Why is polycarboxylate superplasticizer added to concrete and mortar?
Release Time:
2016-05-11
Source:
Why is polycarboxylate superplasticizer added to concrete and mortar?
Polycarboxylate superplasticizer It is a high-efficiency water-reducing admixture for construction materials. For mineral binders—such as ordinary cement, calcium chloride cement, and calcium sulfate cement—it exerts both electrostatic repulsion and steric hindrance, resulting in superior anti-flocculation performance and longer-lasting effectiveness compared with conventional water reducers. In recent years, polycarboxylate superplasticizers have gradually replaced traditional water reducers and come to dominate the market, expanding their applications from primarily concrete to a wide range of mortar formulations. So why are more and more concrete and mortar products incorporating polycarboxylate superplasticizers? The following outlines the key advantages and functions of polycarboxylate superplasticizers:
1. After cement is mixed with water, the intermolecular attractive forces among cement particles cause the cement paste to form a flocculent structure, trapping 10% to 30% of the mixing water within the cement particles. This trapped water cannot participate in free flow or lubrication, thereby reducing the workability of the concrete mix. When a water-reducing admixture is added, its molecules adsorb selectively onto the surface of cement particles, imparting a uniform surface charge—typically negative—to the particles. This generates electrostatic repulsion, which promotes particle dispersion, disrupts the flocculent structure, releases the trapped water, and allows it to contribute to flow, thereby effectively enhancing the workability of the concrete mix.
2. The hydrophilic groups in water-reducing agents are highly polar; consequently, the adsorbed film of the water-reducing agent on the surface of cement particles can form a stable solvated water layer with water molecules. This water layer provides excellent lubrication, effectively reducing the sliding resistance between cement particles and thereby further enhancing workability.
3. Steric hindrance: The water-reducing agent contains hydrophilic polyether side chains that extend into the aqueous solution, thereby forming a hydrophilic three-dimensional adsorption layer of a certain thickness on the surface of the adsorbed cement particles. As cement particles approach one another, these adsorption layers begin to overlap, generating steric hindrance between the particles. The greater the degree of overlap, the stronger the steric repulsive force, and the more effectively it impedes particle agglomeration, thus maintaining good slump retention in concrete.
4. Novel water-reducing agents, such as polycarboxylate superplasticizers, are prepared by grafting branched side chains onto the polymer backbone. These side chains not only impart steric hindrance but also gradually cleave under the highly alkaline conditions of cement hydration, thereby releasing polycarboxylic acids with a fractionating effect. This enhances the dispersion of cement particles and helps control slump loss.
Shandong Xindadi Industrial Group Co., Ltd. specializes in supplying polycarboxylate superplasticizer powders and liquid polycarboxylate superplasticizers. Follow us to learn more about our mortar admixture products.
