Purpose – The purpose of this paper is to determine if a type of cactus mucilage, Opuntia ficus-indica (OFI), may act as a corrosion inhibitor for carbon steel in cement-based materials (mortar) exposed to chloride-laden environment. Design/methodology/approach – Mortar prisms, reinforced with carbon steel rods, were immersed in sodium chloride (NaCl) solution for five wet – dry cycles. The experimentation included electrochemical monitoring (corrosion potential, Ecorr, and polarization resistance, Rp) of carbon steel during the time of exposure until corrosion-induced cracking appeared at the mortar surface. Crack survey on the mortar prisms was performed. Carbon steel rods were retrieved from the mortar after crack survey and steel mass loss at the end of the experimental period was estimated. A comparison between the different mixtures was also performed. Findings – OFI mucilage did perform as a corrosion inhibitor of steel in chloride contaminated mortar. Research limitations/implications – The experimental program needs to be corroborated in concrete specimens with typical dimensions. The surface oxide/hydroxide formation of the carbon steel in contact with the OFI mucilage is still unknown; thus, electrochemical impedance spectroscopy (EIS) and X-ray diffraction (XRD) analyses are needed. Practical implications – OFI mucilage is a suitable natural product that can be used to increase durability of concrete structures not only in countries where OFI cactus is produced, but also in many other countries where this plant is considered a plague. Originality/value – The new information obtained from this paper is the innovative use of a by-product of this cactus plant for construction industry applications.

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La generación de residuos sólidos de concreto hidráulico, considerados como desecho, está convirtiéndose en un problema medioambiental. El material de construcción mayormente fabricado es el cemento Portland (CP), pero un problema es su alta temperatura de fabricación, que genera contaminantes. El uso de agregados triturados provenientes de demolición de concreto hidráulico se aprovecha para generar Concreto Hidráulico Reciclado, un material que puede abatir costos, disminuir la contaminación y abaratar la edificación. Sin embargo,  la elaboración de concreto reciclado se enfrenta a la búsqueda de diseños óptimos para lograr el mayor desempeño mecánico bajo solicitaciones estáticas y dinámicas. En este trabajo se hace una revisión de los avances internacionales en esta temática.

This paper presents results on the physical characterization of mortar cubes fabricated with botanical (green) dehydrated additions such as Nopal (Opuntia Ficus Indica) and Aloe Vera. Eighty four mortar cubes were fabricated with and without these natural additions and tested for a period up to 900 days. Mortar without such additions served as controls. The natural dehydrated additions, Nopal and Aloe Vera, were mixed with CPO at different percent replacements (0%, 1%, 2%, and 4%). To characterize physical properties of such mixtures, four tests were performed at ~900 days: Total void content, compressive strength, ultrasound wave propagation, and wet electrical resistivity. Marginal improvements were observed within the dehydrated Aloe Vera replacement mixtures. Dehydrated Nopal additions did increase the Downloaded by [University of Tennessee, Knoxville] at 06:20 23 December 2014 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 physical performance of the mortar with time.

This research in progress includes results on the corrosion performance of reinforcing steel in alkaline media when two different dehydrated cacti (Opuntia ficus-indica-Nopal-and Aloe Vera) were used as additions in pH 12.5 and 13.3 solutions and in concrete. The dehydrated cactus addition was mixed at different concentrations by either solution or cement mass (0.10%, 0.25%, 0.5%, 1.0%, and 2.0%). Half-cell potentials and LPR measurements were performed at different time periods to characterize the possible corrosion inhibiting effect of the cactus additions tested in such alkaline media. Results showed good corrosion inhibiting effect of dehydrated Nopal on reinforcing steel, in all tested solutions, when chloride ions are present. Aloe Vera did show also corrosion inhibiting improvements in some extent. The addition of such cactus led to an apparent formation of a denser and more packed oxide/hydroxide surface layer on the steel surface that decreased corrosion activity. This oxide/hydroxide layer growth was confirmed by microscopic evaluation of the metal surface layer performed at the end of the research program. The preliminary findings suggest that adding Nopal at concentrations between 1% and 2%, by mass, might be suitable for durability enhancing applications in alkaline media, especially in concrete structures.

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