Formulas for Lightweight Concrete

Fernando Martinez Lewels has a M.S.C.E degree from the University of Texas at El Paso. He is now working with the Agartif company in Chihuahua, Mexico (about 170 miles from El Paso Texas). This Company has developed a type of lightweight aggregate that provides material for all types of construction needs, at reasonable cost and with good thermal insulation values. They manufacture the equipment required to do this according to the needs of their customers; the feed stock are common construction materials that should be available in most locations. Their philosophy in developing this type of aggregate is to be able to use this everywhere, without depending on a lightweight aggregate quarry, so you can have access to this material in any part of the world. In Mexico we have a saying that "we build our homes so we have to go outside in the summer to be fresh, and in the winter we go outside to catch the rays of sun to be warm". Lightweight concrete can help this situation by making available materials for more comfortable homes.

Questions and Answers

Q: Would you be kind enough to recommend a lightweight formula for our tabletops. Size: 48x48x1.5". These tops are tiled with marble mosaics. We can embed steel if necessary. Aesthetics are not important as they will be fully encased. However they must be strong enough to perform as tabletops without worry of breakage.

A: (Bruce Schundler) If it won't be exposed, we would recommend a one to four mix (one part Portland to four parts by volume of perlite or vermiculite) Add some fiber reinforcement (available at mason stores). The problem with the concrete if it is exposed is that it isn't very hard---and the surface would have to be hardened with some special coatings. Of course, I am presuming this concrete will have some kind of structural support under it. If not, lightweight concrete wouldn't work. All concretes are very bad in terms of tensile strengths--or their ability to support weight across spans. They are good for compressive strength, but not tensile strength. Often corrugated metal or metal forms have to be used if the concrete is spanning an area between two beams.

Q: You did not recommend the use of concrete on an exposed deck. We are planning to enclose our deck with a three seasons application. Our current deck boards are 5/4 treated lumber. We want to install radiant heat in the floor using pex tubing incorporated into a suspended slab of 1 1/2 " of concrete that we would lay tile on. Can you recommend a mix for this purpose?

A: (Bruce) I would recommend contacting a local redimix concrete supplier for his advice on what is available locally. Appropriate lightweight aggregates are different depending on what part of the country one is in.

Q: Can you tell me an easy way to aerate concrete with or without chemicals, as here in Indonesia chemicals & pumice etc. are hard to obtain!! I have made a large high speed mixer and am using an emulsifier (detergent) and have had mixed results. Problems in curing! Tried adding more lime etc. Can you advise?

A: (Bruce) Normally lightweight concretes need air entrainment--and normally the air entrainment can be purchased in the concrete by ordering Type 1A portland instead of regular Type 1. Or, in a pinch, people have used non-sudsing detergent (e.g. the type used in washing machines or dish washing machines--not the type used in kitchen sinks. But......different cements and different ingredients and different products can all affect what is used and how and why.

Q: I live in Eugene, OR, and every year this city has what can only be described as a "leaf problem". In other words leaves clog up the streets, drains, etc... Has anyone ever looked into turning leaves into paper products or building materials?

A: (Kelly)This website might interest you, since Phillip has been including various plant materials in his "hybrid adobe": hybridadobe.com