The next Peer-to-Peer webinar will take place on Tuesday September 30, 2025 at 2pm Paris Time and will be one hour long (3*15 minutes presentations + 15-minute interaction). The registration for this webinar is free.
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Theme of the Peer-to-Peer Webinar: Testing natural materials for construction: results from biowaste-based composites, earthen blocks, and joint systems for bamboo structures.
Speaker 1: Halima BELHADAD, University of Constantine 1 & Liverpool John Moores University, United Kingdom
Title 1: Treated vs. Untreated Olive Husk in Bio-Based Concrete: A Multi-Scale Characterization from Aggregate Properties to Composite Performance
The integration of agricultural by-products into construction materials offers an opportunity to valorise waste while improving the environmental footprint of the built environment. Among such resources, olive husk (OH), a fibrous by-product of Mediterranean olive oil production, remains underutilised despite its abundance and promising physical characteristics. Unlike the widely studied olive stones, OH is rarely employed in cementitious composites, primarily due to its relatively high oil residue content (≈8.3%), which is often considered detrimental to binder–aggregate interactions. Yet, it is precisely the fibrous fraction of OH that is responsible for the enhanced thermal and hygric behaviour observed in bio-based composites.
This work addresses this gap through a comparative assessment of raw and thermally treated OH as bio-aggregates for cementitious composites. The thermal treatment was designed not to modify the intrinsic lignocellulosic structure of OH but to selectively reduce its oil content, thereby improving compatibility with cementitious matrices while preserving its fibrous nature. The study is structured in two parts. First, a detailed intrinsic characterisation of OH is conducted in both forms, following the protocols recommended by RILEM TC 236-BBM. Parameters such as particle size distribution, bulk and true density, porosity, and water absorption are determined, providing a rigorous baseline for evaluating their suitability as lightweight aggregates. In the second part, OH is incorporated into bio-concrete formulations, and the resulting materials are evaluated across four performance domains: physical (bulk density and porosity), thermal (thermal conductivity, specific heat capacity, diffusivity, and effusivity), hygric (moisture buffer value), and mechanical (flexural and compressive strength).
By systematically comparing untreated and treated OH concretes, the study underlines the dual outcomes of thermal treatment. The untreated OH, with its residual oil content and fibrous morphology, exhibited superior thermal insulation and moisture buffering capacity, reflecting enhanced pore connectivity and hygric responsiveness. Conversely, the treated OH, in which oil residues were reduced while the fibrous structure was maintained, produced more reliable mechanical performance and stronger interfacial bonding with the cementitious matrix reflected also in enhanced heat storage potential, as indicated by higher specific heat capacity (Cp). Importantly, both forms of OH delivered superior and comparable results to those reported for other bio-based aggregates, underscoring their competitiveness as sustainable construction resources. This work reports a direct comparison of raw and treated olive husk for the production of a lightweight biobased concrete, evidencing their complementary strengths. Olive husk demonstrates a dual role as lightweight insulating filler and moisture-regulating fiber, positioning it as a viable bio-based alternative for eco-efficient and regionally adapted building materials.
Speaker 2: Sourour ELLEUCH, University of Pau and the Pays de l’Adour, France
Title 2: Effect of mechanical loading on the fire behavior of compressed earth bricks.
Earthen construction materials are gaining renewed interest due to their low environmental impact and favorable thermal, hygric and mechanical properties. However, their behavior under fire remains insufficiently understood, limiting broader application.
This study investigates the effect of mechanical loading on the fire behavior of compressed earth bricks. Two types of bricks with comparable compressive strengths were tested: unstabilized bricks compacted at 50 MPa and cement-stabilized bricks (3.5% cement) compacted to Proctor level. After setting the samples to equalizing conditions of 0%, 75% and 100% relative humidity, the samples were subjected to the time-temperature curve defined in the ISO 834-1 standard using a mobile gas furnace, while simultaneously experiencing mechanical loads ranging from 0 to 2.5 MPa.
The results revealed that mechanical loading significantly affects thermal stability during fire. Unstabilized bricks displayed higher thermal instability regardless of loading, while cement-stabilized bricks showed improved thermal stability, particularly under moderate loading. At 75% RH, both materials exhibited load-dependent thermal instability, linked to the interaction between crack propagation, internal pore pressure and vapor transport.
Further load bearing capacity tests conducted on the thermal stable samples confirmed prior hypotheses about the interrelated thermo-hydro-mechanical coupling in the behavior of earthen materials at high temperatures. This underscores the relationship between mechanical loading and fire behavior of earthen materials, emphasizing its importance in evaluating their fire behavior.
To sum up, these findings highlight the necessity of accounting for mechanical stress and moisture conditions when assessing the fire performance of earthen materials, offering new insight for safer, more reliable earthen construction in fire-prone environments.
Speaker 3: Letizia CROCIATI, University of Bologna, Italy
Title 3: Advancing Bamboo Construction: Hybrid Bio-Based Connections for Structural Use.
Bamboo is increasingly recognized as a sustainable building material because it renews quickly, has a high strength-to-weight ratio, and offers architectural flexibility. However, a significant obstacle to its wider use is the need for reliable, eco-friendly joint systems. Traditional bamboo connections often use cement-based fillers, steel bolts, or clamps, which diminish the environmental benefits of bamboo and involve invasive processes that can weaken the structural integrity of the culm. This research proposes a mostly bio-based joint system that avoids drilling, focuses on renewable materials, and aims to match the mechanical performance of traditional solutions.
The proposed connection uses two load-transfer methods: (i) an internal wooden insert aligned with the culm axis and bonded with epoxy resin. This insert transfers force through friction along the inner bamboo wall, and (ii) an external fiber wrap made of burlap fiber, also impregnated with epoxy resin. This wrap provides radial compression and confinement at the joint. This hybrid system combines features of Group 2 and Group 3 bamboo joints as described in the literature, which respectively show connections that transfer force through friction on the inner surface or compression to the diaphragm, and force transfer through friction on the outer surface. It provides load transfer through inner friction and adds resistance via outer shear and hoop stresses. Experimental testing follows ISO 22157:2019 standards for bamboo strength testing. Two main factors are evaluated: the anchorage length of the internal wooden dowel (multiples of the dowel diameter) and the type of external wrap (non-wrapped and epoxy-impregnated burlap wrap). Compression tests parallel to the fibers and four-point bending tests are conducted on these connections using Bambusa stenostachya culms to assess load-bearing capacity, stiffness, and failure modes. Specimens are manufactured to maintain fiber continuity and reduce variability inherent in natural bamboo, with load-displacement curves recorded throughout.
The results are expected to reveal performance patterns for different anchorage lengths and wraps, enabling comparison of mechanical efficiency and structural reliability. In addition to mechanical evaluation, the project aims to demonstrate the practicality of a low-impact jointing method that is easy to replicate, does not require heavy machinery, and enhances bamboo’s environmental benefits. By replacing steel and cement with renewable alternatives, this study promotes bamboo joinery as a viable, sustainable option for modular and low-carbon building systems.
This webinar is brought to you by the RILEM Youth Council (RYC) and hosted by Magda Posani (Europe RYC representative).
