• INTRODUCTION
• COMPOSITE STRAW CONSTRUCTION
• A NEW TYPE OF STRAW BALE CONSTRUCTION
• PICTURES of FIRST LAB PROTOTYPE

David's Bio at Strawjet.com

INTRODUCTION

Modern thought about energy conversation in buildings promotes the application of large amounts of insulation. This practice is at odds with another building trend that promotes non-toxic interior environment because the least expensive and therefore the most commonly used insulation is a major contributor to poor indoor air quality. Imagine if there were a new insulation that was cheaper still, made from natural materials, and had no toxic emissions. Now imagine that this new insulation was also strong enough to replace the studs in the walls, the rafters in the roof, and the joists in the floor. Now imagine that this insulation was made from a material that is available in virtually limitless supply, environmentally friendly, and simple enough to manufacture in the most underdeveloped countries.

We are designing a construction system where buildings would be built out of panels made of straw composite. This material is similar to fiberglass composite except that it is made of braids of straw bonded together with adobe rather than grass fibers and plastic resin. The braids are made of uncrushed straw shafts, and the adobe is reinforced with recycled paper pulp. This arrangement of materials allows the compression and tensile strength of the individual stalks of straw to be combined to form a panel of significant strength. The design results in a material that is 100 times stronger than straw bale construction as well as twice the volume for a given amount of straw.

Our straw harvester cuts and gathers uncrushed stalks of straw and forms them into a continuous braid. This process takes place after the grain has been harvested. The process for making panels is intended to be suitable for developing countries, and is not unlike traditional mud brick construction methods. During construction the panels key together and are held in place with fiber adobe, and stitched with bailing twine. Spaces can be left for doors and windows or the required openings can be cut out with a saw after the mortar is dry. Floors can be made by forming panels that span the width of the desired floor. Sufficient strength can be achieved by following prescribed formula for additives, number of layers, and stitching.

A variety of architectural members such as arches; columns, and door jams can be made by placing braids and adobe in a jig then wrapping the bundle with twine. This harvesting system is designed to cut straw and bundle it into a continuous braid. The machine that accomplishes this is composed of a shear, followed by three converging conveyor belts. These conveyor belts feed the straw into a series of concave rollers that compress the straw into a tight cylinder. When the straw exits the last rollers it is wrapped with continuous filament polyester thread. The thread is applied by a spinning wheel with two spools of thread on it. This device applies two applications of thread at the same time. 

[The photographs here show the original prototype version of the harvester.]

• • Pic# 1 shows the front end of the harvester.
• • Pic#2 shows aside view of the compression roller stage
• • Pic#3 shows one of the spinning wheels.
• • Pic#4 and #5 show the wrapping stage. #5 shows a length of pipe insulation occupying the place where the braid of straw would be.