The use of blended cements enables the production of concretes with low embodied carbon and improved resistance to chloride penetration compared to general-purpose (GP) cement concrete. This paper reports the chloride diffusion characteristics in terms of the apparent diffusion coefficient (Da), surface chloride concentration (Cs), and corresponding aging factors (a and b) of low-carbon concrete (LCC) derived from up to 9-year long-term exposure of small reinforced concrete slabs in both laboratory-simulated and field marine tidal conditions. LCC with either 30% fly ash or 50% slag provides slightly to significantly lower 28-day compressive strength than GP cement concrete at the same water-binder ratio but significantly better resistance to chloride penetration. The long-term chloride profile necessary to determine the concrete cover where the chloride threshold is reached can be determined with the Da.t0, Cs.t0, and corresponding age factors a and b, where t0 is the 1-year time of exposure. The improved resistance to chloride penetration by the use of fly ash and slag as cement replacements was largely due to their intrinsic influence on the microstructure of the concrete. The results highlight that the difference in chloride penetration arises from the change in test methods, thus the importance of calibration when data obtained from laboratory concrete were used as inputs for service-life design.

Studies have revealed that kaolinite-containing marine clay (MC) exhibits pozzolanic reactivity after thermal activation, making it a sound supplementary cementitious material for concrete production. In this study, calcined MC with two different finenesses was used to substitute cement in the mortar at 0, 10, 20, and 30% replacement ratios. The pozzolanic activity of calcined MC was confirmed by the reduced portlandite content in hydration products (by quantitative X-ray diffraction [QXRD]) and the formation of the calcium-silicate-hydrate (C-S-H) and calcium-aluminumsilicate-hydrate (C-A-S-H) gels (by scanning electron microscopy/energy-dispersive X-ray spectroscopy [SEM-EDS]). The microstructural, mechanical, and transport properties of mortar were investigated. The pore volume increased with the incorporation of calcined MC, while obvious pore refinement was noted. Due to the cement dilution effect and higher pore volume in the mortar, the strength and modulus of elasticity generally decreased with higher MC content. Chloride transport in the mortar was greatly inhibited due to the reduced pore sizes and higher chloride-binding capacity of calcined MC. With the addition of 10% fine calcined MC, the low-carbon mortar exhibits an earlier and increased heat release, similar strength, 8% lower water absorption, 14% lower water sorptivity, 44% lower chloride migration coefficient, and 12% loss in modulus of elasticity.

This paper presents results from a comprehensive, cradle-to-grave study in which electrochemical measurements (corrosion potential and corrosion rate), crack progression, and gravimetric metal loss were recorded for one-third-scale Class V prestressed specimens exposed for over 3 years to a simulated outdoor marine environment. These data were used to isolate the effect of cracking on the corrosion rate and determine the appropriate oxygen permeation coefficient values that were used to quantify the differences in corrosion propagation between the cracked and uncracked states. The permeation coefficient in cracked sections was found to be more than 20 times larger than that in uncracked ones. It was also higher than that for reinforced concrete specimens under comparable wetting-and-drying saltwater exposure. The findings predict that comparable (Class V) full-size prestressed pile specimens will crack within 3 years of the destruction of the passive layer (depassivation).

Concrete with fly ash is commonly used in the infrastructures of marine regions. However, the traditional design method does not account for the influences of sustained stress and global warming. This research presents an optimized design approach for low-CO2 marine concrete with fly ash considering chloride penetration with stress and global warming. First, the purpose of optimal design is sustainability (the embodied CO2 of concrete). The constraints of optimization consider strength, slump, and chloride penetration durability with the effects of stress and global warming. Second, a global optimization algorithm, named a genetic algorithm, is used to determine optimal mixtures. The aim of the genetic algorithm is embodied CO2 of concrete, and the performance constraints of the genetic algorithm consist of strength, slump, and chloride penetration durability. The results were as follows: 1) global warming accelerates chloride penetration but has no effect on the results of optimal mixtures. For low-strength concrete free of sustained stress or under low-level compressive stress, strength was the dominant factor for mixture design. However, for low-strength concrete under sustained tensile stress or high-level compressive stress, the durability of concrete under chloride penetration dominated the mixture design. Compared to compressive stress, the influence of tensile stress on the mixtures was much more apparent; 2) for high-strength concrete, the strength rather than the durability of chloride penetration dominated the mixture design; and 3) the optimal mixtures of concrete for other purposes such as material cost were determined. The optimal mixtures with low cost overlapped with those designed for low CO2 emissions. Summarily, the proposed model provides a general method to design mixtures considering sustainability, strength, slump, and durability of chloride penetration with structural stress and global warming.

The improvement of durability and service life of reinforced concrete structures in the marine environment with the incorporation of corrosion inhibitors has attracted significant attention in recent years. The present study aims to evaluate the performance of a commercially available organic corrosion inhibitor in protecting the steel reinforcement of concrete structures in marine conditions. The study was performed on a control mixture and a test mixture with water-cement ratios (w/c) of 0.4 and 0.6, providing aggressive laboratory and field environments following the recommendation of international standards for corrosion inhibitors assessments. Corrosion monitoring methods and visual inspection of reinforcing bars confirmed the effectiveness of migrating corrosion inhibitor in mitigating chloride-induced corrosion. The migratory properties of the corrosion inhibitor and its ability to densify the matrix microstructure were confirmed through scanning electron microscopy and X-ray photoelectron spectroscopy analyses.