Elastic Modulus Of Cement Paste Research Articles

The influence of multi-scale tough liquid fiber toughening agent on the mechanical properties of oil well cement-based composite materials

Cementing is a key process in drilling engineering, and the cement sheath in cementing can sometime have problems such as significant brittleness, low toughness, and low resistance to impact damage, especially in perforation and fracturing environments where the cement sheath is more susceptible to damage. In response to the above issues, three types of inorganic carbon fibers, including 1 mm carbon fiber, 2 mm carbon fiber, and nanocarbon fiber, were studied indoors to investigate the influence of their ratios on the mechanical properties of cement paste. The optimal mixture of 1 mm carbon fiber, 2 mm carbon fiber, and nanocarbon fiber in a ratio of 3:2:1 was selected, and a multi-scale liquid fiber toughening agent BS-54 was obtained through special liquefaction process treatment. The liquid fiber toughening agent BS-54 has good water dispersibility and can evenly disperse in the slurry water, effectively improving the dispersion and addition of multi-scale fibers in cement slurry. The cement slurry prepared with multi-scale dispersed liquid fiber toughening agent has good rheological properties, water loss, and thickening properties. The addition of multi-scale dispersed liquid fiber toughening agent to cement slurry significantly increases the tensile strength, impact strength, and compressive strength of cement paste, effectively reduces the elastic modulus of cement paste, improves the strength of cement paste, and achieves toughening effect. Microscopic analysis shows that the active nanoparticles dispersed by multi-scale dispersed liquid fiber toughening agents can interweave between gaps, and the dense cross-linked structure formed by their multi-scale micro nano structure improves the toughness and strength of cement slurry. Moreover, the multi-scale dispersed liquid fiber toughening agent cement slurry ensures that the cement stone sample has good integrity under external impact, which is conducive to improving the impact resistance of the cement stone.

Influence of Nano-SiO2 Content on Cement Paste and the Interfacial Transition Zone.

Nano-SiO2 (NS) is widely used in cement-based materials due to its excellent physical properties. To study the influence of NS content on a cement paste and the interfacial transition zone (ITZ), cement paste samples containing nano content ranging from 0 to 2% (by weight of cement) were prepared, and digital image correlation (DIC) technology was applied to test the mechanical properties. Finally, the optimal NS content was obtained with statistical analysis. The mini-slump cone test showed that, with the help of superplasticizer and ultrasonic treatment, the flowability decreased continuously, as the NS content increased. The DIC experimental results showed that NS could effectively improve the mechanical properties of the cement paste and the ITZ. Specifically, at the content level of 1%, the elastic modulus of cement paste and ITZ was 20.95 GPa and 3.20 GPa, respectively. When compared to that without nanomaterials, the increased amplitude was 73.50% and 90.50%, respectively. However, with the further increase in NS content, the mechanical properties decreased, which was mainly caused by the agglomeration of nanomaterials. Additionally, the NS content did not exhibit a significant effect on the thickness of the ITZ, and its value was maintained at 76.91-91.38 μm. SEM confirmed that NS would enhance the microstructure of both cement paste and ITZ.

The Effect of Polymer Elastic Particles Modified with Nano-Silica on the Mechanical Properties of Oil Well Cement-Based Composite Materials.

The integrity of oil well cement sheaths is closely related to the long-term production safety of oil and gas wells. The primary material used to form a cement sheath is brittle. In order to reduce the brittleness of oil well cement and improve its flexibility and resistance to stress damage, nano-silica was used to modify polymer elastic particles, and their properties were analyzed. The influence of the modified polymer particles on the properties of oil well cement-based composite materials was studied, and the microstructure of the polymer particle cement sample was analyzed. The results showed that nano-silica effectively encapsulates polymer particles, improves their hydrophilicity, and achieves a maximum temperature resistance of 415 °C. The effect of the modified polymer particles on the compressive strength of cement sample is reduced. Polymer particles with different dosages can effectively reduce the elastic modulus of cement paste, improve the deformation and elasticity of cement paste, and enhance the toughness of cement paste. Microstructural analysis showed that the polymer particles are embedded in the hydration products, which is the main reason for the improvement in the elasticity of cement paste. At the same time, polymer particle cement slurry can ensure the integrity of the cement sample after it is impacted, which helps to improve the ability of oil well cement-based composite materials to resist stress damage underground.

Modeling the elastic modulus of cement paste with X-ray computed tomography and a hybrid analytical-numerical algorithm: The effect of structural heterogeneity

The elastic modulus is a fundamental parameter that controls the mechanical behavior of cement paste. Because of structural heterogeneity, modeling the elastic modulus remains a challenging problem. In this study, X-ray computed tomography images are used to represent the structural features of cement paste; based on that, a hybrid analytical-numerical algorithm is proposed for modeling the elastic modulus. At the voxel level, a power-law formula relating the grayscale value to the elastic modulus is established using a combination of a hydration model and a self-consistent scheme. At the cement paste level, the finite element method is adopted to achieve homogenization. Special attention is paid to the effect of structural heterogeneity. To that end, the multifractal theory is employed.

Evaluation of elastic modulus of cement paste in sodium sulfate solution by an advanced X-CT–hydration–deterioration model with SC method

The compositions and contents of phases in cement paste soaked in sodium sulfate solution changing with time were investigated in this study. First of all, the porosities in cement paste specimens over time were measured by an in situ X-ray computed tomography (X-ray CT) test. Cement hydration and sulfate erosion occur simultaneously during the soaking process of cement paste specimens in sodium sulfate solution. Therefore, the hydration behaviour and the erosion of sulfates in cement paste were combined in a new way to establish an X-CT–hydration–deterioration model, which was used to calculate the variations of the volume fractions of the phases in cement paste. Subsequently, the volume fractions of each phase were used to calculate the elastic moduli of cement paste specimens with the bulk modulus, shear modulus of each phase and a self-consistent (SC) method. Afterward, the calculated elastic moduli were compared with the experimental results obtained by uniaxial compression test and the error values were 1% for 28 d, 2·5% for 88 d and 5% for 148 d, which were all within 5%, indicating that the advanced X-CT–hydration–deterioration model combined with the SC method can successfully predict the elastic modulus of cement paste eroded in sodium sulfate solution.

Effect of Acid Activation-Hydrophilic-Modified Sepiolite on Comprehensive Properties of Oil-Well Cement

In this paper, sepiolite was treated by acid activation, coupling agent treatment, and sulfonation modification. The purpose of this study was to explore the changes in the fluidity and mechanical properties of sepiolite cement slurry before and after modification. Therefore, the comprehensive properties of unmodified sepiolite fiber (HPS) and acid activation-coupling agent treatment-sulfonated sepiolite fiber (S-O-H-HPS) in oil-well cement slurry were evaluated. FT-IR and microscopic mechanism of cement paste fracture surface before and after sepiolite modification were analyzed. The results showed that HPS can effectively improve the toughness of cement paste, but when the content of HPS was more than 1%, the fluidity of cement paste deteriorated sharply and the compressive strength decreased gradually. The addition of S-O-H-HPS can significantly improve the fluidity and stability of HPS slurry. Without affecting the compressive strength, it can effectively improve the flexural strength and impact strength and reduce the elastic modulus of cement paste. The mechanism analysis showed that S-O-H-HPS can not only form network structure in cement paste but also improve the toughness of cement paste by forming a bridge. This also explains why the strength of S-O-H-HPS cement paste does not decrease significantly with the increase of S-O-H-HPS.

Experimental research for elastic modulus of cement paste at ultra-early age based on indentation technique

Based on the principle of indentation method, a testing method for ultra-early elastic modulus (EMod) of cement paste using micro-force testing machine is proposed in this study. The test results show that if the loading time is less than 2 min, the influence of cement paste viscosity can be neglected, and the ultra-early EMod of cement paste can be measured by this indentation method. Experiments prove that the EMod measured by the indentation method of conical indenter with semiangle of 45° are close to that obtained by the traditional stress-strain testing method. In order to verify the test method, different cement pastes in variety of water-binder (w/b) ratio and fly ash content are prepared, and the error between the indentation method and the traditional stress-strain method is less than 15%. The dynamic EMod is tested through using ultrasonic method, and the overall trend is consistent with the results of the indentation method. The experimental results show the relationship between the ultra-early EMod and time is linear function. Defining the EMod of initial setting time as the zero point, the EMod of the earliest measurable time through traditional stress-strain method as the end point, the ultra-early EMod of cement paste would be predicted by two-point connection. Compared with the indentation method, the error is less than 20%.

Thermal expansion prediction of cement concrete based on a 3D micromechanical model considering interfacial transition zone

Thermal expansion of concrete is a main factor of concrete failures especially in underground waterproof engineering, overlong structural engineering and mass concrete construction. Thus, the coefficient of thermal expansion (CTE) of concrete is an important parameter to be determined. A micromechanical model, namely the 3D Two-Layer Built-in Model is developed to obtain the overall CTE of cement concrete. The existence of interfacial transition zone (ITZ) between aggregate and cement paste is considered in the model, and the ITZ model is simplified as a spring layer with a certain stiffness k. According to the existing testing data of three types of cement concrete whose aggregates are siliceous river gravel (RG), dolomitic limestone (DL) and granite (GR) respectively, the CTEs of prediction model are obtained and validated by the measured values. Moreover, the effects of interface, water cement ratio, volume fraction ratio of fine aggregate to coarse aggregate, air voids, CTE of coarse aggregate and elastic modulus of cement paste on the CTE are analyzed.

Integrated experimental-computational approach for evaluating elastic modulus of cement paste corroded in brine solution on microscale

This paper presented an integrated computational-experimental approach for evaluating elastic modulus of cement paste corroded in brine solution on nanoscale. In the first place, the cured specimens were corroded in brine solution at room temperature for 90 days. Subsequently, the elastic moduli of 32 points of the corroded cement paste specimen were measured by nanoindentation test. Then, a three-dimensional nanoindentation model was established with finite element method and modified constitutive relation. The input parameters of the model were calibrated based on the test results and linear interpolation method. Finally, the difference between the simulation results and the experimental results was compared with good agreement. Therefore, the nanoindentation model established in this paper can predict the nanoindentation experiment well and the modified constitutive relation is effective.

Evaluation of elastic modulus of cement paste corroded in bring solution with advanced homogenization method

This paper presents an integrated investigation of elastic modulus of corroded cement paste by experiments and homogenization calculation. First of all, cured cement paste samples were immersed in brine solution with specific chemical compositions for 60d. Then the elastic moduli of the samples were measured by the nanoindentation test. The test results demonstrated that the elastic moduli of the nanoindentation points decreased, compared with the original cement paste. In addition, X-ray Diffraction (XRD) and Scanning Electron Microscope-Energy Dispersive Spectroscope (SEM-EDS) were combined to analyze the compositions of the corroded cement paste quantitatively. As a result, volume fractions of nine compositions of the corroded cement paste in each nanoindentation point were calculated. Afterward, an advanced homogenization method combining Mori-Tanaka (MT) method with self-consistent (SC) method was proposed to calculate the elastic moduli of the nanoindentation points. The calculation results had good agreement with the experimental results due to small relative difference and standard deviation. The back-scattered electron (BSE) image was used to analyze the elastic moduli distribution of the nanoindentation points as well. The result indicated that the elastic moduli of the nanoindentation points were related to the elastic moduli of their main compositions.

Effect of water and nano-silica solution on the early stages cement hydration

The nanoscopic young’s modulus of cement paste during early ages of hydration in water and nano-silica was investigated by the application of atomic force microscopy (AFM). Peak-Force Quantitative Nano-Mechanical (PFQNM) imaging mode in atomic force microscopy was used to determine elastic modulus of cement paste before and after immersion in water and nano-silica solution. The results clearly show how mechanical and physical properties of cement grains changes progressively to higher values during the hydration process in water and nano-silica.Moreover, an empirical theory on mechanism of hydration development is proposed in the current study based on experimental observations. Average Young’s modulus of condensed cement powder was changed from about 15GPa, for unhydrated state, to 11.3GPa after two hours of hydration in water environment. The average roughness trend was also altered from 8.31nm to 18.2nm during hydration process. Results show that the cement hydration rate in nano-silica solution is much higher than water environment. Moreover transition zone between C-S-H colonies have much higher mechanical properties than the hardest colonies in every ages. In the presence of nano-silica, transition zone has a width of less than 10nm and a surface area of 5% of the overall surface area.

Dynamic elastic modulus of cement paste at early age based on nondestructive test and multiscale prediction model

This paper introduced a nondestructive testing method to evaluate the dynamic elastic modulus of cement paste. Moreover, the effect of water-cement ratio and conventional admixtures on the dynamic elastic modulus of cement paste was investigated, in which three kinds of admixtures were taken into account including viscosity modifying admixture (VMA), silica fume (SF), and shrinkage-reducing admixture (SRA). The experimental results indicate that the dynamic elastic modulus of cement paste increases with decreasing water-cement ratio. The addition of SF increases the dynamic elastic modulus, however, the overdosage of VMA causes its reduction. SRA reduces the dynamic elastic modulus at early age without affecting it in later period. Finally, a multiscale micromechanics approach coupled with a hydration model CEMHYD3D and percolation theory is utilized to predict the elastic modulus of cement paste, and the predictive results by the model are in accordance with the experimental data.

Calculation of elastic modulus of early-age cement paste

Cement-based material can be regarded as a highly heterogeneous material with multiple scales and the elastic constants have different values at different scales. To obtain a global elastic constant for a cement-based composite, a homogeneous method is used to perform the upscaling process. This paper presents a method to obtain the global elastic modulus for cement paste with consideration of capillary water pressure. The elastic modulus of different phases is determined using nano-indentation tests. The volume fractions of different phases in the cement paste are determined by using an isothermal conductive calorimeter and a cement hydration kinetic law at early age. The global elastic modulus of cement paste is calculated based on a self-consistent scheme. Considering that, at very early hydration of cement paste with a high water-to-cement ratio, water occupies a relatively high fraction and its pressure may influence the elastic properties of the paste, capillary water with capillary pressure is considered instead of pure air voids without mechanical properties during the upscaling process in this investigation. The global elastic modulus obtained in this way is compared with the value obtained from impact experiments and good agreement is found.

Permeability and elastic modulus of cement paste as a function of curing temperature

The permeability and elastic modulus of mature cement paste cured at temperatures between 8°C and 60°C were measured using a previously described beam bending method. The permeability increases by two orders of magnitude over this range, with most of the increase occurring when the curing temperature increases from 40°C to 60°C. The elastic modulus varies much less, decreasing by about 20% as the curing temperature increases from 20°C to 60°C. All specimens had very low permeability, k<0.1nm2, despite having relatively high porosity, ϕ ~40%. Concomitant investigations of the microstructure using small angle neutron scattering and thermoporometry indicate that the porosity is characterized by nanometric pores, and that the characteristic size of pores controlling transport increases with curing temperature. The variation of the microstructure with curing temperature is attributed to changes in the pore structure of the calcium–silicate–hydrate reaction product. Both the empirical Carmen–Kozeny, and modified Carmen–Kozeny permeability models suggest that the tortuosity is very high regardless of curing temperature, ξ ~1000.

Effect of Admixtures on Dynamic Elastic Modulus of Cement Paste at Early Age

The elastic modulus of cement paste is the key parameter for characterizing the mechanical response of concrete. In modern concrete technology, the admixtures are often used to enhance the performance of concrete. This paper introduces a nondestructive testing method to evaluate the dynamic elastic modulus of cement paste. Moreover, the effect of water-cement ratio and conventional admixtures on the dynamic elastic modulus of cement paste is investigated, in which three kinds of admixtures are taken into account including Viscosity Modifying Admixture (VMA), Silica Fume (SF), and Shrinkage-Reducing Admixture (SRA). The results from experimental investigation indicate that the dynamic elastic modulus of cement paste increases with decreasing water-cement ratio. The addition of SF increases the dynamic elastic modulus, however, the overdosage of VMA causes its reduction. SRA reduces the elastic modulus at early age without affecting the elastic modulus at later period.

Prediction of the Elastic Modulus of Cement Paste as a Kinetic Hydration Model

This paper describes a numerical method for estimating the elastic modulus of cement paste. The cement paste is modeled as a unit cell, which consists of three parts: dehydrated cement grain, gel, and capillary pore. In the unit cell, the volume fractions of the constituents are quantified with a single kinetic function of the degree of hydration. The elastic modulus of cement paste was calculated from the total displacement of constituents when the uniform pressure was applied to the gel contact area in cement paste assumed a homogenous isotropic matrix. Numerical simulations were conducted through the finite element analysis of the three-dimensional periodic unit cell. The model predictions were compared with experimental results. The predicted trends agree with experimental observations. The approach and some of the results might also be relevant for other technical applications.

複合則理論を用いたコンクリートの乾燥収縮ひずみの予測式 : 終局乾燥収縮ひずみの評価方法

Drying shrinkage of concrete exerts a serious influence toward the long-term reliability such as the durability of the structure. The estimation formula of drying shrinkage of concrete is necessary by using examine this behavior of properties. In this paper, the prediction estimation formula of drying shrinkage strain of concrete is obtained with two-phase composite material model as cement paste and aggregate. The results of the this study are summarized as follows: 1) The elastic modulus of cement paste can be explained as a function of the cement-water ratio and age at drying, as well as drying shrinkage strain. 2) Drying shrinkage of aggregate can be explained as a function of its absorption. 3) Drying shrinkage of concrete can be calculated using five parameters of water-cement ratio, age at drying, the absorption of aggregate, the volume of aggregate and volume-surface ratio of member. The calculated results agreed well with the experimental data.