Hydration kinetics study of class G oil-well cement and olivine nano-silica mixtures at 20–60 °C

In this study the heat evolution of standard density slurries (1.89 g/cm3) of Class G oil-well cement and olivine nano-silica additions (0.5–2.0 % bwoc), cured under different temperatures (20–60 °C) and atmospheric pressure, were examined by isothermal calorimetry. Under isothermal and isobaric conditions, the dependency of cement hydration kinetics on curing temperature is related to the activation energy of the cementing slurry. The estimated apparent activation energy of the different slurries with olivine nano-silica varies from 38 to 44 KJ/mol using a dynamic method, at the temperature range of 20–60 °C. It is demonstrated that the addition of olivine nano-silica increases the rate and the heat of hydration of oil-well slurries. These effects are temperature dependent. Finally, comparable hydration degrees were obtained between slurries containing 0.5 % bwoc of olivine nano-silica and 10 % bwoc of oil-well grade micro-silica (mS)

Effect of olivine nano-silica additions on cement based system

In this study, the influence of olivine nano-silica (OnS) additions in cement based systems has been addressed. The obtained results demonstrate that the addition of OnS (1.5–3.8 % bwoc) increases the viscosity, yield point and hydration degree of the cementitious systems, mainly due to the increase of the total specific surface area of the mix. This holds also for the case when a fixed amount of SP is applied. Based on the performed analysis, it is concluded that the OnS acts as an accelerating and pozzolanic agent in concrete

Water layer thickness of silica fines and their effect on the workability of cement pastes

Concrete is used in infrastructure and in buildings. It is composed of granular materials of different sizes and the grading of the composed solid mix covers a wide range. The overall grading of the mix, containing particles from 300 nm to 32 mm, determines the mix properties of the concrete. The properties in fresh state (flow properties and workability) are for instance governed by the particle size distribution (PSD) and the resulting particle packing (PP). One way to further improve the packing is to increase the solid size range, e.g. by including particles with sizes below 300 nm. Possible materials, which are currently available, are limestone and silica fines like silica fume (mS) and nano-silica (nS). This paper addresses the characterization of six different silica fines with respect to their application in cement paste. Given that the fines provide by far the highest percentage of specific surface area in a mix, their packing behavior and water demand is of vital interest for the design of concrete. In the present work, different mixes are compared and analyzed using the mini spread-flow test method. In this way, a deformation coefficient derived by the spread-flow test is confirmed to correlate with the product of computed specific surface area (SSA) based on measured PSD and intrinsic density of the individual silica fines. Similarly, correlations with equal accuracy are found with a computed SSA using the BET method. With the flow experiments of different mixes it is possible to derive an individual deformation coefficient of the silica particles. It is demonstrated that the computed and the BET surface area values have a constant ratio (0.76 to 0.70). Finally, the value of a constant water layer thickness around the powder particles (24.8 nm) is computed for all silica fines at the onset of flowing. This implies the possibility to predict the flow behavior of paste only based on the knowledge of their SSA, either determined by computation or by BET measurements

Production and application of a new type of nano-silica in concrete

In this paper the application of a new nano-silica in concrete is studied. This nano-silica is produced by the dissolution of olivine. The production of nano-silica by the olivine route is a cheaper method than the commercial methods (neutralization of sodium silicate solutions and the flame hydrolysis) because of the low cost of raw materials and the low energy requirements. The produced nano-silica has a specific surface area between 100-400 m2/g, primary particles between 10 to 25 nm (agglomerated in clusters), and an SiO2 content above 95 %. In addition, the pozzolanic properties and the dispersion state of the nano-silica were studied. From these results it is concluded that olivine nano-silica can be applied successfully in concrete because of its high pozzolanic activity

Production and application of a new type of nano-silica in concrete

In this paper the application of a new nano-silica in concrete is studied. This nano-silica is produced by the dissolution of olivine. The production of nano-silica by the olivine route is a cheaper method than the commercial methods (neutralization of sodium silicate solutions and the flame hydrolysis) because of the low cost of raw materials and the low energy requirements. The produced nano-silica has a specific surface area between 100-400 m2/g, primary particles between 10 to 25 nm (agglomerated in clusters), and an SiO2 content above 95 %. In addition, the pozzolanic properties and the dispersion state of the nano-silica were studied. From these results it is concluded that olivine nano-silica can be applied successfully in concrete because of its high pozzolanic activity

Effects of nano-silica (NS) additions on durability of SCC mixtures

In this study, three different types of nano-silica were applied in self-compacting concrete (SCC), one produced by the controlled dissolution of the olivine mineral and two having similar particle size distributions (PSD), but produced through two different processes: fumed powder nano-silica and precipitated silica in colloidal suspension. The influence of the nano-silica on SCC was investigated with respect to the properties of the concrete in fresh (workability) and hardened state (durability properties). Additionally, the densification of the microstructure of the hardened concrete was analyzed by SEM and EDS techniques. The obtained results demonstrate that an efficient use of nano-silica in SCC can improve its durability properties. Considering the reactivity of the different nano-silica studied, the colloidal type showed a higher reactivity at early age, which influenced the final SCC properties

Chloride intrusion and freeze-thaw resistance of self-compacting concrete with two different nano-SiO2

In this study two different types of nano-SiO2 were applied in self-compacting concrete (SCC), both having similar particle size distributions (PSD) but produced in two different processes (pyrogenic and colloidal precipitation). The influence of nano-SiO2 on transport phenomena in SCC was investigated using the accelerated rapid chloride migration test at different ages (28 and 91 days) as well as the long-term diffusion test. The freeze-thaw resistance, expressed by the scaling factor (Sn), was also studied. Additionally, the microstructural characteristics of the hardened concretes were investigated by FEG-SEM and MIP analyses. The obtained results demonstrate that the addition of 3.8% bwoc of nano-SiO2 improves the SCC durability due to the refinement of the microstructure and the reduction in the connectivity of the pores. Additionally, a small difference in the reactivity of both types of applied nano-SiO2 additives was demonstrated

Chloride intrusion and freeze-thaw resistance of self-compacting concrete with two different nano-SiO2

In this study two different types of nano-SiO2 were applied in self-compacting concrete (SCC), both having similar particle size distributions (PSD) but produced in two different processes (pyrogenic and colloidal precipitation). The influence of nano-SiO2 on transport phenomena in SCC was investigated using the accelerated rapid chloride migration test at different ages (28 and 91 days) as well as the long-term diffusion test. The freeze-thaw resistance, expressed by the scaling factor (Sn), was also studied. Additionally, the microstructural characteristics of the hardened concretes were investigated by FEG-SEM and MIP analyses. The obtained results demonstrate that the addition of 3.8% bwoc of nano-SiO2 improves the SCC durability due to the refinement of the microstructure and the reduction in the connectivity of the pores. Additionally, a small difference in the reactivity of both types of applied nano-SiO2 additives was demonstrated

Slump flow of autoclaved aerated concrete slurries

Autoclaved Aerated Concrete (AAC) is already well known in Central Europe for decades. In traditional cement and concrete research a huge increase of knowledge has improved the material behaviour and efficiency. The understanding of the mineral reactions and properties in AAC has also improved, but several relations are still unknown. In this research a closer look is taken on the influence of the water amount and the mixing procedure on the viscosity determined by the slump flow test. Three different cones were evaluated and two possible evaluation methods presented

Photovoltaic's silica-rich waste sludge as supplementary cementitious materials (SCM)

Waste sludge, a solid recovered from wastewater of photovoltaic-industries, composes of agglomerates of nano-particles like SiO2 and CaCO3. This sludge deflocculates in aqueous solutions into nano-particles smaller than 1000 nm. Thus, this sludge is potentially hazardous waste when is improperly dumped. Due to its high content of amorphous SiO2, this sludge has a potential use as supplementary cementitious material (SCM) in concrete. In this study the main properties of three different samples of photovoltaic silica-rich waste sludge (nSS) were physically and chemically characterized. The characterization techniques included: scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), nitrogen physical adsorption isotherm (BET, t-plot and BJH methods), density by Helium pycnometry, particle size distribution determined by laser light scattering (LLS) and dynamic light scattering (DLS). The effects on the hydration kinetics of cement pastes by the addition of nSS in the designed slurries were determined using an isothermal calorimeter. Finally, the compressive strength tests of standard mortars with 7% of cement replacement were performed to determine the puzzolanic activity of the waste nano-silica sludge. The results demonstrate the nSS can be utilized as SCM to replace portion of cement in mortars, thereby decreasing the CO2 footprint and the environmental impact of concrete