Geopolymer-based Materials Research Articles

Microstructure Stability and Thermal Resistance of Ash-Based Geopolymer with Sodium Silicate Solution at High Temperature

Current cement-based building materials have a huge disadvantage that they are easily broken due to thermal decomposition at high temperature (over 500°C) of structures of hydrated cement. This is easily observed at construction works when burned, the cement-based mortar and concrete materials and plaster are susceptible to collapse causing damage to buildings or structures. More seriously, these accidents easily cause injuries or loss of life for residents and people working there. Therefore, research on fire resistance and structural stability at high temperatures of building materials is always an interested topic of many scientists. This study utilized resources of highly active alumino silicate materials such as coal bottom ash and rice husk ash to produce geopolymer using sodium silicate solution as an alkaline activator. The ash-based geopolymer has good engineering properties responding to requirements of ASTM C55 and C90 for lightweight concrete brick. It is interesting to note that the geopolymer product was tested for thermal properties at 1000°C such as heat resistance, volumetric shrinkage, mass loss. The experimental results show that the ash-based geopolymer material has high thermal stability with increasing significantly of compressive strength after heated at 1000°C. Moreover, the geopolymer was also carried out to characterize microstructure before and after exposed at high temperature using methods of X-ray diffraction (XRD), scanning electron microscope (SEM). Thermal analysis methods such as thermogravimetric (TG), differential thermal analysis (DTA), and dilatometry-thermal expansion (CTE) were used to evaluate microstructural stability of the geopolymer-based materials.

Strategies for the valorization of soil waste by geopolymer production: An overview

Abstract The management of huge amounts of waste deriving from several anthropogenic activities, such as manufacturing, construction, mining and quarrying, dredging, represents a great contemporary environmental challenge for many countries worldwide. Among the different recycling possibilities, the use of the excavated soils, obtained from operations such as tunneling, excavations, mining, dredging etc., which are generally considered as soil waste, in the production of innovative eco-sustainable building materials represents an interesting alternative to their disposal. In fact, considering especially their chemical composition, low cost and easy availability, soil wastes seem to be the ideal candidates to be used as secondary raw materials for the manufacture of geopolymer-based materials. The paper intends to present a review of the recent scientific literature regarding the use of different types of soil waste to produce geopolymeric binders. Particular attention is focused on mining waste (deriving from various types of mining industries) and dredged sediments coming from marine harbors and natural and artificial water reservoirs, in order to understand and critically discuss the limits of their disposal approach and, at the same time, show perspectives and challenges for possible future research activities in this field. The production of geopolymer-based building components, starting from mining waste and reservoir sediments, is widely discussed thanks to the numerous scientific findings, while the recycling of marine dredged sediments through geopolymerization represents a completely new and innovative trend in research activity, in fact only few related papers were found in literature. It can be strongly stated that geopolymerization can significantly contribute to a sustainable improvement of soil waste management systems.

Characteristics of Novel Geopolymer Composites Synthesized from Red Mud and Diatomaceous Earth in Autoclave Conditions without Using Alkaline Activators

The geopolymer-based materials have been studied and developed since the last decades of the 20th century and applied in many fields of life. The production of geopolymer also has many different levels of technology from low to high technology which depends on quality and the applied fields of products. The geopolymer composites are also considered as friendly environmentally products related to low energy consumption production technology; reuse industrial wastes as raw materials; low or even zero CO 2 emission; many better properties compared to the same traditional materials, and others. This investigation would like to introduce a novel type of geopolymer-based materials synthesized from red mud and diatomaceous earth in autoclave conditions without using alkaline activators. The geopolymer composites were fabricated in three various temperatures of 120 o C, 150 o C, and 200 o C and evaluated characteristics via the different analytical methods. The method of X ray diffraction (XRD) was used to evaluate phase transitions among raw materials (RM and DE) and the geopolymer composite materials. Characteristics of bondings in the materials were detected by using Fourier transform infrared spectroscopy (FTIR). The differential thermal analysis-thermogravimetric analysis (DTA-TG) is method used to look for the physico-chemical changes of the geopolymer composite materials exposed at high temperature. In addition, the geopolymer – based materials were observed morphologies and microstructures in its solid phase lattice matrixs using scanning electron microscope (SEM).

Production of Green Cement from Slag Enhanced by Egyptian Metakaolin Materials

New geopolymer-based materials offer excellent perspectives for the future; they should not be regarded as competitive materials for Portland cement, which has been the reference construction material for so long, but as alternative materials with a series of important advantages to be considered. Metakaolin (MK) produced from firing kaolin material up to 750 ºC for 2 h with a heating rate of 5ºC/min; leads to an enhancement in mechanical and microstructural properties of alkali activated geopolymer of water cooled slag material using (6:6, wt%) of sodium hydroxide and sodium silicate. In the present work the ratios of MK which will be added are less than 20% of the total mass, because of the used MK was very fine with average pore structure less than 30 mµ, which hinders the geopolymerization reaction if used as high ratio. Curing was performed under 100% relative humidity at a temperature of 38ºC and ages of 7, 14, 28 & 90 days. The properties of geopolymer specimens have been studied through measurement of XRD, SEM imaging, FTIR, compressive strength and water absorption. Results showed that the mixes of metakaolin up to 15% results in an enhancement in the mechanical properties as compared with slag control mix up to 90 days.

Chemical–physical–mechanical stability of MKG mortars under sulfate attacks

Geopolymer-based materials have attracted increasing interest in construction and infrastructure engineering due to their high mechanical properties but low carbon dioxide emissions. However, it remains unclear whether this type of material can work in a stable way in harsh environments. This study investigated the chemical–physical–mechanical stability of metakaolin-based geopolymer (MKG) mortars under the immersing actions of sodium sulfate and magnesium sulfate solutions up to 180 days by testing their visual appearance, mass, dimensions, strength, microstructure and chemical components. Results show that the immersion actions do not cause obvious changes in mass, dimensions or compressive and flexural strengths of the MKG mortars. A white deposit, consisting of magnesium hydroxide, magnesium sulfate, magnesium carbonate and magnesium silicate aluminate hydrate, appeared on the surfaces of the high-alkali MKG specimens immersed in magnesium sulfate solution for 30 days, and disappeared at later ages due to the continual consumption of magnesium hydroxide. Mg–Na exchanges occurred for the MKG mortars immersed in magnesium sulfate solution. Overall, the chemical–physical–mechanical stability of geopolymer-based materials depends on the material components and interactions with the environment. Caution should be used before any engineering applications, and relevant issues deserve further rigorous investigation in the future.

Preparation, characterization, and evaluation of compressive strength of polypropylene fiber reinforced geopolymer mortars

The study of the fiber-matrix interface represents a crucial topic to determine the mechanical performance of geopolymer-based materials reinforced with polypropylene fibers (PPF). This research proposes the use of natural zeolite in the preparation geopolymers mortars through alkaline activation with NaOH, Ca(OH)2 and Na2SiO3, and with river sand as a fine aggregate. PPF were incorporated into the geopolymer-based mortar matrix in different proportions like 0, 0.5, and 1 wt.%. The mortars were cured for 24 h at 60 °C and then aged for six days more at room temperature. All samples analyzed through compressive strength were also characterized by X-ray diffraction, thermal analysis, Infrared Spectroscopy, and scanning electron microscopy techniques. The results indicated that the best mix design among the ones used: NaOH (10 M), Na2SiO3/NaOH = 3, Ca(OH)2 = 1.5 wt.% and PPF = 0.5 wt.%. The optimum mix design showed a compressive strength of 4.63 MPa on average. Besides, the fibers enhanced the compressive strength of those samples which the PP fibers probably have better dispersion inside the matrix of the geopolymer mortar.

A novel composite of layered double hydroxide/geopolymer for co-immobilization of Cs+ and SeO42− from aqueous solution

Geopolymers are always considered as promising materials for the treatment of radioactive wastes. In order to extend the application of geopolymer to the immobilization of anionic species, a novel composite of layered double hydroxide/geopolymer (LDH/GEO) was synthesized and applied for cosorption of Cs+ and SeO42−. The ability of LDH/GEO to sorb Cs+ was maintained as that of pure GEO, even though the surface of geopolymer was homogeneously covered by the LDH platelets. The sorption of Cs+ onto LDH/GEO composite occurred via ion exchange, which was controlled by particle diffusion. It is different with Cs+ sorption onto pure GEO governed by film diffusion. Therefore, “Pocket diffusion” was proposed for the particle diffusion as the case of LDH/GEO because this kind of diffusion would be restricted in a certain distance around the ring entrance gate due to the amorphous essence of GEO. For SeO42− sorption by LDH/GEO, ion-exchange with the interlayer NO3− and surface sorption could be the main mechanisms. Importantly, the sorption speed of SeO42− achieved by LDH/GEO composite was much faster than that by pure LDH. In the binary system (Cs++ SeO42−), the sorption of Cs+ was slightly suppressed compared to the single system, which might be due to the formation of ion-pair complex of [CsSeO4]−. However, it did not have negative effect on the SeO42− sorption. In the presence of other cations or anions, the cosorption performances of Cs+ and SeO42− were satisfactorily obtained. Furthermore, the Cs+ and SeO42- sorption densities were superior to the previously reported values. The combined MgAl-LDH/geopolymer composite could be a promising material for the immobilization of Cs+ and SeO42−, and this work would provide guidance for the development of geopolymer-based materials for environmental applications.

Synthesis and Characteristics of Inorganic Polymer Materials Geopolymerized from Ash of Brickyard

Inorganic polymer materials known as geopolymer-based materials are always interesting topics for researchers. Geopolymer is environmentally friendly material which has been potential applications for many different fields such as technical materials, building materials, insolation or refractories, and others. This study used ash of brickyard (AB) as a raw material for geopolymerization process to develop novel materials with high porosity. AB is industrial waste of the brick factories that need to be managed to reduce their negative impact to the environment. AB contains high alumino-silicate resources were mixed with sodium hydroxide solution for 10 minutes to obtain the geopolymer pastes. Sodium hydroxide solution was used as an alkaline activator to form geopolymer paste. The geopolymer paste was filled into 5-cm cube molds according to ASTM C109/C109M 99, and then cured at room temperature for 28 days. These products were then tested for compressive strength, volumetric weight, and water absorption. Results indicated that the material can be considered lightweight with a compressive strength at 28 days that are in the range of 8.1 to 15.4 MPa, volumetric weight around 600kg/m3 and water absorption is under 210.65 kg/m3. The properties of geopolymer products were also determined by analytical techniques that included mineral composition by X Ray Diffraction (XRD) and microstructure by scanning electron microscope (SEM).

Effect of Alkaline Activators to Engineering Properties of Geopolymer-Based Materials Synthesized from Red Mud

Geopolymer is an inorganic polymer material formed from alumino-silicate structures. Geopolymer has many outstanding functions in comparison with ordinary materials such as high mechanical strength, high heat and chemical resistance, and lightweight property. The engineering properties of geopolymer-based materials depend on raw materials and synthesized conditions. In which, the aluminosilicate materials having high activity and consisting of many alkaline activators have the possibility of increasing pH in geopolymer paste. In the solution of paste, aluminosilicate compounds are solubilized and then react with alkali-activated ions to form geopolymeric networks. The geopolymer can be synthesized in many different conditions depending on factors of temperature, pressure, and curing conditions. In this study, red mud (RM) was used as the main alumino resource for geopolymerization process. RM is a solid waste residue being left from the mining process of bauxite ores with caustic soda for alumina production. Its disposal remains a global issue in terms of environmental concerns. Formation of RM-based geopolymer was affected by many factors, in which, the alkaline activators are the most important factor. This research was conducted with sodium hydroxide and sodium silicate solutions to elucidate the effect of alkaline activator ratio to the engineering properties of RM-based geopolymers. The results showed that the RM-based geopolymer used sodium silicate solution has more outstanding properties than RM-based geopolymer using sodium hydroxide solution.

Effects of cellulose, hemicellulose, and lignin on the morphology and mechanical properties of metakaolin-based geopolymer

Natural fiber-reinforced geopolymer has attracted wide attention in construction and building materials due to its low cost, low density, and excellent mechanical properties. Cellulose, hemicellulose, and lignin are the three basic components of natural fibres, and were investigated to reveal their influence on the metakaolin-based geopolymer. Comparative evaluations were investigated via morphology analysis and mechanical strength analysis. The results showed distinct microstructures and mechanical properties of the geopolymer-based materials with cellulose, hemicellulose, and lignin, respectively. A low content (5 wt%) of lignin, cellulose, and hemicellulose enhanced the flexural and compressive strength of pure geopolymer. Higher lignin and hemicellulose led to the porous morphology, lower density, and brittle fractures of geopolymer-based composites, which reduced the flexural and compressive strength in these geopolymer-based composites. It was noted that the degree of geopolymerization was clearly lowered by the alkaline degradation of hemicellulose. With the increase in cellulose content, in contrast, the denser structure and fewer pores of the geopolymer matrix were detected, as well as ductile failures of geopolymer-based composites. Good bonding was also shown between the geopolymer matrix and cellulose fibres without remarkable degradation. The results of this study will facilitate a better understanding of the effect of lignocellulosic biomass in natural fibre-reinforced geopolymers and should serve as the basis for further research and applications.

Mechanical and chemical properties of composite materials made of dredged sediments in a fly-ash based geopolymer

Dredging activity in harbours and channels produces huge quantities of sediments, generally considered as waste soil (WS) to be disposed: the management of such sediments is a great environmental problem for many countries worldwide. Among the recycling possibilities, the use of dredged sediments for the manufacture of geopolymer-based materials seems to be an interesting alternative to disposal, due to their low cost and easy availability. In order to analyse the possibility to use these geopolymer materials as building materials – for instance as precast construction elements in maritime projects - a multi-disciplinary research activity has been developed at the Federico II University of Napoli (Italy). Some experimental tests have been carried out on different geopolymeric specimens made by mixing sediments from Napoli ‘harbour and industrial fly ashes produced by a power plant in the South of Italy. A siliceous sand was used for comparison as an inert reference material. Chemical, morphological and mechanical properties of different specimens have been studied by X-ray diffraction, Scanning Electron Microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR) and finally unconfined compression tests. The experimental results highlight that the use of dredged sediments in combination with fly ash can lead to geopolymeric matrices with interesting mechanical performances. Some differences in the microstructure of the geocomposite built with the siliceous sand or the dredged materials were found. In terms of environmental impacts, on the basis of standard leaching tests and according to Italian thresholds, the adopted dredged mixtures satisfy the prescribed limit for inert or non hazardous waste.

Lightweight Heat Resistant Geopolymer-based Materials Synthesized from Red Mud and Rice Husk Ash Using Sodium Silicate Solution as Alkaline Activator

Geopolymer is an inorganic polymer composite with potentials to replace Ordinary Portland Cement (OPC)-based materials in the future because of its lower energy consumption, minimal CO 2 emissions and lower production cost as it utilizes industrial waste resources. Hence, geopolymerization and the process to produce geopolymers for various applications like building materials can be considered as green industry. Moreover, in our study, the raw materials we used are red mud and rice husk ash, which are are industrial and agricultural wastes that need to be managed to reduce their impact to the environment. The red mud and rice husk ash combined with sodium silicate (water glass) solution were mixed to form geopolymer materials. Moreover, the geopolymer specimens were also tested for heat resistance at a temperature of 1000°C for 2 hours. Results suggest high heat resistance with an increase of compressive strength after exposed at high temperature.

Manufacturing parameters influencing fire resistance of geopolymers: A review

Geopolymers exhibit various unique properties and characteristics, including high compressive strength, high temperature stability, and low thermal conductivity. As a relatively new and perspective material, the behavior of geopolymers subjected to high temperatures is being intensively studied nowadays. This review summarizes the recent achievements in the development of geopolymer-based fire resistance materials. Technological parameters, which influence thermal behavior of geopolymer-based materials, are also discussed. Besides that, recent applications of geopolymers according to their composition are presented.

Thermally treated clay sediments as geopolymer source material

The management of reservoirs for water supply is a great environmental problem, since regular de-silting operations produce huge quantities of sediments. Among the recycling possibilities, the use of clay sediments for the manufacture of geopolymer-based materials seems to be an interesting alternative to disposal, due to their low cost and easy availability. In particular, two sediments, coming from reservoirs located in Southern Italy, were firstly characterized by X-ray diffraction, differential thermogravimetry, Fourier transformed infrared (FTIR) spectroscopy and 27Al and 29Si Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy. The reactivity of raw and thermally treated clay sediments in alkaline media was also investigated. Finally, geopolymeric samples were produced and chemically, physically and mechanically characterized. The results showed that the calcined clay sediments can be suitable source materials in polycondensation reactions and that the increase of the calcination temperature from 400 to 750°C resulted in an increased reactivity. Moreover, good mechanical properties were obtained by all the geopolymers prepared with heat-treated sediments.

Tensile behaviour of geopolymer-based materials under medium and high strain rates

Geopolymers are a promising class of inorganic materials typically obtained from an alluminosilicate source and an alkaline solution, and characterized by an amorphous 3-D framework structure. These materials are particularly attractive for the construction industry due to mechanical and environmental advantages they exhibit compared to conventional systems. Indeed, geopolymer-based concretes represent a challenge for the large scale uses of such a binder material and many research studies currently focus on this topic. However, the behaviour of geopolymers under high dynamic loads is rarely investigated, even though it is of a fundamental concern for the integrity/vulnerability assessment under extreme dynamic events. The present study aims to investigate the effect of high dynamic loading conditions on the tensile behaviour of different geopolymer formulations. The dynamic tests were performed under different strain rates by using a Hydro-pneumatic machine and a modified Hopkinson bar at the DynaMat laboratory of the University of Applied Sciences of Southern Switzerland. The results are processed in terms of stress-strain relationships and strength dynamic increase factor at different strain-rate levels. The dynamic increase factor was also compared with CEB recommendations. The experimental outcomes can be used to assess the constitutive laws of geopolymers under dynamic load conditions and implemented into analytical models.

Clay sediment geopolymerization by means of alkali metal aluminate activation

Alkali metal aluminate activation of a lake sediment has proved to be successful for the formation of geopolymer-based materials.