The challenge
The Salisbury plant of Johnson Concrete Products makes reinforced concrete pipe (RCP) for stormwater management. It supplies customers such as NCDOT, commercial grading contractors and water works distributors. The plant had two problems with its pipes. It could not achieve the smooth finish required, and minor bug holes appeared on the surface. It also struggled to reach the early strength needed. An admixture was needed to give a smoother finish with fewer bug holes and higher strength.
The DCP solution
DCP recommended Donplast ES1000, a chloride-free plasticising admixture based on polycarboxylic polymers. It is formulated for machine-made (dry-cast) concrete products and helps compaction, early strength and surface finish. Getting the right slump, workability and setting time in a dry-cast mix depends on the right plasticiser, so Donplast ES1000 was selected. It was dosed with DCP's direct feed admixture dispensing system. To gain more strength, DCP also added Donplast HC3, a hydration controlling admixture. At a set dosage it improves curing and gives more strength gain without changing the setting time.
DCP products used
How it was applied
- Fabricate, weld and align the reinforcing steel in the moulds.
- Cast the dry concrete mix dosed with Donplast ES1000 (and Donplast HC3) through the DCP dispensing system.
- Compact the concrete on a vibrating table.
- Strip the moulds straight after compaction and place the pipes in the curing room for one day.
- Move the pipes to the yard to finish curing and test samples for flexural strength.
The result
The pipes passed QC testing and met the Department of Transportation requirements. The finish improved, with minimal bug holes. The plant's Quality Control Department reported that the pipes now reach their 4,000 psi shipping strength in 36 hours, compared with 72 hours before.
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