meaning of water reducer:
water reducer is a kind of concrete admixture that can reduce the mixing water consumption while maintaining the slump of concrete unchanged. Most of them belong to anionic surfactants, such as lignosulfonate, naphthalene sulfonate formaldehyde polymer and so on. Adding concrete mixture can disperse cement particles, improve its workability, reduce unit water consumption and improve the fluidity of concrete mixture; Or reduce the unit cement consumption, saving cement.
classification of water reducing agent:
(1) Appearance is divided into water agent and powder. The solid content of aqueous solution is generally 2%, 4% (also known as mother liquor) and 6%, and the solid content of powder is generally 98%.
(2) According to the water-reducing ability and strengthening ability, water-reducing agents can be divided into ordinary water-reducing agents (also known as plasticizers, with water-reducing rate not less than 8%), high-efficiency water-reducing agents (also known as superplasticizers, with water-reducing rate not less than 14%) and high-performance water-reducing agents (with water-reducing rate not less than 25%), and they can be divided into early strength type, standard type and retarding type respectively.
(3) According to the composition materials, it is divided into lignosulfonates; Polycyclic aromatic salts; Water soluble resin sulfonates.
common water reducing agent is suitable for concrete with daily minimum temperature above 5℃. The superplasticizer is suitable for concrete with daily minimum temperature above ℃, and is also suitable for preparing high fluidity concrete, high strength concrete and steam curing concrete.
Action mechanism of water reducer:
(1) Dispersion: After cement is mixed with water, due to the molecular attraction of cement particles, the cement slurry forms a flocculation structure, so that 1% ~ 3% of mixing water is wrapped in cement particles, which can not participate in free flow and lubrication, thus affecting the fluidity of concrete mixture. When the water reducer is added, the molecules of the water reducer can be directionally adsorbed on the surface of cement particles, so that the surface of cement particles has the same charge (usually negative charge), which forms electrostatic repulsion, which promotes the mutual dispersion of cement particles, destroys the flocculation structure, releases part of the wrapped water and participates in the flow, thus effectively increasing the fluidity of concrete mixture.
(2) Lubrication: The hydrophilic group in the water reducer is very polar, so the water reducer adsorption film on the surface of cement particles can form a stable solvated water film with water molecules, which has a good lubrication effect and can effectively reduce the sliding resistance between cement particles, thus further improving the fluidity of concrete.
(3) steric hindrance: the hydrophilic polyether side chain in the water reducer structure extends in the aqueous solution, thus forming a hydrophilic three-dimensional adsorption layer with a certain thickness on the surface of the adsorbed cement particles. When cement particles approach, the adsorption layers begin to overlap, that is, steric hindrance is generated between cement particles. The more overlap, the greater steric repulsion, and the greater hindrance to the cohesion between cement particles, which makes the slump of concrete keep good.
(4) Slow-release effect of grafted poly-branched chain: In the preparation process of new water reducer, such as polycarboxylic acid water reducer, some branched chains are grafted on the molecule of water reducer, which can not only provide steric effects, but also be cut off slowly in the high alkalinity environment of cement hydration, thus releasing polycarboxylic acid with dispersion effect, thus improving the dispersion effect of cement particles and controlling slump loss.