The challenge
Quality Block makes concrete masonry units in a range of designs, colours and textures for construction, fence and decorative uses. Consistent colour and texture are essential, both for its showroom displays and for blocks supplied to clients. The company had several problems with block quality, including corner cracking. It needed a redesigned mix and an admixture that would give a good surface texture, reduce corner cracking and raise ultimate strength.
The DCP solution
Casting the blocks needs the right slump, workability and setting time, and uniform quality. DCP gave technical support on the mix design and selected Donplast ES500W. This plasticising admixture is based on polycarboxylic polymers with selected additives. It is formulated for machine made (dry cast) concrete products, to give more uniform and consistent quality.
DCP products used
How it was applied
- Redesign the block mix with DCP technical support.
- Add Donplast ES500W plasticising admixture to the dry cast block mix.
- Reduce cement content by 15 lbs per yard, and use river sand from the company's own quarry in place of part of the manufactured sand.
The result
Compared with the former mix, the new mix gave a better surface finish on blocks of all sizes while using less manufactured sand (screenings). Compressive strength rose by around 70% while cement fell by 15 lbs per yard. Corner cracking and stress cracking when strapping blocks for transport were reduced. The company could use a cheaper sand source and, if needed, ship blocks on the same day they leave the kiln. Contractors using the blocks on a large municipal project said they were noticeably smoother.
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