Urban areas in Canada and the United States are struggling to find enough natural materials for making concrete. Scientists tested using old concrete to make new concrete instead of throwing it away. They found that concrete made with recycled materials is just as strong and durable as concrete made with new materials. Sometimes, the recycled concrete is a little weaker, but this can be fixed by changing how the concrete is mixed. Overall, using recycled concrete is a good way to make concrete without harming the environment.