How to control slump loss in hot weather

In summer, concrete mixed at 35–42℃ can lose 30–50 mm of slump in the first 30 minutes. The cause is not the water — it is faster C3S hydration and more water evaporation from the mix. You can compensate with admixture selection before you add more water or superplasticizer.

Three levers that actually work

1. Retarder. A gluconate-based retarder slows early hydration and extends the usable window. It is the most reliable tool when haul time is 30–90 minutes.

2. Water-retaining agent. Cellulose-type water-retaining admixtures hold mixing water inside the paste, reducing slump loss caused by bleeding and surface drying during long hauls.

3. Retarder + water-retaining combined. For extreme cases (transit over 90 minutes or air above 40℃), the combination gives a longer, smoother slump curve than either product alone.

Dosage timing matters

Add the admixture with the mixing water, not after the mixer has already run dry. Delayed addition may work in the lab but is hard to repeat on site. Keep mixing time above 60 seconds and protect the drum from direct sun when parked.

What we recommend

Start from our retarder and water-retaining agent pages, request free samples with COA, and run a 60-minute slump test on your own cement. Dosage guidance is included with every sample.