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International audience; This paper presents a validation of a new protocol for the characterization of drying shrinkage of cement paste. The method consists of using environmental scanning electronic microscope (ESEM) or climatic chamber (CC) assisted by digital image correlation (DIC) to study the drying shrinkage of cement-based materials. The final motivation is to study the influence of the drying rate on cement-based materials’ delayed strain at the microscopic scale. Hence, the impact of specimen shape, size, and the imposed relative humidity history on the drying shrinkage is studied. Results show that for a given material, the amplitude of drying shrinkage is independent of the rate of drying and the specimen shape. Advantage was taken of the two techniques proposed in this paper to perform drying length change measurement both in ESEM and CC.

International audience; The Solidification/Stabilization method for dredged sediments remediation can be very effective for the immobilization of trace metal (TM) pollutants. The ordinary Portland cement (OPC) is largely used in this process. Nevertheless, the mechanical performance of treated sediments can be considerably improved at long term using ground granulated blast furnace slag (GGBS) as was shown in (Gutsalenko et al., 2018). Therefore, it is worth investigating whether this new binder is also relevant in terms of stabilization and mechanisms involved in this process. To meet this objective, leaching test, total attack, sequential extraction (SE) and X-ray Adsorption Near-Edge Structure (XANES) experiments measurements were performed. The results of the leaching tests conducted as part of the study are promising for the use of GGBS in the treatment of the real case project Dublin sediment and it outperforms the OPC-based treatment.. The sequential extraction method was applied to evaluate the potential risks of toxic elements according to their repartition in the Dublin sediment matrix and predicts the release of metals under different environmental conditions. It shows a lower perturbation rate of pollutants with the GGBS-based binder. Finally, XANES experiments demonstrate changes in the chemical environment of Zn and Cu after the treatment of the sediment with OPC compared to the GGBS rich binder. Consequently, this study finds that it is more pertinent to use the GGBS-based binder in terms of trace metal stabilization.

International audience; The use of bio-based materials (BBM) in buildings is an interesting solution as they are eco-friendly materials and have low embodied energy. This article aims to investigate the hygric performance of two bio-based materials: palm and sunflower concretes. The moisture buffering value (MBV) characterizes the ability of a material or multilayer component to moderate the variation in the indoor relative humidity (RH). In the literature, the moisture buffer values of bio-based concretes were measured at a constant temperature of 23 °C. However, in reality, the indoor temperature of the buildings is variable. The originality of this article is found in studying the influence of the temperature on the moisture buffer performance of BBM. A study at wall scale on its impact on the indoor RH at room level will be carried out. First, the physical models are presented. Second, the numerical models are implemented in the Simulation Problem Analysis and Research Kernel (SPARK) suited to complex problems. Then, the numerical model validated with the experimental results found in the literature is used to investigate the moisture buffering capacity of BBM as a function of the temperature and its application in buildings. The results show that the temperature has a significant impact on the moisture buffering capacity of bio-based building materials and its capacity to dampen indoor RH variation. Using the numerical model presented in this paper can predict and optimize the hygric performance of BBM designed for building application.

International audience; The reactivity effect of calcium carbonate, present in ground oyster shells and limestone filler, on the formation of carboaluminate phases in ground granulated blast furnace slag blended cement pastes was reported in this paper. Six different binary and ternary blended cement pastes were prepared using ground granulated blast furnace slag, ground oyster shells and limestone filler with different replacement levels (from 5 to 35%). The carboaluminate formation was assessed and quantified directly using X-ray diffraction (XRD), and indirectly by following the aluminate phase’s reaction (heat flow) and consumed calcium carbonate using Isothermal Calorimetry (IC) and Thermogravimetric Analysis (TGA), respectively. Further, the overall reaction degree calculated based on TGA results and the compressive strength were determined to support the findings obtained. The results revealed that the calcium carbonate present in ground oyster shells is more reactive when compared to that present in limestone filler, where more formed hemi- and monocarboaluminate phases were observed in mixtures containing ground oyster shells. An enhancement in compressive strength and overall reaction degree was observed by adding 5% ground oyster shells as cement replacement.

This work aims to study the valorization and recycling of ceramic wastes (wall tiles) as a fine aggregate instead of sand in the manufacturing of flowable sand concrete (FSC). For this, the sand is substituted with the ceramic wastes at different dosages (0, 5, 10, 15, 20, and 25% by volume of the sand). The influence of the ceramic wastes addition on the physical (workability, density) and mechanical (compressive, flexural and elastic modulus) properties of FSC was studied. The results show that the use of ceramic waste as partial replacement of sand contributes to reduce the workability, bulk density and improves the mechanical strengths of FSC according to the use of 25% of wall tiles waste.

The stability of ettringite under sorption and the conversion into metaettringite are studied using hybrid Grand Canonical Monte Carlo (GCMC) and (classical) Molecular Dynamics (MD) simulations sampling the osmotic ensemble. The desorption branch obtained from simulation and the associated volume changes are in agreement with the experimental evidence. We pay special attention to the structural changes at low RH, which is associated with metaettringite conversion, which is recognized as a disordered polymorph of ettringite with an unknown structure to date. We show that the conversion of ettringite into metaettringite is associated with an increase in entropy. The adsorption branch obtained from simulations is reversible in the ettringite domain in agreement with experiments. The reversibility in the conversion of metaettringite into ettringite, which is observed experimentally, is not captured by the simulation approach adopted. The large deformations associated with ettringite desorption make it difficult to capture reversibility with a direct sampling of the osmotic ensemble. Further, we discuss the role of hydrogen bonds on the hysteresis observed in sorption cycles in ettringite.

International audience

International audience; Hemp shives is a lightweight material known for its insulating properties. Associating these bio-fibers with plant-based matrix instead of a mineral binder in insulation applications is of ecological interest. This article describes the study of a low environmental impact 100% plant-based material made solely from wheat starch and hemp shives. The hemp/starch ratio (H/S) influence and hemp shive size are studied. Samples are evaluated in terms of physical properties, mechanical behaviour and hygrothermal properties through an experimental approach. Results show that increasing 0–5 mm hemp shive proportion from 15% to 30% leads to a significant enhancement of the mechanical and hygric characteristics due to the load transfer and porosity. However, when the H/S ratio increases, mechanical and hygrothermal characteristics decrease slightly. Finally, the hemp-starch agro-material with H/S equal to 8 and 30% of 0–5 mm hemp shive seems to be the optimal composition between the studied samples.

International audience; 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 bio-aggregates 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.

There is no consensus on the physical origin of alkali-silica reaction (ASR) damage in concrete. Atomic-level detail on the intermolecular interactions of ASR products with water is critical to understand the development and to propose solutions to mitigate ASR. We combine molecular dynamics and Monte Carlo simulations to model ASR products under sorption. The hydration of shlykovite, a naturally occurring phyllosilicate structurally similar to ASR products, is analyzed with atomic-level detail. Sodium and potassium, the most relevant alkali in ASR, are considered as charge balancing cations in shlykovite. Intra- and inter-layer water content and volume remain stable under sorption at ambient pressure, which corroborates that swelling of crystalline products cannot be at the origin of ASR damage. Also, we provide the effective interactions of Na- and K-shlykovite under water-saturated conditions. These potentials of mean force can be used in mesoscale simulations to test other mechanisms of ASR damage.

Ettringite (AFt) and monosulfoaluminate (AFm(MS)) are the two of the main hydration products of tricalcium aluminate. Ettringite formation is favored in the presence of gypsum, and monosulfoaluminate is the usual AFm phase in a system with low calcium carbonate content. In this article, a new empirical force field, AFFF, is proposed to describe the interactions among species in ettringite, monosulfoaluminate, and tricalcium aluminate at the molecular level. This force field provides structural data and elastic properties that are consistent with experimental and previous simulation results. Using AFFF, the effects of the hydration state of ettringite and monosulfoaluminate on the lattice parameters and elastic constants are studied. Regarding the molecular modeling of the elastic properties of ettringite, simulations with AFFF are considerably less computationally intensive than the other approaches used so far. These results leave room for a better understanding of the nanoscale processes that affect AF-phases behavior in cement systems.

Energy efficiency and the reduction of greenhouse gas emissions are actual key issues in all the economic sectors and, in particular, in buildings which is acknowledged worldwide as one of the most energy-consuming. In this context, it would be desirable to duly address those issues by searching for and assessing proper solutions and strategies: the usage of eco-friendly construction materials can be considered as one of those. This paper reports upon the performance of three facades containing sustainable products that are manufactured using natural resources and, alternatively, post-consumer waste based materials; those are: hemp-concrete; and Recycled PolyEthylene Terephthalate (R-PET), respectively. The energy performance of each facade was assessed in terms of cooling and heating demands, electrical consumptions and indoor thermal comfort including indoor temperature and relative humidity. Additionally, a Carbon Footprint (CF) assessment was carried out considering both the estimated energy demands and the life-cycle emission factors associated with the energy mix of the countries where the facades were located, i.e. France and Italy. Based upon the findings of the study, the R-PET facade represented the most performing solution between the three facades in all the scenarios considered and, moreover, the humidity-sensitive flow rate ventilation system came out as a solution able to reduce the electricity consumptions. Finally, considering the Carbon Footprint results, the energy country mix emerged as a key issue, making the Italian case study the worst one, though the total electrical energy consumption were comparable with those of the other case studies.