Fly Ash-Based Geopolymer Composites: A Review of the Compressive Strength and Microstructure Analysis

Clean production of geopolymers as an opportunity for sustainable development of the construction industry

Large-scale cement production generates significant amounts of carbon dioxide from the breakdown of limestone, contributing to environmental pollution. Clean production of eco-friendly three-dimensional geopolymers can be used as environmentally friendly building materials. Replacing Portland cement with eco-friendly materials correlates with reduced energy consumption, costs, and negative environmental impact. In addition, geopolymer cement has above-average physical and chemical properties, which in many cases exceed conventional Portland cement. The literature review summarizes the latest research in the production of geopolymers following the principles of green chemistry and sustainable development goals. Examples of upcycling of construction waste, industrial waste (fly ash, silica fume, slag, tailing), demolition waste, agriculture solid waste (rice husk, palm oil), and mining waste into functional geopolymer materials will be discussed. Additionally, the review focused on innovative applications and physicochemical properties of functional geopolymer materials.

Advancements in the Evolution of Engineering Characteristics and Reinforcement Technologies for Subgrade Silt

Technical challenges associated with the treatment of silt subgrades frequently arise in coastal and river delta areas. Given the importance of environmental sustainability, the selection of efficient, cost-effective, and eco-friendly techniques for silt subgrade stabilization is paramount. While recycled polyester fibers primarily sourced from discarded polyester bottles have not yet been systematically employed in silt subgrade reinforcement, their potential is considerable. This paper offers a comprehensive review of the existing literature on the microstructural, physicochemical, and mechanical properties of silt, summarizing prior advancements in silt stabilization methodologies. Building upon this foundation, we introduce a novel approach utilizing recycled polyester fibers for silt subgrade improvement, outlining both its application prospects and challenges, which require further investigation. The findings of this study serve as a robust scientific foundation for the broader adoption and engineering implementation of this technology.

Investigation of the Physical Mechanical Properties and Durability of Sustainable Ultra-High Performance Concrete with Recycled Waste Glass

Construction material sustainability and waste reuse have emerged as significant environmental issues. Concrete is widely used in the building and engineering fields. Ultra-high performance concrete (UHPC), which has remarkably high mechanical properties, has become one of the most common concrete varieties in recent years. As a result, substantial amounts of Portland cement (PC) are frequently used, raising the initial cost of UHPC and restricting its broad use in structural applications. A significant amount of CO2 is produced and a large amount of natural resources are consumed in its production. To make UHPC production more eco-friendly and economically viable, it is advised that the PC in concrete preparations be replaced with different additives and that the recycled aggregates from various sources be substituted for natural aggregates. This research aims to develop an environmentally friendly and cost-effective UHPC by using glass waste (GW) of various sizes as an alternative to PC with replacement ratios of 0%, 10%, 20%, 30%, 40%, and 50% utilizing glass powder (GP). Fine aggregate “sand (S)” is also replaced by glass particles (G) with replacement ratios of 0%, 50%, and 100%. To accomplish this, 18 mixes, separated into three groups, are made and examined experimentally. Slump flow, mechanical properties, water permeability, and microstructural characteristics are all studied. According to the results, increasing the S replacement ratio with G improved workability. Furthermore, the ideal replacement ratios for replacing PC with GP and S with G to achieve high mechanical properties were 20% and 0%, respectively. Increasing the replacement rate of GP in place of PC at a fixed ratio of G to S resulted in a significant decrease in water permeability values. Finally, a microstructural analysis confirms the experimental findings. In addition, PC100-S100 was the best mix compared to PC100-S50 G50 and PC100-G100.

Properties and Cementation Mechanism of Geopolymer Backfill Paste Incorporating Diverse Industrial Solid Wastes

Industrialization has resulted in a large number of industrial waste slags being produced, which severely pollute the environment. This urgently needs resourceful treatment. The objective of this paper is to investigate the preparation, performance, and cementation mechanism of a novel geopolymer backfill paste for goaf. We reused diverse industrial waste slags based on low-calcium silica-alumina precursors (two fly ashes FAI, FAII, and red mud RM), high-calcium-based slags (carbide slag CS, soda residue SR, briquette residue slag BRS, and granulated blast furnace slag GBFS), and two additives (gypsum powder GP and lime powder LP). The hardening of backfill pastes was investigated by analyzing the effects of FAI, GBFS, RM, and LP on physical and chemical performance. The cementation mechanism of the prepared backfill paste was revealed through morphology, mineralogy, and chemical products through the use of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The results show that the prepared backfill paste incorporating various solid wastes (FAI, FAII, RM, CS, SR, GBFS, RBS, etc.) yields a 28-d compressive strength of 2.1 MPa (higher than the required value of 0.6 MPa) and a fluidity of 201 mm. Geopolymer gels (N,C)-A-S-H, calcium silicate hydrated C-S-H, and calcium aluminosilicate hydrated C-A-S-H gels serve as chemical cementers, whereas unreacted particles serve as physical filler skeletons. These findings provide an experimental and theoretical basis for the interchangeable use of various identical component solid wastes in backfill engineering materials.

Durability of Reinforced Concrete with Additions of Natural Pozzolans of Volcanic Origin

In this work, the properties of concrete modified with dosages of natural pozzolans (NP) in substitution of cement or superfine aggregates were evaluated. Proportions of 20/80 pozzolan/cement or pozzolan/superfine aggregates were selected for the additions of quarry and tuff pozzolans. Pozzolanic activity, durability, compressive strength, characteristic resistance, settling consistency, density, electrical resistivity, depth of water penetration, accessible porosity, and carbonation and chloride penetration were determined for the resulting concrete mixtures, and they were subsequently compared to the values obtained for the reference concrete batches without additions. The results of the cementitious mixtures supplemented with tuff (PZT) and quarry (PZQ) pozzolans, expressed in mmol/L, are consistent with the pozzolanism test, with [Ca(OH)₂]/[OH^-] ratios at 7 days are 6.03/60.19 for PZQ and 1.78/92.78 PZT. In addition to the pozzolanic activity at these dosages, the characteristic resistance and durability parameters required by EHE-08 were verified. Particular attention was given to the determination of the diffusion of chloride ions, introducing an instrumental modification of the accelerated integral method. The modification provides values of diffusion coefficients similar to those obtained by the other methods with the advantage of greater stability and quality of the measurement.

Influence of Alkali-Activators on Acid Rain Resistance of Geopolymer-Recycled Pervious Concrete with Optimal Pore Size

Geopolymer-recycled pervious concrete (GRPC) is a novel concrete that can effectively inhibit the corrosion of acid rain and alleviate urban waterlog. The goal of this study is to ascertain the optimal pore size of GRPC and study its acid rain resistance activated by different alkali-activators. Three different sizes (0.8, 1.0, and 1.2 mm) were separately chosen as the pore diameters of GRPC. The alkali-activator solution adopted sodium hydroxide (NaOH), sodium silicate (Na₂SiO₃), and a mixture of the two. The mechanical properties and permeability coefficient were tested to determine the optimal pore size of GRPC. After that, specimens with the optimal pore size were immersed in a simulative acid rain solution (sulfuric acid solution with pH = 4.0) for 6 d and were dried 1 d until 56 d. The effects of different alkali activators on acid rain resistance of GRPC were analyzed by compressive strength, neutralization depth, and mass loss. The results manifested that the mechanical properties of GRPC were excellent, the compressive strength of GRPC_H+N reached more than 60.1 MPa, and their splitting tensile strength attained more than 5.9 MPa, meeting the strength requirement of the road for heavy traffic load. Considering the mechanical properties and the acid rain purification effect of alkaline GRPC required a relatively small permeability coefficient; the optimal pore size was 1 mm. When specimens with optimal pore size were exposed to acid solution, the corrosion products (gypsums) would block the pores of GRPC to inhibit further corrosion, keeping the stability of the compressive strength. GRPC activated by the mixture of NaOH and Na₂SiO₃ generated a more stable amorphous three-dimensional network structure, endowing GRPC_H+N with better mechanical properties and acid corrosion resistance.

Properties and Applications of Geopolymer Composites: A Review Study of Mechanical and Microstructural Properties

Portland cement (PC) is considered the most energy-intensive building material and contributes to around 10% of global warming. It exacerbates global warming and climate change, which have a harmful environmental impact. Efforts are being made to produce sustainable and green concrete as an alternative to PC concrete. As a result, developing a more sustainable strategy and eco-friendly materials to replace ordinary concrete has become critical. Many studies on geopolymer concrete, which has equal or even superior durability and strength compared to traditional concrete, have been conducted for this purpose by many researchers. Geopolymer concrete (GPC) has been developed as a possible new construction material for replacing conventional concrete, offering a clean technological choice for long-term growth. Over the last few decades, geopolymer concrete has been investigated as a feasible green construction material that can reduce CO₂ emissions because it uses industrial wastes as raw materials. GPC has proven effective for structural applications due to its workability and analogical strength compared to standard cement concrete. This review article discusses the engineering properties and microstructure of GPC and shows its merits in construction applications with some guidelines and suggestions recommended for both the academic community and the industrial sector. This literature review also demonstrates that the mechanical properties of GPC are comparable and even sometimes better than those of PC concrete. Moreover, the microstructure of GPC is significantly different from that of PC concrete microstructure and can be affected by many factors.

Properties of 3D Printing Fiber-Reinforced Geopolymers Based on Interlayer Bonding and Anisotropy

The engineering applications and related researches of 3D printing fiber-reinforced geopolymers are becoming more and more extensive. However, compared with traditional mould-casted cement-based materials, the properties of 3D-printed fiber-reinforced geopolymers are significantly different, and their interlayer bonding and anisotropy effects are less studied, so in-depth analysis and summary are needed. Similar to common cement-based materials, the reinforcement fibers for geopolymers include not only traditional fibers, such as steel fibers and carbon fibers, but also synthetic polymer fibers and natural polymer fibers. These fibers have unique properties, most of which have good mechanical properties and bonding properties with geopolymers, as well as excellent crack resistance and enhancement. This paper summarizes and analyzes the effects of traditional fibers, polymer fibers, plant fibers and other reinforcement fibers on the properties of 3D-printed fiber-reinforced geopolymers, especially on the interlayer bonding and anisotropy. The influence of the flow and thixotropic properties of fiber-reinforced fresh geopolymer on the weak bond and anisotropy between layers is summarized and analyzed. At the same time, the influence of fibers on the compressive strength, flexural strength and interlayer binding strength of the hardened geopolymers is investigated. The effect of fibers on the anisotropy of 3D-printed geopolymers and the methods to improve the interlayer binding degree are summarized. The limitations of 3D printing fiber-reinforced geopolymers are pointed out and some suggestions for improvement are put forward. Finally, the research on 3D printing fiber-reinforced geopolymers is summarized. This paper provides a reference for further improving the interlayer bonding strength of 3D-printed fiber-reinforced geopolymers. At the same time, the anisotropy properties of 3D-printed fiber-reinforced geopolymers are used to provide a basis for engineering applications.

Behavior of Concrete Reinforced with Date Palm Fibers

In recent decades, researchers have begun to investigate innovative sustainable construction materials for the development of greener and more environmentally friendly infrastructures. The main purpose of this article is to investigate the possibility of employing date palm tree waste as a natural fiber alternative for conventional steel and polypropylene fibers (PPFs) in concrete. Date palm fibers are a common agricultural waste in Middle Eastern nations, particularly Saudi Arabia. As a result, this research examined the engineering properties of high-strength concrete using date palm fibers, as well as the performance of traditional steel and PPF concrete. The concrete samples were made using 0.0%, 0.20%, 0.60%, and 1.0% by volume of date palm, steel, and polypropylene fibers. Ten concrete mixtures were made in total. Compressive strength, flexural strength, splitting tensile strength, density, ultrasonic pulse velocity (UPV), water absorption capability, and water permeability tests were performed on the fibrous-reinforced high-strength concrete. With a 1% proportion of date palm, steel, and polypropylene fibers, the splitting tensile strength improved by 17%, 43%, and 16%, respectively. By adding 1% fiber, flexural strength was increased by 60% to 85%, 67% to 165%, and 61% to 79%. In addition, date palm fibers outperformed steel and PPFs in terms of density, UPV, and water permeability. As a result, date palm fibers might potentially be employed in the present construction sector to improve the serviceability of structural elements.