Granite Surface Research Articles

The Role of Shear Stress in Fault Healing and Frictional Aging

AbstractThe seismic cycle involves repeated failure and strength recovery of tectonic faults, known as fault healing. In Earth's crust, where fault strength is dominated by friction, frictional healing is the primary agent of fault healing. Laboratory studies document the role of contact aging and cementation as key mechanisms of frictional healing; however, the role of shear stress is not well understood. We describe a laboratory study of frictional healing as a function of shear stress for bare granite surfaces and simulated fault gouge composed of Westerly granite and quartz. Faults are sheared at normal stresses of 5–25 MPa, 100% relative humidity and room temperature. We quantify frictional healing in slide‐hold‐slide tests for shear stresses from 0 to the sliding friction value and monitor the amplitude of elastic waves propagating across the fault zone. Healing of gouge shows a strong negative dependence on shear stress, whereas healing of bare surfaces does not vary systematically with shear stress. In gouge, frictional healing involves shear stress‐dependent compaction and particle rearrangement, while for bare surfaces frictional strength is derived primarily from contact area evolution. The magnitude of compaction in gouge varies with shear stress, which explains the dependence of healing on shear stress. Elastic wave amplitude increases with hold time and varies inversely with shear stress, consistent with fault zone compaction, shear dilatancy, and their impact on strength evolution and healing. Fault zone compaction during shear unloading and reloading operates with contact aging to dictate frictional healing and fault restrengthening following shear failure.

Research results and future orientations for the development of a pre-estimation system for the measure of the quantitative determination of milled granite surfaces

On the manufacturing of different CNC machine-tools, the tables of ultraprecision machine-tools and CNC coordinate measuring machines are made of granite. Despite of the continuous industrial investigations, an accurate estimation system has not been developed so far. Although, an estimation program is necessary to predict the rate of the average edge chipping of different granite types. In this article, a summary of a research work is given connecting to this topic. Furthermore, the trendency of our future research is defined.

Microscale Analysis of Fractured Rock Sealed With Microbially Induced CaCO3 Precipitation: Influence on Hydraulic and Mechanical Performance

AbstractMicrobially induced CaCO3 precipitation (MICP) has shown great potential to reduce permeability in intact rocks as a means to seal fluid pathways in subsurface ground, for example, to secure waste storage repositories. However, much less is known about how to apply MICP to seal fractured rock. Furthermore, there is limited information on the hydraulic and mechanical properties of MICP filled fractures, which are essential criteria to assess seal performance. Here MICP injection strategies were tested on sandstone cores, aimed at obtaining a homogeneous porosity fill that reduced permeability by 3 orders of magnitude. The injection strategy resulting in the most homogenous calcite distribution was then applied to fractured granite cores, to yield transmissivity reduction of up to 4 orders of magnitude. Microscale analysis of these sealed granite cores using X‐ray‐computed tomography and electron microscopy showed that >67% of the fracture aperture was filled with calcite, with crystals growing from both fracture planes, and bridging the fracture aperture in several places. Shear strength tests performed on these cores showed that the peak shear strength correlated well with the percentage of the fracture area where calcite bridged the aperture. Notably, brittle failure occurred within the MICP grout, showing that the calcite crystals were strongly attached to the granite surface. If MICP fracture‐sealing strategies can be designed such that the majority of CaCO3 crystals bridge across the fracture aperture, then MICP has the potential to provide significant mechanical stability to the rock mass as well as forming a hydraulic barrier.

Morphology Variation Analysis for Rock Surfaces Before and After Shearing

The joint roughness of the surfaces influence the rock mass engineering stability significantly. In this paper, morphology characteristics of the granite surfaces were studied comprehensively. The 15 granite surfaces in total were obtained by the spitting method. Subsequently, the direct shear tests for rock surfaces were conducted. Moreover, the rock surfaces were scanned before and after shearing. 13 morphological parameters were utilized to analyze the morphological variation of rock surfaces before and after shearing. From analysis of the morphology of rock surfaces before and after shearing, it is concluded that the Sp, Sv, Sz values of rock surfaces decrease after shearing. The spatial parameters Sal value decreases after shearing and Str variation indicated that the rock surfaces tend to be more isotropic. The hybrid parameters Sdq, Sdr decrease after shearing. The Sdq suggested that the slope of rock surfaces decrease after shearing and the Sdr showed that the rock surface tend to a more flat plane. The average amplitude of wavelength decreasing means that the points of rock surfaces tend to be a constant value after shearing.

Understanding the True Dynamics of Space Manipulators from Air-Bearing Based Ground Testing

A space manipulator can easily handle a large payload having a much larger mass than its own mass. However, physical test of such a manipulator handling a large-mass payload in 3D space on the ground is almost impossible due to gravity effect. A commonly used test method is to support the manipulator with air-bearing pads on a horizontal granite surface so that the robot can freely maneuver on the 2D surface as it were floating in a 2D microgravity environment. However, such a test method suffers a major problem: the air-bearing based support equipment is large and massive when the manipulator is long (e.g., 10 m or longer) and/or its payload is heavy (e.g., 500 kg or heavier), which adds significant inertial loading to the robot when it maneuvers. As a result, the manipulator has to make much more effort on a test than it would need in space. This paper describes a study for understanding the true dynamics of a space manipulator from such an air-bearing supported test. A test-data analysis method is developed, which can decouple and remove the dynamics effect of the air-bearing support equipment from tested manipulator system. With such an approach, the true joint torques for the space manipulator to produce a prescribed end-effector motion trajectory can be determined, although the manipulator has to be constrained to a massive air-bearing based support equipment for the testing. The method has been experimentally validated by a specially designed experiment facility.

Mechanism and Dynamics of Fracture of the Stressed Granite Surface by a Shock Wave

The dynamics of emission of positively charged ions from the granite surfaces containing different concentrations of quartz and feldspar under the action of a shock wave is investigated with a time resolution of 2 ns. The ions are assumed to be emitted at the instants of emergence of dislocations moving in intersecting glide planes at the sample surface. Defects in the form of extended “grooves” are formed in the region of emergence of dislocations. A compressive load suppresses the defect formation.

Numerical simulation and experimental investigation on fracture mechanism of granite by laser irradiation

Numerical simulation and experimental tests are conducted to determine the stress distribution and fragment mechanism of granite during laser perforation. The mechanisms of material removal through laser perforation are spallation, melting and ablation. High intensity laser energy concentrates locally on the granite surface area and causes the local temperature to increase instantaneously. The closer the center of laser beam is, the higher the temperature is. With the laser power increasing the size of laser perforation hole is expanded. In addition, the high heating and cooling rates induced by laser irradiation brings out the generation of high tensile stress (481–536 MPa), which is far higher than the tensile strength (11 MPa) of granite sample, and fracture or spallation occurs. Fracture analysis showed the inner wall of the glassy layer after laser perforation is smooth with lots of pores. Moreover, there is a hackle region with regular strips of micron/nano scale at the edge to the glassy layer, and the secondary cracks propagate perpendicular to the regular strips. Compared with the fracture morphology of the glassy layer, the fracture surface of the interfacial transition zone is coarse, and obvious secondary cracks also generate. Obviously, the fracture mechanism of granite faced to laser irradiation is the typical brittle fracture.

Rapid age assessment of glacial landforms in the Pyrenees using Schmidt hammer exposure dating (SHED)

AbstractSchmidt hammer (SH) sampling of 54 10Be-dated granite surfaces from the Pyrenees reveals a clear relationship between exposure and weathering through time (n=52, R2=0.96, P<0.01) and permits the use of the SH as a numerical dating tool. To test this 10Be-SH calibration curve, 100 surfaces were sampled from five ice-front positions in the Têt catchment, eastern Pyrenees, with results verified against independent 10Be and 14C ages. Gaussian modelling differentiates Holocene (9.4±0.6 ka), Younger Dryas (12.6±0.9 ka), Oldest Dryas (16.1±0.5 ka), last glacial maximum (LGM; 24.8±0.9 ka) and Würmian maximum ice extent stages (MIE; 40.9±1.1 ka). These data confirm comparable glacier lengths during the LGM and MIE (~300 m difference), in contrast to evidence from the western Pyrenees (≥15 km), reflecting the relative influence of Atlantic and Mediterranean climates. Moreover, Pyrenean glaciers advanced significantly during the LGM, with a local maximum at ~25 ka, driven by growth of the Laurentide Ice Sheet, southward advection of the polar front, and a solar radiation minimum in the Northern Hemisphere. This calibration curve is available online (http://shed.earth) to enable wider application of this method throughout the Pyrenees.

Using Hyperspectral Imaging to Quantify Phototrophic Biofilms on Granite

This paper reports a non-invasive method for in situ biofilm quantification based on the use of hyperspectral imaging to analyze a chromatically and texturally heterogeneous substrate as granite colonized by green algae and cyanobacteria. Biofilm-forming microorganisms were inoculated on granite blocks and incubated under laboratory conditions for 21 days. The intensity of the green stains formed on the granite surfaces differed depending on the initial concentration of microorganisms used. A biofilm quantification (BQ) index was computed to determine the level of colonization on the surfaces. The index was obtained by comparing the quotient of the reflectance of the green (G) and red (R) bands of each pixel of the hyperimage against a threshold value, fth. The optimal value of the threshold was determined by examining the linear correlation between the BQ index and the chlorophyll a extracted. The BQ results were then compared with the F0 and ΔE*ab parameters yielded by colour spectrophotometry and PAM fluorometry techniques and used as reference methodologies to quantify greening on stone surfaces. The BQ index showed a high level of consistency with all of the other parameters; it was linearly correlated with the chlorophyll a concentration, F0 andΔE*ab, with high coefficients of determination (r2 > 0.92) for the range from 1.87 to 5.69 µg chl a.cm-2. The strength of the BQ index lies in its double use as a biomarker of quantity and percentage cover, as well as its good performance under different conditions, ranging from initial phototrophic colonization and thin (young) biofilms covering 21.19% of the surface to profuse biological colonization covering 67.36% of the surface. Moreover, the proposed BQ index may be able to be used with other types of rock with less heterogeneous surfaces than granite.

Experimentation and Analysis of Granite Super-Finishing Process for Flatness Testing

Granites are used in high precision machines and metrological applications. Final finishing operation on granite is done by means of manual lapping operation based on three body wear principle. Traditional granite lapping is time consuming process and requires high skill of operator which may lead to variation in process parameters. Taguchi method is applied to optimize the lapping process to reduce variation based on process parameters such as abrasive size, load applied and time of lapping.For this purpose three process parameters with three levels are considered and accordingly L9 orthogonal array is used for experimentation. Analysis of variance (ANOVA) is performed to study the effect of these process parameters on the surface flatness as response variable. For final finishing operation of 630 X 630 X 80 surface plate optimum parameters for surface flatness are found to be 14 µm abrasive size, 8kg load applied and 40 minutes of cycle time and they are ranked based on significance to process. Abrasive size is most significant than other parameters for flatness response of granite surface plate.Thus this experimentation and analysis is useful toobtain optimum parameters for maximum flatness value lapped results in reduction of operation cycle time for finishing of granite surface plates manufactured by reputed industry for various applications.

Schmidt Hammer exposure dating (SHED): Calibration procedures, new exposure age data and an online calculator

Recent research has established Schmidt Hammer exposure dating (SHED) as an effective method for dating glacial landforms in the UK. This paper presents new data and discussion to clarify and to evaluate calibration procedures. These make a distinction between Schmidt Hammer drift following use (instrument calibration), and variation between both individual Schmidt Hammers and between user strategies when utilising age-calibration curves (age calibration). We show that while test anvil methods are useful for verifying that Schmidt Hammers maintain their standard R-values, they are inappropriate for instrument calibration except for the hardest natural rock surfaces (R-values: ≥ 70). A range of surfaces were tested using 3 N-Type Schmidt Hammers, which showed that existing anvil calibration procedures led to consistent overestimation of R-values by up to 17.9%. In contrast, new calibration procedures, which are based on the use of a calibration point which lies within the range of R-values measured in the field [Dortch et al. 2016, Quat. Geochron., 35, 67-68], limit variance to maximum of 4.4% for surfaces typically tested by Quaternary researchers (R-values: 25 - 60). Moreover, these new calibration procedures are more appropriate for age calibration as they incorporate operator variance through choice of sampling location. New calibration procedures are used to compile an updated age-calibration curve based upon 54 granite surfaces (R2 = 0.94, p < 0.01) from across Scotland, NW England and Ireland. The inclusion of a further 29 terrestrial cosmogenic nuclide (TCN) exposure ages extends the calibration period to 0.8 – 23.8 ka, covering the entire post-Last Glacial Maximum (LGM) history of the British-Irish Ice Sheet. To facilitate comparison between studies, an online calculator is made available at http://shed.earth for Schmidt Hammer instrument and age calibration and SHED exposure age calculation. The SHED-Earth calculator provides a rapid and accessible means of exposure age calculation to encourage wider and more consistent application of SHED throughout the British Isles.

A computer vision system for identification of granite-forming minerals based on RGB data and artificial neural networks

Granitic stones are widely used in the field of Cultural Heritage in the north-western Iberian Peninsula. In some activities regarding conservation, such as the laser cleaning, it is of great interest the identification of the minerals on the granitic stone surface in order to improve the treatment and to avoid damages by means of the adaption of the fluence to each different forming mineral. The aim of this work is the optimization of a back propagation artificial neural network (ANN) in order to obtain the rapid and reliable identification of forming minerals in granitic rocks by means of RGB images. Our goal is, eventually, in situ monitoring the laser cleaning of granitic stonework. The results obtained, though preliminary, led a high degree of correct identification of the forming minerals for three different granitic types.

Rock friction under variable normal stress

AbstractThis study is to determine the detailed response of shear strength and other fault properties to changes in normal stress at room temperature using dry initially bare rock surfaces of granite at normal stresses between 5 and 7 MPa. Rapid normal stress changes result in gradual, approximately exponential changes in shear resistance with fault slip. The characteristic length of the exponential change is similar for both increases and decreases in normal stress. In contrast, changes in fault normal displacement and the amplitude of small high‐frequency elastic waves transmitted across the surface follow a two stage response consisting of a large immediate and a smaller gradual response with slip. The characteristic slip distance of the small gradual response is significantly smaller than that of shear resistance. The stability of sliding in response to large step decreases in normal stress is well predicted using the shear resistance slip length observed in step increases. Analysis of the shear resistance and slip‐time histories suggest nearly immediate changes in strength occur in response to rapid changes in normal stress; these are manifested as an immediate change in slip speed. These changes in slip speed can be qualitatively accounted for using a rate‐independent strength model. Collectively, the observations and model show that acceleration or deceleration in response to normal stress change depends on the size of the change, the frictional characteristics of the fault surface, and the elastic properties of the loading system.

In situ evaluation by colour spectrophotometry of cleaning and protective treatments in granitic Cultural Heritage

This paper is focused on the reliability of the colour spectrophotometry as a non-destructive in situ technique to evaluate the cleaning effectiveness. A biofilm composed by filamentous green algae and cyanobacteria developed on a granitic building located in NW Iberian Peninsula was removed using different cleaners commonly used by professionals in stone conservation (distilled water, ethanol, benzalkonium chloride, Hyvar X, ethanol, sodium hypochlorite and the commercial products LimpiaFachadas1 and Biocida). Also, the durability of some water repellents applied after the cleanings was evaluate. The colour measurements expressed in the CIEL*a*b* colour space were performed before and after the cleanings and after the water repelling products application, at eight moments during two years (since June 2011 until June 2013) of exposition under a temperate humid climate.As general results, the colour spectrophotometry resulted in a reliable method to monitor the cleaning effectiveness, allowing to identify the most effective methods, but also the rate of the recolonization of the granitic surface during time. However, this technique was not recommended as re-growth indicator when water repellents were applied after the cleanings, due to the impact produced by the products on the colour of the stone.

Effects of thermal treatment on fracture characteristics of granite from Beishan, a possible high-level radioactive waste disposal site in China

In-situ experimental investigations on fracture behavior of Beishan granite under loading after 125–600°C thermal treatments have been carried out through high temperature Scanning Electron Microscope (SEM) testing system. Thermal microcracks and non-uniform expansion of grains, long and deep thermal cracks along the grain boundary were observed on the surface of Beishan granite with thermal treatments at different temperatures. The initial direction of microcracks and the main crack propagation path are affected by the shape of mineral grains and the distribution of thermal cracks. The effect of the distribution of thermal cracks becomes more dominant with the increasing temperatures. There are multiple mechanisms of thermal effects on strength and fracture toughness of Beishan granite, namely, thermal cracking, water evaporation, hot melting and phase transition of quartz. The main controlling mechanism changes with treatment temperatures. While elastic modulus slightly increases at 275°C because of hot melting, in general, it decreases with the increasing temperature due to increasing thermal cracks. Stress intensity factor for short-span (the ratio of span to height is 2) three-point bending specimen is determined using boundary collocation method. The relationship between fracture toughness and heat treatment temperature can be approximately described by linear decreasing function.

Enabling Capabilities: Innovation and Development in the Outer Hebrides

The existing challenges to non-profit heritage organisations are increasing in these volatile and austere climates. Particularly, existing organisational and strategic mission developments are needed to enable more resilient organisations. This paper explores the relationship between Ionad Hiort and the Glasgow School of Art’s Institute of Design Innovation (INDI) as a six-month case study for understanding how design innovation can build creative capabilities within this unique partnership. In this case, the “building” of a new type of heritage centre on the west coast of the Isle of Lewis in Scotland. It focuses on the concept of innovation in approaching complex situations as an alternative to existing means of problem solving. Through a series of workshops and engaging informal sessions a new strategy was built, which focused the group’s potential. The outcome being a new way to build confidence within communities and build new relationships, enabling new creative capabilities within a rural island community.

Coupling of blasting seismographs to rock and its effectiveness for horizontal ground motion

In order to clarify the requirements for satisfactory coupling on rock, six methods to monitor vibrations with blasting seismographs are investigated in the longitudinal component of the vibratory motion. The methods studied consisted on placing the geophone mount on a granite surface freely (loosely), held with a sandbag, and attached with an anchor (the center of the geophone's mount was fixed with a plastic anchor, a bolt and a nut), thermal adhesive (glue), gypsum plaster (used as an adhesive) and double-sided tape. For each measuring condition, transmissibility in two mounts was assessed on a vibration shaker from 2 to 190Hz at one or two vibration levels (5, 20mm/s). The main findings of this work are: (1) Transmissibility varies with coupling method. It is flat at low frequencies and has a maximum at higher frequencies; in some trials mainly with anchored, glued and plastered such peak occurs outside the frequency range studied. (2) The frequency of the first maximum of transmissibility shifts towards smaller frequencies as the peak velocity increases when the bonding conditions are weak, as for free and sandbagged mounts. However, if the bonding is stiff enough, as for anchored or plastered mounts, transmissibility values at 5 and 20mm/s are very similar. (3) The frequency of the first peak in the measured transmissibility provides a preliminary estimate of the performance of each method, so that its conditions of use should be defined upon frequency and velocity of the imposed motion, rather than using the anticipated peak acceleration, as it is currently made. These have been defined for the methods under study. (4) Anchoring and plastering provide the best performance, the later with smaller errors at high frequencies (>128Hz). (5) The seismograph itself (not the coupling) is another source of error that should not be neglected specially for measurements in the low frequency range; large errors, exceeding by one order of magnitude those from coupling are obtained in the 2‒4Hz band.

Increasing the hydrophobicity degree of stonework by means of laser surface texturing: An application on Zimbabwe black granites

Tailoring the wetting characteristics of materials has gained much interest in applications related to surface cleaning in both industry and home.Zimbabwe black granite is a middle-to-fine-grained natural stone commonly used as countertops in kitchens and bathrooms. In this study, the laser texturing of Zimbabwe black granite surfaces is investigated with the aim to enhance its hydrophobic character, thus reducing the attachment of contaminants on the surface. Two laser sources (λ=1064 and 532nm) were used for this purpose. The treatment is based on the irradiation of the stone by a laser focused on the surface of the targeting sample. The influence of different laser processing parameters on the surface characteristics of granite (wettability, roughness, and chemistry) was statistically assessed. Most suitable laser processing parameters required to obtain the highest hydrophobicity degree were identified. It has been possible to identify the 532nm laser wavelength as the most effective one to increase the hydrophobic degree of Zimbabwe black granite surface. The phenomenon governing wettability changes was found to be the surface roughness patterns, given the unaltered chemical surface composition after laser processing.

Impact of particle morphology on aggregate-asphalt interface behavior

This paper researched interfacial adhesion behavior between asphalt with limestone and granite through surface microtopography comparison. Abrasion was conducted to limestone and granite by Los Angeles Abrader. Angularity coefficient was used to analyze the angularity and roughness changes of limestone and granite before and after abrasion. Digital imaging technique was used to study the macroscopic changes on the particle surface of limestone and granite before and after abrasion. Scanning electron microscope was used to characterize the changes of surface microtopography of limestone and granite before and after abrasion and the interfacial morphology with asphalt binder. The result showed that the texture complexity degree on the particle surface of limestone and granite decreased after abrasion, the relative flat site of surface increased, and the surface texture change of limestone was more significant. The test result of scanning electron microscope showed that asphalt could permeate into the surface texture of particles of limestone longitudinally after limestone was mixed with asphalt to form embedded structure, but there was a single surface adhesion in the interface between granite and asphalt that an embedded structure was not formed.

Analysis of dark crusts on the church of Nossa Senhora do Carmo in Rio de Janeiro, Brazil, using chemical, microscope and metabarcoding microbial identification techniques

The dark crust on the surface of the Nossa Senhora do Carmo church, in the centre of Rio de Janeiro, was shown to contain high salt levels and neogypsum above the original granite. Delamination and scaling were macroscopically obvious. Next generation DNA sequencing techniques were used for the first time to determine the total microbial populations that could be involved in surface deterioration of historic stone buildings in a tropical climate. High levels of halophilic and stress-resistant bacteria and fungi were identified, able to grow at high temperatures, salt and UV levels, and in the presence of low moisture and toxic fossil fuel emissions. Many produced pigments, adding to the discoloration of the stone surface. The most abundant bacterial group was the Actinobacteria, which can burrow into the compromised rock and produce organic acids that further degrade the substrate. Geodermatophilaceae and Micrococcaceae were the major bacterial families. The majority of the fungi identified were dimorphic and present on the façade in their yeast forms, with few filamentous fungi being seen in the scanning electron microscope. Basidiomycetes were the most common group and the Tremellomycetes the most abundant class. Low numbers of phototroph operational taxonomic units, mainly of Chloroflexi, were detected by the MiSeq sequencing method. Initial chemical alterations of the granite surface, together with the climatic conditions in the city of Rio de Janeiro, determined the surface-colonizing microflora. Salt content appeared to be a major driving factor in community structure. This microbial population participated strongly in crust, formation. The final results of biofilm formation on the stone are surface discoloration, induration and degradation of the façade.