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.

scholarly journals Heat-Induced Acceleration of Pozzolanic Reaction Under Restrained Conditions and Consequent Structural Modification

Materials ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 2950
Author(s):  
Nankyoung Lee ◽  
Yeonung Jeong ◽  
Hyunuk Kang ◽  
Juhyuk Moon
Keyword(s):  
High Temperature ◽  
Silica Fume ◽  
High Performance ◽  
Structural Modification ◽  
Cement Hydration ◽  
Mechanical Performance ◽  
High Performance Concrete ◽  
Pozzolanic Reaction ◽  
Strength Development ◽  
Ultra High Performance Concrete

This study investigated the heat-induced acceleration of cement hydration and pozzolanic reaction focusing on mechanical performance and structural modification at the meso- and micro-scale. The pozzolanic reaction was implemented by substituting 20 wt.% of cement with silica fume, considered the typical dosage of silica fume in ultra-high performance concrete. By actively consuming a limited amount of water and outer-formed portlandite on the unreacted cement grains, it was confirmed that high-temperature curing greatly enhances the pozzolanic reaction when compared with cement hydration under the same environment. The rate of strength development from the dual reactions of cement hydration and pozzolanic reaction was increased. After the high-temperature curing, further strength development was negligible because of the limited space availability and preconsumption of water under a low water-to-cement environment. Since the pozzolanic reaction does not directly require the anhydrous cement, the reaction can be more easily accelerated under restrained conditions because it does not heavily rely on the diffusion of the limited amount of water. Therefore, it significantly increases the mean chain length of the C–S–H, the size of C–S–H globules with a higher surface fractal dimension. This finding will be helpful in understanding the complicated hydration mechanism of high-strength concrete or ultra-high performance concrete, which has a very low water-to-cement ratio.

Effect of Copper Slag as a Fine Aggregate on the Durability Characteristics of High-Performance Concrete (HPC) Containing Silica Fume

2020 ◽  
Vol 07 (02) ◽  
pp. 1-10
Author(s):  
Rizwan Ahmad Khan ◽  
Keyword(s):  
Silica Fume ◽  
High Performance ◽  
High Performance Concrete ◽  
Copper Slag ◽  
Chloride Penetration ◽  
Interfacial Transition Zone ◽  
Fine Aggregate ◽  
Fresh Properties ◽  
Fine Aggregates ◽  
Effect Of Copper

This paper investigates the fresh and durability properties of the high-performance concrete by replacing cement with 15% Silica fume and simultaneously replacing fine aggregates with 25%, 50%, 75% and 100% copper slag at w/b ratio of 0.23. Five mixes were analysed and compared with the standard concrete mix. Fresh properties show an increase in the slump with the increase in the quantity of copper slag to the mix. Sorptivity, chloride penetration, UPV and carbonation results were very encouraging at 50% copper slag replacement levels. Microstructure analysis of these mixes shows the emergence of C-S-H gel for nearly all mixes indicating densification of the interfacial transition zone of the concrete.

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.

scholarly journals Enhancement of Material Properties of Lime-Activated Slag Mortar from Intensified Pozzolanic Reaction and Pore Filling Effect

2018 ◽  
Vol 10 (11) ◽  
pp. 4290 ◽  
Author(s):  
Yang-Hee Kwon ◽  
Sung-Hoon Kang ◽  
Sung-Gul Hong ◽  
Juhyuk Moon
Keyword(s):  
Silica Fume ◽  
Material Properties ◽  
Pozzolanic Reaction ◽  
Physical Effect ◽  
Strength Development ◽  
Pore Filling ◽  
Improvement Strategy ◽  
Microstructural Investigation ◽  
Curing Condition ◽  
Activated Slag

To utilize alkali-activated materials widely, this study investigates the effects of an intensified pozzolanic reaction and pore filling by silica fume on various material properties of lime-activated slag mortar. Although ground-granulated blast-furnace slag is classified as a cementitious material, it commonly requires an activator to enhance the performance of structural materials. In the first step of the improvement strategy, slag reaction is activated by hydrated lime. Next, silica fume is added to densify the microstructure by the physical pore filling effect and/or the pozzolanic reaction that additionally forms hydration products. This increased the compressive strength by 18% at 28 days and by 25% at 91 days under ambient curing condition, mainly due to the physical effect. Moreover, elevated temperature curing for three days was highly effective to further improve the strength, and to accelerate strength development. This is because both the physical effect and the chemical reaction are effective at the high temperature curing condition. The conducted microstructural investigation provided the evidence for the intensified pozzolanic reaction and pore filling effect, both of which are closely related to the mechanical properties. It is also found that the use of silica fume positively contributes to the dimensional stability. Since the developed material exhibits high strength (>40 MPa after 14 days) without Portland cement or highly toxic chemicals, it can be practically used as an eco-friendly structural mortar.

The pozzolanic reaction of metakaolinite and its effects on Portland cement hydration

1993 ◽  
Vol 28 (5) ◽  
pp. 1345-1350 ◽  
Author(s):  
A. M. Dunster ◽  
J. R. Parsonage ◽  
M. J. K. Thomas
Keyword(s):  
Portland Cement ◽  
Cement Hydration ◽  
Pozzolanic Reaction ◽  
Portland Cement Hydration

The Influence of the Amount of Silica Fume on the Mechanical Property of Ultra-High Performance Concrete

2008 ◽  
Vol 385-387 ◽  
pp. 701-704 ◽  
Author(s):  
Jung Jun Park ◽  
Gum Sung Ryu ◽  
Su Tae Kang ◽  
Sung Wook Kim
Keyword(s):  
Mechanical Property ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Flexural Strength ◽  
Silica Fume ◽  
High Performance ◽  
Mechanical Characteristics ◽  
High Performance Concrete ◽  
Micro Structure ◽  
Ultra High Performance Concrete

Silica fume constitutes an element of extreme importance in improving the strength and fluidity of UHPC. The adopted amount of silica fume generally is generally exceeding 25% of cement in weight but the influence of this amount on the properties of UHPC is still remaining as a domain to be investigated. Accordingly, this paper investigates the effects of the amount of silica fume on the mechanical characteristics of the fluidity, compressive strength, elastic modulus and flexural strength and on the micro structure of UHPC by means of SEM and MIP. Results revealed that adequate amount of silica fume is improving the fluidity and strength. MIP tests demonstrated that such improvement is brought by the increase of hydrates due to the pozzolan reaction and the effective densification inside concrete due to the filler. It seemed also that similar mechanical characteristics can be obtained for a volumetric ratio to cement ranging between 10 and 25%.

scholarly journals The effects of seawater on the hydration, microstructure and strength development of Portland cement pastes incorporating colloidal silica

2019 ◽  
Vol 10 (8) ◽  
pp. 2627-2638 ◽  
Author(s):  
Pawel Sikora ◽  
Krzysztof Cendrowski ◽  
Mohamed Abd Elrahman ◽  
Sang-Yeop Chung ◽  
Ewa Mijowska ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Synergistic Effect ◽  
Portland Cement ◽  
Colloidal Silica ◽  
Cement Hydration ◽  
Pozzolanic Reaction ◽  
Strength Development ◽  
Hydration Kinetics ◽  
Cement Pastes ◽  
Noticeable Improvement

AbstractThis contribution investigates the effects of seawater and colloidal silica (NS) in the amounts of 1, 3 and 5 wt%, respectively, on the hydration, strength development and microstructural properties of Portland cement pastes. The data reveal that seawater has an accelerating effect on cement hydration and thus a significant contribution to early strength development was observed. The beneficial effect of seawater was reflected in an improvement in compressive strength for up to 14 days of hydration, while in the 28 days compressive strength values were comparable to that of cement pastes produced with demineralized water. The combination of seawater and NS significantly promotes cement hydration kinetics due to a synergistic effect, resulting in higher calcium hydroxide (CH) production. NS can thus react with the available CH through the pozzolanic reaction and produce more calcium silicate hydrate (C-S-H) gel. A noticeable improvement of strength development, as the result of the synergistic effect of NS and seawater, was therefore observed. In addition, mercury intrusion porosimetry (MIP) tests confirmed significant improvements in microstructure when NS and seawater were combined, resulting in the production of a more compact and dense hardened paste structure. The optimal amount of NS to be mixed with seawater, was found to be 3 wt% of cement.

Literature Review: Mechanical Properties of Hardened Silica Fume Concrete

2014 ◽  
Vol 1008-1009 ◽  
pp. 1357-1362
Author(s):  
Xi Xi He ◽  
Qing Wang
Keyword(s):  
Silica Fume ◽  
High Performance ◽  
High Performance Concrete ◽  
Chloride Ion ◽  
High Strength ◽  
Penetration Resistance ◽  
Pozzolanic Reaction ◽  
Mineral Admixture ◽  
Chemical Attack ◽  
Chloride Ion Penetration

Silica fume (SF) has become an environmental mineral admixture in the production of high-strength and high-performance concrete in modern concrete engineering. Through compacting all components and pozzolanic reaction, obvious mechanical enhancement of concrete is observed in the aspects of compressive strength tensile strength, elastic modulus as well as fracture toughness. Further more, durability improvement of silica fume concrete such as chloride-ion penetration resistance and chemical attack resistance are reported accordingly.

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