Superplasticizers have been used for several years now to produce high-slump flowing concrete without adding excess water. The high-slump concrete that's produced can be easily poured or pumped without segregation, but because the increase in slump lasts only 30 to 60 minutes, superplasticizers that have been used in the past have usually had to be added at the jobsite. In the past few years a few admixture manufacturers have developed superplasticizers that can maintain high slump for 1 to 3 hours. Because of the longer slump life, these admixtures can be added to concrete at the batch plant.
BENEFITS OF PLANT ADDITION
- The ready mix producer retains complete control and responsibility for the concrete mix to the point of placement.
- Delivering concrete at a high slump discourages the addition of unnecessary water on site.
- Ready mix trucks are on the jobsite for less time.
- Wear on truck mixers is reduced.
- Setting time of the concrete doesn't vary as much from truckload to truckload.
- Concrete can be placed at higher temperatures.
- Truck-mounted admixture tanks are not required.
- The ready mix producer can market flowing concrete delivered to the jobsite as a customer service.
DISADVANTAGES OF PLANT ADDITION
- Cost is higher with some methods of producing flowing concrete at the batch plant.
- The ready mix producer may have to ship less concrete per truck.
- Some plant-added superplasticizers retard set.
- Slump of the concrete that arrives on site may vary.
- The contractor cannot see the superplasticizer or other admixtures being added to the concrete.