Impact of dissolved salt type and content on mechanical and physical properties of porous cementitious materials

This paper presents a methodology for determining the uniaxial and triaxial compressive strength of heterogeneous material composed of dacite (D) and altered dacite (AD). A zone of gradual transition from altered dacite to dacite was observed in the rock mass. The mechanical properties of the rock material in that zone were determined by laboratory tests of composite samples that consisted of rock material discs. However, the functional dependence on the strength parameter alteration of the rock material (UCS, intact UCS of the rock material, and mi) with an increase in the participation of “weaker” rock material was determined based on the test results of uniaxial and triaxial compressive strength. The participation of altered dacite directly affects the mode and mechanism of failure during testing. Uniaxial compressive strength (σciUCS) and intact uniaxial compressive strength (σciTX) decrease exponentially with increased AD volumetric participation. The critical ratio at which the uniaxial compressive strength of the composite sample equals the strength of the uniform AD sample was at a percentage of 30% AD. Comparison of the obtained exponential equation with practical suggestions shows a good correspondence. The suggested methodology for determining heterogeneous rock mass strength parameters allows us to determine the influence of rock material heterogeneity on the values σciUCS, σciTX, and constant mi. Obtained σciTX and constant mi dependences define more reliable rock material strength parameter values, which can be used, along with rock mass classification systems, as a basis for assessing rock mass parameters. Therefore, it is possible to predict the strength parameters of the heterogeneous rock mass at the transition of hard (D) and weak rock (AD) based on all calculated strength parameters for different participation of AD.

Many engineering structures have been built on the sandstones. The main purpose of this study is to estimate the uniaxial compressive strength (UCS) and modulus of elasticity (Es) of sandstones using regression models. For this purpose, petrographic studies, compressional wave velocity (Vp), porosity, density and uniaxial compressive strength tests were performed on dry and saturated samples of sandstones prepared from Mosha village in the northwest of Damavand city. The studied sandstones were classified as feldspathic litharenite and litharenite. Due to the effect of moisture on the physical and mechanical properties of these sandstones, the density and Vp of the samples in the saturated state compared to the dry state have increased by 4 and 20%, respectively. In contrast, UCS and Es have increased by 18% and 25%, respectively. The results of simple regression showed that the most accurate relationship (the highest correlation coefficient and the lowest error) of porosity, Vp and density with UCS and Es are logarithmic, linear and quadratic polynomials, respectively. Based on the determination coefficient (R2=0.5-0.77) and the errors (RMSE=10.29-18.26; MAPE=1.70-2.80), the relationships presented by simple regression method for estimating UCS and Es showed high accuracy. The Vp and porosity also have the greatest impact on UCS and Es. Evaluation of empirical relationships of other researchers showed that some of these relationships have a determination coefficient of more than 50%. Examination of residual variance homogeneity graphs at the predicted value levels, determination coefficient and error of the methods showed that multivariate regression (R2=0.73-0.74, RMSE=13.36-13.56, MAPE=1.06-1.22, Durbin-Watson= 1.56-1.70) has a high accuracy for estimating UCS and Es as compared to the simple regression.

Cemented paste backfill (CPB) is widely used in backfilling underground mine voids. It consists of fine grained mine tailings with a small dosage of binder (~ 3–10%). Cement is the common binder, which is currently being used in most of the mines in North Queensland, Australia. In an effort to control backfilling costs, investigations are being currently carried out for the use of some alternative binders, that is, pozzolanic binder such as blended cement (BC) containing slag or fly ash in CPB. A thorough study to quantify the effects of additives, such as blast furnace slag and fly ash with ordinary Portland cement, in certain percentages on CPB could save large sums of money for Australian mining companies, if the required cement percentage is reduced in binder for CPB. In an attempt to dispose more tailings underground, the mines prefer increasing the solid content to the maximum possible limit, as dense CPB needs less binder to achieve a target strength. On the other hand, a high solid content slurry has both increased yield stress and viscosity, which increase the likelihood of blocking the reticulation pipeline. In this research, the possibilities of partial replacement of cement binder in CPB were studied through detailed laboratory investigations on influence of binder types as well as dosages in both mechanical and flow properties. Also, five different curing methods for CPB samples were studied to propose proper method. UCS test on 25 identical samples from three different CPB mixes were conducted for the detailed statistical analysis to assess the variability of mechanical properties of CPB samples and to validate the proposed curing method. Furthermore, the possibility of using a relatively smaller cylinder (110 mm height and 110 mm diameter) in slump test is assessed via extensive slump test along with standard slump cone on different CPB mixes. Moreover, series of scanning electron microscopy (SEM) analyses were performed on cracked UCS sample to investigate the relationship between microstructure and long-term mechanical properties. Finally, possibility of using UCS and indirect tensile (IDT) strength to determine the shear strength parameters (c and φ) for CPB was assessed with proper validation based on both experimental test and numerical simulation. For all these studies and investigations conducted in this research, various laboratory experiments, such as uniaxial compressive strength (UCS) test, indirect tensile (IDT) strength test, slump test, yield stress test, triaxial test and SEM analysis, with analytical correlation techniques and numerical simulation were employed. Slag blended cement (60% Slag + 40% Portland cement) can be used as replacement of cement binder in preparation of CPB with less dosage to achieve similar strength and stiffness as like cement binder, even in short curing time. This significant reduction in Portland cement usage not only leads to the significant cost saving, but also may slightly contribute for a sustainable development. In addition, through the extensive laboratory experiments on rheological properties, it is found that the there is hardly any difference between the cement and slag blended cement binders on flow properties namely the yield stress and slump, while the binder dosage has an effect. The smaller cylindrical slump device appears to have good potential for slurries like mine tailings or dredged mud that have high water content for slump test as there was strong correlation between the two different slump test devices used. Also, It is found that there is strong inter-relationship among solid content, slump, yield stress, and bulk density of CPB. In addition, a simple and proper curing method for CPB samples for the laboratory tests was recommended. In addition, the mechanical properties of CPBs cured in this proposed method show less variability for UCS and Young's modulus with relatively small coefficient of variation of less than 10% and 25%, respectively and hence these small variabilities of mechanical properties demonstrates the consistency of sample casting, curing, and testing methods. Furthermore, it is found that there is a positive relationship between microstructure and mechanical properties of CPB. Finally, the estimated shear strength parameters of CPB using the UCS and IDT strengths show good agreement with experimental and numerical simulation. Throughout the thesis, sets of empirical models and correlations were proposed to predict the long term UCS, stiffness, yield stress, slump height, and cohesion. In summary, the great potential of partial replacement of existing cement binder using slag blended cement in preparation of CPB is identified through various laboratory tests. In addition to the mechanical properties, the microstructure and flow properties of modified CPB were extensively investigated. This research will not only help to reduce the cement consumption in CPB production but also provides an alternative way of recycling industrial waste, such as slag and fly ash in vast volumes.

The derivation of geomechanical properties from petrophysical/geophysical data is not only of great importance in the oil industry but also in mining, geothermal projects and tunnelling, for reduction of costs and to improve security. For the oil industry and geothermal sector, it is mainly important for drilling rate and the stability of the borehole and, as a result, the economic factor. A key issue is that geomechanical properties, which can support a better planning of a project, cannot be measured in the borehole or on the surface directly. In this study, the focus is put on anisotropic effects on the correlation between static and dynamic properties, which is neglected in most studies but important because values can vary extremely. Therefore, measurements in the geotechnical laboratory of compressional and shear wave velocity during uniaxial compression strength test were taken. Additionally, typical properties like bulk and grain density as well as porosity were determined too. Different samples (carbonate–silica schist, marble and phyllite) from the "Zentrum am Berg"-research tunnelling centre at the "Erzberg" in Austria were used. Shown are correlations between uniaxial compression strength and compressional wave velocity as well as for static and dynamic Young’s modulus including their anisotropic effect. The results are promising and provide an opportunity for further applications on log data.

Physical and mechanical properties of rock for engineering purposes are indispensable for any civil/construction, mining and other engineering requirment. The results of the uniaxial compressive strength (UCS) test are very much needed in various geotechnical analyzes or engineering, in particular in the mining industry in relation to the calculation of the pit slope design and other mining infrastructure. Rock samples used in this study were obtained from the results of geotechnical drilling (full core drilling). The rock engineering properties test to obtain UCS and PLI values was carried out in the laboratory. Testing the rock hardness index using the point load index (PLI) can be done more quickly, cheaply, practically and can use rock samples with a variety of sample shapes. The focus and object of the research are mudstone and sandstone units as part of the Lati Formation. These two types of layers are the most dominant rock types as a constituent of the pit slopes in the research area. To ensure that the correlation results are in accordance with the rules of scientific research, the distribution of UCS and PLI data from laboratory test results is verified using a statistical approach / testing. Correlation and analysis between the two rock engineering properties test results are very useful for geotechnical analysis data input. The coefficient or constant values obtained can be used to determine the rock strength values used in various geotechnical analyzes so that the analysis can be carried out more efficiently, effectively and quickly and can support geotechnical engineering work.

This study aims to develop fluid–solid coupled similar materials to enhance the reliability of geotechnical model tests simulating reservoir slope stability under water-level fluctuations. Using an orthogonal experimental method, materials were prepared with quartz sand and barite as aggregates, cement and gypsum as binders, and water as the regulator. Tests on density, uniaxial and triaxial compressive strength, and flow properties determined the relationships between material properties and raw components. Uniaxial compressive strength tests under dry–wet cycles revealed that cement-to-binder ratio primarily influenced density, uniaxial compressive strength, cohesion, and hydraulic conductivity, while the binder-to-aggregate ratio affected elastic modulus and internal friction angle. Uniaxial compressive strength continuously degraded with cycles but at a decreasing rate. A water-damage resistance coefficient was defined to quantify degradation. Multiple linear regression analysis established a robust model for uniaxial compressive strength prediction, providing a theoretical basis for material proportioning. These findings improve the simulation accuracy in hydrologically active zones, with applications in designing stable reservoir slopes.

Investigation of granular materials’ geomechanical and geological characteristics could provide invaluable information to researchers working in petroleum and civil engineering, geoscience, and petrophysics. In this study, the effects of normal stress and sand grain size on the petrophysical and geomechanical characteristics of artificial samples (made of a wide range of sand grains and cement) were investigated, while the chemical composition and mineralogy of all the samples were kept identical. The results showed that the rock porosity and permeability, the main criteria for evaluating rock storativity and transmissibility, respectively, were adversely affected by applying normal stress and the increase of grain size. Based on the results, there is a critical range of grain size (i.e., 0.1–0.2 mm) above which rock permeability decreases sharply with an increase in normal stress. The geomechanical outcomes revealed that improving the cementation process by applying compaction force, and thus, increasing the degree of hydration has a greater effect on ameliorating rock strength than reducing rock porosity. Besides, the uniaxial compressive strength (UCS) and Brazilian test results indicated that fine-grained samples fail at lower normal stress (i.e., at 38% and 66% of the coarse samples, respectively) compared with coarse-grained samples because of the large number of grain-to-grain boundaries. The fracture patterns showed a straight line for very fine and fine-grained samples, while an irregular shape appeared for medium and coarse-grained samples. In the end, a comparison of distinct petrophysical and geomechanical rock properties, such as X-ray fluorescence analysis, UCS, porosity, and permeability, between artificial and natural samples has been made to analyze the difference between them.

In this research, the anisotropic behaviour of laminated sandstones, collected from southwest of Qom (central part of Iran), was evaluated using uniaxial compressive strength, point load and Brazilian tests. For this purpose, the eight rock blocks were selected. The rock samples were drilled at different direction with respect to the inclination angles (β) of 0, 30, 45, 60 and 90°. After specimen’s preparation and assessment of mineralogical and physical properties, specimens were subjected to uniaxial compressive strength, point load and Brazilian tests, and their strength and failure modes were evaluated at different inclination angles (β) between loading direction and lamination planes. Transitional angle, which indicates the change in dominant failure mode from parallel to the lamination to across the lamination, were also determined. The results indicate that the anisotropic behaviour of selected sandstones in uniaxial compressive strength test is different compared with the point load and Brazilian tests. Based on the results, the compressive strength anisotropy ratio of the studied sandstones is low, whereas for point load tests, the anisotropy ratio is obtained moderate. Finally, the different failure modes were classified for laminated sandstones.

The purpose of this paper is to investigate the strength, physical and engineering index parameters of selected dolomitic rocks with emphasis on grain size. For this purpose, three groups of dolomite from north western Iran, with the same mineral composition but different grain size, were selected; fine grain, medium grain and coarse grain. Three sets of laboratory experiments are performed on 32 samples: first; petrography tests for determining mineral composition and their percentage, and microstructure of rock containing grain size and grain size distribution, second; experiments to determine the physical properties of the rocks included density, compressional and shear wave velocity, and the third category of experiments included uniaxial compressive strength test, Brazilian tensile strength and point load strength. According to the results; there are significant positive correlation between grain size and uniaxial compressive strength (r = 0.89), point load strength (r = 0.58), Brazilian strength (r = 0.69), and average Young’s modulus (r = 0.64). Also, with increasing grain size, density decreases (r = –0.77). There is strong correlation between compressional wave velocity and shear velocity (r = 0.88). There are also a strong correlation among the uniaxial compressive strength, Brazilian tensile strength and point load strength.

While the uniaxial compression strength ( UCS ) test is the gold standard for determining the UCS of rock for geotechnical and mining applications, empirical correlations between UCS and other test measurements such as point load index ( PLI ) I s(50) values are useful in situations where intact cores are difficult to retrieve and/or the scope of UCS testing is constrained by budget. In this paper, an extensive database of UCS and PLI I s(50) values has been compiled for the Upper Liffey Valley and Northern Units of the Leinster Caledonian granite in Dublin, Ireland. UCS values in the full (unfiltered) database correlated statistically with bulk density but were independent of specimen geometry. Statistical analysis also detected some UCS dependence on formation type but none on weathering, although important caveats apply to these findings. I s(50) values (from the unfiltered database) were found to be independent of loading direction (axial or diametral). An initial attempt to correlate UCS with I s(50) exhibited unacceptable scatter, prompting a systematic filtering process, with strict criteria for UCS specimen diameter and aspect ratio, specimen position within the core and the application of Grubbs process to identify outliers. This provided a significantly more reliable correlation based on ∼20% of the original dataset. A power correlation was found to capture the form of the data better than a linear one. This new correlation ( U C S = 20.36 I s ( 50 ) 0.665 ) agrees well with the expression UCS = 20 I s(50) currently in use for Dublin granites up to UCS ∼30 MPa but renders UCS = 20 I s(50) to be unconservative at higher strengths.

Due to the fact that the estimation of the rock mass properties is very important in any geotechnical project, many studies have become with the aim of their determination. But, the immediate determination is very difficult because the in situ tests are time-consuming, expensive and sometimes unreliable. For this reason, many researches have attempted to calculate the rock mass characteristic through empirical equations, but only few have focused on the ultramafic rocks. The main purpose of this study is to estimate the engineering properties of the ultramafic rock masses through the uniaxial compressive strength of the intact rock, the influence of blast damage, the material constant and the Geological Strength Index with the use of Hoek and Brown criterion (Roclab Software). Thus, sixteen samples, taken from central Greece (the western part of Othrys mt and the Kallidromo mt), were tested (uniaxial compressive strength and triaxial tests) and the results were statistically described and analysed. The manuscript reveals strong positive linear correlation between the estimated (through the Hoek and Brown failure criterion) uniaxial compressive strength and the measured (determined by strength tests) uniaxial compressive strength. The values of the uniaxial rock mass compressive strength, the global rock mass compressive strength, the rock mass tensile strength, and the rock mass modulus of deformation are finally calculated and presented. Furthermore, an attempt to correlate the rock mass deformation modulus (Erm) with the tangent young modulus (Ei) results that there is high correlation between them both for peridotites and serpentinites.

Estimation of punch strength index and static properties of sedimentary rocks using neural networks in south west of Iran

The purpose of this study was to clarify the relationship between axial point load strength and uniaxial compressive strength in hydrothermally altered rocks, which are typical of the soft rocks found in northeastern Hokkaido, Japan. The numbers of specimens tested were 1,755 rock specimens for the axial point load strength test, whereas 329 rock specimens for the uniaxial compressive strength test. These came primarily from the earth’s surface in ancient hydrothermal fields. The rock specimens underwent axial point load strength and uniaxial compressive strength tests using a laboratory testing machine with specimens in forced-dry and forced-wet states. The correlation between the axial point load strength and the uniaxial compressive strength was linear. The forced-dry and forced-wet states can be combined to giving a relationship in which the relation of axial point load strength (Is) and uniaxial compressive strength (qu) was qu = 12.9 Is in the soft rocks with axial point load strengths below 1.5 MPa. This relationship might be applied to on-site tests of rocks with natural moisture content. The number of tested specimens satisfied accuracy requirements, based on the coefficient of variation. The axial point load strength was strongly correlated with the uniaxial compressive strength. Therefore, the relationship between axial point load strength and uniaxial compressive strength established in this study was highly precise. We could calculate the uniaxial compressive strength from axial point load strength tests in the soft rocks only when their axial point load strengths were below 1.5 MPa.

The geomechanical strength of rockmass plays a key role in planning and design of mining and civil construction projects. Determination of geomechanical properties in the field as well as laboratory is time consuming, tedious and a costly affair. In this study, density, slake durability index, uniaxial compressive strength (UCS) and P-wave velocity tests were conducted on four igneous, six sedimentary and three metamorphic rock varieties. These properties are crucial and used extensively in geotechnical engineering to understand the stability of the structures. The main aim of this study is to determine the various mechanical properties of 13 different rock types in the laboratory and establish a possible and acceptable correlation with P-wave velocity which can be determined in the field as well as laboratory with ease and accuracy. Empirical equations were developed to calculate the density, slake durability index and UCS from P-wave velocities. Strong correlations among P-wave velocity with the physical properties of different rock were established. The relations mainly follow a linear trend. Student’s ‘t’ test and ‘F’ test were performed to ensure proper analysis and validation of the proposed correlations. These correlations can save time and reduce cost during design and planning process as they represent a reliable engineering tool.

Shale anisotropy characteristics have great effects on the mechanical behaviour of the rock. Understanding shale anisotropic behaviour is one of the key interests to several geo-engineering fields, including tunnel, nuclear waste disposal and hydraulic fracturing. This research adopted the finite discrete element method (FDEM) to create anisotropic shale models in ABAQUS. The FDEM models were calibrated using the mechanical values obtained from published laboratory tests on Longmaxi shale. The results show that the anisotropic features of shale significantly affect the brittleness and fracturing mechanism at the micro-crack level. The total fracture number in shale under the Uniaxial Compressive Strength (UCS) test is not only related to the brittleness of shale. It is also strongly dependent on the structure of the shale, which is sensitive to shale anisotropy. Two new brittleness indices, BIf and BICD, have been proposed in this paper. The expression for BIf directly incorporates the number of fractures formed inside of the rock, which provides a more accurate frac-ability using this brittleness index. It can be used to calculate the frac-ability of rocks in projects where there are concerns about fractures after excavation. Meanwhile, BICD links brittleness to the CD/UCS ratio in shale for the first time. BICD is easy to obtain in comparison to other brittleness indices because it is based on the Uniaxial Compressive Strength test only. In addition, it has been shown there is a relationship between tensile strength and the crack damage strength in shale. Based on this, an empirical relationship has been proposed to predict the tensile strength based on the Uniaxial Compressive Strength test.