Alkali-silica reaction: Current understanding of the reaction mechanisms and the knowledge gaps

A review of waste products utilized as supplements to Portland cement in concrete

Under the alternating electrical excitation, biological tissues produce a complex electrical impedance which depends on tissue composition, structures, health status, and applied signal frequency, and hence the bioelectrical impedance methods can be utilized for noninvasive tissue characterization. As the impedance responses of these tissue parameters vary with frequencies of the applied signal, the impedance analysis conducted over a wide frequency band provides more information about the tissue interiors which help us to better understand the biological tissues anatomy, physiology, and pathology. Over past few decades, a number of impedance based noninvasive tissue characterization techniques such as bioelectrical impedance analysis (BIA), electrical impedance spectroscopy (EIS), electrical impedance plethysmography (IPG), impedance cardiography (ICG), and electrical impedance tomography (EIT) have been proposed and a lot of research works have been conducted on these methods for noninvasive tissue characterization and disease diagnosis. In this paper BIA, EIS, IPG, ICG, and EIT techniques and their applications in different fields have been reviewed and technical perspective of these impedance methods has been presented. The working principles, applications, merits, and demerits of these methods has been discussed in detail along with their other technical issues followed by present status and future trends.

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Bioelectrical Impedance Methods for Noninvasive Health Monitoring: A Review.

Characterization and quantification of self-healing behaviors of microcracks due to further hydration in cement paste

Comparison of fly ash, silica fume and metakaolin from mechanical properties and durability performance of mortar mixtures view point

Quantifying the effects of crack width, tortuosity, and roughness on water permeability of cracked mortars

ASTM C1567 [1] is a commonly used accelerated test method to determine the required dosage of supplementary cementitious materials (SCMs) to mitigate alkali–silica reaction (ASR) in mixtures containing reactive siliceous aggregates. Past research suggested that fly ash and other SCMs inhibit ASR, primarily through alkali dilution and binding. In ASTM C1567, however, the alkalinity of the pore solution is largely influenced by the penetration of NaOH from the external soak solution; and this could erase the beneficial effects of alkali dilution and binding. To better understand why fly ash inhibits ASR in this test, the present study performs a quantitative evaluation of six potential ASR mitigation mechanisms: (1) alkali dilution, (2) alkali binding, (3) mass transport reduction, (4) increasing tensile strength, (5) altering ASR gel, and (6) reducing aggregate dissolution rate. The results suggest that (2), (3), (4), and (6) are the primary mitigation mechanisms, while (1) and (5) show a negligible impact.

How does fly ash mitigate alkali–silica reaction (ASR) in accelerated mortar bar test (ASTM C1567)?

Cracking can significantly accelerate mass transport in concrete and as such, impact its durability. This paper is aimed at quantifying the effect of saturated cracks on ion diffusion. Electrical conductivity, measured by electrical impedance spectroscopy (EIS), was used to characterize the diffusion coefficient of fiber-reinforced cement paste disks that contained one or two through-thickness cracks. Crack widths in the range 20–100 μm were generated by controlled indirect tension test. Crack profiles were digitized and quantified by image analysis to determine crack volume fraction and average crack width. Crack connectivity (e.g., inverse of tortuosity) was calculated from the conductivity results measured by EIS. The results suggest that the diffusion coefficient of cracked samples is strongly and linearly related to the crack volume fraction; but is not directly dependent on crack width. Crack tortuosity does reduce the ion diffusion through cracks, but its impact is not very significant. Overall, the most important parameter governing ion diffusion in saturated cracked concrete is the volume fraction of cracks. Theoretical justifications of these observations are also provided.

Evaluating ion diffusivity of cracked cement paste using electrical impedance spectroscopy

Ductility enhancement of autoclaved cellulose fiber reinforced cement boards manufactured using a laboratory method simulating the Hatschek process

Cracks in concrete accelerate mass transport and shorten the service life of structures. In this study, cracks were physically simulated using a Plexiglas parallel-plate setup with adjustab...

Alireza Akhavan

Papers

Quantifying the effects of crack width, tortuosity, and roughness on water permeability of cracked mortars

How does fly ash mitigate alkali–silica reaction (ASR) in accelerated mortar bar test (ASTM C1567)?

Evaluating ion diffusivity of cracked cement paste using electrical impedance spectroscopy

Ductility enhancement of autoclaved cellulose fiber reinforced cement boards manufactured using a laboratory method simulating the Hatschek process

Quantifying Permeability, Electrical Conductivity, and Diffusion Coefficient of Rough Parallel Plates Simulating Cracks in Concrete