A model to evaluate quantitatively the alkalinity of pore solution based on phase composition of cement hydrates with SCMs was proposed and was compared with suppressing effect of ASR expansion. The model is devised from the perspective of alkali sorption by C-S-H gel, and the parameters for calculation can be evaluated thanks to phase composition analysis such as XRD/Rietveld analysis and selective dissolution. The experimental results have shown that ASR expansion is strongly correlated to the alkalinity of the pore solution, which can be calculated with the proposed model. Based on the results, the ASR suppressing effects of SCMs are converted to the reduction in total alkali content as available alkali content. Finally, the required replacement level of SCM with the proposed model was compared to the CSA A23.2-27A standard based on numerous experiments and field experiences in Canada. The calculated result was well consistent with the minimum replacement level of SCMs specified in CSA A23.2-27A. A subsequent interpretation of this study supports that the dominant mechanism of SCMs for ASR suppression is a reduction of alkalinity of pore solution.

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A new testing protocol, Alkali-Wrapped Concrete Prism Test (AW-CPT), is proposed to avoid alkali leaching and drying, which considerably influence expansion behavior of concrete affected by alkali-silica reaction (ASR). The approach used in this test is that a concrete specimen is wrapped by wet cloth containing alkali solution mimicking the alkalinity of the concrete pore solution. The proposed testing protocol was validated through laboratory and field-exposure measurements, with a focus on expansion, alkali mass balance, and mass change. The test results clearly showed that alkali leaching and drying were significantly reduced by using the AW-CPT method. AW-CPT gives a conservative threshold total alkali content, while conventional CPT overestimates it. The test results also highlighted that there may be an optimum condition of temperature and level of alkali boosting for each reactive aggregate.

In order to realize the utilization of cement-based materials in the special extreme environment, the deep sea, the authors have launched a project targeted at creating a technology platform with in-situ methods and systems for monitoring and evaluating cement-based materials located at deep ocean bottom sites. The first in-situ test in the world with a view to investigating the time-dependence of the volumetric stability and microstructure of Portland cement mortar following its long-term exposure to deep-sea conditions is currently underway at a 3515-m depth in the Nankai Trough. This paper reviews previous studies about the influences of deep-sea hydraulic pressure on cement-based materials, verifies the action of short-term hydraulic pressure using Portland cement mortars on a laboratory scale, and introduces the ongoing progress of in-situ deep-sea tests. Results from laboratory tests indicate that dimensional changes were provoked by liquid water infiltration and confinement while under short-term hydraulic pressure, however, time-dependent behavior under stresses such as creep has not appeared. Weight gain, changes in pore-size distribution, compressive strength and bending strength of the cement mortar were monitored after pressurization and depressurization processes.

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Reinforced concrete (RC) structures in marine environments are generally affected by harsh marine environmental actions, resulting in early performance degradation mainly due to chloride-induced deterioration. In such conditions, corrosion of rebar progresses rapidly, and also the cross-sectional area of rebar is reduced and consequently structural performance of RC structures will be degraded. In contrast, the surface of concrete structures is often covered with many marine sessile organisms under marine tidal and submerged conditions. These marine sessile organisms have been empirically known to enhance the durability of concrete though the effectiveness is not appropriately evaluated. This paper describes the long-term resistance of concrete with marine sessile organisms to chloride ion penetration in concrete. The effect and its sustainability of marine sessile organisms on chloride ion penetration in concrete were investigated through field exposure tests and laboratory tests. From the test results, the basal membrane, which is a matrix of marine sessile organisms, adheres to concrete strongly on a long-term basis though some gaps between concrete and the basal membrane can be observed. In addition, experimental results and simplified simulation clarified that the attachment of marine sessile organisms can enhance the long-term resistance of concrete to chloride ion penetration.

Alkali release from aggregates is considered to cause expansion due to the alkali-silica reaction (ASR), owing to the increase in the hydroxide ion concentration (namely pH) of the pore solution. However, a direct validation of this assertion has not yet been made. In this research, the effects of the type of soak solution, which might better mimic the composition of the pore solution, on the behavior of alkali release from aggregates are investigated through immersion tests of aggregates. More importantly, accompanying ions dissolved from the aggregates are also measured in order to determine the mechanism for the increase in hydroxide ion concentration of the pore solution. The test results show that this increase can barely be observed, despite a considerable amount of alkalis being released. The results critically question the conventional view that alkali released from an aggregate serves to accelerate the ASR.