Optimization of Alkaline Activator Mixing and Curing Conditions for A fly Ash-Based Geopolymer Paste System

Comparison of thermal performance between fly ash geopolymer and fly ash-ladle furnace slag geopolymer

Strength development of Recycled Asphalt Pavement – Fly ash geopolymer as a road construction material

Recycled asphalt pavement – fly ash geopolymers as a sustainable pavement base material: Strength and toxic leaching investigations

Strength, durability, microstructure and leachate characteristics of Recycled Asphalt Pavement and Fly Ash (RAP-FA) geopolymers and RAP-FA blends as a sustainable pavement material are evaluated in this paper. The strength development of the stabilized materials with and without effect wetting-drying (w-d) cycles was determined by Unconfined Compression Strength (UCS) test. The mineralogical and microstructural changes of the stabilized material were analyzed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The leachability of the heavy metals were measured by Toxicity Characteristic Leaching Procedure (TCLP) and compared with international standard. The results show that both RAP-FA blend and RAP-FA geopolymer increase with increasing the number of w-d cycles (C), reaching its peak at 6 w-d cycles. The XRD and SEM analyses indicate that the strength development of RAP-FA blend occurs due to stimulation of the chemical reaction between the high amount to Calcium in RAP and the high amount of Silica and Alumina in FA leaching to production of Calcium Aluminium (Silicate) Hydrate, while the geopolymerization reaction is observed in RAP-FA geopolymer. For C> 6, the significant macro- and micro-cracks developed during w-d cycles cause strength reduction for both RAP-FA blend and geopolymer. The TCLP results demonstrate that there is no environmental risk for these stabilized materials. Furthermore, FA-geopolymer can reduce the leachability of heavy metal in RAP-FA blend. The outcome from this research confirms the viability of using RAP-FA blend and RAP-FA geopolymer as alternative sustainable pavement materials.

Formulation, mechanical properties and phase analysis of fly ash geopolymer with ladle furnace slag replacement

Fly ash is an industrial waste material of the thermal power plants. At present, India produces about 100 million tons of fly ash per annum and most of them are currently dumped in landfills, thus creating a threat to the environment. In recent years, attempts are made to increase the effective utilization of fly ash in the country. This study reveals the morphological, mineralogical, and geotechnical properties of fly ash and fly ash–kaolinite-based geopolymer materials prepared with low-calcium fly ash (ASTM Class F) and kaloinite with activating solution of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) at different curing conditions. Both the fly ash and the fly ash–kaolinite-based geopolymers are prepared in molds, and the unconfined compressive strength (UCS) for each combination is obtained. The UCS of geopolymers at different concentration of alkali, curing temperature, and time is studied. The microstructural and geotechnical characterization of fly ash and geopolymers are obtained using the X-ray diffraction, X-ray fluorescence, and scanning electron microscope (SEM). The low-calcium fly ash and kaolinite-based geopolymers are found to exhibit excellent UCS as compared to that of other geotechnical materials such as clay. It is also observed that fly ash–kaolinite-based geopolymer exhibits more compressive strength than that prepared only with the fly ash. The compressive strength of the geopolymers increases with the concentration of NaOH up to 12 molar beyond which the strength decreases. The compressive strength of geopolymers increases with the improvement of curing condition. Finally, water absorption test is performed to know the water absorption characteristics of the geopolymers.

The industrial waste which is rich in silica and alumina activated with alkaline activators such as sodium silicate (NS) or potassium silicate combined with sodium hydroxide (NH) or potassium hydroxide forms geopolymer cement. The present investigation aims to utilize the fly ash in an innovative way that is to activate it using alkaline activators. The use of environmentally friendly cement can reduce greenhouse effect, solve disposal problems, and improve waste utilization. The main objective of this study was to investigate the effects of activator and curing conditions on the compressive strength and microstructure of alkali-activated fly ash mortar or geopolymer mortar. Two different activators were used to activate the binder such as NS and NH solutions. Six separate mixes were designed with different NaOH concentrations (8M–18M). Furthermore, the effect of the solution-to-binder ratio on the compressive strength (CS) of fly ash (FA) geopolymer mortar (GPM) was investigated. The outcome of the present study revealed that the compressive strength was found to be enhanced with NaOH concentration up to 14M, and after that, this strength reduced. Further, the compressive strength was increased up to solution-to-binder ratio of 0.6, and beyond that, this strength decreased. Heat-cured specimen was more strengthened than ambient-cured specimen.

ABSTRACTThe stabilisation of marginal lateritic soil using cement and fly ash (FA) geopolymer with a liquid alkaline activator was investigated. In this study, soil with satisfactory gradation and percentage of wear was selected. Only the soaked California Bearing Ratio (CBR) value must be enhanced to satisfy the requirement to form a suitable pavement subbase material. Field CBR tests were conducted for both geopolymer- and cement-stabilised soils used as pavement subbase materials. The soaked CBR of cement- and FA-geopolymer-stabilised marginal lateritic soil of various mixing percentages at 14 days satisfied the standard requirements specified by the government agencies in Thailand. Equations were established from field test data to predict the CBR at any testing time. The CBR development of cement-stabilised soil took more time than that of geopolymer-stabilised soil. The appropriate mixing percentages of cement and FA geopolymer with marginal lateritic soil were 3–5 and 4–8%, respectively. Microstructural analysis indicated that the stabilised soil exhibited a denser structure, which corresponded to the CBR increment. The findings of this study will enable the implementation of cement and FA geopolymer as successful stabilisers for pavement subbase materials.

Role of microwave radiation in curing the fly ash geopolymer

An efficient approach for sustainable fly ash geopolymer by coupled activation of wet-milling mechanical force and calcium hydroxide

31 - Opportunities and future challenges of geopolymer mortars for sustainable development

This paper presents a systematic approach for selecting mix proportions for fly ash and GGBS-based geopolymer concrete. Very little information is available on complete methodology in designing the fly ash and GGBS-based geopolymer mix. The fly ash and GGBS were activated using sodium silicate and sodium hydroxide as alkaline activator solution. The Na2SiO3/NaOH (alkaline activator) ratio was taken as 2.5 and the concentration of NaOH solution was maintained at 8 M. The main parameters considered in this study were binder content and alkaline solution/binder ratio for various combinations of fly ash and GGBS. The variables considered in this experimentation include: binder content (360, 420 and 450 kg/m3), proportions of fly ash and GGBS (70–30, 60–40 and 50–50), alkaline solution/binder ratios (0.45, 0.50, 0.55 and 0.60) and curing condition (outdoor curing and oven curing). Results concluded that the GGBS content, alkaline solution/binder ratio and curing condition are found to be most influential parameters on compressive strength and workability of geopolymer concrete. The paper presents detailed examples of mix designs for various strengths.

A comparative life cycle assessment (LCA), life cycle cost analysis (LCCA), mechanical and long-term leaching evaluation of road pavement structures containing multiple secondary materials

Adding barium sulfate (BaSO4) to fly ash geopolymer increases its compressive strength as X-ray shielding for medical imaging applications

Fly ash–based geopolymers have emerged as a promising alternative to ordinary Portland cement, offering high mechanical strength and reduced environmental footprint. However, they are often limited by significant shrinkage and strength degradation when subjected to elevated temperatures. To enhance their thermomechanical performance and thermal stability, this study investigates the effects of mix proportioning parameters, alkali activator type, and thermal shock on performance deterioration. Compressive strength was evaluated for sodium- and potassium-activated fly ash geopolymer composites as a function of alkaline activator (AA) ratios, both under ambient curing and after exposure to the ISO 834 standard fire curve for 1 and 2 h. Volume change, mass loss, and density variation were analysed to interpret mechanical behaviour and relate it to structural transformations, while XRF, XRD, SEM, and particle size distribution were employed for material characterisation. Results indicate that rapid temperature changes, whether from thermal shock or high fire-heating rates, induced notable additional thermal degradation. Sodium activation achieved the highest compressive strength retention of 145% at one hour of firing, while potassium activation showed superior thermal stability with delayed densification, reaching 154% strength retention at two hours. Furthermore, SiO2/M2O ratio exerted the strongest influence on both mechanical and thermomechanical performance. Overall, the findings highlight that the activator type, SiO2/M2O ratio, and rapid temperature changes collectively exert strong control over the thermomechanical and thermophysical response of fly ash geopolymers at elevated temperatures.