Static Modulus Research Articles

Influence of Calcined Diatoms on the Properties of Conventional Concrete

Today, the construction industry has expressed its preference for the use of sustainable materials due to the significant impact they have on the environment. Although concrete is widely used in construction due to its diverse properties, one of its main components, known as clinker, is a major contributor to CO2 pollution. Therefore, the feasibility of partially replacing this material with alternatives is being investigated. Among them, calcined diatoms are presented as a promising option. These are an extremely fine and highly porous material, composed mainly of silica, which has a large specific surface area. The abundant presence of active silica improves the properties of concrete, such as its strength, while the ultrafine particles of diatoms densify the concrete structure, thus achieving a concrete with greater durability. The objective of this study was to evaluate the properties of conventional concrete, both fresh and hardened, by adding calcined diatomite in proportions of 5%, 10% and 15%, with the purpose of determining the optimum percentage of calcined diatomiteto achieve adequate concrete development. Test specimens were elaborated without the addition of calcined diatoms and with the addition of calcined diatoms, then immersed in water for 7d, 14d and 28d. Tests were carried out in the fresh state to obtain workability, bleeding, setting time, air content, temperature, and unit weight. In the hardened state, tests were carried out to obtain compressive strength, static modulus of elasticity and permeability. It was found that with a lower addition of calcined diatomaceous earth, the concrete can develop as a normal concrete, and improvements in compression were obtained, increasing with respect to the control concrete. However, by increasing the percentage of calcined diatomite, the workability is reduced and in general, the properties do not show an improvement. Concrete with the addition of calcined diatomite can be used as a thermal insulator, since it presents very fine particles that perform a filling effect, densifying the concrete matrix, and it can also be used for lightweight concrete since it reduces 17kg/m3. On the other hand, the compressive strength with 5% calcined diatomite increased by 9% with respect to the standard, due to its high pozzolanic activity.In addition, a lower permeability was found with the addition of 5% calcined diatomite. In general, calcined diatomite in lower proportions can generate resistant and durable concrete.

Investigational studies of asphalt concrete elastic moduli for pavement design

In recent years in the Russian Federation there has been a significant expansion of road materials variety used on highways. However, there is a lack of harmonization of new asphalt concrete of Western European format, with regulatory documents for the non-rigid pavement design, in terms of their design characteristics assignment. In this regard, there is a need to determine and justify the numerical values of the new asphalt concrete mechanical performance used for the non-rigid pavement design when tested for strength. In previous publications authors have presented a new graph-analytical approach to justify the elasticity design moduli of asphalt concrete from GOST R 58406.2-2020. This paper is a continuation of that development and includes the empirical verification results of the analytical method accuracy. Tests were carried out to determine the static laboratory elasticity modulus of asphalt concrete under uniaxial bending loading of bar specimens of some asphalt concrete types from GOST R 58406.2 and best corresponding ones from GOST 9128. To the values obtained, during the experiment, the calculation method developed by the authors earlier was applied. The article presents a study aimed at experimental confirmation of analytically justified calculated values of asphalt concrete elastic moduli according to GOST R 58406.2-2021 for the pavement design.

Formulation and Characterization of Experimental Adhesive Systems Charged with Different Concentrations of Nanofillers: Physicomechanical Properties and Marginal Gap Formation

This study aimed to formulate and characterize experimental dental adhesives charged with different concentrations of nanofillers. Different concentrations (0, 7.5 wt%, and 15 wt%) of nanosized silica (50 nm) were added to the bond of a two-bottle experimental etch-and-rinse adhesive system (EA0, EA7.5, and EA15). The following physicomechanical properties were evaluated: degree of conversion (DC%), ultimate tensile strength (UTS), flexural strength (FS), static modulus of elasticity (SME), dynamic modulus of elasticity (DME), and glass transition temperature (Tg). Marginal integrity (%MG) was evaluated in standardized class I cavities hybridized with the EAs and restored using two dental composites (CON-conventional and OBF-bulk-fill): EA0CON, EA7.5CON, EA15CON, EA0OBF, EA7.5OBF, and EA15OBF. Gap formation was measured in the occlusal and mesial tooth-restoration interfaces using a 3D laser confocal microscope. Microtensile bond strength (µTBS) was evaluated using dentin-composite beams (1 × 1 mm) obtained from restorations. Data were submitted to ANOVA and Tukey’s test (α = 0.05). For DC% and Tg, EA15 < EA0 = EA7.5 (p < 0.05). For UTS, EA0 < EA7.5 < EA15. For FS, SME, and DME, EA0 < EA7.5 = EA15 (p < 0.05). For the gap formation analysis, there were statistical differences only for the conventional composite (EA0CON > EA7.5CON = EA15CON). The lowest values (p < 0.05) of µTBS were observed for the groups restored with EAs without inorganic content. In conclusion, charging dental adhesives with nanofillers may be a suitable strategy for improving their properties as well as their interaction with dental substrates.

Dynamics modeling and simulation of steel cord conveyor belt based on dynamic elastic modulus

Steel cord conveyor belts are widely used in long-distance transportation of various materials. The steel cord belt is composed of rubber and steel cord core, exhibiting excellent viscoelasticity and complex dynamic characteristics during operation. The existing static elastic modulus cannot accurately reflect the real dynamic properties of the conveyor belt. In this paper, based on the catenary theory, the formula for the dynamic elastic modulus of the conveyor belt is derived by introducing the sag and elastic deformation of the steel cord conveyor belt on the basis of the static elastic modulus. The dynamic modeling of the steel cord conveyor belt is carried out using rigid belt block element + flexible beam method. Then, the RecurDyn software is used to establish the dynamic simulation system of the belt conveyor and conduct simulations, which are validated through a test bench. The results show that dynamics simulation based on the dynamic elastic modulus is closer to the real dynamic characteristics of the belt conveyor. Finally, the dynamic characteristics of belt conveyors under different start-up times, different start-up speeds, and idler spacing are analyzed using this modeling and simulation method. The results demonstrate that the dynamic elastic modulus can accurately reflect the real dynamic properties of the conveyor belt, providing a more accurate dynamic modeling and simulation method for the design of belt conveyors.

The formation young’s modulus and textural attributes of the Axx-field from southern Niger delta, Nigeria

This research was carried out to determine the formation brittleness and textural attributes of an Axx-Field in the Niger Delta Basin. Data available for this study were obtained from three wells (A11, A22 and A33). They were analyzed using Microsoft Excel after spurious values were removed. Two techniques (John Fuller and Plumb Bradford) were used to determine static young's modulus but only one is reported because after statistical analysis on both, the one reported was adequate for accurate outcomes although both approaches have low variance. The results indicates that the highest values of static and dynamic young's modulus are 2.05 x 1025N/m2 and 1.93 x 1010N/m2 respectively. The lowest values are 1.1 x 1024N/m2 and 8.5 x 109N/m2 respectively for well A11. The average values are 1.024 x 1025N/m2 and 5.25 x 1023N/m2 for this well. For well A22, the highest and lowest values of dynamic young’s modulus are 1.5848 x 1010N/m2 and 1.5726 x 1010N/m2 while those of static are correspondingly 1.47 x 1025N/m2 and 9.01 x 1014N/m2. Their average values are 1.5787 x 1010N/m2 and 7.35 x 1024N/m2 for dynamic and static young's moduli respectively. Also, for well A33, dynamic has the lowest value as 3.28 x 1010 N/m2; static has 8.36 x 1014N/m2 and their highest correspond to 2.04 x 1010N/m2 and 7.08 x 1025N/m2. The average value for this well are 2.66 x 1010N/m2 and 3.54 x 1025 N/m2 for dynamic and static respectively. The static Young's modulus results define the formation as brittle, whose environment is extremely poorly sorted, very fine skewed and very leptokurtic with low energy for well A11, very poorly sorted, fine skewed and platykurtic for well A22, extremely poorly sorted, very fine skewed and mesokurtic for well A33.

A proposed correlation between dynamic and static plate load test moduli for gravelly soils

ABSTRACT Egypt is currently developing huge housing projects at the New Capital, Alamein, and other Egyptian cities. These projects often require soil replacement for roads and buildings. Among the causes of problems observed in some housing projects in the last decade are improper type of soil replacement material and inadequate compaction. Pit-run gravelly soils are commonly recommended for soil replacement because they have the advantages of providing high stiffness, low permeability inherited from their fines’ content and wide availability in Egypt. It is common to use sand cone test and/or static plate load test (SPLT) to assess the quality of compaction. The sand cone test is simple, cheap and rapid; however, it is not reliable with gravel sizes usually found in pit-run gravel, which may exceed 38 mm. Although the SPLT is efficient to assess the quality of compaction and the deformation modulus, it is relatively expensive and time-consuming. The dynamic plate load test is a reliable solution to combine the advantages of both the sand cone test and SPLT. This research includes a detailed laboratory characterization of pit-run gravel collected from Suez deserts and a field testing program including static and dynamic plate load tests on pit-run gravelly soil carried out at several sites in the new capital of Egypt to obtain static and dynamic plate load tests moduli. A statistical approach based on percent of exceedance criterion is adopted to obtain a simple correlation between the static and dynamic plate load test deformation moduli.

Experimental investigation and statistical evaluation of the effects of steel fiber aspect ratio and fiber rate on static and dynamic mechanical properties of concrete

Static and dynamic mechanical properties of steel fiber concretes were determined by experiments conducted on concretes produced using fibers of different volume ratios and aspect ratios, and variance analysis was applied to the experimental results and evaluated statistically. Flexural toughness, static and dynamic elasticity modules and Poisson ratios of steel fiber reinforced concrete (SFRC) were determined experimentally. Load-deflection curves under flexural loading and stress-strain curves under compressive loading were obtained and compared with each other. The most influential variable was aspect ratio of fibers affecting each feature. As the aspect ratio increased, the static elasticity modulus of concrete increased by 29.66 %, the dynamic elasticity modulus increased by 21.58 % and the Poisson ratio increased by 27.46 % compared to the control sample. The Poisson ratio of SFRC varies between 0.1825 and 0.246. A relation was obtained between static and dynamic modulus of elasticity. Mechanical properties were improved by using steel fibers with low amounts but high AR values. To achieve high flexural toughness, static and dynamic elasticity modules and Poisson ratio, aspect ratio of fiber should be increased.

Static elastic modulus prediction at early ages using a modified resonant test for concrete cylinders using mems microphones

Concrete Young’s modulus is seldom verified on-site due to the time-consuming and costly nature of current testing standards. This article proposes a new, quick and affordable testing methodology to estimate the ultimate static elastic modulus of normal strength concrete cylinders on-site at early ages using a smartphone. Impact-resonance tests were performed on several concrete cylinders from different mixtures at different ages, using an accelerometer and a smartphone microphone to measure the cylinders' flexural and longitudinal resonant frequencies. Measurements from both sensors were compared to show the validity of estimating the dynamic elastic modulus using acoustic signals from the cylinders recorded with a smartphone's built-in microphone. The cylinders' static and dynamic elastic moduli were determined, and the change in elastic modulus over time as the cylinders aged was also examined. This study shows the advantages of microphones over accelerometers, being less susceptible to measurement errors and proposes a filter algorithm to extract the resonant frequencies from environmental noise. A forecasting methodology to estimate static elastic modulus based on early dynamic impact-resonant tests can help engineers make early decisions on their supplied concrete on-site.

Hydrate reservoir deformation under multi-well strategies based on the dynamic elastic modulus relationship

In order to demonstrate the safety of the multi-well mining method, stratum deformation using multi-well systems is discussed. Firstly, ultrasonic experiments and triaxial tests of hydrate-bearing sediments under different confining pressure and hydrate saturation conditions were carried out. The soil static elastic modulus was compared with the dynamic elastic modulus relationship. Then the dynamic elastic modulus relations were applied to the multi-field coupling model to simulate the hydrate mining process in reservoirs by multi-well strategies. The experimental results show that hydrate saturation impacts the elastic modulus more than the effective confining pressure. In the simulation results, with the increase of the reservoir depth, the soil settlement shows a trend from small to large and then to small. The maximum soil displacement is located at the junction between the hydrate and the overlying layers, regarded as the weak point. In addition, increasing the well branches, expanding the well spacing, and increasing the wellhead radius can increase gas production. However, at the same time, it will also increase the reservoir deformation, thus posing risks to the stability of the formation and extraction wells. On this basis, the efficiency-safety factor was set, and the best mining scheme was determined.

Controls on mechanical properties of a carbonate mudstone: Insights from non-destructive techniques and geochemical data

This study quantifies geomechanical properties of carbonate mudrocks in the Arabian intra-shelf basin, focusing on different sedimentologic zones (proximal to distal). Core-based mechanical properties were obtained through unconfined conditions. Micro Rebound Testing (MRT) was conducted on 700′ ft of core at 0.5 ft intervals to capture high-resolution rock hardness (HLD), unconfined compressive strength (UCS), and static Young's Modulus (E). Additional tests validated log-based parameters, including impulse hammer, acoustic velocity testing for (E), P-wave and S-wave velocities (Vp and Vs), scratch testing, and XRF/XRD analyses for mineralogical and elemental variability impact on mechanical properties.Multivariate statistical analysis correlates mechanical properties with elemental data, showing direct proportionality to calcium percentage, (E), Vp, and Vs, while inversely correlated to aluminum, iron, sulfur, and total organic carbon (TOC), especially in distal zones. Porosity, as measured by neutron porosity log, is a significant control on mechanical properties, with higher porosity resulting in lower mechanical properties at any given calcium percentage. Variations in geomechanical properties within each zone are principally controlled by depositional environments, sediment supply, diagenesis, and a pycnocline dividing the water column into anoxic, dysoxic (or suboxic), and oxic conditions.Zone 1A and 4 exhibit high brittleness characterized by high Ca-calcite, HLD, (E), Vp, Vs., low terrigenous elements/minerals, and porosity. Zone 1B and 2A are moderately brittle, showing a slight decrease in brittleness and a slight increase in terrigenous elements/minerals, porosity, and organic matter, particularly in the distal zone (Zone 1B). Zone 2B, 3A, and 3B represent moderate to highly ductile zones with low levels of Ca-calcite, HLD, (E), Vp, Vs, and an increase in terrigenous elements/minerals, porosity, and TOC, especially in the distal zone (Zone 2B and 3B). This study highlights the value of high-resolution mechanical data from cores with applications for improved stress estimation and hydraulic fracture stimulation in unconventional reservoirs.

Prediction Models for Mechanical Properties of Cement-Bound Aggregate with Waste Rubber

The high stiffness of cement-bound aggregate (CBA) is recognized as its main drawback. The stiffness is described by the modulus of elasticity, which is difficult to determine precisely in CBA. Incorporating rubber in these mixtures reduces their stiffness, but mathematical models of the influence of rubber on the mechanical characteristics have not previously been defined. The scope of this research was to define a prediction model for the compressive strength (fc), dynamic modulus of elasticity (Edyn) and static modulus of elasticity (Est) based on the measured ultrasonic pulse velocity as a non-destructive test method. The difference between these two modules is based on the measurement method. Within this research, the cement and waste rubber content were varied, and the mechanical properties were determined for three curing periods. The Edyn was measured using the ultrasonic pulse velocity (UPV), while the Est was determined using three-dimensional digital image correlation (3D DIC). The influence of the amount of cement and rubber and the curing period on the UPV was determined. The development of prediction models for estimating the fc and Est of CBA modified with waste rubber based on the non-destructive test results is highlighted as the most significant contribution of this work. The curing period was statistically significant for the prediction of the Est, which points to the development of CBA elastic properties through different stages during the cement-hydration process. By contrast, the curing period was not statistically significant when estimating the fc, resulting in a simplified, practical and usable prediction model.

Correlation between Static and Dynamic Young’s Modulus of Elasticity of Different Types of Rocks

Correlation between static and dynamic elastic modulus in rocks has often been addressed in various studies. In this study, the correlation between the static and dynamic elastic modulus of six different sedimentary, metamorphic and igneous rock types namely coarse-grained sandstone, fine-grained sandstone, schist, quartzite, basalt and granite are studied. Physical properties such as bulk density and porosity are evaluated of all samples. Static elastic modulus is determined by uniaxial compression test and dynamic elastic modulus is found out by ultrasonic pulse velocity testing. Scanning Electron Microscope experiment, X-Ray Diffraction experiment are also conducted on all the samples for mineralogical and petrological studies. The individual correlation between the static and dynamic elastic modulus of all the rock types have been proposed using linear regression with zero intercept and high values of coefficient of determination. These equations are useful in calculating the static elastic modulus using non-destructive techniques, in a wide range of rock materials. Finally, a general linear equation has been developed to relate ratio of static and dynamic elastic modulus with density of the rock.

Varijacija fizičkih i mehaničkih osobina betona po visini

Introduction/purpose: Concrete, mortar, and cement pastes are materials that have become central in various fields of construction, structures, and civil engineering. About 7 billion cubic meters of concrete are implemented. Concrete is generally considered a homogeneous material, but that is not always the case given its rheological behavior, which can be due to heterogeneous phenomena of segregation and bleeding. Methods: The study tested a concrete column's physical and mechanical characteristics and deformation in elevation. The tests included measuring absolute and apparent density, porosity, capillary absorption, permeability, speed of propagation, compressive strength, and static and dynamic modulus of elasticity. For this purpose, the standards of non-destructive testing (sclerometer, ultrasound, etc.) were used to take the average of a series of points located at different levels of the element to be tested. Results: The results indicate that changes in the column's height affect its physical and mechanical properties, either increasing or decreasing them (such as porosity, absorbency, permeability, compressive strength, and the static and dynamic modulus of elasticity). These changes are influenced by various factors, including the inherent properties of the concrete implementation (such as vibration and curing) and the climate conditions during construction. Conclusion: The findings of this study emphasize the importance of a nuanced approach to testing and evaluating variations in concrete properties by taking into account the multifaceted impact of changes in column height.

Methodological Challenges in Accounting for Test\ Conditions When Determining the Static Elastic Modulus of Advanced Aramid Structural Fibers

Methodological Challenges in Accounting for Test\ Conditions When Determining the Static Elastic Modulus of Advanced Aramid Structural Fibers

FLEXURAL AND DURABILITY CHARACTERIZATION OF CONCRETE REINFORCED WITH TREATED BAMBOO AS AN ALTERNATIVE BUILDING MATERIAL

Abstract The cost and environmental problems associated with steel as a reinforcement material in concrete has necessitated the need to research for alternative reinforcement materials, and bamboo is one of them. The flexural and durability characteristics of bamboo reinforced concrete (BRC) samples under harsh environmental condition was simulated by curing samples in an alkaline solution. Bamboo splints that were coated with sanded bitumen were used to reinforce the concrete samples with unreinforced concrete (UC) serving as control. The BRC samples were cured in normal water and an equal number were cured in 5% Sodium Hydroxide (NaOH) alkaline solution. Samples from both curing conditions and another of the control were tested for flexural strengths after 7, 14, 28, 56, and 76 days of curing respectively and results compared. Water absorption rates after each curing period were also taken. Ultrasonic pulse velocity (UPV) tests were also conducted on the samples to find out the composite qualities. The results showed that BRC had twice as much flexural strength than UC but reduced in strength by 17.9% in the alkaline environment after 28 days of curing. In addition to possessing acceptable strength values under normal water and alkaline solution curing situations by ponding, all the samples had elastic dynamic modulus and static modulus values that exceeded minimum recommended values by the relevant standards.

Assessing the influence of sugarcane bagasse ash for the production of eco-friendly concrete: Experimental and machine learning approaches

The innovative utilization of sugarcane bagasse ash (SCBA) in producing lightweight concrete (LWC) needs to be explored experimentally and quantification with machine learning approaches. Therefore, this study aims to investigate fresh, mechanical and microstructural characteristics and machine learning modeling of incorporating SCBA as a partial substitute of cement. In this investigation, OPC was replaced partially by the weight of SCBA in the proportion of 0 %, 5 %, 10 %, 15 %, and 20 %. The influences of SCBA on the fresh characteristics of concrete were investigated through tests of the slump, compacting factor, Kelly ball, k-slump, density, and air content. In addition, for hardened properties compressive, splitting tensile, flexural strength, and static modulus of elasticity were tested at 7 and 28 days. Furthermore, a microstructural characteristic was carried out for varying content of SCBA. Different machine learning (ML) predictive models were performed utilizing artificial neural network (ANN) and random forest (RF), to predict the fresh and mechanical attributes of the LWC. It was noticed that the workability value of fresh concrete was enhanced almost by 40 % to 50 % with the incorporation of SCBA content. The hardened test results revealed that a mixture having SCBA up to 10 % content SCBA resulted in nearly 10 % to 30 % better performance to satisfy the requirement of LWC. Regarding the sustainability assessment, the less embodied CO2 (eCO2) is produced in SCBA mixes, whereas it is also economically beneficial to produce SCBA mixes. Models' efficacy was evaluated including mean absolute error (MAE), root mean squared error (RMSE), and coefficient of determination (R2). The maximum R2 and minimum RMSE came across for RF (0.989 and 1.393, respectively) which provides the well estimation of the model.

Study on the Characterization of Physical, Mechanical, and Mildew Resistance Properties of Enzymatically Treated Bamboo Fiber-Reinforced Polypropylene Composites

The enhancement of the physical and mechanical properties and the anti-mildew performance of wood–plastic composites are of great significance for broadening their application field. In this research, bamboo fibers underwent treatments with safe, environmentally friendly bio-enzymes. Subsequently, a bamboo–plastic composite (BPC) was developed using the modified bamboo fibers and polyethylene. The effects of biological enzymatic treatments on the surface free energy, the chemical composition of the bamboo fibers, water resistance, thermal stability, bending performance, impact performance, and anti-mildew performance of the BPC samples were analyzed. This study revealed that treating bamboo powder with bio-enzymes (xylanase, lipase, laccase, pectinase, hemicellulase, or amylase) decreased the surface free energy and the polar components of the bamboo fibers while improving the surface O/C atomic ratio of the bamboo fibers. These enzyme treatments enhanced the water resistance, bending performance, and anti-mildew performance of the BPC samples. However, on the whole, the thermal stability of the composites decreased. Particularly, after hemicellulase treatment, the composites had the lowest water absorption, reflecting a decrease of 68.25% compared to the control group. With xylanase modification, the 24 h water absorption thickness swelling rate of the composites was the lowest, reflecting a decrease of 71.27% compared to the control group. After pectinase modification, the static bending strength and elastic modulus of the prepared composites were the highest, with an increase of 15.45% and 13.31%, respectively, compared to the unmodified group. After xylanase modification, the composites exhibited the best anti-mildew effect, with an anti-mold effectiveness of 74.67%. In conclusion, bio-enzyme treatments can enhance the physical and mechanical properties and anti-mildew performance of BPCs. This research provides a theoretical foundation for the preparation of high-performance wood–plastic composites.

Effect of hybrid polypropylene fibers on mechanical and shrinkage behavior of alkali-activated slag concrete

The growing global demand for cement in construction led to an increase in environmental concerns from the carbon dioxide gas release associated with its production. To foster the acceptance of other alternatives, such as alkali-activated slag (AAS) systems, mitigation of their main drawbacks, notably high shrinkage, is imperative. This study explores the influence of macro and micro polypropylene (PP) fiber hybridization in AAS concrete. Seven mixes with different fiber volume fractions (VF) of macro and hybrid fibers, in addition to a control mix, were investigated. Three macro-PP fiber mixes had fiber VFs of 0.3 %, 0.6 %, and 0.9 %. The other three hybrid PP fiber mixes were like macro fiber mixes with the addition of 0.1 % microfibers. The influence of PP fiber hybridization was explored concerning flowability, static elastic modulus, compressive, splitting tensile, and 3-point flexural strength and compared to control and macro-PP fiber mixes. Additionally, Shrinkage was measured for control and optimum fiber mixes. The results showed that the hybridization of PP fibers led to reductions in shrinkage up to 15 % compared to the control mix, while macro-PP fibers reached a maximum reduction of 6 %. Furthermore, the study evaluates the applicability of various literature and current code guidelines for predicting elastic modulus and tensile strength with the experimental results. ACI 318 could provide relatively accurate predictions in terms of splitting tensile and flexural strengths. Apart from that, with some exceptions, other codes and proposed equations in the literature were inadequate in providing satisfactory predictions.

Digital rock advances from a material point method approach for simulation of frame moduli and a sedimentary petrology-inspired method for creation of synthetic samples through simulation of deposition and diagenesis

We compare hydromechanical simulation results that use two alternative sources of 3D digital rock input: micro-CT analysis and “synthetic rocks” created by using a newly developed process simulation methodology that more rigorously reflects knowledge from sedimentary petrology compared with previous efforts. We evaluate the performance of these alternative representations using St. Peter Sandstone samples where “dry” static bulk modulus ( K) and shear modulus ( G) are simulated using a new extension of the material point method that resolves contacts using high-resolution surface meshes and considers three alternative contact modeling approaches: “purely frictional,” “fully bonded,” and “cohesive zones.” We evaluate the model performance on two samples from the data set with multiple static moduli measurements (sample 1_2: porosity 24.6 vol%, K 10.2–14.7 GPa, and G 11.6–14.0 GPa; sample 11_2: porosity 12.4 vol%, K 13.5–24.6 GPa, and G 12.8–17.9 GPa). Purely frictional results underpredict measured modulus values, whereas fully bonded results overpredict them. Measured values are most closely approximated by results with cohesive zones that consider sets of discrete spring-like features at contacts. In contrast, shear modulus results from finite-element model simulations on structured grids tend to be significantly greater than measured values, particularly for samples with <18 vol% porosity. Permeability values from digital rock-physics simulations for the studied samples are within factors of 2–5 of conventional core analysis measurements (2860 and 58 mD for samples 1_2 and 11_2, respectively). We determine that the process modeling approach (1) accurately reproduces the measured rock microstructure parameters from thin-section analysis, (2) leads to simulation results for dry static moduli and permeability with accuracy comparable to simulations that use micro-CT samples, and (3) provides a rigorous basis for predicting diagenetically induced variations in hydromechanical properties over the range from unconsolidated sand to indurated rock.

A comparison of magneto-responsive particles and testing protocols for active rheology control of cementitious materials

Magneto-responsive cementitious materials with magnetic interventions enable on-demand and real-time adjustment of rheology. This research aims to elaborate the early-stage magneto response of cement pastes using different types of Fe3O4 particles and carbonyl iron particles. A series of methods to evaluate the magnetorheological response of cementitious materials were established. The magneto-responsive cement pastes were tested by shear test and small amplitude oscillatory shear test at constant and time-varying magnetic fields. The increase of static yield stress and storage modulus after applying a magnetic field was a time-dependent process, while the decrease of static yield stress and storage modulus was an instant process at the moment of removing magnetic fields. Such a procedure can be reversibly controlled in real time. The cement pastes containing different magneto-responsive particles showed significant difference in the onset of flow and structural build-up. With the intervention of a magnetic field, the static yield stress and storage modulus of mixtures with carbonyl iron particles were able to increase with one order of magnitude. Compared with the particle size distribution and particle morphology, the magnetic parameters of magneto-responsive particles dominated the magnetorheological properties of cementitious materials. Shear tests were found the most effective to evaluate the magneto response of cement pastes with the intervention of a magnetic field.