Concrete mixers

"Concrete mixers must keep mixing their load--or the concrete will harden! These trucks are fascinating to watch as they move forward while the drum they carry turns around and around. Readers will . . . learn about this hardworking machine and why it's needed on so many construction projects. Low-ATOS text offers comprehensible explanations, and . . . photographs add to this . . . book's appeal"--Provided by publisher.