Tunnel rock recycling

Crushers and screeners normally used in quarries are stationed at the tunnel site for the purpose which is to crush and screen the rock debris for further use.

Additionally, the need for transporting aggregate could be significantly reduced as the utilization of the rock could be placed close by a processing facility and a concrete batching plant.

The investment cost of this facility would be repaid in the long run as the project would be close to self-supplied in construction aggregates.

TBMs create rock particles with excessive amounts of fines; this is a problem affecting quality for both subbase and concrete aggregate.

When using the tunnel excavation method D&B the particles can get up to 800 mm and there is a much coarser fraction, too large for subbase and concrete aggregate.

The processing facility has the following choices to manipulate the rock mass: reduce rock size, remove fines, reduce moisture content add commercial gravel and sand to blend it with the recycled tunnel debris.

By 2018, there are seven confirmed projects worldwide which have accomplished recycling tunnel rock (TBM) on an industrial level.

Rock crushing is divided into two methods based on compression or impact resulting in different type of fragmentation of the material.

Setup of the crushers, feed size and speeds plays a major role in production of high quality construction aggregates.

Classification accuracy will be of relevance as concrete aggregates do have boundary limits according to Particle-size distribution (grading) on Filler (materials) in the sand fraction.

Recycling rock to produce concrete aggregate is a complex procedure and will require an on-site laboratory at the tunnel project.