Soil Geopolymer Research Articles

Performance of Zeolite-Based Soil–Geopolymer Mixtures for Geostructures under Eccentric Loading

Performance of Zeolite-Based Soil–Geopolymer Mixtures for Geostructures under Eccentric Loading

Experimental Study on Geopolymerization of Lunar Soil Simulant under Dry Curing and Sealed Curing.

The construction of lunar surface roads is conducive to improving the efficiency of lunar space transportation. The use of lunar in situ resources is the key to the construction of lunar bases. In order to explore the strength development of a simulated lunar soil geopolymer at lunar temperature, geopolymers with different sodium hydroxide (NaOH) contents were prepared by using simulated lunar regolith materials. The temperature of the high-temperature section of the moon was simulated as the curing condition, and the difference in compressive strength between dry curing and sealed curing was studied. The results show that the high-temperature range of lunar temperature from 52.7 °C to 76.3 °C was the suitable curing period for the geopolymers, and the maximum strength of 72 h was 6.31 MPa when the NaOH content was 8% in the sealed-curing mode. The 72 h strength had a maximum value of 6.87 MPa when the NaOH content was 12% under dry curing. Choosing a suitable solution can reduce the consumption of activators required for geopolymers to obtain unit strength, effectively reduce the quality of materials transported from the Earth for lunar infrastructure construction, and save transportation costs. The microscopic results show that the simulated lunar soil generated gel substances and needle-like crystals under the alkali excitation of NaOH, forming a cluster and network structure to improve the compressive strength of the geopolymer.

A comparative analysis of ambient-cured metakaolin geopolymer mortar and flash-calcined soil geopolymer

This paper focuses on the development of a geopolymer (GP) mortar that can be cured under ambient conditions using flash-calcined dredged sediment (FCS) and flash-calcined excavated clay (FCC), as a substitute for Metakaolin (MK). Granulated blast furnace slag (GBFS) is also added to some of the GP mixes to study its effect on GP performance. Potassium silicate (K2SiO2) was used as an alkaline reagent (AR). Therefore, this study investigates the effect of binder composition on the mechanical and durability performance of the GP mortar samples. Acid attack test, high-temperature resistance test, and microstructural analysis tests such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were conducted to compare the reference mix with other substitute mixes containing FCS and FCC. Finally, the nuclear magnetic resonance (NMR) test is done on all GP mixes to verify their network classification. The results show that using FCS/FCC and only 10–20 % wt. of GBFS in the GP mortar mixes can result in similar or better properties in terms of strength and durability, while the NMR test identifies their tetrahedral network can vary between formulations.

The Study on the Properties and TCLP of GGBFS-Based Heavy-Metal-Contaminated Soil Geopolymer

The objective of this study is to use the geopolymer technique to solidify/stabilize heavy metal contaminated soil. There are over 739,700 square meters of heavy-metal-contaminated sites in Taiwan; most sites are soil farmlands. These heavy metal contaminants in soil can also infiltrate into groundwater and cause more serious pollution problems. This study explores the possibility of using the geopolymer technique to solidify heavy metal contaminated soil (CS), stabilize heavy metal, and produce good mechanical and physical properties. The ground granulated blast furnace slag (GGBFS) was activated by an alkali solution to form a geopolymer binder that can be used to solidify CS and stabilize the heavy metal. The effect of GGBFS and CS mixing ratio on the mechanical and physical properties and the TCLP test was investigated. The test results show that the compressive strength of specimens made with a 1.5 CS/GGBFS ratio can reach 46.61 MPa and 47.66 MPa after curing for 14 and 28 days, respectively. TCLP tests show only 2 ppm Cu was detected from a geopolymer-treated contaminated soil sample. The influence of alkali solution, such as the molarity of the NaOH, SiO2/Na2O, and SiO2/Al2O3 molar ratio, were also evaluated. The specimens prepared with 8 M NaOH, 0.96 SiO2/Na2O, and 1.28 SiO2/Al2O3 molar ratio alkali solution have a compressive strength of 51.74 MPa and 58.63 MPa after 14 and 28 days of curing. The TCLP tests show no heavy metal ions leached from the sample.

Lateritic soil geopolymer composites for ceramics and engineering construction applications

AbstractCharacterization of an Amazonian, laterite‐doped, kaolinitic soil (LK) or “lateritic soil” and laterite‐doped metakaolin (LMK) calcined at two distinct rates, as well as granite‐marble (GM) particulate industrial wastes was performed by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X‐ray diffraction (XRD), energy dispersive X‐ray fluorescence (XRF) spectrometry, and particle size and distribution analysis. In addition, an LMK geopolymer (GP) and a lateritic metakaolin‐based GP reinforced with granite‐marble composite (LMKGP‐GM) were tested for water resistance and for mechanical strength. XRD and XRF were used to investigate the composition of the composite materials, while XRD confirmed the formation of GP. Just as in the case of highly reactive commercial metakaolin used in construction, according to this study, lateritic soil‐based metakaolin presented similar characteristics. Therefore, it could be used in the development of more sustainable ceramics and construction materials, including the use of GM waste as a reinforcing phase/aggregate.

Exploring soil geopolymer technology in soft ground improvement: a brief excursion

Due to environmental concerns of global warming, a new generation of aluminosilicate binders called geopolymers has gained attention in recent years to replace cement and other calcium-based materials. The trend in the development/application of soil geopolymers was discussed in the present study for better performance and wide adoption in soft ground improvement. The current and future trends in the analyses of micro-level changes in connection with the macro properties of soil geopolymers were presented initially. The factors that affect soil geopolymer development were then discussed including curing conditions, type of liquid alkali activator, a ratio of hydroxide to silicate alkali, the concentration of the alkali hydroxide, the water content in the mixture, preparation method/mixing time, precursor and ratio of alkali activator to precursor content. These factors were separated into those with ascertained effects and those with inconclusive outcomes, needing further research. In addition, the existing areas of application of soil geopolymers were presented, and the potential areas of application were pointed out, based on the requisite properties of soil geopolymers for various ground improvement applications. The soil geopolymer properties, which require more in-depth study, were identified. Regulatory and optimisation issues associated with the development/application of soil geopolymers were elucidated, including the presentation of preliminary experimental results, to further consolidate the discussion. The potential effect of the interaction of factors in studying soil geopolymer development was revealed, as a means to address anti-synergistic effects that may result. The upshots of the study were assessed to provide useful insights for future development/application of soil geopolymers in soft ground improvement.

Hydraulic conductivity behaviour of expansive soil geopolymer binders

Geoenvironmental engineering facilities are required to be robust for effective long-term performance. In the present study, a robust experimental design approach was adopted for the development of expansive soil geopolymer binders for use as barriers in landfill systems. Palm oil fuel ash and quarry fines were used as precursor types (PT). The effects of other factors including precursor content, liquid activator type (LT), ratio of activator to precursor (A/P) and method of preparation were considered, in which compaction was done using British standard light energy. The results obtained show that the crucial factors which affect the soil geopolymer are the LT and A/P based on ANOVA. Two interactions including that between PT and LT and that of PT and A/P were found to be significant but yielded anti-synergistic effects on the hydraulic conductivity. The effect of moisture content on hydraulic conductivity for the two significant factors revealed that the variations in hydraulic conductivity are influenced by micro-level changes at the diffuse double layer, which affects the soil shrink-swell behaviour. Scanning electron microscope (SEM) and image processing of the SEM images using Otsu multi-thresholding and watershed segmentation algorithm correlated changes in the hydraulic conductivity with the pore changes in the soil geopolymer. Moreover, X-ray diffraction and Fourier transform infrared spectroscopy analyses further revealed the nuances, which occurred in the soil due to geopolymerisation.

Delineating the Aptness of Improved Geomaterial Strength for Ground Improvement Through Microstructure and Cluster Analysis

In this study, a sustainable technology using geopolymer synthesised from industrial waste materials was adopted to treat black clay soil for use in a geotechnical application such as in slope stability. A robust experimental design was applied, considering precursor type, precursor percentage (Pc), liquid activator type (LT), activator-to-precursor ratio and method of preparation (M) as the process factors for the unconfined compressive strength (UCS) determination. The results obtained following Taguchi optimisation and ANOVA revealed the most crucial factors to be LT, Pc and M. Optimum increment in UCS of about four times was achieved and validated using confirmatory experiment at 90% confidence level. An R2 value of 0.937 obtained between the experimental and predicted UCS underlines the prediction accuracy. The predicted values of the full factorial space for the developed soil geopolymers were used to classify them for reliability in a geotechnical application using minimum strength of 200 kPa, via hierarchical cluster analysis (HCA). A novel Taguchi hierarchical cluster standardisation procedure was implemented to execute the HCA, integrating geopolymer factors and their levels. The approach was found to be efficient in grouping the data by achieving high similarity levels in the resulting clusters. Moreover, HCA delineated the aptness level of the developed soil geopolymers and complemented/validated the ANOVA and Taguchi optimisation result of factor effects. The microlevel changes in the geopolymer-treated soil were delineated through mineralogical identification, morphological and elemental analyses. The geopolymer soil treatment is superior to lime treatment based on the outcome of the microlevel analyses.

Development of expansive soil geopolymer binders for use in waste containment facility

Waste containment facilities require liners and covers for safe waste disposal, which can be efficiently achieved using robust green technologies. In the present study, a systematic approach was adopted towards the development of reliable expansive soil geopolymers suitable for waste containment application. Various factors that influence geopolymerisation were considered including the precursor type (PT), precursor content, liquid alkali hydroxide type (LT), activator-to-precursor ratio (A/P) and method of preparation. Multiresponse optimisation for permeability, volumetric shrinkage and unconfined compressive strength was executed to achieve soil geopolymers that satisfy the regulatory requirement as hydraulic barrier materials. This was done using a robust experimental design and the utility concept to prescribe a framework for achieving reliable soil geopolymers. The results obtained show that significant interactions between the factors (PT × LT) and (PT × A/P) affected the response characteristics and consequently the soil geopolymer performance. The aptness of the multiresponse optimisation was confirmed at 95% confidence interval, which revealed that the developed soil geopolymers can be used in waste containment facility under certain conditions. Evidence of the geopolymerisation process was clarified using microstructural analyses. Scanning electron microscopy and energy-dispersive spectroscopy supported the formation of N–A–S–H and K–A–S–H gels. Moreover, diffraction patterns for new minerals such as muscovite and crystobalite were formed, with the disappearance of clay minerals. The presence of aluminosilicate gel binding systems was revealed by Fourier transform infrared spectroscopy. The participation of clay minerals in the geopolymerisation distinguishes the developed expansive soil geopolymer from the conventional geopolymers developed for concrete applications.

Strength performance of sodium hydroxide-activated fly ash, rice straw ash, and laterite soil geopolymer mortar

The geopolymer of fly ash (FA), rice straw ash (RSA) and laterite soil (LS) was prepared. The strength of the geopolymer mortar with the FA/RSA/LS percentage ratio of 41.67/16.67/41.67 was tested. The geopolymer was activated with sodium hydroxide (NaOH). Effect on air curing on compressive strength as well as the optimum mix proportion of geopolymer mortar was investigated. It is possible to achieve compressive strengths of 1.64 N/mm2, 1.72 N/mm2, and 3.22 N/mm2, respectively for the 12 M sodium hydroxide-activated geopolymer mortar after 3, 7 and 28 days of casting when air cured. Results indicated that the increase in the curing period increased the compressive strength.

Physical properties and thermal conductivity of soil geopolymer block

This research aimed to study the mixing ratios of fly ash and rice husk ash on the physical properties and thermal conductivity of soil geopolymer block. Fly ash to rice husk ash ratios for this experiment were 100:0, 80:20, 70:30, 50:50, 30:70, 20:80 and 0:100 %wt, respectively. The properties analysis of soil geopolymer block such as the compressive strength, water absorption, apparent porosity, bulk density and thermal conductivity were tested. The results indicated that soil geopolymer block of 80:20 %wt at 28 days of curing gave the maximum compressive strength of 131.43 kg/cm2. The minimum water absorption of 7.70 %, minimum bulk density of 2, 056.34 kg/cm3, minimum apparent porosity of 15.64 %, minimum thermal conductivity of 1.8674 W/m.K, were obtained. The compressive strength of soil geopolymer block increased up to 87 % and the thermal conductivity has decreased to 35 % compared to commercial cement block. The compressive strength, the water absorption and the bulk density of 80:20 %wt mixtures was in accordance with the standard product community at 602/2547 that can be used in construction applications.

Strength and Microstructure of Palm Oil Fuel Ash–Fly Ash–Soft Soil Geopolymer Masonry Units

AbstractThe application of palm oil fuel ash (POFA) and fly ash (FA) as an alumino-siliceous precursor to create a viable geopolymer binder for the manufacture of unfired lightweight masonry units,...

Synthesis of a one-part geopolymer system for soil stabilizer using fly ash and volcanic ash

A novel approach one-part geopolymer was employed to investigate the feasibility of enhancing the strength of in-situ soil for possible structural fill application in the construction industry. Geopolymer precursors such as fly ash and volcanic ash were utilized in this study for soil stabilization. The traditional geopolymer synthesis uses soluble alkali activators unlike in the case of ordinary Portland cement where only water is added to start the hydration process. This kind of synthesis is an impediment to geopolymer soil stabilizer commercial viability. Hence, solid alkali activators such as sodium silicate (SS), sodium hydroxide (SH), and sodium aluminate (SA) were explored. The influence of amount of fly ash (15% and 25%), addition of volcanic ash (0% and 12.5%), and ratio of alkali activator SS:SH:SA (50:50:0, 33:33:33, 50:20:30) were investigated. Samples cured for 28 days were tested for unconfined compressive strength (UCS). To evaluate the durability, sample yielding highest UCS was subjected to sulfuric acid resistance test for 28 days. Analytical techniques such as X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscope/energy-dispersive X-ray spectroscopy (SEM/EDX) were performed to examine the elemental composition, mineralogical properties, and microstructure of the precursors and the geopolymer stabilized soil.

Effect of hydrated lime on compressive strength mortar of fly ash laterite soil geopolymer mortar

This paper explored the suitability of fly ash, hydrated lime, and laterite soil with several activator (sodium hydroxide and sodium tiosulfate) to produce geopolymer mortar. Furthermore, the heat that released by hydrated lime was used instead of oven curing. In order to produce geopolymer mortar without oven curing, three variations of curing condition has been applied. Based on the result, all the curing condition showed that the hardener mortar can be produced and exhibited the increasing of compressive strength of geopolymer mortar from 3 days to 7 days without oven curing.

Palm oil fuel ash-soft soil geopolymer for subgrade applications: strength and microstructural evaluation

This paper presents the strength and microstructural properties of a geopolymer stabilised soft soil (SS) using palm oil fuel ash (POFA) as a precursor. The liquid alkaline activator, L used was a mixture of sodium silicate solution (Na2SiO3) and sodium hydroxide solution (NaOH). Compressive strengths were measured to assess the viability of POFA-SS geopolymer as a stabilised subgrade. Specialised tests were undertaken on POFA-SS geopolymers to investigate the geopolymerisation mechanisms under various Na2SiO3:NaOH ratio, L content and POFA:SS ratio. These specialised tests included; X-ray diffraction, scanning electron microscope with energy dispersive X-ray spectroscopy (SEM/EDX) and Fourier transform infrared (FTIR) spectroscopy tests. The lower POFA:SS ratios required more NaOH and L to be absorbed by both external and internal negative layer surfaces of SS to develop the stabilised soil structure. The optimum Na2SiO3:NaOH ratios providing the highest strength were at 40:60, 50:50, and 60:40 for POFA:SS ratios of 30:70, 40:60, and 50:50, respectively. The L providing the highest strength was determined at the optimum liquid alkaline activator content, OLC (L = 22.8%), 1.2OLC (L = 31.4%) and 1.4OLC (L = 44.55%) for POFA:SS ratios at 30:70, 40:60, and 50:50, respectively. The main chemical products in POFA-SS geopolymers were calcium aluminate silicate hydrate (C–A–S–H) and calcium sodium aluminate silicate hydrate (C–(N)–A–S–H).

Mercury Intrusion Porosimetry Studies with Geopolymers

The present study examines the role of micro-structure on the compressive strengths of geopolymers using mercury intrusion porosimetry technique. Geopolymers were synthesized from pozzolanas such as, class-F fly ash, kaolinite, metakaolinite, ground granulated blast furnace slag and red soil. Geopolymer reactions were accomplished by alkali activation of the pozzolanas using 10 M NaOH solution at 100 °C for 7-days. The geopolymers exhibited tri-modal nature of pores i.e., macro-pore mode (entrance pore radius: 25–5000 nm), meso-pore mode (entrance pore radius: 1.25–25 nm) and air void mode (entrance pore radius >5000 nm). The micro pores (entrance pore radius <1.25 nm) do not contribute to porosity of the geopolymers. The fly ash geopolymer exhibited largest total intruded volume (0.3908 cm3/g), while the red soil geopolymer exhibited the least intruded volume (0.0416 cm3/g). Interestingly, geopolymers with higher intruded volumes were characterized by larger compressive strengths. The experimental results also indicated that geopolymers with larger air voids + macro pores volume exhibited superior compressive strength; the results imply that geopolymers which develop an open microstructure during polymerization are characterized by larger compressive strength, possibly from stronger bond formation in the silico aluminate structure.

Investigation on Soil–Geopolymer with Slag, Fly Ash and Their Blending

Ground granulated blast furnace slag (GGBS)-based geopolymer is an excellent binder that attains high strength by curing at room temperature. Fly ash-based geopolymer binder, on the other hand, attains high strength when heated in particular temperature range. Although literatures on GGBS- and fly ash-based geopolymer are plenty, reported literatures on soil–geopolymer system are limited. An attempt has therefore been made in the present paper to investigate soil–geopolymer incorporating slag, fly ash and blending of slag and fly ash as source materials. It was observed that unconfined compressive strength of soil–geopolymer system increases with the source material content. Molar concentration of alkali activator, alkali-to-source material ratio and percent content of source material altogether affect the unconfined compressive strength of stabilized soil that is not straightforward. Na/Al and Si/Al ratios of the geopolymer mix ultimately govern the strength of stabilized soil. It was also observed that slag content is the most dominating factor affecting unconfined compressive strength rather than Na/Al ratio in case blending of GGBS and fly ash.

THE INFLUENCE OF INITIAL MATERIALS ON THE COMPRESSIVE STRENGTH OF GEOPOLYMER SOILS

In recent years, geopolymers have received significant attention because they show environmental benefits, such as a reduction in the consumption of natural resources and a decrease in the net production of CO2. In addition, as green material, soil has low carbon dioxide production emissions compared to other building materials. In this research, soil was combined with activator alkaline to produce hardening materials as geopolymer soils. An alkaline solution with sodium hydroxide, sodium silicate and fly ash was used. The influence of clay content on the geopolymer soils’ compressive strength was investigated. The best strengths were obtained from 5% to 12% clay content. SEM photos were also taken from specimens to investigate the structure of geopolymer soils. When combined with soil and fly ash in geopolymerization, fly ash reacted to the alkali solution quickly. The relationships between many variables such as clay content, fly ash, alkaline solution, curing time, and curing temperature were investigated by using a statistical analysis program with over 100 initial parameters. These results also indicate that the use of soils in geopolymer soil should have been limited. Additionally, increasing the sodium silicate in the alkaline liquid affected the geopolymerization reaction significantly. However, the suitable Si on the alkaline solution and soil should be limited.

Influence of Curing Condition and Clay Content on Strength of Geopolymer Soils

Soil is known as green material with low carbon dioxide production emissions in comparison with another building material. In this research, soil combined to activator alkaline to produce hardening materials as eco-friendly to the environment. The alkaline with sodium hydroxide, sodium silicate and fly ash are used. Curing temperature ranging from 80, to 140 degrees Celsius and curing time from 4 to 10 hours are investigated. The results show the strength of geopolymer soil is depended on curing time, temperature and sodium hydroxide-sodium silicate ratio. On the influence of clay content, soil is replaced by sand ranging from 20 to 80%, shows suitable clay which is from 4.79-12.43% by weight.