Investigation of Water Absorption Characteristics in Fly Ash and Bottom Ash-Based Geopolymer Paving Blocks

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

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

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

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

<p class="zhengwen"><span lang="EN-GB">This article reports the strength development and microstructure characteristics of a fly ash (FA) geopolymer system prepared with an alkaline activator consisting of sodium hydroxide (NaOH) solution and liquid sodium silicate (Na<sub>2</sub>SiO<sub>3</sub>). The effect of Na<sub>2</sub>SiO<sub>3</sub>/NaOH mass mixing ratio on the compressive strength and microstructure characteristics of hardened FA geopolymers at different ages was investigated. The influence of different curing conditions on the strength development of the FA geopolymer was also explored. The experimental results revealed that the alkaline activator prepared with Na<sub>2</sub>SiO<sub>3</sub>/NaOH ratio of 1.00 provides sufficient alkalinity to promote the geopolymerization reaction and development of high-strength FA geopolymer material. The </span><span lang="EN-GB">scanning electron microscopy (SEM) results showed that the dissolution rates of the FA extremely affected by the content of NaOH solution in the liquid activator. </span><span lang="EN-GB">Also, the most effective curing regime was 70 °C for 24 h to produce geopolymers with optimal strength at different aging periods. </span></p>

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.

Geopolymers are made by adding aluminosilicates to concentrated alkali solutions for dissolution and subsequent polymerization to form a solid. They are amorphous to semicrystalline three dimensional aluminosilicate networks. Although they have been used in several applications their widespread use is restricted due to lack of long term durability studies and detailed scientific understanding. Three important tools for the study of geopolymers are transmission electron microscopy (TEM), solid state magic angle spinning nuclear magnetic resonance (MAS NMR) and infra red (IR) spectroscopy.Cs and Sr are two of the most difficult radionuclides to immobilize and are therefore suitable elements to study in assessing geopolymers as matrices for immobilization of radioactive wastes. In this study Cs or Sr was added to geopolymer samples prepared using fly ash precursors. A commercial metakaolinite geopolymer was studied for comparison.The geopolymers were mainly amorphous as shown by TEM, whether they were made from fly ash or metakaolinite. In the fly ash geopolymer, Cs preferentially inhabited the amorphous phase over the minor crystalline phases, whereas Sr was shared in both. The MAS NMR showed that Cs is held mostly in the geopolymer structure for both fly ash and metakaolinite geopolymers. The IR spectra showed a slight shift in antisymmetric Si-O-Al stretch band to a lower wavenumber for the fly ash geopolymer, which implies that more Al is incorporated in this geopolymer structure than in the metakaolinite geopolymer.

Electrodialytic remediation of municipal solid waste incineration fly ash as pre-treatment before geopolymerisation with coal fly ash

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.

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

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.

Applicability of waste foundry sand stabilization by fly ash geopolymer under ambient curing conditions

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

In this study, edge-oxidized graphene oxide (EOGO) was used as an additive in fly ash (FA) geopolymer paste. The effect of EOGO on the properties of the fly ash geopolymer was investigated. EOGO was added to the FA geopolymer at four different percentages (0%, 0.1%, 0.5% and 1%), and the mixture was cured under two different conditions: room curing (~20 °C) and heat curing (~60 °C). To characterize the FA-EOGO geopolymer, multiple laboratory tests were employed, including compressive strength, Free-Free Resonance Column (FFRC), density, water absorption, and setting tests. The FFRC test was used to evaluate the stiffness at small strain (Young's modulus) via the resonance of the specimen. The mechanical test results showed that the strength and elastic modulus were high during heat curing, and the highest compressive strength and elastic modulus were achieved at 0.1% EOGO. In the physical test, 0.1% EOGO had the highest density and the lowest porosity and water absorption. As a result of the setting time test, as the EOGO content increased, the setting time was shortened. It is concluded that the optimum proportion of EOGO is 0.1% in FA geopolymer paste.

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