BEST CON A71 High Range Water Reducing Leader For Pre-cast Concrete Products. Best Con A71 is a soluble Silica formaldehyde resin based superplasticizer. It has no air-entraining. A chloride free admixture based on Silica formaldehyde, formulated for the production of rheoplast concrete. Available as a liquid or in powder form which must be dissolved in water prior to use. A rheoplast concrete is a fluid, but cohesive mix with a slump value of at least 200mm. It is virtually self compacting, but as the same time free from segregation and with a water/cement ratio as a no-slum concrete with an mixture. It is preferable to use for Pre-cast Concrete Products. It increases strength of concrete , uni-block, hollow block , pre-cast wall.