What is PCE in admixture and some essential questions about it
PCE in admixture is a high-performance water reducer and a cement dispersant used in cement concrete applications. It is widely used in highways, bridges, dams, tunnels, high-rise buildings, and other engineering projects. This product is green, environmentally friendly, non flammable, non explosive, and can be safely transported by train and car
Differences between PCE in admixture and naphthalene based water reducing agents:
- One is the diversity and adjustability of molecular structure;
- The second is to further concentrate and improve the advantages of high-efficiency water reducing agents, and achieve green and pollution-free production process.
- In terms of action mechanism, the molecular structure of polycarboxylic acid series water reducer is comb type, the polar anion “anchor” group with strong main chain is used to adsorb on cement particles, and the outward extending comb structure supported by many branch chains provides sufficient spatial arrangement effect for further dispersion of cement particles. Compared to the double layer electric repulsion effect of naphthalene based water reducing agents, the steric hindrance effect results in a much longer retention time for dispersion.
- By appropriately changing the comb structure of polycarboxylate water reducing agents and changing the density and length of side chains, a high water reducing and high early strength water reducing agent suitable for prefabricated components can be obtained.
- Polycarboxylic acid series water reducer can be adjusted and changed in molecular structure as required to achieve the purpose of changing performance, rather than modified by simple compound. Based on this understanding, it may be enlightening for us to improve the application technology in the future.
Adaptability of PCE in admixture to cementing material：
- The saturation point of polycarboxylate based water reducing agents varies greatly among different types of cement, so it is important to find the saturation point for different types of cement. However, if the user specifies that only 1.0% is allowed to be added, and the adaptability of the selected cement is not good at this dosage, it is difficult for the admixture provider to do so, and the use of composite methods often has little effect.
- The adaptability of the first level ash is good, and there are many situations where the second and third levels of ash do not adapt. At this time, even increasing the amount of polycarboxylic acid added does not have a significant effect. Often, when a certain type of cement or fly ash has poor adaptability to external additives, you may not be completely satisfied with changing to another additive, and ultimately you may have to replace the cementitious material.
The dosage problem of PCE in admixture：
Polycarboxylic acid water reducing agent has low dosage, high water reducing rate, and good slump retention, but the following problems also occur in application:
The dosage is very sensitive when the water binder ratio is small, and it shows a higher water reduction rate. When the water binder ratio is large (above 0.4), the water reduction rate and its change are not so obvious, which may be related to the action mechanism of polycarboxylic acid series water reducer. Its dispersion and retention role lies in the steric effect of the formation of molecular structure. When the water binder ratio is large, there is enough water molecule spacing in the cement dispersion system, Therefore, the steric hindrance of polycarboxylic acid molecules is naturally smaller.
When the dosage of cementitious materials is large, the effect of the dosage is more significant. Under the same conditions, the water reduction effect when the total amount of cementitious materials is less than 300 kg/m3 is less than the water reduction rate when the total amount of cementitious materials is>400 kg/m3, and there is also a superposition effect when the water cement ratio is large and the amount of cementitious materials is small.
Polycarboxylic acid water reducing agent is developed for high-performance concrete, so its performance and price are more suitable for application in high-performance concrete.