M. Criado

Stevia rebaudiana Bertoni as a natural antioxidant/antimicrobial for high pressure processed fruit extract: Processing parameter optimization

Response surface methodology was used to evaluate the optimal high pressure processing treatment (300-500 MPa, 5-15 min) combined with Stevia rebaudiana (Stevia) addition (0-2.5% (w/v)) to guarantee food safety while maintaining maximum retention of nutritional properties. A fruit extract matrix was selected and Listeria monocytogenes inactivation was followed from the food safety point of view while polyphenoloxidase (PPO) and peroxidase (POD) activities, total phenolic content (TPC) and antioxidant capacity (TEAC and ORAC) were studied from the food quality point of view. A combination of treatments achieved higher levels of inactivation of L. monocytogenes and of the oxidative enzymes, succeeding in completely inactivating POD and also increasing the levels of TPC, TEAC and ORAC. A treatment of 453 MPa for 5 min with a 2.5% (w/v) of Stevia succeeded in inactivating over 5 log cycles of L. monocytogenes and maximizing inactivation of PPO and POD, with the greatest retention of bioactive components.

Copper deterioration: causes, diagnosis and risk minimisation

Abstract Copper is widely used in many applications such as heat exchangers, condensers, heating and air conditioning systems, electricity, electronic circuitry and ornamental parts. This paper reviews the issue of copper corrosion in different environments and applications. Special attention is paid to the influence of relative humidity and low molecular weight carboxylic acids. These acids are present in rain, snow, clouds and particulate matter and contribute about 15-35% of rain acidity. Attention is also paid to copper corrosion originated by formic, acetic, propionic and butyric acid vapours. Corrosion product layers (patina) are analysed, showing the relationship between potential and current density cathodic peaks, and models are proposed that show a proportionality factor of the dimensions of a resistor. These results are of practical importance in copper roofing applications. Before 1985, copper was almost universally considered to be a corrosion resistant conduit of potable water, and few instances of copper tube failure were reported. Where unacceptable performance was identified, the problem was usually attributed to reticulation and plumbing systems. In air conditioning applications, premature failure of copper tubing frequently occurs due to pitting corrosion after a short time in service or even during post-installation leakage tests. This type of corrosion is described in the literature as formicary corrosion, and its morphology is characterised by microscopic caverns connected by tunnels. Specimens are analysed to assess the reasons for such premature corrosion failure. Finally, procedures to mitigate copper corrosion are addressed. Pickling in dilute mineral acids (H2SO4 and HCl) is discussed as the most common method for removing oxides formed on the surface of copper based materials during mill processing and manufacturing operations. The use of corrosion inhibitors, such as immersion corrosion inhibitors and volatile corrosion inhibitors (VCI), is a widespread practice to reduce copper corrosion, achieving significant delays in the corrosion process. Reference is made to the search for new environmentally friendly inhibitors for copper and bronze using organic compounds in acid, neutral and alkaline media, and a number of ecological alternatives are reviewed.

Microstructural and Mechanical Properties of Alkali Activated Colombian Raw Materials

Microstructural and mechanical properties of alkali activated binders based on blends of Colombian granulated blast furnace slag (GBFS) and fly ash (FA) were investigated. The synthesis of alkali activated binders was conducted at 85 °C for 24 h with different slag/fly ash ratios (100:0, 80:20, 60:40, 40:60, 20:80, and 0:100). Mineralogical and microstructural characterization was carried out by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) and Nuclear magnetic resonance (NMR). Mechanical properties were evaluated through the compressive strength, modulus of elasticity and Poisson’s ratio. The results show that two different reaction products were detected in the slag/fly ash mixtures, a calcium silicate hydrate with Al in its structure (C-A-S-H gel) and a sodium aluminosilicate hydrate (N-A-S-H gel) with higher number of polymerized species and low content in Ca. It was found that with the increase of the amount of added slag, the amount of C-A-S-H gel increased and the amount of N-A-S-H gel decreased. The matrix was more dense and compact with almost absence of pores. The predominance of slag affected positively the compressive strength, Young’s modulus and Poisson’s ratio, with 80% slag and 20% fly ash concrete being the best mechanical performance blend.

Durability and Testing – Degradation via Mass Transport

In most applications of reinforced concrete, the predominant modes of structural failure of the material are actually related more to degradation of the embedded steel reinforcing rather than of the binder itself. Thus, a key role played by any structural concrete is the provision of sufficient cover depth, and alkalinity, to hold the steel in a passive state for an extended period of time. The loss of passivation usually takes place due to the ingress of aggressive species such as chloride, and/or the loss of alkalinity by processes such as carbonation. This means that the mass transport properties of the hardened binder material are essential in determining the durability of concrete, and thus the analysis and testing of the transport-related properties of alkali-activated materials will be the focus of this chapter. Sections dedicated to steel corrosion chemistry within alkali-activated binders, and to efflorescence (which is a phenomenon observed in the case of excessive alkali mobility), are also incorporated into the discussion due to their close connections to transport properties.

The corrosion behaviour of reinforced steel embedded in alkali-activated mortar

Corrosion of reinforcement steel is one of the main causes of the premature degradation of reinforced concrete structures. Due to their high alkalinity, alkali-activated mortars should limit reinforcement corrosion to negligible levels, as anticipated by the Pourbaix diagram. This chapter first discusses how the passivating capacity and the permanence of the passive state, once reached, depend on the nature and the dosage of binder, on the type of activator used and on the environmental conditions. The chapter then discusses two corrosion prevention strategies (inhibitors and stainless steel) as a palliative method to increase the reinforced Portland or alkali-activated concrete service life.

Alkali activated slag mortars provide high resistance to chloride-induced corrosion of steel

The pore solutions of alkali-activated slag cements and Portland-based cements are very different in terms of their chemical and redox characteristics, particularly due to the high alkalinity and high sulfide content of alkali-activated slag cement. Therefore, differences in corrosion mechanisms of steel elements embedded in these cements could be expected, with important implications for the durability of reinforced concrete elements. This study assesses the corrosion behaviour of steel embedded in alkali-activated blast furnace slag (BFS) mortars exposed to alkaline solution, alkaline chloride-rich solution, water, and standard laboratory conditions, using electrochemical techniques. White Portland cement (WPC) mortars and blended cement mortars (white Portland cement and blast furnace slag) were also tested for comparative purposes. The steel elements embedded in immersed alkali-activated slag mortars presented very negative redox potentials and high apparent corrosion current values; the presence of sulfide reduced the redox potential, and the oxidation of the reduced sulfur-containing species within the cement itself gave an electrochemical signal that classical electrochemical tests for reinforced concrete durability would interpret as being due to steel corrosion processes. However, the actual observed resistance to chloride-induced corrosion was very high, as measured by extraction and characterisation of the steel at the end of a 9-month exposure period, whereas the steel embedded in white Portland cement mortars was significantly damaged under the same conditions.

Alternative inorganic binders based on alkali-activated metallurgical slags

Alkali-activation technology has been used to produce inorganic cements for over a century, as a means of valorizing wastes or industrial by-products derived from different commercial activities. Granulated blast furnace slags (GBFS), derived from the iron-making industry, have been widely utilized for the production of alkali-activated cements. Significant advances in understanding the roles of different factors which govern the properties of alkali-activated GBFS cements have been made in recent decades, to the point that concretes based on alkali-activated GBFS are commercially deployed in several parts of the world. However, GBFS is not the only slag that can be used as a raw material for producing Portland clinker-free inorganic binders. Various other metallurgical slags, which currently have little or no commercial value, can also be utilized as raw materials for producing inorganic cements. The main difficulty to overcome in this area is the generally lower hydraulic reactivity of these slags compared with GBFS, and the high content of heavy metals which can limit the utilization of some such slags as building materials. Alkali-activation can thus, in some instances, also be seen as a means for the consolidation and safe disposal of such materials, which may otherwise pose an environmental hazard. This chapter provides an overview of inorganic cements produced via alkali-activation, particularly those which utilize nonblast furnace metallurgical slags including steel, ferronickel, titaniferous, stainless steel, lead, copper, zinc, nickel, manganese, silicomanganese, and phosphorus slags.

Precipitation mechanism of soluble phosphates in mortar

Abstract The penetration of three phosphate compounds in mortar bulk matrix, sodium monofluorophosphate (Na2FPO3) (MFP), disodium hydrogen phosphate (Na2HPO4) (DHP) and trisodium phosphate (Na3PO4) (TSP) has been evaluated using two water:cement ratios (0.5 and 0.6). The mortar samples were immersed in a 5% MFP, DHP or TSP solution for a period of 40 days. Microprobe line profile analysis for phosphorus (P) and fluorine (F) showed similar behaviour for the three soluble phosphates, which penetrated the mortar to a depth of more than 2 mm, below which the P and F contents dropped to almost zero. The stability of the phosphate ions vs. pH was calculated using thermodynamic data to obtain the following stability ranges: pH 2–4 for ion, pH 5−9 for ion, pH 3–6 for ion, pH 8–12 for ion, and pH above 11 for ion. The use of the MFP, DHP and TSP as corrosion inhibitors presents some limitations in the case of total or partial immersion.

Corrosion behaviour of hybrid sol-gel coated steel embedded in carbonated Portland and fly ash mortars contaminated with chlorides

Abstract The protection of metals from their surrounding environment is usually achieved by deposition of protective coatings on the metal surface to establish a physical barrier against aggressive ions. The corrosion behaviour of hybrid organic–inorganic coatings for carbon steel embedded in carbonated ordinary Portland cement (OPC) and alkali activated fly ash (AAFA) mortars was studied, after different periods of immersion in a 3 wt.% sodium chloride solution using electrochemical techniques. Hybrid organic–inorganic films employed as protective coatings have been prepared via sol–gel using several silicon compounds: 3-methacryloxy-propyltrimethoxysilane or methyltriethoxysilane (MTES) and tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS) precursors using a molar ratio of 1 and deposited on carbon steel substrates by dip-coating. The corrosion potential (Ecorr) values were higher and the current density (icorr) values were lower for AAFA mortars, indicating that the coatings were more efficient against rebar corrosion in this system than in OPC mortars. On the other hand, the hybrids synthesised with TEOS/MTES and TMOS/MTES for carbon steel embedded in carbonated AAFA mortars showed the lowest icorr values. This enhanced protection could be due to a structure denser and more compact and greater adhesion to the metallic surface.

Corrosion Behavior of Hybrid Organic-Inorganic Coated Steel in Simulated Concrete Pore Solution

This work compares the anticorrosion features of polysiloxane hybrid films deposited on carbon steel substrates by dip-coating. To assess the influence of the components, sol-gel coatings were prepared from condensation and polymerization of TEOS and MPTS, TEOS and MTES, TMOS and MPTS or TMOS and MTES in three molar ratios. The corrosion resistance of the coatings was evaluated by means of polarization curves and the coatings’ thicknesses and compositions were analyzed by a field emission-scanning electron microscopy.