Enhancement of Properties of Fly Ash Geopolymer Paste with Low NaOH Concentrations Using a Pressing Approach

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.

Fly ash and palm oil fuel ash (POFA) were used individually as a precursor to produce geopolymer paste samples. Both of the raw precursor were then mixed with 12 M sodium hydroxide solution to produce a hardened pastes. The pastes were oven cured at 60 °C for 24 h before being ambient cured to its testing age which were 7, 14 and 28 days. The liquid to binder ratio of fly ash and POFA geopolymer pastes was 0.30 and 0.40 respectively. Compressive strength test and sorptivity test were conducted on both geopolymer pastes. Durability in MgSO4 and Na2SO4 solutions were also conducted where compressive strength was recorded at the end of the test. Fly ash geopolymer pastes were found to achieve higher compressive strength compared to POFA geopolymer pastes. It also performs better in both sulfate solutions with lower strength loss compared to POFA geopolymer. Therefore, it can be concluded that fly ash performs better as a raw precursor for geopolymer compared to POFA.

This paper is aimed to evaluate the engineering properties of fly ash-based geopolymer bricks. Four geopolymer brick mixtures were designed with a constant solution-to-binder ratio of 0.40 and various concentrations of sodium hydroxide solution. The engineering properties of fly ash-based geopolymer bricks consisting of compressive strength, unit weight, water absorption, water permeability, and ultrasonic pulse velocity were investigated. The microstructure of fly ash-based geopolymer bricks was also investigated by using the scanning electron microscope (SEM). Test results indicated that the compressive strength, unit weight, and ultrasonic pulse velocity (UPV) of geopolymer bricks increased, while the water absorption and water permeability of geopolymer bricks reduced with increasing NaOH concentration. Moreover, brick samples with high NaOH concentration showed a higher geopolymeric reaction of fly ash than brick samples with low NaOH concentration. All geopolymer brick samples produced in this study showed a good quality with compressive strength of above 10.1 MPa, water absorption of below 9.4%, water permeability of below 1.84 L/m2 .h, and UPV of above 2500 m/s.

Influencing factors and mechanism of water absorption process of iron ores during sintering

In the present work, a comparative study of the effect of the different molarities of sodium hydroxide (NaOH) on fly ash geopolymer paste was investigated. The geopolymer pastes were prepared by mixing fly ash with alkali activator (a mixture of sodium hydroxide and sodium silicate) at solid/liquid ratio of 2.5. The NaOH were used 6M, 8M, 10M, 12M and 14M with fixed sodium silicate/NaOH ratio of 2.5. The geopolymers were cured at room temperature (29°C) for 24 hours and at 60°C for another 24 hours. The testing and analysis of the fly ash geopolymers were performed after 28 days. The geopolymer paste showed highest compressive strength (35MPa) with 8M of NaOH solution.

The need for locally produced, durable and robust, readily available, inexpensive and environmentally friendly building materials has led to persistent bottlenecks in sustainable housing delivery. "The construction industry is exploring exciting new materials that are eco-friendly and perfect for construction projects." The major problem associated with compressed earth bricks is the high rate of water absorption and lack of durability properties because most soil in its natural condition needs more strength, dimensional stability, and durability, which are required for building materials. The effect of high rate of water absorption and other strength and durability issues make bricks to be soluble in water and limits its use and performance of the bricks. This experimental study assesses the effect of locust bean (Parkia biglobosa) pod ash and Portland cement on compressed earth bricks' strength and durability properties. Compressed earth bricks were tested for density, compressive strength, permeability, water absorption, shrinkage, sorptivity and abrasion resistance. The maximum compressive strength was achieved at 10%C:10%LBPA stabilization with a strength of 2.52 N/mm2 and 2.80 N/mm2 at 28 and 56 days, which shows a 50% and 53.21% increase in strength over the control brick samples, respectively. Bricks produced with cement and locust bean pod ash were less permeable and had high resistance to abrasion, less shrinkage, less porous and less sorptivity than 0% stabilization. In conclusion, cement and locust bean pod ash are good stabilizing agents in compressed earth bricks. The use of Portland cement and locust bean pod ash as a stabilizing material seems to be a feasible solution not only to the problem associated with compressed earth bricks but also helps in the adoption of Indigenous waste material of locust bean pod in the production of bricks which will help reduce the environmental problem. Therefore, this research recommends using cement and locust bean pod ash at 10%C:10%LBPA in compressed earth bricks, leading to robust, stabilized and durable bricks.

Experimental study of freeze–thaw resistance of a one-part geopolymer paste

The objective of this study was to investigate the effect of curing temperature on the mechanical properties of sanitary ware porcelain powder-based geopolymer paste and mortar under various curing temperatures. The setting time, porosity, water absorption, and compressive strength of specimens mixed with alkaline concentrations of 8M, 10M, 12M, and 14M were compared. All mortar cube (50×50×50 mm) specimens were placed into drying ovens for 24 hours at 60°C, 75°C, 90°C, and 105°C, respectively. The specimens were then air-cured for 1, 3, 7, 14, and 28 days. The results showed that the elevated curing temperature accelerated the polymerization process of the porcelain geopolymerization reaction. The setting time varied between 89 mins and 380 mins. It showed variability depending on alkaline concentration and initial curing temperature. The setting time of pastes decreased when alkaline concentrations increased. An increasing temperature in the drying oven decreased the initial and final setting times. Similar to this, the rate of water absorption and permeability of porcelain-based geopolymer mortar specimens decreased with drying oven temperatures and increments in alkaline concentration. The lowest water absorption and porosity of the specimen were 2.1% and 15.7%, respectively. The compressive strength increased as drying oven temperatures and alkaline concentrations increased. The highest 28 day compressive strength was found in 14M specimens with 105°C curing temperatures. The ultimate compressive strength was 64.45 N/mm2. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were investigated to study the microstructural properties of the geopolymers. Doi: 10.28991/CEJ-2023-09-08-01 Full Text: PDF

Objective: To analyze the effect of variation of Na2O content on the compressive strength and water absorption of geopolymer paste and mortar specimens. Method: Alkali Activator solution was prepared by mixing sodium silicate solution and sodium hydroxide pellets in appropriate proportions 1 day before its use. The prepared solution was mixed with fly ash (FA) for 5 minutes in Hobart Mixer for geopolymer paste preparation and further sand was mixed to obtain geopolymer mortar. These specimens were placed in a mold and kept in an oven at 48oC for 48 hours. Compressive strength and water absorption tests were conducted on the specimens afterward. In this study, Na2O with 5%, 6.5% & 8.0% was analyzed for its effect on geopolymer paste and mortar.Findings: This research helped in determining the appropriate quantity of NaOH pellets required for geopolymer composite preparation and reducing the cost of construction, as NaOH pellets are more expensive than sodium silicate solution. Maximum compressive strength was achieved by using 8% Na2O content and water absorption was observed maximum at 6% of Na2O content. Novelty: This study is the first of its kind, which has analyzed the effect of Na2O content variation on water absorption and compressive strength of geopolymer paste and mortar specimens. Keywords: Geopolymer composite; compressive strength; water absorption; Sodium Oxide; fly ash

Sustainable concrete production: Mechanical and durability behaviour of slag-based geopolymer containing recycled geopolymer aggregate

Effective management of auto glass waste is essential for environmental sustainability, with recycling as pivotal strategies. This study aimed to valorise auto glass waste as a raw material for high-performance geopolymer composites. In the experiment, 0–40% auto glass powder (AGP) by weight was used as a substitute for high-calcium fly ash in the geopolymer paste. The setting time, workability, compressive strength, heavy metals leaching potential, and morphology of the geopolymer composites were investigated. The increase in the AGP content significantly increased the flow value and the setting time. The use of 10% AGP resulted in the paste with the highest compressive strength, and the 20% AGP paste displayed an acceptable compressive strength of approximately 90% compared to the reference paste. Microstructure analysis confirmed that an optimised AGP content of 10% resulted in a dense and homogenous geopolymer matrix with high compressive strength. Moreover, AGP inclusion also decreased the leaching potential of heavy metals, including chromium, copper, cobalt, zinc, nickel, and aluminium from fly ash geopolymer paste, making it more environmentally friendly. This research could thus lay a foundation for the development of guidelines for integrating AGP into geopolymer production, thereby encouraging eco-friendly practices in the construction sector.

Characteristics, microstructures, and optimization of the geopolymer paste based on three aluminosilicate materials using a mixture design methodology

In order to study the mechanical behavior of recycled fine aggregate mortar, 11 kinds of different recycled fine aggregate replacement rate (ranged from 0% to 100%, level differential 10%) of cement mortar test specimens are designed. The failure pattern and the mechanical performance indexes of the cement mortar under different recycled fine aggregate replacement rate are gained by test. And the different physical indexes of natural fine aggregate and recycled fine aggregate are measured in detail. The experiment findings indicate that because the water absorption rate of the mortar with high porosity is higher, and there are mass microcracks in recycled fine aggregate interior due to damage accumulation, the lower apparent density, the higher water absorption rate and the quicker water absorption speed of recycled fine aggregate are caused. So the fluidity of recycled fine aggregate mortar is fine, but the water retention is bad, the compressive strength is lower than the natural fine aggregate mortar about 50%. But the replacement rate has little effect on the mortar strength.

Rapid absorption and elimination of dietary water should be particularly important to flying species and were predicted to vary with the water content of the natural diet. Additionally, high water absorption capacity was predicted to be associated with high paracellular nutrient absorption due to solvent drag. We compared the water absorption rates of sanguivorous, nectarivorous, frugivorous, and insectivorous bats in intestinal luminal perfusions. High water absorption rates were associated with high expected dietary water load but were not highly correlated with previously measured rates of (paracellular) arabinose clearance. In conjunction with these tests, we measured water absorption and the paracellular absorption of nutrients in the intestine and stomach of vampire bats using luminal perfusions to test the hypothesis that the unique elongated vampire stomach is a critical site of water absorption. Vampire bats' gastric water absorption was high compared to mice but not compared to their intestines. We therefore conclude that (1) dietary water content has influenced the evolution of intestinal water absorption capacity in bats, (2) solvent drag is not the only driver of paracellular nutrient absorption, and (3) the vampire stomach is a capable but not critical location for water absorption.

Effects of NaOH concentrations on physical and electrical properties of high calcium fly ash geopolymer paste