Showing papers on "Geopolymer published in 2022"

Geopolymer concrete incorporating recycled aggregates: A comprehensive review

Abstract: Several industrial by-products are extensively used again as a supplementary cementitious material or aggregates in the interest to reduce environmental footprints in terms of energy depletion, pollution, waste disposition, resource depletion, and global warming related with conventional cement. A remarkable quantity of industrial scrap materials, primarily designated as construction and demolition waste from the construction industry, has transformed into crucial apprehension of governments. In the recent past, substantial explorations have been accomplished to appreciate the distinct characteristics of concrete, employing recycled aggregates from construction and demolition waste. Geopolymer composite is a new cementitious material, and it appears to be a potential replacement for conventional cement concrete. This paper summarises the previous research concerning the utilisation of recycled aggregate as a partial or complete supplants for conventional aggregates in geopolymer concrete. The influence of recycled aggregate addition on the fresh and hardened properties of geopolymer concrete is comprehensively reviewed in this paper. The studies suggest significant improvement in the workability on addition of recycled aggregates to geopolymer concrete. However, the addition results in increased water absorption and sorptivity.

High-temperature behavior of polyvinyl alcohol fiber-reinforced metakaolin/fly ash-based geopolymer mortar

Abstract: Polyvinyl alcohol (PVA) fiber-reinforced geopolymer mortar is an eco-friendly construction material with excellent mechanical properties and durability. Visual observation, mass loss measurement, cubic and prism compressive tests , flexural tests, thermogravimetric and differential thermal analysis , scanning electron microscopy, and bubble parameter tests were conducted to evaluate the effect of PVA fiber and exposure temperature on the behavior of PVA fiber-reinforced geopolymer mortar after exposure to high temperatures. The PVA fiber contents were selected as 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, and 1.2%, and the target temperatures were 25 °C, 200 °C, 400 °C, 600 °C and 800 °C. The results indicate that significant mass loss of the geopolymer mortar could be observed when the exposure temperature increased from 25 °C to 250 °C, whereas slight mass loss occurred from 250 °C to 700 °C, and no mass loss was detected from 700 °C to 800 °C. As the temperature increased, the geopolymer mortar gradually densified, while the geopolymer mortar continuously developed more cracks and pores. The compressive and flexural strengths of the geopolymer mortar improved as the temperature increased from 25 °C to 200 °C, but it decreased significantly as the temperature further increased to 800 °C. In addition, on exposure to 200 °C, the presence of PVA fibers significantly improved the cubic and prism compressive strengths and flexural strength by 50.5%, 29.4%, and 66.3%, respectively, compared with the geopolymer mortar without fibers. As the temperature increased above 200 °C, although the PVA fiber decomposed, the defects left by the melt fibers slightly influenced the strength of the geopolymer mortar.

High-strength high-ductility Engineered/Strain-Hardening Cementitious Composites (ECC/SHCC) incorporating geopolymer fine aggregates

Abstract: In this study, Engineered/Strain-Hardening Cementitious Composites (ECC/SHCC) incorporating geopolymer fine aggregates were successfully developed with high strength and high ductility. A multi-scale investigation was conducted to gain an in-depth understanding of the microstructure and ductility enhancement mechanism of geopolymer aggregate ECC (GPA-ECC). The use of geopolymer fine aggregates enabled the high-strength ECC to achieve higher tensile ductility and finer crack width compared to existing ones with similar compressive strength in the literature. It was found that the GPA reacted with the cementitious matrix, and the width of the GPA/matrix interfacial transition zone (ITZ) was larger than that of the silica sand/matrix ITZ. Moreover, the GPA achieved a strong bond with the cementitious matrix and could behave as “additional flaws” in high-strength matrix, resulting in saturated multiple cracking and excellent tensile ductility of ECC. This study provides a new avenue for developing high-performance fiber-reinforced cementitious composites based on artificial geopolymer aggregates.

High-strength high-ductility Engineered/Strain-Hardening Cementitious Composites (ECC/SHCC) incorporating geopolymer fine aggregates

Abstract: In this study, Engineered/Strain-Hardening Cementitious Composites (ECC/SHCC) incorporating geopolymer fine aggregates were successfully developed with high strength and high ductility. A multi-scale investigation was conducted to gain an in-depth understanding of the microstructure and ductility enhancement mechanism of geopolymer aggregate ECC (GPA-ECC). The use of geopolymer fine aggregates enabled the high-strength ECC to achieve higher tensile ductility and finer crack width compared to existing ones with similar compressive strength in the literature. It was found that the GPA reacted with the cementitious matrix, and the width of the GPA/matrix interfacial transition zone (ITZ) was larger than that of the silica sand/matrix ITZ. Moreover, the GPA achieved a strong bond with the cementitious matrix and could behave as “additional flaws” in high-strength matrix, resulting in saturated multiple cracking and excellent tensile ductility of ECC. This study provides a new avenue for developing high-performance fiber-reinforced cementitious composites based on artificial geopolymer aggregates. • Geopolymer fine aggregates were successfully applied to develop high-strength high-ductility ECC with fine crack width. • Geopolymer fine aggregates reacted with cementitious paste, resulting in a strong interfacial bond. • Geopolymer fine aggregates acted as “additional flaws” in high-strength ECC matrix, leading to saturated multiple cracking. • Compared with existing ambient-cured high-strength ECC, geopolymer aggregate ECC exhibited superior tensile ductility.

The role of nanomaterials in geopolymer concrete composites: A state-of-the-art review

Abstract: Geopolymers are novel cementitious materials that have the potential to replace conventional Portland cement composites completely. The production of geopolymer composites has a lower carbon footprint and uses less energy than the production of Portland cement. Recently efforts have been made to incorporate different types of nanoparticles (NPs) in geopolymer composites to enhance the properties of the composite with improved performances. Nanotechnology is one of the most active research areas with novel science and valuable applications that have gradually gained attention, especially during the last two decades. Many studies have been undertaken to date in order to understand better the impacts of NPs addition on the fresh, physical, mechanical, durability, and microstructure properties of geopolymer composites. In the current comprehensive review paper, the effects of different NP types on the most essential fresh, mechanical, durability, and microstructure characteristics of geopolymer paste, mortar, and concrete composites were reviewed, analyzed, and discussed in detail. In this regard, more than 280 published papers were used to create an extensive database that includes the main features of geopolymer composites modified with different NPs. In addition, the main mechanisms behind the influence of different NP types on the properties of geopolymer composites were examined. Past progress, recent drifts, current obstacles, and the benefits and drawbacks of these geopolymer composites enhanced with NPs were also highlighted. Based on the findings of this study, the addition of NPs has a promising future for developing high-performance geopolymer composites that the construction industry can efficiently implement due to significant improvements in strength, durability, microstructure by providing additional C–S–H, N-A-S-H, and C-A-S-H gels as well as filling nano-pores in the geopolymer matrix.

Influence of nano-TiO2, nano-Fe2O3, nanoclay and nano-CaCO3 on the properties of cement/geopolymer concrete

Abstract: In past decades, researchers have tried to improve the durability of concrete by integrating supplementary cementitious materials into concrete. Recent advancements in the field of nano-engineered concrete have reported that nanomaterials significantly improve the mechanical and durability properties of concrete. This paper provides a comprehensive summary of recent developments on the use of nanomaterials as a performance enhancer in cement/geopolymer concrete. Many significant correlations associated with the reinforcement of cementitious matrices using nano-TiO2, nano-Fe2O3, nanoclay/metakaolin, and nano-CaCO3 were studied. Performance aspects such as fresh properties, microstructure, mechanical and durability characteristics, and the influence of various particle sizes have been reviewed. The findings from this review confirm the feasibility of using the nanomaterials in cement concrete, with the required properties of building materials. It is also expected that this review provides better insight into using nanomaterials in concrete for the benefit of academic and fundamental research and promotes its practical application in the construction industry.

Geopolymer concrete as a cleaner construction material: An overview on materials and structural performances

Abstract: • A comprehensive review on the fresh, mechanical, and structural performances of GPC is presented. • Like traditional concrete, GPC has good fresh and mechanical properties. • The general behavior of the structural beam members is comparable to that of typical reinforced concrete structural elements. • Structural member design codes are applicable, but they are conservative in nature. The manufacture of ordinary Portland cement (OPC) produces a lot of CO 2 in the atmosphere. Researchers have recently focused on exploring the behaviour of geopolymer concrete (GPC) as an alternative to Portland cement concrete (PCC) in micro and macro dimensions. Geopolymers (GP) are innovative cement-based materials that could totally replace OPC composites. Geopolymer composites (GC) have a reduced carbon footprint and utilize less energy than OPC. The construction industry's main concerns are material characteristics and the performance of reinforced concrete (RC) structural components. Therefore, this review paper is going to look at some important material properties, like fresh characteristics, compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity, as well as the evidence of the structural behaviour of GPC beams. According to the findings of this review, GPC offers similar or superior fresh and mechanical properties to conventional concrete composite. In addition, it was mentioned that GPC might be utilized to design GPC members securely in terms of their strength capabilities and standard codes of practice. Nevertheless, further study is suggested to include more detailed and cost-effective design methods for the potential use of GPC for large-scale field applications.

A novel synthesis of lightweight and high-strength green geopolymer foamed material by rice husk ash and ground-granulated blast-furnace slag

Abstract: This study reports the preparation and characterization of alkali-activated slag based geopolymer foamed material (GFM). The roles of rice husk ash (RHA) on thermal stability and thermal insulation of GFM were systematically investigated. Thanks to the low self-weight and good reactivity of RHA, the compressive strength and specific compressive strength of GFM are enhanced, promoting the lightweight and high-strength developments of GFM. More importantly, the replacement of GGBS by RHA efficiently mitigates the strength degradation, reduces the weight loss and increases the volumetric stability of GFM during thermal exposure. The thermal conductivity of GFMs registered from 0.1102-0.2891 W/m•K reflects good thermal insulation characteristic, which is better than the reported thermal insulation properties of other alkali-activated foamed materials system at the same strength/density level. The mechanism of RHA acting on GFMs is closely related to the property characteristics of RHA itself, basic properties enhancement and pore structure development of GFMs. With the use of 20 wt.% RHA, the GFM containing 2 wt.% H2O2 exhibits the optimal comprehensive properties: 0.01270 × 103kN•m/kg specific compressive strength, 827 kg/m3 volume density, 10.5MPa compressive strength, 0.1331 W/m•K thermal conductivity and better volumetric stability.

Comprehensive review of the properties of fly ash-based geopolymer with additive of nano-SiO2

Abstract: Abstract Nano-SiO2 is a non-toxic, tasteless, and pollution-free material with hydroxyl groups that facilitate the adsorption of water on its surface. Nano-SiO2 is characterized by small particle size, high purity, low density, large surface area, and good dispersion properties. In addition, nano-SiO2 has excellent stability, reinforcement, thixotropy, and optical and mechanical properties. The additive of nano-SiO2 can enhance the mechanical properties and microstructure of concrete. Therefore, nano-SiO2 is widely used as an additive in the field of building materials. Geopolymers have excellent mechanical properties, acid–alkali resistance, fire resistance, and high-temperature resistance. In addition, mineral waste and construction waste can be used as raw materials for geopolymers. Therefore, geopolymers have the potential to substitute ordinary Portland cement and have good prospects for application as construction materials. The application of nanomaterials in geopolymer products has shown that nano-SiO2 is effective in increasing the rate of geopolymerization reaction and reducing the setting time of geopolymers in a controlled quantity. Related results indicate that an appropriate quantity of nano-SiO2 can make the microstructure of fly ash-based geopolymers denser and produce higher mechanical strength. In this study, based on the mechanism of geopolymerization, the effects of nano-SiO2 on the properties of fly ash-based geopolymers including compressive strength, microstructure, hardening properties, shear bond strength, durability, and practical applications have been summarized. This study can provide a basis for understanding the effects of nano-SiO2 on the mechanical properties and durability of fly ash-based geopolymers.

A novel synthesis of lightweight and high-strength green geopolymer foamed material by rice husk ash and ground-granulated blast-furnace slag

Abstract: This study reports the preparation and characterization of alkali-activated slag based geopolymer foamed material (GFM). The roles of rice husk ash (RHA) on thermal stability and thermal insulation of GFM were systematically investigated. Thanks to the low self-weight and good reactivity of RHA, the compressive strength and specific compressive strength of GFM are enhanced, promoting the lightweight and high-strength developments of GFM. More importantly, the replacement of GGBS by RHA efficiently mitigates the strength degradation, reduces the weight loss and increases the volumetric stability of GFM during thermal exposure. The thermal conductivity of GFMs registered from 0.1102-0.2891 W/m•K reflects good thermal insulation characteristic, which is better than the reported thermal insulation properties of other alkali-activated foamed materials system at the same strength/density level. The mechanism of RHA acting on GFMs is closely related to the property characteristics of RHA itself, basic properties enhancement and pore structure development of GFMs. With the use of 20 wt.% RHA, the GFM containing 2 wt.% H2O2 exhibits the optimal comprehensive properties: 0.01270 × 103kN•m/kg specific compressive strength, 827 kg/m3 volume density, 10.5MPa compressive strength, 0.1331 W/m•K thermal conductivity and better volumetric stability.

A review on shrinkage-reducing methods and mechanisms of alkali-activated/geopolymer systems: Effects of chemical additives

Abstract: Alkali-activated binders or geopolymers are identified as an ideal substitute for ordinary Portland cement (OPC) binders because of their outstanding mechanical characteristics and durability. However, the high-magnitude shrinkage for alkali-activated composites induces uneven deformation across the material and further triggers the formation of harmful cracks, which creates ways for various aggressive substances to permeate the composites, severely reducing the load capacity and threatening the durability of concrete structures. Recently, relevant researchers have reported adding chemical additives is an effective way in alleviating the shrinkage for alkali-activated or geopolymer systems. However, to date, only limited information summarizing and classifying these chemical additives and their shrinkage-reducing mechanisms is available. Therefore, this paper presents a well-documented literature review on the shrinkage characteristics for alkali-activated or geopolymer composites, and systematically summarizes chemical additive types and their shrinkage-reducing mechanisms. The frequently-used chemical additives in alkali-activated or geopolymer systems can be divided into four types: expansive agents (EAs), shrinkage-reducing admixtures (SRAs), superabsorbent polymers (SAPs), and nano-particles (NPs). Then, the influences of these chemical additives on the mechanical behavior and shrinkage for geopolymer or alkali-activated systems were compared and discussed. It was found that the inclusion of SAPs achieved the best shrinkage-mitigating effect, followed by SRAs, EAs, and NPs, respectively. There were about 30%, 45%, and 55% declines in the shrinkage of alkali-activated or geopolymer systems when 3% NPs, EAs, and SRAs were added. Whereas, a reduction of about 70% can be observed by incorporating only 0.3% SAPs. Additionally, it is concluded that the shrinkage reduction mechanisms achieved by the application of these chemical additives are primarily ascribed to densifying the pore structures, reducing the total porosity as well as the proportion of mesopores, coarsening the pore structures, and promoting the generation of crystalline phases (i.e., calcium hydroxide, AFt, and AFm).

A Study on the Properties of Geopolymer Concrete Modified with Nano Graphene Oxide

Abstract: This paper reports the results of a study conducted to examine the impacts of adding graphene oxide (GO) to GBFS-fly ash-based geopolymer concrete. The geopolymer concrete’s compressive strength, thermal conductivity, and modulus of elasticity were assessed. X-ray diffraction (XRD) analysis was conducted to understand the differences in mineralogical composition and a rapid chloride penetration test (RCPT) to investigate the changes in the permeability of chloride ions imposed by GO addition. The results showed that adding 0.25 wt.% GO increases the modulus of elasticity and compressive strength of GBFS-FA concrete by 30.5% and 37.5%, respectively. In contrast, permeability to chloride ions was reduced by 35.3% relative to the GO-free counterparts. Thermal conductivity was decreased as GO dosage increased, with a maximum reduction of 33% being observed in FA65-G35 wt.% samples. Additionally, XRD showed the suitability of graphene oxide in geopolymer concrete. The present research demonstrates very promising features of GO-modified concrete that exhibit improved strength development and durability compared to traditional concrete, thus further advocating for the wider utilization of geopolymer concrete manufactured from industrial byproducts.

The Effect of Organic and Inorganic Modifiers on the Physical Properties of Granite Residual Soil

Abstract: As a kind of highly weathered special soil in South China, granite residual soils (GRS) feature high strength and high void ratio in a dry environment, so they tend to disintegrate in water and cause geological disasters including collapse. Therefore, modifying GRS for higher strength has become a hot spot. Glass fiber reinforced soils boast fewer cracks, higher energy absorption, and residual strength. This study aims to analyze the reinforcement effect of glass fibers on GRS with inorganic and organic solutions and its environmental feasibility. The inorganic solution contains silicon ion and sodium ion at the ratio of 1 : 4 (hereinafter referred to as Si : Na = 1 : 4 solutions), and the organic one is a modified polyvinyl alcohol solution (hereinafter referred to as SH solution). The reinforced samples were subjected to plate and impact load tests, SEM, and XRD analysis to investigate their mechanical properties, microcharacteristics, and the components produced. Results indicate that the reinforcement effect of glass fibers on GRS under Si : Na = 1 : 4 solutions was better than that of SH solutions. After being reinforced by Si : Na = 1 : 4 solutions, the samples reached maximum impact resistance. SEM results show that glass fibers bond more soil and form an integral structure; thereby the strength was improved as glass fibers share external impact load. XRD results show that geopolymer and alkali-activated materials and potassium feldspar were formed. Geopolymer and alkali-activated materials are pollution-free, inorganic polymers featuring viscosity and high compressive strength. Potassium feldspar is an aluminosilicate mineral with high strength and stable chemical properties, which can adhere to more granules and form a stronger whole structure with geopolymers playing a role. Therefore, it is feasible to reuse these soils sustainably by reinforcing them with glass fibers and the best Si : Na = 1 : 4 solutions. This study finds a new direction for recycling and reusing construction waste, GRS.