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Quantification of hydration products in cementitious materials incorporating silica nanoparticles
L. P. SINGH,A. GOEL,S. K. BHATTACHARYYA,G. MISHRA
Front. Struct. Civ. Eng.. 2016, 10 (2): 162-167.
https://doi.org/10.1007/s11709-015-0315-9
In the present work, silica nanoparticles (30-70nm) were supplemented into cement paste to study their influence on degree of hydration, porosity and formation of different type of calcium-silicate-hydrate (C-S-H) gel. As the hydration time proceeds, the degree of hydration reach to 76% in nano-modified cement paste whereas plain cement achieve up to 63% at 28 days. An influence of degree of hydration on the porosity was also determined. In plain cement paste, the capillary porosity at 1hr is ~48%, whereas in silica nanoparticles added cement is ~35 % only, it revealed that silica nanoparticles refines the pore structure due to accelerated hydration mechanism leading to denser microstructure. Similarly, increasing gel porosity reveals the formation of more C-S-H gel. Furthermore, C-S-H gel of different Ca/Si ratio in hydrated cement paste was quantified using X-ray diffractometer and thermogravimetry. The results show that in presence of silica nanoparticles, ~24% C-S-H (Ca/Si<1.0) forms, leading to the formation of polymerised and compact C-S-H. In case of plain cement this type of C-S-H was completely absent at 28 days. These studies reveal that the hydration mechanism of the cement can be tuned with the incorporation of silica nanoparticles and thus, producing more durable cementitious materials.
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Microstructural and photocatalytic characterization of cement-paste sol-gel synthesized titanium dioxide
Elena CERRO-PRADA,Miguel MANSO,Vicente TORRES,Jesús SORIANO
Front. Struct. Civ. Eng.. 2016, 10 (2): 189-197.
https://doi.org/10.1007/s11709-015-0326-6
A route for the in paste synthesis of TiO2 loaded cement is described. TiO2 sols are blended with fresh cement paste as an alternative process to add photocatalytic functionality to cement. The modification of cement paste structure after the addition of TiO2 sols is analyzed by XRD, SEM and TGA. As a particular microstructural feature, TiO2 containing calcium silicate hydrate (C-H-S) particles are identified as networking centers of a C-S-H gel fiber matrix. The increase of the TiO2 sol concentration induces a decrease of pore size and an increase in the specific surface area in the cement composites. The photocatalytic activity of the TiO2/cement system is evaluated from the degradation of Methylene Blue (MB) under UV irradiation, monitored through the absorbance at 665 nm. The results show that, although TiO2 phases reveal no long range order structure, the cement paste exothermal treatment in presence of hydrate products and alkaline conditions leads to a photocatalytic composite. Such new cement matrix may be twofold advantageous since it additionally promotes the formation of C-S-H gel, main determinant of cement mechanical properties.
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New approach to determine the plastic viscosity of self-compacting concrete
M. BENAICHA,X. ROGUIEZ,O. JALBAUD,Y. BURTSCHELL,A. Hafidi ALAOUI
Front. Struct. Civ. Eng.. 2016, 10 (2): 198-208.
https://doi.org/10.1007/s11709-015-0327-5
The rheology of concrete is best measured with the use of a rheometer. The slump flow test gives a good indication of the flowability of the mixture and is therefore still used extensively to judge the workability of SCC mixtures. However, this test presents some defects. The objective of this paper is to develop a new methodology for measuring the workability of a SCC. In this article, we have proposed a correlation between the plastic viscosity of concrete, the time and the characteristics of the flow final profile from the V-funnel coupled to a Plexiglas horizontal channel. The proposed approach, verified by experimental results, represents a simple, economical and usable tool on building site, and it allows to characterize rheologically the SCC from its flow. The comparison between our approach and the experimental values of the plastic viscosity shows that, in a laboratory or on site, instead of using a rheometer we can use our approach to characterize the rheological behavior of a SCC.
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Carbonized nano/microparticles for enhanced mechanical properties and electromagnetic interference shielding of cementitious materials
Rao Arsalan KHUSHNOOD,Sajjad AHMAD,Luciana RESTUCCIA,Consuelo SPOTO,Pravin JAGDALE,Jean-Marc TULLIANI,Giuseppe Andrea FERRO
Front. Struct. Civ. Eng.. 2016, 10 (2): 209-213.
https://doi.org/10.1007/s11709-016-0330-5
In the present work, carbon nano/microparticles obtained by controlled pyrolysis of peanut (PS) and hazelnut (HS) shells are presented. These materials were characterized by Raman spectroscopy and field emission-scanning electron microscopy (FE-SEM). When added to cement paste, up to 1 wt%, these materials led to an increase of the cement matrix flexural strength and of toughness. Moreover, with respect to plain cement, the total increase in electromagnetic radiation shielding effect when adding 0.5 wt% of PS or HS in cement composites is much higher in comparison to the ones reported in the literature for CNTs used in the same content.
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The effect of carbon nanotubes and polypropylene fibers on bond of reinforcing bars in strain resilient cementitious composites
Souzana P. TASTANI,Maria S. KONSTA-GDOUTOS,Stavroula J. PANTAZOPOULOU,Victor BALOPOULOS
Front. Struct. Civ. Eng.. 2016, 10 (2): 214-223.
https://doi.org/10.1007/s11709-016-0332-3
Stress transfer between reinforcing bars and concrete is engaged through rib translation relative to concrete, and comprises longitudinal bond stresses and radial pressure. The radial pressure is equilibrated by hoop tension undertaken by the concrete cover. Owing to concrete’s poor tensile properties in terms of strength and deformability, the equilibrium is instantly released upon radial cracking of the cover along the anchorage with commensurate abrupt loss of the bond strength. Any improvement of the matrix tensile properties is expected to favorably affect bond in terms of strength, resilience to pullout slip, residual resistance and controlled slippage.The aim of this paper is to investigate the local bond of steel bars developed in adverse tensile stress conditions in the concrete cover. In the tests, the matrix comprises a novel, strain resilient cementitious composite (SRCC) reinforced with polypropylene fibers (PP) with the synergistic action of carbon nano-tubes (CNT). Local bond is developed over a short anchorage length occurring in the constant moment region of a four-point bending short beam. Parameters of investigation were the material structure (comprising a basic control mix, reinforced with CNTs and/or PP fibers) and the age of testing. Accompanying tests used to characterize the cementitious material were also conducted. The test results illustrate that all the benefits gained due to the synergy between PP fibers and CNTs in the matrix, namely the maintenance of the multi-cracking effect with time, the increased strength and deformability as well as the highly increased material toughness, were imparted in the recorded bond response. The local bond response curves thus obtained were marked by a resilient appearance exhibiting sustained strength up to large levels of controlled bar-slip; the elasto-plastic bond response envelope was a result of the confining synergistic effect of CNTs and the PP fibers, and it occurred even without bar yielding.
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