THe following sentences are about using scrap tires for a number of purposes and some of the sentences which I makred red are very confusing. I need your help.
1. Dr. Hoening is on to the next wave in building materials: used tires. He has identified the next fashion in recycled materials for building materials
2. They have been studying engineering applications for these scrap tires. Way in which they can be used for engineering projects
3. There are some 500 million used tires stockpiled in the U.S., with a growth rate equal to about 250 million per year, creating hazards. The number of tyres being discarded annually in the US is +/- 250 millions tyres
4. When they( the tires) are placed in landfills, they tend to rise the surface, which has caused 33 states to forbid landfill placement altogether. Owing to their physical nature, tyres buried in landfill rubbish dumps will rise through to the surface. This has led to 33 states banning the burying of tyres in landfills.