scholarly journals Modelling Long-Term Durability Performance of Cementitious Materials under Sodium Sulphate Interaction

2018 ◽  
Vol 8 (12) ◽  
pp. 2597 ◽  
Author(s):  
Yogarajah Elakneswaran ◽  
Eiji Owaki ◽  
Toyoharu Nawa
Keyword(s):  
Waste Disposal ◽  
Reactive Transport ◽  
Power Plants ◽  
Transport Model ◽  
Cementitious Materials ◽  
Sodium Sulphate ◽  
High Concentration ◽  
Essential Components ◽  
Term Performance

Cementitious materials are one of the essential components for low- and intermediate-level waste disposal sites. Low-level nuclear waste from power plants consists of highly concentrated (~25 wt %) Na2SO4, and the wastes are solidified with cementitious materials. Degradation of cementitious materials that result from chemical and physical sulphate attack is a major concern in the safety of the waste disposal. In this study, hydration and reactive transport models, developed in previous works by the authors, were applied with Pitzer interactions coefficients to evaluate the long-term performance of Portland cement (PC) solidified with high concentration of Na2SO4. Expansive sulphate-bearing products of ettringite and mirabilite were formed and filled the pores in the hydrating PC with 25% of Na2SO4 by weight, but they were destabilised as temperature increased. Influence of Na2SO4 concentration and temperature on mineralogical changes is discussed. The simulation results from the reactive-transport model showed that the degradation of solidified Na2SO4 waste by cementitious materials exposed to 10% Na2SO4 for 1000 years is due to dissolution of mirabilite and secondary formation of ettringite, but not Na2SO4 crystallisation. The phases and porosity became stable close to exposure surface after 10 years, although the deterioration progressed from the surface to core with exposure time.

scholarly journals Mineralogical, numerical and analytical studies of the coupled oxidation of pyrite and coal

2003 ◽  
Vol 67 (2) ◽  
pp. 381-398 ◽  
Author(s):  
K. A. Evans ◽  
C. J. Gandy ◽  
S. A. Banwart
Keyword(s):  
Reactive Transport ◽  
Transport Model ◽  
Pyrite Oxidation ◽  
Spoil Heap ◽  
Reaction Fronts ◽  
Order Of Magnitude ◽  
Magnitude Variation ◽  
Discharge Chemistry ◽  
Analytical Expressions

Mineralogical, bulk and field leachate compositions are used to identify important processes governing the evolution of discharges from a coal spoil heap in County Durham. These processes are incorporated into a numerical one-dimensional advective-kinetic reactive transport model which reproduces field results, including gas compositions, to within an order of magnitude. Variation of input parameters allows the effects of incorrect initial assumptions on elemental profiles and discharge chemistry to be assessed. Analytical expressions for widths and speeds of kinetic reaction fronts are developed and used to predict long-term development of mineralogical distribution within the heap. Results are consistent with observations from the field site. Pyrite oxidation is expected to dominate O2 consumption in spoil heaps on the decadal timescale, although C oxidation may stabilize contaminants in effluents on the centennial scale.

Long Term Performance of PE4710 Materials in Disinfectant Treated Nuclear Raw Water Systems

2013 ◽  
Author(s):  
Alexander M. Summe ◽  
Douglas P. Munson ◽  
Kenneth Oliphant ◽  
Sarah Chung
Keyword(s):  
Power Plants ◽  
Slow Crack Growth ◽  
Life Time ◽  
Water Systems ◽  
Superior Performance ◽  
Mechanical Degradation ◽  
Service Water ◽  
Long Term Performance ◽  
Term Performance

Degradation of service water systems is a major issue facing nuclear power plants and many plants will require repair or replacement of existing carbon steel piping components. High-density polyethylene (HDPE) has been used in non-safety service water systems for over ten years and has demonstrated superior performance. However, there still exist knowledge gaps around material properties, inspectability, and long-term performance. Specifically, there is a lack of insight on the aging of HDPE piping in disinfectant treated service water systems. This paper summarizes the methodology and results of predicting the expected life time of HDPE piping exposed to oxidizing biocides in numerous end-use scenarios. The aging mechanism of concern is Stage III Chemical-Mechanical degradation, where the polymer is oxidized by biocides and then experiences slow crack growth (SCG). An Aging Model is used to provide general predictions of pipe service life. The results were analyzed for trends and limiting or sensitive operating parameters were identified. For most applications, the specific resin used in the model demonstrated good performance for lifetimes of well over 40 years.

scholarly journals Preparation, Physicochemical Properties, and Long-Term Performance of Photocatalytic Ceramsite Sand in Cementitious Materials

2017 ◽  
Vol 7 (8) ◽  
pp. 828 ◽  
Author(s):  
Du Zhao ◽  
Fazhou Wang ◽  
Peng Liu ◽  
Lu Yang ◽  
Shuguang Hu ◽  
...  
Keyword(s):  
Physicochemical Properties ◽  
Cementitious Materials ◽  
Long Term Performance ◽  
Term Performance

scholarly journals Evolution of the Reaction and Alteration of Mudstone with Ordinary Portland Cement Leachates: Sequential Flow Experiments and Reactive-Transport Modelling

Minerals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1026
Author(s):  
Keith Bateman ◽  
Shota Murayama ◽  
Yuji Hanamachi ◽  
James Wilson ◽  
Takamasa Seta ◽  
...  
Keyword(s):  
Reactive Transport ◽  
Chemical Properties ◽  
Reactive Transport Modelling ◽  
Transport Modelling ◽  
General Sequence ◽  
Long Term Performance ◽  
Term Performance ◽  
Physical And Chemical ◽  
Flow Experiments

The construction of a repository for geological disposal of radioactive waste will include the use of cement-based materials. Following closure, groundwater will saturate the repository and the extensive use of cement will result in the development of a highly alkaline porewater, pH > 12.5; this fluid will migrate into and react with the host rock. The chemistry of the fluid will evolve over time, initially high [Na] and [K], evolving to a Ca-rich fluid, and finally returning to the groundwater composition. This evolving chemistry will affect the long-term performance of the repository, altering the physical and chemical properties, including radionuclide behaviour. Understanding these changes forms the basis for predicting the long-term evolution of the repository. This study focused on the determination of the nature and extent of the chemical reaction, as well as the formation and persistence of secondary mineral phases within a mudstone, comparing data from sequential flow experiments with the results of reactive transport modelling. The reaction of the mudstone with the cement leachates resulted in small changes in pH with the precipitation of calcium aluminium silicate hydrate (C-(A-)S-H) phases of varying compositions. As the system evolves, secondary C-(A-)S-H phases re-dissolve and are replaced by secondary carbonates. This general sequence was successfully simulated using reactive transport modelling.

Grouted Waste Leach Tests: Pursuit of Mechanisms and Data for Long-Term Performance Assessment

1989 ◽  
Vol 176 ◽  
Author(s):  
R. Jeff Serne
Keyword(s):  
Diffusion Processes ◽  
Scale Up ◽  
Liquid Waste ◽  
Effective Diffusivity ◽  
Cementitious Materials ◽  
Solidified Waste ◽  
Effective Diffusivities ◽  
Long Term Performance ◽  
Term Performance

ABSTRACTAt Hanford, low-level liquid nuclear waste is being mixed with cementitious materials (grout) to form leach-resistant solid waste. Prior to grouting each liquid waste, an assessment must be performed to evaluate the long-term environmental impact. These predictions rely upon a diffusioncontrolled release model and short-term laboratory leach data on small grout samples. This paper describes size scale-up and inventory scale-up experiments that evaluate whether diffusion does in fact control the release of contaminants. The results of the volume scale-up test suggest that tests on grout cylinders between the sizes 3 cm dia. by 3 cm length and 30 cm dia. by 29 cm length yield comparable results. These data and other available literature suggest that extrapolation of leach results to large blocks of solidified waste is defensible.The inventory scale-up tests for 125I and selenium show a constant effective diffusivity regardless of the original inventory. This suggests that diffusion processes do in fact control the release of iodide and selenium from grout. The 99Tc effective diffusivities may not remain constant with changes in inventory.

scholarly journals Impacts of coal burning on ambient PM<sub>2.5</sub> pollution in China

2017 ◽  
Vol 17 (7) ◽  
pp. 4477-4491 ◽  
Author(s):  
Qiao Ma ◽  
Siyi Cai ◽  
Shuxiao Wang ◽  
Bin Zhao ◽  
Randall V. Martin ◽  
...  
Keyword(s):  
Coal Combustion ◽  
Power Plants ◽  
Fine Particles ◽  
Transport Model ◽  
National Level ◽  
National Average ◽  
Primary Concern ◽  
High Concentration ◽  
Coal Burning ◽  
Average Contribution

Abstract. High concentration of fine particles (PM2.5), the primary concern about air quality in China, is believed to closely relate to China's large consumption of coal. In order to quantitatively identify the contributions of coal combustion in different sectors to ambient PM2. 5, we developed an emission inventory for the year 2013 using up-to-date information on energy consumption and emission controls, and we conducted standard and sensitivity simulations using the chemical transport model GEOS-Chem. According to the simulation, coal combustion contributes 22 µg m−3 (40 %) to the total PM2. 5 concentration at national level (averaged in 74 major cities) and up to 37 µg m−3 (50 %) in the Sichuan Basin. Among major coal-burning sectors, industrial coal burning is the dominant contributor, with a national average contribution of 10 µg m−3 (17 %), followed by coal combustion in power plants and the domestic sector. The national average contribution due to coal combustion is estimated to be 18 µg m−3 (46 %) in summer and 28 µg m−3 (35 %) in winter. While the contribution of domestic coal burning shows an obvious reduction from winter to summer, contributions of coal combustion in power plants and the industrial sector remain at relatively constant levels throughout the year.

scholarly journals Impacts of Coal Burning on Ambient PM<sub>2.5</sub> Pollution in China

2016 ◽  
Author(s):  
Qiao Ma ◽  
Siyi Cai ◽  
Shuxiao Wang ◽  
Bin Zhao ◽  
Randall V. Martin ◽  
...  
Keyword(s):  
Coal Combustion ◽  
Power Plants ◽  
Fine Particles ◽  
Transport Model ◽  
National Level ◽  
National Average ◽  
Primary Concern ◽  
High Concentration ◽  
Coal Burning ◽  
Average Contribution

Abstract. High concentration of fine particles (PM2.5), the primary concern about air quality in China, is believed to closely relate to China’s large consumption of coal. In order to quantitatively identify the contributions of coal combustion in different sectors to ambient PM2.5, we developed an emission inventory for the year 2013 using up-to-date information on energy consumption and emission controls, and conducted standard and sensitivity simulations using the chemical transport model GEOS-Chem. According to the simulation, coal combustion contributes 22 μg m−3 (40 %) to the total PM2.5 concentration at national level (averaged in 74 major cities), and up to 37 μg m−3 (50 %) in Sichuan Basin. Among major coal-burning sectors, industrial coal burning is the dominant contributor with a national average contribution of 10 μg m−3 (17 %), followed by coal combustion in power plants and domestic sector. The national average contribution due to coal combustion is estimated to be 18 μg m−3 (46 %) in summer and 28 μg m−3 (35 %) in winter. While the contribution of domestic coal burning shows an obvious reduction from winter to summer, contributions of coal combustion in power plants and industrial sector remain at relatively constant levels through out the year.

Study on the Effects of Natural Pozzolan and Limestone Powder on Mechanical Properties of Roller Compacted Concrete Pavements

2011 ◽  
Vol 250-253 ◽  
pp. 3619-3623 ◽  
Author(s):  
Morteza Madhkhan ◽  
Armin Hamidi ◽  
Navid Salehi
Keyword(s):  
Compressive Strength ◽  
Cementitious Materials ◽  
Production Costs ◽  
Limestone Powder ◽  
Concrete Pavements ◽  
Natural Pozzolan ◽  
Two Factors ◽  
Long Term Performance ◽  
Term Performance

Due to high maintenance and production costs of conventional asphalt pavements in recent years, substitution of concrete pavements has been taken into account. One important factor of such pavements is the long-term performance. The substitution of pozzolanic materials with existing cement in the mixture is a common choice to improve the durability factors and to increase the long term compressive strength. Owing to this change in cementitious materials, a general anticipation of the pozzolanic behavior to be observed is that the early age compressive strength gets decreased. On the other hand, this defect will be compensated in the long-term compressive strength. Furthermore, as conventional loads of road pavements are concerned, the tensile and flexural strengths have their own importance. Regarding these two factors, the related tests were also performed and the results were analyzed. The main purpose is to find the optimum material among these 2 types of pozzolanic supplements and its percentage of substitution with the preference of having the best average strength in both long and short term performances. Altogether, the natural pozzolan had better performance than limestone powder.

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