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Sample test walls constructed of traditional and non-traditional masonry units.
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Research shows that solid wood fiber-ash masonry units have many benefits.

As the world's population continues to grow, so does the importance of sustainable buildings. Sustainable building materials, therefore, must be affordable and available for use in these structures.

Recently, researchers at the University of Missouri-Rolla investigated the potential for using an unusual alternative construction material in manufacturing masonry units for non-load bearing applications. Their goal was to develop products for infill wall systems, a practice common throughout the world.

These sustainable masonry units would perform similarly to standard masonry products. They would look about the same, and they'd be lighter. But the real difference is producers would manufacture them using alternative materials, including wood fiber and fly ash.

We studied a series of mix designs to better understand the optimal levels of wood fiber and fly ash content that would meet target strengths for the product. We also measured the change in the compressive strength when we added various amounts of portland cement to predict the strength of the material with and without cement. We also investigated the effect of variation in fly ash chemistry on compressive strength development.

It was a complex task, as we studied 36 mix proportions. We tried mix designs with varying degrees of fly ash, cement, and wood fiber content. We tested specimens for compressive strength at 14, 28, and 56 days. Their stress-strain behavior was also investigated, as well as other properties such as shrinkage, freeze-thaw resistance, fiber moisture condition, and fiber length.

An untapped filler

Our goal was to investigate the potential for using green timber material, commonly called wood fiber raw material in the manufacturing of masonry units. Wood fiber is a plentiful, renewable product. Unfortunately, only a small portion is often recovered for recycling or composting while the remainder is often sent to combustion facilities or landfills.

This waste fiber has tremendous potential as a high value constituent to manufacture building products. Also, their lightweight, toughness, ease of use (especially nailing connection capability), and excellent insulating properties makes them unique. We thought these properties would make the fibers a good product for infill wall applications.

Infill walls composed of infill blocks are considered non-structural elements of a building. Usually, the walls fill in between concrete or steel primary supporting elements in a building system. Infills walls are often covered with a finishing material, such as drywall or stucco.

Using a wood fiber fly ash (WFFA)-based composite system in these wall systems is promising for several reasons. Some advantages of this material are apparent, such as the material availability and low cost. This blend provides an end use for the mass recycling of fly ash and wood fibers. It is environmental friendly and does not require the same energy consumption of a kiln to produce it, as is the case with clay masonry.

Excellent ductility

The material has demonstrated excellent sound resistance, fire resistance, and insulation properties. It can be mechanically fastened by screwing (as needed) and cut easier than traditional concrete and masonry products. The material has outstanding impact and ballistic resistance, making it an attractive infill wall or wall panel application. It also has excellent damping and ductility characteristics.

The purpose for this study was to determine if wood fiber properties have an effect on material properties, in particular compressive strength, and to recommend a course of action to better define these effects. We studied the effect of several parameters, such as curing conditions, fiber length, bark content, and moisture content, on the compressive strength development of the masonry units.