Development of Iron-Silicate Composites by Waste Glass and Iron or Steel Powders.

There is growing interest in the opportunities regarding construction and demolition wastes, such as glass and metal powders, for developing a circular economy and their transformation into new materials. This management and recycling of construction and demolition waste offers environmental benefits and conservation of natural resources. In this paper, new magnetic composite materials were prepared by wet chemical synthesis methods using crushed glasses and iron and steel waste powders as raw materials. The prepared iron-silicate composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, infrared (IR), ultraviolet-visible, and electron paramagnetic resonance (EPR) spectroscopy, and magnetic measurements. The XRD data confirm the formation of varied crystalline phases of the iron ions. The presence of the Fe3O4 crystalline phase was detected in the composites containing the iron waste powders. The inspection of the SEM micrographs revealed slightly better homogeneity for the composite material containing larger amounts of iron waste and heterogeneous morphology with cracks and random crystallinity for the composite doped with steel waste. By doping with different contents of iron or steel waste powder, structural modifications in the silicate network and the formation of new bands in the IR spectra were evidenced. The UV-Vis spectra were characterized by the absorption peaks for both the tetrahedral and octahedral geometries of the Fe3+ ions and the octahedral coordination of the Fe2+ ions with oxygen anions. The EPR data show resonance lines with g ~2, 4.3, and 6.4, corresponding to the Fe3+ ions. Using hysteresis curves, the superparamagnetic properties of the iron-silicate composites were evidenced.

Circular Economy of Construction and Demolition Waste for Nanocomposite Cement: XRD, NMR, Vickers, Voltammetric and EIS Characterization.

In this paper, we present the structural, mechanical and electrical properties of composite cement materials that can be widely used as substituent for cement. We start with the characterization of a composite cement sample using an analysis of X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) spectra. The measurements of the Vickers hardness, cyclic and sweep linear voltammetry and electrochemical impedance spectroscopy (EIS) of composite cement materials were also recorded. This study compared the effect of the different nanocomposites added to cement on the mitigation of the alkali-silica reaction, which is responsible for the swelling, cracking and deleterious behavior of the material. The enhancement in Vickers hardness was more pronounced for composite cement materials. In contrast, the values of Vickers hardness decreased for the composite cement containing mortar and the control sample, suggesting that the long-term performance of cement was compromised. In order to obtain information about the bulk resistance of the composite cement material, electrochemical impedance spectroscopy (EIS) data were employed. The results suggest that for composite cement materials, there is an improvement in bulk electrical resistance, which can be attributed to the lower amounts of cracks and swelling due to lower expansion. In the control sample, a reduction in the bulk resistance suggests the formation of microcracks, which cause the aging and degradation of the material. The intersection of arcs in the EIS spectrum of the mixed composite cement sample gradually increased by an alkaline exposure of up to 21 days and finally shifted towards a low value of high frequency with an increase in alkaline exposure of up to 28 days.

Nanocomposites Derived from Construction and Demolition Waste for Cement: X-ray Diffraction, Spectroscopic and Mechanical Investigations.

In the production of cement, raw materials can be partially substituted by regenerable waste provided from glasses, construction and demolition waste in order to reduce the environmental problem and burden of landfills. In this study, limestone-silicate composites were synthesized using starting materials such as glass waste and lime, brick, autoclaved aerated concrete (ACC), mortar or plaster waste. The structure and mechanical properties of the nano-composite materials have been studied. The mean CaCO3 crystallite sizes are higher for composites containing ACC and brick than for doping with lime, mortar and plaster. Cement-based materials are formed by replacing 2.5% of the Portland cement with limestone-silicate composites. The results indicate new possibilities for introducing 2.5%of composites in cement paste because they promote the formation of the C-S-H network, which provides strength and long stability for the cement paste. The influence of varied types of mix composites in the expired cement on the initial cracking strain and stress, tensile strength and compressive strength were investigated. The compressive strength values of composite-expired cement specimens are situated between 11.8 and 15.7 MPa, respectively, which reflect an increase from 22.9 up to 63.54% over the compressive strength of expired cement matrix.

Nanocomposites as Substituent of Cement: Structure and Mechanical Properties.

To date, the scientific research in the field of recycling of construction and demolition wastes was focused on the production of concrete, cements, and bricks. The attainment of these products was limited to the addition of suitable binder contents, such as lime or cement, compaction, and possibly heat treatment, without a concrete recycling method. In this paper, new cement materials consisting of 2.5 weight% composite and originating from construction and demolition waste powder, were prepared and investigated in view of applications in the construction industry as a substituent of cement. The materials with recycled powder from construction and demolition wastes were characterized by X-ray diffraction (XRD), infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy. The XRD data indicate vitroceramic structures with varied crystalline phases. The NMR relaxometry data show four reservoirs of water associated with bounded water and with three types of pores in the composite construction material. The micro-Vickers hardness was measured to reflect the influence of composite nature in the local mechanical properties of the composite-cement for the mixture with Portland cement and (EC) expired cement.