Chloride migration in concrete with superabsorbent polymers

Superabsorbent polymers (SAP) can be used as a means for internal curing of concrete. In the present study, the development of transport properties of concrete with SAP is investigated. The chloride migration coefficient according to NT BUILD 492 is used as a measure of this. Twenty concrete mixtures are tested 7, 14, and 28 days after casting. The development of degree of hydration is followed for 20 corresponding paste mixtures.Both when SAP is added with extra water to compensate the SAP water absorption in fresh concrete and without extra water, the internal curing water held by SAP may contribute to increase the degree of hydration. No matter if SAP is added with or without extra water, it appears that the so-called gel space ratio can be used as a key parameter to link age and mixture proportions (water-to-cement ratio and SAP dosage) to the resulting chloride migration coefficient; the higher the volume of gel solid relative to the space available for it, the lower the chloride migration coefficient, because the pore system becomes more tortuous and the porosity becomes less.     

AgNO<Subscript>3</Subscript> spray tests: advantages,weaknesses, and various applications to quantify chloride ingress into concrete. Part 1: Non-steady-state diffusion tests and exposure to natural conditions

Within the framework of the evaluation and the prediction of chloride-induced corrosion risks, simple and rapid AgNO₃ spray tests can be proposed for various issues. This paper forms the first part of a series. In this first part, the Maultzsch procedure (spraying of 0.1-N AgNO₃ solution + K₂CrO₄) as well as the procedure based on the use of a sole AgNO₃ solution have been investigated on a broad range of concretes. These procedures have also been compared to the Collepardi procedure (spraying of 0.1-N AgNO₃ + fluoresceine). The feasibility of these colorimetric techniques on saturated specimens cast in laboratory, after non-steady-state diffusion tests carried out in various conditions, is discussed. In addition, the results obtained from applying such spray tests in field conditions on cores drilled out from various RC test specimens exposed to a marine environment (tidal zone) and to a road and cold environment (freezing-thawing cycles and spraying of deicing salts) are presented. Colorimetric methods have in particular been applied here to the assessment of the average chloride penetration depth and of its evolution versus time (kinetics). Moreover, the detection threshold of these techniques has been investigated in various environments. The possible sources of discrepancy on the results have been analysed.     

Diffusion-controlled size-selective chloride ion sensing in the presence of bromide ion using a thin, nanoporous, plasma-polymerized coating on an Ag/AgCl electrode

We have developed a diffusion-controlled size-selective method for sensing chloride ion in the presence of bromide ion, based on a thin, nanoporous, plasma-polymerized coating of hexamethyldisiloxane on an Ag/AgCl electrode. Sub-nanometer-sized pores responsible for a highly cross-linked polymer network in the plasma-polymerized coating allowed diffusion-controlled permeation of chloride ion while blocking the larger bromide ion. An electrode coating of thickness greater than 70 nm enabled chloride detection in the concentration range 1-10 mM in the presence of 0.63 mM bromide ion. Advantages of this approach are: (1) simple design compared with ionophore-based strategies and (2) compatibility with microfabrication and mass production processes.     

Encapsulation of PV modules using ethylene vinyl acetate copolymer as a pottant: A critical review

The primary purpose of this work is to review the literature about what is and is not known about using ethylene vinyl acetate (EVA0 copolymer as the encapsulant (or pottant) material in photovoltaic (PV) modules. Secondary purposes include elucidating the complexity of the encapsulation problem, providing an overview about encapsulation of PV cells and modules, providing a historical overview of the relevant research and development on EVA, summarizing performance losses reported for PV systems deployed since ca. 1981, and summarizing the general problems of polymer stability in a solar environment. We also provide a critical review of aspects of reported work for cases that we believe are important.Failure modes resolved in the early work to establish reliability of deployed modules and the purposes and properties of pottants, are summarized. Typical performance losses in large field-deployed, large-scale systems ranging from 1% to 10% per year are given quantitatively, and qualitative reports of EVA discoloration are summarized with respect to ultraviolet (UV), world-wide location and site dependence.The general stability of polymers and their desirable bulk properties for solar utilization are given. The stabilization formulation for EVA, its effectiveness, and changes in it during degradation are discussed. The degradation mechanisms for the base resin, e.g., unstabilized Elvax 150^TM, and stabilized EVA are indicated for literature dating to the early 1950s, and the role played by unsaturated chromophores is indicated. The limited number of studies relating discoloration and PV cell efficiency are summarized.Observed degradation of EVA or the unstabilized base resin in the laboratory and examples used to measure the degradation are summarized in sections entitled: (1) thermally-induced degradation; (2) photodegradation and photothermal degradation of EVA in different temperature regimes; (3) photobleaching and photodegradation of the UV absorber and cross-linking agent; (4) acetic acid and metal and metal-oxide catalyzed oxidative degradation; and (5) discolaration and PV cell efficiency losses.Processing effects/influences on EVA stability are discussed in sections entitled: (1) EVA raw materials and extruded, uncured films; (2) thermal encapsulation processes; (3) effects of lamination, curing, and curing peroxide on gel content and chromophores formed; and (4) incomplete shielding of curing-generated chromophores. A summary is given for the limited number of accelerated lifetime testing efforts and examples of erroneous service lifetime predictions for EVA are discussed. The known factors that effect the discoloration rate of several EVA formulations are discussed in which the reduction in rate by using UV-absorbing superstrates is a prime example. A summary is given of what is and is not known about EVA degradation mechanisms, degradation from exposures in field-deployed modeules and/or laboratory testing, and factors that contribute to EVA stability or degradation. Finally, conclusions about using Elvax 150 in EVA formulations are summarized, and future prospects for developing the next-generation pottant for encapsulating PV modules are discussed.     

Magnetic resonance imaging of H, Na, and Cl penetration in Portland cement mortar

The first magnetic resonance imaging profiles of chloride content in low- and high-permeability Portland cement mortar have been obtained using a novel material science imaging technique. The penetration of water as well as chloride and sodium ions, into mortar specimens was monitored for a period of 72 h. Marked differences in penetration depth were observed in low- and high-permeability mortar. These preliminary experiments show significant differences between the extent and nature in the penetration of chlorides compared to water and sodium.     

Statistical studies of branched ester latex and paint properties

Vinyl versatate, butyl acrylate and 2-ethylhexyl acrylate were compared as comonomer, for colloid-stabilized vinyl acetate latex polymers to assess their impact on latex coating properties. Vinyl versatate afforded advantages in scrub resistance, gloss, hydrophobicity and higher glass transition temperatures. Butyl acrylate developed better wet adhesion efficiency, gel content and hiding efficiency. 2-Ethylhexyl acrylate offered performance comparable to butyl acrylate in hiding efficiency, lowering copolymer glass transition temperatures, and gloss development. Combinations of these monomers, in many instances, afforded a better balance of performance properties than individual monomers alone. In the subject study, a simplex-centroid design was utilized to statistically map polymer compositions for determining the effect of comonomer composition on latex and paint film properties. In addition to developing contour maps of polymer and paint properties as a function of composition, a technique for studying structure-property relationships is presented.     

Vinyl acetate monomer—a pilot plant study

The kinetics of the reaction of acetic acid and acetylene over zinc acetate-activated carbon catalyst was investigated over a wide range of process variables in a pilot reactor. Although various catalytic reaction mechanisms were postulated, the rate of reaction was most satisfactorily correlated by a mechanism of surface reaction between charged adsorbed acetic acid and acetylene, which assumes that the rate controlling step was the irreversible charged adsorption of acetylene and acetic acid.     

Properties of latex blends and its modified cement mortars

In this paper, the mechanical properties of three latex blends and the mechanical properties and chloride diffusivity of the latex-modified mortars are studied. The relationships between the properties of polymer films formed from latex blends and the properties of the latex blend-modified mortars are illustrated. The test results showed that the modified mortar with the blend of styrene-acrylic ester (SAE) and styrene-butadiene rubber (SBR) showed synergistic effect; especially the flexural strength of the SAE/SBR blend-modified mortars was about 20-40% higher than that of monolatex-modified mortars. However, the vinyl chloride-vinylidene chloride copolymer (PVDC)/SBR and PVDC/SAE blends-modified mortars showed antisynergistic effect. The compressive strength of the modified mortars increased with the increasing of the tensile strength of the latex films, while the flexural strength of the modified mortars did not depend on the tensile strength of the latex films. When PVDC with the mass fraction of 0.2 or SAE copolymer emulsion with mass fraction of 0.4 was blended into SBR latex, the latex blend-modified mortars showed lower chloride diffusivity. The chloride diffusivity of the modified mortars increased approximately linear with the tensile strength of the latex blend films, and decreased with increase of the elongation at rupture of the latex blend films. When the elongation at rupture of the latex blend films increased from 200-300% to more than 800%, the chloride diffusivity of the modified mortars decreased from 10-15×10⁻¹² to 3-4×10⁻¹² m²/s.     

Impact of specification changes on chloride-induced corrosion service life of bridge decks

A model was developed to determine the time to first repair and to subsequently rehabilitate concrete bridge decks exposed to chloride deicer salts. Said model incorporates the statistical nature of factors affecting the corrosion process. The time to first repair and rehabilitate was predicted for 10 bridge decks built in Virginia between 1981 and 1994.The model was validated using historical service life data for 129 bridge decks built in Virginia between 1968 and 1972. The time for rehabilitation predicted for the newer set of bridge decks was approximately 13 years longer than the normalized time for rehabilitation projected for the older bridge decks. The increase in time for rehabilitation for the newer set of bridge decks was attributed to a reduction in the specified maximum water/cement ratio and increase in clear cover depth. The probabilistic model is shown to be an advancement over the deterministic model currently in use.