Analyzing the early structural build-up of accelerated cement pastes

AbstractExtrusion-based additive manufacturing imposes high requirements on the material stability right after the extrusion. Therefore, a thorough understanding of the chemical reactions that determine the early reduction in processability is necessary. Accelerators are especially considered here, which have a major influence on the early reaction. This study contributes to these issues by analyzing the influence of 0.1 wt% TEA (triethanolamine) and 2.0 wt% Ca(NO3)2 on the hydration of two CEM I 52.5 R. The hydration was analyzed by isothermal heat flow calorimetry and in-situ X-ray diffraction. Vicat needle penetration, a penetrometer of own design, and ultrasonic P-wave velocity development were used to monitor the early change in workability. The obtained results indicate that ettringite formation is the main factor influencing workability during the first 60 min of hydration. Afterwards, the influence of ettringite is exceeded by the formation of C–S–H. Ca(NO3)2 was shown to enhance C–S–H formation and had no significant effect on the workability during the first 60 min of hydration while rapidly decreasing workability during the induction period. TEA was shown to increase brownmillerite dissolution and ettringite formation and, consequently, promote the workability loss during the initial hydration period. The time of initial and final setting determined by the Vicat needle test depended mainly on the formation of C–S–H phases.

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Simulation of the effect of stress-induced anisotropy on borehole compressional wave propagation

Geophysics ◽

10.1190/geo2013-0186.1 ◽

2014 ◽

Vol 79 (4) ◽

pp. D205-D216 ◽

Cited By ~ 13

Author(s):

Xinding Fang ◽

Michael C. Fehler ◽

Arthur Cheng

Keyword(s):

Wave Propagation ◽

Stress Concentration ◽

Elastic Properties ◽

Wave Velocity ◽

Wave Amplitude ◽

P Wave ◽

Azimuthal Variation ◽

P Wave Velocity ◽

Velocity Region

Formation elastic properties near a borehole may be altered from their original state due to the stress concentration around the borehole. This can lead to an incorrect estimation of formation elastic properties measured from sonic logs. Previous work has focused on estimating the elastic properties of the formation surrounding a borehole under anisotropic stress loading. We studied the effect of borehole stress concentration on sonic logging in a moderately consolidated Berea sandstone using a two-step approach. First, we used an iterative approach, which combines a rock-physics model and a finite-element method, to calculate the stress-dependent elastic properties of the rock around a borehole subjected to an anisotropic stress loading. Second, we used the anisotropic elastic model obtained from the first step and a finite-difference method to simulate the acoustic response of the borehole. Although we neglected the effects of rock failure and stress-induced crack opening, our modeling results provided important insights into the characteristics of borehole P-wave propagation when anisotropic in situ stresses are present. Our simulation results were consistent with the published laboratory measurements, which indicate that azimuthal variation of the P-wave velocity around a borehole subjected to uniaxial loading is not a simple cosine function. However, on field scale, the azimuthal variation in P-wave velocity might not be apparent at conventional logging frequencies. We found that the low-velocity region along the wellbore acts as an acoustic focusing zone that substantially enhances the P-wave amplitude, whereas the high-velocity region caused by the stress concentration near the borehole results in a significantly reduced P-wave amplitude. This results in strong azimuthal variation of P-wave amplitude, which may be used to infer the in situ stress state.

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Investigation on the Effect of Hydroxyapatite Nanorod on Cement Hydration and Strength Development

Journal of Nanoscience and Nanotechnology ◽

10.1166/jnn.2021.17387 ◽

2021 ◽

Vol 21 (3) ◽

pp. 1578-1589

Author(s):

Han Yan ◽

Qianping Ran ◽

Yong Yang ◽

Xin Shu ◽

Qian Zhang ◽

...

Keyword(s):

Isothermal Calorimetry ◽

Superior Performance ◽

Strength Development ◽

Hydration Reaction ◽

X Ray Diffraction ◽

Early Hydration ◽

Cement Pastes ◽

Supplementary Cementitious Material ◽

Acceleration Period

This work investigated the effect of hydroxyapatite (HA) nanorods on the strength development and hydration of cement. Undispersed HA nanorods (HA-UD) and dispersed HA nanorods (HA-DN) were prepared by atom-efficient neutralization. The strength of mortars modified by HA nanorods was tested, as well as their compatibility with supplementary cementitious material. The hydration of HA-modified cement pastes was characterized via in situ X-ray diffraction, isothermal calorimetry and scanning electron microscopy. As the results suggest, the undispersed HA-DN caused a considerable increase in superplasticizer demand to achieve the same level of flow. Both HA nanorods showed a significant accelerating effect on early hydration, with approximately 100% strength enhancement at 12 h at 2.0% dosage. The effect on early strength of the nanorods is retained in systems with up to 30% fly ash in the binder mass. According to the characterizations, the rate of the hydration reaction in the acceleration period was enhanced by HA nanorods, and C3S consumption was also increased. In all of the testing situations, HA-DN showed superior performance, likely due to improved spatial distribution of the hydroxyapatites. The results suggest that proper dispersion of the nanorods is necessary to optimize its performance.

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Determination of rock densities in the Carpathian-Pannonian Basin lithosphere: based on the CELEBRATION 2000 experiment

Contributions to Geophysics and Geodesy ◽

10.1515/congeo-2016-0016 ◽

2016 ◽

Vol 46 (4) ◽

pp. 269-287 ◽

Cited By ~ 1

Author(s):

Barbora Šimonová ◽

Miroslav Bielik

Keyword(s):

Lower Crust ◽

Pannonian Basin ◽

Average Density ◽

East European Craton ◽

P Wave ◽

Seismic Velocities ◽

Upper Crust ◽

East European ◽

P Wave Velocity

Abstract The international seismic project CELEBRATION 2000 brought very good information about the P-wave velocity distribution in the Carpathian-Pannonian Basin litosphere. In this paper seismic data were used for transformations of in situ P-wave velocities to in situ densities along all profiles running across the Western Carpathians and the Pannonian Basin: CEL01, CEL04, CEL05, CEL06, CEL09, CEL11 and CEL12. The calculation of rock densities in the crust and lower lithosphere was done by the transformation of seismic velocities to densities using the formulae of Sobolev-Babeyko, Christensen-Mooney and in the lower lithosphere also by Lachenbruch-Morgan’s formula. The density of the upper crust changes significantly in the vertical and horizontal directions, while the interval ranges of the calculated lower crust densities narrow down prominently. The lower lithosphere is the most homogeneous - the intervals of the calculated densities for this layer are already very narrow. The average density of the upper crust (ρ̅ = 2.60 g · cm−3) is the lowest in the Carpathian Foredeep region. On the contrary, the highest density of this layer (ρ̅ = 2.77 g · cm−3) is located in the Bohemian Massif. The average densities ρ̅ of the lower crust vary between 2.90 and 2.98 g · cm−3. The Palaeozoic Platform and the East European Craton have the highest density (ρ̅ = 2.98 g · cm−3 and ρ̅ = 2.97 g · cm−3, respectively). The lower crust density is the lowest (ρ̅ = 2.90 g · cm−3) in the Pannonian Basin. The range of calculated average densities ρ̅ for the lower lithosphere is changed in the interval from 3.35 to 3.40 g · cm−3. The heaviest lower lithosphere can be observed in the East European Craton (ρ̅ = 3.40 g · cm−3). The lower lithosphere of the Transdanubian Range and the Palaeozoic Platform is characterized by the lowest density ρ̅ = 3.35 g · cm−3.

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Tomographic imaging of velocity and Q, with application to crosswell seismic data from the Gypsy Pilot Site, Oklahoma

Geophysics ◽

10.1190/1.1444281 ◽

1997 ◽

Vol 62 (6) ◽

pp. 1804-1811 ◽

Cited By ~ 25

Author(s):

Qingbo Liao ◽

George A. McMechan

Keyword(s):

Velocity Ratio ◽

Synthetic Data ◽

P Wave ◽

Reconstruction Technique ◽

Shift Method ◽

New Information ◽

P Wave Velocity ◽

Iterative Reconstruction Technique ◽

Interwell Connectivity

The centroid frequency shift method is implemented, tested with synthetic data, and applied to field data from three contiguous crosswell seismic experiments at the Gypsy Pilot in northern Oklahoma. The similtaneous iterative reconstruction technique is used for tomographic estimations of both P‐wave velocity and Q. No amplitude corrections or spreading loss corrections are needed for the Q estimation. The estimated in‐situ velocity and Q distributions correlate well with log data and local lithology. The Q/velocity ratio appears to correlate with the sand/shale ratio (ranging from an average of ∼15 s/km for the sand‐dominated lithologies to an average of ∼8.5 s/km for the shale‐dominated ones), with the result that new information is provided on interwell connectivity.

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Identification of gas hydrate dissociation from wireline-log data in the Shenhu area, South China Sea

Geophysics ◽

10.1190/geo2011-0324.1 ◽

2012 ◽

Vol 77 (3) ◽

pp. B125-B134 ◽

Cited By ~ 16

Author(s):

Xiujuan Wang ◽

Myung Lee ◽

Shiguo Wu ◽

Shengxiong Yang

Keyword(s):

Wave Velocity ◽

Gas Hydrate ◽

Seismic Data ◽

Pore Space ◽

P Wave ◽

Well Log ◽

Hydrate Dissociation ◽

Free Gas ◽

P Wave Velocity

Wireline logs were acquired in eight wells during China’s first gas hydrate drilling expedition (GMGS-1) in April–June of 2007. Well logs obtained from site SH3 indicated gas hydrate was present in the depth range of 195–206 m below seafloor with a maximum pore-space gas hydrate saturation, calculated from pore water freshening, of about 26%. Assuming gas hydrate is uniformly distributed in the sediments, resistivity calculations using Archie’s equation yielded hydrate-saturation trends similar to those from chloride concentrations. However, the measured compressional (P-wave) velocities decreased sharply at the depth between 194 and 199 mbsf, dropping as low as [Formula: see text], indicating the presence of free gas in the pore space, possibly caused by the dissociation of gas hydrate during drilling. Because surface seismic data acquired prior to drilling were not influenced by the in situ gas hydrate dissociation, surface seismic data could be used to identify the cause of the low P-wave velocity observed in the well log. To determine whether the low well-log P-wave velocity was caused by in situ free gas or by gas hydrate dissociation, synthetic seismograms were generated using the measured well-log P-wave velocity along with velocities calculated assuming both gas hydrate and free gas in the pore space. Comparing the surface seismic data with various synthetic seismograms suggested that low P-wave velocities were likely caused by the dissociation of in situ gas hydrate during drilling.

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Estimating uniaxial compressive strength, density and porosity of rocks from the p-wave velocity measurements in-situ and in the laboratory

REM - International Engineering Journal ◽

10.1590/0370-44672021740022 ◽

2021 ◽

Vol 74 (4) ◽

pp. 521-528

Author(s):

André Cezar Zingano ◽

Paulo Salvadoretti ◽

Rafael Ubirajara Rocha ◽

João Felipe Coimbra Leite Costa

Keyword(s):

Compressive Strength ◽

Uniaxial Compressive Strength ◽

Wave Velocity ◽

P Wave ◽

Velocity Measurements ◽

P Wave Velocity

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P-wave velocity differences between surface-derived and core samples from the Sulu ultrahigh-pressure terrane: Implications for in situ velocities at great depths

Geology ◽

10.1130/g33045.1 ◽

2012 ◽

Vol 40 (7) ◽

pp. 651-654 ◽

Cited By ~ 10

Author(s):

Shengsi Sun ◽

Shaocheng Ji ◽

Qian Wang ◽

Matthew Salisbury ◽

Hartmut Kern

Keyword(s):

Wave Velocity ◽

P Wave ◽

Ultrahigh Pressure ◽

Core Samples ◽

P Wave Velocity

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Influence of superplasticizers on the evolution of ultrasonic P-wave velocity through cement pastes at early age

Cement and Concrete Research ◽

10.1016/j.cemconres.2013.04.007 ◽

2013 ◽

Vol 51 ◽

pp. 22-31 ◽

Cited By ~ 14

Author(s):

G. Trtnik ◽

G. Turk

Keyword(s):

Wave Velocity ◽

P Wave ◽

Early Age ◽

Cement Pastes ◽

P Wave Velocity

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In‐situ, high‐frequency P-wave velocity measurements within 1 m of the earth’s surface

Geophysics ◽

10.1190/1.1444537 ◽

1999 ◽

Vol 64 (2) ◽

pp. 323-325 ◽

Cited By ~ 31

Author(s):

Gregory S. Baker ◽

Don W. Steeples ◽

Chris Schmeissner

Keyword(s):

Wave Velocity ◽

Speed Of Sound ◽

P Wave ◽

Sound Waves ◽

Low Velocity ◽

Near Surface ◽

Wave Velocities ◽

P Wave Velocity ◽

P Wave Velocities

Seismic P-wave velocities in near‐surface materials can be much slower than the speed of sound waves in air (normally 335 m/s or 1100 ft/s). Difficulties often arise when measuring these low‐velocity P-waves because of interference by the air wave and the air‐coupled waves near the seismic source, at least when gathering data with the more commonly used shallow P-wave sources. Additional problems in separating the direct and refracted arrivals within ∼2 m of the source arise from source‐generated nonlinear displacement, even when small energy sources such as sledgehammers, small‐caliber rifles, and seismic blasting caps are used. Using an automotive spark plug as an energy source allowed us to measure seismic P-wave velocities accurately, in situ, from a few decimeters to a few meters from the shotpoint. We were able to observe three distinct P-wave velocities at our test site: ∼130m/s, 180m/s, and 300m/s. Even the third layer, which would normally constitute the first detected layer in a shallow‐seismic‐refraction survey, had a P-wave velocity lower than the speed of sound in air.

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