Browsing by Author "Aldridge, LP"
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- ItemAppraisal of a cementitious material for waste disposal: neutron imaging studies of pore structure and sorptivity(Elsevier, 2010-08) McGlinn, PJ; de Beer, FC; Aldridge, LP; Radebe, MJ; Nshimirimana, R; Brew, DRM; Payne, TE; Olufson, KPCementitious materials are conventionally used in conditioning intermediate and low level radioactive waste. In this study a candidate cement-based wasteform has been investigated using neutron imaging to characterise the wasteform for disposal in a repository for radioactive materials. Imaging showed both the pore size distribution and the extent of the cracking that had occurred in the samples. The rate of the water penetration measured both by conventional sorptivity measurements and neutron imaging was greater than in pastes made from Ordinary Portland Cement. The ability of the cracks to distribute the water through the sample in a very short time was also evident. The study highlights the significant potential of neutron imaging in the investigation of cementitious materials. The technique has the advantage of visualising and measuring, non-destructively, material distribution within macroscopic samples and is particularly useful in defining movement of water through the cementitious materials. © 2010 Crown Copyright published by Elsevier Ltd.
- ItemAppraisal of a cementitious material for waste disposal: neutron imaging studies of pore structure and sorptivity(Laboratoire SUBATECH, 2008-10-14) McGlinn, PJ; de Beer, FC; Aldridge, LP; Radebe, MJ; Nshimirimana, R; Brew, DRM; Payne, TE; Olufson, KPTo characterise and to evaluate the durability, structural properties and sorptivity of a candidate wasteform for ILW and gain an understanding of the factors that control water movement through the matrix and the matrix and the resultant degradation process.
- ItemThe composition of cement hydrating at 60 deg C from synchrotron radiation(Australian X-ray Analytical Association, 2002-07-01) Auld, J; Turner, KS; Thorogood, GJ; Ball, CJ; Aldridge, LP; Taylor, JCCement consists of 5 phases C3S, C2S, C3A, C4AF (where C denotes CaO, S denotes SiO2, A denotes AI2O3 and F denotes Fe2O3) and gypsum. When cement hydrates it forms an amorphous calcium silicate hydrate (C-S-H) as well as the crystalline ettringite and calcium hydroxide. The x-ray diffraction pattern of the hydrated cement is difficult to interpret because of its complexity. In addition, the overlapping lines from the remaining cement compounds make it difficult to quantify the amount of the crystalline components present. Using Rietveld analysis we have been able to interpret the patterns obtained from synchrotron x-ray diffraction patterns obtained at the Photon Factory at the Australian National Beamline Facility using BIGDIF. The changes in the composition of the hydrated cement paste were determined as a function of time during hydration at 60 deg C. © 2002 Australian X-ray Analytical Association Inc
- ItemCracks and pores - their roles in the transmission of water confined in cementitious materials.(Springer, 2010-10-01) Bordallo, HN; Aldridge, LP; Wuttke, J; Fernando, K; Bertram, WK; Pardo, LCCement paste is formed through a process called hydration by combining water with a cementitious material. Concrete, the worlds most versatile and most widely used material, can then be obtained when aggregates (sand, gravel, crushed stone) are added to the paste. The quality of hardened concrete is greatly influenced by the water confined in the cementitious materials and how it is transmitted through cracks and pores. Here we demonstrate that the water transport in cracks and capillary pores of hardened cement pastes can be approximately modeled by simple equations. Our findings highlight the significance of arresting the development of cracks in cementitious materials used in repository barriers. We also show that neutron scattering is an advantageous technique for understanding how water transmission is effected by gel pore structures. Defining measurable differences in gel pores may hold a key to prediction of the reduction of water transport through cement barriers. © 2010, Springer.
- ItemHindered water motions in hardened cement pastes investigated over broad time and length scales.(American Chemical Society, 2009-10-28) Bordallo, HN; Aldridge, LP; Fouquet, P; Pardo, LC; Unruh, T; Wuttke, J; Yokaichiya, FWe investigated the dynamics of confined water in different hydrated cement pastes with minimized contributions of capillary water. It was found that the water motions are extremely reduced compared to those of bulk water. The onset of water mobility, which was modified by the local environment, was investigated with elastic temperature scans using the high-resolution neutron backscattering instrument SPHERES. Using a Cauchy−Lorenz distribution, the quasi-elastic signal observed in the spectra obtained by the backscattering spectrometer was analyzed, leading to the identification of rotational motions with relaxation times of 0.3 ns. Additionally, neutron spin echo (NSE) spectroscopy was used to measure the water diffusion over the local network of pores. The motions observed in the NSE time scale were characterized by diffusion constants ranging from 0.6 to 1.1 × 10−9 m2 s−1 most likely related to water molecules removed from the interface. In summary, our results indicate that the local diffusion observed in the gel pores of hardened cement pastes is on the order of that found in deeply supercooled water. Finally, the importance of the magnetic properties of cement pastes were discussed in relation to the observation of a quasi-elastic signal on the dried sample spectra measured using the time-of-flight spectrometer. © 2009, American Chemical Society
- ItemHydrohalite formation in frozen clay brines(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Gates, W; Bordallo, HN; Ferhervari, A; Klapproth, A; Acikel, A; Bouazza, A; Aldridge, LP; Iles, GN; Mole, RAHydrated forms of cryosalts in frozen brines play important roles in the polar landscape and troposphere of Earth [1], and their melting [2] is implicated in recurring slope lineae (RSL) in Antarctica’s McMurdo Dry Valley [3] and equator-facing, mid-latitude (42ºN-52ºS) slopes of Mars [4]. Observation of the widespread occurrence of clay minerals and salts on the Martian surface [5] indicates that saline groundwater [6] may still be present on Mars. The surface of Mars ranges in temperature from 293 K on the equator at noon to 120 K at the poles and mobility of sub-surface water ice will depend on the local temperature and the mobility of confined water in the crustal clays. We applied quasielastic neutron scattering using the backscattering spectrometer EMU (Australian Nuclear Science and Technology Organisation) at 1 μeE resolution, to the system: sodium montmorillonite – 5M NaCl (Na-Mt-NaCl and calcium montmorillonite – 5M CaCl2 (Ca-Mt-CaCl2); to establish boundary conditions influencing the dynamics of confined water. Results from elastic fixed window (EFW) data indicate a substantial increase in the mean square displacement of hydrogen (H) in the brine conditions at all temperatures above 100K, indicating enhanced mobility of water in the presence of brines. A phase transition was observed in Na-Mt-NaCl at 255K (on heating) indicating the presence of the cryosalt hydrohalite (NaCl·2H2O), but no phase transition was observed in Ca-Mt-CaCl2. In addition, quasielastic neutron scattering (QENS) spectra highlighted that water in the Ca-Mt-CaCl2 system was strongly confined at room temperature. Recently [6] hydrohalite was observed to form in frozen gels of Na-Mt brines, but not in Ca-Mt brines. They considered that textural differences in the two forms allowed the gel pores of the Na-Mt to retain liquid saline pore water to well below the freezing point of pure water. Based on our analysis, water is restricted to rotational mobility in the Na-Mt-NaCl below 255K, but presents more translational mobility above 255K. These findings largely support those of Yesilbas [7] in the importance of pore structure in controlling cryosalt formation, and further implicate their role in associated phenomena such as RSL.
- ItemIndustrial application experiments on the neutron imaging instrument DINGO(Elsevier, 2017-01-01) Garbe, U; Ahuja, Y; Ibrahim, R; Li, HJ; Aldridge, LP; Salvemini, F; Paradowska, AMThe new neutron radiography / tomography / imaging instrument DINGO is operational since October 2014 to support the area of neutron imaging research at ANSTO. The instrument is designed for a diverse community in areas like defense, industrial, cultural heritage and archaeology applications. In the field of industrial application it provides a useful tool for studying cracking and defects in concrete or other structural material. Since being operational we gathered experience with industrial applications and commercial customers demanding beam time on DINGO. The instrument is a high flux facility with is 5.3 × 107 [n/(cm2s)] (confirmed by gold foil activation) for an L/D of approximately 500 at HB-2. A special feature of DINGO is the in-pile collimator position in front of the main shutter at HB-2. The collimator offers two pinholes with a possible L/D of 500 and 1000. A secondary collimator separates the two beams by blocking one and positions another aperture for the other beam. The neutron beam size can be adjusted to the sample size from 50 × 50 mm2 to 200 × 200 mm2 with a resulting pixel size from 27 μm to ∼100 μm. The whole instrument operates in two different positions, one for high resolution and one for high speed. We would like to present our first experience with commercial customers, scientific proposals with industrial applications and how to be customer ready. © 2017 The Author(s). Published by Elsevier B.V.
- ItemThe micro pore structure of concrete determined by small angle neutron scattering(Australian and New Zealand Institutes of Physics, 1994-02-10) Sabine, TM; Bertram, WK; Aldridge, LPSmall angle neutron scattering (SANS) is a complementary technique to electron microscopy for the elucidation of the shape and size of inhomogenities in the nanometric size range. SANS has the advantage that a large volume ( - 0.5 cm3 ) of the specimen is illuminated by the beam, and experiments can be earned out at atmospheric pressure on water saturated samples. It has the disadvantage mat, except for very simple systems, interpretation of the experimental data is not unambiguous. We have collected SANS data on a range of samples of concrete containing different water/cement ratios. The data was collected on the LOQ instrument at the ISIS spallation neutron source. We discuss interpretation of the data in terms of microscopic inhomogenities in the structure of concrete.
- ItemModelling the microstructure of cement(Australian and New Zealand Institutes of Physics, 1994-02-10) Bertram, WK; Sabine, TM; Aldridge, LPTo gain a better understanding of the factors that influence the strength and durability of concrete the microporosity of hydrated cement paste has been investigated, by small angle neutron scattering (SANS). The great advantage that SANS has over the more conventional methods of microporosity analysis such as mercury or gas intrusion, is that for SANS measurements it is not necessary to dehydrate the samples and the process is non-intrusive. However the results from SANS are often open to several different interpretations and it is necessary to obtain additional information where possible .One method of obtaining such additional information is through computer modelling of the process of cement hydration. In this poster we present the results of a 3- dimensional computer model that simulates the growth of a layer of calcium-silicate-hydrate (CSH) on a surface. The model used is similar to that for random aggregates (TA Witten and LM. Sanders, Phys. Rev. Lett. 19,1400 (1981)). The model calculates the porosity and the pore size distributions, which can men be compared with those obtained from SANS measurements.
- ItemWater transport through cement-based barriers - a preliminary study using neutron radiography and tomography(Elsevier, 2009-06-21) Brew, DRM; de Beer, FC; Radebe, MJ; Nshimirimana, R; McGlinn, PJ; Aldridge, LP; Payne, TEIn this preliminary study we use neutron radiography and tomography to examine differences in water transport through cement pastes and mortars. Bulk residual water contents and sorptivity curves determined using neutron radiography are compared with data obtained gravimetrically. In addition, macro-pore volume distributions of each sample were measured. Furthermore, it was possible to use neutron radiography to monitor the change in the mass of water when samples were dried or when water moved into the samples. The trends and absolute values of weight loss and gain obtained using both approaches are very consistent for mortars, especially when a neutron-scattering correction is applied. © 2009, Elsevier Ltd.