Each tire bale measures approximately 5’x5’x2-1/2′ high, with approximately 120 compressed tires. They weigh about 1 ton each, and are stacked like bricks. All tire bale walls can go up on 2 – 3 days.
A Typical Tire Bale Earthship at 2,200 square feet will use approximately 20,000 tires.
In the earthship building process, scrap tires rammed full of compacted earth are used to construct building walls. It is also possible to construct building walls from compacted bales of scrap tires, or tire bales.
How are Tire Bales made?
Tire bales are made by compressing waste tires into a rectangular shape with a large hydraulic press and banding them with with 5 or more, .115 inch diameter, galvanized or stainless steel wires. The bales are typically 5 feet wide x 5 feet long x 2.5 feet high, although sizes can vary depending on the particular press that is used. Smaller half bales are also available. One bale requires approximately 100 passenger car and/or recreational vehicle tires. Each full bale weighs approximately one ton. The bales, when stacked in running bond and finished with a cement-based grout and plaster/stucco have the potential of forming a strong, stable wall.
How Strong are Tire Bales?
Tire bales are incredibly strong. A study of tire bales conducted by undergraduate students at the Colorado School of Mines (CSM)* concluded that about 150,000 pounds of compressive force were required before the first steel wire band broke. Even with a single broken wire, the tire bale did not entirely fail, but continued to support its load, albeit with more deformation, up to a force of 600,000 lbs. No ultimate failure was observed, as one would see in concrete, wood, or many other conventional building materials.
Regarding residential or commercial building.
Assume that a tire bale is supporting an overhead roof load. Assume also that the roof load from the roof beams, rafters, or trusses is transmitted to the tire bale by a spreader beam or bond beam sufficient to ensure that the roof load is transmitted uniformly across the tire bale. Then the load per linear foot of wall required to “break” the first band of the tire bale is about:
150,000 lbs / 5 feet = 30,000 lbs / linear foot
This is nearly an order of magnitude greater than one could expect in a usual residential or commercial application, even in an area where severe snow loads could be expected.
These characteristics relate, of course, to a single tire bale in a testing machine rather to the strength of an assembled and finished wall. An additional factor that has not been considered with respect to the strength of completed walls is that tire bale building walls are typically grouted with pneumatically applied cement-based material (i.e., gunnite or shotcrete), stabilized earthen (adobe) plasters or other stucco materials. Then the walls are faced with stucco wire and surfaced with the same material. This material fills the voids between the bales as well as many of the voids within the bales and provides a thick, even surface on the walls. Although no laboratory or field tests have been done, addition of the grouting and surfacing to the assembled bales is certain to improve the strength and stability of the completed wall.
* Colorado School of Mines (CSM) Study: “Recycled Tire-Bales for Wall Construction” Final Report submitted to The Multi-Disciplinary Senior Design Program, Colorado School of Mines, Davis et al, Arthur Lakes Library, Colorado School of Mines, Golden, Colorado, 2000.
Deformation Under Load
The same CSM study referenced above indicates that tire bale deformation is near-linear under compressive loads from zero to at least around 70 PSI (equivalent to a force of around 250,000 lbs). After this point, the deformation per unit of load increases in a more-or-less exponential fashion. A portion of the deformation appears to be plastic, as the tire bale does not completely return to its original shape when the load is removed.
Some, including the authors of the CSM study, would say that the deformation was indicative of “failure” and that tire bales are not suitable as construction material on that account. On the other hand, and in my opinion, this is not so. The compressive loads used in the CSM testing are, again, nearly an order of magnitude greater than wall loadings that can be reasonably expected in single story residential or commercial use. Moreover, the CSM study seemed to indicate little possibility of a precipitous failure like those occasionally seen in conventional wall building materials such as wood, concrete, or masonry, even under much greater loads than would be expected.
Additionally a stack of tire bales, 10 high, at the Tire Disposal Facility located near Fountain, Colorado was examined and measured. It is worth noting that there was no measurable difference in size or shape of the heavily loaded bottom layer bales compared to the size and shape of the not loaded top layer. In this case, the bottom bales were bearing much more weight than could be expected in any reasonable building design.
An additional factor, which has not been tested in the laboratory or in practice, is the cement-based grout and stucco/plaster that is applied to tire bale walls, as described above in paragraph 2. The addition of this
An adequate bond beam is required to support the roof beams, trusses, or rafters and to secure them to the walls. Experience suggests that this bond beam be constructed of reinforced concrete (3000 psi or greater) formed and poured in place on top of the wall. A nominal 6” x 24” or equivalent bond beam with 3 #4 rebars 10” on center all around is suggested. An alternative bond beam configuration is shown at Figure 3. Low slump concrete should be used so as to avoid losing too much concrete into the porous tire bales beneath the bond beam. The near-complete fit of the concrete into the bales will lock the bond beam into place. This may be supplemented by additional #4 rebars wired into the tire bales on 4 foot centers and tied into the horizontal reinforcing or by field fabricated anchors extending from beneath the final layer of tire bales.
Outgassing From Tires
When a tire bale building is initially enclosed, the tires may be left uncovered for a time. During this period it is possible that occupants may be able to smell the “rubbery” odor of the tires. However, when the walls are completed, they are covered with a 2 – 4 inch thick coating of cement- based plaster. The tires are completely covered and sealed away from the occupied space. It seems very unlikely that any out-gassing would reach the occupied space once the plaster is in place. Any residual odor will slowly but steadily be reduced by continuing ventilation of the enclosed space.
This issue has been studied and commented upon extensively by designers, builders, and owners (as well as detractors) of related rammed tire earthship buildings, previously referred to. I have done much reading in this area and I have been unable to find a single case where any human or animal sickness occurred that was attributable to outgassing tires. The use of discarded tires for occupied structures is relatively new compared to other building technologies, and it is possible that long-term problems may arise. However, other outgassing issues inherent in conventional buildings, like the chemicals used in commercial glues, carpets and engineered wood, seem to be at least as serious.
After examining several tire bale structures and the issues that have been raised concerning tire bale walls, I can find no substantial reason why they should not be used for walls in residential and commercial structures in non-seismic areas as long as they are assembled and finished as described above. Using tire bales in this way has the potential for reducing landfill utilization, waste, and inappropriate/illegal disposal of scrap tires in a way that results in a product that can have positive societal impact.
Municipalities are building with tires.
Over the last decade, more states have studied the engineering specifications for tire bales in different applications. New York, New Mexico, Pennsylvania, Texas and Colorado led the way. Below, a few of their stories……….
Chautauqua County, New York’s Department of Public Facilities, led the way. Their response came in the aftermath of a tire fire. They baled the unburned tires that remained and used the bales in the late 1990s and early 2000s for subgrade lightweight fill for road construction throughout the county. In each project, roadbed material in the existing road was excavated. Filter fabric underlayment was installed, tires bales were placed over the fabric as subgrade and granular material was used to fill voids. The final road surface consisted of 18 inches of compacted gravel, covering the bales. The sites have been monitored and the County found the following benefits of using tire blocks as lightweight fill over marginal soils: (1) thermal insulation and frost penetration, (2) better drainage, (3) lower cost than conventional fill, (4) less installation labor since the blocks were already compacted, and (5) less settling over time.
The Fort Worth District of the Texas Department of Transportation, in a geotechnical investigation and analyses of a slope failure repair using baled tires on Interstate Highway 30, west of Oakland Boulevard in Fort Worth, Tarrant County Texas found that the use of baled tires as partial replacement for fill soils used in slope repair projects appears to provide a significant improvement to long term stability while simultaneously providing for the beneficial reuse of waste tires. Specifically, they found that a considerable improvement was shown in long term repaired slope stability where baled tires are substituted for soil backfill in areas where high plasticity clays are predominant. They concluded that baled tires used as partial replacement for fill soils should be considered whenever economically practicable.
The Starr Tire Pile is Pennsylvania’s largest tire pile with over 8 million tires. The Center for Dirt and Gravel Road Studies with Penn State, inspired by the success of New York’s program, studied the benefits of using baled tires in severely entrenched dirt and gravel roads. Most dirt roads are located next to streams, making them the largest source of sedimentary pollution. When rainwater collects and travels in concentrated volumes, unstable soil from banks and ditches accumulates and descends into streams. Diehl Road was chosen due to its proximity to the Starr Tire Pile. 200,000 tires were used in the project. The project was so successful, the Center for Dirt and Gravel Road Studies completed another project on Pattonhill Grouse Road in December of 2006.