Crushed or recycled concrete aggregates (CCA/RCA) is an increasingly popular material as a replacement for natural aggregates in concrete due to industry demands for more recycled, lower carbon and responsibly sourced materials. In the UK, the majority of CCA is utilised in non-structural applications such as: a general fill material, road base/subbase or in low-grade concrete. Recycled aggregate producers however, are seeking new ways to incorporate CCA into higher value applications such as structural concrete to increase profits. Opportunities to incorporate CCA into structural concrete may also arise because of project demands for sustainability or in situations where natural aggregates are in short supply. Limited research has been published regarding the effect of coarse CCA on the durability of structural concrete, particularly in respect to water and chloride ion ingress and possibility of corrosion initiation. The aim of this EngD research programme was to investigate the effect of coarse CCA and supplementary cementitious materials (SCMs) on the durability performance of structural concrete, with particular emphasis on the key liquid transport mechanisms within concrete, namely absorption by capillary action, diffusion and migration. This addressed an industry concern regarding the detrimental effect of coarse CCA which has resulted in a limit on replacement levels of coarse natural aggregates in structural concrete, as defined in Eurocodes and local national standards for concrete. In this study, structural concrete was produced with varying levels of coarse CCA replacement (up to 100%), from five different sources and/or structural elements across the UK, with various combinations of SCMs to replace in part the Portland cement. Petrographic analysis was used as an innovative technique to characterise the coarse CCA sources to determine suitability which yielded positive results. The durability performance of the resultant concrete was analysed by exposing the concrete to aggressive chloride environments. The results indicate that the inclusion of coarse CCA, even as low as 20%, had a detrimental effect on the durability performance of structural concrete, in relation to absorption by capillary action, diffusion and migration. This effect however, can be offset through the use of SCMs, which have been shown to outperform control Portland cement concrete with 100% natural aggregates in durability performance tests. The results also suggest that cementitious materials had a greater influence on durability performance than the type and source of coarse aggregates used. It is recommended that the replacement of natural aggregate with coarse CCA be limited to 30% in cases where compliance with the 28 day characteristic strength is of particular importance. If the criterion for compliance at 28 days can be relaxed and the compressive cube strength of concretes with SCMs tested at later ages for conformity (56 or 90 days), then higher quantities of coarse CCA may be incorporated up to 60% to produce a more sustainable structural concrete. It is recommended that Portland cement is partially replaced with 50% ground granulated blast-furnace slag (GGBS) to produce a CEM III/A concrete. This is a significant step towards the potential wider implementation of coarse CCA in structural concrete, provided a suitable quantity of SCM is adopted along with a reliable and consistent source of coarse CCA.

Corrosion-related degradation incurs a significant cost to infrastructure and society. In 2016, the direct corrosion cost was estimated at $276 billion, which is 3.1% of the U.S. gross domestic product. Despite the known consequences of corrosion damage, many unknowns still exist, such as the mechanisms and rates of chloride-induced corrosion initiation and propagation. There is also a lack of high-quality quantitative kinetic data and analysis that can obtain the fundamental micro- and nanostructural mechanisms and initiation of metal corrosion. The corrosion initiation in metals is considered to be governed by dynamic processes that take place at the nanoscale. Thus, the measurement of nanoscale surface structures correlated with electrochemical properties in metals is critical in the understanding of corrosion initiation, and microstructure-corrosion relationship, as well as efforts toward materials design for corrosion mitigation. As a fundamental approach to this study, a systematic review of different surface characterization techniques was initially discussed. This entailed their principles, applications, and perspectives for surface corrosion monitoring, enabling the development of next-generation inhibition technologies, and improving corrosion predictive models. Unprecedented, this research study presented a novel application of a quantitative phase microscopy technique, spectral modulation interferometry (SMI), for in situ nanoscale characterization of corrosion of different alloys in real-time. SMI offers high sensitivity, rapid image acquisition, and speckle-free images; thus, real-time quantification of surface topography evolution during corrosion can be obtained accurately to evaluate the temporally- and spatially-dependent corrosion rates. With an innovative additive-manufactured fluid cell, experiments were performed under flowing solution conditions. Electrochemical tests via stepwise polarization and solution chemistry through collected aliquots of outflow solution were also performed alongside the nanoscale SMI experiment to simultaneously provide corroborating corrosion rate measurements. This innovative approach to measuring dissolution rates of metal at three levels can provide highly quantitative kinetic data of reacting surfaces that are rarely explored in the literature. First, the in situ SMI combined with the stepwise potentiostatic tests and the solution chemistry analysis was used to investigate the nanoscale characterization of corrosion of an AA6111-T4 aluminum alloy in real-time. The corrosion experiment was conducted in a 0.5 wt.% NaCl flowing solution acidified to pH ⁓2.9 by acetic acid. Based on the quantitative 3D height profiles across the corroded surface, pit formation resulting from rapid local corrosion was predominant, which is heterogeneously distributed and was appearing at different times. The computed time-dependent dissolution rates of aluminum also varied as the experiment proceeded, with the combination of linear and nonlinear surface normal distributions. An initial mean linear dissolution rate of (0.40 ± 0.007) μmol m−2 s−1 transitioned to a more rapid mean rate of (1.95 ± 0.035) μmol m−2 s−1, driven by the anodic polarization. Dissolution rates from the three performed methods follow similar trends and there is the visibility of linking the nanoscale in situ SMI data to the electrochemical corrosion measurements and ex situ chemical solution analysis. At the end of the corrosion period, rates of 118, 71, and 2.45 μmol m−2 s−1 were obtained from electrochemical measurements, ex situ solution analyses, and in situ SMI corrosion measurements, respectively. In addition, SMI–electrochemical experiments were performed to evaluate the effect of thermal history on corrosion modes and rates of AA6111. Quantitative estimates of the corrosion initiation and propagation in the alloy were also assessed. A single coil of AA6111 alloy that was solution heat treated at a temperature above 500°C and quenched with 2 different water quench rates (i.e., slow-quenched at 131ºC/s and fast-quenched at 506ºC/s) with each in T4 and T82 temper condition was investigated in this study. Irrespective of the quenched and/or temper conditions, the electrochemical potential-current (E-i) results showed a similar pattern in the polarization curve and similar current response over the immersed time, and a small difference in their corrosion behavior will be difficult to detect due to the dissolution kinetics that takes place on the nanoscale. As revealed from the SMI topography map, the corrosion modes at the nanoscale were very distinct despite having similar electrochemical responses and chemical compositions. Primarily, heterogeneous dissolution of intergranular corrosion (IGC) and crystallographic pitting was observed in the tested alloy substrates, with the slow-quenched samples susceptible to IGC and the fast-quenched samples susceptible to crystallographic pitting. The nucleation of IGC sites is triggered by the increased coarsening and formation of precipitates in the grain boundary, while the pitting corrosion is attributed to the coarsening of the precipitates in the grain bodies. The quantitative analysis of topography evolution from the SMI data revealed a non-uniform (i.e., heterogenous) surface dissolution, as is typical for aluminum alloys. Notably, the fast-quenched material resisted corrosion initiation for a longer time and showed great resistance even at higher anodic polarization. However, an instant breakdown then occurred after 60mV of polarization and corrosion accelerated faster, relative to the slow-quenched material which initiated sooner (i.e. with less overpotential). In this setup, it is now possible to detect and evaluate these differences quantitatively through a quick corrosion test with the combined electrochemical-SMI technique. Therefore, this work showed that the corrosion susceptibility of AA6111 alloy is influenced by the thermal history, which can be controlled with a proper quench rate and further tempering. Additionally, this research also utilized the novel SMI techniques to investigate in situ chloride-induced corrosion of A615 low-carbon steel at the nanoscale. Along with surface topography monitoring, a potentiostat was connected to simultaneously monitor the bulk electrochemical activity of the carbon steel. Experiments were conducted in chloride-free and chloride-enriched solutions at pH 5 to investigate the role of chloride on topography evolution, dissolution mode, and corrosion kinetics. The 3D topography map acquired from the SMI showed an early formation of localized shallow pits on the surface subjected to the chloride free-solution. A more detrimental form of corrosion was obtained on the samples in chloride-enriched solution, which revealed early-age microcracks or intergranular defective sites associated with the heterogeneous roughening of the sample surface. The presence of chloride ions also influenced the initiation period of corrosion. Indeed, higher grain defects were obtained in samples immersed in 5.0 wt.% NaCl solution than the sample in 1.0 wt.% NaCl solution. The quantitative analysis of the height profile data (acquired from SMI) verified the heterogeneity of the corrosion process of both samples either susceptible to pitting corrosion and/or intergranular corrosion behavior. A faster dissolution rate was acquired on the sample immersed in 5.0 wt.% NaCl solution, with the rate of (3.53 ± 0.103) μmol m−2 s−1 and (5.64 ± 0.0225) μmol m−2 s−1 computed at the initiation and propagation stages, respectively. Likewise, the estimated volume loss followed a similar trend to the 3D surface topography data, but a distinct behavior in the volume loss was observed when compared to the void volume obtained from the electrochemical monitoring. This confirmed that the electrochemical measurement overestimates metal loss and does not present a good representation of material dissolution on the nanoscale. Finally, a different perspective of corrosion mitigation in the metallic alloy was presented. The extensive application of deicing salts has led to significant deterioration in many transportation infrastructures and automobiles due to corrosion. In this regard, the work investigated the corrosion inhibition performance of 2 corn-derived polyols, namely: sorbitol, and mannitol, on reinforced steel rebar. The results demonstrated that the incorporation of polyols in the deicing solution reduced the corrosion initiation while the inhibition rate increased as the polyol content increased from 0% to 5wt.%. The outcome of this study contributed to the search for mitigation strategies to minimize the impact of deicing chemicals on steel infrastructures. Overall, it is evident that corrosion is a huge durability problem and requires significant consideration when designing metals or alloys that are usually exposed to hostile environments. Understanding the nanostructural and kinetics of corrosion at both the initiation and propagation periods, as well as its thermodynamics, is important for designing a suitable protection strategy. This dissertation is expected to present the application of the surface technique to directly quantify the dynamic evolution of site-specific local corrosion of metals during early initiation stages at the nanoscale. / Doctor of Philosophy / Corrosion-related degradation incurs a significant cost to infrastructure and society. In 2016, the direct corrosion cost was estimated at $276 billion, which is 3.1% of the U.S. gross domestic product. Despite the known consequences of corrosion damage, many unknowns still exist, such as the mechanisms and rates of chloride-induced corrosion initiation and propagation. There is also a lack of high-quality quantitative kinetic data and analysis that can obtain the fundamental micro- and nanostructural mechanisms and initiation of metal corrosion. The corrosion initiation in metals is considered to be governed by dynamic processes that take place at the nanoscale. Thus, the measurement of nanoscale surface structures correlated with electrochemical properties in metals is critical in the understanding of corrosion initiation, and microstructure-corrosion relationship, as well as efforts toward materials design for corrosion mitigation. As a fundamental approach to this study, a systematic review of different surface characterization techniques was initially discussed. This entailed their principles, applications, and perspectives for surface corrosion monitoring, enabling the development of next-generation inhibition technologies, and improving corrosion predictive models. Unprecedented, this research study presented a novel application of a quantitative phase microscopy technique, spectral modulation interferometry (SMI), for in situ nanoscale characterization of corrosion of different alloys in real-time. SMI offers high sensitivity, rapid image acquisition, and speckle-free images; thus, real-time quantification of surface topography evolution during corrosion can be obtained accurately to evaluate the temporally- and spatially-dependent corrosion rates. With an innovative additive-manufactured fluid cell, experiments were performed under flowing solution conditions. Electrochemical tests via stepwise polarization and solution chemistry through collected aliquots of outflow solution were also performed simultaneously with the nanoscale SMI experiment to provide corroborating corrosion rate measurements. This innovative approach to measuring dissolution rates of metal at three levels simultaneously can now provide highly quantitative kinetic data of reacting surfaces that are not explored in the literature.

Fundamental understanding of atmospheric corrosion mechanisms requires an in-depth understanding on the dynamic interaction between corrosive constituents and metal/alloy surfaces. This doctoral study comprises field and laboratory investigations that assess atmospheric corrosion and metal release processes for two different groups of alloys exposed in chloride-rich environments. These groups comprise two commercial Zn-Al alloy coatings on steel, Galfan™ (Zn5Al) and Galvalume™ (Zn55Al), and four copper-based alloys (Cu4Sn, Cu15Zn, Cu40Zn and Cu5Zn5Al). In-depth laboratory investigations were conducted to assess the role of chloride deposition and alloy microstructure on the initial corrosion mechanisms and subsequent corrosion product formation. Comparisons were made with long-term field exposures at unsheltered marine conditions in Brest, France. A multitude of surface sensitive and non-destructive analytical methods were adopted for detailed in-situ and ex-situ analysis to assess corrosion product evolution scenarios for the Zn-Al and the Cu-based alloys. Scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS) were employed for morphological investigations and scanning Kelvin probe force microscopy (SKPFM) for nobility distribution measurements and to gain microstructural information. SEM/EDS, infrared reflection-absorption spectroscopy (IRAS), confocal Raman micro-spectroscopy (CRM) and grazing incidence x-ray diffraction (GIXRD) were utilized to gain information on corrosion product formation and possibly their lateral distribution upon field and laboratory exposures. The multi-analytical approach enabled the exploration of the interplay between the microstructure and corrosion initiation and corrosion product evolution. A clear influence of the microstructure on the initial corrosion product formation was preferentially observed in the zinc-rich phase for both the Zn-Al and the Cu-Zn alloys, processes being triggered by microgalvanic effects. Similar corrosion products were identified upon laboratory exposures with chlorides for both the Zn-Al and the Cu-based alloys as observed after short and long term marine exposures at field conditions. For the Zn-Al alloys the sequence includes the initial formation of ZnO, ZnAl2O4 and/or Al2O3 and subsequent formation of Zn6Al2(OH)16CO3·4H2O, and Zn2Al(OH)6Cl·2H2O and/or Zn5(OH)8Cl2·H2O. The patina of Cu sheet consists of two main layers with Cu2O predominating in the inner layer and Cu2(OH)3Cl in the outer layer, and with a discontinuous presence of CuCl in-between. Additional patina constituents of the Cu-based alloys include SnO2, Zn5(OH)6(CO3)2, Zn6Al2(OH)16CO3·4H2O and Al2O3. General scenarios for the evolution of corrosion products are proposed as well as a corrosion product flaking mechanism for some of the Cu-based alloys upon exposure in chloride-rich atmospheres. The tendency for corrosion product flaking was considerably more pronounced on Cu sheet and Cu4Sn compared with Cu15Zn and Cu5Al5Zn. This difference is explained by the initial formation of zinc- and zinc-aluminum hydroxycarbonates Zn5(OH)6(CO3)2 and Zn6Al2(OH)16CO3·4H2O on Cu15Zn and Cu5Al5Zn, corrosion products that delay the formation of CuCl, a precursor of Cu2(OH)3Cl. As a result, the observed volume expansion during transformation of CuCl to Cu2(OH)3Cl, and the concomitant flaking process of corrosion products, was less severe on Cu15Zn and Cu5Al5Zn compared with Cu and Cu4Sn in chloride-rich environments. The results confirm the barrier effect of poorly soluble zinc and zinc-aluminum hydroxycarbonates Zn5(OH)6(CO3)2 and Zn6Al2(OH)16CO3·4H2O, which results in a reduced interaction between chlorides and surfaces of Cu-based alloys, and thereby reduced formation rates of easily flaked off corrosion products. From this process also follows reduced metal release rates from the Zn-Al alloys. / Bättre molekylär förståelse för metallers atmosfäriska korrosion kräver en fördjupad kunskap i det dynamiska samspelet mellan atmosfärens korrosiva beståndsdelar och metallytan. Denna doktorsavhandling omfattar laboratorie- och fältundersökningar av korrosions- och metallfrigöringsprocesser av två grupper av legeringar som exponerats i kloridrika atmosfärsmiljöer: två kommersiella Zn-Al beläggningar på stål, Galfan™ (Zn med 5% Al, förkortat Zn5Al) och Galvalume™ (Zn55Al), samt fyra kopparbaserade legeringar (Cu4Sn, Cu15Zn, Cu40Zn och Cu5Zn5Al). Undersökningar har genomförts i renodlade laboratorie-miljöer med för-deponerade NaCl-partiklar i en atmosfär av varierande relativ fuktighet. Syftet har varit att utvärdera betydelsen av kloriders deposition och legeringarnas mikrostruktur på korrosionsmekanismen samt bildandet av korrosionsprodukter. Jämförelser av korrosionsmekanismer har även gjorts efter flerårsexponeringar av samma legeringar i en marin fältmiljö i Brest, Frankrike. Undersökningarna har baserats på ett brett spektrum av analysmetoder för detaljerade studier dels under pågående atmosfärisk korrosion (in-situ), och dels efter avslutad korrosion (ex-situ). Legeringarnas mikrostruktur och tillhörande variation i ädelhet hos olika faser har undersökts med svepelektronmikroskopi och energidispersiv röntgenmikroanalys (SEM/EDS) samt med en variant av atomkraftsmikroskopi (engelska: scanning Kelvin probe force microscopy, SKPFM). Korrosionsprodukternas tillväxt har analyserats in-situ med infraröd reflektions-absorptionsspektroskopi (IRAS), samt morfologi och sammansättning av bildade korrosionsprodukter ex-situ med SEM/EDS, konfokal Raman mikro-spektroskopi (CRM) samt röntgendiffraktion vid strykande ifall (GIXRD). Det multi-analytiska tillvägagångssättet har medfört att det komplexa samspelet mellan de skilda legeringarnas mikrostruktur, korrosionsinitiering och bildandet av korrosionsprodukter kunnat studeras i detalj. En tydlig påverkan av mikrostruktur på det initiala korrosionsförloppet har kunnat påvisas. Korrosionsinitieringen sker företrädesvis i mer zinkrika faser för såväl Zn-Al- som Cu-Zn-legeringar och orsakas av mikro-galvaniska effekter mellan de mer zinkrika, mindre ädla, faserna och omgivande faser. Deponerade NaCl-partiklar påskyndar den lokala korrosionen oberoende av mikrostruktur. Snarlika sekvenser av korrosionsprodukter har kunnat påvisas såväl efter laboratorie- som fältexponeringar. För Zn-Al-legeringar bildas först ZnO, ZnAl2O4 och/eller Al2O3, därefter Zn6Al2(OH)16CO3·4H2O och Zn2Al(OH)6Cl·2H2O och/eller Zn5(OH)8Cl2·H2O. På ren koppar bildas ett inre skikt dominerat av Cu2O, ett mellanskikt av CuCl och ett yttre skikt med i huvudsak Cu2(OH)3Cl. Beroende på legeringstillsats har även SnO2 och Zn5(OH)6(CO3)2 kunnat identifieras. En mekanism för flagning av korrosionsprodukter på kopparbaserade legeringar i kloridrika atmosfärer har utvecklats. Tendensen för flagning har visat sig vara mycket mer uttalad på ren Cu och Cu4Sn än på Cu15Zn och Cu5Al5Zn. Skillnaden kan förklaras med hjälp av det tidiga bildandet av Zn5(OH)6(CO3)2 och Zn6Al2(OH)16CO3·4H2O på Cu15Zn och Cu5Al5Zn som fördröjer bildandet av CuCl, en föregångare till Cu2(OH)3Cl. Därigenom hämmas även den observerade volymexpansionen som sker när CuCl omvandlas till Cu2(OH)3Cl, en process som visar sig vara den egentliga orsaken till att korrosionsprodukterna flagar. Resultaten bekräftar barriäreffekten hos de mer svårlösliga faserna Zn5(OH)6(CO3)2 och Zn6Al2(OH)16CO3·4H2O, vilken dels resulterar i en minskad växelverkan mellan klorider och de legeringsytor där dessa faser kan bildas, och dels i en reducerad metallfrigöringshastighet. / <p>QC 20140915</p> / Autocorr, RFSR-CT-2009-00015 Corrosion of heterogeneous metal-metal assemblies in the automotive industry / Atmospheric corrosion and environmental metal dispersion from outdoor construction materials