Microstructure Of Geopolymer Research Articles

Geopolymer Concrete, Mortar, and Paste: A Review

The problems of global warming and environmental pollution with gaseous and solid wastes, made researchers think of finding effective alternatives to reduce the proportion of carbon dioxide in the atmosphere and make use of solid waste for iron manufacturing stations and power production stations. Thus, geopolymers are considered one of the most promising solutions in the field of structural engineering. Therefore, this paper presents a review of previous studies on geopolymer mixtures, which were investigated in three main parameters, included: slag addition, solution ratios, adding fibers, and Nano silica. The results of the previous investigation showed that the compressive strength increased with the increase in the slag ratio. At certain proportions, the compressive strength increases with increasing the sodium silicate to sodium hydroxide and increasing the sodium hydroxide concentration (M). While it was reduced fresh properties such as flow-ability and setting time. It was also found that the addition of fibers or Nano silica improved the microstructures of geopolymers, and thus a significant improvement in tensile strength and compressive strength. Finally, the addition of external water was found to improve flow-ability but reduce compressive strength, while the addition of the superplasticizer in certain proportions improves fresh properties.

Effects of load types and critical molar ratios on strength properties and geopolymerization mechanism

Abstract In this study, the effect of SiO2/Al2O3 (S/A), Na2O/Al2O3 (N/A) and H2O/Na2O (H/N) molar ratios on bending and compressive strength of geopolymer were investigated. The geopolymerization mechanism was also analyzed from microstructure difference by FTIR. The experimental results showed that compressive strength and bending strength of geopolymer has an opposite reaction under different critical molar ratios. The increase of S/A molar ratio and the decrease of N/A and H/N molar ratios have resulted in an increase of the compressive strength. However, it caused a noticeable decrease in bending strength. The microstructure of geopolymer indicated that the degree of polymerization and cohesion of geopolymer have systematical depending on these critical molar ratios, making the mechanical properties of geopolymer susceptible to different types of loads. This paper reveals the relationship between the microstructure of geopolymer and different mechanical properties and helps to selectively prepare corresponding geopolymer for different loading patterns.

Strength, durability, and microstructure of geopolymers based on recycled-glass powder waste and dolomitic lime for soil stabilization

Glass waste in soil stabilization is a promising use as a precursor of forming geopolymers and avoid its discard in landfills as well as decreasing the consumption of traditional binders like lime and cement. Thus, the impact of low, intermediate, and high contents of recycled-glass powder (GP) waste on soil behavior was evaluated by determining the unconfined compressive strength (qu), splitting tensile strength (qt), and durability against wetting/drying cycles (W-D) for the long-term. GP contents were defined as 5%, 15%, and 30% by weight, and a fixed percentage of 5% for lime was selected to ensure the pozzolanic activity of blends based on the pH criterion of optimum lime content. The results indicated improvement in the microstructure and the mechanical properties (qu and qt) of soil-GP-dolomitic lime compacted blends with increasing GP contents, as well as decreases in the accumulated loss of mass (ALM). All of these results were dependent on a novel index given by the ratio of the porosity η to the sum of the percentages of GP and lime in volumetric terms (volumetric binder content Biv), or η/Biv. None of the blends may be used for subbase applications after 7 days of curing time, but all of them are suitable for engineering earthworks after 90 days of curing time.

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กำลังอัดและโครงสร้างทางจุลภาคของจีโอพอลิเมอร์ที่ใช้เถ้าถ่านหินและซิลิกาที่สกัดจากเถ้าแกลบ

Workability, strength and microstructural properties of ground ferronickel slag blended fly ash geopolymer mortar

This study evaluated the effect of using ground ferronickel slag (GFNS) with fly ash (FA) to produce geopolymer mortar. Workability of mortar was found to decrease with the increase of GFNS content due to its angular shape. Compressive strength was found to maximize at GFNS content of 75%. The 28-day and 90-day compressive strengths of geopolymer mortar using 40% alkaline liquid were 75 and 96 MPa, respectively. The SEM images showed more compact microstructure of geopolymers using GFNS compared to that using 100% fly ash. The quantitative XRD results confirmed the production of amorphous geopolymer product. The energy dispersive X-ray spectra (EDS) revealed that the main reaction product of FA-GFNS geopolymer is sodium magnesium alumino-silicate hydrate (N-M-Al-Si-H) gel, which is provided the denser microstructure and the resulting strength increase by GFNS. The porosity and sorptivity of the mortar were found to decrease with the increase of GFNS.

Analysis of Changes in the Microstructure of Geopolymer Mortar after Exposure to High Temperatures.

The inorganic structure formed at the stage of setting of the geopolymer binder ensures high durability of the material under high-temperature conditions. However, changes in the microstructure of the material are observed. The purpose of the study was to analyze changes in the structure of geopolymer mortar after exposure to high temperatures T = 200, 400, 600, 800, and 1000 °C. Mortars with a binder based solely on fly ash (FA) and mixed in the 1:1 ratio with a binder containing fly ash and ground granulated blast-furnace slag (GGBFS) were tested. The descriptions of their microstructures were prepared based on digital microscope observations, scanning electron microscope (SEM) observations, EDS (energy dispersive spectroscopy) analysis, and mercury intrusion porosimetry (MIP) porosity test results. Changes in the material due to high temperature were observed. The differences in the microstructure of the samples are also visible in the materials that were not exposed to temperature, which was influenced by the composition of the materials. Porosity increases with increasing annealing temperature. The distribution of individual pores also changes. In both materials, the proportion of pores larger than 1000 nm increases with the temperature increase. Moreover, the number of cracks and their width also increases, reaching 20 µm in the case of GGBFS. Furthermore, the color of geopolymers has changed. The obtained results extend the current state of knowledge in the field of changes in the microstructure of geopolymers subjected to high temperature.

Effects of Na/Al ratio on mechanical properties and microstructure of red mud-coal metakaolin geopolymer

In this study, red mud (RM) and coal metakaolin (CMK) were alkali-activated to produce geopolymer material (RM-CMK). The effects of different Na/Al molar ratios on mechanical properties and microstructure of the geopolymer were studied. When Na/Al was 1.0, RM-CMK showed the highest 28d compressive strength of 56.2 MPa and peak strain of about 2%. When Na/Al was too high, the compressive strength decreased due to carbonation of excessive alkali reacting with CO2 in the air. Microstructure study of the RM-CMK material showed that amorphous geopolymer gel and zeolite mineral formed. When Na/Al was 1.0, the pore structure of RM-CMK was greatly improved compared to that of the RM-CMK with Na/Al of 0.8. Results showed that the appropriate Na/Al molar ratio can contribute to the geopolymerization, but ultra-high Na/Al molar ratio caused high alkali state to destroy the microstructure of geopolymers.

Preparation of Highly Dispersed Graphene and Its Effect on the Mechanical Properties and Microstructures of Geopolymer

The dispersibility of graphene is one of the determining factors which affect its efficacy in practice. In the present work, highly dispersed graphene [namely, titanium dioxide (TiO2)-reduced graphene oxide (RGO) nanocomposites] was fabricated by a novel TiO2 intercalation method to the RGO. Such a highly dispersed graphene with a marginal doping amount of the solid aluminosilicate precursors (i.e., 0.01% and 0.02% by weight of geopolymer paste) was used to modify geopolymer pastes. Experimental results showed that such TiO2-RGO nanocomposites can effectively improve mechanical properties of geopolymer matrix, especially the flexural strength, which increased 85%–125% with 0.02% by weight graphene. The graphene enabled the reduction of concentrated stress, which prevents the development of cracks in geopolymer matrix. Compared with the control specimens, the graphene-modified geopolymers are more compact and denser due to the refined pore structures of graphene/geopolymer composites, which is confirmed by the scanning electron microscopy and mercury intrusion porosimetry results.

Microstructural characteristics of geopolymer materials with twenty eight days of curing and after eight years stored at room temperature

The main purpose of this study was to perform a microstructural evaluation in geopolymer samples with 28 days of curing (GP28D) and after 8 years of storage (GP8Y). The knowledge on the microstructure of geopolymers in the long run is crucial for the use of these materials, given their great potential applicability. Equally important is the use of industrial waste as raw materials for the manufacture of new materials. In this perspective, this study employed two industrial wastes to produce the samples: bottom ash from mineral coal (BA) and residues from white paper recycling industries. The latter was treated to use the kaolin present in composition. The treatment of the paper waste was carried out by burning the cellulose. Then, the resulting material was subjected to chemical reaction in hydrochloric acid (HCl) to separate the CaCO3 from kaolin. In addition to kaolin, calcium chloride (CaCl2) and water were also obtained as reaction products. The kaolin obtained from the paper residue was dehydroxylated at a temperature of approximately 850 °C for 2 h to obtain processed metakaolin (PMK). To obtain the geopolymer samples, BA/PMK proportions of 2:1 were activated with NaOH solutions of 5, 10 and 15 M mixed with sodium silicate. After the synthesis, the samples were cured for 28 days and subjected to analysis. Then they were stored for more eight years and again underwent microstructural analysis. The results of the analyzes showed significant changes in the microstructure of the materials with 28 days of cure and after eight years. The micrographs obtained in SEM showed a denser structure and the micrographs obtained in TEM showed that the amorphous structure was partially replaced by a crystalline structure. The samples aged for eight years did not show significantly higher mechanical resistance in relation to the samples analyzed with 28 days of cure. It is important to highlight that the results did not show microstructural degradation after eight years.

Thermal stability and microstructure of metakaolin-based geopolymer blended with rice husk ash

Thermal stability of metakaolin -based geopolymer blended with rice husk ash with replacement levels of 5–20% by weight of MK was investigated. The phase composition, thermal stability and microstructure of geopolymer before and after high-temperature exposure were explored by using X-ray diffraction(XRD), Thermogravimetric analysis (TGA), Fourier Transform Infrared Spectrometer (FTIR), BET specific surface area test (BET) and Scanning electron microscope (SEM). The optimum chemical activity of rice husk ash can be obtained when calcined at 600 °C for 4 h. The addition of rice husk ash increases the compressive strength of geopolymer by accelerating the alkali-activated reaction process. The compressive strength at 28 days of curing increases by 24% with 15 wt% rice husk ash. The porous rice husk ash accelerates the discharge of water vapor from geopolymer and protects geopolymer from cracking caused by air pressure. The high chemical activity of rice husk ash accelerates the high-temperature geopolymerization process and contributes to the healing of microcracks. Rice husk ash reduces the melting sintering temperature of geopolymer from 870 °C to 780 °C, improves the formation of compact ceramic protective layer and prevents the high temperature spalling of geopolymer.

Influence of SiC Sludge on the Microstructure of Geopolymers

There are considerable resource reuse and environmental concerns regarding SiC sludge (SiCS) that results from cutting silicon ingots into wafers. In the current study, the effect of the Na2SiO3 solution/sodium hydroxide solution (NS/SS) mass ratio and SiCS amount on metakaolin geopolymers was found during geopolymerization system performance. The results indicate that while NS/SS ratio was relatively low, increasing the NaOH content resulted in a sufficient amount of OH− in the system to increase the solubility and hinder polycondensation, as indicated by the bulk density and setting-time results; since the polycondensation was inhibited, the mechanical strength was reduced. This study demonstrated that a geopolymer can be formed from a substitution of 10% SiCS and with an NS/SS ratio of 1.6, and that this geopolymer is a feasible material.

Influence of nano SiO2 and nano CaCO3 particles on strength, workability, and microstructural properties of fly ash‐based geopolymer

AbstractThe influence of nano SiO2(NS) and CaCO3(NC) particles on the properties of class F fly ash based geopolymer mortar activated with different sodium ion concentrations have been investigated. Mortar mixture proportions were 1:3:0.3 for binder, sand, and water, respectively. Nano SiO2 and CaCO3 particles were replaced with a binder by weight basis at the ratios of 1, 2, and 3% in the mixtures. Sodium concentrations amount used were 8, 10, and 12% Na+ of binder content. Geopolymer mortar samples were cured at 60, 75, and 90°C in a furnace for 24, 48, and 72 hr. After the heat curing process, flexural, and compressive strength tests were performed. The changes in the microstructure of geopolymer due to influence of nanoparticles were examined by utilizing isothermal calorimetric studies on geopolymer paste, and field‐emission scanning electron microscopy (FESEM). Based on laboratory work results, it was concluded that for all sodium ion concentrations, the addition of nano SiO2 and CaCO3 particles improved the flexural and compressive strengths after 24 hr heat curing. However, the favorable effects of nanoparticles on strength properties tend to disappear after 48 and 72 hr heat curing. The results of isothermal calorimetric studies showed that nano SiO2 and CaCO3 particles accelerated the geopolymeric reactions at an early age. FESEM results showed that additions of nanoparticles made the microstructure of geopolymer products more intense and compact.

Using mechanical activation of quartz to enhance the compressive strength of metakaolin based geopolymers

The present work synthesized geopolymer with quartz mechanical activated at different time, and the strengthening mechanism of geopolymer by activated quartz was investigated. The changes of quartz before and after activation and the microstructure of geopolymer was explained by the determinations of particle size, specific surface area and the concentration of reactive Si, as well as XRD, XPS and NMR measurement. With the activation time of quartz increasing from 0 to 60 min, the compressive strength of geopolymer increased from 31.5 to 55.2 MPa. The results showed that increase of quartz reactivity is mainly due to the formation of the Si-centered radicals and non-bridging oxygen on the surface rather than the changes in physical property or crystal structure of quartz. The high activity tetrahedra Si with non-bridge oxygen on the surface of quartz replace the tetrahedra Al in geopolymer gel, which lead to a Si-rich gel formed around quartz and the improvement of compressive strength.

Geopolymer composites using natural pozzolan and oil-shale ash base materials: A parametric study

The mechanical properties, capillary porosity and microstructure of Geopolymer (GP) composites made using different natural Jordanian base materials were investigated. GP mortar mixtures were prepared using oil shale ash, Jordanian natural Pozzolan and a blend of both considering different salient parameters related to the composition of alkaline activator and GP binder content. GP mortar specimens (40 × 40 × 160 mm3) cast from 36 different mixtures were left to rest in molds for 24 h before unmolded then exposed to 60 °C temperature to cure for 24 h and finally moved to laboratory shelves to cure for the remainder of the curing periods of 7 and 28 days. Compressive and flexural tensile strengths, capillary porosity, and Scanning Electron Microscopy (SEM) pictures of the hardened GP composite were obtained, analyzed, and compared to study the significance of the study parameters. The results indicate a good potential of producing GP composites using Jordanian natural Pozzolan alone or with oil shale ash for masonry and structural applications with strength grades of up to 24 MPa. A very good statistical correlation was established between the compressive strength and capillary porosity for present GP composites. SEM pictures for GP composites confirm the experimentally-measured mechanical and durability properties.

Effects of Steel Slag on Mechanical Properties and Mechanism of Fly Ash–Based Geopolymer

AbstractIn order to study the effects of steel slag on the mechanical properties and microstructure of geopolymers, the compressive strength and flexural strength of a fly-ash steel slag–based geop...

Effect of cristobalite on the mechanical behaviour of metakaolin-based geopolymer in artificial seawater

ABSTRACTFew studies have focused on the effect of mineral composition on the mechanical behaviour and evolution of a geopolymer binder in artificial seawater environment. In this study, a geothermal clay-based geopolymer rich in micron-size cristobalite and metakaolin was compared with a metakaolin-based geopolymer in artificial seawater. The effects of the cristobalite on the mechanical behaviour and microstructure of geopolymers were characterised through compressive strength measurements, x-ray diffraction (XRD), scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The micro-size cristobalite enhanced the compressive strength of the geothermal clay-based geopolymer. Without cristobalite, zeolite formed in metakaolin-based geopolymer and led to compressive strength decrease obviously first then increase slightly. The formation of the geothermal clay-based geopolymer gel was delayed in seawater. The cristobalite in the geothermal clay-based geopolymer hindered the formation of Q4(4Al), Q4(3Al) and Q4(2Al).

Structural characterizations of fly ash-based geopolymer after adsorption of various metal ions

ABSTRACT Geopolymer, an amorphous substance, has been viewed as good adsorbent or catalyst and attracted much attentions from all over the world. In order to achieve the better applications of geopolymer in these fields, a deep understanding of the microstructure of geopolymer would be strongly required. In the present study, geopolymer was synthesized from coal fly ash, and the structural analysis of geopolymer after adsorption of various metal ions (Li+, Cs+, Sr2+ and Co2+) was studied using XRD, SEM-EDX, FTIR, UV-VIS DRS, TG-DTA as well as surface area and pore distribution analysis. Pair distribution function preferably illustrated that geopolymer was successfully prepared from calcined fly ash. Geopolymer possesses different affinities towards various metal ions. After exchanging with other metal ions, the main structure of geopolymer was maintained. Metal ions with a large radius would have greater effect on the existing state and amount of water molecules in geopolymer. Moreover, the specific surface area of geopolymer after exchanging with metal ions decreased as a function of the radius of them. The spectra corresponding to d-d transitions indicated that the Co2+ could be incorporated into the deformed six-member rings or eight-membered rings. It could be deduced that the sites for ion exchange could be different rings or even cavities distributed on the surface layer of geopolymer. Furthermore, the rings distributed in the geopolymer structure were predominant in the 6-, 8-, 10- or even 12-member rings to maintain the structure stability and charge balance with the cations.

Effect of Concrete Waste on Compressive Strength and Microstructure Development of Ceramic Geopolymer Pastes

ABSTRACTCeramic industry generates a large amount of wastes, which pollutes and damages the environment. This paper presents the effects of concrete waste incorporating dolomite aggregate on ceramic-based geopolymer pastes in terms of microstructure and compressive strength. Recently, attention has been drawn to the use of geopolymer technology in the production of building units. Geopolymers were prepared from alkali activation of ceramic waste by 6%, 8%, 10% and 12% NaOH. To enhance the mechanical properties, alkali-activated ceramic geopolymer with 10% and 12% NaOH was partially substituted with concrete waste containing dolomite coarse aggregate at proportions of 5%, 10%, 15%, 20% and 30% by weight. Likewise, other geopolymer mixtures were manufactured by replacing ceramics with 5%, 10%, 15%, 20% and 30% calcined concrete waste at 850oC. Water/binder ratio as well as compressive strength of all mixtures was determined at 1, 7, 14 and 28 days. Phase composition and microstructure of geopolymer were identified using Fourier transform infrared spectroscopy and scanning electron microscopy techniques. Incorporation of 10% concrete waste and 20% calcined concrete waste enhanced the compressive strength and the microstructure of ceramic geopolymer pastes, while embedding extra amounts led to adverse effects.

Influence of calcium content on structure and strength of MSWI bottom ash-based geopolymer

This study explored the strength limitations of municipal solid waste incineration (MSWI) bottom ash-based geopolymer, which can limit its use in building materials. The calcium content in MSWI bottom ash was increased by the addition of varying amounts of granulated blast furnace slag (GBFS) and calcium-containing chemicals. The results showed that the low calcium content of MSWI bottom ash in geopolymer was the main cause of insufficient polymerisation. Both GBFS and calcium-containing chemicals improved geopolymer microstructure and enhanced the degree of polymerisation, which clearly improved the compressive strength. However, further increases in geopolymer compressive strength were not significant when the GBFS content was greater than 40%, and the compressive strength decreased sharply when hydrated Ca(OH)2content was greater than 5%.

Geopolymer Mortar Incorporating High Calcium Fly Ash and Silica Fume

AbstractAn attempt was made in the present work to study the compressive strength and microstructure of geopolymer containing high calcium fly ash (HCFA) and silica fume. Concentration of sodium hydroxide solution 8M, 10M, 12M & 14M, liquid to binder ratio 0.5 and sodium hydroxide to sodium silicate ratio 2.5 were selected for the mixes. Geopolymer mortar test results indicated that the mix with 40% silica fume by the weight of HCFA yielded higher compressive strength under ambient curing. The XRD pattern typically shows the major portion of amorphous phase of geopolymer. The existence of C-A-S-H gel, N-A-S-H gel and hydroxysodalite gel products were observed through SEM which developed dense microstructure and thus enhanced strength of HCFA and silica fume geopolymer.