Heat curing cycle for insulated (polystyrene) concrete panels

[ione]

I should heat cure sandwich concrete panels (walls) in a curing tunnel.
The panels are 30 cm thick (two layers of concrete each one 7.5 cm thick, with a polystyrene layer of 16 cm in between). The tunnel has a door at each of its ends and it's loaded on a continuous basis with 5 pcs/hour. The use of live steam to increase the temperature is not allowed. I was thinking about using forced warm air, keeping the relative humidity inside the curing tunnel above 80%.
I'm not familiar with that kind of product and was wondering whether anyone could point me in the right direction about recommended temperatures and duration for an effective heat curing cycle.

Thanks

 

[concretemasonry]

This is not a structural question.

The process and facility is not adequate for quality products with repeatable results. You cannot seal an entire building and maintain a manufacturing process at the same time with controlled high humidity and temperatures.

Raising the temperature of the concrete with warm water will provide higher earlier early strength to handle and then achieve long term strengths.

In many countries, vertical forms for casting panels are heated and the entire assembly is removed to be stripped when desired. Some wall panels are made using normal concrete for one side and very lightweight concrete on the other side that is simultaneously cast around a EPS or XPS foam for use in loadbearing wall panels. The forms are heated.

Continuous sandwich precast panels are made in long horizontal beds (up to 400 feet long)are cured in forms with warm water or steam circulated and the individual panels are saw cut the next day while production continues on adjacent beds. - Very significant cost expenditures for facilities.

There is a myriad of different processes in the world depending on the intended use of the products around the world and almost all can be structural.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[ione]

Thanks for your comment.

Indeed I don't need to insulate the whole buiding. The line consists of a carousel and there will be an insulated tunnel where panels will be loaded for the heat curing phase, together with their forms. And yes I think I can keep temperature and relative humidity almost consistent all along the tunnel. What I'm looking for are suggestions about curing temperature and duration of the curing process for this kind of product.

 

[concretemasonry]

Assuming that the sandwich has the concrete on the exterior faces and the polystyrene on the inside, it is possible, but the 5 hour cycle is a problem. I also assume you have some sort of tie between the concrete portion.

You might want to investigate using warmer concrete (heated mixing water) and a faster setting cement type (Type III in the U.S.) to speed up the reaction and make the walls panels easier to strip and handle once they are out of the forms. This is a very minor cost in a plant environment and is a very economical method to produce quality products. Keep the mixing water below 140F. The "heated" air in the carousel does not do a lot considering the time involved to warm the forms and transmit the heat to the single surface of each layer of concrete that is exposed because the polystyrene foam on the center will prevent the "heated" air and 80% humidity from having a great effect, based on the 5 hour limitation.

Rotating carousels can be costly and pose operating problems, but I have seen floating "boats" that have the forms built into them and are 95% in contact with warm water and they use warmer temperatures that your air and has better thermal and mass properties and can easily be maintained 24/7.

A single plant operation may require specific aggregate requirements for operational, quality and economic reasons. It not costly or difficult to obtain what is needed and reasonable price once the annual demand is proven. Most current aggregate specifications are only very loose guidelines and some even have a footnote that stated that non-complying aggregates (gradation especially, but also particle shape) may be used if it can be shown the use and quality is proven. This is very important because of the unique needs and requirements for different products, processes and uses. - This is important for plant-produced concrete products, since most specifications are written for very general uses.

I hope this applies for your situation.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.