Concentration Of Sodium Hydroxide Solution Research Articles

Effect of treatment conditions on the morphology of date empty fruit bunch lignocellulosic fiber for biocomposite applications

The fiber of the empty date fruit is one of the waste products left after the date fruit is harvested from the date palm. Optimization of the treatment parameters as well as the economics of the treatment process are critical to the successful commercialization of the treatment of natural fibers for the production of biocomposites. Of the natural fiber treatment methods described in previous work, hot water and alkali treatments are the most cost-effective, which justified the choice of these treatment methods in this work. Here, date empty fruit bunch fibers were pulverized to a particle size of 0–500 µm and then treated with boiling water at 100 °C for 3 h or with sodium hydroxide at different concentrations (2, 5, 10%) for 3 h at room temperature with constant stirring at 800 rpm. To confirm the effect of temperature on the fiber treatment, another fiber sample was treated at a 5% concentration of sodium hydroxide solution at an elevated temperature of 80 °C for the same period and stirring condition. The untreated and treated DEFB fibers were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), X-ray fluorescence (XRF), and scanning electron microscopy (SEM). Chemical analysis of the fibers showed that DEFB fiber treated with 5% sodium hydroxide solution at room temperature had the highest cellulose content (52.0%), which was also confirmed by the XRD analysis. The DEFB fiber treated with boiling water exhibited higher thermal stability while the sodium hydroxide-treated fiber exhibited higher crystallinity index and cellulose content. Apparently, DEFB fiber treated with sodium hydroxide solution at 5% concentration for 3 h at room temperature for continuous stirring at 800 rpm offered the best properties. The treated fibers are expected to be viable reinforcement in the production of biocomposites with the goal of achieving energy efficiency. The developed materials could be used in industrial applications such as insulating building systems, automotive parts, and home furniture.

Design and characterization of iron–calcium–aluminium–silicate–hydrate as low-temperature binder

This work aims to synthesize new cementitious materials (binders) using marble powder, rice husk ash, activated laterite and NaOH solution by applying low energy process. The binder was used to stabilize solid precursors (laterite and pozzolan). To achieve this objective, calcium–silicate–hydrate (CSH) was first synthesized at different temperatures (26, 50, 80 and 100 °C). The best physical–mechanical properties were chosen to produce iron–calcium–aluminium–silicate–hydrate [Fe–C(A)SH] at different concentrations of sodium hydroxide solution: 4, 5, 6 M. Finally, the formulated binder at 6 M of NaOH solution was used to stabilize laterite and pozzolans at the following proportions 20%, 30%, 40% and 50%. The samples were characterized after 28 days of curing at room temperature. FT-infrared spectroscopy, X-ray diffraction, and environmental scanning electron microscope ESEM-EDS permitted to confirm the formation of CSH, and Fe–C(A)SH. The mechanical test used to evaluate the performance showed that the incorporation of 10% iron-rich laterite into CSH increased the strength up to 42.93 MPa and the addition of Fe–C(A)SH in the laterite/pozzolans increased the compressive strength of the final product (15.34 and 15.8 MPa for laterite and pozzolan, respectively). The highest concentration (6 M) increases the alkalinity and reduces the efficiency of silicate polymerization affecting the final structural compound. From the results, low-energy Fe–C(A)SH-based cement and stabilized compounds appeared promising for the development of sustainable infrastructures.

PHYSICO-CHEMICAL PROCESSES OF ALKALINE ACTIVATION OF SILICA DURING HEAT TREATMENT IN THE SIO2-NaOH-H2O SYSTEM

The physicochemical processes during alkaline activation of the SiO2-NaOH-H2O system with crystalline silica have been investigated. The studies were carried out using thermogravimetric, X-ray phase analysis methods and IR spectroscopy data. Compositions with different silicate modulus (SiO2/Na2O 4-7), the amount of the introduced silica fume (10-30%) in substitution of marshalite and the concentration of sodium hydroxide solution (30-60 wt.%) are considered. According to the results of the study, the reactions of interaction of the components and a model of phase transformations in the composition when it is heated to 850 °C are proposed. At the stage of interaction of the components (30-130 °C), hydration processes occur with the formation of sodium hydrosilicate Na2SiO3(OH), with on the surface of which a layer of crystallohydrate water and a water layer to be formed without formation of free water. When the composition is heated to temperatures of 130-300 °С the water layer and then the crystallohydrate water are removed. The removed water interacts with unreacted silica and forms hydrated forms of silica. Upon further heating to temperatures of 310-800 °C, OH groups are removed from sodium hydrosilicates and hydrated forms of silica and it turns into anhydrous silicates. Heating the composition to 850 °C leads to the formation of a pyroplastic mass from a eutectic melt (Na2O·2SiO2–SiO2) and residual silica. The two-stage mechanism of formation of a porous frame is established at the stage of decomposition of sodium hydrosilicate crystallohydrates (80-200 °C) and at the stage of melt foaming at high temperatures (790-850 °C). Foaming occurs due to the removal of water vapor (80-200 °C) and the expansion of the volume of gases (790-850 °C) in the porous structure formed at the first stage of foaming. The developed compound of the high-modulus composition (SiO2/Na2O 5,7) is a basis to obtain a porous glass composite using a two-stage alkaline technology with the introduction of additional oxides that increase chemical resistance. The composition includes the following components, wt.%: marshalite – 50, silica fume – 23, sodium hydroxide – 16, water – 11.

Extraction process, physicochemical properties, and digestive performance of red yeast rice starch.

In the present study, taking red yeast rice (RYR) as the raw material, the optimum extraction process of RYR starch was investigated through a single-factor experiment and the Box-Behnken design: The liquid-to-solid ratio was 5mL/g, the concentration of sodium hydroxide solution was 0.075mol/L, and the extraction time was 3.1h. Under these extraction conditions, the extraction rate of starch reached 90.077%. To explore the influence of solid-state fermentation on RYR starch, three different fermentation stages of RYR starch, raw rice starch, semi-gelatinized rice starch, and RYR starch were used as test materials to determine the changes in the physicochemical properties and glycemic index (GI) values of RYR starch during solid-state fermentation. The results showed that with the advancement of the RYR solid-state fermentation process, the starch particle size gradually increased, the light transmittance gradually decreased, and the solubility and swelling power significantly increased. In addition, the amylose content of starch gradually increased, whereas the amylopectin content gradually decreased; the content of fast digestible starch and slow digestible starch decreased, whereas the content of resistant starch increased. In parallel, during solid-state fermentation, the hydrolysis index significantly decreased, and the GI values also decreased. In summary, solid-state fermentation reduced the digestibility of RYR starch. These results provide a theoretical basis for the structural and physicochemical properties of RYR starch and lay a foundation for its subsequent application and expansion of RYR starch.

In-situ synthesis of fluorine-free MXene/TiO2 composite for high-performance supercapacitor

MXene (Ti3C2Tx) is a promising electrode material for supercapacitors. However, the current MXene material preparation process often requires hydrofluoric acid, and the etched MXene is easily oxidized and stacked, which is not conducive to the transfer of electrons and ions. In this study, we proposed a high concentration of sodium hydroxide solution mixed with sodium hypochlorite solution as an etchant for the preparation of fluorine-free MXene (Ti3C2Tx). Based on the alkali-assisted hydrothermal method, Ti3AlC2 was used as the raw material, and 10 % NaClO aqueous solution was added as the oxidant during the etching process to accelerate the etching and in-situ generate TiO2 with excellent conductivity. When the oxidation time is 12 h and the amount of NaClO is 0.2 mL, the TiO2 particles in-situ generated by the oxidation of Ti element in MXene are evenly distributed on the surface and interlayer of the material, which effectively curbs the stacking problem between the Ti3C2Tx layers and improves the specific surface area of the material. The prepared MXene/TiO2 electrode in 1 M H2SO4 electrolyte, − 0.5–0.2 V voltage window, the highest mass specific capacity can reach 321F/g, and after 10,000 charge–discharge cycles, the capacitance retention rate can still reach 86.4 %, which is higher than the capacitance retention rate of Ti3C2Tx material (81.7 %).

Hydrous RuO2 film synthesized in an alkali-assisted steam thermal reactor: Low temperature synthesis and pseudocapacitance

The method of preparing RuO2 thin film by decomposing RuCl3 precursor in steam has shown a potential of having lower temperature and higher capacitance in our previous research work. We have further improved the method of thermal decomposition in steam in our previous work and proposed the alkali-assisted steam thermal reactor (AASTR) method, which has achieved the synthesis of RuO2 thin film with a capacitance of 514 F·g−1 at a low temperature of 150 °C. In the AASTR method, a concentrated sodium hydroxide solution is chosen and placed at the bottom of the reactor. The Ti foil substrates are placed in the vapor phase and do not contact the sodium hydroxide solution. The sodium hydroxide solution is employed to absorb hydrogen chloride generated in the hydrolysis process of RuCl3 and thus promotes the hydrolysis process. As a result, thermal decomposition at a lower temperature (around 150 °C, the critical crystallization temperature) becomes possible due to the modified hydrolysis process. The film exhibits an almost ideal surface controlled pseudocapacitive performance due to its low charge transfer resistance in the charge/discharge process. Therefore, the AASTR method has promising applications in low-temperature synthesis of other hydrous metallic oxides.

Hydrogen Generation from Waste Aluminum Foil AA 1235 Promoted by Sodium Aluminate in Sodium Hydroxide Solutions

The primary barrier to hydrogen production through the aluminum-water reaction is the oxide layer which forms on the exterior surface of the aluminum. In this work, the passivation was minimized by optimizing the concentration of sodium hydroxide solution (0.3 - 0.5 M) promoted by NaAlO2 at room temperature reaction conditions. The aluminum used is waste aluminum foil AA1235 chips having dimensions of 20 mm x 30 mm. The results showed that the hydrogen production rate increases as the NaOH solution concentration increases. The higher the solution’s pH, the shorter the hydrolysis process of the alumina layer, hence the hydrogen production is faster. Adding NaAlO2 as a promoter could increase the hydrogen production rate compared to sole NaOH, i.e., 11.162 ml/minute and 9.86 ml/minute, respectively. This increase occurred significantly during the fast reaction stage. It indicates that the solution containing NaOH and NaAlO2 work synergistically whereby NaOH can accelerate the reaction rate in the aluminum core and NaAlO2 functions as the booster for producing Al(OH)3.

Chemical modification of sustainable bagasse fiber and its absorption mechanism on SBS-modified emulsified bitumen

At present, there are few reports on the application of bagasse fibers (BFs) in the pavement field, and the interaction mechanism between BFs and bitumen is still blank. In this paper, novel chemical modified BFs were introduced as sustainable additives and absorption mechanism between chemical modified BFs and styrene–butadiene–styrene (SBS)-modified bitumen was also revealed through theoretical models and experimental methods. The results show that the concentration of sodium hydroxide solution as 1.5 %, reaction temperature of 40 °C and soaking time of 100 min are the optimal experimental parameters of chemical modification. Compared to virgin BFs, the chemical modified BFs increase the oil absorption rate from 6.46 times to 8.96 times, heat loss decreases from 7.76 % to 1.65 % and total pore volume, micro-pore area and volume increase by 241 %, 170 % and 276 %, respectively. The main component of modified BFs adsorbing SBS-modified bitumen is resin and per unit mass of adsorbed resin by modified BFs decreases gradually with the increased contents of modified BFs. The equilibrium adsorption capacity calculated by quasi-second-order model is closer to the experimental results than that calculated by the pseudo-first-order model. The resin is first adsorbed by adsorption sites on outer surface of fiber, and then diffuses into interior of fiber. With the decrease of resin concentration during absorption, the gradually saturation of adsorption sites leads to weakening adsorption, which finally reaches equilibrium.

Where do ferrate ions form? A dual dynamic voltammetry study

One of the most effective methods to produce ferrate ions (FeO42–) is electrochemical synthesis. During the transpassive anodic dissolution of iron, the formation of ferrate ions and the evolution of oxygen occur simultaneously, and only the sum of the currents generated by the two processes can be observed in the voltammetric curves. Products of the above process have been investigated in 45% (m/m) aqueous NaOH solutions by using the dual dynamic voltammetry (DDV)&rotating ring-disk electrode (RRDE) method (i.e., applying dynamic potential programs to the disk and the ring electrodes of the RRDE disk electrode and the RRDE ring electrode simultaneously) combined with spectrophotometric measurements. Fedisk/Ptring and Ptdisk/Ptring RRDE tips were used in the voltammetric experiments. The electrode potential regions where ferrate ions and oxygen are forming could effectively be identified. The results imply that, under the applied experimental conditions, the oxygen evolved at the disk cannot be reduced at the ring. This can be explained by the fact that elemental oxygen practically does not dissolve in concentrated aqueous sodium hydroxide solutions due to the “salting-out effect”. By using the dual voltammetric method, it was also possible to determine the optimal potential range for the electrochemical production of ferrate ions in terms of charging efficiency. The latter quantity has an important impact on the economics of practical applications. The approach proposed in this study proved to be very promising for the simultaneous detection of different dissolution products.

Optimization of microwave pyrolysis of castor oil to sebacic acid

Castor oil is a widely used biomass energy source. In this paper, the process conditions for the preparation of sebacic acid by cracking castor oil using the microwave method were investigated using environmentally friendly and recyclable liquid paraffin (petrolatum) as a solvent. The optimum conditions for the reaction were determined in the experiments as follows: the mass ratio of solvent: castor oil: sodium hydroxide was 4:1:2.5 and the concentration of sodium hydroxide solution was 50% (w/t). The average microwave power was 210 W, the temperature was about 280 °C, the cracking time was 25 min under nitrogen protection, and the yield of sebacic acid was measured to be 85%. The solvents can be recycled and the recovered solvent can be used again without affecting the yield of sebacic acid. The solvent recovery was more than 92%.

Utilization of agricultural wastes as fiber, binder and aggregates of geopolymer mortars: Application of taguchi method for strength and durability optimization

The present study deals with the compressive strength, flexural strength, capillary water absorption, dry shrinkage, resistance to freeze-thaw cycles, and high temperature resistance of geopolymer mixtures based on agricultural wastes. For the construction of geopolymer mixtures, rice husk ash was used as binder, corn stalk was used as aggregates, and wheat straw, barley straw, and sugarcane straw were used as fibers. Since geopolymer mixtures might be influenced by many factors, the present study used the Taguchi method to design experiments, to optimize factors, and to predict properties so as to avoid the relevant full-fledged experimental works. The present study took into account the factors of curing method (heat curing and ambient curing), concentration of sodium hydroxide solution (6, 9, and 12 M), mass ratio of sodium silicate to sodium hydroxide (2, 2.5, and 3), mass ratio of alkaline activator to binder (0.3, 0.4, and 0.5), mass ratio of aggregate to binder (1, 2, and 3), type of fiber (wheat straw, barley straw, and sugarcane straw), and fiber volume (0, 4, and 8% in terms of the binder weight) as inputs for Taguchi analysis. Given the number and levels of considered factors, 18 mix designs were examined on the basis of the L18(63×12) orthogonal array proposed by Taguchi. The results indicated that the optimal levels of the factors of curing method, concentration of sodium hydroxide solution, mass ratio of alkaline activator to binder, and mass ratio of sodium silicate to sodium hydroxide for almost all tests were respectively equal to heat curing, 12, 0.5, and 3, while the optimal levels of other factors were variable depending on the type of test.

Development of Alkali Activated Concrete using flyash for reducing carbon footprint

The consumption of cement is increasing day by day due to the remarkable development in the infrastructure. One tonne of cement produced emits approximately one tonne of carbon dioxide into the atmosphere. To reduce the use of cement, new-generation concretes such as Alkali Activated Concrete, also known as geopolymer concrete (GPC), have been developed. Geopolymer is a novel material with the potential to replace conventional Portland cement. It is an inorganic material with an amorphous to semi-crystalline polymeric structure that is manufactured by alkali activation of amorphous aluminosilicates at ambient or slightly higher temperatures. In this study, geopolymer concrete was made with low-calcium fly ash. The geopolymer was created by combining sodium silicate and sodium hydroxide solutions with fly-ash. Other materials used for GPC include locally obtainable coarse aggregate and fine sand that is surface dried. Mettur Thermal Power Plant's low-calcium, Class F fly ash was used to make geopolymer concrete. Alkaline solution to fly ash ratio was varied from 0.3 to 0.45. The sodium hydroxide solution concentration was kept constant at 12M (Molars). After being cast in moulds; the specimens were placed in a 60°C oven for 24 hours before being allowed to air dry at room temperature. The compressive strength of geopolymer concrete was tested at 7 and 28 days of age. The test results show that compressive strength increases with an increase in alkali ratio and alkali-to-fly-ash ratio. The slump value for GPC is very less compared with conventional concrete.

Alkaline hydrothermal activation of molybdenum tailings to prepare one-part geopolymer: Activation mechanism and strength

Molybdenum tailings (MT) are solid waste from molybdenum ore beneficiation, which can cause environmental pollution when stored in tailings ponds for a long time. The use of alkaline hydrothermal activation to improve the low reactivity of MT as an active precursor to one-part geopolymers is a novel way to resource MT. This paper evaluates the feasibility of alkaline hydrothermal activation of MT and investigates the mechanical properties of the activated MT base polymer prepared by a one-part method. The results showed that alkaline hydrothermal activation greatly promoted the dissolution of silicon in MT, weakened the crystal properties of quartz phase in MT and destroyed the original structure of MT. The amorphous sodium aluminosilicate on the surface of activated MT dissolves in water and provides an alkaline environment for the geological polymerization reaction. Combined with the analytical results of XRD and FTIR, the alkaline hydrothermal activation of MT was controlled by the optimal sodium hydroxide solution concentration, activation temperature and activation time of 5 M NaOH, 200 °C and 4 h, respectively. Based on this, the one-part geopolymer was prepared directly by adding water to activated MT 5-4-200 and slag, and the compressive strength can be improved. SEM and EDS results show that alkaline hydrothermal activation treatment renders inert MT reactive and the reaction product of activated MT and slag forming a one-part geopolymer is an amorphous C(N)A-S-H gel.

Generation and Observation of Long-Lasting and Self-Sustaining Marangoni Flow.

When solute molecules in a liquid evaporate at the surface, concentration gradients can lead to surface tension gradients and provoke fluid convection at the interface, a phenomenon commonly known as the Marangoni effect. Here, we demonstrate that minute quantities of ethanol in concentrated sodium hydroxide solution can induce pronounced and long-lasting Marangoni flow upon evaporation at room temperature. By employing particle image velocimetry and gravimetric analysis, we show that the mean interfacial speed of the evaporating solution sensitively increases with the evaporation rate for ethanol concentrations lower than 0.5 mol %. Placing impermeable objects near the liquid-gas interface enforces steady concentration gradients, thereby promoting the formation of stationary flows. This allows for contact-free control of the flow pattern as well as its modification by altering the objects shape. Analysis of bulk flows reveals that the energy of evaporation in the case of stationary flows is converted to kinetic fluid energy with high efficiency, but reducing the sodium hydroxide concentration drastically suppresses the observed effect to the point where flows become entirely absent. Investigating the properties of concentrated sodium hydroxide solution suggests that ethanol dissolution in the bulk is strongly limited. At the surface, however, the co-solvent is efficiently stored, enabling rapid adsorption or desorption of the alcohol depending on its concentration in the adjacent gas phase. This facilitates the generation of large surface tension gradients and, in combination with the perpetual replenishment of the surface ethanol concentration by bulk convection, to the generation of long-lasting, self-sustaining flows.

Efficient magnesium recovery from seawater desalination brine via CO2 mineralization to synthesize hydromagnesite for uranium extraction

Magnesium (Mg2+) is the most abundant resource in the seawater desalination brine. The efficient and economical extraction of Mg2+ is crucial for recovery of other ions. In this work, we proposed a facile and cost-effective method to completely transform Mg2+ to hydromagnesite via carbon dioxide (CO2) mineralization. The effects of the injection time of CO2, concentration of sodium hydroxide solution, reaction temperature, and aging time on the synthesis of hydromagnesite and utilization ratios of Mg2+ and CO2 were investigated. The synthesized hydromagnesite exhibited flower-like spherical morphology, and the utilization ratios of Mg2+ and CO2 could reach 99.91 % and 87.75 %, respectively. The formation process of hydromagnesite was illustrated by the time-dependent experiment. The synthesized hydromagnesite was applied to the uranium extraction with the coinstantaneous high maximum adsorption capacity and adsorption efficiency. Especially, it could exhibit good selectivity with the adsorption capacity of 0.32 mg·g−1 and adsorption efficiency of approaching 90 % in 5 L of natural seawater for 10 days. The cycling experiments suggested that the synthesized hydromagnesite possessed the good stability. Therefore, the recovery of Mg2+ to synthesize hydromagnesite via CO2 mineralization is a high-efficiency and low-cost method; meanwhile, the synthesized hydromagnesite shows promising application prospects in the uranium extraction.

ИЗУЧЕНИЕ ПРОЦЕССОВ АГРЕГИРОВАНИЯ И ДЕЗАГРЕГИРОВАНИЯ ЧАСТИЦ ВЫСОКОДИСПЕРСНОГО ПОРОШКА ЦИРКОНИЯ

During long-term storage of wet fine zirconium metal powder under certain conditions the process of particles aggregation may start, which leads to powder transformation into a solid lumpy material, which significantly limits its application range. The purpose of this work was to establish the probable causes leading to the aggregation of zirconium powder particles during long-term storage, and to assess the possibility of transferring the lumpy material to its initial powdery state while preserving its basic physical and chemical properties. Particles aggregation most likely happens due to participation of zirconium atoms of the metal layers in formation of oxo-bridging bonds in acidic medium. Lumpy material formed in the process of storage of sodium-thermal zirconium metal powder (PZrN-A) was used as an example for testing the method of particles disaggregation by means of sodium hydroxide solution treatment, which makes it possible to transform the lumpy material into a stable powdery state typical for standard powder. The mechanism of alkaline treatment consists in the irreversible rupture of oxo-bridging bonds in the material, and the formation of hydroxyl groups on the surface of zirconium particles, which is accompanied by the destruction of aggregates and their disintegration into individual particles. Treatment with sodium hydroxide solution of different concentration demonstrates no significant changes in chemical composition of particles surface layers and makes it possible to maintain the main physical and chemical characteristics of zirconium powder. Samples of zirconium powder were studied by scanning electron microscopy, X-ray spectral microanalysis. The content of total and active zirconium, the value of the specific surface area of the powders was determined. Their sensitivity to friction and electric spark is evaluated.

Improvement of Nitrite Analysis Method in Food Products

The conventional analysis method has problems with extraction efficiency, operability, and reproducibility. In this study, we attempted to solve these problems and improve the analytical method to obtain sufficient extraction efficiency and good operability and accuracy. The conventional method was able to get sufficient extraction in dried meat products, where the extraction efficiency of the conventional method was low, by increasing the concentration of sodium hydroxide solution at the time of homogenization. Suction filtration after adding the defoaming agent was added allowed for accurate volume adjustment. The turbidity of the extract caused by insufficient addition of zinc acetate solution was removed by increasing the amount of zinc acetate solution that was added. Turbidity caused by starch was removed by adding pancreatin. The RSD of the quantitative values was improved by adding sodium hydroxide solution and 80-90℃ water and immediately homogenizing. Furthermore, by changing the dilution factor of the extract solution in the colorimetric method, the inhibition of coloration by reducing substances was suppressed, and more accurate quantitative values could be obtained than with the conventional method. The recovery rate was 78.5-105% (RSD 0.7-5.8%), which was a good result. This method was considered to be a useful analytical method that can contribute to improving the inspection accuracy of nitrite ion analysis.

Effect of sillimanite sand on the mechanical property and thermal resistance of alkali-activated slag mortar

The change in the properties of fine aggregate has significant potential in altering the efficacy of alkali-activated slag. Therefore, this study investigated the influence of sillimanite sand on the mechanical and microstructural properties of alkali-activated slag (AAS) mortar at ambient temperature, and after exposure to elevated temperatures (250, 500, 750, and 1050 °C). In addition, the effect of the concentration of sodium hydroxide solution (6, 8, 10, and 12 M) was evaluated. The silicious normal sand was replaced with sillimanite sand at 25, 50, 75, and 100 % by volume. The results show that the superior physical properties of sillimanite sand improved the strength of the AAS mortar, compared with silicious normal sand. After heating at 250 °C, all AAS mortar mixes showed a significantly higher increase in compressive strength compared to unheated samples. Utilization of the largest concentration of sodium hydroxide solution (12 M) as well as sillimanite sand resulted in a residual compressive strength equivalent to the control sample after 500 °C temperature exposure. A significant drop in residual compressive strength was observed for all mixes at 750 °C. Visual observation of the heated samples revealed that casting the mortar samples with sillimanite sand limited the number, width and extent of thermal cracks. XRD analysis revealed the decomposition of C-S-H and the formation of silica oxide at 750 °C. The results of this study suggest that replacing silicious normal sand with sillimanite sand can help the modification of the engineering properties of AAS mortar at ambient temperature, and after exposure to elevated temperatures.

Experimental Investigation on Geopolymer Concrete:- Sustainable and Eco-Friendly Construction Material

The research for the new environmental friendly construction material that will match the durability of ancient concrete has provoked interest into the study of alkali activated cementitious systems over the last two decades. It results in the development of Geopolymer Concrete. This paper represents the development of geopolymer mixes of various ratios of fly ash and GGBS and their mechanical properties were studied. aa Literature review on mechanical and durability properties of geopolymer concrete also been done. The ratio of sodium hydroxide to sodium silicate is 1:2 which is kept a constant to prepare the mix and alkaline liquid to binder ratio as 0.70, but changing the concentration of sodium hydroxide solution as 6M, 4M and 3M to prepare the mix Id. i.e. F75G25, F50G50 and F25G75, respectively (where F and G are Fly Ash and GGBS and the numerical value indicates the percentage of replacement of fly ash by GGBS) were prepared in AML laboratory, CSIR-SERC, Chennai. Ambient curing of concrete at room temperature was adopted.The compressive strength at age of 3, 7 and 28 days were determined. The strength of geopolymer concrete was increased with increase in percentage of GGBS in a mix. It was observed that the mix Id F25G75 gave maximum compressive strength for concentration of NaOH as 3M . Leaching of GPC reduces with increase in percentage of GGBS in a mix. Thus the geopolymer concrete have a relatively higher strength.

Compressive Strength and Chloride Resistance of Slag/Metakaolin-Based Ultra-High-Performance Geopolymer Concrete

Ultra-high performance geopolymer concrete (UHPGC) has been favored due to its excellent sustainability and outstanding mechanical properties. This study was conducted to explore the mechanical and durability properties of slag/metakaolin-based UHPGC with steel fibers reinforcement. The uniaxial compression test and rapid chloride migration test were conducted to measure the compressive strength and chloride penetration resistance of UHPGC. A total of nine groups of mixture proportions were designed and tested to investigate the influences of steel fiber dosage and sodium hydroxide (NaOH) solution concentration. The results showed that an increased steel fiber dosage and alkali concentration can improve compressive strength, and the maximum compressive strength can reach more than 140 MPa. In addition, the rapid chloride migration test showed that the chloride penetration resistance of the slag/metakaolin-based concrete was moderate, with a non-steady chloride migration coefficient ranging from 6.5 × 10-12 m2/s to 14.1 × 10-12 m2/s. The increase in steel fiber volume content slightly enlarged chloride penetration depth, while the higher concentration of sodium hydroxide solution was beneficial as it improved chloride penetration resistance. The results suggest that although ultra-high compressive strength can be achieved, the durability issues of steel fiber reinforced slag/metakaolin-based geopolymer concrete still need considerable attention.