Olive Stone Ash as Secondary Raw Material for Fired Clay Bricks

This work evaluates the effect of incorporation of olive stone ash, as secondary raw material, on the properties of fired clay bricks. To this end, three compositions containing 10, 20, and 30 wt% olive stone ash in a mixture of clays (30 wt% red, 30 wt% yellow, and 40 wt% black clay) from Spain were prepared. The raw materials, clay and olive stone ash, were characterized by means of XRD, XRF, SEM-EDS, and TG-TDA analysis. The engineering properties of the press molded specimens fired at 900°C (4 h) such as linear shrinkage, bulk density, apparent porosity, water absorption, and compressive strength were evaluated. The results indicated that the incorporation of 10 wt% of olive stone ash produced bricks with suitable technological properties, with values of compressive strength of 41.9 MPa but with a reduced bulk density, by almost 4%. By contrast, the incorporation of 20 wt% and 30 wt% sharply increased the water absorption as a consequence of the large amount of open porosity and low mechanical strength presented by these formulations, which do not meet the standards for their use as face bricks. The bricks do not present environmental problems according to the leaching test

Valorization and inertization of galvanic sludge waste in clay bricks

Galvanic sludge wastes (GSW) are produced by the physico-chemical treatments of wastewater generated by electroplating plants. These materials have a significant potential for the production of clay ceramic bricks. This paper focuses on the viability of the inertization of heavy metals from GSW mixed with clays. The original materials were obtained by mixing three types of raw clay (red, yellow and black) in equal parts with GSW. These mixtures were characterized by XRD, XRF, and chemical elemental analysis CHNS. The dosage of GSW in the clay–GSW bricks was up to 5 wt.%. The bricks were then manufactured using conventional processes. The influence of the amount of GSW was evaluated after firing the clay–GSW composites at 950 °C for 1 h. The engineering properties of the fired samples, such as density, water absorption, open porosity, water suction and compressive strength, with and without the GSW, were determined. The incorporation of GSW into the clay mix clearly decreased the linear shrinkage and bulk density of the bricks in comparison with the fired clay used as a control. These GSW–clay composites also showed lower open porosity. According to the results obtained for the bulk density of the bricks, samples with GSW addition showed slightly lower values of open porosity than clay bodies, indicating that the GSW–clay samples had slightly higher closed porosity values. This was also shown by SEM. The open porosity, SEM and pore size distribution tests indicated that the porosity generated by the addition of GSW was mainly closed and, therefore, GSW bricks had excellent mechanical properties. The environmental risks of the incorporation of GSW, rich in heavy metals (Cr, Zn, Ni and others), to a clay matrix were evaluated by leaching tests of the fired products. The results indicated a successful inertization of the pollutants.Peer reviewe

Valorisation of rice husk ash as an activator in the preparation of alkali-activated cements based on electric arc furnace slag

Rice husk ash (RHA) was employed as a silica source to produce an alternative sodium silicate solution through the dissolution of varying quantities of RHA in an 8 M NaOH solution. The solution was employed in the production of alkali-activated cements based on electric arc furnace slag (EAFS). Solutions were prepared with varying activator modules (Ms, molar ratio SiO₂/Na₂O) of 0.60, 0.85, 1.00, and 1.15. As control samples, slags were activated with 8 M NaOH (Ms = 0.0) and with 8 M NaOH in conjunction with commercial sodium silicate (Ms = 1.0). Mechanical, physical, mineralogical (XRD, FTIR), and microstructural (SEM/EDS) tests were conducted to characterize the obtained pastes. The results of the FTIR and SEM analyses indicated that the SiO₂/Na₂O ratio exerts a significant influence on the reaction products formed. At Ms values higher than 0.85, the predominant reaction product was observed to be a more cross-linked hybrid gel (N,C)-A-S-H. Lower modules resulted in the predominant formation of C-A-S-H gel and a more porous structure with lower mechanical properties. Pastes activated with the alternative RHA solution and Ms = 1.0 exhibited a composition, microstructure, and strength that was similar to or superior to those prepared with conventional commercial activators.This work has been funded by the project PID2020-115161RB-I00: Applying the circular economy in the development of new low carbon footprint alkaline activated hydraulic binders for construction solutions (CongActiva), CIN/AEI/https://doi.org/10.13039/501100011033 FEDER “A way of making Europe”. Authors thank Siderúrgica Balboa company for supplying slags. Technical and human support provided by CICT of Universidad de Jaén (UJA, MINECO, Junta de Andalucía, FEDER) is gratefully acknowledged.Funding for open access publishing: Universidad de Jaén/CBUA. This work has been funded by the project PID2020-115161RB-I00: Applying the circular economy in the development of new low carbon footprint alkaline activated hydraulic binders for construction solutions (CongActiva), CIN/AEI/10.13039/501100011033 FEDER “A way of making Europe”.Peer reviewe