Relationship between Fluidity and Stability of Self-Consolidating Mortar Incorporating Chemical and Mineral Admixtures

In this study, the effect of chemical and mineral admixtures, including superplasticizer, viscosity modifying agent (VMA), limestone powder and fly ash in different W/C on fluidity, viscosity, and stability of self-consolidating mortar is investigated and proper workability regions for the prepared mixtures are presented. The obtained results indicate that W/C is the most significant parameter influencing the rheological properties of cementitious mixtures, specially their stability. Furthermore, the maximum allowable W/C for preventing inhomogeneity could not be a fixed value for all the mixtures and should be adjusted for the target fluidity. On the other hand, using VMAs is an effective method for stabilizing self-consolidating mortars and preventing any kinds of instability while limestone powder and fly ash mainly affect bleeding and aggregate blockage. Besides, these mineral admixtures improved the fluidity of the mixtures to some extent

Repeatability, Responsiveness and Relative Cost Analysis of SCC Workability Test Methods

There are several workability test methods proposed to evaluate workability of self-consolidating concrete (SCC). Most of these methods are not standard, and their reliability is still under question. In this study, a comprehensive experimental program and statistical analysis were performed to evaluate the repeatability, responsiveness and relative cost of commonly used SCC workability test methods. Ten different tests including the slump flow, V-funnel, J-ring, L-box, U-box, column segregation, segregation probe, flow trough, sieve stability and surface bleeding tests were considered herein. For evaluating the suitability of these tests, each test was repeated several times on SCC mixtures with different workability levels. The obtained results show that the slump flow and the J-ring tests are well suited for evaluating the flowability, and the segregation probe, column segregation and surface bleeding tests are appropriate tests for assessing the stability of SCC. Furthermore, when SCC is planned for use in congestly reinforced members, it is recommended to use the U-box and the V-funnel tests in addition to the former ones to ensure the passing ability of SCC mixture and avoid any blockage

Volume stability of calcium-silicate-hydrate/polyaniline nanocomposites in aqueous salt solutions

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.Peer reviewed: YesNRC publication: Ye

Interaction of 2-, 3- and 4-nitrobenzoic acid with the structure of calcium\u2013silicate\u2013hydrate

Interaction of nitrobenzoic acid (NBA) with the structure of calcium\u2013silicate\u2013hydrate (C\u2013S\u2013H) was investigated. Phase pure C\u2013S\u2013H and C\u2013S\u2013H with 2-, 3- or 4NBA (0.01 and 0.02 mol/mol of Ca) were synthesized, and characterized by the X-ray diffraction, thermal analysis, Fourier transform infrared spectroscopy and scanning electron microscope techniques. Nitrogen adsorption measurements were also performed to estimate the surface area of the samples. It is suggested that all NBA isomers with the concentration of 0.01 mol/mol of Ca were able to fill the defects on the surface of the C\u2013S\u2013H layers, block access to the space between the stacked C\u2013S\u2013H layers, and possibly partially intercalate the layered structure. The C\u2013S\u2013H-based samples prepared with different types of NBA compounds, however, had different characteristics. The interaction of organic and inorganic phases was limited in the samples incorporating higher concentration of NBA. Traces of unreacted NBA were detected in a few samples with 0.02 mol of NBA/mol of Ca.Peer reviewed: YesNRC publication: Ye

Volume stability of calcium sulfoaluminate phases

The volume stability of calcium sulfoaluminate phases exposed to water, lime, and gypsum environments was investigated. The length changes of compacted specimens of synthetic monosulfate and ettringite were monitored in distilled water, lime-saturated water, gypsum-saturated water, and saturated water vapor. The X-ray diffraction analysis was also performed on the samples to assess the changes in the crystalline structure of each phase. Evidence was provided in support of the significant role of dissolution of monosulfate and ettringite, and the leaching of their constituent ions, on the expansion of these phases. \ua9 2012 The American Ceramic Society.Peer reviewed: YesNRC publication: Ye

Durability and mechanical properties of C\u2013S\u2013H/nitrobenzoic acid composite systems

The influence of nitrobenzoic acid on the nanostructure of calcium-silicate-hydrate (C\u2013S\u2013H) systems has been recently investigated by the authors. This study focuses on the assessment of durability and mechanical performance of the C\u2013S\u2013H/nitrobenzoic acid composite systems. In this context different nitrobenzoic acid isomers in various concentrations were studied. The C\u2013S\u2013H-based preparations were compacted into porous bodies. Their dimensional stability and the leaching of calcium ions in aqueous salt solutions containing Mg\ub2\u207a, Li\u207a, Cl\u207b or SO\u2084\ub2\u207b 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\u2013S\u2013H 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.Peer reviewed: YesNRC publication: Ye

Volume stability of calcium-silicate-hydrate/polyaniline nanocomposites in aqueous salt solutions

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.Peer reviewed: YesNRC publication: Ye