Thermodynamic Modelling of the Sorption of Radioelements onto Cementitious Materials

1995 ◽  
Vol 412 ◽  
Author(s):  
T. G. Heath ◽  
D. J. Ilett ◽  
C. J. Tweed
Keyword(s):  
Surface Chemistry ◽  
Calcium Ions ◽  
Cementitious Materials ◽  
Molar Ratio ◽  
Iodide Ions ◽  
Zeta Potentials ◽  
High Calcium ◽  
Cement Based Materials ◽  
Calcium Silicon ◽  
Modelling Approach

AbstractA model has been developed for the sorption of radioelements onto cementitious materials based on the diffuse-layer modelling approach. The model assumes that silicon sites (>SiOH) and calcium sites (>CaOH) dominate the surface chemistry and the sorption of radioelements onto the cementitious materials. Both types of site may undergo surface protonation and deprotonation reactions. Cement-based systems vary greatly in their chemistry depending on their calcium-tosilicon molar ratio, and the corresponding variation in the surface chemistry has been incorporated by allowing sorption of calcium ions onto silicon sites. This process results in a change from a silica-type surface, at very low calcium-silicon ratios, to a calcium hydroxide-type surface for high-calcium cement-based materials. The predicted variation in the surface chemistry is consistent with literature data on measured zeta potentials of cements. The model has been applied successfully to describe the sorption of simple caesium and iodide ions at varying calciumsilicon ratios. In a Nirex repository for low and intermediate level wastes, a high-calcium cementitious backfill would be specified. This model has allowed a consistent interpretation of experimental data for sorption of key radioelements, including uranium and plutonium, onto the backfill, under saline and non-saline conditions.

Effects of Packing Degree and Calcium-Silicon Ratio of Cementitious Material on Strength of Reactive Powder Concrete

2010 ◽  
Vol 168-170 ◽  
pp. 1034-1037
Author(s):  
Tao Ji ◽  
Bao Chun Chen ◽  
Yi Zhou Zhuang ◽  
Zhi Bin Huang ◽  
Yong Ning Liang
Keyword(s):  
Silicon Dioxide ◽  
Cementitious Materials ◽  
Strength Test ◽  
Cementitious Material ◽  
Molar Ratio ◽  
Reactive Powder Concrete ◽  
Mix Proportion ◽  
Study Results ◽  
Calcium Silicon ◽  
Reactive Powder

Aim & Goff model was used to predict the packing degree of cementitious materials including cement and silica fume. The mix proportions of reactive powder concrete (RPC) with different packing degree and calcium-silicon ratio of cementitious materials were designed and a strength test was carried out. The study results reveal that the flexural strength and compressive strength of RPC are related to the packing degree and calcium-silicon ratio of cementitious materials. For the mix proportion of RPC with the calcium- silicon molar ratio of 1.353 that is slightly less than the theoretical value of 1.42, where calcium hydroxide can react with silicon dioxide more fully, its strength of RPC approaches summit although its packing degree of cementitious material is not the largest one.

Fibrinogen Bern I: A Hereditary Fibrinogen Variant With Defective Conformational Stabilization By Calcium Ions

1981 ◽  
Author(s):  
C Rupp ◽  
C Kuyas ◽  
A Häberli ◽  
M Furlan ◽  
E A Beck
Keyword(s):  
Calcium Ions ◽  
Gel Electrophoresis ◽  
Calcium Binding ◽  
Negative Charge ◽  
Fibrinopeptide A ◽  
Isoelectric Focussing ◽  
High Calcium ◽  
Two Generations ◽  
Polypeptide Chains ◽  
Conformational Stabilization

Inherited hypodysfibrinogenemia (fibrinogen Bern I) was found in four members (two generations) of a family with no haemorrhagic or thrombotic history. Fibrin aggregation curves (350 nm, 37°C) with patient plasma or purified fibrinogen Bern I, after addition of thrombin, were normal at high calcium concentrations (5mM) but delayed at lower calcium concentrations (≤0.lmM). The release of fibrinopeptide A was normal. Whereas the polypeptide chains of fibrinogen Bern I were indistinguishable from normal fibrinogen by SDS-gel-electrophoresis, an abnormal γ-chain with a decreased negative charge was found by isoelectric focussing.Plasmic degradation o| normal fibrinogen, in the presence of calcium (≥ImM), results in only one terminal D fragment which is stabilized by calcium against further degradation of γ-chains. In contrast, degradation of fibrinogen Bern I, under the same conditions, yielded at least two additional smaller D fragments. In conclusion, fibrinogen Bern I is characterized by defective calcium binding in the D domain of the γ-chain.

Electrokinetic Phenomena and Surface Characteristics of Fly Ash Particles

1984 ◽  
Vol 43 ◽  
Author(s):  
R. I. A. Malek ◽  
D. M. Roy
Keyword(s):  
Fly Ash ◽  
Surface Characteristics ◽  
Ionic Species ◽  
Point Of Zero Charge ◽  
Fly Ashes ◽  
Electrokinetic Phenomena ◽  
Zeta Potentials ◽  
Low Calcium ◽  
High Calcium

AbstractThe zeta-potentials of two fly ashes were studied (high-calcium and low-calcium). It was found that they possess a point of charge reversal at pH = 10.5 to 12. The point of zero charge (low-calcium fly ash) was found to be at pH = 5. Furthermore, it shifted to more acidic values after the fly ash is aged in several calcium-containing solutions. The surficial changes that could happen when mixing fly ashes with cement and concrete were further evaluated by aging fly ashes in different solutions: Ca(OH)2, CaSO4·2H2O, NaOH and water solutions. Information from analyses for different ionic species in the solutions and characterization of the solid residues (XRD and SEM) was used in tentative explanations for the different behavior of the two types of fly ash in cementitious mixtures and concrete.

scholarly journals Minimum Water Requirement Method for High-Performance Sulphoaluminate Cement-Based Materials

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
Hong-ping Zhang ◽  
Pei-kang Bai ◽  
Jian-hong Wang ◽  
Yan-li Dong ◽  
Yun-shan Han
Keyword(s):  
Cement Paste ◽  
High Performance ◽  
Steel Slag ◽  
Cementitious Materials ◽  
Water Requirement ◽  
Mineral Admixtures ◽  
Poor Correlation ◽  
Sulphoaluminate Cement ◽  
Cement Based Materials ◽  
Orthogonal Tests

In this work, we propose the use of steel slag instead of slag powder, in addition to fly ash and silica fume, to obtain high-performance sulphoaluminate cement-based materials. According to the closest-packing theory and on the basis of the minimum water requirement test, the influence of mineral admixtures on the minimum water requirement was evaluated for sulphoaluminate composite system paste. The optimal composition of the cementitious materials was thus determined. Orthogonal tests were used to assess the validity of this ratio. The correlation between minimum water requirement and the standard consistence was not only analyzed in the system of the minimum water requirement method decided but also in the complicate system of the orthogonal tests determined. Experimental results show that the influence of steel slag on the minimum water requirement is the largest in composite cement paste; minimum water requirement and standard consistency have a good correlation; the cement paste designed with the optimum composite had the highest strength of all the tested materials, but minimum water requirement and strength have a poor correlation in the orthogonal tests. We demonstrate that standard consistency evaluation can replace the minimum water requirement method to determine the optimum ratio of cement mineral admixtures. The proposed method not only simplifies the process but also makes the method more scientific.

scholarly journals Enhanced bioactivity and osteoinductivity of carboxymethyl chitosan/nanohydroxyapatite/graphene oxide nanocomposites

RSC Advances ◽  
2018 ◽  
Vol 8 (32) ◽  
pp. 17860-17877 ◽  
Author(s):  
Zhang Yu ◽  
Caiwen Xiao ◽  
Yazhuo Huang ◽  
Mingjiao Chen ◽  
Wei Wei ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Surface Chemistry ◽  
Bone Regeneration ◽  
Calcium Ions ◽  
Carboxymethyl Chitosan

The CMC/nHA/GO scaffold with the surface chemistry and roughness dual effects and the release of phosphate and calcium ions synergistically assist the mineralization and facilitate the bone regeneration.

Dissolution and leaching mechanisms of calcium ions in cement based materials

2018 ◽  
Vol 180 ◽  
pp. 103-108 ◽  
Author(s):  
Xuebing Wang ◽  
Kangning Xu ◽  
Yexue Li ◽  
Shengbo Guo
Keyword(s):  
Calcium Ions ◽  
Cement Based Materials

Effect of intracellularly applied sodium ions on the dark voltage of isolated retinal rods

1990 ◽  
Vol 4 (4) ◽  
pp. 331-336 ◽  
Author(s):  
Karl-Friedrich Schmidt ◽  
Gottfried N. Nöll ◽  
Christian Baumann
Keyword(s):  
Calcium Ions ◽  
Time Course ◽  
Sodium Ions ◽  
Sodium Calcium ◽  
Retinal Rods ◽  
High Calcium ◽  
Simple Medium ◽  
Cytoplasmic Content ◽  
Calcium Exchange ◽  
Sodium Effect

AbstractIsolated retinal rods of the frog consisting of the outer segment and the ellipsoid were patch-clamped and recorded in the whole-cell mode. The recording pipettes were filled with solutions of different composition in order to alter the cytoplasmic content of sodium, phosphate, and calcium ions, and guanine nucleotides. When a simple medium with potassium as the principal cation was used, the dark voltage slowly approached more negative values. This tendency of spontaneous hyperpolarization was reduced significantly when cGMP or GTP were present in the pipette medium. Sodium ions, on the other hand, clearly increased the speed of hyperpolarization. In the presence of sodium (20 mM), the stabilizing effect of GTP did not occur and that of cGMP was clearly diminished. Phosphate (20 mM) neutralized the sodium effect. High calcium levels (100 μM) did not measurably influence the time course of hyperpolarization. We conclude that the normal cytoplasmic sodium level in rods does not exceed 10 mM and that higher internal sodium concentrations interfere with the sodium–calcium exchange mechanism.

scholarly journals Effects of Curing Method on Properties and Salt-Scaling Resistance of Concrete under Lab Testing

2021 ◽  
Author(s):  
Greg Richards ◽  
Medhat Shehata
Keyword(s):  
Fly Ash ◽  
Cementitious Materials ◽  
Supplementary Cementitious Materials ◽  
Alkali Concentration ◽  
Salt Scaling ◽  
High Calcium ◽  
Curing Methods ◽  
Curing Method ◽  
High Alkali ◽  
Scaling Resistance

This paper presents a study of the effect of curing on the salt-scaling resistance of concrete containing supplementary cementitious materials (SCMs) under lab conditions. Two curing methods were examined: moist curing and wrapping in a tight plastic sheet. Wrapping concrete slabs in plastic was adopted to represent curing methods that do not supply the concrete with additional water. The two curing methods produced different scaling results; however, the outcomes did not change in terms of meeting or failing the acceptance limit. Curing in plastic wraps produced higher carbonation depth prior to exposing the sample to the salt solution. This could have contributed, partly, to the higher scaling obtained in wrapped samples, other than the sample with 40% high-calcium fly ash. For this sample, there is evidence that curing using plastic wraps maintained high alkali concentration in the surface concrete, which could have enhanced the pozzolanic activity of the fly ash at the surface.

scholarly journals Prediction Models for Thermal Conductivity of Cement-based Composites

2018 ◽  
Vol 58 (1) ◽  
pp. 163-171 ◽  
Author(s):  
Mohammad H. Baghban ◽  
Mahdi Kioumarsi ◽  
Sotirios Grammatikos
Keyword(s):  
Thermal Conductivity ◽  
Construction Industry ◽  
Prediction Models ◽  
Cementitious Materials ◽  
Mix Design ◽  
Structural Elements ◽  
Building Envelopes ◽  
Heating Systems ◽  
Cement Based Materials ◽  
Floor Heating

Abstract Cement-based materials are the most consumed materials in the construction industry. Low or high thermal conductive cement-based materials are of interest in applications such as embedded floor heating systems, building envelopes or structural elements. This paper describes prediction models for thermal conductivity of cementitious composites by considering different variables such as constituent materials, porosity and moisture content. The presented prediction models may be used for thermal conductivity based mix design of cementitious materials. Based on the desired accuracy, different solutions are proposed.

scholarly journals Meta-Analysis and Machine Learning Models to Optimize the Efficiency of Self-Healing Capacity of Cementitious Material

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4437
Author(s):  
Shashank Gupta ◽  
Salam Al-Obaidi ◽  
Liberato Ferrara
Keyword(s):  
Meta Analysis ◽  
Cementitious Materials ◽  
Initial Crack ◽  
Supplementary Cementitious Materials ◽  
Structural Performance ◽  
Self Healing ◽  
Design Strategies ◽  
Healing Efficiency ◽  
Cement Based Materials ◽  
Artificial Neural Network Ann

Concrete and cement-based materials inherently possess an autogenous self-healing capacity. Despite the huge amount of literature on the topic, self-healing concepts still fail to consistently enter design strategies able to effectively quantify their benefits on structural performance. This study aims to develop quantitative relationships through statistical models and artificial neural network (ANN) by establishing a correlation between the mix proportions, exposure type and time, and width of the initial crack against suitably defined self-healing indices (SHI), quantifying the recovery of material performance. Furthermore, it is intended to pave the way towards consistent incorporation of self-healing concepts into durability-based design approaches for reinforced concrete structures, aimed at quantifying, with reliable confidence, the benefits in terms of slower degradation of the structural performance and extension of the service lifespan. It has been observed that the exposure type, crack width and presence of healing stimulators such as crystalline admixtures has the most significant effect on enhancing SHI and hence self-healing efficiency. However, other parameters, such as the amount of fibers and Supplementary Cementitious Materials have less impact on the autogenous self-healing. The study proposes, through suitably built design charts and ANN analysis, a straightforward input–output model to quickly predict and evaluate, and hence “design”, the self-healing efficiency of cement-based materials.

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