Search

The hydration reaction mechanism of geopolymers is intimately linked to their composition and structure. Additionally, pore structure characteristics play a vital role in the properties of hardened geopolymer pastes, significantly influencing the material's strength, impermeability, and thermal conductivity. In this study, fly ash geopolymer (FAG) was synthesized by utilizing NaOH, Na2SiO3 , and low-calcium fly ash. The pore structure characteristics of FAGs were analyzed using mercury intrusion porosimetry (MIP), and the fractal dimension of FAGs was calculated using the Menger sponge model (Df) and a fractal model based on thermodynamic relationships (Ds). Fourier infrared spectroscopy (FTIR), thermogravimetric differential thermal (TG/DTA), and scanning electron microscopy secondary electron phase (SEM-SE) were used to test the composition of the hydration products of FAGs and their microscopic morphology. The results showed that after 90 days of maintaining ambient temperature, the porosity of FAG is between 20% and 30%, and the most available pore size is 10–50 nm. The fractal dimension calculated using the analytical model based on thermodynamic relations can more comprehensively determine the pore structure characteristics of FAG. The geopolymerization reaction process of fly ash particles can be categorized into four primary processes, forming an amorphous aluminosilicate gel as the hydration product. [ABSTRACT FROM AUTHOR]

Decarbonizing the building sector to achieve sustainable development goals (SDGs) is a complex issue that poses significant challenges to the scientific community. In this context, the current paper aims to assess the viability of employing incinerated by-products as a sustainable mineral resource to produce sustainable geopolymers. To this end, the study focuses on the formulation of geopolymer binders using fly ash with various proportions (ranging from 0 % to 50 %) of metakaolin (MK), investigating their physico-mechanical, microstructural analysis as well as their sealing capacity. The results indicate that incorporating 30 % MK not only preserves good workability but also significantly improves mechanical strength, ensuring long-term durability by increasing bulk density and concurrently reducing water absorption and harmful porosity. Moreover, the results of the Toxicity Characteristic Leaching Procedure (TCLP) demonstrated that the released contaminants remained within the regulatory limits established by the USEPA. The geopolymer binder developed exhibited a significant reduction of 77.23 % and 57.92 % in terms of carbon dioxide equivalent (CO 2 -e) emissions and energy demand compared to conventional cement. This study introduces a novel approach to promoting a circular economy within the building sector. [Display omitted] [ABSTRACT FROM AUTHOR]

The dissolution behavior of the main elements of fly ash in acid-base systems. Fly ash mainly leaches aluminum-iron elements in the acid system, and the leaching rate of iron is much higher than that of aluminum. Under alkaline conditions, silicon-aluminum elements are mainly dissolved, and the leaching rate of silicon elements is much higher than that of aluminum elements. Silicon aluminum exists in the amorphous phase state, and the extraction rate of silicon aluminum is low by acid leaching and alkali solution alone, and the use of high temperature melting combined with acid leaching and alkaline solution process can make silicon aluminum bond break and improve the element extraction rate. The types of fly ash synthetic flocculants are summarized, and they are divided into inorganic polymer flocculants and inor- ganic-organic hybrid polymer flocculants according to the chemical components of fly ash to prepare flocculants, among which inorganic polymer flocculants are divided into monoacids, diacids and polyacids according to the number and types of acids contained in their anion series, and anionic acids are mainly silicate, sulfate, chloride ion and phosphate. The development of fly ash synthetic flocculants and the problems to be solved urgently are prospected. [ABSTRACT FROM AUTHOR]

Phosphoric acid-based geopolymer (PGEO) belongs to acidic material and has many applications in environmental disposal. The curing method has an important impact on the mechanic performance of geopolymers, the existing research concerning PGEO synthesized from fly ash (FA) and phosphoric acid (PA) are performed on the specimens cured at sealed environment, but no related research on the PGEO cured at an open environment is found. Therefore, to investigate the mechanic performance, pH and of PGEO cured in an open environment, the unconfined compressive strength tests were conducted on PGEO specimens cured in an open environment, and its mechanism was investigated using Scanning Electron Microscope, X-Ray diffraction, and Fourier transform infrared reflection (FTIR) tests. Moreover, the thermogravimetric was measured using the thermogravimetric tests. The results showed that in the scope of this study, the compressive strength of the PGEO decreased with the PA concentration and the liquid–solid ratio (L/S) increasing. When the L/S was a fixed value, as the curing time increased, an obvious strength loss was observed for the PGEO with the content of 40 and 50%, but the compressive strength increased first and then, reduced for the PGEO with the content of 40 and 50%, a maximum strength was obtained at 60 days of curing. The open curing for the PGEO is not conducive to the later growth of compressive strength. As the PA concentration and L/S increased, the pH descended. As the curing time lengthened, the pH first raised and then droped, the maximum pH was obtained at 60 days. Furthermore, the compressive strength increased with the pH with a good correlation. The microscopic analysis showed that the crystalline compounds AlSiP3, Ca2P2O7(H2O)2, molecular sieve SAPO-20 (Al0.47Si0.13P0.4)O2, AlPO4-5 (AlPO4), CaHPO4, and AlPO4 in PGEO were detected. Overall, the open curing environment is not conducive to PGEO, and sealed curing should be used in engineering applications. [ABSTRACT FROM AUTHOR]

In this article, the potential of employing self-compacting geopolymer concrete in massive elements has been investigated. The main binder consisted of 85% ground granulated blast furnace slag and 15% fly ash. An alkaline solution of sodium hydroxide and sodium silicate was utilised. The effects of four parameters (binder content, water-to-binder [W/B] ratio, Na2O% and coarse-to-fine aggregate [C/F] ratio) on the fresh, mechanical and thermal properties of Massive Self-Compacting Geopolymer Concrete (MSCGC) mixes were evaluated. Taguchi's design of experiments was used to minimise the number of trial mixes. The heat of geopolymerisation of MSCGCs was monitored using a semi-adiabatic chamber and then applied to concrete samples using a temperature match curing system. The maximum compressive and splitting tensile strengths and modulus of elasticity were 62.7 MPa, 5.04 MPa and 33.26 GPa, respectively. Binder content was identified as the most significant parameter affecting the thermal and mechanical properties of the mixtures. The impact of the C/F ratio was greater than the W/B ratio on the thermal characteristics. The results of a numerical analysis reveal that although a higher binder content enhances the mechanical properties of the MSCGCs, it leads to an increased risk of cracking owing to greater heat production. [ABSTRACT FROM AUTHOR]

Rubber wood fly ash (RWFA) is one of the main components of biomass ash materials. This research investigates the possibility of using RWFA geopolymer (RWFAG) to stabilize marginal lateritic soil (MLS) as green subbase materials. RWFA was used as a starting material. The studied influence factors included MLS/RWFA ratio, sodium silicate (NS)/sodium hydroxide (NH) ratio, soaked and unsoaked conditions, and curing time. The study involved testing the unconfined compressive strength (UCS), indirect tensile strength (ITS), and conducting microstructure. The test results revealed that the optimal liquid content for the MLS-RWFAG specimens ranged between 12 and 24% for all ingredients. As the RWFA content increased, the maximum dry unit weight of the MLS-RWFAG decreased due to the lower specific gravity of RWFA. The MLS-RWFAG specimen with 30% RWFA content and an NS/NH ratio of 70:30 yielded the maximum UCS and ITS. The SEM–EDS analysis demonstrated the production of C–S–H and N–A–S–H gels, resulting in a dense and homogeneous matrix in the MLS-RWFAG specimens. Considering cost-effectiveness, the optimum ingredients for the MLS-RWFAG specimen were identified at an MLS/RWFA ratio of 70:30 and an NS/NH ratio of 10:90, meeting the 7-day soaked UCS requirement for pavement subbase materials. Moreover, the CO2-eq emissions from MLS-RWFAG specimens were lower compared to those from 3% cement-stabilized MLS samples. These findings strongly support the use of RWFAG as a viable alternative to Portland cement for stabilizing MLS in subbase materials. [ABSTRACT FROM AUTHOR]

Geopolymer materials, alternatives to cement that are synthesized using industrial byproducts, have emerged as some of the leading champion materials due to their environmentally friendly attributes. They can significantly reduce pollution by utilizing a plethora of waste products and conserving natural resources that would otherwise be used in the production of conventional cement. Much work is being carried out to study geopolymers' characteristics under different conditions. Here, a geopolymer derived from fly ash (FA) was synthesized using a combination of sodium silicate and potassium hydroxide (KOH) (2.5:1 ratio) as an alkali activator (AA) liquid. The FA/AA ratios were optimized, resulting in distinct geopolymer samples with ratios of 1.00, 1.25, 1.50, and 1.75. By adjusting the contribution of alkaline liquid, we investigated the impacts of subtle changes in the FA/AA ratio on the morphology and microstructure using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. The FESEM analysis illustrated a mixed matrix and morphology, with the sample with a ratio of 1.00 displaying consistently fused and homogenous morphology. The XRD results revealed the prevalent amorphous nature of geopolymer with a few crystalline phases of quartz, sodalite, hematite, and mullite. An electrical study confirmed the insulating nature of the geopolymer samples. Insulating geopolymers can provide energy-efficient buildings and resistance to fire, hurricanes, and tornadoes. Additionally, using KOH as a part of the alkali activator introduced a less-explored aspect compared to conventional sodium hydroxide-based activators, highlighting the novelty in the synthesis process. [ABSTRACT FROM AUTHOR]

Geopolymer materials, considered to be an alternative to Portland cement-based concretes, can be produced from various types of waste aluminosilicate raw materials. This article presents the results of research related to the use of diatomite as an additive in geopolymers. The results of testing geopolymer composites with 1%, 3%, and 5% additions of diatomite with a grain size of 0–0.063 mm after and without thermal treatment were presented. This article presents the physical properties of the diatomite additive, the morphology of diatomite particles SEMs, thermal analysis, and compressive strength test results. In this research, diatomite was treated as a substitute for both fly ash and metakaolin (replaced in amounts of 1 and 3%) and as a substitute for sand introduced as a filler (in this case, 5% of diatomite was added). As a result of this research, it was found that the addition of diatomite instead of the main geopolymerization precursors in amounts of 1 and 3% had a negative impact on the strength properties of geopolymers, as the compressive strength was reduced by up to 28%. The introduction of crushed diatomite instead of sand in an amount of 5% contributed to an increase in strength of up to 24%. [ABSTRACT FROM AUTHOR]

Sludge refers to the solid waste produced after sewage treatment. Unreasonable disposal of sludge can cause environmental pollution. Nonetheless, the sludge contains large amounts of silica‐aluminate, which has pozzolanic activity by treatment, and the sludge can be used as a sustainable building material. The previous studies have recommended that it is reasonable to produce geopolymers, that is, a green low‐carbon cementitious material with excellent mechanical and durability properties, from sludge. This article provides an overview of recent advancements in the study of sludge‐based geopolymer. It delves into the mechanisms behind alkali‐activated geopolymer, examines the feasibility of preparing geopolymer from sludge, and discusses various preparation methods. Additionally, it elaborates on the impact of incorporating different auxiliary materials on sludge‐based geopolymer. The comprehensive performance of sludge‐based geopolymer, encompassing mechanical properties, durability, and setting time, is thoroughly summarized. An environmental assessment is conducted, evaluating heavy metal leaching and the lifecycle of sludge‐based geopolymer. Finally, we briefly discuss some problems in the current research and development trends in the future on sludge‐based geopolymer. The aim of this article is to provide comprehensive support and guidance for both the research and practical engineering applications of sludge‐based geopolymer. [ABSTRACT FROM AUTHOR]

Recently, the usage of a cold-bonded method in the production of artificial green geopolymer coarse aggregates (GCA) has been crucial from an economic and environmental perspective because the sintering method consumes an enormous quantity of energy and generates a significant quantity of pollutants. This research investigated the manufacture of GCA via cold-bonded pelletization using two distinct industrial byproducts (GGBFS and FA) via a new and simpler pelletization technology. Three different binders were used to produce three distinct types of GCAs as partial replacements for natural coarse aggregate (NCA) at varying replacement rates (0%, 25%, 50%, and 75%). The first group used ground-granulated blast furnace slag, while the second used GGBFS with perlite, and the third used FA with perlite. An alkaline activator was commonly used with all three groups. The physical and mechanical properties of three distinct varieties of GCA were recorded. The results indicated that the mechanical and chemical properties of three different types of GCAs were nearly identical to those of natural aggregate, with the exception of their increased water absorption. According to the findings, the recommended mixtures were suitable for usage in the construction industry. The results indicated that the ratio of all investigated attributes declined as the number of GCAs increased. In contrast, lightweight concrete can be obtained at a ratio of GCA (FA with perlite) equal to 75%, where unit weight, compressive, splitting tensile, flexural, and water absorption strengths were 1.87 gm/cm3, 20.2 MPa, 1.8 MPa, 8 MPa, and 6.0%, respectively (FA with perlite). [ABSTRACT FROM AUTHOR]

Geopolymers show great potential in complex wastewater treatment to improve water quality. In this work, general geopolymers, porous geopolymers and geopolymer microspheres were prepared by the suspension curing method using three solid waste products, coal gangue, fly ash and blast furnace slag. The microstructure, morphology and surface functional groups of the geopolymers were studied by SEM, XRD, XRF, MIP, FTIR and XPS. It was found that the geopolymers possess good adsorption capacities for both organic and inorganic pollutants. With methylene blue and potassium dichromate as the representative pollutants, in order to obtain the best removal rate, the effects of the adsorbent type, dosage of adsorbent, concentration of methylene blue and potassium dichromate and pH on the adsorption process were studied in detail. The results showed that the adsorption efficiency of the geopolymers for methylene blue and potassium dichromate was in the order of general geopolymers < porous geopolymers < geopolymer microspheres, and the removal rates were up to 94.56% and 79.46%, respectively. Additionally, the competitive adsorption of methylene blue and potassium dichromate in a binary system was also studied. The mechanism study showed that the adsorption of methylene blue was mainly through pore diffusion, hydrogen bond formation and electrostatic adsorption, and the adsorption of potassium dichromate was mainly through pore diffusion and redox reaction. These findings demonstrate the potential of geopolymer microspheres in adsorbing organic and inorganic pollutants, and, through five cycles of experiments, it is demonstrated that MGP exhibits excellent recyclability. [ABSTRACT FROM AUTHOR]

Every structure might be exposed to fire at some point in its lifecycle. The ability of geopolymer composites to withstand the effects of fire damage early before it is put out is of great importance. This study examined the effects of fire on geopolymer composite samples made with high-calcium fly ash and alkaline solution synthesised from waste banana peduncle and silica fume. A ratio of 0.30, 0.35, and 0.4 was used in the study for the alkaline solution to fly ash. Also used were ratios of 0.5, 0.75, and 1 for silica oxide (silica fume) to potassium hydroxide ratio. The strength loss, residual compressive strength, percentage strength loss, relative residual compressive strength, ultrasonic pulse velocity, and microstructural properties of the thirteen mortar mixes were measured after exposure to temperatures of 200, 400, 600, and 800 °C for 1 h, respectively. The results reveal that geopolymer samples exposed to elevated temperatures showed great dimensional stability with no visible surface cracks. There was a colour transition from dark grey to whitish brown for the green geopolymer mortar and brown to whitish brown for the control sample. As the temperature rose, weight loss became more pronounced, with 800 °C producing the most significant weight reduction. The optimum mixes had a residual compressive strength of 25.02 MPa after being exposed to 200 °C, 18.72 MPa after being exposed to 400 °C, 14.04 MPa after being exposed to 600 °C, and 7.41 MPa after being exposed to 800 °C. The control had a residual compressive strength of 8.45 MPa after being exposed to 200 °C, 6.67 MPa after being exposed to 400 °C, 3.16 MPa after being exposed to 600 °C, and 2.23 MPa after being exposed to 800 °C. The relative residual compressive strength decreases for green geopolymer mortar are most significant at 600 and 800 °C, with an average decrease of 0.47 and 0.30, respectively. The microstructure of the samples revealed various phase changes and new product formations as the temperature increased. [ABSTRACT FROM AUTHOR]

Copyright of Misr Journal of Agricultural Engineering is the property of Egyptian National Agricultural Library (ENAL) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The dynamic compression test of geopolymer concrete (GC) before and after water saturation was carried out by the split Hopkinson pressure bar (SHPB). And the effects of water saturation and strain rate on impact toughness of GC were studied. Based on Weibull statistical damage distribution theory, the dynamic constitutive model of GC after water saturation was constructed. The results show that the dynamic peak strain and specific energy absorption of GC have strain rate strengthening effect before or after water saturation. The impact toughness of GC decreases after water saturation. The size distribution of GC fragments has fractal characteristics, and the fractal dimension of GC fragments after water saturation is smaller than that before water saturation. The dynamic constitutive model based on Weibull statistical damage distribution theory can accurately describe the impact mechanical behavior of GC after water saturation, and the model fitting curves are in good agreement with the experimental stress–strain curves. [ABSTRACT FROM AUTHOR]

Cement, as a construction material, has low thermal resistance, inherent fire resistance, and is incombustible up to a certain degree. However, the loss of its mechanical performance and spalling are its primary issues, and it thus cannot retain its performance in refractory applications. The present study explores the performance of geopolymer formulations that have excellent fire resistance properties for potential refractory applications. This study is unique, as it investigates advanced solid geopolymer formulations that need only water to activate and bind. Various solid geopolymer formulations with fly ash as a precursor; potassium hydroxide and potassium silicate as activators; and mullite and alumina as refractory aggregates were studied for their compressive strength at up to 1100 °C and compared with their two-part conventional liquid alkaline geopolymer counterparts. Advanced solid geopolymer formulations with mullite and alumina as refractory aggregates had mechanical strength values of 84 MPa and 64 MPa post-1100 °C exposure and were further exposed to ten thermal cycles of 1100 °C to study their fatigue resistance and post-exposure compressive strengths. The geopolymer sample with mullite as a refractory aggregate yielded 115.2 MPa compressive strength after the fourth cycle of exposure. This sample was also studied for its temperature distribution upon direct flame exposure. All the geopolymer formulations displayed a drop in compressive strength at 600 °C due to viscous sintering and then a rise in strength at 1100 °C due to phase transformation. X-ray diffraction studies revealed that the formation of crystalline phases such as leucite, sanidine, and annite were responsible for the superior strengths at 1100 °C for the alumina- and mullite-based geopolymer formulations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this article, the influence of nano-silica (NS) added geopolymer-based grout (GBG) mixtures for use in grouting columns was investigated experimentally. For this purpose, the rheological characteristics (shear stress, apparent viscosity, yield stress, plastic viscosity and rheological behaviour) of GBG mixtures obtained with nano-silica (NS) together with fly ash (FA) replacements were measured at a wide range of NS dosages of 0% (only FA for control), 0.5%, 1.0%, 1.5%, 2.0% and 2.5%, and extensive effects of water to binder (w/b) ratios (w/b = 0.50, 0.75, 1.00, 1.25, and 1.50), by dry weight. From a proper and common consistency of water effects (w/b = 1.00), the fresh state properties (mini-slump, Marsh funnel viscometer and bleeding) and unconfined compressive strength (UCS) performance of geopolymer grouting columns were tested. Results of the study indicated that incorporating NS into GBG mixtures had positive effects on the rheological characteristics. The mini-slump and flow time of the Marsh funnel increased slightly with NS dosages up to the rate of 1.5% while increasing the NS proportions led to a reduction of bleeding that was prominent beyond 1.5%NS. Among the treatments of geopolymer mixtures with NS, the highest UCS performance was obtained at the dosage rate of 1.5%NS. [ABSTRACT FROM AUTHOR]

The release of CO2 from the construction industry poses an alarming condition to the society/environment and necessitates the development of a sustainable replacement to the ordinary portland cement (OPC). Geopolymer Concrete (GPC) is a futuristic sustainable alternative to use as a binder. The characteristics of GPC is evidently proved to be better than OPC based on the literature. From the existing studies, the base materials for the production of GPC generally differs. Therefore, the hydration of the final output (GPC) differs. Thus the behaviour of GPC under corrosion is required to be studied specifically. This aspect has narrowed the available literature on the behaviour of GPC under corrosion. In this study the behaviour of the fly ash based GPC and OPC specimens under accelerated corrosion were compared. GPC specimens under accelerated corrosion showed an average corrosion rate of 13 to 15 g/year demonstrating a moderate corrosion rate. Concurrently, the rate of corrosion in OPC specimens is around 25 g/year exhibiting a high corrosion rate. It is evidently proven that, comparatively GPC has better resistance to corrosion than OPC. [ABSTRACT FROM AUTHOR]

The sustainability of cement concrete is always a subject of concern and hence, less polluting concrete alternatives are being explored. Geopolymer concrete can be an alternative, which may be partly or fully cement-free. However, there exists a huge gap in the knowledge of quantification for ecological advancements that can be achieved. This study reports on the life cycle assessment (LCA) of five different geopolymer concrete mixes made up of ternary blends of sugarcane bagasse ash, blast furnace slag and fly ash. The results coupled with 28-day mechanical test results were compared with traditional cement concrete of similar grade. Correlation analysis was carried out among the obtained results to determine Pearson's coefficient and Spearman's rho factor. The aspect of cost and embodied energy was also studied simultaneously. The analyses showed that conventional concrete is more harmful in all ecological impact categories as compared to other alternative concretes except majorly Ozone layer depletion, Carcinogens and Mineral extraction. The sugarcane bagasse ash-based geopolymer concrete mixtures were also found to be cost and embodied energy-effective as compared to traditional concrete. [ABSTRACT FROM AUTHOR]

Steel slag is an industrial by-product of the steelmaking process, which is under-utilized and of low value due to its characteristics. Alkali-activated technology offers the possibility of high utilization and increased value of steel slag. A geopolymer composition was composed of steel slag, fly ash, and calcium hydroxide. Four experimental groups utilizing steel slag to substitute fly ash are established based on varying replacement levels: 35%, 40%, 45%, and 50% by mass. The final samples were characterized by compressive strength tests, and Fourier-transform infrared spectroscopy measurements, thermogravimetric measurements, scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction, and mercury intrusion porosimetry were used to investigate the chemical composition and microstructure of the final products. Higher steel slag/fly ash ratios lead to a lower bulk density and lower compressive strength. The compressive strength ranges from 3.7 MPa to 5.6 MPa, and the bulk density ranges from 0.85 g/cm3 to 1.13 g/cm3. Microstructural and energy-dispersive X-ray spectroscopy analyses show that the final geopolymer products were a type of composite consisting of both calcium aluminate silicate hydrate and sodium aluminate silicate hydrate, with the unreacted crystalline phases acting as fillers. [ABSTRACT FROM AUTHOR]

The hazardous environmental effects of greenhouse gas emissions and climate change demand alternative sources for cementitious materials in the construction industry. The development of geopolymer structures provides a way of producing 100% cement-free construction. In this research work, a novel and simple way of deriving nano particles from waste fly ash particles is promoted. The effect of adding the synthesized nano fly ash particles as a filler medium in geopolymer mortars was investigated by considering strength and durability properties. Parameter optimization was done by using regression analysis on the geopolymer mortar and the impact of adding nano fly ash particles was studied by varying different percentages of addition ranging from 0 to 7.5% by weight of binder content. From the results, it was observed that 1% nano fly ash acted not only as a filler but also as nano-sized precursors of the polymerization process, resulting in denser geopolymer medium. This can explain the extraordinary gain in strength of 72.11 MPa as well as the denser core with negligible level of chloride ion penetration, making the material suitable for the development of structures susceptible to marine environment. [ABSTRACT FROM AUTHOR]

The present research employs new boosting-based ensemble machine learning models i.e., gradient boosting (GB) and adaptive boosting (AdaBoost) to predict the unconfined compressive strength (UCS) of geopolymer stabilized clayey soil. The GB and AdaBoost models were developed and validated using 270 clayey soil samples stabilized with geopolymer, with ground-granulated blast-furnace slag and fly ash as source materials and sodium hydroxide solution as alkali activator. The database was randomly divided into training (80%) and testing (20%) sets for model development and validation. Several performance metrics, including coefficient of determination (R2), mean absolute error (MAE), root mean square error (RMSE), and mean squared error (MSE), were utilized to assess the accuracy and reliability of the developed models. The statistical results of this research showed that the GB and AdaBoost are reliable models based on the obtained values of R2 (= 0.980, 0.975), MAE (= 0.585, 0.655), RMSE (= 0.969, 1.088), and MSE (= 0.940, 1.185) for the testing dataset, respectively compared to the widely used artificial neural network, random forest, extreme gradient boosting, multivariable regression, and multi-gen genetic programming based models. Furthermore, the sensitivity analysis result shows that ground-granulated blast-furnace slag content was the key parameter affecting the UCS. [ABSTRACT FROM AUTHOR]

Flexible and rigid road pavement deteriorates over time and needs high-performance patching repair materials. Cold mix asphalt patching is an easy and inexpensive repair material to repair potholes and other damaged roads. However, the repaired road pavement fails because it doesn't have adequate compressive and bonding strength to the substrate. Thus, this research uses high-performance geopolymer repair materials to patch against road pavement potholes substrate. Geopolymer repair materials could improve the bonding strength, making them suitable for road repair purposes. For making geopolymer repair materials, the main materials used were high calcium aluminosilicate source materials such as fly ash, sodium hydroxide, sodium silicate, and water. This study tested the compressive and bonding strength of geopolymer repair materials after 1, 7, 14, and 28 days. This study found that the compressive strength of 90 g of alkali activator was the highest, at 37.0 MPa. The bonding strength improved gradually from day 1 to day 14, and then considerably on day 28. The compressive strength and bonding strength both increase in direct proportion to the amount of alkali activator present. Alkali activator is optimal at 90 grams for compressive strength and bonding strength of geopolymer repair materials. [ABSTRACT FROM AUTHOR]

Cement production is energy-intensive resulting in the emission of carbon dioxide (CO2) which is responsible for global warming. Rapid surge in the global energy demands needs to pave way for the need for a viable and sustainable alternative to concrete, which not only reduces our dependence on natural resources but also can be a possible alternative to the concrete industry and geopolymer technology can be one such material. Geopolymer technology can use secondary raw materials from the agricultural and industrial waste with alumina-silicate phase in presence of alkali activator for the production of geopolymer concrete. This paper comprehensively summarizes the previous research; along with analysis is carried out to propose descriptive equations to establish the correlation between the mechanical strengths (Compressive strength with Split tensile strength, Flexural strength and Modulus of Elasticity) of geopolymer. Current findings suggest substantial practicality and a possible alternative to cement in the construction industry [ABSTRACT FROM AUTHOR]

The purpose of this study is to synthesize geopolymer binders as an environmentally friendly alternative to conventional cement using available local raw materials. Waste materials such as chalcedonite (Ch), amphibolite (A), fly ash from lignite combustion (PB), and diatomite dust (D) calcined at 900 °C were used to produce geopolymer binders. Metakaolin (M) was used as an additional modifier for binders based on waste materials. The base materials were subjected to fluorescence X-ray fluorescence (XRF) analysis and X-ray diffractometry (XRD) to determine chemical and phase composition. A laser particle size analysis was also performed. The various mixtures of raw materials were activated with a 10 M solution of NaOH and sodium water glass and then annealed for 24 h at 60 °C. The produced geopolymer binders were conditioned for 28 days under laboratory conditions and then subjected to microstructural analysis (SEM) and flexural and compressive strength tests. The best compressive strength results were obtained by the Ch + PB samples—more than 57 MPa, while the lowest results were obtained by the Ch + D+A + M samples—more than 20 MPa. On the other hand, as a result of the flexural strength tests, the highest flexural results were obtained by D + A + M + PB binders—more than 12 MPa, and the lowest values were obtained by binders based on Ch + D+A + M—about 4.8 MPa. [ABSTRACT FROM AUTHOR]

The utilization of industrial by-products (IBPs) in cement (OPC)-solidified sludge has been extensively studied as an approach to enhance the mechanical performance, but the presence of salt in groundwater and wetting–drying action would compromise the mass and mechanical behavior of such solidified sludge. Unfortunately, there is a paucity of research on the single or coupled impacts of these two phenomena on IBP–OPC-solidified sludge. This paper aims to address the research gap by exploring the durability of IBP–OPC-solidified sludge in distilled water, sulfate solution and chloride solution through the full immersion tests (IT) and cyclic wetting–drying (WD) tests. Samples were prepared where collected sludge was mixed with OPC and various types of IBPs (including fly ash, slag, calcium carbide residue and silica fume). The resulting unconfined compressive strength, mass loss, and visual changes of samples were evaluated after IT and WD tests. Furthermore, scanning electron microscopy, physisorption experiments, and X-ray diffraction tests were conducted to examine the microstructure, pore evolution and mineralogical characteristics, respectively. Grey correlation model analysis was used to quantify the relationship between components inside IBPs and strength. The results indicate that the use of IBPs is effective in minimizing the mass loss and strength degradation of OPC-solidified samples, with the exception of calcium carbide residue in a sulfate environment. The use of IBPs can promote the formation of C-(A)-S-H gels and increase the amount of hydrated products through pozzolanic reactions and reactions between salt and aluminosilicate phases. Furthermore, the pore volume of solidified samples tends to be reduced, creating a denser matrix with more smaller pores that contribute to excellent mechanical properties and durability. Overall, the findings suggest that IBP–OPC has the potential for promising applications in the high performance of solidified sludge in severe conditions, such as coastal and offshore engineering. [ABSTRACT FROM AUTHOR]

Copyright of Romanian Journal of Civil Engineering / Revista Română de Inginerie Civilă is the property of Matrix Rom and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Geopolymers are comparatively new generation of construction materials made from industrial by-products and supplemental cementitious materials (SCM) with high silica and alumina content. Currently, the demand for SCM has enlarged significantly based on global climate change action plans, so its use through the geopolymerisation process has attracted the attention of researchers from all over the world. This article focuses on the main mechanisms of construction and demolition (C&D) waste on the resulting physical, mechanical and durability properties of geopolymer concrete (GPC) on fresh and hardened state. This article deals with the partial substitution of coarse aggregates (CA) by C&D waste on GPC. The partial replacement of CA was carried out in five proportions, that is, 0%, 10%, 20%, 30% and 40%, and every sample was analysed to determine the slump cone, the compressive strength, flexural strength and splitting tensile strength for 7 and 28 d. It is observed that the percentage variation of C&D waste influences the hardening properties of GPC. The analysis of Finite element (FE) is taken by using FE software ANSYS. [ABSTRACT FROM AUTHOR]

Advanced and eco-friendly construction materials are being developed to reduce pollution and improve wastewater treatment efficiency. One such material is a photocatalytic nanocomposite that uses industrial wastes and natural substances to eliminate pollution. A recent study explored using an inorganic polymer composite (FM) made from a mixture of 70% fly ash and 30% metakaolin, with sodium hydroxide and sodium silicate as an alkali activator. The study evaluated the mechanical and hydration characteristics of the FM composite after 28 days in 100% humidity at room temperature. The study also examined the effect of adding 2.5 wt.% of Nano-TiO2 to FM composite and how it affects its properties. Results indicate that adding Nano-TiO2 to FM composite enhances its mechanical, antibacterial, and photocatalytic capabilities. Specifically, FM-TiO2 composite showed 90% removal of reactive blue 19 dye effluent in sunlight after 90 min, making it an excellent choice for sustainable wastewater treatment. This study presents a cost-effective, eco-friendly solution to wastewater treatment, with added antimicrobial properties from Nano-TiO2. [ABSTRACT FROM AUTHOR]

Geopolymers prepared with class C fly ash (FA) often suffer from a flash geopolymerisation rate, making it difficult to work. Class F FA, however, may have low reactivity, so an admixture must be added to solve this problem. This research highlighted the use of mixed class C and class F FA as a precursor for geopolymer preparation to alleviate such problems. Optimisation of the precursor recipe and the solid-to-liquid ratio (S/L) was assessed. The highest compressive strength (30.54 MPa) and a suitable initial (136 min) and final (240 min) setting times were obtained with S/L = 2.00, and 50 : 50 proportions of class C to class F FA. The fire resistance test on a 10 mm thick geopolymer panel at 1000°C for 180 min showed a maximum temperature of ∼570–580°C on the reverse side without catastrophic failure, suggesting it can be applied for use in fire retardation. [ABSTRACT FROM AUTHOR]

Nowadays low calcium fly ash-based geopolymer concrete can be replaced with cement-based concrete to avoid the adverse effect of manufacturing cement on the environment. Utilization of geopolymer concrete instead of traditional concrete using low calcium fly ash and nano silica reduces a significant amount of CO-2 emission towards the atmosphere. However, the performance of geopolymer concrete is less than that of Portland cement concrete. To improve the performance of geopolymer concrete nano silica was used in the present study. In this work, geopolymer concrete was made utilizing fly ash, ground granular blast furnace slag (GGBS), and sugarcane bagasse ash. In the first instance, binary combinations i.e. fly ash and GGBS were employed as cementitious materials for the production of geopolymer concrete. In the second instance, a ternary mixture of pozzolanic material was prepared by taking 25% GGBS, 65% Fly ash, and 10% bagasse ash. In the third instance, varying percentages of nanoparticles were used for the above ternary mixture. The mechanical and durability properties of the geopolymer composite that was made earlier were tested. The compressive strength and split tensile strength of geopolymer composites were assessed for mechanical properties and a rapid chloride permeability test, water absorption test, and acid attack test were done to know about the porosity of concrete. Results showed that, with a dose of 4% nanoparticles, the durability and strength properties of the concrete had improved the most. The GCBA-N4 mixture had the highest split tensile and compressive strength was measured to be 2.91 MPa and 41.33 MPa and the rapid chloride permeability test, water absorption rate, and percentage of mass loss due to sulfate attack were found as a minimum for GCBA-N4 specimen. [ABSTRACT FROM AUTHOR]