Full Characterization of Self-Compacting Concrete Containing Recycled Aggregates and Limestone.

This work deals with the study of self-compacting concretes (SCCs) containing recycled aggregates (RAs) recovered from demolition waste and limestone filler as a partial replacement for natural aggregates (NAs) and cement, respectively. Four mix designs were developed and characterized in both the fresh and hardened states. In the fresh state, the properties studied included slump, sieve stability, and t500 viscosity. In the hardened state, the properties studied were compressive strength and porosity at 15 h and 28 days, thermogravimetric analysis, and durability tests involving freeze-thaw cycles and accelerated carbonation. The results indicate the RAs lead to a decrease in slump flow. However, the substitution rate of aggregate replacement does not affect the compressive strength. This can be attributed to the optimized mix design, resulting in all SCC mixtures achieving the same compressive strength class of 30-35 MPa. As for the durability tests, the incorporation of recycled aggregates modifies the behavior of the concrete during freeze-thaw cycles. Throughout the 300 freeze-thaw cycles, all concrete mixtures exhibited a mass loss accompanied by a slight strain increase, but the materials remained visually intact. Additionally, the carbonation depth is strongly influenced by the rate of aggregate replacement due to changes in the microstructure, particularly in porosity.

Influence of Pozzolans and Hemp Shives on the Properties of Non-Autoclaved Foamed Concrete.

In this study, new foam concretes incorporating hemp shives without the use of autoclaving have been developed and studied. Several protocols and parameters were investigated. Firstly, the influence of the addition of pozzolanic additives on the resulting density, mechanical behaviour and thermal conductivity was examined. Secondly, the effects of the incorporation of hemp shives at 5, 10 and 15 vol% on the previous three properties in such concretes were investigated. Moreover, economic cost and CO2 emissions were estimated to outline an optimized formulation of non-autoclaved biobased foam concretes. First, the target characteristics in terms of compressive strength (minimum of 2 MPa), thermal conductivity (less than 0.2 Wm-1K-1) and density (800 kg/m3) were achieved. It was noted that pozzolanic additions slightly improved the mechanical and thermal strength of non-autoclaved foamed concrete, while the addition of hemp shives improved the thermal strength but had an unfavourable effect on the mechanical strength. Moreover, both reduced the CO2 emissions.

Mud-Based Construction Material: Promising Properties of French Gravel Wash Mud Mixed with Byproducts, Seashells and Fly Ash as a Binder.

The French gravel industry produces approximatively 6.5 million tons of gravel wash mud each year. This material offers very promising properties which require an in-depth characterization study before its use as a construction material, otherwise it is removed from value cycles by disposal in landfills. We examined the suitability of gravel wash mud and seashells, with fly ash as a binder, as an unfired earth construction material. Thermal and mechanical characterizations of the smart mixture composed of gravel wash mud, Crepidula fornicata shells and fly ash are performed. The new specimens exhibit high compressive strengths compared to usual earth construction materials, which appears as a good opportunity for a reduction in the thickness of walls. The use of fly ash and Crepidula shells in addition to gravel wash mud provides high silica and calcium contents, which both react with clay, leading to the formation of tobermorite and Al-tobermorite as a result of a pozzolanic reaction. Considering the reduction in porosity and improvements in strength, these new materials are good candidates to contribute significantly to the Sustainable Development Goals (SDGs) and reduce carbon emissions.

Insight into the structural, elastic and electronic properties of a new orthorhombic 6O-SiC polytype.

Different polytypes of SiC are described and predicted in literature. Here, we report the first occurrence of an orthorhombic 6O-SiC polytype as rock-forming mineral in the nickel laterite mine of Tiebaghi (New Caledonia). This new class of SiC crystallizes in the space group Cmc21 with 12 atoms per unit cell [a = 3.0778(6) Å, b = 5.335(2) Å, c = 15.1219(6) Å, α = 90°, ß = 90°, γ = 120°]. The density of 6O-SiC is about 3.22 g/cm3 and the calculated indirect bandgap at room temperature of 3.56 eV is identical to 6H-SiC. Our results suggest that 6O-SiC is the intermediate state in the wurtzite to rocksalt transformation of 6H-SiC.