Tuff-Cement or Concrete Interactions in the Repository Environment

1984 ◽  
Vol 44 ◽  
Author(s):  
Sridhar Komarneni ◽  
Della M. Roy ◽  
Amitabha Kumar
Keyword(s):  
Cement Hydration ◽  
Cation Exchanger ◽  
Confining Pressure ◽  
Pozzolanic Reaction ◽  
Binding Agent ◽  
Hydrothermal Conditions ◽  
Interaction Product ◽  
Calcium Silicates ◽  
Acidic Conditions ◽  
Repository Sealing

AbstractHydrothermal interactions of tuff or tuff minerals with cement or concrete were investigated at 200 0C under a confining pressure of 8 or 30 MPa for I to 20 weeks. These chemical interactions produced crystalline hydrous calcium silicates such as Al-substituted tobermorite, xonotlite and gyrolite. Tobermorite was the most common interaction product of cement and tuff or tuff minerals because of pozzolanic reaction. The extent of cement hydration and the quantity of cement in the cement mix affected the abundance of tobermorite as expected. The reaction of concrete with tuff resulted in the formation of smectite in addition to tobermorite due to the generation of slight acidic conditions in this reaction mixture under the present hydrothermal conditions. The formation of tobermorite by the interaction of tuff with cement or concrete has positive implications to the physical (bonding) and chemical (sorption) properties in the repository sealing system because tobermorite (Al-substituted) acts both as a binding agent and as a cation exchanger.

scholarly journals Surface microstructures developed on polished quartz crystals embedded in wet quartz sand compacted under hydrothermal conditions

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Peter M. Schutjens ◽  
Christopher J. Spiers ◽  
André Rik Niemeijer
Keyword(s):  
Quartz Sand ◽  
Axial Stress ◽  
Dissolution Kinetics ◽  
Confining Pressure ◽  
Pressure Solution ◽  
Hydrothermal Conditions ◽  
Quartz Crystals ◽  
Surface Microstructures ◽  
Quartz Aggregates ◽  
Intergranular Pressure

AbstractIntergranular pressure solution plays a key role as a deformation mechanism during diagenesis and in fault sealing and healing. Here, we present microstructural observations following experiments conducted on quartz aggregates under conditions known to favor pressure solution. We conducted two long term experiments in which a quartz crystal with polished faces of known crystallographic orientation was embedded in a matrix of randomly oriented quartz sand grains. For about two months an effective axial stress of 15 MPa was applied in one experiment, and an effective confining pressure of 28 MPa in the second. Loading occurred at 350 °C in the presence of a silica-saturated aqueous solution. In the first experiment, quartz sand grains in contact with polished quartz prism ($$\overline10{1 }0$$ 1 ¯ 010 ) faces became ubiquitously truncated against these faces, without indenting or pitting them. By contrast, numerous sand-grain-shaped pits formed in polished pyramidal ($$17\overline{6 }3$$ 17 6 ¯ 3 ) and ($$\overline{4 }134$$ 4 ¯ 134 ) crystal faces in the second experiment. In addition, four-leaved and (in some cases) three-leafed clover-shaped zones of precipitation formed on these prism faces, in a consistent orientation and pattern around individual pits. The microstructures observed in both experiments were interpreted as evidence for the operation of intergranular pressure solution. The dependence of the observed indentation/truncation microstructures on crystal face orientation can be explained by crystallographic control of stress-induced quartz dissolution kinetics, in line with previously published experimental and petrographic data, or possibly by an effect of contact orientation on the stress-induced driving force for pressure solution. This should be investigated in future experiments, providing data and microstructures which enable further mechanism-based analysis of deformation by pressure solution and the effect of crystallographic control on its kinetics in quartz-rich sands and sandstones.

scholarly journals Durability of pulverised fuel ash (PFA) concrete exposed to acidic and alkali conditions

2019 ◽  
Vol 258 ◽  
pp. 05015 ◽  
Author(s):  
Saiful Baharin Duraman ◽  
Md. Fadhil Hakim Haji Omar
Keyword(s):  
Concrete Structures ◽  
Pozzolanic Reaction ◽  
Polluted Water ◽  
Alkali Silica Reaction ◽  
Acid Attack ◽  
Fuel Ash ◽  
Alkaline Environments ◽  
High Alkalinity ◽  
Acidic Conditions ◽  
Strength And Durability

Pulverised Fuel Ash (PFA) is becoming an important component in concrete due to potentially improved properties such as workability, later age strength and durability. Concrete structures may be susceptible to acid attack due to exposure to acid rain, acidic soil or polluted water. Concrete structures exposed to high alkaline environments, in addition to the alkalinity level of the cement and aggregates, may promote alkali-silica reaction (ASR) leading to swelling and reduction in durability. This study looks into the durability properties of PFA incorporated concrete at various replacement levels when exposed to highly acidic and alkali conditions. Compressive strengths and water absorption tests were compared between concrete cured under normal conditions with concrete exposed to highly acidic and highly alkali conditions. All specimens exposed to acidic conditions showed significant decreases in mass and compressive strengths compared to specimens cured normally. Higher PFA replacement resulted in improved resistance to acid attack. All specimens exposed to alkali conditions showed minor increases in mass suggesting ASR occurring. Reductions in compressive strengths were found at lower replacement levels. At higher replacement levels, increases in compressive strengths were found, suggesting the possibility of increased pozzolanic reaction of the PFA due to the high alkalinity.

scholarly journals Effect of Nanosilica on Impermeability of Cement-Fly Ash System

2020 ◽  
Vol 2020 ◽  
pp. 1-13 ◽  
Author(s):  
Huaqing Liu ◽  
Yan Zhang ◽  
Ruiming Tong ◽  
Zhaoqing Zhu ◽  
Yang Lv
Keyword(s):  
Fractal Dimension ◽  
Fly Ash ◽  
Bond Strength ◽  
Pore Structure ◽  
Calcium Hydroxide ◽  
Cement Hydration ◽  
Pozzolanic Reaction ◽  
Surface Protection ◽  
Durability Of Concrete

Surface protection has been accepted as an effective way to improve the durability of concrete. In this study, nanosilica (NS) was used to improve the impermeability of cement-fly ash system and this kind of material was expected to be applied as surface protection material (SPM) for concrete. Binders composed of 70% cement and 30% fly ash (FA) were designed and nanosilica (NS, 0–4% of the binder) was added. Pore structure of the paste samples was evaluated by MIP and the fractal dimension of the pore structure was also discussed. Hydrates were investigated by XRD, SEM, and TG; the microstructure of hydrates was analyzed with SEM-EDS. The results showed that in the C-FA-NS system, NS accelerated the whole hydration of the cement-FA system. Cement hydration was accelerated by adding NS, and probably, the pozzolanic reaction of FA was slightly hastened because NS not only consumed calcium hydroxide by the pozzolanic reaction to induce the cement hydration but also acted as nucleation seed to induce the formation of C-S-H gel. NS obviously refined the pore structure, increased the complexity of the pore structure, and improved the microstructure, thereby significantly improving the impermeability of the cement-FA system. This kind of materials would be expected to be used as SPM; the interface performance between SPM and matrix, such as shrinkage and bond strength, and how to cast it onto the surface of matrix should be carefully considered.

Micromechanical Properties of Calcium Silicate Hydrate

2013 ◽  
Vol 539 ◽  
pp. 75-79
Author(s):  
Wu Yao ◽  
Li He
Keyword(s):  
Fly Ash ◽  
Reaction Zone ◽  
Calcium Silicate ◽  
Calcium Silicate Hydrate ◽  
Cement Hydration ◽  
Cementitious Materials ◽  
Pozzolanic Reaction ◽  
Indentation Modulus ◽  
Micromechanical Properties ◽  
Secondary Hydration

The indentation modulus of several cementitious materials is discussed with the assumption that the C-S-H gel is an aggregation of precipitated, colloidal-sized particles. At least two kinds of structurally distinct but compositional similar phases are found existent during the hydration process. In addition, the C-S-H originated from the pozzolanic reaction of fly ash is found to be the same to that of cement hydration in micromechanical properties; however, the C-S-H gel formed from the secondary hydration is inclined to develop into high density packing configuration, due to the limitation of reaction zone available.

The Pozzolanic Reaction of Silica Fume

2012 ◽  
Vol 1488 ◽  
Author(s):  
Ole M. Jensen
Keyword(s):  
Silica Fume ◽  
High Performance ◽  
Cement Hydration ◽  
Theoretical Calculations ◽  
Pozzolanic Reaction ◽  
Interfacial Transition Zone ◽  
Strength Development ◽  
Micro Structure ◽  
Cementitious Binder ◽  
Portland Cement Hydration

ABSTRACTSilica fume is a very important supplementary cementitious binder in High-Performance and Ultra High-Performance Concretes. Through its pozzolanic reaction the silica fume densifies the concrete micro-structure, in particular it strengthens the paste-aggregate interfacial transition zone. In the present paper different aspects of the pozzolanic reaction of silica fume are investigated. These include chemical shrinkage, isothermal heat development and strength development. Key data for these are given and compared with theoretical calculations, and based on presented measurements the energy of activation of the pozzolanic reaction of silica fume is estimated. The results show that the pozzolanic reaction of silica fume has notable differences from Portland cement hydration.

Influence of Physicochemical Properties of Sugarcane Bagasse Ash (SCBA) in Portland Cement Hydration

2018 ◽  
Vol 765 ◽  
pp. 324-328
Author(s):  
Tiago Assunção Santos ◽  
José da Silva Andrade Neto ◽  
Vitor Souza Santos ◽  
Daniel Véras Ribeiro
Keyword(s):  
Portland Cement ◽  
Sugarcane Bagasse ◽  
Cement Hydration ◽  
New Technologies ◽  
Pozzolanic Reaction ◽  
Cement Industry ◽  
Partial Replacement ◽  
Cement Pastes ◽  
Sugarcane Bagasse Ash ◽  
Portland Cement Hydration

Due to the concern with the environmental impacts caused by the gases emitted by the cement industry and by the inadequate disposal of wastes generated in the sugar-alcohol industry, such as sugarcane bagasse ash (SCBA), a search for the development of new technologies, which are less aggressive to the environment and that propose feasible alternatives, began in order to reuse these wastes properly. Among these alternatives is the reuse of SCBA as partial replacement to cement or as addition to cementitious matrices. In this way, the present research has the objective of analyzing the influence of SCBA obtained by the calcination of sugarcane bagasse (SCB), at 600°C, in the process of Portland cement hydration. Initially, the SCBA was characterized physically, chemically and mineralogically, and then cement pastes with 20% and 35% substitution contents were elaborated, besides the reference paste, which were analyzed through X-ray diffraction (XRD) and thermogravimetric (TG) techniques. The results obtained show that there is a consumption of portlandite as a consequence of the use of SCBA, evidencing the pozolanicity of these ashes. In the pastes with 35% substitution content, there was an intense consumption of the portlandite, indicating, in this proportion, the pozzolanic reaction was more intense.

Influence of Opoka Additive on Composite Cement Hydration

2015 ◽  
Vol 244 ◽  
pp. 3-11 ◽  
Author(s):  
Irmantas Barauskas ◽  
Rimvydas Kaminskas ◽  
Aivaras Stanaitis ◽  
Ieva Vilkaite
Keyword(s):  
Compressive Strength ◽  
Cement Hydration ◽  
Strength Properties ◽  
Pozzolanic Reaction ◽  
Hydration Properties ◽  
Composite Cement ◽  
Natural Pozzolana ◽  
Standard Table

The purpose of this research is to identify influence of natural pozzolana - opoka additive on hydration properties of the composite cement consisting of clinker, slag, opoka and gypsum. Recipes are created by reducing the amount of clinker from 60% to 20% to meet the requirements of cement composition according EN 197-1 standard (table 3).It was estimated that slag and opoka are increasing strength properties of the samples and accelerates the hydration of C3S, moreover, participate in pozzolanic reaction in the composite cement. Slag has a greater effect on the compressive strength of samples after 1 month of hydration and opoka - after 3 months. It was found that opoka additive accelerates the hydration of C3S more to compare with slag.

Determination of cement hydration and pozzolanic reaction extents for fly-ash cement pastes

2012 ◽  
Vol 27 (1) ◽  
pp. 560-569 ◽  
Author(s):  
Qiang Zeng ◽  
Kefei Li ◽  
Teddy Fen-chong ◽  
Patrick Dangla
Keyword(s):  
Fly Ash ◽  
Cement Hydration ◽  
Pozzolanic Reaction ◽  
Cement Pastes

Synthesis of clay-sized iron oxides under marine hydrothermal conditions

Clay Minerals ◽  
2002 ◽  
Vol 37 (4) ◽  
pp. 719-731 ◽  
Author(s):  
N. Taitel-Goldman ◽  
A. Singer
Keyword(s):  
Crystal Growth ◽  
Short Range ◽  
Elevated Temperatures ◽  
Complete Oxidation ◽  
Alkaline Ph ◽  
Hydrothermal Conditions ◽  
Atlantis Ii Deep ◽  
Pure Phase ◽  
Acidic Conditions ◽  
Morphology Changes

AbstractGoethite, lepidocrocite, magnetite and akaganeite were synthesized in 0.8 M, 2 M and 5 M NaCl solutions at various temperatures (25, 40, 60°C) under slightly acidic to slightly alkaline pH with or without Si additions. Elevated temperatures prevent complete oxidation of initial Fe2+ solutions and magnetite and siderite precipitate, accompanied by goethite and lepidocrocite. At higher salinity, O2 solubility is reduced and its distribution is limited, leading to coprecipitation of lepidocrocite, akaganeite and goethite.Lepidocrocite morphology changes from plates at pH 5.5 through rods at pH 7 to multi-domainic crystals at pH 8.2, due to enhanced crystal growth along the c axis. Salinity and temperature have opposite effects on lepidocrocite crystallinity.Goethite crystals are multi-domainic and twinning appears only at elevated temperatures. Increases in temperature and salinity improve goethite crystallinity as observed by IR spectra. Addition of Si up to Si/Fe = 0.1 retards crystal growth and Si-OH-stretching bands appear. At Si/Fe = 1 most of the precipitate is short range ordered.Platy and rod-shaped lepidocrocite from the Thetis and Atlantis II Deeps, were probably formed under the slightly acidic conditions of the hydrothermal brines. The Si concentration was greater in Atlantis II Deep than in Thetis Deep, leading to larger lepidocrocite and goethite crystals in the latter.Multi-domainic goethite could have precipitated throughout. Pure phase goethite might have precipitated in the less concentrated brine, whereas mixtures of goethite and lepidocrocite might have precipitated in the more concentrated brine, depending mainly on oxidation rate and oxygen mobility within the brine.

scholarly journals The Effects of Nanosized-Palm Oil Fuel Ash on Early Age Hydration of Hardened Cement Paste: The Microstructure Studies

2021 ◽  
Vol 82 (2) ◽  
pp. 87-95
Author(s):  
Mohd Azrul Andul Rajak ◽  
Zaiton Abdul Majid ◽  
Mohammad Ismail
Keyword(s):  
Cement Paste ◽  
Palm Oil ◽  
Cement Hydration ◽  
Pozzolanic Reaction ◽  
Early Age ◽  
Hardened Cement ◽  
Hardened Cement Paste ◽  
Palm Oil Fuel Ash ◽  
Fuel Ash ◽  
Oil Fuel

Integration of cement-based products with nanosized-palm oil fuel ash as supplementary cementing material (SCM) amend its hydration’s degree at early age phase and the microstructural groundworks are relevant to explain the findings. Hence, the present work investigates the microstructure properties of the hardened cement paste (HCP) incorporating nPOFA to study on the effect of nPOFA in cement hydration at an early age phase. An Ordinary Portland Cement (OPC) paste as a set of HCP blended with microsized-palm oil fuel ash (mPOFA) (10-30%) and nPOFA (10-60%) were prepared and cured for 28 days. The microstructural examination of OPC, mPOFA and nPOFA cement pastes at 28 days curing age via Thermogravimetric (TG) analysis, X-Ray diffraction (XRD) analysis, morphology study and Fourier transform infrared (FTIR) spectroscopy analysis. In TG analysis, the relative weight loss of calcium hydroxide (CH) of nPOFA pastes is lower than OPC and mPOFA. Based on the CH peaks at 2?= 18.1°and 34.0° in the diffractogram, it shows that nPOFA pastes give the low CH peaks compare to OPC and mPOFA pastes. In addition, the nPOFA pastes form the dense and compact microstructure of HCP compare to other pastes. Observations from FTIR analysis, nPOFA pastes display a high frequency of Si-O band due to the high rate of pozzolanic reaction. Overall, the findings confirmed the contribution of nPOFA in accelerating the rate of cement hydration and pozzolanic reaction as it reduced the amount of CH in the cementitious matrix.

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