FAQs: Structural Lightweight Concrete for Ready Mix Producers
For ready mix customers, structural lightweight concrete presents unique storage, handling, and pumping considerations. Clint Chapman, Western Region Marketing & Technical Manager at Arcosa Lightweight, addresses common questions on optimizing lightweight concrete for ready mix applications.
For Ready Mix Customers
Are there any special requirements for storage and handling?
ANSWER: It’s a little bit different. The biggest requirement is order lead time. You want to ensure the material arrives with enough time for saturation before it’s pump placed.
Saturation can be achieved in several ways, like submersion in water or setting up sprinkler systems on your stockpile. You can submerge stockpiles in a water pond, or perform an ambient soak with sprinklers. The material is free-draining, allowing water to penetrate through. Avoid over-handling or turning the stockpile, as this can degrade the material. Just stack it, apply sprinklers, and allow time for saturation.
Is it true that lightweight concrete doesn’t pump?
ANSWER: No, that is not true. Lightweight concrete has been pumped over substantial distances. For example, the Salesforce Tower in San Francisco and the Wilshire Grand in Los Angeles both used pumped lightweight concrete for over 70 stories.
When proportioned and pumped correctly, lightweight concrete can be transported over great distances effectively.
What do I need to consider regarding pump configuration?
ANSWER: We recommend adhering to ACI guidelines, including using a minimum five-inch line throughout the system. Reduce rubber line usage as much as possible.
Opt for steel slick line whenever possible, and maintain a flat boom angle to avoid pumping vertically and allowing concrete to fall straight down. Using a pump primer at the start of pumping is also recommended for best results.
Keep pump pressures low and control stroke limits, aiming for pumping rates of about 60-70 yards per hour.
Can I finish lightweight concrete the same as I do with normal concrete?
ANSWER: Yes, generally finishing lightweight concrete is similar to finishing normal weight concrete. The primary difference is that most lightweight concrete is air-entrained, resulting in a reduced bleed rate.
Patience is key when finishing lightweight concrete. Starting too early can trap moisture, leading to blistering. Allow adequate time to ensure the concrete is ready for finishing.
