Showing papers on "Sodium silicate published in 2013"

Hydration and properties of sodium sulfate activated slag

Abstract: Interest in alkali-activated slag as a construction material is increasing, primarily due to its environmentally friendly nature. Although strong alkaline activators, such as sodium hydroxide and sodium silicate solution, are preferred for high strength, none of them exists naturally and their manufacturing process is quite energy intensive. Whilst sodium sulfate (Na2SO4) can be obtained from natural resources, the early strength of Na2SO4 activated slag is usually low. In this paper, the effects of slag fineness and Na2SO4 dosage on strength, pH, hydration and microstructure were investigated and compared with those of a pure Portland cement (PC). Test results indicated that increasing the slag fineness is a more effective approach than increasing Na2SO4 dosage for increasing both the early and long-term strength of Na2SO4 activated slags. In addition, increasing the slag fineness can also increase the strength without increasing the pH of the hardened matrix, which is beneficial for immobilizing certain types of nuclear waste containing reactive metals and resins.

Synthesis of silica nanoparticles from Vietnamese rice husk by sol–gel method

Abstract: Silica powder at nanoscale was obtained by heat treatment of Vietnamese rice husk following the sol–gel method. The rice husk ash (RHA) is synthesized using rice husk which was thermally treated at optimal condition at 600°C for 4 h. The silica from RHA was extracted using sodium hydroxide solution to produce a sodium silicate solution and then precipitated by adding H2SO4 at pH = 4 in the mixture of water/butanol with cationic presence. In order to identify the optimal condition for producing the homogenous silica nanoparticles, the effects of surfactant surface coverage, aging temperature, and aging time were investigated. By analysis of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, the silica product obtained was amorphous and the uniformity of the nanosized sample was observed at an average size of 3 nm, and the BET result showed that the highest specific surface of the sample was about 340 m2/g. The results obtained in the mentioned method prove that the rice husk from agricultural wastes can be used for the production of silica nanoparticles.

Structure and properties of sodium aluminosilicate glasses from molecular dynamics simulations

Abstract: Addition of alumina to sodium silicate glasses considerably improves the mechanical properties and chemical durability and changes other properties such as ionic conductivity and melt viscosity. As a result, aluminosilicate glasses find wide industrial and technological applications including the recent Corning® Gorilla® Glass. In this paper, the structures of sodium aluminosilicate glasses with a wide range of Al/Na ratios (from 1.5 to 0.6) have been studied using classical molecular dynamics simulations in a system containing around 3000 atoms, with the aim to understand the structural role of aluminum as a function of chemical composition in these glasses. The short- and medium-range structures such as aluminum coordination, bond angle distribution around cations, Qn distribution (n bridging oxygen per network forming tetrahedron), and ring size distribution have been systematically studied. In addition, the mechanical properties including bulk, shear, and Young's moduli have been calculated and compar...

Ethyl silicate for surface protection of concrete: Performance in comparison with other inorganic surface treatments

Abstract: The protection of concrete surface from environmental aggressions is often a basic issue for the enhancement of its durability. Due to the unsatisfactory long-term performance of many organic products and the subsequent need for frequent re-application, growing interest has been recently addressed toward inorganic materials. In the present study, ethyl silicate, widely used for the consolidation of weathered stones in architectural restoration and recently investigated for surface treatment of reinforced concrete structures, is compared with some inorganic products based on sodium silicate and nanosilica, generally used for the protection of concrete floors. Performance and effectiveness of the treatments are investigated in terms of morphology and microstructure; water absorption rate; water contact angle; chloride, carbonation and abrasion resistances. The results obtained highlight ethyl silicate, among the products investigated, as the most effective protection treatment for reinforced concrete structural elements.

Alkaline Activation of Ceramic Waste Materials

Abstract: Ceramic materials represent around 45 % of construction and demolition waste, and originate not only from the building process, but also as rejected bricks and tiles from industry. Despite the fact that these wastes are mostly used as road sub-base or construction backfill materials, they can also be employed as supplementary cementitious materials, or even as raw material for alkali-activated binders. This research aimed to investigate the properties and microstructure of alkali-activated cement pastes and mortars produced from ceramic waste materials of various origins. Sodium hydroxide and sodium silicate were used to prepare the activating solution. The compressive strength of the developed mortars ranged between 22 and 41 MPa after 7 days of curing at 65 °C, depending on the sodium concentration in the solution and the water/binder ratio. These results demonstrate the possibility of using alkali-activated ceramic materials in building applications. Ceramic materials represent around 45 % of construction and demolition waste in Spain. In the present study, two different ceramic materials, red ceramic bricks and porcelain stoneware were alkali-activated in order to produce pastes and mortars. The figure shows the microstructure of pastes obtained using a sodium silicate solution and NaOH pellets as activators. Both materials presented differences related to the process and the optimum concentration of activator. Mortars with compressive strengths ranging from 22 to 41 MPa were obtained after 7 days of curing at 65 °C, which make them suitable for building applications.

Structure, Mechanisms of Reaction, and Strength of an Alkali‐Activated Blast‐Furnace Slag

Abstract: This research examines the chemical activation of blast-furnace slag pastes with alkaline solutions by means of various characterization techniques. Pastes were activated using sodium silicate solutions with modulus (Ms) of 0, 1, 1.5, 2, and Na2O at 5%, 10%, and 15%. Compressive strengths of up to 108 MPa were achieved for Ms = 1–1.5 after 720 d of curing at 20°C. The addition of Na2O > 10% resulted in the formation of hydrotalcite and carbonated pastes with low compressive strength. X-ray diffraction, microanalysis of outer products (OP), and nuclear magnetic resonance (NMR) results showed that the main reaction products in the activated cements with Ms = 1 and 5%Na2O had an average ratio Ca/Si = 0.71–0.9 and consisted of a mixture of two kinds of C–S–H; one similar to a 9 A tobermorite-type calcium silicate hydrate (Ca5Si6O16(OH)2 and other amorphous related to a cross-linked structure of C–N–(A)–S–H gel. Both were intermixed with hydrotalcite and cross-linked structures of silica gel.

Degradation of Acid Blue 29 in visible light radiation using iron modified mesoporous silica as heterogeneous Photo-Fenton catalyst

Abstract: The evaluation of heterogeneous Fenton degradation on dye pollutant, Acid Blue 29 (AB29), has been investigated. The solid catalyst prepared by both sol–gel and incipient wetness impregnation methods was developed by occlusion of Fe3+ ions on synthesized mesoporous silica from sodium silicate. The prepared catalysts were characterized for their textural and surface morphology. High concentration of soluble metal precursor with 8.0 wt% Fe3+ can be easily deposited on silica. The results showed that the Fe-SiO2 catalyst demonstrated good performance in the degradation of 50 ppm Acid Blue 29 (AB29) which was nearly completed in 100 min under visible light irradiation with optimum operating conditions at 0.4 g Fe-SiO2/L, pH 3.0 and 10 mM H2O2. A possible mechanism on visible light irradiated Fenton process was proposed. The catalyst is reusable over four consecutive cycles and minimal leaching of iron ions (

Kaolin-based geopolymers with various NaOH concentrations

Abstract: Kaolin geopolymers were produced by the alkali-activation of kaolin with an activator solution (a mixture of NaOH and sodium silicate solutions). The NaOH solution was prepared at a concentration of 6–14 mol/L and was mixed with the sodium silicate solution at a Na2SiO3/NaOH mass ratio of 0.24 to prepare an activator solution. The kaolin-to-activator solution mass ratio used was 0.80. This paper aimed to analyze the effect of NaOH concentration on the compressive strength of kaolin geopolymers at 80°C for 1, 2, and 3 d. Kaolin geopolymers were stable in water, and strength results showed that the kaolin binder had adequate compressive strength with 12 mol/L of NaOH concentration. When the NaOH concentration increased, the SiO2/Na2O decreased. The increased Na2O content enhanced the dissolution of kaolin as shown in X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. However, excess in this content was not beneficial for the strength development of kaolin geopolymers. In addition, there was the formation of more geopolymeric gel in 12 mol/L samples. The XRD pattern of the samples showed a higher amorphous content and a more geopolymer bonding existed as proved by FTIR analysis.

Rice husk ash as a source of silica in alkali-activated fly ash and granulated blast furnace slag systems

Abstract: This study assesses the viability of using an agro-industrial by-product, rice husk ash (RHA) from a Colombian rice company’s combustion facility, as a total replacement for the commercial sodium silicate ordinarily used in alkaliactivated binders. Fly ash (FA), granulated blast furnace slag (GBFS) and binary 50FA:50GBFS blended pastes were activated with a mix of sodium hydroxide and either sodium silicate or one of two types of RHA. The pastes were characterised for strength, mineralogy and microstructure. The findings showed that the agro-industrial by-product can be used to yield alkali-activated materials with 7-day mechanical strengths on the order of 42 MPa. The study confirmed that both amorphous silica and part of the crystalline silica present in RHA participate in the alkaline activation process, providing the alkalinity is suitably adjusted.

Alkali-activated slag-metakaolin pastes: strength, structural, and microstructural characterization

Abstract: Pastes of granulated blast furnace slag (GBFS) and metakaolin (MK) at GBFS/MK mass ratios of 100/0, 50/50, and 0/100 were activated with sodium silicate with modulus (Ms) SiO2/Na2O of 1, 1.5, and 2, and with 5, 10, and 15% Na2O, relative to the mass binder. Samples were cured at 20 °C for up to 720 days, compressive strength, structural, and microstructural characteristics were investigated. Binders of 100% GBFS developed the highest strength of 120 MPa with 5% Na2O, while those of 100% MK required 15% Na2O to develop high strength. The composites 50% GBFS/50% MK required 10% of Na2O to reach up to 88 MPa. In general, the best Ms was 1–1.5. Structural and microstructural examination of the formulation 50/50 indicated the combined formation of a matrix of reaction products of crystalline C–S–H, an Al-substituted alkali charge-balanced calcium silicate hydrate C–N–(A)–S–H–type gel and geopolymeric gel (N–A–S–H), while 100% GBFS binders showed a 9 A tobermorite-type calcium silicate hydrate (Ca5Si6O16(OH)2) ...

Effect of water-to-geopolymer binder ratio on the production of fly ash based geopolymer concrete

Abstract: Geopolymer is a new invention in the world of concrete in which cement is totally replaced by pozzolanic material that is rich in silica and alumina like fly ash and activated by alkaline liquids to act as a binder in the concrete. Experimental investigation has been carried out to study the effect of water-to-geopolymer binder ratio on workability in terms of flow and compressive strength tested after heat curing in oven at 900C for 8 hours duration. Activated liquid to fly ash ratio of 0.35 by mass was maintained constant on the basis of past research. Sodium silicate solution with Na2O = 16.37%, SiO2 = 34.35% and H2O = 49.28% and 13 mole concentrated sodium hydroxide solution were used as alkaline activators. Test results show that the flow of geopolymer concrete increases with increase in the water-to-geopolymer binder ratio. But the compressive strength decreases with increase in water-to-geopolymer binder ratio similar to water/cement ratio in cement concrete.