Concentration Of Alkali Activator Research Articles

Bond performance of reinforcing bars in fly ash-based engineered geopolymer composites under uniform and nonuniform corrosion conditions

While concrete is the most popular building material in the world, corrosion of the steel reinforcement in reinforced concrete (RC) structures poses ongoing durability issues. In this study, the effects of alkali activator modulus, concentration, and different corrosion periods are rigorously investigated utilizing accelerated electrochemical corrosion techniques under both uniform and nonuniform corrosion conditions. Bond stress and bond stress deterioration are evaluated to provide a thorough examination of corrosion-induced fracture formation through pull-out experiments. X-CT 3D imaging is also used to understand the spread of rust in both corrosion scenarios. Results show that mixes with lower alkali activator modulus and higher alkali activator concentration might result in better bond stress preservation and higher ultimate bond stress under corrosion. High bond stress, however, usually corresponds to a more brittle failure when subjected to pull-out force. Nonuniform corrosion treatment can result in differential rust formation and a quicker bond breakdown between steel bars and engineered geopolymer composites (EGCs) than uniform corrosion. Furthermore, under corrosion, EGCs with high alkali activator modulus tend to form more penetrating cracks with limited width and depth. Both narrow and deep penetrating fractures can arise from EGCs with low alkali activator concentration.

Mix design strategy and optimization considering characteristic evaluation of geopolymer concrete

In this study, a unique strategy for mix design of geopolymer concrete (GPC) was suggested by integrating fly ash, silica fume, and GGBFS as precursors with varied alkali activator molarities in both ambient and oven curing environments. GPC's crystalline and microscopic qualities were assessed by X-ray diffraction and scanning electron microscopy tests; while its' mechanical properties were assessed using compressive strength test (CST). The experimental results showed a rising trend between the alkali activator (NaOH) concentration and the compressive strength of the GPC. GGBFS precursor based GPC had the highest compressive strength of 87.53 MPa at 14 molarity of NaOH after oven curing at 60°C. Furthermore, Artificial Neural Network (ANN) and Response Surface Method (RSM) were used to evaluate significant correlation and interaction between different parameters considered in mix design. By incorporating six input variables from the experimental test data, namely total precursor content used, secondary precursor content used, curing temperature, number of curing days, total aggregate content, and molarity of NaOH used, and compressive strength as output/response variable. The R-value for ANN found to be 0.99, while the R2 value for the RSM model was 0.98, indicating a satisfactory fit having a good interaction and optimization of GPC parameters. The optimize values of different independent parameters evaluated can obtain maximum CST value of 111.104 MPa.

Experiment on Compressive Properties and Microscopic Analysis of Sea Sand Geopolymer-Based Recycled Concrete.

For marine and coastal engineering, construction resources have become scarce due to a limited local supply. Sea sand geopolymer-based recycled concrete (SSGRC) is an innovative cementitious material known for its eco-friendly benefits and corrosion resistance. This study explores the mechanical properties of SSGRC. The influences of the replacement rate of mineral slag, alkali activator concentrations, fine aggregate types, and curing ages on the compression strength of SSGRC were studied. The failure mechanism was analyzed using the failure patterns and compressive stress-strain curves. The results show that sea sand had a positive effect on geopolymer-based material. The SSGRC reached peak strength with an alkali activator concentration of 10 mol/L and a mineral slag replacement rate of 60%. The maximum stress and strain increased with an increasing curing age. The ratios of strength to the peak value were 55% and 85% after 1 day and 7 days, respectively. Using SEM, in the last hydration stage, the C-(A)-S-H gel was formed with a dense microstructure, and the geopolymer exhibited a favorable bonding performance. The constitutive models describing the complete stress-strain relationship under compression were developed.

Mechanical properties and environmental characteristics of the synergistic preparation of cementitious materials using electrolytic manganese residue, steel slag, and blast furnace slag

The high content of heavy metals in electrolytic manganese residue (EMR) makes it difficult to utilize in engineering, and direct disposal can pose a threat to the environment. This study uses EMR as a raw material combined with steel slag (SS) and blast furnace slag (GGBS) to prepare electrolytic manganese residue-based cementitious material (ESGM) under the action of an alkali activator (NaOH), and studies the effects of the EMR to SS ratio and alkali activator concentration on the flowability, setting time, compressive strength, and toxic leaching of ESGM. In addition, XRD, FTIR, SEMEDS, and MIP were used to study the microscopic characteristics of ESGM and its stabilization/solidification mechanism for heavy metals. The results indicate that an increase in EMR content will reduce the fluidity and setting time of the slurry, while an increase in alkali activator concentration will increase the fluidity of the slurry and reduce the setting time. When the content of EMR, SS, and GGBS is 50%, 20%, and 30%, respectively, and the concentration of alkali activator is 0.2, the strength of ESGM reaches its maximum, reaching 23.0 MPa in 28 days. The heavy metal leaching in ESGM is lower than the allowable range of Chinese standard GB 89781–996, and the material meets environmental requirements. The microscopic analysis showed that the ESGM gelling products were mainly C-(A)-S-H and N-A-S-H gels, and the formation of ettringite was also observed. Mn2+ in EMR was mainly stabilized in ESGM in the form of MnO2 and H2Mn8O16·2.4 H2O.

Mechanical and bond behaviour of high volume Ultrafine-slag blended fly ash based alkali activated concrete

The development of Geopolymer concrete (GPC) mixes by employing large volume of ultrafine ground granulated blast furnace slag (UBFS) blended with Fly ash (FA) and activated by sodium hydroxide (SH) has been presented in this study. Several GPC mixes has been prepared to investigate the effect of varying alkali content, fine aggregate to total aggregate ratio (s/a) and molar concentration (M) of alkali activator on the fresh and hardened characteristics, including the bond strength with Portland cement concrete (PCC). The properties of the GPC mixes are assessed by workability test, compressive strength test, split tensile strength test and slant shear test, including the microstructure through FESEM (Field Emission Scan Electron Microscopy) and X-ray diffraction (XRD). The test result shows that s/a ratio is a crucial factor in controlling segregation and bleeding in GPC. However, an ideal GPC mix with s/a ratio 0.41 provides a better packing resulting in improved mechanical properties. Application of high volume UBFS in the GPC exhibits better reaction products as shown by the microstructure at a relatively lower alkali concentration which ultimately leads to higher strength. Superior bond strength is achieved between the GPC and old PCC substrate; however, the molarity of SH significantly affects the adhesion property of GPC.

Investigation on the Effect of Calcium on the Properties of Geopolymer Prepared from Uncalcined Coal Gangue

In this paper, the influence of calcium on coal gangue and fly ash geopolymer is explored, and the problem of low utilization of unburned coal gangue is analyzed and solved. The experiment took uncalcined coal gangue and fly ash as raw materials, and a regression model was developed with the response surface methodology. The independent variables were the CG content, alkali activator concentration, and Ca(OH)2 to NaOH ratio (CH/SH). The response target value was the coal gangue and fly-ash geopolymer compressive strength. The compressive strength tests and the regression model obtained by the response surface methodology showed that the coal gangue and fly ash geopolymer prepared with the content of uncalcined coal gangue is 30%, alkali activator content of 15%, and the value of CH/SH is 1.727 had a dense structure and better performance. The microscopic results demonstrated that the uncalcined coal gangue structure is destroyed under an alkali activator's action, and a dense microstructure is formed based on C(N)-A-S-H and C-S-H gel, which provides a reasonable basis for the preparation of geopolymers from the uncalcined coal gangue.

Study on mechanical properties of metakaolin based geopolymer pervious concrete

In this study, geopolymers were used as binder materials and large-sized aggregates as coarse aggregates to prepare pervious concrete. Design different alkali activator modulus, concentration, and coarse aggregate: geopolymer binder materials in mass, and test the physical, and mechanical properties. According to the compression test, the stress-strain curve of the metakaolin-based polymer pervious concrete was obtained, and the elastic modulus and strain were analyzed. The test results show that: with the increase of the modulus of the alkali activator, the compressive strength and splitting tensile strength show a trend of increasing first and then decreasing. The higher alkali activator concentration and the ratio of the crude aggregate to the polymer binder material are detrimental to the development of strength in pervious concrete. The mass ratio of geopolymer binder material to coarse aggregate is 1: 5, the concentration of alkaline activator is 40%, the modulus is 1.3, and the mass ratio of alkali activator solute (sodium silicate+sodium hydroxide) to metakaolin is the geopolymer pervious concrete prepared at 0.35 has higher strength and water permeability.

Characterization of class C and F fly ashes based geopolymers incorporating silica fume

Geopolymers have been proposed as an alternative to ordinary concrete with their appropriate mechanical performances and eco-friendly impacts. In current study investigated the interaction between the class C and F fly ashes on the properties of silica fume incorporated geopolymers. For that purpose, the concentration of the alkali activator were determined according to compressive and flexural strengths. Then, the geopolymers prepared with different fly ash/silica fume ratios at specified alkali activator concentration. Mechanical, physical, chemical and microstructural properties of these geopolymers were evaluated by FT-IR, XRD, TGA, and SEM-EDX. The mechanical properties of geopolymers were enhanced remarkably by NaOH molarity and it was detected that the compressive strength and flexural strength values reached the highest (21.13 ± 1.11 MPa and 6.61 ± 0.56 MPa, respectively) at 10 M. Results were compared according to the fly ash type and the fly ash/silica fume ratios of the geopolymers. Due to the high water demand of silica fume, prominent cracks were seen in the geopolymers including 100% silica fume. Besides, inadequate mechanical properties were obtained when 100% fly ash was used. Consequently, it was clearly revealed that the properties of geopolymers obtained with only fly ash or silica fume were improved by the use of both. Finally, higher mechanical properties (σC: 31.91 ± 1.90 MPa, σF: 8.34 ± 0.23 MPa) and less cracks in the bodies were obtained with class F fly ash (75% wt.).

Influence of cleaning agent reuse on cleaning effectiveness

The Clean-In-Place (CIP) operation use a pump to move a cleaning solution or water over the surfaces of pipelines or alternative food-contact surfaces. In order to improve the overall efficiency of CIP operations, the reuse of cleaning solutions could reduce the demand for water and for cleaning agents. The objective of this study was to investigate the influence of cleaning agent reuse on effectiveness in removal of residues from a food-contact surface during CIP operation. Based on experimental trials conducted with a bench-scale CIP system, more than 99.95% of protein residues were removed by cleaning agent used for the third time. The effectiveness of removal was reduced to approximately 98% when the cleaning agent was used for the fourth and fifth time. The rate constant for removal of the protein residue decreased with the reusing the cleaning agents over three times. When the reused cleaning agents were evaluated in a pilot-scale CIP system, a reduction in the effectiveness of a 0.05% NaOH cleaning agent was detected during the seventh reuse. A 0.5% NaOH cleaning solution maintained cleaning effectiveness through at least seven uses. The pH, electric conductivity, and active alkali concentration of the cleaning solution were monitored, and were found to decrease with the number of uses. The reduced effectiveness of cleaning agents was attributed to the reduced OH- concentration caused by chemical reactions with food residues. Estimation of reduced operating costs associated with the reuse of cleaning solutions was from $7,920 to $ 2,555 per square meter of fouled surface, or about 67%. In general, the outcomes from the project demonstrate that reuse of cleaning solutions can be effective and reduce costs for CIP operations. • After several uses of cleaning solution, the cleaning rate was significantly reduced. • The measurement of chemical properties confirmed the reduction of OH- groups. • The reusing practice would reduce the cost of total cleaning operation by 67%.

Effect of superplasticizer on the strength of fly ash based geopolymer concrete

In this research, the effect of a polycarboxylate based superplasticizer on the strength of Geopolymer Concrete (GPC) was investigated. A fixed amount of superplasticizer (1.5 % of Fly Ash weight) was utilized along with alkali activators Sodium Hydroxide (NaOH) and Sodium Silicate (Na2SiO3). The Ultrasonic Pulse Velocity Test determined the strength development of concrete. The quality of the GPC improved when a higher concentration of alkali activator was applied based on the Concrete Quality Designation. In detecting the color development of GPC, samples were put through MATLAB and specimens became lighter as time passes due to dehydration (a process where water escapes from the sample). Stress strain diagrams were generated which generally indicate that GPC specimens are ductile. The researchers were able to assess the workability of the mix designs using a rating from 1 to 5, with 1 being the least workable and 5 being the most workable.

Alkali activation of blast furnace slag using a carbonate-calcium carbide residue alkaline mixture to prepare cemented paste backfill

The utilization of calcium carbide residue (CCR) as alkali activator is promising to reduce production cost and ensure production safety. In this study, CCR/carbonates system and Ca(OH)2/carbonates system were used to replace the NaOH and KOH to activated blast furnace slag developing cemented paste backfill (CPB), and the difference of reaction products was also investigated. Then, the fluidity and compressive strength of the CPB prepared by different alkali activators were studied. Finally, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and fourier transform infrared spectroscopy (FTIR) were used to characterize the hydration products, respectively. Meanwhile, microscopy intrusion porosimetry (MIP) was also carried out to characterize pore structure of hardened specimens. Results indicate that at the same concentration of alkali activator, the CPB sample with mixed alkali activator showed lower fluidity but higher strength compared with the sample with single alkali activator. Due to the large amount of Ca+ and CO32– in the mixed alkali activator, the content of C-S-H in the CPB sample increased significantly and new hydration products, hydrotalcite and CaCO3 were observed. Using CCR as a replacement of Ca(OH)2 to prepare alkali activator could achieve a better fluidity but little lower compressive strength. Hence, the utilization of CCR could effectively reduce its storage problem and the cost of alkaline activator while maintaining the CPB performance simultaneously.

Experimental study on mechanical properties and microstructure of metakaolin based geopolymer stabilized silty clay

Geopolymer is an environmentally friendly green building material with fast hardening, high strength, low shrinkage, low cost, and low carbon dioxide emission. Based on the above characteristics of geopolymer, this study aims to explore the feasibility of taking geopolymer as a new choice for silty clay foundation treatment. In this study, unconfined compressive strength tests, scanning electron microscopy (SEM), and X-ray energy dispersive spectroscopy (EDS) experiments were carried out on silty clay stabilized by metakaolin based geopolymer (MKG). The influences of metakaolin content, modulus, and concentration of alkali activator on the mechanical properties of geopolymer stabilized soil were discussed. The mechanism of MKG improving the soil strength was also discussed from the microscopic point of view. The result showed that when the modulus of alkali activator is 1.3, the concentration is 40%, and the mixed mass of metakaolin is 1.2 times that of alkali activator, MKG stabilized soil showed higher unconfined compressive strength (UCS). Through comparative tests with untreated plain soil, lime stabilized soil and ordinary Portland cement stabilized soil, the strength performance and stabilizing effect of MKG stabilized soil were further studied. MKG has an obvious effect on improving the UCS of soil, and its mechanical indexes including UCS, Young's modulus, failure strain were also enhanced compared with samples stabilized with lime and ordinary Portland cement. SEM observation confirmed the formation of cementitious materials in the stabilized soil sample, the soil showed a more uniform and denser microstructure after treatment with MKG. Through EDS energy dispersion spectroscopy analysis, it is not easy to cause salt swelling damage with no large amount of calcium ions in the sample. This experimental study indicated that MKG can be an effective soil solidification agent for silty soil.

Regularized multivariate polynomial regression analysis of the compressive strength of slag-metakaolin geopolymer pastes based on experimental data

The compressive strength of geopolymer pastes is a fundamental parameter in the research on the macromechanical performance of geopolymer concrete. However, the factors that affect the strength are complex. In this work, we developed a regularized multivariate polynomial regression (MPR) model to predict the compressive strengths of 40%/60% ground granulated blast furnace slag (GGBFS)-metakaolin (MK)-based geopolymer pastes. Moreover, by conducting experiments on 120 groups of specimens, a dataset that considers the effects of the alkali activator concentration, SiO2/Na2O molar ratio, and mass ratio of the alkali activator to aluminosilicate materials (i.e., the liquid–solid ratio) is created. Based on the framework of machine learning, the established dataset is used to train and test the MPR model. Notably, in the optimizing process of the MPR model, Lasso regularization is employed to prevent the overfitting problem caused by regression coefficients that are too large. The proposed MPR models show robust estimation capabilities, with R2 values of 0.946 and 0.927 for predicting the 7-day and 28-day compressive strengths in the testing processes. Unlike other black-box algorithms such as artificial neural networks, the proposed MPR model is much more transparent and easier to use by researchers. In addition, a partial dependence plot (PDP) is utilized to quantify the importance of influencing factors of the experimental dataset. The regularized regression method discussed in this work can help researchers map the nonlinear relationship between the experimental variables and results.

Comparative Analysis Between Fly Ash Geopolymer and Reactive Ultra-Fine Fly Ash Geopolymer

This study investigates novel geopolymers by combining Reactive Ultra-fine Fly Ash (RUFA) with 4M sodium hydroxide as an alkali activator. Comparing with general fly ash geopolymers, RUFA geopolymer pastes are characterized in terms of compressive strength, microstructure, and crystalline phases. The RUFA geopolymer is successfully obtained as alumina-silicate bonding materials with the same properties as the general fly ash-based geopolymer. The high compressive strength of the RUFA-based geopolymer samples (13.33 MPa) can be attributed primarily to Ca-based alumino-silicate hydration products and Na-based alumino-silicate complexes. This research presents an innovative application for geopolymers using RUFA. In the follow-up study, the influence of synthesis and concentration of alkali activator can be considered in RUFA-based geopolymers.

Effect of alkali activator concentration on waste brick powder-based ecofriendly mortar cured at ambient temperature

The main goal of this research was to investigate the effect of alkali activator concentrations and fine aggregate types on the performance of waste brick powder (WBP)-based alkali-activated mortar. Ground granulated blast furnace slag was used to modify the properties of WBP. Na2SiO3 and NaOH were used as the alkali activator solutions, with Na2O content varying between 2 and 10% and the SiO2/Na2O ratio varying between 0.25 and 2. Waste ceramic sand (WCS) and recycled concrete fine aggregate (RFA) were used as the alternative fine aggregate materials to replace natural fine aggregate (NFA). The mortar mixtures were successfully developed at significantly lower alkali activators concentrations (starting from 4% Na2O and SiO2/Na2O ratio of 0.5) than previously reported in the literature. The compressive strengths of the mortar were measured between 8 and 46 MPa. The partial replacement of NFA by WCS enhanced the compressive strength of mortar. Scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analysis were used to study the microstructural properties of mortar. Higher compressive strength and an increasingly compact microstructure were observed as Na2O content increases from 4 to 10% and as the SiO2/Na2O ratio rise from 0.5 to 1.5.

Study on the mechanical properties and microstructure of chitosan reinforced metakaolin-based geopolymer

Due to the high brittleness and poor toughness, the applications of geopolymer as building materials are highly limited. In this paper, the chitosan (CS), a type of organic polymer, was used to improve the mechanical properties of metakaolin-based geopolymer (MKG), especially its flexural toughness. The effects of chitosan content, modulus ratio of alkali activator (molar ratio of SiO2 to Na2O), and the concentration of alkali activator on the mechanical properties were investigated. Fourier Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR), and Scanning Electron Microscopy (SEM) were employed to study the microstructure and the toughening mechanisms. The results showed that the strength and flexural toughness of MKG were significantly improved in the presence of chitosan. As the dosage of chitosan increased from 0 to 2.0 wt%, the flexural and compressive strength of MKG increased first and then decreased. When the chitosan content was 1.0 wt%, the compressive strength and flexural strength of MKG at 28 d increased by 15.5% and 33.3%, respectively, compared with those of the blank group. Furthermore, the flexural toughness coefficient at 28 d was 83.63% higher than that of the blank group. It was noteworthy that with the addition of 1.0 wt% chitosan, the optimal modulus ratio and the concentration of alkali activator were 1.6 wt% and 10.0 wt%, respectively. Microscopic measurements indicated that –CONH2 in chitosan and –OH in MKG could bond together to form C-O-Si and lead to the decrease of the polymerization degree of [SiO4] tetrahedron. Moreover, the long chain molecules of chitosan bonded with MKG could form a three-dimensional interpenetrating network, thus resulting in the reinforcement of MKG at both molecular and submicroscopic levels. This study reveals the toughening mechanism of chitosan on MKG and can provid a technical support for the composition design of chitosan-reinforced geopolymer materials.

Design of a chitosan modifying alkali-activated slag pervious concrete with the function of water purification

A kind of alkali-activated slag pervious concrete (AAS-PC) was designed to purify rainwater to prevent it from polluting groundwater resources. The pervious concrete was designed from two aspects: the cementitious material and the volumetric structure parameters of pervious concrete. Chitosan was used in the cementitious material paste to enhance the adsorption capacity for heavy metal ions and other pollutants. In consideration of adsorption, composition parameters of the cementitious material paste such as the chitosan content, the mole ratio of SiO2/Na2O, and the concentration of alkali activator wereoptimized by orthogonal experiment. The influences of the bulk porosity of aggregate (BPA) and the ratio of paste to aggregate (P/A, mass ratio) on water purification capability, water permeability, and mechanical properties of the AAS-PC were investigated. It is found that, with the BPA increasing, the adsorption to Pb2+ and the compressive strength of pervious concrete decreased gradually but its water permeability improved; meanwhile, with the P/A increasing, its adsorption to Pb2+ and the compressive strength increased, but its water permeability decreased. There is a negative correlation between the water purification and the water permeability of the pervious concrete. Considering the water purification, water permeability and strength properties of the pervious concrete, the optimum BPA was 30% and the optimum P/A was 0.25.

Thermal and compressive behaviors of fly ash and metakaolin-based geopolymer

This paper studies the heat evolution and compressive behavior of KOH activated geopolymer materials based on low-calcium fly ash, metakaolin, and fly ash with slag. An isothermal calorimeter was adopted to study the heat evolution. Study variables include alkali activator concentration, curing temperature, and slag replacement ratio. It was found that the cumulative released heat for both fly ash and metakaolin-based geopolymer increased with the increase in alkali concentration and slag replacement ratio. The increase in curing temperature significantly increased both the heat flow and the cumulative heat of the heat evolution during geopolymerization, especially the fly ash-based geopolymers. The compressive behavior of geopolymers with different initial curing temperatures was also investigated experimentally. Results showed that the 28-day compressive strength for all geopolymers increased with the increase of alkali concentration and slag replacement ratio cured under ambient temperature. The initial curing temperature has a significant influence on the compressive strength of the fly ash-based geopolymer, but a negligible influence on the compressive strength of the metakaolin-based geopolymer.

Electrical resistivity of fly ash and metakaolin based geopolymers

In this paper, the electrical resistivity behavior of fly ash and metakaolin based geopolymer was investigated with the two-probe measurement method. The effects of alkali activator concentration, curing temperature and slag substitution rate on the electrical resistivity and pore size distribution were discussed. It was found that the electrical resistivity for fly ash based geopolymer is much higher than that for metakaolin based geopolymers. With the increase of alkali concentration, the electrical resistivity for both fly ash and metakaolin based geopolymers decreased significantly. The curing temperature has a significant influence on the electrical resistivity for fly ash based geopolymers, while the influence of curing temperature for metakaolin based geopolymer is negligible with a prolonged curing period. The increase of slag replacement ratio would increase the electrical resistivity for fly ash based geopolymer.

The manufacture of bleached kraft pulp from persimmon byproducts

The authors explored the possibility of using persimmon byproducts as raw materials for obtaining kraft pulps. Various unbleached and bleached kraft pulps via pulping and bleaching processes were prepared. Then, their characteristics were determined and compared with those of commercial kraft pulps. For the highest screened yield of persimmon byproduct unbleached kraft pulps, the optimal pulping conditions were a liquid ratio of 5:1, an active alkali concentration of 25%, a sulfidity of 30%, and a cooking time of 3 h. Furthermore, the authors obtained persimmon byproduct bleached kraft pulps (PB-BKPs) with an ISO brightness of 73% via three-stage bleaching using 3% ClO2, 1.5% NaOH, and 3.5% ClO2. Moreover, PB-BKP prepared under optimal pulping and bleaching conditions had physical characteristics similar to those of commercial mixed-hardwood bleached kraft pulp, but with relatively low ISO brightness. Therefore, as raw materials, persimmon byproducts can be used for manufacturing a bleached kraft pulp.