshooting

Strength Problems Check List

1)  Preparation procedures
A. Cube mold releasing agent. To much or an incorrect releasing agent is the number one reason for false low strengths.

2)  Chemistry
A. C3S increase - 1 day up, 28 days down.
B. C3A increase - 1 day up, 28 days down.
C. C2S increase - 1 day down, 28 days up.
D. Chemistry being diluted by Fe2O3 or other increasing components - low breaks across the board.
E. Alkalies decrease - 1 day down.
F. Clinker SO3 changes, altering the amount of gypsum added. With low breaks across the board, run optimum SO3. Optimum SO3 should be ran twice a year!
G. Microscope analysis by Ono method:
a. Alite size (10-40um)
b. Belite size (10-40um)
c. Birefringence (>0.007)
d. Belite color (clear)
*These would all cause the best 28 day breaks.
H. Analysis accuracy.
I. X-Ray diffraction - Analyze cement for possible pore reactions in kiln or possible gyp
contamination.

3)  Fineness
A. Check particle size distribution - mills may be grinding differently.
B. 325 decreases - 1 day the same, 28 days lower. Check the nozzle, water pressure , and sieve calibration.
C. Blaine decreases - low across the board. Check blaine calibration.
D. When using outside clinker, do not touch mills, because the blaine will go up automatically. The higher blaine will give strengths as before. If the same blaine is used, strengths will be low across the board.

4)  Compression Strength Machine
A. Is machine still in calibration?
B. The upper bearing block may be cocked or unable to move, which causes strengths to be low across the board. The upper bearing block may need to be lubricated. To do this, use lubricating flake graphite.
C. If cubes are being broken too slowly, there will be low breaks across the board. The
opposite will occur if the cubes are broken too quickly.
D. If cube molds are worn, they will make uneven cubes. This will cause low breaks across the board.

5)  Moist Cabinet Temperature
A. If the cubes are stored in an environment that is too cold, it will slow the curing process, which in turn, causes low breaks across the board. The opposite occurs if they're stored in an environment that is to warm.

6)  Cube Flow
A. If the flow decreases, it may be caused by false setting, which causes the cement to require more water. If this occurs, the strengths will be low in the field across the board.

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