Damage Characteristics of Argillaceous Quartz Sandstone Mesostructure under Different Wetting-drying Conditions

Extensive water–rock interaction in the Three Gorges Reservoir area of the Yangtze River leads to rock mass deterioration along the reservoir banks. However, mineral evolution behavior and its effect on the mesostructure deterioration of rocks under the wetting–drying cycle condition remain unknown. So, the wetting–drying cycle tests were conducted on peculiar argillaceous quartz sandstone in TGRA under neutral (pH = 7) and alkaline (pH = 10) water environments. Here, we provided detailed physical and microscopy images data to determine the control mechanism of mineral behavior on the evolution of sandstone’s mesostructure. Under the neutral condition, repeated “absorption and swelling–dehydration and contraction” of clay minerals leads to the repeated physical action of “squeezing–unloading” in the interior of a rock. This results in the initiation and gradual expansion of cracks in the framework mineral quartz, exhibiting failure mode from the interior to the exterior. In contrast, under the alkaline condition, the dissolution on the surface of quartz particles leads to the expansion and connection of pores, implying that the sandstone exhibits failure mode from the exterior to the interior. Moreover, the internal mechanical analysis indicates the minerals are at high pressure because of the expansion of clay minerals in the neutral solution. However, in an alkaline water environment, the extrusion pressure of framework mineral quartz decreases significantly and is not easily broken due to increased porosity. Thus, the evolution behavior of minerals in different water environments plays an important role in the damage of the rock

Evaluation of the Loss of Uniaxial Compressive Strength of Sandstones Due to Moisture

The reduction in uniaxial compressive strength (UCS) was investigated for sandstones under various moisture levels. Thirty-four UK Darney sandstone samples were tested under six different moisture conditions. The time-dependent moisture gain and loss were also evaluated. For 77 sandstones identified in the literature, the loss of UCS between oven-dry and saturated conditions was up to 45%, with an average of 20%. For Darney stone, the average loss of UCS was around 20%, with UCS around 72 N/mm2 when oven-dry and 58 N/mm2 when fully saturated. During saturation, significant loss of UCS occurred soon after exposure to water with 80% of UCS being lost within the first 2.5–6 hours. For Darney stone 50% of UCS was lost at air-dry conditions. Results from the 78 sandstone types were compared with the equivalent compressive strength defined by BS EN 772–1:2011 for oven-dry, air-dry, and saturated conditions. The estimated values by BS EN 772–1:2011 for dry and saturated UCS agreed well with the available test data and indicated a lower-bound solution. For immersed conditions, BS EN 772–1:2011, however, overestimates the reduction in UCS for a large number of samples and provides an average, instead of a lower-bound solution

Biogeochemical and ecological responses to warming climate in High Arctic polar deserts

High Arctic polar deserts cover 26% of the Arctic and are found to store a larger amount of soil organic carbon (SOC) in the permafrost and to emit higher amounts of the main greenhouse gases (GHGs) than previously expected. However, the mechanisms of the main GHG production are not clear. Furthermore, polar deserts are predicted to dramatically transform under rapidly warming temperatures and have uncertainty regarding a potential positive GHG-feedback to the warming climate. Freeze-thaw cycles develop frost-boil landscape and diapirs within frost-boil profiles. Diapirs are cryoturbic nutrient patches and support vascular plants in polar deserts. Frost-boil development and diapirs are expected to increase with the increase in temperatures and the permafrost thaw and are likely key for projected polar-desert evolutions. This dissertation investigated soil properties including the chemical structure of SOC, microbial processes responsible for GHG emissions, and the main GHG emissions associated with diapirism. Diapirs had increased polysaccharides known to raise soil viscosity, which in turn facilitates diapirism. In addition to this, diapirs contained more recalcitrant SOC, which was consistent with the decreases in gross nitrogen mineralization by 30–48% and in carbon dioxide (CO2) emissions by 19–38%. Similarly, diapiric frost boils slowed net methane (CH4) emissions. With higher archaeal amoA abundance, diapiric frost boils had a higher magnitude of the emissions leading to a higher estimate of the emissions under dry conditions. On the other hand, a higher estimate of the emissions from diapiric frost boils linked to a higher probability of the emissions under wet conditions. Freeze-thaw treatment increased CO2 emissions by 1.3–3.5 times and estimation of N2O emissions by 72–204% but apparently reduced CH4 consumption more than CH4 production to increase net CH4 emissions. This dissertation found that diapirisms alter SOC components and the main GHG emissions. The higher abundance of polysaccharides and recalcitrant SOC suggests that biological factors are involved in diapirism and that diapirs supply vascular plants with nutrients as a result of a mutualistic relationship. Furthermore, this dissertation suggests that freeze-thaw triggers the main GHG emissions leading to the distinct emission patterns during snowmelt season from later growing season

Railway ballast characteristics, selection criterion and performance

This work is a comprehensive investigation to find to what extent simple laboratory tests e.g. Los Angeles abrasion and micro-Deval might be suitable for predicting real railway ballast performance with respect to deformation and degradation. A number of tests to measure essential properties of ballast aggregate have been performed in addition to advanced material testing. Large cyclic triaxial loading test and full scale railway track model test were employed to simulate the effects of train loading and tamping, and to study settlement, stiffness and degradation of a range of ballast materials. The testing programme included both wet and dry testing conditions. All the rock types tested were mainly composed of combinations of principal rock-forming silicate minerals. They represent all together a wide variety of igneous, metamorphic and consolidated/metamorphosed sedimentary rocks mainly fine to very fine grained. Mechanical properties Change in the ballast grading proved to affect the ballast breakage development over time. However, the abrasion property expressed by the micro-Deval value did not show any association with the degradation of ballast under repeated load testing. Simulation of repeated tamping seemed to be the main source of ballast breakage. Most rocks showed high frost resistance after long term impact, but samples with high content of amphibole were less frost resistant. The rocks’ mechanical strength in terms of the Los Angeles abrasion or micro-Deval value did not show any correlation with either the amount of microcracks or the rocks’ average mineral grain size. A new method to measure the amount of microcracks based on luminescence measurements was developed. It is suggested that micro-cracks represent open channels for water to penetrate into the aggregate, which was confirmed by good correlation between water absorption and the amount of micro-cracks. Moisture had generally a negative effect on rocks’ mechanical strength according to Los Angeles abrasion and Point Load strength results. On the other hand, dry and wet triaxial tests with cyclic loadings did not confirm this effect. Neither did mineral grain size distribution show any correlation with mechanical strength, but the range of coefficient of conformity (Cu = D60/D10) was probably too narrow to obtain a reliable conclusion. A new method to quantify the mineral grain size distribution was developed under these test series. Functional properties Both resilient modulus of the ballast layer and the stiffness of the track were governed by the materials’ grading curve and specific density. A possible relation between the amount of microcracks in the aggregate and resilient modulus as well as ballast breakage is suggested. The permanent vertical strain during repeated load testing was affected by both the micro-Deval value, the grading curve of the ballast and the aggregate’s content of soft minerals. Improvements of test methods The Los Angeles abrasion test distinguished clearly between the superior quality material and the very poor material. The Los Angeles abrasion value is, however, a poor parameter to indicate how the intermediate material will behave in service regarding ballast breakage. This study proposes to improve the ranking of ballast materials by introducing two additional methods. One which is able to measure some rocks’ ability to recover mechanical strength after repeated crushing, and one which measures the production of fines (0/0.125 mm) during crushing. Saturation of ballast material before micro-Deval testing did not have any significant effect on degradation. Neither did the use of 1 % sodium-chloride solution have any effect

Use of the Micro-Deval Test for Assessing Alaska Aggregates

INE/AUTC 12.1

Earthquakes: from chemical alteration to mechanical rupture

In the standard rebound theory of earthquakes, elastic deformation energy is progressively stored in the crust until a threshold is reached at which it is suddenly released in an earthquake. We review three important paradoxes, the strain paradox, the stress paradox and the heat flow paradox, that are difficult to account for in this picture, either individually or when taken together. Resolutions of these paradoxes usually call for additional assumptions on the nature of the rupture process (such as novel modes of deformations and ruptures) prior to and/or during an earthquake, on the nature of the fault and on the effect of trapped fluids within the crust at seismogenic depths. We review the evidence for the essential importance of water and its interaction with the modes of deformations. Water is usually seen to have mainly the mechanical effect of decreasing the normal lithostatic stress in the fault core on one hand and to weaken rock materials via hydrolytic weakening and stress corrosion on the other hand. We also review the evidences that water plays a major role in the alteration of minerals subjected to finite strains into other structures in out-of-equilibrium conditions. This suggests novel exciting routes to understand what is an earthquake, that requires to develop a truly multidisciplinary approach involving mineral chemistry, geology, rupture mechanics and statistical physics.Comment: 44 pages, 1 figures, submitted to Physics Report

Improving the technical properties of recycled aggregates for road construction

Sustainable construction, operation and maintenance of road infrastructure are currently of high priority in Norway. The development of the highway standards and specifications (e.g., N200) plays an important role, so that optimized use of recycled excavation materials and crushed concrete is achieved in the sub-base and base layers. Generally, factors that hinder the use of EM include geological complexity (i.e., composition of mechanically weak rocks), the absence of declaration policies, and a standard framework to characterize the testing frequency of general properties. Considering their application in permitted quantities in the base layer, it is expected that compliance with the mechanical performance, that is, Los Angeles (LA) and micro-Deval (MD) and other geometric properties designed for conventional materials will be met. In addition, given the related geological complexity, it is essential to identify the effects of chemical and mineralogical features, as this may enhance the opportunity to classify geological variations and optimize the performance by mixing the masses with other materials. In this study, the first approach involved the identification of knowledge gaps pertaining to the relationship between the local geology and the mechanical performance (LA and MD) of the aggregates.publishedVersio