Peat soils are highly heterogeneous and considered problematic because they have a high moisture content and low shear strength. It requires stabilization to enhance its engineering properties before it is transformed into a viable construction material. The use of geopolymers as stabilizer materials for weak soils has been on the rise recently due to their low carbon footprint compared to the use of conventional stabilizer materials like cement. Geopolymerization occurs as a result of the alkali activation of aluminosilicate materials. In this study, peat soil and the aluminosilicate materials Palm Oil Fuel Ash (POFA) and Ground Granulated Blast Furnace Slag (GGBFS) are characterized to assess their suitability as geopolymer precursor materials. A series of laboratory studies were carried out to determine the physicochemical properties of the materials, such as particle size distribution, moisture and organic content, specific gravity, pH, and electrical conductivity. Furthermore, the XRD, XRF, and FESEM tests were carried out to ascertain the mineral characteristics, elemental chemical composition, and morphological characteristics of these materials, respectively. The peat soil is classified as hemic peat with sufficient aluminosilicate content (Si/Al ratio of 2.11). The POFA is identified as Class F pozzolan with adequate Si+Al+Fe oxide content (67.9%), as stipulated by ASTM C618. The GGBFS material was found to be appropriate for geopolymer production, with a Si/Al ratio of 2.17, a hydration modulus of 2.38 (good hydration), and a basicity coefficient of 1.32 (alkaline material favorable for geopolymerization). Based on the geopolymer precursor material suitability assessment criteria, all the materials assessed were deemed suitable for geopolymerization, and the effectiveness of POFA-GGBFS geopolymer to improve peat soil properties should be studied in depth. At present, there are limited studies pertaining to the use of alkali-activated POFA-GGBFS blends to improve peat soil properties. As a result of this material characterization phase, planned works involving the compressive strength testing program on alkali-activated POFA-GGBFS-peat soil blends at ambient temperature will be carried out in the near future. The eventual aim of this research is to remediate the peat soil to be repurposed as road subgrade material. Doi: 10.28991/HIJ-2023-04-02-07 Full Text: PDF

Weak soils are characterised by their high compressibility and low shear strength, which requires stabilisation to improve their compaction and strength characteristics before being used for construction projects. Recent trends in soil stabilisation show an increased interest in the application of waste-derived geopolymers as low-carbon materials to address the carbon emission problem related to cement production. This paper presents the preliminary findings of using Palm Oil Fuel Ash (POFA) and Ground Granulated Blast Furnace Slag (GGBFS) binary blends as geopolymer precursor materials. These binary waste material blends were activated using alkaline solutions, namely Sodium Hydroxide (NH) and Sodium Silicate (NS), to synthesise geopolymers at ambient temperatures. Three main factors were considered for the optimisation of the geopolymer mix design, as recommended by past research: alkali equivalent (8-11.5%), activator modulus (0-0.7), and slag replacement (fixed at 30%). Alkali equivalent and activator modulus parameters were varied and tested to establish its initial and final setting times, workability and strength properties, while the slag replacement percentage was set at 30%. This study aimed to determine the most influential parameters to produce the geopolymer material with the highest compressive strength and satisfactory setting times and workability. Single-source alkali activators (NH only) used on POFA-GGBFS produced specimens with smaller flow diameters, longer initial and final setting times, and lower compressive strength than specimens activated with NH and NS. Geopolymer specimens synthesised with NH and NS produce stiffer compounds possessing higher compressive strength values and explosive-type failure modes due to their higher silica content. At ambient temperatures, TM-Mix 2 (7% alkali equivalent and 0.7 activator modulus) produced the highest compressive strength value of 67.3 MPa at 28 days curing, flow diameter of 227 mm, with the initial and final setting time of 25 minutes and 45 minutes, respectively. Consequently, the results show that the preliminary POFA-GGBFS geopolymer mix design could produce sustainably sourced geopolymer compounds with adequate strength and acceptable setting time and workability. This study is part of a current investigation to further optimise the POFA-GGBFS mix design for the purpose of weak soil stabilisation.

Different fuel properties and chemical kinetics of two different fuels would make it challenging to predict the combustion parameters of a binary fuel. Understanding the effect of blending methane and hydrogen gas is the main focus of this paper. Utilizing a horizontal tube combustion rig, methane-hydrogen fuel blends were created using blending laws from past literature, over a range of equivalence ratios from 0.6 – 1.2 were studied, while keeping one combustion parameter constant, the theoretical laminar burning velocity. The selected theoretical laminar burning velocity for all the mixtures tested were kept constant at 0.6 ms⁻¹. Different factors affected the flame propagation across the tube, including acoustic pressure oscillations, heat loss from the rig, and obvious difference in hydrogen percentage in the fuel blends. The average experimental laminar burning velocity of all the flames was 0.368 ms⁻¹, compared to the expected value of 0.6 ms⁻¹. In an attempt to keep the theoretical laminar burning velocity constant for different mixtures, it was discovered that this did not promise the same flame propagation behaviour for the tested mixtures. Further experimentation and analysis are required in order to better understand the underlying interaction of the fuel blends.

Premixed flame propagation in an open-ended horizontal tube has been investigated. Methane-air flames (ø =1.2) enriched with hydrogen were filmed with a high-speed camera and the pressure captured. Two-thirds along the tube, the flames encountered an acoustic field and were subjected to longitudinal oscillations. Depending on the hydrogen content, significant differences were observed in the behaviour of the flames. For lower hydrogen concentrations (RH 0.1 – 0.3), the flame speed initially decreased as it entered the field, and was then subjected to violent oscillations, resulting in a high acceleration and speed. The accelerations were attributed by the formation of Rayleigh-Taylor instabilities, which existed in the form of spikes of unburned mixture into the burned gasses that coupled with the pressure oscillations. This satisfied the Rayleigh criteria that the acoustically driven instabilities require the heat release and pressure waves to be in phase. When the hydrogen content was increased, as the flame passed through the acoustic field, the flame speed decreased, and no Rayleigh-Taylor instabilities were observed. This difference in behaviour with hydrogen content was attributed to the higher flame speeds with higher hydrogen concentrations.