Showing papers on "Sodium silicate published in 2014"

Effects of NaOH concentrations on physical and electrical properties of high calcium fly ash geopolymer paste

Abstract: The effects of sodium hydroxide (NaOH) concentration on setting time, compressive strength and electrical properties at the frequencies of 100 Hz–10 MHz of high calcium fly ash geopolymer pastes were investigated. Five NaOH concentrations (8, 10, 12, 15 and 18 molar) were studied. The liquid to ash ratio of 0.4, sodium silicate to sodium hydroxide ratio of 0.67 and low temperature curing at 40 °C were selected in making geopolymer pastes. The results showed that NaOH concentration had significant influence on the physical and electrical properties of geopolymer paste. The pastes with high NaOH concentrations showed increased setting time and compressive strength due to a high degree of geopolymerization as a result of the increased leaching of silica and alumina from fly ash. The dielectric constant and conductivity increased with NaOH concentration while tan δ decreased due to an increase in geopolymerization. At the frequency of 103 Hz, the dielectric constants of all pastes were approximately 104 S/cm and decreased with increased frequency. The relaxation peaks of tan δ reduced with an increase in NaOH concentration and ranged between 2.5 and 4.5. The AC conductivity behavior followed the universal power law and the values were in the range of 3.7 × 10−3–1.5 × 10−2 at 105–106 Hz.

Effect of activator type and content on properties of alkali-activated slag mortars

Abstract: Investigation of alkali activation of Turkish slag (AAS) was carried out using sodium silicate and sodium hydroxide activators within the scope of this study. The objective of the present work is to determine the SiO 2 /Na 2 O ratios ( M S ) and Na 2 O contents of the solutions on the development of workability, setting times, mechanical properties, drying shrinkage, water absorption characteristics and microstructure of alkali activated slag cement binders. Test results showed that M S and Na 2 O contents of activator solution are of great importance on the properties of AAS. Portland cement free high performance composite with compressive strength values about 100 MPa can easily be achieved by activation of slag without heat curing. Moreover, in case of activation by optimum M S ratio, sodium silicate activated AAS mortars present higher compressive strength, lower water absorption, higher workability, lower porosity and a wide range of setting times compared to NaOH activated AAS mortars and Portland cement mortar. Consequently, it can be said that this new binder is likely to have enormous potential to become an alternative to Portland cement.

Effect of Sodium Silicate to Sodium Hydroxide Ratios on Strength and Microstructure of Fly Ash Geopolymer Binder

Abstract: Geopolymerization can transform a wide range of waste aluminosilicate materials into building and mining materials with excellent chemical and physical properties. The present experimental study investigates the effect of sodium silicate/sodium hydroxide ratios on the feasibility of geopolymer synthesis at 80 °C using fly ash. The sodium silicate/sodium hydroxide (S/N) ratios 0.5, 1.0, 1.5, 2.0 and 2.5 were studied. The result showed that the compressive and flexural strength increases as the curing age increases. Also, the compressive strength increases as the sodium silicate/sodium hydroxide ratio increases from 0.5 to 1.0 and then decreases. Morphology studies, conducted by SEM analysis of the geopolymer samples, indicated that geopolymers gel had the fly ash particles and pores embedded in a continuous matrix. At S/N = 1 a homogeneous and less porous microstructure was observed.

Microstructure, strength, and moisture stability of alkali activated glass powder-based binders

Abstract: Thermally assisted alkali activation of silica-rich glass powder to produce sustainable binders is investigated. Glass powder activated using NaOH provides higher compressive strengths than NaOH activated fly ash binders at lower heat curing temperatures. Sodium silicate gel is the reaction product when glass powder alone is used as the source material, while a combination of sodium silicate and sodium aluminosilicate (N–A–S–H) gels form in activated glass powder–fly ash blends. The activated glass powder-containing binders are found to disintegrate and lose strength when exposed to moisture or an alkaline solution, with the pure glass powder binders suffering the highest strength loss. Structural changes to the reaction product on exposure to moisture are explained using microstructural and FTIR spectroscopic observations. Doping the systems with Al containing (metakaolin) and Ca containing (slag) source materials, while retaining glass powder as the major component (50% or more), result in the formation of moisture-stable reaction products thereby mitigating the strength loss to a large extent.

Effect of Concentration of Sodium Hydroxide and Degree of Heat Curing on Fly Ash-Based Geopolymer Mortar

Abstract: Geopolymer concrete/mortar is the new development in the field of building constructions in which cement is totally replaced by pozzolanic material like fly ash and activated by alkaline solution. This paper presented the effect of concentration of sodium hydroxide, temperature, and duration of oven heating on compressive strength of fly ash-based geopolymer mortar. Sodium silicate solution containing Na2O of 16.45%, SiO2 of 34.35%, and H2O of 49.20% and sodium hydroxide solution of 2.91, 5.60, 8.10, 11.01, 13.11, and 15.08. Moles concentrations were used as alkaline activators. Geopolymer mortar mixes were prepared by considering solution-to-fly ash ratio of 0.35, 0.40, and 0.45. The temperature of oven curing was maintained at 40, 60, 90, and 120°C each for a heating period of 24 hours and tested for compressive strength at the age of 3 days as test period after specified degree of heating. Test results show that the workability and compressive strength both increase with increase in concentration of sodium hydroxide solution for all solution-to-fly ash ratios. Degree of heating also plays vital role in accelerating the strength; however there is no large change in compressive strength beyond test period of three days after specified period of oven heating.

Dicyclopentadiene and Sodium Silicate Microencapsulation for Self-Healing of Concrete

Abstract: Considerable interest has been directed in recent years toward the use of self-healing materials in concrete. The concept of microcapsule healing is based on a healing agent being encapsulated and embedded in the concrete. The objective of this study was to evaluate the effects of preparation parameters, namely, temperature, agitation rate, and pH on the shell thickness and size (diameter) of the microcapsules as well as to evaluate the self-healing mechanism in concrete through experimental testing performed in laboratory. Two healing agents were evaluated in this study, i.e., dicyclopentadiene (DCPD) and sodium silicate. Based on the results of the experimental program, it was determined that, as the pH was increased from 3.0 to 3.7, the shell thickness increased for sodium silicate, while the shell thickness reached a minimum at a pH value of 3.4 for DCPD. Sodium silicate shell thickness was almost twice the shell thickness for DCPD. The most uniform and coherent microcapsules were produced at ...

Sodium silicate solutions from dissolution of glasswastes. Statistical analysis

Abstract: It has studied the solubility process of four different waste glasses (with different particle sizes, 125 µm) in alkaline solutions (NaOH and NaOH/Na₂CO₃) and water as a reference and under different conditions of solubility (at room temperature, at 80°C and a mechano-chemical process). Have established the optimal conditions of solubility and generation of sodium silicates solutions, and these were: the smaller particle size (<45 µm), with NaOH/Na₂CO₃ solution and with temperature during 6 hours of stirring time. The statistical analyses of the results give importance to the studied variables and the interactions. Through ²⁹Si NMR MAS it has confirmed the formation after dissolution processes of monomeric silicate, suitable for use as an activator in the preparation of alkaline cements and concretes.

Characterization of natural pozzolan-based geopolymeric binders

Abstract: Properties and characteristics of fly ash- or slag-based geopolymers have been extensively explored but comparatively less information is available for natural pozzolan-based geopolymers. The present work focuses on microstructural characteristics of natural pozzolan-based geopolymers activated by sodium hydroxide and a mixture of sodium hydroxide and sodium silicate. Synchrotron XRD and SEM-EDS studies combined with compressive strength tests successfully demonstrate the feasibility of the use of natural pozzolan for sustainable construction material. It is concluded that the geopolymers have sufficient strength as structural materials and matrices contain C–S–H like crystal as well as zeolites of hydroxysodalite and zeolite Y. Two zeolites of hydroxysodalite and zeolite Y are found as the main activation products in sodium hydroxide activation. Substitution with sodium silicate solution yields higher compressive strength and a denser microstructure with dominant activation products of C–S–H like crystal, zeolite Y, and phillipsite. It has been proposed that the crystal size of the activation products ranges from 10 nm to 1 μm. Different microstructural characteristics found herein provide a valuable information to develop natural pozzolan-based sustainable structural materials with improved properties.

Using bagasse ash as a silica source when preparing silica aerogels via ambient pressure drying

Abstract: Silica aerogels were prepared using bagasse ash as a silica source through a route involving the surface modification of wet gels and ambient pressure drying (APD). The silica in the bagasse ash was extracted using a NaOH solution to form the sodium silicate precursor for the silica aerogels. Trimethylchlorosilane (TMCS) and hexamethyldisalazane (HMDS) were used to replace the surface silanol groups with alkyl groups to prevent the condensation and shrinkage of the gel structure during APD. The prepared silica aerogels exhibited strong hydrophobicity. The silica aerogels aged in water possess a higher surface area than those aged in hexane. The mixing time for the silylating agents with the silica precursor influences the surface area of the silica aerogels. The highest surface area and pore volume of the silica aerogels were 1114 m2/g and 2.16 cm3/g, respectively.

Factors Affecting Alkaline Sodium Silicate Gelation for In-Depth Reservoir Profile Modification

Abstract: Alkaline sodium silicate (Na-silicate) is environment-friendly and possesses water-like viscosity during the injection stage for in-depth reservoir treatment to enhance sweep efficiency. Gel setting time (tg) and gel strength are interrelated. Factors that accelerate tg are Na-silicate content (wt%), low pH, presence of divalent ions and temperature. Pressure drop across the gel accelerates syneresis; however, the gel appeared to remain intact. Presence of Ca2+ and Mg2+ ions is shown to increase gel strength. With a Na-silicate content of 4.5 wt%, for example, at a pH of 10.3 and a temperature of 20 °C, gel strength almost tripled and was reached about eight times faster at the combined tested concentration of 0.009 M, based on the average effect from the coexistence of both ions. Low-salinity water (LSW) has an ion composition of 25-fold diluted seawater, did not show precipitation, and could accordingly be a candidate for a pre-flush before the injection of a Na-silicate solution in the event of a field application. This is important since LSW for enhancing oil recovery is a popular method in oil industry. A suggested predictive tool (simple graphical method) to estimate the effect of different factors on gelation time and gel strength is presented.

A Sustainable Approach for the Geopolymerization of Natural Iron-Rich Aluminosilicate Materials

Abstract: Two iron-rich clayey materials (L1 and L2, with the main difference being the level of iron accumulation) have been studied for their suitability as solid precursors for inorganic polymer composites. L1, with the lower iron content, was calcined at 700°C for 4 h and used as replacement, in the range of 15–35 wt%, for both raw laterites in the formulations of geopolymeric composites. The different mixtures were activated with a highly concentrated alkaline solution containing sodium hydroxide and sodium silicate. River sand with semi-crystalline structure was added to form semi-dry pastes which were pressed to appropriate shape. X-ray diffraction, Infrared spectroscopy, Scanning Electron Microscopy and Mercury Intrusion Porosimetry results demonstrated the effectiveness of the calcined fraction of L1 to act as nucleation sites and extend the geopolymerization to the matrix composites. A highly compact matrix with low porosity and good stability in water, together with a strength comparable to that of standard concretes was obtained allowing for conclusions to be made on the quality of laterites as promising solid precursor for sustainable, environmentally-friendly, and cost-efficient structural materials.

Comparison of Using NaOH and KOH Activated Fly Ash-Based Geopolymer on the Mechanical Properties

Abstract: Geopolymer synthesis has two main requirements to fulfil which are the source material that is rich in Silicon (Si) and Aluminum (Al) and alkali activator such as sodium/potassium hydroxide. Sodium hydroxide (NaOH) is widely used for the synthesis of geopolymer compared to potassium hydroxide (KOH) with addition of silicate solution for the purpose of increasing dissolution process. However, the comparison of using different activator in the absence of silicate solution for geopolymer synthesis is not well established. This paper presents an evaluation on compressive strength of fly ash–based geopolymer by using different activator (KOH and NaOH) with respect to different curing conditions (time and temperature) in the absence of sodium silicate. The samples were mixed using mortar mixer and prepared in 50mm x 50mm x 50mm mould for determination of compressive strength. It can be observed that the highest compressive strength up 65.28 MPa was obtained using NaOH. Meanwhile, synthesis using KOH only recorded 28.73 MPa. The compressive strength was better when cured at elevated temperature (60°C) than room temperature (25°C). Further analysis on the microstructure of the highest compressive strength geopolymer samples for both activators was carried out using Field Emission Scanning Microscopy (FESEM) and Raman spectroscopy.

Cellulose–silica composite aerogels from “one-pot” synthesis

Abstract: Cellulose-silica composite aerogels were prepared via "one-pot" process: aqueous solutions of cellulose-8 wt% NaOH and sodium silicate were mixed, coagulated and dried with supercritical CO2. The system was studied both in the fluid and solid (dry) states. Cellulose and sodium silicate solutions were mixed at different temperatures and concentrations; mixture properties were monitored using dynamic rheology. The gelation time of the mixture was strongly reduced as compared to that of cellulose-NaOH solutions; we interpret this phenomenon as cellulose self-aggregation inducing partial coagulation due to competition for the solvent with sodium silicate. The gelled cellulose/sodium silicate samples were placed in aqueous acid solution which completed cellulose coagulation and led to in situ formation of sub-micronic silica particles trapped in a porous cellulose matrix. After drying with supercritical CO2, an organic-inorganic aerogel composite was formed. The densities obtained were in the range of 0.10-0.25 g/cm3 and the specific surface area was between 100 and 200 m2/g. The silica phase was shown to have a reinforcing effect on the cellulose aerogel, increasing its Young's modulus