Technical articles 7 min read
Lightweight concrete mix design: four recurring mistakes
Most lightweight concrete problems on site start in the mix design, not in the aggregate.
1. Designing by weight instead of by volume. Expanded clay has a different density from normal aggregate, so conventional weight ratios shift the actual aggregate volume in the mix. Lightweight mixes must be proportioned by volume.
2. Ignoring absorption. Dry aggregate takes up part of the mixing water and slump falls in transit. A 30-minute pre-soak removes that drift.
3. Over-vibration. Lower particle density means the aggregate wants to rise. Prolonged vibration drives it to the surface and leaves the section non-uniform. Vibrate for less time than you would normal-weight concrete.
4. Skimping on early curing. Water held inside the granule assists internal curing, but it does not replace surface curing — least of all in hot, dry weather.
2. Ignoring absorption. Dry aggregate takes up part of the mixing water and slump falls in transit. A 30-minute pre-soak removes that drift.
3. Over-vibration. Lower particle density means the aggregate wants to rise. Prolonged vibration drives it to the surface and leaves the section non-uniform. Vibrate for less time than you would normal-weight concrete.
4. Skimping on early curing. Water held inside the granule assists internal curing, but it does not replace surface curing — least of all in hot, dry weather.