What a Truck Mixer Does

Concrete is made at a batching plant by mixing cement, sand, stone (aggregate), water and sometimes chemical admixtures. From the moment water meets cement, the concrete starts to stiffen. It must reach the site and be placed before it sets. The truck mixer carries it there and keeps it mixed on the way.

A truck mixer is also called a concrete mixer truck, a transit mixer or a ready-mix truck. It is a heavy truck chassis carrying a large rotating drum. Inside the drum, spiral blades keep the concrete moving. At the site, the drum turns the other way and the concrete comes out down a chute, into the formwork, a pump, a skip or a wheelbarrow.

Why the truck is so heavy

Normal-weight concrete weighs about 2.4 tonnes per cubic metre. A common truck mixer is rated to carry about 8 cubic metres. That is roughly 19 tonnes of concrete (8 × 2.4 = 19.2), on top of the weight of the truck and the drum. Many truck mixers are 8x4: four axles, eight wheel positions, four of them driven, with two steering axles at the front. The exact rated load is on the mixer's rating plate and differs between models.

Much of that weight sits high up, in a drum that turns. This is the source of several of the hazards in this course.