Sika® ViscoCrete® GL 27

Sika® ViscoCrete® GL 27 is a new high range water-reducing admixture, based on chains of modified polycarboxylate ether. Primarily developed for the ready-mix concrete industry where slump retention, high strength and durability are required. It has a primary role in producing ‘self-compacting concrete’.

     
CHEMISTRY
What differentiates Sika® ViscoCrete® GL 27 from the traditional high range water reducing action with good workability is a new unique mechanism of action that greatly improves the effectiveness of cement dispersion. Traditional high range water reducing like melamine and naphthalene sulphonates are based on polymers which are absorbed by the cement particles. They wrap around the cement particles at the very early stage of the concrete mixing process. The sulphonic groups of the polymer chains increase the negative charge of the cement particle surface and disperse these particles by electrical repulsion. This electrostatic mechanism causes the cement paste to disperse and has the positive consequence of requiring less mixing water to obtain a given concrete workability.       
Sika® ViscoCrete® GL 27 has a different chemical structure than that of traditional high range water reducing products. It consists of a carboxylic ether polymer with long side chains. At the beginning of the mixing process, it imitates the same electrostatic dispersion mechanism as the traditional high range water reducing action, but the side chains linked to the polymer backbone generate a steric hindrance which stabilises the particles ability to separate and disperse.      With this process, flowable concrete with greatly reduced water content is obtained. The alkalinity created by the paste allows the polymers of Sika® ViscoCrete® GL 27 to ‘open up and progressively release’ many additional polymer chains that will prevent the early flocculation or stiffening of the mix. This mechanism allows considerably longer workability, reduction of mixing water content and higher early strengths, compared to traditional or retarding, high water reducing admixtures.