Bio building bricks. Using sludge in bricks: Improves quality Reduces weight Saves energy
Bowie, Md. — THE building is attractive and functional, a picnic shelter built of quality face bricks, worthy of any building in the country. It should last for a century at least, probably much longer. Tom Shaw would have rejoiced at the thought. He's the Englishman who, exactly 100 years ago, developed a method for making the type of bricks used in erecting the shelter, another like it, and two large maintainance buildings in the Washington, D.C., area. Shaw surprised everyone at the time by making his bricks with sludge - sewage sludge that is. He was granted patent rights in 1889.
But the invention was ahead of its time. Sludge presented few disposal problems a century ago, and when concern began to surface toward the end of World War I, Shaw's idea was forgotten, lost in the dusty archives of a nation preoccupied with war. Now its time may finally have come. Drs. James Alleman at Purdue University and Ed Bryan of the National Science Foundation in Washington are among those who feel it has.
In this century, sludge volumes have increased geometrically, and disposal problems have been compounded by industrial contaminants. Ideally, clean waste could be composted or applied directly to the land as a fertilizer indefinitely. It has proven most effective in restoring vegetative cover to mine tailings and other scars of the mining industry.
But that still leaves a high percentage, too contaminated with heavy metals from industrial waste to go this route. As a result, research into encapsulating the waste in ceramic materials has become fairly widespread - and Shaw's ideas have surfaced again.
In the United States, much pioneering work on the concept was done by Dr. Alleman while he was at the University of Maryland. He had already made his first experimental bricks in the laboratory kiln when he uncovered the Shaw patent.
In many ways sludge is the ideal additive to the clay-shale mix of bricks. How can that be? Because it is an organic material with the added advantage of being wet. Organic additives improve laying qualities of bricks.
From the mason's point of view, pure clay makes for a less-than-ideal brick. There was even a time when masons considered English bricks more satisfactory to lay than the American-made variety. They accepted mortar more readily, providing a suction that held the brick in place while the mortar began to set.
Investigation showed that English bricks were lighter and slightly more porous, the result of organic ``contaminants'' in the original clay. When fired, the organic material burned up, leaving tiny voids throughout the brick. It has become a common practice to include some organic materials in the clay mix for most though not all brickmaking. Sawdust and coal fines are commonly used, according to Donald Agee, plant manager for the Maryland Clay Products brick company, which has made approximately half a million of the experimental sludge bricks.
Apart from making better quality bricks, an organic additive has several other important advantages for brickmaking. Using such material lengthens the life of a brickmaking plant. Clay is never brought to a brickmaking plant, the plant is sited where the clay is. ``When we eventually run out of clay here,'' says Agee, ``this place shuts down.'' Brick weight is reduced.
This factor is important in an industry where transportation beyond the immediate vicinity of the factory contributes most to the end cost. As Mr. Agee explains: ``Volume is never the limiting factor in delivery; weight is. If we can reduce brick weight by 10 percent we can can carry 10 percent more bricks to a load. That can make a significant difference in the delivered price.'' Energy consumption is cut.
By adding 2 to 3 percent (dryweight) of sludge to the mix, Maryland Clay Products ``saved 500 cubic feet of gas equivalent [the plant burns sawdust as a fuel] for every thousand bricks.'' This is because the sludge ignites to provide a significant amount of ``baking energy'' to the process.
Sludge, however, has another advantage that coal or sawdust does not: It is wet. Water has to be added to the clay and shale to make a plastic mix before it can be extruded and cut into individual bricks. This moisture has to be driven out of the raw bricks before the final firing takes place, but there is no way it can be excluded from the initial mix. ``In a drought year, like this, that shows up as a big plus for sludge,'' says Agee.
Alleman is doing research to find out if any of the heavy metals escape as gasified pollutants during the firing process. Most are expected to remain trapped and inert within the brick. Early findings are that few, if any, do escape, but further work is needed to verify this.
Even so, removing the pollutants would be relatively inexpensive since all hot gasses leaving the furnace are automatically trapped for reuse. This is done so the heat can be used to dry the raw bricks before they are fired.
``Existing scrubber technology could be used to remove the pollutants during this recycling period,'' says the National Science Foundation's Dr. Bryan, who has followed the biobrick program closely since its inception.
The first ``biobricks'' - so named to preempt any less savory option that ``earthy humor'' might suggest - have involved a relatively insignificant proportion of sludge to clay (50 tons in the first half million factory-made bricks).
But, Bryan points out, compression tests of laboratory-produced bricks show that up to 40 percent sludge can be included and still meet American Society for Testing Materials standards for structural bricks - bricks used in walls that support the roof or floor above. ``Higher sludge percentages could be used in bricks that are used simply as a veneer on existing walls,'' he says.
More than 50 percent sludge, on the other hand, has a distorting effect. But even that turned out to be a plus. The result was a brand new brick with a century-old appearance, appropriate for historic restoration work. Bryan laughs at the thought, ``but it might even become the best seller'' in a line of sludge-made bricks.