Microstructure Of Geopolymer Research Articles

Synergistic gel formation in geopolymers of superior mechanical strength synthesized with volcanic ash and slag.

The present work studies gel evolution and microstructure of geopolymers synthesized with volcanic ash (VA) and blast furnace slag (BFS). The synthesis parameters such as BFS proportions on geopolymer formation were investigated. Gel evolution and microstructure of the geopolymers were studied by FTIR, X-ray diffraction (XRD), 29Si NMR spectroscopy and scanning electron microscopy measurements. Silicate gels (N-S-H) were mainly formed in VA-based geopolymers of low compressive strength (14.07MPa). While with VA and BFS each account for 50%, VA-BFS-based geopolymers possessed a compressive strength of 55.6MPa, as well as the homogeneous C-(A)-S-H and N-A-S-H gels were formed. The C-(A)-S-H and N-A-S-H gels show synergistic effects on the mechanical property of the geopolymers. This work provides a clue for the synthesis of geopolymers with superior mechanical properties in areas of architecture. Detailed characterization gel evolution and microstructure of geopolymers synthesized with volcanic ash (VA) and blast furnace slag (BFS) were studied. Silicate gels (N-S-H) were mainly formed in VA-based geopolymers of low compressive strength (14.07MPa). When VA and BFS each account for 50%, VA-BFS-based geopolymers possessed a compressive strength of 55.6MPa, as well as the homogeneous C-(A)-S-H and N-A-S-H gels formed. Synthesis protocol for VA-BFS-based geopolymers.

Effects of alkaline activators on pore structure and mechanical properties of ultrafine metakaolin geopolymers cured at room temperature

Geopolymer is a new type of green gelling and environmental protection material, but the curing temperature limits the application of geopolymer in the construction industry. In this paper, the effects of NaOH on the pore structure and mechanical properties of ultrafine metakaolin (UMK) geopolymers under room temperature curing conditions were investigated. In this experiment, different concentrations of alkaline activators were prepared by changing the concentration of NaOH in the composite alkaline activator, and geopolymers were prepared with different alkaline activators and UMK. Different UMK geopolymers have been extensively analyzed to characterize their pore distribution, pore structure, and mechanical properties. The relationship between NASH gel and NaOH concentration was quantified by simultaneous thermal analysis (TG-DTG) and X-ray diffraction (XRD). The evolution of pore distribution and pore structure of UMK geopolymers with NaOH concentration was characterized by scanning electron microscopy (SEM) and proton nuclear magnetic resonance spectroscopy (1H NMR). The results show that UMK only generates the NASH phase in the geopolymerization reaction. With the increase of sodium hydroxide concentration, the formation of NASH gel increases, and the crystallinity of the sample increases. SEM and 1H NMR results show that the UMK geopolymer prepared with a high concentration of NaOH is fully hydrated and has a dense structure. Through comparative analysis of UMK geopolymer pore distribution and pore structure characteristics, it was found that the porosity of UMK geopolymer decreased with the increase of sodium hydroxide concentration. The proportion of small pores did not change much, while the large pores gradually evolved into mesopores. In addition to this, curing time was found to have no significant effect on geopolymer microstructure and strength development. This research provides a theoretical basis for the practical engineering application of UMK.

Experimental Research on the Compression Property of Geopolymer Concrete with Molybdenum Tailings as a Building Material

This paper experimentally studied the effects of different molybdenum tailings (MoT) content, standard curing and 60 °C water curing conditions on the compressive strength of fly ash-based geopolymers at different ages. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectrometer (SEM/EDS) and Fourier-transform infrared spectroscopy (FTIR) were applied to investigate the effect of the content of MoT and different curing conditions on the reaction products, microstructure and chemical composition of fly ash-based geopolymers. The results show that MoT content and curing conditions have synergistic effects on the compressive strength of fly ash-based geopolymers. For standard curing, the increase in MoT content is detrimental to the development of compressive strength, and an obvious weak interfacial transition zone between MoT and the gel product is observed in specimen containing 40 wt% MoT; meanwhile, under water curing conditions, the compressive strength of geopolymers first increases and then decreases with the increase in MoT, and the 28-day compressive strength can reach 90.3 MPa when the content of MoT is 10 wt%. The SEM results show that the curing conditions have a great influence on the microstructure of the geopolymer matrix, and the microstructure of the specimens under the water curing conditions is smoother and denser, with fewer pores. EDS analyses show that the gel product constituting the geopolymer matrix is N(C)-A-S-H gel; MoT can participate in the reaction, and the mass ratio of Ca/(Si + Al) of N(C)-A-S-H gel increases with the increase in MoT, resulting in a decrease in compressive strength. In addition, the results of the FTIR confirm that water curing can increase the degree of crosslinks in the gel phase.

Strength development and microstructure of sustainable geopolymers made from alkali-activated ground granulated blast-furnace slag, calcium carbide residue, and red mud

Red mud (RM) and calcium carbide residue (CCR) are waste generated from alumina refining and acetylene gas producing, respectively. This study utilized alkali-activated ground granulated blast-furnace slag (GGBS) and wet-basis CCR stabilized RM to prepare geopolymers material. The alkali activator solution was composed of CCR supernatant, sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). CCR supernatant was used to reduce the amount of strong alkali. The effects of alkali activator on chemical composition and microstructure of geopolymers were studied by X-ray diffraction (XRD), thermogravimetric-derivative thermogravimetric (TG-DTG) analysis, and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). The results show that the utilization of alkali activator improved the compressive strength and especially significantly improved the flexural strength of geopolymers. The strength was negatively correlated with the RM content: the geopolymers containing 30 % RM achieved a maximum 28-day compressive and flexural strength value of 20.3 MPa and 4.3 MPa, respectively. The microstructural analysis revealed that the strength increased due to the formation of calcium aluminate hydrates (C-A-H) and calcium silicate hydrates (CSH). The toxic heavy metals (Cr, Ni, Cu, Pb, Sb, and Zn) from RM formed some complex compounds and were combined in the geopolymers. The 28-day leaching experiment showed that the toxic heavy metals levels were below the test limits. In summary, this study confirmed the safety and feasibility of preparing RM-GGBS-CCR based geopolymers via alkali-activated method.

Strength and Microstructure of Geopolymer Based on Fly Ash and Metakaolin.

The production of Portland cement is widely regarded as a major source of greenhouse gas emissions. This contributes to 6–7% of total CO2 emissions, according to the International Energy Agency. As a result, several efforts have been made in recent decades to limit or eliminate the usage of Portland cement in concrete. Geopolymer has garnered a lot of attention among the numerous alternatives due to its early compressive strength, low permeability, high chemical resistance, and great fire-resistant behaviour. This study looks at the strength and microstructure of geopolymer based on fly ash and a combination of metakaolin and fly ash. Compressive strengths were measured at 7, 14, and 28 days, and microstructure was examined using SEM and XRD.

Effect of Elevated Temperature on the Microstructure of Metakaolin-Based Geopolymer.

Currently, geopolymer is being considered as a future oil-well cement. For wellbore applications, geopolymers are initially tested at specific temperature conditions. However, an oil-wellbore may experience a sudden increase in temperature which may adversely affect geopolymer systems designed for low to moderate temperature conditions. In this work, the effect of elevated temperatures on the microstructure of the geopolymer was simulated. Metakaolin-based geopolymer systems cured at 163 °F for 48 h were subjected to a temperature ramp of 194 °F and 248 °F for 24 h. X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetry analysis techniques were used to study the microstructural changes. The analytical techniques show the formation of new crystalline phases when the geopolymer cured at 163 °F was suddenly exposed to higher temperatures. These crystalline phases, for instance, gobbinsite and anorthite, observed in the microstructure have the potential to cause thermal stress, weaken the system, and ultimately affect the geopolymer’s ability to effectively isolate the formation and support the casing.

Evolution of a natural pozzolan-based geopolymer alkalized in the presence of sodium or potassium silicate/hydroxide solution

The present work studied the effect of the type of alkali on the structural evolution of a natural pozzolan from Hidalgo, México, alkalinized with sodium or potassium solution to obtain geopolymers. The Pozzolan is composed of clinoptilolite-type zeolite, calcite, and quartz. The alkali solution was a mixture of silicate/hydroxide of sodium or potassium with a volume ratio of 12. Alkali solution/pozzolan weight ratio was 0.6, and curing was at 25 °C. The geopolymerization reaction from the natural pozzolan alkalized to geopolymer was followed at different stages by isothermal calorimetry showing that the sodium solution promotes higher aluminosilicates dissolution from the pozzolan than the potassium one, and the condensation step is favored to allow the generation of interconnected structures. This step is delayed at intermediates curing times at the presence of potassium solution due to the less dissolution of aluminosilicates and the loss of water observed by FT-IR analysis, consequently slowing down the evolution of compressive strength at this curing time. The alkalized pozzolan produces a gel identified by the amorphous halo at 2θ < 10° and between 20°-40° 2θ in the XRD patterns. This gel is characteristic of the presence of geopolymer. The final geopolymer microstructure shows the morphology of thick plates. The compressive strength of the geopolymers at 28 days shows similar values (±10.8 MPa) independent of the type of alkali solution used, although this evolved differently.

Geopolymer concrete with metakaolin for sustainability: a comprehensive review on raw material's properties, synthesis, performance, and potential application.

In the last three decades, the gigantic demand for sustainable and environmentally friendly concrete with reduced environmental footprints has resulted in the development of low carbon concretes such as geopolymer concrete. Metakaolin which is commonly used as an admixture or partial replacement of cement owing to its most effective pozzolanic properties, which improve the microstructure and strengthen the mechanical and durability properties of cement concrete, has been investigated as a precursor in geopolymer concrete. Several studies have been conducted to comprehend the effect of metakaolin as an additive in geopolymer mortar and concrete prepared with various aluminosilicate sources as precursors such as fly ash and rice husk ash to enhance geopolymerization, densify microstructure, and elevate durability. The present paper recapitulates these investigations primarily concentrating on the various properties of metakaolin-based concrete. The effect of various factors such as alkali content, solids/liquids ratio, alkali reactant ratio, molar ratio, water content, and curing regime has been compiled. Most of them revealed that metakaolin is used as a precursor and yields better geopolymer products. XRD studies reported the peaks demonstrating the development of enhancement in hydration products in comparison to other precursors. Examination of SEM graphs reveals that the addition of a smaller quantity of silica-rich materials densifies the microstructure of geopolymers and produces higher mechanical strength. Durability studies reveal that metakaolin geopolymers possess better water resistance, thermal resistance, and anti-corrosion properties. The possible applications of metakaolin-based geopolymeric materials are also pointed out. The comprehensive knowledge presented here is expected to support the prospective researchers to decide their future course of the research area. Graphical abstract.

Influences of Multi-Component Supplementary Cementitious Materials on the Performance of Metakaolin Based Geopolymer

In this study, the workability and reaction mechanism of metakaolin (MK) based geopolymer blended with rice husk ash (RHA) and silica fume (SF) was investigated. The prepared samples were subjected to tests including compressive strength and fluidity tests. X-ray diffraction (XRD) and Scanning electron microscope (SEM) were employed to explore the phase composition and microstructure of geopolymers. The molecular bonding information of geopolymer was provided by Fourier transform infrared spectroscopy (FTIR). Meanwhile, the porosity of geopolymer was obtained by Mercury intrusion porosimeter (MIP) analysis. The high-activity RHA obtained after calcination at 600°C was used as a supplementary cementitious material to prepare geopolymer. The properties of preventing morphology cracking and compressive strength are improved. The addition of RHA and SF changes the working performance of MK based geopolymer and provided a theoretical basis for future practical applications. Meanwhile, the high chemical activity of SF and RHA contributes to the healing of microcracks.

Role of Calcium Oxide in Nucleation and Microstructure of Geopolymers and Alkali Activated-Based Cements

Role of Calcium Oxide in Nucleation and Microstructure of Geopolymers and Alkali Activated-Based Cements

Hybrid Effect of PVA Fibre and Carbon Nanotube on the Mechanical Properties and Microstructure of Geopolymers

The concept of geopolymers has been widely studied since it was proposed. However, the wide range of applications of geopolymers is affected by brittleness and poor crack resistance. In this study, the mechanical properties of geopolymers with single-doped PVA fibres, single-doped carbon nanotubes, and mixed PVA fibers and carbon nanotubes were studied respectively first. It was found that PVA fibres and carbon nanotubes had a positive effect on improving the mechanical properties of geopolymers, especially bending strength and flexural strength. Moreover, the incorporation of PVA fibre could improve the damage morphology of geopolymers. Additionally, the phase analysis, structural group analysis, and strengthening mechanism were studied via scanning electron microscopy, mercury intrusion porosimetry analysis, X-ray diffraction pattern characterisation, Fourier transform infrared spectroscopy analysis, and magic angle spinning nuclear magnetic resonance analysis. It was found that the strengthening effect of PVA fiber to the geopolymer was primarily a physical strengthening effect, whereas the strengthening effect of carbon nanotubes to the geopolymers was both chemical and physical. Finally, based on the previous study, a multi-scale dual-fibre strengthening mechanism was proposed. Micro-nano fibre composites were used to improve microstructure via physical and chemical effects. This is helpful to improve the performance and application of geopolymers. Furthermore, it lays a preliminary theoretical foundation for engineering applications and technical improvement of geopolymers in the future.

Thermal stability of geopolymer modified by different silicon source materials prepared from solid wastes

Cement is a construction material responsible for greenhouse gases and CO2 emissions. As a green building material that replaces cement, geopolymer has received widespread attention. Both glass powder (GP) and rice husk ash (RHA) contain large amounts of active silica, but they are solid waste produced in different fields and their microstructures vary greatly. In this study, the thermal stability of metakaolin-based geopolymer blended GP and rice husk ash RHA was investigated. The prepared samples were subjected to elevated temperatures (T = 300 ℃, 500 ℃, 700 ℃ and 900 ℃), and the compression strength and volume shrinkage tests were carried out after high-temperature calcination to evaluate the thermal stability. X-ray Diffraction (XRD), Fourier Transform Infrared Spectrometer (FT-IR) and Scanning Electron Microscope (SEM) were employed to explore the phase composition and microstructure of geopolymer before and after high-temperature calcination. The rice husk ash with optimum chemical activity can be obtained when calcined at 550 ℃ for 4 h. The properties of preventing morphology cracking, loss of compressive strength and volume shrinkage of the samples are improved. After calcination at various temperatures with the addition of glass powder and rice husk ash, the inner parts of the samples maintain the stable chemical bond and amorphous structure after high-temperature exposure. The doping of glass powder and rice husk ash improves the Si/Al ration and SiO2/Na2O ratio. The introduction of GP is more effective in affecting the unstable Al-O bond, while the introduction of RHA is more effective in increasing the degree of polymerization. Meanwhile, the highly active silica in GP and RHA contributes to the healing of microcracks.

Role of particle fineness and reactive silicon-aluminum ratio in mechanical properties and microstructure of geopolymers

The main two factors of the mechanical properties and structure of geopolymers including reactive silicon-aluminum ratios and particle fineness were investigated. Vanadium-bearing shale residue (VSR), fly ash (FA), and silica fume (SF) were subjected to alkali thermal activation (ATA) to increase the content of reactive silicon and aluminum, then a leaching experiment was carried out to quantify the content of active silica and aluminum in the raw materials, which indicated that the reactive silicon-aluminum ratios are well linearly related with those in the raw materials. High compressive strength (82 MPa at 28 days) geopolymers were prepared at ambient temperature curing of the three solid wastes after ATA, and the effect of FA fineness to geopolymers was also investigated during the preparation. As the FA content in the raw materials increases within a certain range, the compressive strength of the geopolymer is significantly enhanced, along with the main band is relevant to asymmetric stretching of Si-O-Si/Al has shifted towards a lower frequency, which is results from structural alteration of the Al-Si network. The appropriate reactive silicon-aluminum ratios accelerate the geopolymerization reaction process, which is conducive to the formation of the silicon-aluminum gel microstructure. The fineness of FA has a notable effect on the mechanical properties of geopolymers. It is interesting to found that the geopolymers with finer FA fineness have lower compressive strength, which can be explained by the looser structure and more pores due to the agglomeration of fine particles, resulting in difficult geopolymerization reactions.

Rice-Husk-Ash-Based Geopolymer Coating: Fire-Retardant, Optimize Composition, Microstructural, Thermal and Element Characteristics Analysis.

Geopolymer using aluminosilicate sources, such as fly ash, metakaolin and blast furnace slag, possessed excellent fire-retardant properties. However, research on the fire-retardant properties and thermal properties of geopolymer coating using rice husk ash (RHA) is rather limited. Additionally, the approach adopted in past studies on geopolymer coating was the less efficient one-factor-at-a-time (OFAT). A better approach is to employ statistical analysis and a regression coefficient model (mathematical model) in understanding the optimum value and significant effect of factors on fire-retardant and thermal properties of the geopolymer coating. This study aims to elucidate the significance of rice husk ash/activated alkaline solution (RHA/AA) ratio and NaOH concentration on the fire-retardant and thermal properties of RHA-based geopolymer coating, determine the optimum composition and examine the microstructure and element characteristics of the RHA-based geopolymer coating. The factors chosen for this study were the RHA/AA ratio and the NaOH concentration. Rice husk was burnt at a temperature of approximately 600 °C for 24 h to produce RHA. The response surface methodology (RSM) was used to design the experiments and conduct the analyses. Fire-retardant tests and thermal and element characteristics analysis (TGA, XRD, DSC and CTE) were conducted. The microstructure of the geopolymer samples was investigated by using a scanning electron microscope (SEM). The results showed that the RHA/AA ratio had the strongest effect on the temperature at equilibrium (TAE) and time taken to reach 300 °C (TT300). For the optimization process using RSM, the optimum value for TAE and TT300 could be attained when the RHA/AA ratio and NaOH concentration were 0.30 and 6 M, respectively. SEM micrographs of good fire-resistance properties showed a glassy appearance, and the surface coating changed into a dense geopolymer gel covered with thin needles when fired. It showed high insulating capacity and low thermal expansion; it had minimal mismatch with the substrate, and the coating had no evidence of crack formation and had a low dehydration rate. Using RHA as an aluminosilicate source has proven to be a promising alternative. Using it as coating materials can potentially improve fire safety in the construction of residential and commercial buildings.

The effect of pore behavior and gel structure on the mechanical property at different initial water content

This study synthesized geopolymers with different content of water from 34.35% (10 mol) to 43.97% (15 mol), and the effect of initial water content in pore behavior and gel structure of geopolymer was investigated. The microstructure of geopolymer was characterized through MIP analysis, SEM, TGA-MS, XRD, FTIR and NMR measurement. As the water content in synthesis increasing, the compressive strength of geopolymer significantly decreased from 40.3 MPa to 10.2 MPa. The high initial water content results in a large increase in the diameter of pore in geopolymer, which lead to the transformation of harmless pores to harmful pores. In addition, excess water will also introduce more water to participate in the geopolymer network, so that the content of Q3 structures increased 2.94% from 19.24%, which leads to a decrease in the degree of polymerization. Both of pore behavior and gel structure changes reduce the mechanical property of geopolymers. When the initial water content is low (10–11 mol), the change of geopolymer gel structure has a greater impact on the strength of the geopolymer, while when it is high (12–15 mol), the compressive strength is dominated by the pore structure.

The Effect of Various Si/Al, Na/Al Molar Ratios and Free Water on Micromorphology and Macro-Strength of Metakaolin-Based Geopolymer.

The current work aimed to explore the effect of Na/Al ratios of 0.43, 0.53, 0.63, 0.73, 0.83, and 0.93, using NaOH to alter the molar ratio, on the mechanical properties of a geopolymer material, with fixing of the Si/Al molar ratio. While fixing the Na/Al molar ratio, alteration of the Si/Al ratios to 1.7, 1.75, 1.8, 1.85, 1.9, 1.95 was used, with silica fume and sodium silicate as a silica corrector. The influence on the micromorphology and macro-strength of samples was characterized through SEM, EDS, and compressive strength characterization methods. The results show that Si/Al and Na/Al molar ratios play a significant role in the microstructure and mechanical behavior of MK-based geopolymers, and revealed that the optimal molar Si/Al and Na/Al ratios for attaining maximum mechanical strength in geopolymers are 1.9 and 0.73, respectively. Under various Si/Al ratios, the macro-strength of the geopolymer mainly relies on the formation of NASH gel, rather than zeolites or silicate derivatives. The appropriate Na/Al molar ratio can contribute to the geopolymerization, but a ultra-high Na/Al molar ratio caused a high alkali state that destroyed the microstructure of the geopolymers. Regardless of the amount of water contained in the initial geopolymer raw material, the water content of Si/Al = 1.65 and Si/Al = 1.75 after curing for 10 days was almost the same, and the bound water content of the final geopolymer was maintained at about 15%. Structural water exists in geological polymer gels in the form of a chemical structure. It has effects on the structural performance strength, while free water affects the volume stability of the geological polymer. Overall, the current work provides a perspective on the elemental composition analysis, combined with the molecular structure and micromorphology, to explore the mechanical performance of geopolymers.

The effects of lithium slag on microstructure and mechanical performance of metakaolin-based geopolymers designed by response surface method (RSM)

This study reports the effects of lithium aluminosilicate residue (LARS) powder, a byproduct in the process of extracting lithium from lithium pyroxene, on microstructure and mechanical performance of metakaolin (MK)-based geopolymer, and RSM was used to obtain the optimal mixing proportions. The compressive strength of all groups of samples was tested to characterize the mechanical properties of the LARS-MK geopolymer, whereas Scanning Electron Microscopy-Energy Dispersive Spectrometer (SEM-EDS) and BET were employed to characterize the microstructures and pore structure. To identify the products formed in the geopolymerization process, the phase compositions and molecular bonds were analyzed using X-ray diffraction (XRD) and Fourier infrared spectrometer (FT-IR). The results show that the introduction of LARS degrades the microstructure of geopolymer in the early ages. However, it is beneficial for the strength development after 28 days of curing when a proper amount of LARS powder was introduced, and the optimal compressive strength of the samples cured for 28 days with about 10% LARS and 105% activator is 77.5 MPa. Meanwhile, the deteriorated mechanical performance at the age of 180 days indicates that the addition of LARS powders may not favor the late age performance of samples. Furthermore, the microstructural analysis indicates that the introduction of LARS may lead to new phases such as rankinite or albite. The findings suggest that LARS has a great potential in developing geopolymers and provides a unique solution to its waste management.

Effects of initial SiO2/Al2O3 molar ratio and slag on fly ash-based ambient cured geopolymer properties

Geopolymers cured at ambient temperature are of high interest since they provide promising environmentally friendly alternative to cement. This paper discusses the effect of the initial molar ratio of SiO2/Al2O3 and fly ash replacement with ground granulated blast furnace slag (GGBFS) on the properties of fly ash-based geopolymers. Geopolymer mixtures developed in this study are user-friendly (SiO2/Na2O larger than 1.4) and suitable for producing self-compacting geopolymer concrete at ambient temperature. Results showed that the increase in SiO2/Al2O3 ratio accelerated the setting of fly ash-slag geopolymer systems, which was quite different from that reported for metakaolin-based geopolymers. An increasing–decreasing trend in compressive strength was observed by increasing the SiO2/Al2O3 ratio. The maximum compressive strength achieved when the SiO2/Al2O3 ratio was 3.37 (Si/Al = 1.68). The higher compressive strength at this ratio could be related to the alumina-silica bondings in the amorphous area, which comprised more than 81%-84% of geopolymer microstructure. Furthermore, the study revealed that the decrease in fly ash replacement with GGBFS prolonged the setting of geopolymer mixtures and reduced their compressive strength significantly.

Effect of silane coupling agent on the rheological and mechanical properties of alkali-activated ultrafine metakaolin based geopolymers

Fluidity modification on geopolymer without changing its compositions is necessary. This study, firstly, investigated the optimal oxides molar ratios of geopolymers, then rheology, rheokinetics, fluidity and mechanical properties tests were conducted to study the influence of silane coupling agent (SCA) on geopolymers. Finally, characterization techniques of SEM, pore size distribution, FTIR and DSC were used to reveal the mechanisms. The results show when SiO2/Al2O3 = 3.4, M2O/Al2O3 = 1, and H2O/M2O = 11, geopolymer’s fluidity reaches 144 mm with the best compressive strength. The addition of 2 wt% SCA can reduce viscosity, increasing the fluidity to 167 mm, while excessive SCA can’t. SCA can also increase the viscosity growth rate and influence the microstructure of geopolymers.

Mechanical Property and Microstructure of Fly Ash-Based Geopolymer Activated by Sodium Silicate

Sodium silicate is one of the common alkali activators of geopolymers. The modulus, concentration and dosage of sodium silicate have significant effects on the activation of fly ash, the strength and microstructure of geopolymer. In this paper, unconfined compressive strength test, X-ray diffraction analysis (XRD), Fourier transform infrared light (FTIR), 29Si nuclear magnetic resonance (29Si NMR), scanning electron microscope and energy disperse spectroscopy (SEMEDS), and physisorption experiment (BET) were carried out to study the effects of the sodium silicate modulus and dosage on the mechanical property and microstructure of fly ash-based geopolymer. The results indicated that the main product of the geopolymer activated by sodium silicate was hydrated sodium aluminosilicate (N-A-S-H). When modulus value decreased and meanwhile dosage of sodium silicate increased, the reorganization and polymerization of gel products were accelerated so that the integrity and continuity of the microstructure of geopolymer were improved, and then the strength increased. When the modulus of sodium silicate was 3.28, the maximum value of the strength was at the dosage of 10%. According to this study, it was investigated that modulus value and dosage of sodium silicate had obvious influence on the alkali- activated reaction of fly ash, which can provide an engineering reference for the special soil solidification with geopolymers.