Utilization of the accelerated weathering test method for evaluating the durability of sedimentary rocks

Bulletin of Engineering Geology and the Environment - The durability and geotechnical properties of 12 sedimentary rock samples collected from the Damghan area, Iran, were investigated. The rocks...     

Correlation between slake durability and rock properties for some carbonate rocks

The paper reports a study to assess the relationship between slake durability indices and uniaxial compressive strength, Schmidt hardness, P-wave velocity, modulus of elasticity, effective porosity, water absorption and dry and saturated unit weight for seven types of carbonate rocks obtained from south west Turkey. It was found that the dry unit weight, saturated unit weight and Schmidt hardness gave the best relationship with first cycle slake durability (r = 0.99) while uniaxial compressive strength has a strong relationship with fourth cycle slake durability (r = 0.94). The results showed little difference in the correlation coefficients obtained after the fourth cycle. It is concluded that, for the rocks studied, the first and fourth cycles provide sufficiently good data on the durability for preliminary engineering/design works and that the second to fourth cycle results could be estimated using the first cycle slake durability index (r = 0.99–0.97).     

Anisotropy of strength and deformability of fractured rocks

Anisotropy of the strength and deformation behaviors of fractured rock masses is a crucial issue for design and stability assessments of rock engineering structures, due mainly to the non-uniform and non- regular geometries of the fracture systems. However, no adequate efforts have been made to study this issue due to the current practical impossibility of laboratory tests with samples of large volumes con- taining many fractures, and the difficulty for controlling reliable initial and boundary conditions for large-scale in situ tests. Therefore, a reliable numerical predicting approach for evaluating anisotropy of fractured rock masses is needed. The objective of this study is to systematically investigate anisotropy of strength and deformability of fractured rocks, which has not been conducted in the past, using a nu- merical modeling method. A series of realistic two-dimensional （2D） discrete fracture network （DFN） models were established based on site investigation data, which were then loaded in different directions, using the code UDEC of discrete element method （DEM）, with changing confining pressures. Numerical results show that strength envelopes and elastic deformability parameters of tested numerical models are significantly anisotropic, and vary with changing axial loading and confining pressures. The results indicate that for design and safety assessments of rock engineering projects, the directional variations of strength and deformability of the fractured rock mass concerned must be treated properly with respect to the directions of in situ stresses. Traditional practice for simply positioning axial orientation of tunnels in association with principal stress directions only may not be adequate for safety requirements. Outstanding issues of the present study and su~zestions for future study are also oresented.     

Influence of weathering on the engineering properties of Harsit granitic rocks (NE Turkey)

Weathering and hydrothermal alteration of the granitic rocks in the Eastern Black Sea Region (NE Turkey) are important phenomena affecting the engineering projects in the region. The study investigated the probable paths of rock-forming mineral transformations due to weathering in the Harsit granitoid rocks, the changes of the major oxides as a consequence of weathering and the effects of weathering on the engineering properties. To identify the changes in the major oxides, the volume concentrations were considered in relation to the dry density. Chemical leaching during weathering was shown to be significant in changing the minerals. It was concluded that the engineering properties of the weathered granitic rocks can be most reliably predicted by P-wave velocity.      

Numerical evaluation of strength and deformability of fractured rocks

Knowledge of the strength and deformability of fractured rocks is important for design, construction and stability evaluation of slopes, foundations and underground excavations in civil and mining engineering. However, laboratory tests of intact rock samples cannot provide information about the strength and deformation behaviors of fractured rock masses that include many fractures of varying sizes, orientations and locations. On the other hand, large-scale in situ tests of fractured rock masses are economically costly and often not practical in reality at present. Therefore, numerical modeling becomes necessary. Numerical predicting using discrete element methods(DEM) is a suitable approach for such modeling because of their advantages of explicit representations of both fractures system geometry and their constitutive behaviors of fractures, besides that of intact rock matrix. In this study, to generically determine the compressive strength of fractured rock masses, a series of numerical experiments were performed on two-dimensional discrete fracture network models based on the realistic geometrical and mechanical data of fracture systems from feld mapping. We used the UDEC code and a numerical servo-controlled program for controlling the progressive compressive loading process to avoid sudden violent failure of the models. The two loading conditions applied are similar to the standard laboratory testing for intact rock samples in order to check possible differences caused by such loading conditions. Numerical results show that the strength of fractured rocks increases with the increasing confning pressure, and that deformation behavior of fractured rocks follows elasto-plastic model with a trend of strain hardening. The stresses and strains obtained from these numerical experiments were used to ft the well-known Mohr-Coulomb(MC) and Hoek-Brown(H-B) failure criteria, represented by equivalent material properties defning these two criteria. The results show that both criteria can provide fair estimates of the co     

谈山区高速公路桥梁混凝土抗风化养护和耐久性

在检测福建山区高速公路桥梁实际情况的基础上,充分考虑了该区环境温湿度和混凝土强度等内外因素影响,建立了高速公路桥梁混凝土碳化模型,对福建山区高速公路桥梁混凝土的耐久寿命进行了分析,并对裂缝和冻融存在情况下桥梁混凝土的碳化寿命进行了比较研究,提出了山区高速公路桥梁混凝土抗风化养护应当采取的措施。     

Thermal effect on the physical properties of carbonate rocks

The effect of thermal damage on the physical properties of five carbonate rocks has been investigated. The tests were conducted on two marbles and three limestones, mainly composed of calcite but with different grain sizes, porosities, structural and textural characteristics. Cubic samples prepared from these rocks were gradually heated to a specific temperature level of 100, 200, 300, 400 and 500 °C, and gradually cooled down to room temperature without causing thermal shock in order to investigate the effect of heating temperature on physical properties such as microstructure, bulk density, effective porosity and P-wave velocity. Microscopic investigations from thin sections showed that damage in rocks at elevated temperatures was induced in different severity depending on grain size, porosity, structural and textural characteristics. Colour changes were also observed in porous limestones (Lymra and Travertine) due to organic material. In accordance with the degree of calcite dilation depending on heating temperature and in turn new microcrack occurrence, separation along intragrain and/or intergrain boundaries and widening of existing cracks, P-wave velocity decreased to various levels of the initial value, whereas porosity increased. Microscopic analyses and P-wave velocity measurements indicate that compaction of rock structure up to 150 °C occurred and induced calcite dilation had no significant damage effect on the rock material. Compaction of rock structure led to an increase in P-wave velocity and slight decrease in porosity. Most of the damage occurred within 24 h of heating time and further heating treatments brought relatively minor changes in physical properties. Damage intensity was well explained with P-wave velocity and effective porosity values depending on temperature increase.     

Experimental assessment of long-term durability of some weak rocks

Slake durability tests, point load strength tests and X-ray diffraction analyses were carried out on thirteen rock types in an attempt to correlate the durability of the rocks with their strengths and mineral compositions. A concept is proposed to describe the rock degradation characteristics from the results of slake durability test cycles. A new classification system is introduced for rock durability, which allows the prediction of the strength of a rock when it has been affected by the weathering process. The aim of the study was to predict the influence of the weathering process (simulated by wetting and drying and heating and cooling) on the durability and strength of the volcanic, metamorphic and sedimentary rocks outcropping in eastern Thailand. Field studies were carried out in an attempt to relate the heat absorption of the rocks in situ to that measured on the laboratory specimens.     

Estimating the index properties of deteriorated carbonate rocks due to freeze–thaw and thermal shock weathering

Laboratory tests were conducted on 12 different carbonate rocks to investigate index properties of deteriorated rocks due to physical weathering. Physical weathering due to freeze–thaw and thermal shock action for 20 cycles, was simulated, following the procedure suggested by standard methods. Index properties, P-wave velocity, uniaxial compressive strength and Schmidt hardness, for the three series of the rock samples were determined for fresh, freeze–thaw and thermal shock conditions. It was found that the index properties of rocks treated with freeze–thaw and thermal shock decrease in varying levels with respect to initial values. A model equation predicting the index properties of rocks due to freeze–thaw and thermal shock treatment was developed by multiple regression analysis of measured data. This model explains decrease in index property of a deteriorated rock depending on its initial property and porosity of rock with the coefficients for a specific index property, given in the paper for the both freeze–thaw and thermal shock treatments. Model was validated by statistical tests. In order to estimate the index property for any cycle of freeze–thaw or thermal shock treatment, this model equation was incorporated into a previously suggested model to eliminate a decay constant required for that model to be determined for a specific rock in the laboratory. So, the final model equation could accurately predict a property of a deteriorated carbonate rock depending on treatment cycle, and initial index property and porosity. This was also proved by comparing the model with compressive strength data of a researcher for freeze–thaw cycles.     

Evaluation of the long-term durability of yellow travertine using accelerated weathering tests

The study investigated the long-term performance/durability of yellow travertine against various environmental processes using several accelerated weathering tests: wet–dry, freeze–thaw and salt crystallization. Prior to the accelerated weathering tests, the specimens were separated into two groups based on their porosities. The re-crystallization pressure of Na₂SO₄ salt was found to be the most destructive factor in the deterioration of the yellow travertine, with a maximum of 50% loss of integrity recorded. The recurrent cycles of wetting–drying and freezing–thawing caused relatively minor damage. After the experimental studies, the disintegration rate was statistically evaluated using the alteration index–alteration velocity and the decay function approaches. Both statistical models confirmed that the rate of disintegration was higher with salt re-crystallization pressures in the less porous yellow travertines compared with that resulting from wet–dry and freeze–thaw cycles.     

Uranium and thorium in weathering and pedogenetic profiles developed on granitic rocks from NW Spain

Uranium and thorium were analyzed in seven weathering and pedogenetic soil profiles developed on granitic rocks from NW Spain. Concentrations were measured by X-ray fluorescence spectrometry (XRF) and the U- and Th-bearing minerals were studied by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). Both elements were determined in rock, bulk soil and in different grain-size fractions (sand: 2000-50 microm, silt: 50-2 microm, and clay: <2 microm). U concentrations in the rock varied between 5.3 and 27.7 mg kg(-1) and Th concentrations from 5.5 to 50.7 mg kg(-1). The most alkalic rocks can be considered as U-rich granites. Bulk soil U and Th concentrations are similar to those of the rocks (4.8-29.2 and 7.4-56.7 mg kg(-1), respectively), but in the grain-size fractions both elements show the lowest concentrations in the sand and the highest in the clay. In the latter, concentrations are always higher than those of the rocks, particularly in the C horizons with enrichments up to 4 times for U and 5 times for Th. The concentration profiles and the ratios to the parent rock suggest that U and Th are leached from the surface soil and accumulate in the deeper horizons. Mass balance calculations, using Ti as a reference immobile element, also support U and Th leaching in the solum and supergene enrichment in bottom horizons. Leaching seems to be more intense on horizons with gravel content higher than 20%. The leaching of U and Th in the topmost horizons and the accumulation in the bottom soil horizons can be considered as a natural attenuation of the impact of these radiogenic elements in the environment. But their enrichment in the potentially airborne fraction poses some risk of redistribution in the ecosystems.     

The effect of weathering on a crude oil residue exposed at sea

Kuwait crude oil residues have been exposed to weathering at sea (Langstone Harbour, Portsmouth) for 2 yr. in the form of a water-in-oil emulsion (“chocolate mousse”) in a floating layer about 1·4 cm thick. One batch of oil was exposed in a tank open to tidal flushing below the water line, and a second batch was exposed in a closed tank. A number of chemical and physical properties of the oil were measured at intervals, as were the concentrations of mineral nutrients and bacterial numbers in the sea water. Asphaltenes, specific gravity and viscosity all increased, as did the “polar” fraction from liquid chromatography. The n-alkanes decreased to about half the original levels in the open tank but were little altered in the closed tank. The constancy of vanadium and nickel concentrations suggest that no net loss of oil occurred, the substantial changes in properties deriving from chemical modification (probably oxidation and polymerization) of oil components, rather than mineralization (conversion to carbon dioxide and water) of some components leaving a residue of altered composition. It was not determined which of several processes predominated in causing these changes, but it is thought likely that in this thick layer of mousse auto-oxidation predominated over biodegradation.     

Effect of weathering on properties of coarsely fragmented residual rock

Conclusions 1. Atmospheric weathering of residual, coarsely fragmented rock formations causes mainly a change in their physical properties, and in this connection it is recommended that the weathering intensity should be determined from the change in the grain-size distribution.2. The weathering coefficient K_W is a complex parameter which takes into account both the degree of natural disintegration of the rock and the disruptions of the crystal bonds in its fragments.3. Weathering over a period of one year depends on the initial weathering of the coarsely fragmented residual rock, and intensifies as K_W increases. The maximum weathering rate is observed during the first 15 days of each of the typical seasons of the year. The most intensive weathering time is the autumn-spring period.4. Compaction by tamping is one of the effective methods of increasing the bearing capacity of weathered, coarsely fragmented rock materials during prolonged idle periods of excavation work, and likewise in using excavated, coarsely fragmented materials in earthen structures and bedding fills of various types.Ural Polytechnic Institute. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, pp. 26–28, January–February, 1976.     

Anisotropy effect on strengths of metamorphic rocks

This paper aims to study the effect of anisotropy on strengths of several metamorphic rocks of southern(Cine) submassif of Menderes metamorphic massif in southwest Turkey. Four different metamorphic rocks including foliated phyllite, schist, gneiss and marble(calcschist) were selected and examined.Discontinuity surveys were made along lines for each rock and evaluated with DIPS program. L-type Schmidt hammer was applied in the directions parallel and perpendicular to foliation during the field study. Several hand samples and rock blocks were collected during the field study for measurements of dry and saturated densities, dry and saturated unit weights and porosity, and for petrographic analysis and strength determination in laboratory. L-and N-type Schmidt hammers were applied in the directions perpendicular(anisotropy angle of 0°) and parallel(anisotropy angle of 90) to the foliation on selected blocks of phyllite, schist, gneiss and marble(calcschist). The phyllite and schist have higher porosity and lower density values than the other rocks. However, coarse crystalline gneiss and marble(calcschist) have higher rebound values and strengths, and they are classified as strong-very strong rocks. Generally, the rebound values in the direction perpendicular to the foliation are slightly higher than that in the direction parallel to foliation. Rebound values of N-type Schmidt hammer are higher than the L-type values except for phyllite. Sometimes, the rebound values of laboratory and field applications gave different results. This may result from variable local conditions such as minerals differentiation,discontinuities, water content, weathering degree and thickness of foliated structure.     

渗透结晶型外表面涂层对混凝土耐久性的防护作用

外表面涂层是防护混凝土耐久性劣化的有效方法之一，可以防止水分子和有害介质的侵入。水泥基渗透结晶型材料具有良好的抗老化和抗侵蚀能力，在1．0kg／m^2的涂层厚度下，可能使混凝土的抗碳化性和抗氯离子渗透性大幅提高。     

尺寸效应对混凝土耐久性影响研究

选择标准试件与钻芯取样试件,研究尺寸效应对C40和C60复合掺合料混凝土耐久性的影响.结果表明,尺寸效应对混凝土耐久性有一定影响,钻芯试件耐久性能明显低于标准试件,但两者性能的发展变化规律相似.     

The effect of sample size on Schmidt rebound hardness value of rocks

The Schmidt hammer has been commonly used device for hardness determination and for predicting the unconfined compressive strength and other mechanical properties of rocks, due to the fact that it is a quick, easy, inexpensive and non-destructive testing method. Testing is most commonly performed following the ISRM and ASTM standards. The effect of sample size for a consistent hardness value has not been well defined in previous works. ISRM [Rock characterization testing and monitoring ISRM suggested methods, suggested methods for determining hardness and abrasiveness of rocks, Part 3. Oxford: Pergamon; 1981. p. 101–3] suggested that block edge length should have at least 6 cm, while ASTM [Standard test method for determination of rock hardness by Rebound Hammer Method, D5873-05, 2005] indicated at least 15 cm. In this study, in order to analyze the effect of sample size on Schmidt rebound hardness (SRH) property of rocks, rock samples were collected from eight locations. Cubic samples having different edge dimensions of 6, 7, 8, 10, 12 and 15 cm were prepared. In the laboratory, Schmidt hammer tests were conducted according to the suggested procedure by ISRM (1981) together with different methods of recording SRH. By evaluating the measured data, it is showed that the size of the cubic samples significantly affects the SRH values. Edge dimension of the cubic block should be at least 11 cm for determining a consistent hardness value. An equation predicting the consistent hardness value from samples smaller than 11 cm was also suggested.     

Estimating the uniaxial compressive strength of pyroclastic rocks from the slake durability index

Because the preparation of standard samples may not always be possible for weak or soft rocks, the prediction of uniaxial compressive strength (UCS) from indirect methods is widely used for preliminary investigations. In this study, the possibility of predicting UCS from the slake durability index (SDI) was investigated for pyroclastic rocks. For this purpose, pyroclastic rocks were collected from 31 different locations in the Cappadocian Volcanic Province of Turkey. The UCS and SDI tests were carried out on the samples in the laboratory. The UCS values were correlated with the SDI values and a very strong exponential relation was found between the two parameters. Since some data were scattered over the UCS values of 20 MPa, the correlation plot was redrawn for above and below the UCS values of 20 MPa, respectively. Very strong linear correlations were developed for two cases. Our concluding remark is that the UCS of pyroclastic rocks can be estimated from the SDI.