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The role of polycarboxylate superplasticizer in mortar and concrete
he role of polycarboxylate superplasticizer in mortar and concrete
The water reducing agent can mainly improve the strength of the mortar. It is an admixture with water reducing and reinforcing effects without affecting the construction workability of the mortar and concrete. Polycarboxylate water reducing agent is a new type of high performance water reducing agent developed in recent years, which has excellent water reducing rate, fluidity and permeability. The strength of the cement mortar is obviously enhanced, but the production process is complicated and the price is slightly higher than other water reducing agents. The water reducing agent has many functions, and is divided into an air-inducing type water reducing agent (a water reducing agent which also acts as a bleed air), an early-strong water reducing agent (a water reducing agent which acts as an early strong action), and a retarding type water reducing agent. (water reducing agent which also acts as a retarding agent).
The principle of action of the water reducing agent: the water reducing agent is usually a surfactant and is an anionic surfactant. It adsorbs on the surface of the cement particles to make the particles exhibit electrical properties. The particles repel each other due to the same charge, so that the cement particles are dispersed to release excess water between the particles to produce water reduction. On the other hand, due to the addition of the water reducing agent, the surface of the cement particles forms a suction film, which affects the hydration speed of the cement, makes the growth of the cement stone crystal more perfect, reduces the capillary gap of water evaporation, and the network structure is more compact and improved. The hardness and structural compactness of cement mortar.
After the cement is mixed with water, due to the molecular gravitational effect of the cement particles, the cement slurry forms a flocculation structure, so that 10% to 30% of the mixing water is wrapped in the cement particles, which cannot participate in free flow and lubrication, thereby affecting The fluidity of the concrete mix. When the water reducing agent is added, since the water reducing agent molecules can be adsorbed on the surface of the cement particles, the surface of the cement particles carries the same electric charge (usually a negative charge), forming an electrostatic repulsion, causing the cement particles to disperse and disintegrate the flocculation structure. , releasing part of the water that is wrapped and participating in the flow, thereby effectively increasing the fluidity of the concrete mixture.
The hydrophilic group in the water reducing agent has a strong polarity, so the water reducing agent adsorption film on the surface of the cement particle can form a stable solvated water film with the water molecule, and the water film has a good lubricating effect and can be effective. The sliding resistance between the cement particles is reduced, so that the fluidity of the concrete is further improved.
Steric steric effect
The hydrophilic polyether side chain in the water reducing agent structure extends in the aqueous solution to form a hydrophilic stereoscopic adsorption layer having a certain thickness on the surface of the adsorbed cement particles. When the cement particles are close, the adsorption layers begin to overlap, that is, steric hindrance occurs between the cement particles. The more overlap, the greater the steric hindrance force, and the greater the hindrance to the cohesion between the cement particles, causing the concrete to fall. The degree is kept good.