Impact of Bio-Aggregates Properties on the Chemical Interactions with Mineral Binder, Application to Vegetal Concrete

Abstract

Plant concretes were developed and are currently used as filling material in a timber frame. Their properties are strongly related to the bio-aggregates characteristics. In addition, since hemp shiv, the reference bio-based aggregate, has a limited availability, it is necessary to consider alternative bio-aggregates largely and locally available. Thus, this paper focused on identifying and understanding mechanisms of interaction between different bio-aggregates and mineral binders. To address this issue, the first objective was to determine the properties of five hemp shives and two alternative bioaggregates for vegetal lightweight concrete: corn and sunflower bark particles. The study of the chemical interactions between bio-aggregates and a pozzolanic binder was conducted on model pastes mixed with filtered solutions containing bio-aggregates extractives. The mechanical properties of the paste, as well as their hydration and their mineralogical evolution were studied. In the last part, the mechanical behavior of vegetal concretes was assessed. The results highlight a strong relation between the mechanical behavior of pastes and concretes and the extractive content of the different tested bio-aggregates. Finally, pastes appeared as a relatively good model to predict the behavior of concretes by following their early age performances: setting delay and 3-day mechanical strength.

A Review of the Multi-Physical Characteristics of Plant Aggregates and Their Effects on the Properties of Plant-Based Concrete

“…All the studies agreed with the detrimental effects of extractives on mineral binders, such as disruption of the early setting and hardening mechanism, modifying the mechanical performance in the hardened state, and influencing the long-term durability [56,65,72,119]. Bourdot et al (2019) prepared binder pastes by mixing the pozzolanic binder with the extractives of five different hemp shives, sunflower and corn bark, and also the plant aggregates from them. As shown in Figure 16, in the case of the five tested hemp shives, the hydration delay in the model paste and the mechanical performance of the hemp concrete were directly related to the extractives content of the shiv.…”

“…These results showed that the maximum compressive stress was not a good indicator of the use of composites. Consequently, other indicators corresponding to the stresses in the elastic behavior phase (the strain equal to 1.5% or 5%) were proposed in the literature to have comparable results representing the performance of the composites in use [15,38,42,43,65]. The decreasing trend of the compressive strength corresponding to a stress level of 1.5% with the content of aggregates is shown in Figure 18.…”

“…No particular treatments are carried out on these aggregates as reported in the literature. Instead, they are directly mixed with either cement, lime, or pozzolanic binder [17,43,65].…”

“…Figure 8 presents the extreme major and minor axis length curves (i.e., the maximum limits of the major axis and the minimum limits of the minor as observed in the literature) of seven different plant aggregates and shows the extent of each particle size. Nevertheless, in terms of shape and size, two hemp shives of different origins differed more significantly than a hemp shiv compared with a corn or sunflower bark [65]. Indeed, the particle size of plant aggregates is an easily adjustable parameter according to the calibration process.…”

“…Compressive strength of model pastes after seven days as a function of watersoluble mass content (HS: hemp shiv; SB: sunflower bark; LS: lavender straw; and CB: corn bark) [65,72,119]. Diquélou et al (2015) correlated the delaying of the setting for three cement pastes made from the leaching solutions of the three different hemp shives with the compressive strength of the model pastes [72].…”