International Concrete Abstracts Portal

Nowadays, recycling and recovery of construction waste are major environmental issues. Gypsum, which is widely used in construction industry, generates around 400 000 tons of waste per year in France. Thermal activation of gypsum is well known and controlled, especially for the implementation of plaster or anhydrite. This study focuses on the recovery by flash calcination of a recycled gypsum from a gypsum recycling factory, using a flash furnace prototype allowing adjustment of multiple calcination parameters. In order to compare the thermal activation behaviour of recycled gypsum, a “noble” gypsum, derived from a hydrated industrial gypsum plaster is also used. Different calcination temperatures allow to obtain multiphase products with different degrees of reactivity. The raw gypsums (recycled and noble) as well as calcined materials are characterized by XRD, TGA, and Helium pycnometry. The hydration reactivity and setting time of calcined products and mechanical performances are also evaluated. The results highlight a similar behaviour regarding the thermal activation by flash calcination between a noble gypsum and a recycled one. They also emphasize a high reactivity of some of the calcined products. This study leads to identify the calcination conditions usable to reach the different hydrated or anhydrous calcium sulphate phases. Carefully tailored calcium sulphate binder is then accessible from recycled material.

Boron efficiently absorbs neutrons due to its large cross section. Thus, boron containing materials are an effective shield to neutrons and are commonly used as containment barriers in nuclear reactors. The most economical way to include boron into shielding structures is to prepare B-rich mortars or concretes, to be used as structural elements or as plastering. However, colemanite [Ca(B₃O₄(OH)₃)∙(H₂O)], the most abundant Bcontaining mineral, is sufficiently soluble to release enough borate ions in solution to indefinitely stop Portland cement hydration.

Here we present the formulation of hydraulically active binders containing 50% of colemanite. They are based on blends of calcium aluminate cements and blastfurnace slag. The main hydration product in the absence of colemanite is strätlingite along with other AFm phases. MgO causes an increasing hydrotalcite precipitation, and fly ashes further increase strätlingite content. The presence of colemanite causes the precipitation of B-ettringite, where B(OH)₄^¯ ions substitute for sulphate ions. These binders set in one day and harden in 4 days. The addition of hydrated lime in the formulations brings about the additional precipitation of B-containing AFm phases, where the trigonal HBO₃^2- ion constitutes the interlayer between positive [Ca₂Al(OH)₆]+ sheets. These binders set in few hours and harden in one day.

John Earley created beautiful architectural concrete with colors that came from the optical effect of the exposed crushed pebbles and sands. His palette of colors comprised 10 hues, five values from light to dark, and four chromas or intensities, resulting in 200 colors. Earley’s polychrome mosaic concrete projects included church interiors, campus decorations, reptile house at the zoo, residential houses, and murals. His studio continued his work after he passed away in 1945.

The goal of this research was to evaluate the behavior over time of mortars obtained from three different types of recycled material, and specifically aimed to obtain thermal insulation plasters.

The typology of samples was identified based on experimentations conducted at the University of Madrid, with 11 different types of specimens made with cement, river sand, expanded clay (with different particle size), recycled XPS (with different particle size), and recycled ceramic remains.

The good results suggested submitting the samples in the laboratory of Building Engineering of the University of Naples Federico II to the following tests: rainfall resistance, thermal shock resistance, accelerated aging resistance in climatic chamber.

In the present paper, the final results, with a preliminary assessment of the suitability for use of these mortars with external coating function in determined climatic contexts, are proposed.

A shake table investigation was carried out on a full-scale U-shaped masonry assemblage to study the effectiveness of Steel Reinforced Grout (SRG) for the improvement of the out-of-plane seismic capacity of masonry walls. Natural accelerograms were applied with increasing scale factor up to failure. A first session of tests was performed on the unreinforced specimen, that collapsed by out-of-plane overturning. Steel tie bars were then installed to prevent overturning. In this case, severe damage developed due to bending. Finally, the wall was retrofitted with horizontal strips of Ultra High Tensile Strength Steel cords, externally bonded to the masonry with lime based mortar, and steel connectors. SRG led to a significant improvement of the seismic capacity, strongly limited damage development, and entailed small modifications of the dynamic properties of the specimen. Since the reinforcement had a thickness of less than 10mm, it is suitable for applications within the plaster layer during the maintenance work of the façades without modifying their appearance.