Characterization of hemp aggregates – comparison of several size analysis
Bio-based concretes are mixes of vegetal aggregates with a mineral binder. These new materials are used for buildings as coating, wall or roofing. They provide good properties to the constructions in terms of hygrometry, acoustic, thermic and lightness. Bio-based aggregates used in these new materials are very different from classical mineral aggregates used in concrete. Their intrinsic characteristics have strong impacts on bio-based concrete properties. There are no official standard methods to describe bio-based aggregates and so it appears as an important issue to develop this field. This study is focused on hemp aggregates, which is a material commonly used in bio-based concrete. It is about how to evaluate the size of these nonmineral particles. Mineral aggregates size is defined with a single measurement because they are assimilated as a sphere, with eventually a shape coefficient to characterize flattening. Biosourced aggregates have a more parallelepiped shape. Two methods already exist to characterize them and are frequently used: sieving and image analysis. This study proposes a new method based on the use of a videogranulometer device. This device is based on shadowgraph principle and makes a continuous measurement on particles. It enables to obtain the width and length of each particle simultaneously, as image analysis method, with a better efficiency. This article details the elaboration of this method of evaluation of aggregate size properties: the choices of the parameters and the adaptation of the device. Compared results between the three methods, the two usual ones and the videogranulometer one, show a good correlation between the videogranulometer method and the classic ones. As a conclusion, the method developed here has the best amount of analyzed aggregates time necessary ratio and describes as well each particle, offering a great representativeness of a hemp stock.