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Khoshnazar R.,National Research Council Canada | Beaudoin J.J.,National Research Council Canada | Raki L.,National Research Council Canada | Alizadeh R.,Giatec Scientific
Materials and Structures/Materiaux et Constructions | Year: 2016

The influence of nitrobenzoic acid on the nanostructure of calcium-silicate-hydrate (C–S–H) systems has been recently investigated by the authors. This study focuses on the assessment of durability and mechanical performance of the C–S–H/nitrobenzoic acid composite systems. In this context different nitrobenzoic acid isomers in various concentrations were studied. The C–S–H-based preparations were compacted into porous bodies. Their dimensional stability and the leaching of calcium ions in aqueous salt solutions containing Mg2+, Li+, Cl− or SO4 2− ions were evaluated. The resistance of the compacted samples to the diffusion of isopropyl alcohol was also obtained by the mass-change measurements. The microindentation technique was used to measure the creep modulus and the hardness of the samples. Evidence was obtained that nitrobenzoic acid has the potential to significantly improve the durability and mechanical properties of the C–S–H systems. This improvement, however, only occurred in the systems with the lower concentration of nitrobenzoic acid. The systems with higher concentration of nitrobenzoic acid had reduced durability and mechanical performance due to the limited interaction of the organic and inorganic phases in these systems. © 2016 RILEM Source


Pourbeik P.,University of Ottawa | Beaudoin J.J.,National Research Council Canada | Alizadeh R.,Giatec Scientific | Raki L.,National Research Council Canada
Materials and Structures/Materiaux et Constructions | Year: 2015

A dynamic mechanical analysis (DMTA) technique was used to assess the mechanical performance of 1.4 nm tobermorite (T), jennite (J) and mixtures of tobermorite and jennite and tobermorite and calcium hydroxide (CH). A comparison of E′ (storage modulus) and tan∂ (internal friction) versus temperature curves for compacted solid bodies of these mineral systems with corresponding curves for cement paste hydrated for 2 month and 3 years (both referred to as ‘young’) and 45-year-old paste (referred to as ‘old’) was made. Original data was provided to assess the practical validity of the Richardson–Groves composition-based models for the C-S-H in cement paste. Differences in mechanical performance between the ‘young’ paste and the ‘old’ paste could be accounted for by application of a T/J dominant model (‘young’ paste) and a J–T/CH structural model with a minor amount of T (‘old paste’). © 2014, RILEM. Source


Nguyen D.-T.,University of Ottawa | Alizadeh R.,Giatec Scientific | Beaudoin J.J.,National Research Council Canada | Raki L.,National Research Council Canada
Materials and Structures/Materiaux et Constructions | Year: 2013

Microindentation creep measurements were obtained on compacted specimens of several secondary hydrated cement phases in equilibrium with water vapor at 11%RH. Values of creep modulus, indentation modulus and indentation hardness for calcium hydroxide, ettringite, gypsum and calcium carbonate are reported. The porosity dependence of these parameters was established and the significance of porosity on the time-dependent deformation of these materials was discussed. In addition the microindentation creep behavior of pure C-S-H and C3S paste hydrated 32 years was determined. The discussion focuses on the relative importance of the contribution of the secondary phases in hydrated cement-based materials to creep with respect to the more 'active' C-S-H phase. © 2012 RILEM. Source


Pourbeik P.,National Research Council Canada | Beaudoin J.J.,National Research Council Canada | Alizadeh R.,Giatec Scientific | Raki L.,National Research Council Canada
Advances in Cement Research | Year: 2015

Dynamic mechanical thermal analysis (DMTA) measurements for layered calcium silicate systems (1.4 nm tobermorite, jennite, synthetic calcium-silicate-hydrate and hydrated Portland cement paste) are reported. Elastic modulus results were obtained for samples initially conditioned to 11% relative humidity (RH) and dried during the DMTA test and for samples subjected to prolonged vacuum and thermal drying prior to a DMTA test. Decreases in elastic modulus relative to the 11% RH starting condition typically observed during a DMTA test were recovered subsequent to the prolonged thermal treatment. A possible 'regeneration' mechanism for the elastic modulus is discussed. The 'regeneration' occurs for all the calcium silicate systems studied. The results are consistent with the notions expressed for nanostructural models of calcium-silicate-hydrate in cement paste that comprise structural units based on 1.4 nm tobermorite and jennite. Source


Khoshnazar R.,University of Ottawa | Beaudoin J.J.,National Research Council Canada | Raki L.,National Research Council Canada | Alizadeh R.,Giatec Scientific
ACI Materials Journal | Year: 2014

The volume stability of phase pure calcium-silicate-hydrates (C-S-H) and C-S-H/polyaniline nanocomposites prepared with two CaO-SiO2 molar ratio (C/S) variations (0.8 and 1.2) was assessed in MgSO4, MgCl2, LiCl, and NaCl aqueous solutions. The change in the crystalline structure of the samples with the time of immersion was also explored using X-ray diffraction, scanning electron microscopy, and thermal gravimetric analysis techniques. It was observed that the modification of the C-S-H samples with polyaniline significantly enhanced their volume stability and durability in all the salt solutions. The beneficial effect of the polyaniline modification was more pronounced in the C-S-H host with higher C/S (C/S = 1.2). The longitudinal expansion of the C-S-H/polyaniline nanocomposites with C/S = 1.2 in the salt solutions was about 30% of that of the phase pure C-S-H with a similar C/S ratio. In addition, the polyaniline modification of C-S-H samples reduced the rate of formation of gypsum, brucite, and other reaction products in the samples. © 2014, American Concrete Institute. Source

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