Effect of Polycarboxylate Superplasticizer in Mortar and Concrete


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2020-04-13

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Water reducing agent can mainly improve the strength of mortar, it is not affect the mortar and concrete construction workability conditions, with water reducing and strengthening the role of admixture. Polycarboxylate superplasticizer is a new type of high-performance water-reducing agent developed in recent years, which has excellent water-reducing rate, fluidity and permeability. Significantly enhance the strength of cement mortar, but the production process is complex, the price is slightly higher than other water reducing agent.

Effect of Polycarboxylate Superplasticizer in Mortar and Concrete

Water reducing agent can mainly improve the strength of mortar, it is not affect the mortar and concrete construction workability conditions, with water reducing and strengthening the role of admixture. Polycarboxylate superplasticizer is a new type of high-performance water-reducing agent developed in recent years, which has excellent water-reducing rate, fluidity and permeability. Significantly enhance the strength of cement mortar, but the production process is complex, the price is slightly higher than other water reducing agent. Water reducing agent has many functions, which are divided into air-entraining water reducing agent (water reducing agent with air-entraining effect), early strength water reducing agent (water reducing agent with early strength effect), retarding water reducing agent (water reducing agent with retarding effect), etc.

The action principle of water reducing agent: water reducing agent is usually a kind of surfactant, which is an anionic surfactant. It is adsorbed on the surface of the cement particles to make the particles show electrical properties, and the particles repel each other due to the same charge, so that the cement particles are dispersed and the excess water between the particles is released to produce water reducing effect. On the other hand, due to the addition of water reducing agent, the surface of the cement particles to form a suction film, affecting the hydration rate of cement, so that the growth of cement stone crystal is more perfect, reduce the water evaporation of the capillary gap, the network structure is more compact, improve the hardness and structural density of cement mortar.

dispersion

After the cement is mixed with water, due to the molecular gravity of the cement particles, the cement slurry forms a flocculated structure, so that 10% to 30% of the mixing water is wrapped in the cement particles, which cannot participate in the free flow and lubrication, thus affecting the fluidity of the concrete mixture. When the water reducing agent is added, the water reducing agent molecules can be adsorbed on the surface of cement particles, so that the surface of cement particles with the same charge (usually negative charge), the formation of electrostatic repulsion, promote the mutual dispersion of cement particles, flocculation structure destruction, release part of the wrapped water, participate in the flow, so as to effectively increase the fluidity of concrete mixture.

Lubrication

The hydrophilic base in the water-reducing agent is very polar, so the water-reducing agent adsorption film on the surface of cement particles can form a stable solvated water film with water molecules. This water film has a good lubricating effect and can effectively reduce the sliding resistance between cement particles, thus further improving the fluidity of concrete.

steric hindrance

The hydrophilic polyether side chain in the structure of the water reducing agent is stretched in the aqueous solution, so that a hydrophilic three-dimensional adsorption layer with a certain thickness is formed on the surface of the adsorbed cement particles. When the cement particles are close to each other, the adsorption layer begins to overlap, that is, the steric hindrance effect is generated between the cement particles. The more overlap, the greater the steric repulsion, the greater the obstacle to the cohesion between the cement particles, so that the slump of the concrete remains good.















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