Fly Ash—Slag One-Part Geopolymers

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1		Iman Faridmehr	--	1235	2023-12-28 12:22:12	\|
2	update references and layout	Rita Xu	Meta information modification	1235	2023-12-29 02:16:21	\|

This entry is adapted from the peer-reviewed paper 10.3390/ma16062348

One-part geopolymer concrete/mortar is a pre-mixed material made from industrial by-products and solid alkaline activators that only requires the addition of water for activation. Apart from being environmentally friendly, it also reduces complexity and improves consistency in the mixing process, leading to more efficient production and consistent material properties.

one-part geopolymer concrete compressive strength artificial neural network

1. Introduction

Concrete is the world’s second most consumed commodity after water and the most used construction material globally. This results in a colossal environmental footprint with considerable carbon emissions and depletion of natural resources. Around 8% of all CO₂ emissions worldwide are related to concrete, and most of those emissions come from the manufacture of cement ^[1]. According to some estimates, 4.2 billion tons of cement are produced annually worldwide, causing about 4 billion tons of CO₂ emission into the atmosphere ^[2]. The manufacture of one ton of ordinary Portland cement (OPC) emits about 0.8 to 1 ton of CO₂. Thus, there is growing pressure on the concrete industry to develop different binders to reduce the need for OPC. To produce environmentally friendly concrete, it is necessary to develop viable alternatives to OPC that emit little or no CO₂ ^[3]^[4].

One of the potential options to lessen the environmental impact of OPC binders is the development of low-carbon binders ^[5]^[6]. Aluminosilicate materials react with water slowly, but when exposed to hydrolysis and condensation reactions in an alkaline solution, they react more quickly to produce inorganic polymers that can withstand mechanical loads. The structure of aluminosilicates significantly impacts the binding behavior that results from the amorphous aluminosilicate gels and the reactivity of the source materials, and numerous studies have been devoted to this issue ^[7].

The synthesis of aluminosilicates using alkalis can be categorized into low-calcium aluminosilicates and high-calcium aluminosilicates, depending on the calcium content of the source materials. Low calcium content aluminosilicate materials produce a sodium aluminosilicate hydrate (N-A-S-H), whereas high calcium content aluminosilicate materials produce calcium aluminosilicate hydrate (C-A-S-H), which resembles Portland cement C-S-H. Geopolymer binders are environmentally friendly materials used as a substitute for OPC binders. The polymerization mechanism of geopolymers is an intensely rapid chemical reaction of silica-alumina minerals in an alkaline environment that yields a three-dimensional polymeric sequence and ring structure consisting of Si–O–Al–O bonds. Geopolymer concrete production does not require the use of OPC, but the reaction of an aluminosilicate ingredient with strong alkaline liquids can produce a binder.

A novel method called one-part alkali-activation has been created to simplify the handling of traditional geopolymers, which involves mixing aluminosilicate precursors with powdered activators instead of an alkaline solution ^[8]^[9]. In contrast to traditional geopolymer binders, where solutions are used as the activation phase, the activators in the one-part binders are in dry powder form, and the reaction begins as soon as water is added to the binder. This method avoids producing geopolymer concrete in large quantities using corrosive and caustic solutions. One-part geopolymers emit less carbon dioxide into the atmosphere than conventional geopolymers because only a small portion of the framework is formed during the polymerization process ^[10]. Similar to OPC concrete preparation, one-part alkali-activated binders are made by adding water to a dry mixture comprising a solid aluminosilicate precursor and a solid alkali activator. Compared to OPC mixtures, manufacturing one-part geopolymers increases the geopolymer’s economic viability and the potential to curb CO₂ emissions significantly.

A computational model based on an artificial neural network (ANN) mimics the biological neural networks in the brain to process information. Neural networks can “learn” and correlate massive datasets gleaned from simulations or experiments. The trained neural network can be used as an analytical tool to make accurate predictions about problem outcomes. They can produce excellent prediction accuracy with practical approaches for training and validation. Hence, this research uses ANNs to estimate the compressive strength of one-part geopolymer pastes. An experimental database was compiled from information available in the open literature and used to train the ANN models. Five input parameters were used to train the ANN model: constituent materials, alkaline source content, curing temperature, and water/binder ratio. A “trial-and-error” approach was used to determine the input parameter weights that would produce the most accurate prediction of compressive strength. The best effective pattern for predicting compressive strength during the training approach was found by the Levenberg–Marquardt training (LM).

2. Fly Ash—Slag One-Part Geopolymers

The conventional method of using an alkaline activator solution in geopolymer production involves the use of highly caustic sodium- or potassium-based hydroxide, silicates, carbonates, or their combinations. This makes it dangerous to handle, store, and transport, requiring additional safety precautions that can slow down production and increase costs. To overcome these challenges, researchers have explored the use of solid activators to produce a user-friendly one-part geopolymer that only requires the addition of water. Some of the notable materials used as alkali sources include sodium hydroxide combined with various silica sources such as fly ash, rice husk ash, micro silica, calcium hydroxide, different grades of sodium metasilicate, and red mud. In recent years, many studies have focused on investigating the mechanical properties and durability of one-part geopolymer mortars and concrete.

Askarian and colleagues ^[8] created one-part hybrid concrete mixes using a combination of ordinary Portland cement (OPC) and geopolymers. They added solid potassium carbonate, which made up 7.5% of the total geopolymeric raw materials, as the primary activator. The researchers blended fly ash and ground granulated blast-furnace slag with the geopolymeric raw materials in various proportions and found that the addition of OPC decreased workability and setting time. However, it notably enhanced early age and ultimate compressive strength due to the rapid reaction of OPC with alkali activators.

Muthukrishnan et al. ^[11] conducted a study on the rheochemical approach to analyze the early strength development resulting from alkali reactions and formulate a suitable 3D printable one-part geopolymer concrete. The researchers evaluated the impact of different design parameters, such as activator content, thixotropic additive (Magnesium Alumino Silicate—MAS), and retarder (sucrose) dosage, on the rheological properties of the concrete. The findings indicated that the one-part geopolymer formulation exhibited improved printing characteristics when the binder contained 0.75 wt% MAS, 10 wt% activator, and 1.5 wt% sucrose.

Muhammad Riaz Ahmad et al. developed a new type of energy-efficient and sustainable concrete based on industrial waste materials and vegetal aggregate for hygrothermal and low load-bearing applications. They conclude that the vegetal concrete mixtures containing red mud exhibited higher capillary and water absorption as compared to other mixtures. Moreover, all concrete mixtures were classified as good to excellent moisture buffer materials.

Dongthe et al. ^[12] studied the solid activator, the synthetic sodium metasilicate pentahydrate against water, and a hybrid sodium silicate and sodium hydroxide activator solution to develop a high-strength one-part geopolymer mortar. They conclude that the solid activator using sodium silicate pentahydrate outperformed the often-used liquid activator in terms of the compressive strength of the mortar. Nevertheless, the compressive strength decreased, and efflorescence increased significantly once the metasilicate content exceeded Na₂O% = 6%.

Wangthe et al. ^[13] investigated the early-age properties of one-part fly ash/ground granulated blast-furnace slag (FA/GGBS) geopolymer through the utilization of hybrid activators, such as anhydrous sodium metasilicate (Na₂SiO₃), sodium carbonate (Na₂CO₃), and sodium aluminate (NaAlO₂). They indicated that Na₂SiO₃-activated one-part geopolymer released high reaction heat and achieved a faster setting. Such shortcomings could be improved by partially replacing Na₂SiO₃ with Na₂CO₃ in a solid form. Besides, incorporating slight NaAlO₂ decreased the self-flow of geopolymer paste, whereas the slump-flow properties remained unchanged.

References

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Vishwakarma, V.; Ramachandran, D. Green Concrete mix using solid waste and nanoparticles as alternatives—A review. Constr. Build. Mater. 2018, 162, 96–103.
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Shubbar, A.A.; Sadique, M.; Shanbara, H.K.; Hashim, K. The development of a new low carbon binder for construction as an alternative to cement. In Advances in Sustainable Construction Materials and Geotechnical Engineering: Select Proceedings of TRACE 2018; Springer: Berlin/Heidelberg, Germany, 2019; pp. 205–213.
Hattaf, R.; Aboulayt, A.; Lahlou, N.; Touhami, M.O.; Gomina, M.; Samdi, A.; Moussa, R. Influence of the Integration of Geopolymer Wastes on the Characteristics of Binding Matrices Subjected to the Action of Temperature and Acid Environments. Polymers 2022, 14, 917.
Askarian, M.; Tao, Z.; Adam, G.; Samali, B. Mechanical properties of ambient cured one-part hybrid OPC-geopolymer concrete. Constr. Build. Mater. 2018, 186, 330–337.
Haruna, S.; Mohammed, B.S.; Wahab, M.M.A.; Kankia, M.U.; Amran, M.; Gora, A.U.M. Long-term strength development of fly ash-based one-part alkali-activated binders. Materials 2021, 14, 4160.
Ma, C.; Zhao, B.; Wang, L.; Long, G.; Xie, Y. Clean and low-alkalinity one-part geopolymeric cement: Effects of sodium sulfate on microstructure and properties. J. Clean. Prod. 2020, 252, 119279.
Muthukrishnan, S.; Ramakrishnan, S.; Sanjayan, J. Effect of alkali reactions on the rheology of one-part 3D printable geopolymer concrete. Cem. Concr. Compos. 2021, 116, 103899.
Dong, M.; Elchalakani, M.; Karrech, A. Development of high strength one-part geopolymer mortar using sodium metasilicate. Constr. Build. Mater. 2020, 236, 117611.
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Subjects: Engineering, Civil

Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :

Iman Faridmehr

Mohammad Ali Sahraei

Moncef L. Nehdi

Kiyanets A. Valerievich

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Update Date: 29 Dec 2023

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1. Introduction

2. Fly Ash—Slag One-Part Geopolymers

References