Observation of fracture sealing in high-strength and ultra-low-permeability concrete by micro-focus X-ray CT and SEM/EDX

Abstract

Fracture sealing by precipitation is known to occur in high-strength and ultra-lowpermeability concrete (HSULPC) immersed in water. Because a high ability to retard radionuclide migration is required for HSULPC, understanding both the sealing process and the composition of sealing deposits is important to identify optimum conditions for significant sealing. In this study, sealing of a macro-fractured HSULPC specimen with initial aperture of approximately 0.1 mm was investigated in simulated seawater over 49 days. The composition of sealing deposits at 49 days after immersion was clarified by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDX), and the progress of sealing during the 49 days was clarified by image analysis with micro-focus X-ray computed tomography (X-rayCT). Both the SEM/EDX and X-rayCT results showed that significant sealing was attained only near the outermost part of the specimen. The SEM/EDX results showed that a thin brucite layer formed on the entire specimen surface over which significant precipitation of calcium carbonate occurred and sealed the macro-fracture only near the outermost part of the specimen. The X-rayCT results indicated that the amount of sealing deposits in the macro-fracture (P seal ) reached 70 % in the mostly sealed region at 49 days and the rate of change in P seal became maximum (3.7 % day -1 ) during 7-21 days after immersion, then decreased. In conclusion, Revised_Manuscript Click here to download Manuscript: IJF_manuscript_FRAC_Rev1.doc Click here to view linked References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 the findings in this study represent an important clue in the search for optimum conditions to achieve fracture sealing in HSUPLC.

An Experimental Study of Dynamic Tensile Failure of Rocks Subjected to Hydrostatic Confinement

“…Its application to engineering fields such as geomechanics is becoming popular as high-resolution industrial micro-computed tomography systems are more widely available. For example, CT imaging has been used to characterize the internal structure of geomaterials such as soil (Elyeznasni et al 2012;Garbout et al 2013;Hapca et al 2015;Otani et al 2001), rock (Huang et al 2013;Huang and Xia 2015;Ito et al 2001;Liu et al 2014b;Sugawara et al 2004;Vervoort et al 2004), concrete (Darma et al 2013;Fukuda et al 2014;Henry et al 2014), and asphalt (Liu et al 2014a;Masad and Kassem 2009;Taniguchi et al 2012;Tomoto and Moriyoshi 2009). In this paper, the Brazilian disc (BD) sample is adopted to measure the dynamic tensile strength of rock materials (Zhou et al 2012) under hydrostatic confinement.…”

Validation of Self‐Healing Properties of Construction Materials through Nondestructive and Minimal Invasive Testing

“…An example is shown in Figure . Fukuda et al studied the healing efficiency in the interior of the crack of ultrahigh performance concrete when being exposed to seawater by SEM/EDX analysis. SEM/EDX was performed on a surface sawn orthogonal to the crack to determine the composition of the sealing deposits, as shown in Figure .…”

“…Note that cps indicates count per second. Reproduced with permission . Copyright 2014, Springer Nature.…”

“…Furthermore, it is possible to study the porosity and the pore size distribution. X‐ray CT was also used by Fukuda et al to visualize the progress of crack sealing in cementitious materials by extracting the precipitated region. It was confirmed that healing occurred mainly near the outermost part of the sample.…”

Precipitation of calcium compounds onto rock surfaces in water with cementitious material

“…Atkinson (1984) clarified the effects of the surrounding environment on subcritical crack growth in HSULPC, under various environmental conditions. Fukuda et al (2012Fukuda et al ( , 2013Fukuda et al ( , 2014 observed the self-sealing of cracks and pores in HSULPC in water using micro-focus X-ray computed tomography (CT) and reported that self-sealing occurred by the precipitation of Ca compounds.…”