Papers by Keyword: Alkali-Activation

Abstract: The article presents the results of research focused on the behavior of composites with a matrix based on alkali-activated materials when exposed to extreme temperatures (up to 1200°C). The behavior of the material based on alkali-activated fly ash, blast furnace slag, metakaolin, their mutual combinations respectively was analyzed in detail. The effect of thermal exposure on the properties of the developed materials was assessed by a complex of physical, mechanical and chemical methods. A specific area of research was the examination of the rheological properties of the developed mixtures in the fresh state.

Abstract: Over the last years, the increasing need of cost saving and environmental protection has led to finding alternative methods and materials in construction. One of these methods is the alkali-activation, which can transform alumino-silicate binders, like siliceous fly ashes, blast furnace slags, into useful materials. On the other hand, little focus has been given to study the potential uses of high calcium fly ashes (HCFAs), which are also produced in Europe and constitute the half of total fly ash output.In this paper, a calcareous fly ash (F) from Agios Demetrios power plant in Greece was studied in combination with different alumino-silicate materials such as pozzolan, diatomite and brick dust in order to improve their physico-mechanical characteristics. Pastes were mixed with an alkaline activator, which consists of a sodium silicate solution and sodium hydroxide solution 10M. The weight ratio of NaOH:Na₂SiO₃ was 1:1. At the fresh state, setting time of the mixture was measured after mixing. Prismatic specimens were matured at different temperature conditions (25°C for 2 days and 65°C for 2 days). The samples were tested under flexural and compressive strength at the ages of 2, 7 and 28 days. Volume deformation and open porosity were also determined.

Abstract: The alkali-activated slag is an alternative building material to ordinary Portland cement based materials. This type of material is effective in reducing CO₂ emissions and energy consumption. Addition of graphite powder increases its electric conductivity, hence, introducing new functionality to building materials such as self-sensing and self-heating properties. In this study, the effect of graphite filler on the crack initiation of alkali-activated slag composite is investigated. The graphite powder was added in the amount of 5, 10 and 15% with respect to the slag mass. Beam specimens with an initial stress concentrator were tested in three-point bending at the age of 28 days. The load versus crack mouth crack opening displacement (F–CMOD) diagrams were recorded during the fracture tests and subsequently evaluated using the Double-K fracture model. This model allows the quantification of two different levels of crack propagation: initiation, which corresponds to the beginning of stable crack growth, and the level of unstable crack propagation. The course of fracture tests was also monitored by acoustic emission (AE) method.

Abstract: Alkali-activated slag has a higher resistance against exposure to high temperature compared to ordinary Portland cement concrete. Nevertheless, its mechanical properties are also deteriorated due to partial decomposition of the C-A-S-H matrix. This paper investigates the effect of various curing regimes applied to the samples which were exposed to temperature 200–1200 °C on the mechanical properties and microstructure of the alkali-activated slag/limestone blends. The amount of limestone was 15% from the mass of slag. On set of specimens was treated on air at laboratory conditions, the second set was immersed in water and the last was treated stored in humid chamber with 95% relative humidity for the period of 60 days. The results showed that water curing has a strong positive influence on the compressive as well as flexural strength of the specimens exposed to temperatures up to 600 °C. Specimens which were exposed to 800 and 1000 °C showed the best performance after treatment in humid chamber, and after exposure to 1200 °C the best compressive strength exhibited the air cured samples.

Abstract: Geopolymerization are chemical reaction between raw material and alkaline activator where a rapid change of some partial armorphous, specific structure into a compact cemented framework. It was treated with an alkali silicate solution at 45 – 80 °C whereas it’s formed from reaction of mineral clays or aluminosilicate-bearing industrial waste. The previous study about geopolymer has been done for many years due to the physical and chemical properties which is suitable to use in the construction industry. A Geopolymer material that was containing most Silica (Si) and Aluminium (Al) is such as fly ash, bottom ash, metakaolin and ground granulate blast slag (GGBS). Bottom ash is produced from coal fired thermal power plant and has a physical characteristic similar as sand or gravel sand that makes it ideal for industrial application like a green concrete. The different performance of geopolymer is according to the different content of silica, alumina and calcium. To obtain the best geopolymer material, parameter of raw materials content, the types and ratio of alkaline activators also the curing method will affect the high result of compressive strength. This paper will summarize a previous researchers work about the alkali-activated binder in geopolymer raw materials to become green product.

Abstract: The objective of this study is to evaluate the use of polyurethane (PU) coated textile wastes processed with ethylene-vinyl acetate (EVA) as lightweight aggregates in fly ash-based and alkali-activated metakaolin mortars, targeting the development of non-structural elements for civil construction. The PU/EVA waste was processed in three different proportions: 30/70, 50/50 and 70/30. Reference mortars were prepared using a 1:2 (fly ash + metakaolin: conventional construction sand) ratio, by mass. The PU/EVA-waste-containing mortars were prepared via partial replacement of natural sand with the waste in percentages of 10%, 20%, 30% and 40%, relative to the volume of the sand. The activators used in all mortars were NaOH and Na₂SiO₃. The mortars were cured at 80 °C for 21 hours and subsequently removed from the molds and maintained at room temperature until testing was conducted for compressive strength (at ages of 7, 28 and 91 days), leaching (7 days) and solubilization (7 days). Based on the results for compressive strength, the optimum PU/EVA content was 50% for a sand-to-waste replacement percentage of 40%. At an age of 28 days these mortars reached strengths greater than 2.5 MPa which, from a mechanical standpoint, allows for the production of non-structural elements for civil construction like sealing blocks, side walls or finish mortars. From an environmental perspective, no hazardous substances were detected in the leaching and solubilized extracts in any of the PU/EVA waste containing mortars.

Abstract: Inorganic foams offer several unique properties such as low thermal conductivity, fire resistance, or UV stability. Inorganic foam specimens were synthesized from fly ash and aluminium powder through an alkali-activation process. Depending on mix proportions, bulk densities ranged between 400 and 800 kg/m³. Thermal treatment at 80°C for 12 hours accelerated curing process. Compressive strength was found in the range 4.5-9.0 MPa, flexural strength 0.6-1.7 MPa, Young's modulus 0.6-1.1 GPa, thermal conductivity 0.14-0.16 W/m/K and thermal capacity around 1100 J/kg/K. Exposing the foams to temperature 800°C led to a small decrease of compressive strength while exposure to 1100°C sintered the foam to higher strength of 13 MPa. Volumetric shrinkage 20% occurred at 1100°C without further disintegration. Residual compressive strength was determined after exposure to NaCl, HCl, Na₂SO₄, MgSO₄, H₂SO₄. The highest reduction to 20% occured in both acids with pH=2 after one year of exposition. Digitized microstructures entered finite element analysis to validate a stress-strain diagram.

Abstract: In this paper, a kind of core-shell structured ceramsite was proposed to reuse the soda residue and to control the chloride ion release, wherein the ceramsite has a core having a high content of soda residue and a vitrified shell. Experimental results showed that the amount of free chloride ions in the mixture containing 58%(by weight) of fly ash, 2%(by weight) of glass powder and 40%(by weight) of soda residue, after being mixed with water at the water/powder ratio of 0.5 and cured at 90% RH, 25°C for 7 days, was found to decrease from 5.92% to 2.84%. That is, the chloride ion was immobilized by the alkali activated fly ash in the mixture and the immobilization rate was as high as 52%. The core-shell structured ceramsite was prepared successfully with the above mixture as the core and the mixture of waste glass powder and shale as the shell and fired at 1120°C for 8 min. No chloride ion was detected in the eluent after the as-prepared ceramsite was soaked in deionized water at 25°C for 24h.

Abstract: With the fast development of modern industry, the fact that coal dominates the main energy structure will not change for a long time. While the output of coal gangue has accounted for 15%~20% in that of coal. Therefore, coal gangue has become one of the greatest contributions to industrially discharged solid waste in China currently. Nowadays the comprehensive utilization ratio is less than 20%, so there is so much room for the activity and comprehensive utilization of coal gangue. In this article, coal gangue in Tongchuan stimulated by thermal, mechanical and chemical activation has been used as supplementary gelatinize material in cement. The optimal activated ways and technological parameter have been selected by the test of strength, fluidity, water requirement for normal consistency of cement paste, and stability. Also XRD and SEM are used to discuss the change of microstructure which has taken place in activated coal gangue preliminarily.

Abstract: In order to stimulate the potential cementitious property of granulated blast furnace slag (GBFS), the ground GBFS sample (Wei Fang Iron and Steel Corporation, China) was activated by lime and gypsum under different dosages. The results showed that lime is an effective activator for the slag, and the optimum dosage of lime is about 10% (w/w) of the slag. At the optimum dosage of lime, the 28 days compressive strength of the lime-slag paste is higher than that of 32.5 ordinary Portland cement (OPC). But, the early age strength (3 and 7 days compressive strength) of the lime-slag paste is lower than that of the OPC. Addition of gypsum can effectively improve the early age strength of the lime-slag paste. At the ratio of gypsum:lime:slag of 8.2:9.2:82.6 (w/w), both the early and long-term compressive strengths of the gypsum-lime-slag paste are higher than that of the OPC. According to XRD, TG-DTA and SEM detections of the hydration products of the lime-slag paste, the gypsum-lime-slag paste and the OPC paste, it reveals that the hydration process of the GBFS-based cementitious material is different from the ordinary Portland cement and the presence of ettringite (AFt) contributes to the early age strength of the pastes. The major hydration product of the OPC paste (<7 days) were measured as ettringite (AFt), but the AFt phase was not detected in the hydration product of the lime-slag paste and the major hydration product of the lime-slag paste was determined as amorphous CSH gel. However, AFt was detected in the hydration products of the gypsum-lime-slag paste in the early stages of hydration, and the formation of AFt is favorable for the early strength improvement of the material.