Abstract:Important properties in cementitious materials, such as concrete, are related to the presence of additives that influence the rigidity and the physical and chemical resistances. For the evaluation of the additive effectiveness, known as pozzolanic activity, a simple procedure, the Chapelle test, is commonly used, and it essentially consists in a reaction between the additive with calcium oxide in aqueous medium. However, such procedure presents limitations in terms of processing time and lack of information re… Show more
“…SF has a diffuse dome at 13°–32° 2θ, and is almost entirely 100% amorphous 51 , 52 . Quartz powder has a high crystallinity (98% by Rietveld refinement, in mass), i.e., the milling process has little influence on the long-range ordering of quartz despite the high fineness of the particles obtained 29 , 52 . Figure 1 XRD patterns of quartz powder and silica fume.…”
Supplementary cementitious materials interact chemically and physically with cement, influencing the formation of hydrate compounds. Many authors have analyzed the filler and pozzolanic effect. However, few studies have explored the influence of these effects on hydration, properties in the fresh and hardened states, and durability parameters of cementitious composites separately. This study investigates the influence of the replacement of 20% of Portland cement for silica fume (SF) or a 20-µm medium diameter quartz powder (QP) on the properties of cementitious composites from the first hours of hydration to a few months of curing. The results indicate that SF is pozzolanic and that QP has no pozzolanic activity. The use of SF and QP reduces the released energy at early times to the control paste, indicating that these materials reduce the heat of hydration. The microstructure with fewer pores of SF compounds indicates that the pozzolanic reaction reduced pore size and binding capability, resulting in equivalent mechanical properties, reduced permeability and increased electrical resistance of the composites. SF and QP increase the carbonation depth of the composites. SF and QP composites are efficient in the inhibition of the alkali-aggregate reaction. The results indicate that, unlike the filler effect, the occurrence of pozzolanic reaction strongly influences electrical resistance, reducing the risk of corrosion of the reinforcement inserted in the concrete.
“…SF has a diffuse dome at 13°–32° 2θ, and is almost entirely 100% amorphous 51 , 52 . Quartz powder has a high crystallinity (98% by Rietveld refinement, in mass), i.e., the milling process has little influence on the long-range ordering of quartz despite the high fineness of the particles obtained 29 , 52 . Figure 1 XRD patterns of quartz powder and silica fume.…”
Supplementary cementitious materials interact chemically and physically with cement, influencing the formation of hydrate compounds. Many authors have analyzed the filler and pozzolanic effect. However, few studies have explored the influence of these effects on hydration, properties in the fresh and hardened states, and durability parameters of cementitious composites separately. This study investigates the influence of the replacement of 20% of Portland cement for silica fume (SF) or a 20-µm medium diameter quartz powder (QP) on the properties of cementitious composites from the first hours of hydration to a few months of curing. The results indicate that SF is pozzolanic and that QP has no pozzolanic activity. The use of SF and QP reduces the released energy at early times to the control paste, indicating that these materials reduce the heat of hydration. The microstructure with fewer pores of SF compounds indicates that the pozzolanic reaction reduced pore size and binding capability, resulting in equivalent mechanical properties, reduced permeability and increased electrical resistance of the composites. SF and QP increase the carbonation depth of the composites. SF and QP composites are efficient in the inhibition of the alkali-aggregate reaction. The results indicate that, unlike the filler effect, the occurrence of pozzolanic reaction strongly influences electrical resistance, reducing the risk of corrosion of the reinforcement inserted in the concrete.
“…The VAD system is designed for the fabrication of completely amorphous silica glass of high transparency, destined for the production of optical fiber preforms and other photonic components [26,27]. Therefore, due to the high purity and morphological control of the silica, and to the wide availability of characterization data of these particles [12,27,28], the use of the in-situ synthesized nanoparticles was preferred over commercially available materials.…”
This work presents an optical fiber dynamic light scattering sensor capable of simultaneously assessing concentration and flow speed of nanofluids. Silica nanoparticles (189 nm) in water were tested, yielding a sensitivity of 0.78288 × 10³ s−1 for static conditions. Then, the sensor was submitted to situations that simulate spatial concentration changes, offering better results than those obtained by traditional mathematical models. Finally, in flow tests, the light backscattered by the nanoparticles were collected by a fiber probe placed parallel to the streamline, whereas intensity values were processed by artificial neural networks. The sensor provides average errors of 0.09 wt% and 0.26 cm/s for concentration and speed measurements, respectively, and can be further applied to assess different types of nanofluids and inline processes.
“…Silica soot nanoparticles were synthesized by the Vapor-phase Axial Deposition (VAD) method, according to the procedure described in previous research where the process parameters are detailed (Soares et al, 2018). Basically, a high-temperature O 2 -H 2 flame promotes the hydrolysis and oxidation of SiCl 4 on the surface of a rotating target, producing the silica nanoparticles in accordance with Reaction 1.…”
Section: Silica Nanoparticle Synthesis and Characterization And Preparation Of Colloidal Suspensionsmentioning
confidence: 99%
“…When irradiated for a long time, these areas become saturated with electrical charges and start repelling electrons from the microscope beam, making it impossible to obtain images of the regions (Raimer, 1998). It can also be noted that the uncertainties (95% CI of the average diameter) are relatively low in comparison to the respective mean diameter (~7.2% of the mean diameter, for the 125 nm particles, S1, and ~5.7%, for the 159 nm particles, S2), showing the low polydispersity characteristic of the VAD synthesis process (Soares et al, 2018).…”
Section: Silica Nanoparticle Synthesis and Characterization And Preparation Of Colloidal Suspensionsmentioning
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