Influence of hemp retting on the hydration of ordinary Portland cement (OPC) and the properties of hemp wood-OPC concrete
This work shows the influence of hemp retting on the hydration of Ordinary Portland Cement (OPC) and the properties of Hemp-OPC concrete. Hemp is a very efficient thermal insulating material (Lambda = 0.055 W/m.K.). Hemp is also a powerful retarder of OPC hydration. Less than 1 kg of unretted Hemp can block the hydration of 10 kg of OPC (CEM I) for a minimum period of 7 days. The soluble organics of Hemp are the main retarders of hydration. They contain mainly glucose, fructose, maltotetraose and maltotriose. Hemp retting reduces the clarity of Hemp. The yellow degree b* (measured by a DR LANGE colorimeter) decreases from 16.1 to 9.9 with the retting level. Hemp retting also reduces the soluble organic content of Hemp represented by TOC content from 3.76 to 2.4%. We observed a good correlation between the color degree (Yellow degree b*) and the soluble organics content of Hemp. On a composition of Hemp-OPC concrete (Wetting water/Hemp ratio = 3, Efficient water/OPC ratio = 0.35, Hemp/OPC ratio = 0.23) with different retting levels of Hemp (b* = 16.1 to 9.9), the density of dry concrete varies from 480 to 690 kg/m3; the compressive strength at 7 days increases from 0.1 to 2.4 MPa and the Lambda increases from 0.1 to 0.175 W/m.K. We also observed a good correlation between the properties of concrete and the degree of hemp retting.