Properties Of Geopolymer Research Articles

State-of-the-art review of geopolymer concrete carbonation: From impact analysis to model establishment

Geopolymer concrete (GPC) is a relatively new, innovative and sustainable green civil engineering material, which has many advantages similar to ordinary Portland Cement (OPC). Through the investigations and analyses of published literature, this review paper summarizes the state-of-the-art research progress with respect to the carbonization performances of GPC from the following aspects. First of all, the advantages, carbonization mechanism, and carbonization identification methods of GPC are introduced. Second, the carbonization properties between GPC and OPC are compared, as well as the influences of different factors on the carbonization performance of GPC are analyzed, such as admixtures, additives, environment, etc. Finally, a series of models to evaluate the degree of carbonization are listed, and the future prospect of GPC carbonization research is also put forward. Based on the literature summaries, existing researchers still have great controversy about the research results on the anti-carbonization properties of geopolymer gelling materials, mainly because of the diversity of raw materials in the geopolymer system, resulting in large differences in the hydration products and microstructure of various geopolymer pulps, so there are differences in their anti-carbon performance. It is significant that the influential factors will be of great importance to determine the carbonization performances of GPC, which can also be extended to the anti-carbonization properties of GPC, such as the filling effect of nanoparticles, changing the proportion of silicon and aluminum substances, and improving the mechanical properties and durability of GPC. In addition, more types of numerical models for the carbonization of GPC should be established, considering more impact factors, to ensure the applicability and accuracy, and the integration of the models needs be more strengthened to serve for the complex engineering practices. Overall, the carbonization model establishment will contribute to analyzing the durability of GPC and provide some clues for prolonging its life.

Feasibility of using building-related construction and demolition waste-derived geopolymer for subgrade soil stabilization

A high-value utilization approach is essential to improve the utilization rate of building-related construction and demolition waste (brCDW). This study developed a novel approach by synthesizing a brCDW-derived geopolymer to stabilize high liquid limit subgrade soil. The unconfined compressive strength (UCS) test, shear strength test, resilient modulus test, and permanent strain test were conducted to investigate the effects of brCDW-derived geopolymer dosage, curing time, stress state, and moisture condition on the engineering properties of geopolymer stabilized soil. These test results demonstrated that increasing the geopolymer dosage effectively improved the UCS, shear strength and resilient modulus of stabilized soil and reduced the permanent strain of stabilized soil. The 8% brCDW-derived geopolymer provided adequate UCS, shear strength, resilient modulus, and resistance to permanent strain for stabilized soil, which showed the most economical improvement. Mechanistic-empirical models were employed to accurately estimate the stress-dependent resilient modulus and permanent strain of geopolymer stabilized soil at any given stress state. The Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) test were performed to investigate the strengthening mechanism of brCDW-derived geopolymer stabilization of subgrade soil. The SEM test results indicated that the porosity of stabilized soil was significantly decreased when the geopolymer dosage increased to 8%. The EDS test results demonstrated that the predominant gel types generated from the geopolymer stabilization might be Calcium–Aluminum-Silicate-Hydrate (C-A-S-H), Calcium-Silicate-Hydrate (C–S–H), and Calcium-Aluminate-Hydrate (C-A-H) gels. There was also a small amount of Sodium-Alumino-Silicate-Hydrate (N-A-S-H) gel detected in the geopolymer stabilized soil. Finally, the sustainability of brCDW-derived geopolymer stabilization approach was assessed in terms of material production cost, carbon dioxide emission, and energy consumption. The brCDW-derived geopolymer was proven as a sustainable stabilizer for subgrade soil.

Corrosion resistance and mechanisms of class C fly ash-based geopolymer in simulated oil well environments: Mud contamination and salt solutions at high temperature

Geopolymer presents great potential in oil well environment. For class G oil well cement (OWC) and class C fly ash-based geopolymer, the comparative experiments under simulated oil well environment were performed. The early age properties of geopolymer were measured. Considering the higher downhole temperature, the high temperature resistance of geopolymer at 60 ℃ and 180 ℃ was investigated. Also, the mud contamination resistance of geopolymer at 60 ℃ was explored. A self-designed percolation pipe was used to simulate the process of fresh geopolymer slurry exposed to three salt solutions (5% Na2SO4, 5% NaHCO3 and 2.5% Na2SO4 + 2.5% NaHCO3). The corrosion resistance to salt solution of geopolymer at 60 ℃ was studied. The results showed that geopolymer had higher early strength and high temperature stability than OWC. Meanwhile, compared with OWC, geopolymer possessed better mud contamination resistance due to the smaller pore diameter and the denser matrix. Additionally, all of three salt solutions decreased the compressive strength of OWC, especially the simultaneous existence of Na2SO4 and NaHCO3 accelerated the deterioration of OWC. By contrast, the porosity and pore diameter of geopolymer declined and the compressive strength increased in Na2SO4 solution. Although the compressive strength of geopolymer decreased in NaHCO3 solution, the deterioration degree was lower than OWC. Overall, geopolymer presented better adaptability and durability than OWC in oil well cementing.

Research on the long-term strength development of Datça Pozzolan-based geopolymer

This study examined the influence of long-term curing duration on the properties of geopoly- mers produced through the geopolymerization reaction between Datça Pozzolan and sodium silicate and potassium hydroxide solutions. The specimens were heat cured at 90 °C, 95±5% RH for 24 h initially and then kept under ambient conditions until the tests were conducted at 7, 90, and 365 days. The results showed that applied initial heat curing was appropriate to achieve high early and long-term strength. Geopolymer mortars with 12.5 M and 2.5 activator ratios had the lowest porosity (20.90%) and the highest ultrasound pulse velocity (UPV) (3.10 km/s), compressive strength (10.57 MPa), and flexural strength (5.20 MPa) after seven days. While the porosity of the identical specimens decreased by up to 15.77%, the UPV, compres- sive strength and flexural strength increased by 3.37 km/s, 15.32 MPa, and 6.06 MPa, respectively, after 365 days. The physical and mechanical improvement in the first 90 days exceeded 90–365 days. A higher rate of improvement was obtained when the activator ratio was low, i.e., the improvement decreased inversely as the sodium silicate content of the mortar increased. An increasing trend was observed in the plot of compressive strength as a function of UPV, and the slope values presented a strongly related linear function relation.

3D-printable construction and demolition waste-based geopolymer: Investigating the effects of additives on engineering properties

This paper focuses on the investigating the effects of various additives on the engineering properties of construction and demolition waste (CDW)-based geopolymer mortars. In this study, low-activity CDW-based precursors, specifically brick waste (BW) and concrete waste (CW), were employed. Additionally, industrial waste-based precursors such as slag (S) and silica fume (SF) were utilized to enhance the overall composition. To facilitate activation, a 5 M solution of NaOH was used. To address the efflorescence issue prevalent in geopolymer mixtures and to eliminate potential cracks that may arise due to the dimensional stability problem of 3D-printed CDW-based geopolymer, various kind of additives including calcite, polypropylene fiber, nano SiO2, Al2O3, and TiO2, carbon nano tubes (CNTs), graphene nanoplatelet (GNP), methyl cellulose (MC), Na2SiO3, calcium oxide (CaO), calcium aluminate cement (CAC), and Ca(OH)2 were incorporated into the matrix. The research utilized a comprehensive testing methodology, allowing for a detailed exploration of various properties and the performance of the geopolymer mixtures. The results indicated that nano SiO2 and Al2O3, Na2SiO3, BW, and CAC were recognized for their positive impact on improving the mechanical properties of the geopolymer. Notably, the geopolymer exhibited an impressive compressive strength of 29.8 MPa and a flexural strength of 5.4 MPa following a 28-day ambient curing (23 ± 2 °C and 50 ± 5% relative humidity). Furthermore, the inclusion of nano SiO2 and Al2O3, GNP, MC, Na2SiO3, CaO, CAC, and Ca(OH)2 proved effective in preventing efflorescence, while MC, Na2SiO3, CaO, CAC, and Ca(OH)2 successfully mitigated cracks formation. The results also demonstrated that the CDW-based geopolymer mixture is suitable for 3D printing, displaying satisfactory buildability, shape retention, and extrudability. A thorough testing approach highlighted the effectiveness of additives in shaping the properties of CDW-based geopolymer, positioning them as promising for improvement and addressing challenges.

Comparison of feldspar and meta-halloysite geopolymers by alkaline and acidic activation

Geopolymerization, a sustainable route to advanced binders, has traditionally been explored using common activators and single precursors such as metakaolin. Although previous investigations have explored the potential of feldspathic minerals, particularly with metakaolin as a partial replacement, there remains a gap in understanding the nuances of feldspar-phosphate-based geopolymers. This study seeks to fill this gap by providing an in-depth investigation of the properties and reactivity behaviour of three different feldspar quarry wastes, each modified with meta-halloysite at a 15% inclusion rate. This research not only evaluates the effects of both acidic and alkaline activators on the resulting geopolymer properties, but also explores the broader implications of such modifications in different environments at ambient conditions. Using a series of experimental assessments, we have explored how the mineralogical and crystalline identities of these feldspars influence key aspects such as reaction kinetics, physico-mechanical performance, structural and microstructural properties, and even thermal behaviour. The results of the physico-mechanical properties showed that lower water absorption (i.e. less than 9.2%) as well as higher flexural (i.e. about 30 MPa) and compressive strength (i.e. about 40 MPa) can be achieved with the feldspar-based geopolymer in alkaline medium. In acidic medium, the highest flexural and compressive strengths were less than 10 and 19 MPa, respectively, with about 13.5% of water absorption. In acidic to basic medium, the highest cumulative pore volume of the geopolymers increases from 26.5 to 75.2 mm3/g, respectively. The outcomes of this study hold promise for tailoring geopolymer properties for various applications and provide a basis for further work in this area.

Synthesis of Electrolytic Manganese Slag-Solid Waste-Based Geopolymers: Compressive Strength and Mn Immobilization.

The massive stockpiling of electrolytic manganese residue (EMR) has caused serious environmental pollution. In this study, EMR, coal gangue (CG), and fly ash (FA) were used as raw materials to obtain the optimal mix ratio based on Design-Expert mixture design. The effects of activator modulus, liquid-solid (L/S) ratio, and curing temperature on the mechanical properties of geopolymers were investigated. The results showed that the compressive strength of the prepared geopolymer was 12.0 MPa, and the 28d leaching of Mn was 0.123 mg/L under the conditions of EMR:CG:FA = 0.43:0.34:0.23, L/S = 0.9, a curing temperature of 60 °C, and a curing time of 24 h. This indicates that the geopolymer is an environmentally friendly material with high compressive strength. The mineral composition of the geopolymer is mainly hydrated calcium silicate and geopolymer gel. In addition, a more stable new mineral phase, MnSiO3, was generated. The Fourier transform infrared (FTIR) spectrogram showed that the peak at 1100 m-1 was shifted to 1112 cm-1, which indicated that a geopolymerization reaction had occurred. Through scanning electron microscopy (SEM) and energy dispersive spectrum (EDS) analysis, it was identified that the geopolymerization produced a large amount of amorphous gelatinous substances with a relatively dense structure, the major elements being oxygen, silicon, aluminum, calcium, and sodium.

Coupling effects of sewage sludge and recycled fine aggregate on the properties of geopolymer recycled mortars

The utilization of sludge from sewage treatment plants, ground granulated blast furnace slag (GGBFS) and recycled fine aggregate (RFA) from demolition of abandoned buildings in the production of geopolymer recycled aggregate mortar (GRM) offers a sustainable solution to reduce Ordinary Portland cement (OPC) application, and to address the growing volume of municipal sludge and construction waste. This work aims to investigate the workability, mechanical performance and microstructure of GGBFS and sewage sludge ash (SSA) based alkali activated GRM. GGBFS and SSA based geopolymer was used to replace 100% of OPC and RFA was employed to substitute various proportions (0%, 15%, 30% and 50%) of natural fine aggregates (NFA). Influences of SSA and RFA content on the consistency, setting time, compressive strength and flexural strength of GRM were investigated. The geopolymerization products were characterized through scanning electron microscopy (SEM), x-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) tests. Results show that the consistency value and setting time of GRM decrease when the SSA and RFA content increases. When SSA content is 10% and RFA content is 15% (S10R15 sample), sample's microstructure becomes more compact, displaying robust mechanical properties. And S10R15 sample attained an average 28-day compressive strength of 51.7 MPa and flexural strength of 7.2 MPa. This demonstrates that GRM exhibits satisfactory working performance, mechanical properties. This study is expected to offer more insights into the application of SSA and RFA.

Solidification and stabilization of heavy metals in medical waste ash through alkali activation

In the present work, medical waste ash was used as an aluminosilicate precursor to produce a geopolymer binder with stabilised heavy metals. The ash was initially calcined at a temperature of 800 °C for two hours to reduce the organic content. Calcined kaolin and medical waste ash were used as precursors to produce the geopolymer binder and sodium silicate and calcium oxides were used as alkaline activators. The effect of curing temperature (23, 60, and 100 °C) and the calcium oxide addition (0, 5, and 10%) on the geopolymer properties were evaluated. Eighteen geopolymer samples were prepared and evaluated for immobilizing heavy metals through the Toxicity Characteristic Leaching Procedure (TCLP). When compared to raw materials, TCLP results indicated that geopolymerization can significantly reduce the concentration of heavy metals in the medical waste ash leachate. The metal fixation percentages of the geopolymers ranged from 70 to 100%. The sequential extraction test results showed that geopolymerization (stabilization/solidification) is very beneficial in reducing the bioavailable fraction in the solid waste and maximizing the difficulty of fraction extraction.

Preparation of one-part geopolymers using coal gasification slag: Effect of alkali fusion product additive and liquid/solid ratio

In this work, one-part geopolymers were synthesized through the alkali fusion and component additive method (AFCAM), utilizing coal gasification slag as the primary raw material. The investigation delved into the influence of varying fusion product contents and liquid/solid (L/S) ratios on the geopolymer properties. The experimental results demonstrated a non-linear correlation between the increase in fusion product content and the compressive strength of geopolymers, revealing an initial ascent followed by a subsequent decline. Additionally, a lower L/S ratio of 0.3 was observed to enhance compressive strength compared to the L/S ratio of 0.4. Notably, the optimal combination of an L/S ratio of 0.3 and a fusion product percentage of 30 % resulted in a remarkable compressive strength of 25.2 MPa. The comprehensive strength analysis suggested that an adequate amount of fusion product enhances the geopolymerization reaction, evidenced by the transformation of aluminum coordination states. Specifically, the conversion of five-coordinated and six-coordinated aluminum in slag to four-coordinated aluminum in geopolymers was observed. Concurrently, increased silicon and aluminum reactivity led to the formation of a robust Q4(4Al) network in the geopolymer gel. The impact of L/S ratios was attributed to the accelerated dissolution and hydrolysis of aluminosilicates at an elevated L/S ratio of 0.4, hindering polycondensation. These outcomes underscore the pivotal role of fusion product content and L/S ratio in governing the strength development of one-part geopolymers.

Micro-assessment of heavy metal immobilization within alkali-activated copper tailings-slag geopolymer

To address the challenge of mitigating heavy metal pollution stemming from the utilization of industrial solid wastes like copper tailings, this study focused on the development of copper tailings-granulated blast furnace slag (CT-GBFS) geopolymer through alkali activation. The primary objective was to effectively immobilize heavy metals, specifically copper (Cu) and zinc (Zn), within the geopolymer. This investigation encompassed an exploration of how Cu and Zn impacted the mechanical properties of CT-GBFS geopolymer, along with an analysis of the leaching behavior of these heavy metals in various environmental conditions. The study also delved into the underlying mechanisms responsible for immobilizing these heavy metals. The experimental findings revealed that the inclusion of up to 2% heavy metals could enhance the mechanical properties of geopolymer. However, as the heavy metal content increased, a detrimental effect on the mechanical properties became evident. Furthermore, CT-GBFS geopolymer exhibited excellent heavy metal immobilization capabilities across different environmental conditions. Specifically, the immobilization rate for copper exceeded 98%, while zinc exhibited an immobilization rate exceeding 93%. The geopolymer has a physical encapsulation fixation mechanism for both Cu and Zn. Additionally, copper was observed to form a covalent bond with non-bridging oxygen in the geopolymer, manifesting as a Si–O–Cu structure, thereby effectively immobilizing the metal. Conversely, zinc was immobilized within the geopolymer through ionic bonding. In conclusion, the technology proposed in this study represents a significant step toward achieving the safe and resourceful utilization of copper tailings by effectively immobilizing heavy metals, thus mitigating their environmental impact.

In-Depth Insight into the Effects of Steel Slag and Calcium Hydroxide on the Properties of a Fly Ash-Red Mud Geopolymer.

The low mechanical strength of a low-calcium fly ash (FA)-red mud (RM) geopolymer severely limits its application. Steel slag (SS) and Ca(OH)2 can provide calcium and alkali for the hydration process of a low-calcium FA-based geopolymer. In this study, SS was used to replace part of the RM, and Ca(OH)2 was introduced. The effects of SS and Ca(OH)2 on the properties of the FA-RM geopolymer were investigated. The experimental results show that SS promoted the matrix to generate more C(N)-A-S-H and C-S-H gels and optimized the pore structure, thereby improving the mechanical properties of the FA-based geopolymer. The addition of 4 wt.% Ca(OH)2 increased the hydration products of the FA-based geopolymer, the microstructure was denser, and the mechanical properties were significantly improved. The 28 d compressive strength of the FA-based ternary composite geopolymer prepared by replacing part of the RM with SS and adding Ca(OH)2 reached 30.6 MPa, which provided an experimental basis for the resource utilization of various bulk solid wastes.

Influence of Starch Powder on Compressive Strength and Microstructural Properties of Geopolymer Composite Materials Based on Metakaolin

The main objective of the present study is the investigation of the behaviour of starch powder incorporated at different levels (0, 5, 10, 15, 20, 25, and 30 wt%) on the compressive strength and microstructural properties of metakaolin-based geopolymers. Sodium silicate with a molar ratio of SiO2/Na2O of 1.6 was used as the hardener and standard metakaolin was used as the aluminosilicate source. The results showed that when metakaolin was replaced by starch from 0 to 15 wt%, the compressive strength increased from 36.50 to 64.12 MPa. When metakaolin was replaced by starch above 15 wt%, the compressive strength decreased from 64.12 to 29.43 MPa. That of the reference geopolymer material is 36.50 MPa.The infrared spectra of the geopolymer composites indicate that the Si-O-C bonds are formed. The thermal behaviour of geopolymer composites containing starch shows a mass loss at around 100 and 278 °C. The geopolymer material without starch only shows a loss of mass at around 100 °C. The micrographs of the geopolymer composite with 15% by weight of starch show that the matrix is more compact, more homogeneous, and denser than the one without starch. On the contrary, possibly due to a large amount of unreacted starch in its network, the micrographs of the geopolymer composite obtained after the incorporation of 30 wt% starch show a heterogeneous microstructure. It can be concluded that suitable starch content for the synthesis of geopolymer composites would be around 15% by weight.

Novel alkaline solid reagent for the preparation of one-part metakaolin-based geopolymers

In recent years, there has been a growing interest in one-part geopolymers due to their simplified preparation process, which involves adding water instead of highly alkaline and corrosive solutions. This study aimed to synthesize a solid reagent (SR) based on NaOH and colloidal silica and investigate its impact on the processing stages and resulting physico-mechanical properties of one-part geopolymers based on metakaolin. After curing the samples at 40 °C, various properties, including elastic modulus, cold crushing strength, apparent porosity, and density, were evaluated. Optimal results were achieved with a mixing time of 20 min and a formulation containing 50 % by weight of SR. Under these conditions, the cured samples exhibited an elastic modulus of 8.2 GPa, a crushing strength of 14.04 MPa, an apparent porosity of 16 %, and a density of 1.51 g/cm3 after one day. These findings highlight the potential application of the developed solid reagent in the design of geopolymers for thermal and acoustic insulation in modern construction projects.

Study of the damage mechanism on mechanical properties of super absorbent polymer-improved geopolymers under dry–wet cycling

Study of the damage mechanism on mechanical properties of super absorbent polymer-improved geopolymers under dry–wet cycling

Microstructure and mechanical properties of geopolymers utilizing excavated soils, metakaolin and slags

This paper presents a study on the potential of geopolymer (GP) as a substitute for ordinary Portland cement (OPC) in construction applications. OPC is widely used in construction due to its high strength and durability. However, manufacturing is extremely energy-intensive and produces large amounts of carbon dioxide (CO2) emissions. Also, In France, 130 million tons of excavated soils are generated each year [1] and classified as waste material without proper disposal methods. Therefore, the use of excavated clays coming from construction projects in GP formulations will have a positive impact on decreasing waste materials. Moreover, flash calcination used as heat thermal technique eliminate the organic matter and enhance the geopolymerization reaction with the alkaline reagent used in GP. On the other hand, GP are a type of alternative material made from industrial by-products such slags. This study used various methods to optimize GP mix design by evaluating the fresh and hardened properties. The results has shown that GP has a higher compressive strength than OPC in short term (between +5% and 76% at 1 day) and present a comparable strength in long term. The analysis of the microstructure throughout nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), X-ray diffraction (XRD) and Thermogravimetric analysis (TGA) has shown the GP designed has a stable reticulated polymeric structure. Mercury porosity has shown a finer nonometric porosity that corresponds to a compacted and fitted micelle structure. This study provides a solid contribution to the sustainability of the construction industry by developing a GP binder composed of flash-calcined excavated clay (FCC), metakaolin (MK), and slag (GBFS) that can achieve better results than OPC binder.

Residual water and interfacial bonding effects on the mechanical performance of CNT/fly ash geopolymer binder

AbstractNowadays, geopolymers are advanced alternatives to cementitious materials, where their excellent chemical and fire resistance are some of its most appealing properties. Fly ash geopolymers enable the use of industrial waste materials while converting them into a novel binding material. Their production is accompanied by a much lower CO2 emission when compared to Portland cement. Reinforcing fly ash geopolymers with carbon nanotubes would significantly strengthen its microstructure and with this enhancing the long‐term mechanical and durability performance. The aim of this work is to use reactive molecular dynamics simulation method to optimize the mechanical properties of fly ash geopolymers with nano‐reinforced carbon nanotubes (CNTs). During this study, the impact of humidity and interfacial bonding strength between carbon nanotube and geopolymer is investigated. Our findings show that structural transformations under hydration process comes from the weakening of AlO bond, leading to the elongation of AlO and NaOH bonds, forming aluminum and sodium hydroxyls. Conversely, silicate is not sensitive to water and exhibits hydrophobic behavior. In addition, our results show that there is an optimal value of water content (7.17 wt.%) that makes the geopolymer nanostructure strengthen. The related elastic modulus rises by 21.56%, 20.60%, and 18.41% for Si/Al ratio of 1, 2, and 3, respectively. Inserting carbon nanofillers to fly ash nanostructure has remarkably shown an interesting strength enhancement. More precisely, when interfacial bonding concentration is around 19.36%, it is observed a positively increasing of the compressive strength, shear, indentation and elastic modulus with 39%, 65.2%, 72.3%, and 144.85%, respectively. Reduced density gradient supports that the interaction between carbon nanotube and fly ash geopolymer is dominated by a van der Waals one.

The microstructure and mechanical properties of recycled metakaolinite-based geopolymer: Dependence of recycled powder replacement ratio

Recycled geopolymer powder (RGP) is an environmentally friendly substitute for precursors in geopolymer preparation. In this study, the influence of RGP with different compressive strengths (10 and 30 MPa, labeled RGP10 and RGP30, respectively) and substitution ratios (5%, 10%, 30%, 50%, and 100%) on the microstructure and properties of metakaolinite-based geopolymers was investigated. The chemical structure and composition of the recycled geopolymer were characterized by X-ray diffraction and Fourier-transform infrared spectroscopy. The microstructure was characterized by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and mercury intrusion porosimetry. The results showed that the incorporation of RGP10 at a low substitution ratio (≤10%) destroyed the microstructure of the resulting geopolymer, thereby decreasing its compressive strength. The geopolymer formed by substituting RGP30 in ratios of ≤10% exhibited a dense microstructure due to the filling effect, and the 28-d compressive strength increased by 9.5% when the substitution ratio was 10%. At high substitution ratios (≥10% and ≤50%), the compressive strength of all geopolymers decreased due to the low reactivity of RGP. However, the decrease in the compressive strength of geopolymer induced by RGP10 was less notable than that of RGP30, as the presence of a larger amount of unreacted metakaolinite in the RGP10 scenario let to the formation of more geopolymer during alkali activation. Notably, the alkali-activated RGP exhibited a low compressive strength (approximately 3.0 MPa) regardless of its original strength.These observations indicate that both the substitution ratio and original strength of RGP significantly influence the microstructure and mechanical properties of metakaolinite-based geopolymers. Additionally, the incorporation of an appropriate amount of RGP can help enhance the properties of metakaolinite-based geopolymers.

Study on the mechanical behavior of construction and demolition waste-based geopolymers under high-temperature conditions

ABSTRACT This study explores the mechanical properties of geopolymers derived from construction and demolition waste exposed to high temperatures. Geopolymers were exclusively crafted from waste bricks or ceramic tiles, activated with potassium hydroxide/sodium silicate solution. We assessed compressive deformation during 850°C − 1050°C exposure and residual strength post 600°C − 1050°C exposure (simulating ISO 834 curve). Microstructure and bulk properties were also examined.Both geopolymers exhibitecd consistent post-fire behavior. Compressive strength decreased between 600°C and 800°C but rebounded at 1050°C, surpassing initial levels. At 1050°C, density dropped by 8–9%, with a 7–10% mass loss. In fire tests, ceramic tile-based geopolymers displayed plastic deformation at all tested temperatures without macro-fractures, whereas brick-based geopolymers remained elastic up to 1000°C with evident macro-fractures.These findings suggest the potential of both geopolymers as fire-resistant building materials, contributing to advancements in construction materials.

Micro and macro properties of silico-aluminophosphate geopolymer: Role of incinerated sewage sludge ash (ISSA)

The mechanistic insights into silico-aluminophosphate (SAP) geopolymer formation remain an enigma. Here, we aim to elucidate this process and improve the early-age performance of SAP geopolymers by utilizing incinerated sewage sludge ash (ISSA). Interestingly, phosphoric acid-ISSA interaction released Ca2+ and Al3+ ions from ISSA faster than the dealumination of metakaolin. These ions agglutinated with the active soluble (PO4)3- units, evidenced by transmission electron microscopy (TEM), enhancing the early-age compressive strength of ISSA-incorporated SAP geopolymer binders. In contrast, the later strengths were relatively similar to the reference. Such binders had primary silico-alumino-phosphate (S-A-P) gels, possibly intimate with calcium-phosphate (C-P) and alumino-phosphate (A-P) gels, improving the micromechanical properties of the binder. The elastic moduli of these gels lay between 23–25 GPa, higher than conventional N-A-S-H gels. Furthermore, ISSA switched the chemistry of reaction products by favoring AlIV-OP units over AlVI-OP units in SAP geopolymers, even though the Si environment remained unchanged, as confirmed by NMR.