Self-compacting geopolymer concrete using Class F Fly Ash

The development of self-compacting geopolymer concrete has the dual advantages of reducing environmental pollution and managing waste. The objective of the current experimental study is to create self-compacting geopolymer concrete with the best sodium silicate to sodium hydroxide ratio utilizing class F fly ash and sodium hydroxide. With varying sodium silicate to sodium hydroxide ratios (2.1, 2.3, 2.5, and 2.7), different molarities of sodium hydroxide (NaOH) (10M, 12M, and 14M) have been examined for workability and strength behavior. Self-compacting geopolymer concrete is found to be the ideal combination for a 12M sodium hydroxide solution and a 2.5 ratio of sodium silicate to sodium hydroxide solution.


Introduction
Considerable research has been done on low-carbon cementitious materials to reduce CO2 emissions into the atmosphere to promote sustainable development and eco-friendly products.Utilizing abundant alumina-silicate wastes from the industrial sectors, such as metakaolin or fly ash furnace slags (GGBS), is one way to promote alternative cementitious binders.Recent research has revealed the production of fly ash-based geopolymer concrete, which is produced entirely of fly ash and activated directly by alkali solution without the usage of OPC.Fly ash-based geopolymer concrete has gained the most attention because it can carry out a wide range of tasks, which is one of its primary advantages over OPC.Other techniques have also been employed to lessen environmental degradation, including the utilization of recycled materials, glass fibers, glass powder, and other waste products [1], [2], [3], and [4].Due to its high viscosity, geopolymer concrete exhibited the risk of compaction failure.As a solution to the issue, Self-Compacting Geopolymer Concrete (SCGC) has been presented.Vibration is not necessary for the placement or compacting of innovative SCGC concrete.It can flow under its weight, filling shapes and achieving full compaction even amid dense reinforcement.In this study, self-compaction advantages and the use of geopolymer cement are combined with this kind of concrete.The production of cement releases enormous amounts of carbon dioxide into the environment.For every tonne of cement, 0.7-0.8tonnes of carbon dioxide are discharged into the atmosphere [21].The building industry is responsible for more than 40% of worldwide emissions, and this number is rising as more and more building activities are undertaken.According to projections, 40% of the infrastructure needed to support the world by 2050 already exists, while the 1327 (2024) 012005 IOP Publishing doi:10.1088/1755-1315/1327/1/012005 2 other 60% still needs to be constructed [5].Hazardous landfills and waste disposal facilities are also produced by the various industries.Chemically and physically, industrial wastes and byproducts like fly ash, silica fume, ground-granulated blast-furnace slag, etc., are similar to cement.Utilizing waste materials such as silicate from industries and waste products is the most effective way to replace cement because it uses less cement [22].Because of their pozzolanic qualities, fly ash, GGBFS, and agricultural wastes like rice husk ash are the most frequently utilized industrial by-products as cement alternatives.The word "geopolymer" was originally used in 1991 by Davidovits [6] to refer to a class of mineral binders.By [7], the chemical composition and shape of these mineral binders are reminiscent of zeolites.In very alkaline conditions, a polycondensation process known as geopolymerization takes place.This reaction occurs when aluminosilicate materials react with alkali metallic silicates, and it ensures the creation of polymer "Si-O-Al-O-links," which results in the development of geopolymers [8].Portland cement pastes required a longer initial setting time when the temperature dropped to 0 C because of their high viscosity and low temperature.Because of the alkaline solution's phase separation at low temperatures, the initial setting time for geopolymer pastes was shortened.The ultimate setting time for both Portland cement and geopolymer pastes was shortened by increasing the MPCM concentration [9].Davidovits estimates that "approximately 0.184 tons of CO2 per ton of precursor (binder)" are released into the environment during the manufacture of geopolymers [10].Furthermore, the chloride ion permeability and absorption of geopolymer concrete were decreased by raising the SS/SH ratio.The morphological results demonstrated that when the SS/SH ratio increased, the deboning width at the interfacial transition zone (ITZ) between the binder and RCA reduced [11].Geopolymers show a reduction in CO2 emission of about 80% as compared to OPC.According to research, a sodium silicate solution/solid material ratio of 0.7 or 0.8, along with a percentage of fly ash in the binder material that is 20% and a percentage of slag that is 80%, are the ideal mixtures for achieving a favorable chemical reaction inside the geopolymer structure as well as increased compressive and indirect tensile strengths.[12].It has been discovered that compressive strength is closely connected with the molarity of the alkali activator solution and the AAB (alkali activator binder) ratio.As the molarity rises, the microstructure gets rather dense, which could be connected to a high degree of polymerization [13].Alkali activation solution, comprising sodium silicate (SS) and sodium hydroxide (SH), affects the fundamental characteristics of both freshly poured and fully cured geopolymer concrete.In particular, for the flowability and segregation resistance tests, it was shown that the ratio of SS/SH (2.5) was the optimal option for meeting the standards of EFNARC 2005 [14].The reactivity of the precursor fly ash determines the porosity of the geopolymer matrix in geopolymer concrete, and thus in turn [15].A binder comprising 45% FA, 45% GGBFS, 10% SF, 1.5% superplasticizer, a Na2SiO3/NaOH ratio of 1.5, and a molar concentration of 12 showed the greatest effective compressive strength.[16].The microstructures and compressive strengths of geopolymer pastes were investigated in this work by including high-calcium fly ash and waste glass powder.The geopolymer pastes with a median particle size of 21.26 µm were prepared using waste glass powder at weight percentages of 10%, 20%, 30%, and 40% instead of high-calcium fly ash.Glass containers and fluorescent lamp trash comprised the waste glass powders, with median particle sizes of 11.72 µm and 4.65 µm, respectively.NaOH and Na silicate were the two kinds of activated solutions that were used.The proportions of sodium hydroxide to sodium silicate for the alkaline liquid and binder were 1.0 and 0.6, respectively.After a 48-hour curing period at 60±2ºC, all samples were kept in storage at 23±2ºC until further analysis The results demonstrated that waste glass powder could be used to make geopolymer pastes with 34-48 MPa 7-d compressive strengths instead of fly ash.[17].Rheological studies revealed that the composite pastes had a yield stress that was nearly twice as high as fly ash paste, suggesting that the pastes were quite stiff when slag addition exceeded 25 weight percent.The hardened pastes' compressive strength decreased with increasing water-binder ratio, whereas it increased with increasing slag content and activator dosage.The accumulation of reaction products on the surfaces of the fly ash/slag particle and the dense microstructures observed in the FESEM both supported the higher activator and slag components.A mortar with a compressive strength of around 72 Mpa was produced by using regular sand in a 1:2 ratio with the paste creation.[18].When compared to Portland cement, geopolymers are generally becoming more and more popular as building materials because of their extremely low carbon dioxide emissions.These days, nanotechnology plays a big part in the construction sector.It has been observed that various nanomaterials have an impact on a few of the properties of cement-based concretes.An alternative to cement-based concrete or mortar is fly-ash-based geopolymer concrete, and the properties of geopolymers are impacted by nanoparticles.The properties of geopolymer mortars are significantly altered by the addition of nanomaterials such as carbon nanotubes, graphene, nano silica, etc.When introduced, nano TiO2 functions as a photocatalyst.A few nanomaterials, such as nanosilver, have antibacterial properties.The roles played by various nanomaterials in altering the characteristics of geopolymer mortars and concretes have been examined and explored [19].An unfavorable environment has been produced for the polymerization of aluminosilicate precursors due to excessive water absorption from OPS fibers.But when OPS was present in the right amounts, it helped the fly ash particles absorb more water, which increased the hydroxide activity and allowed the hydroxyl ions to be transported.After ambient curing, 10% OPS and 25% limestone were the optimal replacement amounts for the fine and coarse aggregate fraction in geopolymer concrete.Merely 10% of the quantity of limestone used in oven curing produced geopolymer concrete that outperformed the control group.[20].

Fly ash
Coal is used in thermal power stations to produce fly ash, a byproduct.Fly ash is the term for fuel ash.Precursors can be replaced with better results by adding fly ash to concrete mixtures.A fly ash sample from class F was obtained from Rajpura (Punjab) and used as a predecessor in the current experiment.The particle size of fly ash varies between 0-150 microns, and it is composed of 57.76% Silica and 34.56% Alumina.SEM image of fly ash as shown in Fig. 2 indicates the crystalline structure of Fly ash particles.

Fine Aggregates
In the present work, fine aggregates that adhere to grading zone II and specific gravity 2.63 have been utilized.

Coarse aggregates
The self-compacting geopolymer concrete was developed using coarse particles with a size range of 12 to 15 mm and a specific gravity of 2.67.

Chemicals
Chemicals required such as Sodium hydroxide, Sodium silicate, and superplasticizers have been used from local suppliers from Jalandhar.

SUSTAINABILITY APPROACH
The use of industrial waste class F fly ash as a precursor in the production of self-compacting geopolymer concrete has been chosen as a sustainable option for concrete.According to the ratio of Na2SiO3 to NaOH solution and the molarity of NaOH solution, as stated in Table 1, the produced selfcompacting geopolymer concrete has been designated and put through various workability tests.Mix code Id has been created such that FGC indicates Fly ash-based geopolymer concrete, where a numeral before FGC indicates the ratio of Na2SiO3 to NaOH solution and a numeral after FGC indicates the molarity of NaOH used in trials as per When Si4 + and Al3 + are in fourfold coordination with oxygen, they form the silico-aluminates that make up geopolymers.There are three fundamental units: polysilane, polysialate-siloxo, and polysialate-disiloxo.These materials are a variety of crystalline and amorphous structures.
In Al-Si materials, polymerization is accomplished through chemical processes as formalized: (Davidovits, 1991), Mn−SiO2z−AlO2n⋅wH2O where n is the degree of polymerization, z is 1, 2, or 3, and w is the number of moles of water, where M is an alkali cation (Na+), and n is the number of  2 shows the crystalline shape of fly ash particles.The strength behaviour of self-compacting geopolymer concrete has been given in Table 3 and shown graphically in Figure 4. Mix ID 2.5FGC12 is showing the best strength behaviour with satisfactory workability as SCC.

Discussion of results
Slump flow values for all mix codes vary from 0.665 to 0.712 micro millimeters, based on the experimental results that were observed and displayed in Tables 2 and 3.The concrete mix is more workable if the slump flow value is.Therefore, 2.5FGC10 with a slump flow of 0.712 micromillimeters exhibits the highest workability among all the mixed codes.
Slump Flow T50: Slump flow T50 represents the time taken for the concrete to reach a slump flow of 50 cm.The values for all mixed mixes range from 3.

Conclusion:
It can be concluded from the above observed data that mix code 2.5FGC12 demonstrates compatible workability behavior and high strength among all the mix codes tested, Therefore, a 12 M sodium hydroxide solution and a 2.5 sodium silicate to sodium hydroxide ratio can be recommended for self-compacting geopolymer concrete.Strength is mostly unaffected by

Figure 4 .
Figure 4. Showing the result for the strength behavior of various mix codes

Table 1 Table 1 .
Design mix for several trials for Class F-based geopolymer concrete

Table 2 .
Workability behaviour of Self-Compacting Geopolymer Concrete Instead of being constructed of a calcium silicate and hydrate gel, like regular Portland cement, geopolymers are instead strengthened structurally by the polycondensation process.Figure

Table 3 .
Strength behaviour of Self-Compacting Geopolymer Concrete 2 to 4.8 seconds.A lower value indicates faster flow, which is desirable for good workability.2.5FGC10 and 2.7FGC10 have the lowest slump flow T50 values, indicating better workability in terms of flow.V-Funnel T0 ranges from 10 to 12.2 seconds, while V-Funnel T5 min values range from 11.5 to 15.2 seconds.2.5FGC10 and 2.5FGC14 show the lowest values for both tests, indicating better workability.L-Box: 2.5FGC10 has the highest L-Box ratio, suggesting better flowability and passing ability.J-Ring: The results for the J-Ring test range from 6 to 12 mm.A smaller value indicates better passing ability.2.5FGC10 and 2.5FGC12 exhibit the lowest J-Ring values, indicating better workability.Mechanical properties exhibited are best for mix ID 2.5FGC12.