Agrobloc project: bio-based concrete masonry blocks
Agricultural resources can be used after crushing to replace mineral aggregates in concrete. Being natural and renewable materials they convey a positive image and contribute to reducing the use of mineral aggregates that are extracted from quarries. In order to assess the application of these bio-based aggregates in the French concrete industry, a project was lead aiming at creating concrete blocks made of aggregates produced by the agriculture. This project was funded by Centre-Val de Loire region and lead by a local plant. Hemp, flax and miscanthus were chosen for this study as their cultures are widespread in the area. They are beneficial for agriculture soil and environment-friendly as they require few agricultural inputs.
Concrete made of bio-based aggregates is usually a very light material (200 to 500 kg/m3) with low mechanical strength (less than 1 MPa compressive strength) and good thermal insulating properties. The study was focused on two main objectives. The first one was the formulation of bio-based concrete with more than 5 MPa in compressive strength. The second one was on trying to find the adequate consistency for the concrete in order to manufacture blocks on a vibrating press (ability to compaction and immediate mold release). Laboratory tests were conducted on cubic samples and on hollow blocks produced on a laboratory press.
Then tests were operated in a plant where masonry blocks and shuttering blocks made of hemp concrete were manufactured. These trials pointed out the necessity to adapt the settings of the vibrating press (cycle duration, frequency, amplitude). However they proved the capacity of producing the blocks in the plant with the usual tools. The field of application of the blocks needs to be defined because of the possible reduction of mechanical strength due to humidity and the high dimensional changes (drying shrinkage and swelling).