scholarly journals An Efficient Approach of Predicting the Elastic Property of Hydrating Cement Paste

2021 ◽  
Vol 8 ◽  
Author(s):  
Baoyu Ma ◽  
Guansuo Dui ◽  
Zhenglin Jia ◽  
Bo Yang ◽  
Chunyan Yang ◽  
...  
Keyword(s):  
Elastic Properties ◽  
Cement Paste ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Empirical Method ◽  
Elastic Behavior ◽  
Engineering Practice ◽  
Proposed Model ◽  
Hydration Model ◽  
Semi Empirical

Although elastic properties of hydrating cement paste are crucial in concrete engineering practice, there are only a few widely available models for engineers to predict the elastic behavior of hydrating cement paste. Therefore, in this paper, we derive an analytical model to efficiently predict the elastic properties (e.g., Young’s modulus) of hydrating cement paste. Notably, the proposed model provides the prediction of hydration, percolation, and homogenization of the cement paste, enabling the study of the early age elasticity evolution in cement paste. A hydration model considering the mineral composition and the initial w/c ratio was used, while the percolation threshold was calculated adopting a phenomenological semi-empirical method describing the effects of the solid volume fraction and the w/c ratio. An efficient mixing rule based on the degree of solid connectivity was then adopted to calculate the elastic properties of the hydrating cement paste. Moreover, for ordinary Portland cement, a simplified model was built using Powers’ hydration model. The obtained modeling results are following experimental data and other numerical results available in the literature.

Chemo-Micro-Dilatation Modeling of Carbonation Shrinkage Phenomenon of the Porous Mortars

2011 ◽  
Vol 261-263 ◽  
pp. 680-684 ◽  
Author(s):  
T. X. Dinh ◽  
J. Jeong ◽  
H. Ramézani ◽  
Z. Q. Feng
Keyword(s):  
Cement Paste ◽  
Cement Mortar ◽  
Ph Value ◽  
Empirical Method ◽  
Micro Structure ◽  
Unknown Parameters ◽  
Scientific Goal ◽  
Different Types ◽  
Semi Empirical ◽  
Carbonation Shrinkage

In this paper, we investigate the CO2 carbonation on porous materials such as the cement paste mortar. Our scientific goal is to model the CO2 carbonation effect on the porous cement mortar by the micro-dilatation theory and to determine the chemo-mechanical stress development due to the chemical reactions. In fact, this phenomenon will modify not only the pH value of the cement paste but also the micro-structure due to collapsing pore-network. Based upon the micro-dilatation theory originally proposed by Cowin and Nunziato, four unknown parameters related to the micro-structure will be determined for the cement mortar using the semi-empirical method and numerical modeling. The experimental carbonation tests on two different types of cement paste (CEMI and CEMIII) have been realized to capture carbonated affected zones and to measure their shrinkage deformations.

Measurement of Scattering Coefficients

2011 ◽  
Author(s):  
Dale Chimenti ◽  
Stanislav Rokhlin ◽  
Peter Nagy
Keyword(s):  
Wave Propagation ◽  
Reflection Coefficient ◽  
Transmission Coefficient ◽  
Elastic Properties ◽  
Volume Fraction ◽  
Ultrasonic Field ◽  
Guided Wave ◽  
Scattering Coefficient ◽  
Elastic Behavior ◽  
Scattering Coefficients

In the previous chapters, we saw how waves in composites behaved under various circumstances, depending on material anisotropy and wave propagation direction. The most important function that describes guided wave propagation, and the plate elastic behavior on which propagation depends, is the reflection coefficient (RC) or transmission coefficient (TC). More generally, we can call either one simply, the scattering coefficient (SC). It is clear that the elastic properties of the composite are closely tied to the SC, and in turn the scattering coefficient determines the dispersion spectrum of the composite plate. Measuring the SC provides a route to the inference of the elastic properties. To measure the SC, we need only observe the reflected or transmitted ultrasonic field of the incident acoustic energy. In doing so, however, the scattered ultrasonic field is influenced by several factors, both intrinsic and extrinsic. Clearly, the scattered ultrasonic field of an incident acoustic beam falling on the plate from a surrounding or contacting fluid will be strongly influenced by the RC or TC of the plate material. The scattering coefficients are in turn dependent on the plate elastic properties and structural composition: fiber and matrix properties, fiber volume fraction, layup geometry, and perhaps other factors. These elements are not, however, the only ones to determine the amplitude and spatial distribution of energy in the scattered ultrasonic field. Extrinsic factors such as the finite transmitting and receiving transducers, their focal lengths, and their placement with respect to the sample under study can make contributions to the signal as important as the SC itself. Therefore, a systematic study of the role of the transducer is essential for a complete understanding and correct interpretation of acoustic signals in the scattered field. The interpretation of these signals leads ultimately to the inference of composite elastic properties. As we pointed out in Chapter 5, the near coincidence under some conditions of guided plate wave modes with the zeroes of the reflection coefficient (or peaks in the transmission coefficient) has been exploited many times to reveal the plate’s guided wave mode spectrum.

Circular footings on a cemented layer above weak foundation soil

2005 ◽  
Vol 42 (6) ◽  
pp. 1569-1584 ◽  
Author(s):  
Antônio Thomé ◽  
Maciel Donato ◽  
Nilo Cesar Consoli ◽  
James Graham
Keyword(s):  
Void Ratio ◽  
Lower Layer ◽  
Empirical Method ◽  
Engineering Practice ◽  
Layered System ◽  
Residual Soil ◽  
Layer System ◽  
Foundation Soil ◽  
Predicted Values ◽  
Semi Empirical

This work proposes a method for predicting the behavior of shallow footings bearing on an upper layer of processed cemented soil that overlies a lower layer of weakly bonded residual soil with a high void ratio. The paper describes the results of a series of field plate tests and numerical simulations. The results lead to a semi-empirical method for designing shallow foundations on a double-layer system. The method has been validated by comparison of predicted values with results from a separate series of plate-loading tests. For engineering practice, the proposed method provides acceptable predictions of bearing capacities and load–settlement curves.Key words: footings, cemented layer, layered system, weakly bonded, high void ratio.

scholarly journals Effect of different high surface area silicas on the rheology of cement paste

2020 ◽  
Vol 70 (340) ◽  
pp. 231
Author(s):  
J. I. Tobón ◽  
O. Mendoza ◽  
O. J. Restrepo ◽  
M. V. Borrachero ◽  
J. Payá
Keyword(s):  
Surface Area ◽  
Cement Paste ◽  
Water Demand ◽  
Volume Fraction ◽  
Setting Time ◽  
High Surface ◽  
Solid Volume Fraction ◽  
High Surface Area ◽  
High Specific Surface Area ◽  
Cement Pastes

This work studies the effect of nanosilica (NS) on the rheology of cement paste by comparing it with two high specific surface area silicas: silica fume (SF) and pyrogenic silica (PS). Portland cement pastes were produced with different water-to-cementing material ratios and different solid substitutions of cement by silica. Water demand, setting time, and rheology tests were performed. Results showed that NS and SF decreased plastic viscosity, while PS increased it. Only PS was found to have an effect on yield stress. NS showed the most decreasing effect on viscosity, regardless of its higher water demand. It was concluded that the behavior of pastes containing NS and SF is governed by the “ball-bearing” effect from silica particles, by their agglomeration degree, and their impact on the solid volume fraction. The behavior of pastes containing PS is governed by its ability to absorb a portion of the mixing water.

scholarly journals Mechanisms of Phase Transformation and Creating Mechanical Strength in a Sustainable Calcium Carbonate Cement

2020 ◽  
Author(s):  
Jesús Rodríguez-Sánchez ◽  
Teresa Liberto ◽  
Catherine Barentin ◽  
Dag Kristian Dysthe
Keyword(s):  
Phase Transformation ◽  
Calcium Carbonate ◽  
Mechanical Strength ◽  
Cement Paste ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Fractal Model ◽  
Amorphous Calcium Carbonate ◽  
Carbonate Cement ◽  
In Situ Xrd

Calcium carbonate cements have been synthesized by mixing amorphous calcium carbonate and vaterite powders with water to form a cement paste and study how mechanical strength is created during the setting reaction. In-situ XRD was used to monitor the transformation of ACC and vaterite phases into calcite and a rotational rheometer was used to monitor the strength evolution. There are two characteristic time scales of the strengthening of the cement paste. The short timescale of the order 1 hour is controlled by smoothening of the vaterite grains, allowing closer and therefore adhesive contacts between the grains. The long timescale of the order 10-50 hours is controlled by the phase transformation of vaterite into calcite. This transformation is, unlike in previous studies using stirred reactors, found to be mainly controlled by diffusion in the liquid phase. The evolution of shear strength with solid volume fraction is best explained by a fractal model of the paste structure.

Pressure effect on the hardness of diamond and W2B5: First-principle calculations

2017 ◽  
Vol 31 (12) ◽  
pp. 1750137 ◽  
Author(s):  
Shi-Quan Feng ◽  
Yang Yang ◽  
Jun-Yu Li ◽  
Xiao-Xu Jiang ◽  
Hai-Ning Li ◽  
...  
Keyword(s):  
High Pressure ◽  
Electronic Properties ◽  
Elastic Properties ◽  
Structural Stability ◽  
Pressure Effect ◽  
Empirical Method ◽  
First Principle ◽  
First Principle Calculations ◽  
Semi Empirical

In this paper, we employed first-principle calculations to investigate the elastic properties, electronic properties and hardness of diamond and hexagonal W2B5 compounds under high pressure. The elastic properties were carried out to discuss the structural stability and the bond components of diamond and hexagonal W2B5. The electronic properties were presented to analysis the change of the bond components for W2B5. In addition, the hardness of these two crystals under high pressure was calculated by a semi-empirical method considering the role of metallic components and the effect of pressure on the hardness of diamond and hexagonal W2B5 was discussed.

YIELD STRESS OF FRACTAL AGGREGATES

Fractals ◽  
2015 ◽  
Vol 23 (03) ◽  
pp. 1550028 ◽  
Author(s):  
YUE XI ◽  
JINJIAN CHEN ◽  
YONGFU XU ◽  
FEIFEI CHU ◽  
CHUANXIN LIU
Keyword(s):  
Fractal Dimension ◽  
Yield Stress ◽  
Power Law ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Published Data ◽  
Proposed Model ◽  
Wide Range ◽  
The Relationship ◽  
Theory And Experiments

A model for the yield stress of aggregates is presented that incorporates fractal dimension taking into account the solid volume fraction and the aggregate diameter. The model shows the yield stress (σy) of aggregates increases with the solid volume fraction (ϕs) as a power law, and is given by [Formula: see text], where the exponent (m) is related to fractal dimension (D), and σy0 is a referenced parameter. The relationship between exponent (m) and fractal dimension is validated by published data of aggregates and represents the measured data very well, over a wide range of the solid volume fractions. The referenced parameter (σy0) is calibrated from experiments of yield stress using power law fittings. The agreement between theory and experiments supports the idea that yielding is ultimately caused by the rupture of a few interparticle bonds within aggregates. In addition, the proposed model for the yield stress of aggregates is found to match better with experiments by comparing with all models in literature.

Endoscopy Analysis for the Peristaltic Flow of Nanofluids Containing Carbon Nanotubes with Heat Transfer

2015 ◽  
Vol 70 (9) ◽  
pp. 745-755 ◽  
Author(s):  
Noreen Sher Akbar
Keyword(s):  
Carbon Nanotubes ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Peristaltic Flow ◽  
Governing Equations ◽  
Long Wavelength ◽  
Flow Parameters ◽  
Proposed Model ◽  
Frictional Forces ◽  
Temperature And Pressure

AbstractCu–water nanofluid with carbon nanotubes is considered for the peristaltic flow in an endoscope. The peristaltic flow for nanofluid is modelled considering that the peristaltic rush wave is a sinusoidal wave that propagates along the walls of the tube. The governing equations for the proposed model are simplified by using the assumptions of long-wavelength and low Reynolds number. Exact solutions have been evaluated for velocity, temperature, and pressure gradient. Graphical results for the numerical values of the flow parameters, i.e. Hartmann number M, the solid volume fraction ϕ of the nanoparticles, Grashof number Gr, heat absorption parameter β, and radius of the inner tube ε, have been presented for the pressure difference, frictional forces, velocity profile, and temperature profile, and trapping phenomena have been discussed at the end of the article.

scholarly journals Mechanisms of Phase Transformation and Creating Mechanical Strength in a Sustainable Calcium Carbonate Cement

Materials ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 3582
Author(s):  
Jesús Rodríguez-Sánchez ◽  
Teresa Liberto ◽  
Catherine Barentin ◽  
Dag Kristian Dysthe
Keyword(s):  
Phase Transformation ◽  
Calcium Carbonate ◽  
Mechanical Strength ◽  
Cement Paste ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Fractal Model ◽  
Amorphous Calcium Carbonate ◽  
Carbonate Cement ◽  
Carbonate Cements

Calcium carbonate cements have been synthesized by mixing amorphous calcium carbonate and vaterite powders with water to form a cement paste and study how mechanical strength is created during the setting reaction. In-situ X-ray diffraction (XRD) was used to monitor the transformation of amorphous calcium carbonate (ACC) and vaterite phases into calcite and a rotational rheometer was used to monitor the strength evolution. There are two characteristic timescales of the strengthening of the cement paste. The short timescale of the order 1 h is controlled by smoothening of the vaterite grains, allowing closer and therefore adhesive contacts between the grains. The long timescale of the order 10–50 h is controlled by the phase transformation of vaterite into calcite. This transformation is, unlike in previous studies using stirred reactors, found to be mainly controlled by diffusion in the liquid phase. The evolution of shear strength with solid volume fraction is best explained by a fractal model of the paste structure.

Sign in / Sign up

Export Citation Format

Share Document