Tatiana Pyatina

Set-Controlling Additive for Thermal Shock-Resistant Cement

The present work discusses retardation of hydration of sodium metasilicate (SMS)-activated calcium aluminate cement (CAC)/ Class F fly ash blend at 85oC. Screening of common retarders, including citric-, tartaric-, and boric-acids, via isothermal calorimetric measurements identified tartaric acid as the most efficient in delaying the set of the blend. None of these retarders compromised the development of long-term compressive strength or toughness at concentrations of up to 1% by weight of blend (bwob) at 200and 300o C. The reaction products of tartaric acid and the components of the blend were characterized by XRD and Fourier-transform infrared. The main conclusions drawn from this study were that SMS not only activates the hydration of waterinert fly ash F, but also delays the set of the CAC/Class F fly ash blend. Adding tartaric acid further retards the set of the blend and formation of crystalline hydrates at 85oC, so promoting sodalite crystallization at 300oC. Hypothesis to explain the set-retarding mechanism are proposed.

Effect of Tartaric Acid on Hydration of a Sodium-Metasilicate-Activated Blend of Calcium Aluminate Cement and Fly Ash F

An alkali-activated blend of aluminum cement and class F fly ash is an attractive solution for geothermal wells where cement is exposed to significant thermal shocks and aggressive environments. Set-control additives enable the safe cement placement in a well but may compromise its mechanical properties. This work evaluates the effect of a tartaric-acid set retarder on phase composition, microstructure, and strength development of a sodium-metasilicate-activated calcium aluminate/fly ash class F blend after curing at 85 °C, 200 °C or 300 °C. The hardened materials were characterized with X-ray diffraction, thermogravimetric analysis, X-ray computed tomography, and combined scanning electron microscopy/energy-dispersive X-ray spectroscopy and tested for mechanical strength. With increasing temperature, a higher number of phase transitions in non-retarded specimens was found as a result of fast cement hydration. The differences in the phase compositions were also attributed to tartaric acid interactions with metal ions released by the blend in retarded samples. The retarded samples showed higher total porosity but reduced percentage of large pores (above 500 µm) and greater compressive strength after 300 °C curing. Mechanical properties of the set cements were not compromised by the retarder.

Role of Tartaric Acid in Chemical, Mechanical and Self-Healing Behaviors of a Calcium-Aluminate Cement Blend with Fly Ash F under Steam and Alkali Carbonate Environments at 270 °C

Tartaric acid (TA) changes short-term mechanical behavior and phase composition of sodium-metasilicate activated calcium-aluminate cement blend with fly ash, type F, when used as a set control additive to allow sufficient pumping time for underground well placement. The present work focuses on TA effect on self-healing properties of the blend under steam or alkali carbonate environments at 270 °C applicable to geothermal wells. Compressive strength recoveries and cracks sealing were examined to evaluate self-healing of the cement after repeated crush tests followed by two consecutive healing periods of 10 and 5 days at 270 °C. Optical and scanning electron microscopes, X-ray diffraction, Fourier Transform infrared and EDX measurements along with thermal gravimetric analyses were used to identify phases participating in the healing processes. Samples with 1% mass fraction of TA by weight of blend demonstrated improved strength recoveries and crack plugging properties, especially in alkali carbonate environment. This effect was attributed to silicon-rich (C,N)-A-S-H amorphous phase predominant in TA-modified samples, high-temperature stable zeolite phases along with the formation of tobermorite-type crystals in the presence of tartaric acid.

Evaluation of the Performance of O-rings Made with Different Elastomeric Polymers in Simulated Geothermal Environments at 300°C

Notice: This manuscript has been authored by an employee of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH 10886 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for the United States Government purposes.