At World of Concrete, exhibitors unveil thousands of new and/or improved products. Despite the tough economic conditions, more than 75 new products have been entered into the Most Innovative Products award program. Even if you can't attend World of Concrete, Feb. 2-5, in Las Vegas, you can help rate how these innovations will affect your business by helping to select the best. To cast your vote, visit www.theconcreteproducer.com.
In the last few years, engineers have embraced concrete as a high-performance material which provides a wide host of great solutions to tough technical problems. In doing so, they often set some fresh concrete measurements as constraints for acceptance.
One common constraint is maximum placement temperature. Many performance mixes use higher levels of cementitious materials to achieve flowability and high strength, raising concerns about elevated placement temperatures. Engineers often specify an easily measured maximum “as placed” concrete temperature on projects to control strength, durability, plastic-shrinkage cracking, thermal cracking, and drying shrinkage.
It's no surprise that producers are now being asked to supply cooled concrete on many projects. Usually, cooling water, aggregate, or operating at night are the first procedures for cooling mixes. But when these don't work, members of ACI 305 Hot Weather suggest, “Concrete can be cooled by using ice for part of the mixing water.”
On most projects, the maximum temperature reduction for concrete mixes using ice is about 20° F. The amount of cooling is limited by the amount of mixing water available for ice substitution. Balancing the weight of water to ice in each batch accomplishes this.
Drawbacks of block ice
ACI warns that a major constraint to using block ice is often supply and production rate. Producers should plan for the added expense of using block ice. These additional costs include refrigerated storage, handling and crushing equipment, additional labor, and, if required, weighing the ice.
When the project specifies a few pours of large volumes of cooled concrete, producers often rent portable crusher/slinger machines. The units first pulverize chunks of block ice into small chips. Their output is often conveyed directly into the truck's mixer before batching the dry materials. The ice chips and nearly frozen water are quickly incorporated into the concrete mix.
Some producers are updating their plants to include automated ice batching systems. Some set up an ice plant near the concrete plant. As the ice is produced, it is weighed, crushed, and conveyed into the plant's batching set-up.
When several key clients were faced with cooling concrete on some important projects in Mexico, Rafael Pescador's team at Odisa Concrete Equipment developed a modular system so producers can cool fresh concrete with block ice. The fully automated system mixes batch water with weighed crushed ice. The new weigh batching system, installed onto a central or transit mix plant, enables producers to accurately add cooled water and ice to the mix.
This batcher is a two-compartment container; the outer silo is for water and has a two-yard capacity. This compartment has a discharge butterfly gate and a pneumatic actuator. The inside component weighs crushed ice and has a 1.43-yard volume. The batcher has a live bottom discharge with three 12-inch diameter screw conveyors. The conveyors can load the ice/water mixer to the plant's feed gate at up to 61,600 pounds per hour.
Pescador is bringing this technology to the U.S. by unveiling the system at World of Concrete (booth #N937).