Admixture dose too low, too high or unstable
Symptom
The dose is low, high or varies batch to batch, air content or slump changes with no recipe change, no flow in winter, or sludge in a tank.
Likely causes
- Air in the suction line, worn pump, blocked strainer or fouled meter (dose low).
- Valve leaking through, meter drift or siphoning (dose high).
- Tank not agitated, product separated, wrong product filled, or frozen product not remixed.
- Old product or contamination in the tank.
Most likely and cheapest to check first.
Checks
- Daily - tank levels and labels, leaks, agitation or circulation running.
- Look at the line after dosing for drips.
- Check strainers weekly and the meter calibration when the product changes.
- Check delivery records and tank labels when concrete behaviour changes.
Fix
- Bleed air; service the pump; clean the strainer.
- Repair the leaking valve; fit an anti-siphon valve; recalibrate.
- Agitate before use; never mix products in one tank; clean a tank fully before changing product.
- Thaw frozen product slowly and mix thoroughly; insulate and heat tanks and lines before winter.
Parts you may need
A dripping valve changes the mix design
A few drops each batch add up, especially with strong superplasticisers. Check the line for drips after dosing. Label every tank, line and valve with the product name, and keep a bund around tanks so spills stay out of drains.
CAUTIONRead the safety data sheet of every admixture. Some are corrosive or irritant: gloves, goggles and an eye-wash point near the tanks.
⚠ Every check inside a machine starts with full lockout. Safety disclaimer