A new type of concrete water reducer has been invented. It is grafted with lignosulfonate and carbonyl aliphatic compounds to improve its fluidity. The resultant graft water reducer has a good water reducing ratio and excellent compatibility with cement.
Lignosulfonate is a hydrophobic, low molecular weight compound, which is usually produced by modifying black liquor from paper making. Its adsorption to cement particles can be used to enhance the hydrating effect. However, it can also affect the setting and strength of the cement paste.
The morphology of the final product is also affected by the graft process. Lignosulfonate is formed from a lyophilic group, which is introduced into the lignin macromolecules. This modification removes the components with a too small relative molecular mass.
Lignosulfonate, a hydrated and complex molecular molecule, has the ability to reduce the surface energy of the solid-liquid interface. During hydration, its macromolecular anions can negatively charge the cement particles. This adsorption reduces the zeta potential.
Besides, it can prevent flocculation of fine cement particles. Its polar hydrophilic organic chain can keep the cement particles separated by electrostatic repulsion.
Several factors, including cement and admixture composition, affect compatibility. The usual dosage of a water reducer is 0.3- 0.5% liquid by weight of the cement.
Higher dosages of a water reducer can cause excessive retardation and bleeding. Incompatibility between the cement and water reducer can lead to rapid loss of workability. For instance, high dosages of a water reducer may produce a reduction in the concrete's flexural strength, quicken the setting of the cement paste, and promote the deterioration of its fluidity.
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