As we have stated previously, we are going to be taking the ideas developed in this column over the last couple of years and developing them into design practices. This is how it works. We will provide the basic narrative here for one design practice each week. We will keep it open for comments for one month. After that, we will finish it in formal form and offer it for sale at a modest price. Here is where you come in. If you make a substantive contribution to a standard, the organization for which you work will be granted a pro bono license to use that standard with its current issue number for as long as you like. We have had good response so far! Contribute, please.
This week's: Lightweight aggregate concrete (LGM 2013.005.01 when issued)
Lightweight aggregate concrete, or foamed concrete, is a versatile material which consists primarily of a cement based mortar mixed with at least 20% of volume air, and offers several distinct advantages over heavier aggregates: it is approximately 20% to 40% lighter than normal weight concrete, mixtures can be designed to achieve similar strengths and performance, requires less reinforcing steel, lower concrete volume, easier to handle and transport, improved fire resistance and can be utilized for a wide range of applications.
To utilize lightweight aggregate for structural concrete
Lightweight aggregates suitable for structural concrete may be natural materials such as pumice or scoria, or they may be processed aggregates such as expanded shales, clays, slates and slags.
Lightweight concrete can be treated in the same way as normal weight concrete, provided that it is pre-wetted properly. It can placed using conventional methods such as pumps, chutes or crane and buckets and requires similar setting time. Pre-wetting is required when pumping as the porous nature of the lightweight aggregate may cause the concrete to absorb water when subjected to pumping pressures. Methods to pre-wet lightweight aggregate particles include: thorough sprinkling, thermal quenching and vacuum saturation.
Note: It is important not to over-vibrate lightweight concrete, as this may result in the aggregate gravitating to the top because it is lighter than the paste (the heavier mortar).
So, give us your comments by 6 March 13, please!
Still open for comments Felted Dryer Drives with integral motor pulleys (Open until 27 Feb 13)
Still open for comments Fabric Roofs (Open until 20 Feb 13)
Still open for comments CPVC Dryer Bearing Drains (Open until 13 Feb 13)
As always, your comments will be appreciated.
Brian Brogdon, Ph.D.
Send us your comments!