Mechanical and Durability Analysis of Fly Ash Based Geopolymer with Various Compositions for Rigid Pavement Applications

Preparation and Application of Polyaluminum Ferric Sulfate from Red Mud: Behaviors of Leaching, Polymerizing, and Coagulation

Red mud is a solid waste containing valuable components, such as aluminum and iron. This paper aims to recover aluminum and iron from red mud by acid leaching and prepare polyaluminum ferric sulfate (PAFS) to apply for the turbidity reduction treatment of coal slurry water. The behaviors of leaching, polymerizing, and coagulation were analyzed by leaching thermodynamics and advanced micro-detection methods. More than 90% of aluminum and 60% of iron in red mud were dissolved into the leaching solution by using 50% sulfuric acid (v/v) with 7 mL/g at 100 °C for 2 h, where the crystal lattice of cancrinite was significantly destroyed to promote the dissolution of aluminum. The low polymerization (Al + Fe)a, medium polymerization (Al + Fe)b, and high polymerization (Al + Fe)c could be generated in PAFS by adjusting the basicity of the leaching solution with 0.7-0.9. The removal efficiency of turbidity of wastewater could reach more than 95% by using PAFS at 25 mg/L in the pH range of 6.0-7.0. The turbidity reduction mechanism included not only the electric neutralization of (Al + Fe)a but also the adsorption of (Al + Fe)b and the entrapment effect of (Al + Fe)c. This current study contributes to the future development of red mud based on flocculants containing aluminum and iron for wastewater treatment.

Strength, porosity and life cycle analysis of geopolymer and hybrid cement mortars for sustainable construction

Owing to the application of industrial wastes, geopolymers are generally regarded as a sustainable alternative to traditional construction materials. However, their lack of adoption on the industrial scale demands detailed investigations. This study conducts a comparative analysis of the compressive strength of different geopolymer and hybrid cement mortars with varying proportions of sodium hydroxide (from 5 to 25 wt%) and ordinary Portland cement (OPC) (from 15 to 35 wt%), respectively. The porosity of all designed mixtures was also analyzed using X-ray computed tomography (XCT) and water absorption tests. ReCiPe 2016 Midpoint (H) method was used for the Life cycle analysis of the geopolymer and hybrid cement mortars. Multi-criteria decision making (MCDM) approach was used to assess the sustainability potential of the designed mixtures based on compressive strength, porosity and overall environmental impact. Experimental results revealed that the increase in sodium hydroxide in geopolymer mortars up to 15 wt% offered its maximum compressive strength. Superior compressive strength was obtained at 35 wt% of OPC in hybrid cement mortars due to the formation of more C-S-H, C-A-S-H and N-A-S-H gels which fill up the voids and pores. Analysis of the macro and micro-porosity revealed that hybrid cement mortars yield denser structure than geopolymer mortars. Life cycle analysis based on 8 distinct impact categories showed that hybrid cement mortars outperform the geopolymers in all impact categories except 'mineral resource scarcity'. However, the overall environmental impact assessment using the 'coefficient of performance' depicts that hybrid cement mortars offer a significantly lower environmental burden than geopolymers. MCDM analysis shows that hybrid cement mortar with 5 wt% of sodium hydroxide and 35 wt% of OPC is the best choice for construction applications. This idea of sustainable hybrid cement mortar will be helpful for the construction industry to limit the environmental impact without compromising their structural performance.

Mix design process for sustainable self-compacting geopolymer concrete

Faster growth of infrastructure emphasizes the utilization of eco-friendly construction materials with a low carbon footprint. The objective of this experimental study is to propose a mix design methodology for self-compacting geopolymer concrete (SCGC) considering various influencing parameters recommended for self-compacting concrete (SCC) and geopolymer concrete (GPC). The experimental test results depict that SCGC had similar flow deformability with comparatively lesser flow speed compared to SCC. The increase in a sodium hydroxide (NaOH) molarity from 8 M to 16 M negatively affected the flow deformability as well as the flow speed of SCGC. The optimum compressive strength of 37 MPa was attained for SCGC having silica sand as fine aggregate, NaOH concentration of 16 M, fly ash to sand ratio (FA/S) of 0.75, and cured for 48 H at 80 °C. A mathematical equation is proposed to calculate Young's modulus of SCGC which is around 15 GPa. Young's modulus of SCGC was lesser than OPC concrete recommended by the ACI 318, however, Poisson's ratio of SCGC was found in the recommended range of OPC concrete. A flow chart is proposed for the mix design of SCGC with consideration of experimental test results in fresh and hardened stages.

Wind erosion control using alkali-activated slag cement: Experimental investigation and microstructural analysis

This paper aims to mitigate wind erosion of soil by employing alkali-activated slag. Wind tunnel tests were conducted on soil samples treated with varying percentages of slag at different wind speeds (7, 14, 21, and 28 m/s) and under a sand bombardment condition. In the absence of saltating particles, the erodibility ratios of the alkali-activated slag-treated samples with weight percentages of 1%, 2%, 4%, and 6% to the untreated sample at the highest wind speed (i.e., 28 m/s) correspond to 0.19%, 0.10%, 0.08%, and 0.06%, respectively. Moreover, in the presence of saltating particle bombardment, these samples exhibited erodibility reductions of 98.5%, 98.8%, 99.4%, and 99.6% compared to the untreated sample. The strength of the formed crusts, determined by penetrometer tests, increased significantly for the treated samples, ranging from 1300 to 6500 times greater than the untreated sample. The complementary analysis using x-ray diffraction and field emission scanning electron microscopy revealed the formation of albite and anorthite crystals along with the formation of calcium aluminosilicate hydrate, sodium aluminosilicate hydrate, and calcium silicate hydrate gels in the cementation process. Overall, the study highlights the effectiveness of alkali-activated slag in forming strong crusts that provide substantial protection against wind erosion, resulting in a significant decrease in wind erodibility.

An Experimental Study on the Properties of Concrete and Fiber-Reinforced Concrete in Rigid Pavements

The complex effect of the amount of cement, polypropylene fiber (the fiber length was 39 mm, and the diameter was 0.45 mm), and polycarboxylate superplasticizer on concrete properties for rigid pavement was determined using the methods of experiment planning and experimental-statistical modeling. The fluidity of all the mixtures was S1. The W/C of the mixtures depended on the composition of the concrete and variable from 0.32 to 0.46. It was found that, by increasing the amount of superplasticizer from 1% to 1.8-2%, the compressive strength of concrete increased by 4.5-6 MPa after 3 days and by 7-9 MPa after 28 days. The flexural strength in this case increased by 0.6-0.9 MPa. The use of polypropylene fiber in the amount of 1.5-1.8 kg/m3 increased the compressive strength of concrete by an average of 3 MPa, increased the flexural strength by 0.5-0.6 MPa, reduced the abrasion capacity by 9-14%, and increased the frost resistance by up to 50 cycles. When using a rational amount of superplasticizer and fiber, the compressive strength of concrete, even with a minimum cement amount of 350 kg/m3, was at least 65 MPa, its flexural strength was at least 6 MPa, its frost resistance was F200, and its abrasion capacity was not more than 0.30 g/cm2. Concrete with such properties can be used for roadways of any type. Low abrasion capacity and high frost resistance provide the necessary durability of concrete for rigid pavement during operation.

Synthesis and Characterization of Eco-Efficient Alkali-Activated Composites with Self-Cleaning Properties for Sustainable Construction

In this research, we aimed to design an eco-efficient composite based on alkali-activated materials (AAMs) with self-cleaning properties for sustainable construction. Significant emphasis was placed on determining the role of the type of precursor, the amount of sodium silicate, and the addition of titanium dioxide on the rheological and mechanical properties of AAMs. An important aspect of the research was the modification of AAM with titanium dioxide to obtain the self-cleaning properties. Titanium dioxide, thanks to its photocatalytic properties, enables the reduction of organic pollutants and nitrogen oxides in the urban atmosphere and promotes the cleaning of material surfaces. Blast furnace slag (BFS) was used as the source material, which was then substituted in subsequent formulations with metakaolinite at 50% and fly ash and zeolite at 30%. The best-activated AAMs, in which blast furnace slag and its mixture with metakaolinite were used as precursors, achieved compressive strengths of 50 MPa. BFS mixtures with pozzolans were more difficult to polymerize, although their final strengths were still relatively high, in the range of 33-37 MPa. Adding titanium dioxide (T) improved the final strengths and slightly lowered the heat of hydration and spreading of the AAM mortars. The best self-cleaning properties were achieved with composites that comprised a mixture of blast furnace slag, fly ash, and 2% titanium dioxide.

Obtaining and Characterizing New Advanced Materials

This editorial highlights the results presented in the second Special Issue dedicated to obtaining and characterizing new materials, wherein one review paper and 13 research articles have been published. The most important field covered is that of materials involved in civil engineering, focusing on geopolymers and insulating materials alongside developing new methods for enhancing the characteristics of different systems. Another important field is that of the materials used for environmental issues, and finally, those involved in human health.

Mechanical Performance of Fly Ash Based Geopolymer (FAG) as Road Base Stabilizer

This study examines the strength development of fly ash-based geopolymer (FAG) as a stabilizer for road base material for pavement construction. In the last decade, there has been a rapid development of conventionally treated bases, such as cement-treated bases. However, a major problem with this kind of application is the shrinkage cracking in cement-treated bases that may result in the reflection cracks on the asphalt pavement surface. This study explores the effects of FAG on base layer properties using mechanistic laboratory evaluation and its practicability in pavement base layers. The investigated properties are flexural strength (FS), unconfined compressive strength (UCS), shrinkage, and resilient modulus (RM), as well as indirect tensile strength (ITS). The findings showed that the mechanical properties of the mixture enhanced when FAG was added to 80-85% of crushed aggregate, with the UCS being shown to be a crucial quality parameter. The effectiveness of FAG base material can have an impact on the flexible pavements' overall performance since the base course stiffness directly depends on the base material properties. As a stabilizing agent for flexible pavement applications, the FAG-stabilized base appeared promising, predicated on test outcomes.

Influence of Fe2O3, MgO and Molarity of NaOH Solution on the Mechanical Properties of Fly Ash-Based Geopolymers

The use of waste from industrial activities is of particular importance for environmental protection. Fly ash has a high potential in the production of construction materials. In the present study, the use of fly ash in the production of geopolymer paste and the effect of Fe₂O₃, MgO and molarity of NaOH solution on the mechanical strength of geopolymer paste are presented. Samples resulting from the heat treatment of the geopolymer paste were subjected to mechanical tests and SEM, EDS and XRD analyses. Samples were obtained using 6 molar and 8 molar NaOH solution with and without the addition of Fe₂O₃ and MgO. Samples obtained using a 6 molar NaOH solution where Fe₂O₃ and MgO were added had higher mechanical strengths compared to the other samples.

Interaction of Geopolymer Filler and Alkali Molarity Concentration towards the Fire Properties of Glass-Reinforced Epoxy Composites Fabricated Using Filament Winding Technique

This paper aims to find out the effect of different weight percentages of geopolymer filler in glass-reinforced epoxy pipe, and which can achieve the best mechanical properties and adhesion between high calcium pozzolanic-based geopolymer matrices. Different weight percentages and molarities of epoxy hardener resin and high calcium pozzolanic-based geopolymer were injected into the glass fiber. By manually winding filaments, composite samples were produced, and they were then allowed to cure at room temperature. To determine how well the geopolymer matrices adhere to the fiber reinforcement, the microstructure of the composites' surfaces and perpendicular sections were examined. Maximum values of compressive strength and compressive modulus were 94.64 MPa and 2373.58 MPa, respectively, for the sample with a weight percentage of filler loading of 30 wt% for an alkali concentration of 12 M. This is a relatively wide range of geopolymer weight percentage of filler loading from 10 wt% to 40 wt%, at which we can obtain high compressive properties. By referring to microstructural analysis, adhesion, and interaction of the geopolymer matrix to glass fiber, it shows that the filler is well-dispersed and embedded at the fiber glass, and it was difficult to determine the differences within the range of optimal geopolymer filler content. By determining the optimum weight percent of 30 wt% of geopolymer filler and microstructural analysis, the maximum parameter has been achieved via analysis of high calcium pozzolanic-based geopolymer filler. Fire or elevated temperature represents one of the extreme ambient conditions that any structure may be exposed to during its service life. The heat resistance or thermal analysis between glass-reinforced epoxy (GRE) pipe and glass-reinforced epoxy pipe filled with high calcium pozzolanic-based geopolymer filler was studied by investigating burning tests on the samples, which shows that the addition of high calcium pozzolanic-based geopolymer filler results in a significant reduction of the melted epoxy.