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Field measurements of 42 in-service reinforced concrete bridges in coastal environments of Southeast China, covering a wide range of service year, span length, and concrete mixture, were carried out to investigate the chloride penetration. 323 sets of chloride measurement data were collected in total and then analysed to optimize the parameters involved in the common chloride diffusion model derived based on Fick's second law. A modified chloride diffusion model was then proposed, taking into consideration a range of influencing factors including ambient temperature, relative humidity, stress state, carbon dioxide, chloride binding, and ageing. Verification of the modified model with field measurement data was performed. The sensitivity of the chloride diffusion to variations of each parameter was discussed in detail eventually. [ABSTRACT FROM AUTHOR]

Owing to the unique molecular structure and high ion exchange capacity, hydrotalcites are believed to have a potential to be modified and tailor-made as an active component of mortar and/or concrete. In this paper, two types of modified hydrotalcites (MHT-pAB and MHT-NO 2 ) were incorporated into cement mortars with two dosage levels replacing 5% and 10% weight of cement. Designated testing programme including workability test, strength test, porosity test, and rapid chloride migration and diffusion test were employed to investigate the effect of the two modified hydrotalcites on chloride penetration in cement mortar. The results based on these tests indicated that the incorporation of MHT-pAB at 5% dosage in mortar produced a notably improved chloride diffusion resistance with no remarkably negative influence on the development of mechanical strength and the workability of fresh mortar, which therefore validated that the MHT-pAB could be a promising alternative in hindering the chloride transport in mortar when an appropriate mixing dosage is adopted. [ABSTRACT FROM AUTHOR]

Abstract: Two modified hydrotalcites (MHTs) intercalated with nitrate and aminobenzonate anions, (i.e., CaAl-MHT-NO3 and CaAl-MHT-pAB) have been synthesized. The intercalation of CaAl-MHT-pAB was achieved by anion exchange of nitrate in the host material, CaAl-MHT-NO3, which was prepared by a coprecipitation method. Materials characterization was conducted by means of X-ray diffraction (XRD), thermal analysis, IR-spectroscopy and environmental scanning electron microscope (ESEM). Element analysis further confirmed both nitrate and p-aminobenzonate anions were successfully intercalated into the interlayer space of MHTs with an intercalating ratio of 81.2% and 33.1% respectively. Volhard’s titrimetric analysis demonstrated that ion exchange occurred between free chlorides in simulated concrete pore solution and anions intercalated in MHTs. The preliminary results reported in this paper shed light on the promising use of MHTs as a new type of additive for improved corrosion protection of reinforced concrete. [Copyright &y& Elsevier]

Highlights: [•] The anticorrosion behavior of modified hydrotalcites (MHTs) was evaluated. [•] MHTs have a twofold beneficial effect against chloride-induced corrosion. [•] Ion-exchange between chloride and aminobenzoate reduced free chloride concentration. [•] Critical chloride concentration for initiating corrosion was increased by MHTs. [•] MHTs could be a promising additive of concrete for improved corrosion protection. [Copyright &y& Elsevier]

Abstract: This work aims to validate the design assumptions by the California Department of Transportation in order to better define the strategies used to design concrete structures with adequate corrosion mitigation and thus a “maintenance-free” service life. To this end, various laboratory tests were conducted to investigate the compressive strength of and chloride diffusivity in mortar and concrete samples with cement partially replaced by various minerals (class F and class N fly ash, ultra-fine fly ash, silica fume, metakaolin, and ground granulated blast-furnace slag), the porosity of mineral concretes, the freeze–thaw resistance of mineral mortars in the presence of deicers, and the effect of supplementary cementitious materials on the chloride binding and chemistry of the pore solution in mortar. [Copyright &y& Elsevier]

Abstract: We evaluated the chloride permeability and microstructure of Portland cement mortar modified by styrene–butadiene rubber (SBR) latex, using mortar samples with various polymer/cement (P/C) mass ratios. The incorporation of SBR improved the chloride penetration resistance along with the general ionic permeability of the mortar, while increasing its ionic transport resistance and decreasing its electric capacitance. These data suggest that admixing SBR led to denser and more refined microstructure of the cured cement mortar. Field-emission scanning electron microscopy images confirmed such improvements in the pore structure and the formation of an interpenetrating network structure of SBR and cement hydrate phases at relatively higher P/C ratios. Besides slightly reducing Portlandite content and mitigating carbonation with the increasing P/C ratio in mortar, SBR was also found to promote the formation of calcium aluminate trisulfate hydrate phases and facilitated chloride binding. [Copyright &y& Elsevier]

Conceptual analysis is performed to examine the effects of pore features on the water continuity in unsaturated porous systems. The roles of pore features in relative chloride diffusion coefficient (D rc) of mortar specimens at various degrees of water saturation (S w) were studied based on mercury intrusion porosimetry and resistivity tests. It is found that the role of pore structure in the D rc - S w relationship is a result of its effect on the water continuity. Porosity and tortuosity are not relevant to the D rc - S w relationship. A finer pore size distribution or lower pore connectivity tends to result in a lower D rc. The pore size effect on the D rc is pronounced primarily at high S w , while the D rc is dominated by the pore connectivity at low S w. Cement mortar with a higher water-to-binder ratio shows larger chloride diffusion at high relative humidity levels but smaller chloride diffusion at low relative humidity levels. [ABSTRACT FROM AUTHOR]

• Cementitious composites with ferronickel slag (FNS) were prepared. • The chloride penetration resistance was increased due to the inclusion of FNS. • The hydrotalcite of FNS cement pastes enhanced the chloride binding which can be described by the Langmuir isotherm. • The FNS facilitated the formation of amorphous C-S-H phases in cementitious systems. Sufficient utilizations of ferronickel slag (FNS), an industrial waste discharged from nickel smelting and stainless-steel production process, are essential under the background of sustainability development. In this work, the replacement of ordinary Portland cement by FNS and its influence on chloride penetration are systematically investigated. A range of measurements including RCPT, corrosion current, natural diffusion, pore structure and X-ray diffraction was carried out. The results show that the concrete pore structure can be refined with an appropriate dosage (up to 30%) of FNS, whereby a higher resistance to reinforcement corrosion and a reduction of electrical conductivity are found. With the inclusion of FNS the chloride binding capacity of cement pastes is enhanced and the binding behavior can be expressed by the Langmuir isotherm. The addition of FNS leads to a higher amount of amorphous C-S-H phases. The formation of hydrotalcite-like phases and the higher C-S-H content account for the enhanced chloride binding of FNS pastes. [ABSTRACT FROM AUTHOR]

• A formula for describing the time-dependent chloride diffusion coefficient in unsaturated cementitious materials is proposed. • The role of the degree of water saturation in long-term chloride diffusion is analyzed. • Effects of w/b and SCMs on unsaturated chloride diffusion are discussed. • Durability design of marine concrete structures based on unsaturated chloride diffusion coefficient is emphasized. Concrete is rarely saturated. Reliable durability design of marine concrete structures requires a solid understanding of the long-term chloride transport in unsaturated concretes. This paper presents a critical analysis of the time-dependent chloride diffusion coefficient in unsaturated cementitious materials exposed to marine environment. Evolutions of pore structure and chloride diffusion coefficient in saturated cementitious materials, along with the role of the degree of water saturation in long-term chloride diffusion, are analyzed. It is emphasized that the long-term sharp decrease of the chloride diffusion coefficient in marine cementitious materials is not primarily caused by densification of the microstructure due to hydration, but by the decreasing degree of water saturation with depth in the surface part of the materials. The effects of water/binder ratio and supplementary cementitious materials on chloride diffusion coefficient are different between saturated and unsaturated cementitious materials. [ABSTRACT FROM AUTHOR]

A comprehensive study from detailed microstructure analyses to mass transport investigations was implemented to explore chloride penetration of unsaturated alkali-activated slag (AAS) mortars accounting for chloride binding behaviors. Unsaturated chloride penetrations reflected from diffusion cases of instantaneous plane source and sorption cases of wetting-drying exposure were elaborated in relation to solid hydrates and pore structure features. It is found that the specimen with lower saturation has a slower chloride diffusion but a larger chloride penetration under wetting-drying cycles. Slag mortars with sodium hydroxide activation exhibit higher chloride binding capacity owing to more hydrotalcite-like phases and higher Ca/Si ratio of C-(N-)A-S-H gels in the outer product zones as compared to sodium silicate activated slag mortars, regardless of the saturation. Accelerations of the chloride penetration under the wetting-drying exposure are limited in saturated AAS specimens while for unsaturated AAS specimens more wetting-drying cycles result in the inner layers to be gradually diffusion-controlled. The chloride binding capacity of AAS specimens follows Langmuir's isotherm and clearly decreases with a lower saturation. It is advised to consider the electrical double layer effect within narrow pores when applying rapid chloride migration tests for AAS systems. [ABSTRACT FROM AUTHOR]

Abstract: For snow and ice control on winter roads, the direct cost of corrosion-inhibited chemicals can be much higher than that of the non-inhibited chemicals. Yet, prior to this work, little was known about how long the corrosion inhibitors and the anti-icing products remain effective on the pavement once applied. This case study investigated the longevity of inhibitors and the performance of corrosion-inhibited anti-icing products after pavement application during winter storms. The field operational tests included the daily sampling of anti-icer residuals on the pavement for seven days after anti-icer application for a black ice event, a man-made snow event, and a natural snow event, respectively. Subsequently, multiple analytical methods were used to examine the properties of pavement-collected samples in the laboratory. It was found that more than 62% of the inhibitor in the CCB anti-icer and more than 20% of the chlorides (especially for FreezGard and NaCl+GLT) could remain on the pavement four days after the application of liquid anti-icers to treat black ice. The longevity of chlorides and inhibitors on the pavement after anti-icer application can vary greatly depending on the pavement temperature, the amount of precipitation, etc. [Copyright &y& Elsevier]