Post Date:26,Jan,2026

1. Compatibility with Cement:

Cement and cementitious materials have complex and diverse compositions. Based on the adsorption-dispersion mechanism, it’s impossible to find a single universal water reducer. While polycarboxylate water reducers have a wider range of compatibility than naphthalene-based water reducers, they may still be less compatible with some cements. This compatibility is often reflected in reduced water reduction rates and increased slump loss. Even for the same cement, the water reducer’s performance can vary depending on the fineness of the ball-milled cement. (1) Phenomenon: A mixing station used a local P-042.5R cement to supply C50 concrete to a construction site. It also used a polycarboxylic acid-based high-efficiency water reducer. When making the concrete mix ratio, it was found that the amount of water reducer added to this cement was slightly higher than that of other cements. However, during the actual mixing, the slump of the concrete mixture leaving the factory was visually 210mm. When the concrete was unloaded into the concrete pump truck at the construction site, it was found that the concrete in the truck could not be unloaded. After notifying the factory to send a bucket of water reducer to add to the mixing, the visual slump was 160mm, which basically met the pumping requirements. However, during the unloading process, the concrete could not be unloaded again. The concrete in the truck was immediately returned to the factory. A large amount of water and a small amount of water reducer were added, and it was barely unloaded. It almost solidified in the mixer truck. (2) Cause analysis: Failure to insist on conducting a compatibility test with admixtures for each batch of cement before opening. (3) Prevention: Conduct a compounding test using the construction mix ratio for each batch of cement before opening. Choose appropriate admixtures. Cement with “coal gangue” as admixture has poor compatibility with polycarboxylic acid water reducers, so avoid using it.

2. Sensitivity to water consumption

Due to the use of polycarboxylic acid water reducers, the water consumption of concrete is greatly reduced. The water consumption of single cubic meter concrete is mostly 130-165kg; the water-cement ratio is 0.3-0.4, or even less than 0.3. Under low water consumption conditions, fluctuations in water addition may cause large changes in slump, causing the slump of the concrete mixture to suddenly increase and water seepage.

(1) Phenomenon: A mixing station uses P-032.5R cement from a cement factory to prepare C30 concrete. The contract requires the slump to be 150mm:t30mm at the construction site. When the concrete leaves the factory, the actual slump is 180mm. After being transported to the construction site, the slump of the concrete is measured at the construction site to be 210mm. Two trucks of concrete were returned. When they were returned to the factory for verification, the slump was still 210mm, and there was water seepage and stratification.

(2) Cause: The cement has good compatibility with this water reducer, and the water reducer dosage is slightly larger. The mixing time is insufficient. The concrete slump at the time of leaving the machine is not the actual slump due to the short mixing time.

(3) Prevention: For cements that are sensitive to the dosage of polycarboxylic acid-based high-efficiency water-reducing agent admixtures, the admixture dosage should be appropriate and the metering accuracy should be high. The mixing time should be appropriately extended. Even for a twin-shaft forced mixer, the mixing time should not be less than 40 seconds, and preferably more than 60 seconds.