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Displaying 76 - 100 of 164

Direct Measurements of 3D Structure, Chemistry, and Mass Density During the Induction Period of C3S Hydration

July 27, 2016
Author(s)
Qinang Hu, Mohammed Aboustait, Taehwan Kim, Tyler Ley, Jeffrey W. Bullard, Jay C. Hanan, Volker Rose, Robert Winarski
The reasons for the start and end of the induction period remain a mystery in cement hydration. One long-standing hypothesis is the importance of early hydration products on the surface of cement particles. However, because this material is not widely

Direct Three-Dimensional Observation of the Microstructure and Chemistry of C3S Hydration

July 14, 2016
Author(s)
Qinang Hu, Mohammed Aboustait, Taehwan Kim, Tyler Ley, Jay C. Hanan, Jeffrey W. Bullard, Robert Winarski, Volker Rose
While portland cement has been widely studied for over 100 years, there are still widespread disagreements on the mechanisms of hydration. One reason for this is that direct observation of the change in microstructure and chemistry are challenging for many

Reclamation-NIST Exploratory Research Symposium Summary Report

April 6, 2016
Author(s)
Nicholas Barbosa, Jessica Torrey
The Reclamation-NIST Exploratory Research Symposium was held on August 4-5, 2015, at the Reclamation Denver Federal Center facility in Lakewood, CO, and the NIST facility in Boulder, CO. Staff from the Bureau of Reclamation and the National Institute of

Advances in shape measurement in the digital world

March 22, 2016
Author(s)
Edward Garboczi, Xiaodong Jia
The importance of particle shape in affecting the behaviour of powders and other particulate systems has long been recognised, but until fairly recently particle shape information has been rather difficult to obtain and use compared to its more well-known

The Influence of Water Activity on the Hydration Rates of Triclinic Tricalcium Silicate

January 20, 2016
Author(s)
Tandre Oey, Aditya Kumar, Gabriel Falzone, Jian Huang, Sierra Kennison, Mathieu Bauchy, Narayanan Neithalath, Jeffrey W. Bullard, Gaurav Sant
Tricalcium silicate stops hydrating at relative humidities (RH) less than 80 %. But the rate at which its hydration rate decreases as a function of the RH has not yet been elucidated. By invoking correspondence between RH and water activity (aH, unitless)

Effect of a micro-copolymer addition on the thermal conductivity of fly ash mortars

November 5, 2015
Author(s)
Alejandro Duran-Herrera, Joana K. Campos-Dimas, P Valdez, Dale P. Bentz
In this study, a copolymer composed of hollow spherical particles with an average particle size of 90 µm was evaluated as a lightweight aggregate in Portland cement-fly ash mortars to improve the thermal conductivity (k) of the composite. Mortars were

Numerical Simulation of Heat and Mass Transport during Hydration of Portland Cement Mortar in Semi-adiabatic and Steam Curing Conditions

October 22, 2015
Author(s)
Emilio Hernandez-Bautista, Dale P. Bentz, Sadoth Sandoval-Torres, Prisciiano Cano Barrita
The mass and heat transport during steam curing of concrete has a bearing on both the mechanical and durability properties. Therefore, it is essential to take into account the temperature evolution and the moisture distribution to prevent premature damage

Microstructural Origins of Cement Paste Degradation by External Sulfate Attack

October 15, 2015
Author(s)
Pan Feng, Edward Garboczi, Pan Feng, Jeffrey W. Bullard
A microstructure model has been applied to simulate near-surface degradation of portland cement paste in contact with a sodium sulfate solution. This new model uses thermodynamic equilibrium calculations to guide both compositional and microstructure

Metrology Needs for Predicting Concrete Pumpability

June 22, 2015
Author(s)
Myoungsung Choi, Chiara C. Ferraris, Nicos Martys, Didier Lootens, Van Bui, Trey Hamilton
With the increasing use of pumping to place concrete, the development and refinement of the industry practice to ensure successful concrete pumping is becoming an important need for the concrete construction industry. To date, research on concrete pumping

Damage Development in Cementitious Materials Exposed to MgCl2 Deicing Salt

June 15, 2015
Author(s)
Yaghoob Farnam, Andrew Wiese, Dale P. Bentz, Jeffrey M. Davis, Jason Weiss
MgCl2 is used in deicing applications due to its capability to depress freezing temperatures to a lower point than other salts like NaCl. The constituents of concrete (i.e., pores solution, calcium hydroxide, aluminate phases, and calcium silicate hydrate

Experimental and Numerical Investigation on the Effect of Cooling/Heating Rate on the Freeze-Thaw Behavior of Mortar Containing Deicing Salt Solution

June 3, 2015
Author(s)
Yaghoob Farnam, Hadi S. Esmaeeli, Dale P. Bentz, Pablo Zavattieri, Jason Weiss
In North America, some concrete pavements and sidewalks have shown severe damage during freezing. Research has been performed to better understand the cause of damage. A test method (called longitudinal guarded comparative calorimeter (LGCC)) has been

D90: The strongest contributor to setting time in MTA and Portland Cement

April 15, 2015
Author(s)
William Ha, Dale P. Bentz, Wyatt Kahler, Laurence Walsh
Introduction: The setting times of commercial mineral trioxide aggregate (MTA) and Portland cements vary. It was hypothesized that much of this variation was due to differences in particle size distribution. Methods: Two gram samples from 11 MTA-type

Modeling the apparent and intrinsic viscoelastic relaxation of hydrating cement paste

January 31, 2015
Author(s)
Xiaodan Li, Zachary Grasley, Edward Garboczi, Jeffrey W. Bullard
Finite element procedures combined with microstructure development modeling are integrated to quantitatively predict the viscoelastic/viscoplastic relaxation of cement paste due to intrinsic calcium silicate hydrate viscoelasticity and microstructure

New Insights into the Prehydration of Cement and Its Mitigation

January 27, 2015
Author(s)
Julyan Stoian, Tandre Oey, Jeffrey W. Bullard, Jian Huang, Aditya Kumar, Magdalena Balonis, Judith E. Terrill, Narayanan Neithalath, Gaurav Sant
Ordinary Portland cement (OPC) prehydrates during storage or handling in moist environments, forming hydration products on or near its particles' surfaces. Prehydration is known to reduce OPC reactivity, but the extent of prehydration has not yet been

The Prehydration of Cement and Its Mitigation

December 6, 2014
Author(s)
Julyan Stoian, Tandre Oey, Jeffrey W. Bullard, Jian Huang, Aditya Kumar, Magdalena Balonis, Narayanan Neithalath, Gaurav Sant
Ordinary portland cement (OPC) prehydrates during storage or handling in moist environments, forming hydration products on or near its particles' surfaces. Prehydration is known to reduce OPC reactivity, but the extent of prehydration has not yet been
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