Silicate Solution Research Articles

Hygroscopicity and Morphology of Bio-Based Boards—The Influence of the Formulation

The internal structures and the hygroscopicity of bio-based boards consisting of giant reed (Arundo donax L.) and hazelnut shells as bio-aggregates, and a sodium silicate solution as the adhesive, were investigated. The aim was to evaluate the influence of each material (the bio-aggregates and adhesive) and their distributions in the boards on the final performance. By carrying out X-ray computed tomography, the internal structures and the porosities of the boards were determined, allowing important considerations of their hygroscopicity. The voids’ percentages were between 26% and 36% of the total volume of the composites. Both the materials and the composites demonstrated high hygroscopicity. In particular, the mixtures of the bio-aggregates and the sodium silicate allowed reaching a moisture buffering value of 7.44 g/(m2%RH) for the A. donax-based composite, 3.86 g/(m2%RH) for the hazelnut-shell-based composite, and 4.65 g/(m2%RH) for the mixture-based composite. Besides the identification of the contributions of the materials, a detailed discussion of the assessed properties was carried out to use these bio-based boards in vernacular historic construction. The results show how the aggregate type and the adhesive content affected the final behavior, demonstrating the importance of a conscious material choice. Furthermore, helpful information for the future development of these types of bio-based boards and their possible optimization was provided.

Effect of Microwaves on the Rapid Curing of Metakaolin- and Aluminum Orthophosphate-Based Geopolymers.

This paper deals with the influence of microwaves on the hardening and curing of geopolymer binders synthesized from metakaolin or aluminum orthophosphate with sodium silicate solution as the activator. Pure geopolymer pastes as well as geopolymer mortars were considered. The variable parameters were the modulus of the sodium silicate solutions (molar ratio of SiO2 to Na2O: 1.5, 2.0 and 2.5) and the Si/Al ratio (3/1 and 2/1). Selected samples were cured in a microwave oven until hardening, so the curing time depended on the mixture. For comparison some samples were cured at ambient temperature. To investigate the influence of microwave radiation on the reaction kinetics, isothermal heat flow calorimetry, ultrasonic velocity measurements and rheological investigations into the variation of curing temperature were used. In addition, the mechanical properties of the cured samples were characterized. The results show that microwave curing only takes a few minutes, so it is the most time-saving method. Key factors influencing the geopolymer reaction under microwave radiation are the raw materials as well as the Si/Al ratio. Metakaolin-based geopolymer binders are more stable than those based on aluminum orthophosphate, especially regarding their salt efflorescence. Microwave radiation is an efficient method to accelerate the geopolymer reaction.

An experimental investigation on mitigating cracks and augmenting the endurance of concrete structures in marine environment by bio-mortar immobilised with halophilic bacteria

In coastal areas, built structures encounter hostile conditions and forces that can cause them to deteriorate over time owing to saltwater exposure, tidal forces, reinforcement corrosion, and freeze–thaw cycles. Early age cracks in such structures accelerate the rate of deterioration, and the current research focuses on alleviating such threats. This paper evaluates the performance of a self-healing mortar made by encapsulating expanded perlite with the bacterium Halobacillus Halophilus MCC2188. Mortar cube specimens of size 70.6 mm × 70.6 mm× 70.6 mm were prepared with cement: fine aggregate in 1:3 ratios. A 10% volume of the fine aggregate fraction was substituted with the expanded perlite immobilised with bacterial spores and nutrients. The expanded perlite aggregates were coated with sodium silicate and cement solution to protect the spores from the nonconducive environment. The specimens were subjected to fully and partially submerged marine water curing. The mechanical properties and self-healing potential were evaluated, and the precipitated polymorphs in completely healed cracks were identified and examined by characterisation techniques such as XRD, FEGSEM, FTIR, and TGA-DTG. The marine bacterium under investigation can tolerate the high salt concentrations commonly found in seawater and saline marshy soil and produce calcite through the metabolism of organic compounds, making it a suitable microorganism for self-healing applications. Crack widths of up to 0.84 mm and 92.79% average strength recovery were achieved in 56 days post-cracking, and the pace of healing was quicker in partially submerged curing conditions. The results showed improved self-healing, strength regain and mechanical strength and proved to be an efficient tool for enhancing the endurance of biomortar in severe marine exposure conditions.

The effect of silica nanoparticles obtained from different sources on mechanical properties of polyurethane nanocomposites

Spherical silica particles were synthesized from two different sources, tetraethyl orthosilicate (TEOS) and sodium sili-cate obtained from wheat straw ash, respectively. In the first case, monodispersed and microporous silica particles with average particle size of 400 nm were prepared by hydrolysis and condensation of TEOS. In the second case, the silica particles were generated from supersaturated sodium silicate solution. The extraction of silicate solution from wheat straw ash (WSA) was performed by the multi-step sequential extraction using 2,5 mol/L NaOH. WSA silica particles were polydispersed and contain the primary silica particles with average size of ~250 nm and agglomerates obtained by aggregation of primary silica particles, with average size of ~1.5 mm and 5 mm. The silica particles obtained from WSA have the average pore size of 28.3 nm, total pore volume of 0.1638 cm 3 /g and average surface area of 23.131 m 2 /g. Flexible polyurethane/silica composites with my(TEOS silica and WSA silica) and different filler concentration were synthesized. Dispersion of silica fillers in polyol system preceded the mixing with isocyanate resulted in formation of cavities in polyurethane-silica composite. On the other hand, dispersion of TEOS silica filler into isocyanate which preceded the mixing with polyol system resulted in homogenous and compact composite. The application of silica filler obtained from TEOS at filler concentration of 4 wt.% increased Young's modulus for 20% relative to that of polyurethane without filler. On the other side, the application of WSA silica filler resulted in reduced Young' s modulus probably due to large silica aggregates.

Lithium germanosilicate glass formation, kinetics, stability and crystallization

Lithium disilicate glass (Li2O•2SiO2) was modified using GeO2 resulting in compositions Li2O•2GeO2•2SiO2 (L1G2S2), Li2O•GeO2•SiO2 (L1G1S1), and GeO2•SiO2 (L0G1S1). The glass formation was investigated and confirmed for compositions L1G2S2 and L1G1S1 through differential thermal analysis and X-ray diffraction. Two heat treatments were conducted in order to form a glass-ceramic and a sample with a larger crystalline fraction. The crystalline phase was identified through X-ray diffraction as a Li2(Ge,Si)2O5 solid solution of lithium silicate (PDF 010-70-4856). Raman spectra of all samples were analyzed and discussed. The presence of bands associated with Ge in defect sites in silica glass, and those associated with Si–O-Ge bonds suggest the network is established by both SiO2 and GeO2 and not two separate networks, which is consistent with the formation of a solid solution. The refractive index was measured for the glasses and glass-ceramics samples, revealing a very small dispersion between 0.3 and 0.8 μm.

Effect of Molarity of Sodium Hydroxide Solution Over GGBS-based Self Compacting Geopolymer Concrete

Applications of geopolymer concrete are increasing at a faster rate globally and are actively replacing cement concrete in all its facets. Regarding this, the advancement of, self-compacting geopolymer concrete is inevitable. The present study deals with the investigation of the effect of the molarity of sodium hydroxide solution that is to be used as part of an alkaline solution, over self-compacting and hardened properties of geopolymer concrete. Ground granulated Blast Furnace Slag (GGBS) is used as precursor material; hence, ambient curing is adopted. The alkaline activator solution is a combination of silicate solution and hydroxide based on sodium. In this work, the hydroxide solution’s molarity is varied to 8, 10, 12, 14, 16, and 18. Self-compacting properties are investigated through spread flow, T-50, V-funnel test, and L-box. The compressive strength of the hardened concrete is investigated over 7 and 28 days. Further water absorption test was also assessed in this investigation to determine the basic durability. All the specimens with different molarities exhibited fair self-compacting properties. Further optimum molarity required for the synthesis of self-compacting geopolymer concrete with fair compressive strength and excellent reduced water absorption capability is determined. The findings of this work tend to augment significant contributions to the geopolymer concrete in the facets of self-compacting nature.

Characterization of Sodium Silicate Solution Synthesized from Waste Rice Husk and Manufacturing of Copper Slag-Based Geopolymers

Characterization of Sodium Silicate Solution Synthesized from Waste Rice Husk and Manufacturing of Copper Slag-Based Geopolymers

A study on preparation and properties of fly ash-based SiO2 aerogel material

Using fly ash acid leaching residue as the silicon source, sodium silicate solution was produced by alkali leaching and the wet gel was obtained by the sol-gel method. Hexamethyldisiloxane (HMDSO) was used to modify the surface of the wet gel, thereby reducing the capillary tension during the atmospheric pressure drying process, and finally preparing a silica aerogel material with hydrophobic properties. The effects of different alkali leaching conditions, different sol pH, HMDSO dosage on the aerogel density and the changes of aerogel material properties and composition during the preparation process were investigated, and the reaction mechanism of silica aerogel preparation by atmospheric pressure drying was described. The results showed that the optimum conditions for alkali leaching were 20 wt% NaOH concentration, 2 h reaction time and 100 °C, and the desilication rate was 81.72%; the lowest Silica aerogel density of 108 mg/cm3 at pH 5 to 6; the lowest density of silica aerogel was 110 mg/cm3 at a modifier to wet gel volume ratio of 1:1.4.

Setting time, sulfuric acid resistance, and strength development of alkali-activated mortar with slag & fly ash binders

This study evaluated the effect of initial molar ratios SiO2/Al2O3 and (CaO + SiO2)/Al2O3, on the setting time of mortar with alkali-activated Ground Granulated Blast Furnace Slag (GBS) and fly ash (FA) binders. The study also evaluated the chemical resistance of alkali-activated mortar and the effect of NaOH alkaline activator on resistance to sulfuric acid in particular. Mortar samples were cured at 22 ± 2 °C and 70% relative humidity (RH). Three GBS/FA binder combinations were evaluated: 1:1, 3:1, and 1:0 (100% GBS). Activation was done using a combination of sodium hydroxide, with concentrations from 10 mol/L to 16 mol/L, combined with sodium silicate solution. Chemical resistance was evaluated by immersing mortar samples in sulfuric acid. Geopolymer mortar samples cured in an open system exhibited an increase in compressive strength from the age of 1 day–28 days. However, at the age of 90 days, all air-cured mortar samples, irrespective of activator concentration, decreased in strength. Similar mortar specimens immersed in sulfuric acid 24 h after casting exhibited a continuous increase in strength until the age of 90 days. Water evaporates from an open system which may cause partial precipitation of dissolved silicates rather than the formation of geopolymer products. The medium containing the sulfuric acid provided a closed system simulating a physical barrier against evaporation, and making dissolved silicates available to participate in the formation of geopolymerization products. Setting time was found to have a stronger correlation with the initial molar ratio of (CaO + SiO2)/Al2O3, than the molar ratio SiO2/Al2O3. Several mathematical models for predicting splitting tensile strength were developed and the goodness-of-fit to test data was evaluated using the integral absolute error (IAE).

Rapid fabrication of porous metakaolin-based geopolymer via microwave foaming

Microwave foaming was used for the first time to rapidly fabricate the metakaolin-based porous geopolymers. Mechanical, thermal, and microstructural (optical and scanning electron microscope) investigations coupled with X-ray diffraction, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance techniques were conducted to characterize the obtained foams. High porosity metakaolin-based porous geopolymers could be obtained at 4 min of foaming/curing. The effect of the sodium silicate solution content on the total porosity as well as the mechanical and thermal properties was investigated. The total porosity decreased firstly and then increased in the range of ∼74 to ∼84 vol% with the increase of Na2SiO3 content. The foams with 47.7 wt% Na2SiO3 exhibited the lowest thermal conductivity (0.104 W/mK) and the highest total porosity (83.2 vol%). The fabrication time, mechanical, and thermal properties were compared with those of foams obtained by the conventional direct foaming method. With this approach, the preparation time can be greatly reduced, and the compressive strength (1.89–2.04 MPa) and thermal conductivity (0.104–0.155 W/mK) of the materials obtained were not inferior to similar components obtained by other foaming routes. The rapidly obtained porous geopolymers with high porosity and high strength as well as low thermal conductivity can be employed as thermal insulation materials and ceramic precursors.

Accelerated aging resistance, abrasion resistance and other properties of alkali-activated slag mortars containing limestone powder

The Earth's crust is widely recognized for its abundance of limestone (LS). Limestone powder (LSP) has a wide range of potential properties that make it suitable for various applications and fields. It has found extensive usage in Portland cement-based materials. Recently, the incorporation of LSP into geopolymers is becoming more of a concern than before and has become a hot topic. In this article, high range of LSP (2.5–50 wt%) was introduced into alkali-activated slag (AAS) mortars activated with NaOH and sodium silicate solution as a substitution of slag. For the first time, the effect of LSP on the accelerated aging resistance and abrasion resistance of AAS mortars was examined. In addition, the typical traditional routine properties such as flowability, setting time, mechanical strength, water absorption, and total porosity were studied. Sophisticated equipment was utilized to observe the changes in crystalline phases, hydration products, and microstructures of selected samples. The results showed higher flowability and longer setting time with including LSP. As the amount of LSP increased as the flowability and setting time increased. The introduction of 2.5–25% LSP positively affected the mechanical strength, aging resistance, abrasion resistance and transport properties. In contrast, the introduction of 35% did not show an essential change, whilst the introduction of 50% LSP negatively affected the mentioned properties.

Differences between Using Mortars and Solutions When Testing Sodium Silicate as Corrosion Inhibitor for Construction Steel

Corrosion inhibitors are regularly used to minimize corrosion progress in reinforced concrete. Nitrite ions are very effective inorganic inhibitors but not environmentally friendly, since they can leach and contaminate the surrounding soil and water [1, 2]. Among other promising inorganic ions, silicate ions are of particular interest due to their low cost and low toxicity, although most results have been reported in pore simulating solutions. There is little information in the literature where silicate ions are evaluated as corrosion inhibitors in mortar or cement pastes. The purpose of this study is to show some contrasts between the effectiveness of silicate ions as carbon steel inhibitors when they are tested in solution or in mortar.The results in solution (ASCl) were obtained in an alkaline electrolyte (pH=13) that simulates good quality concrete contaminated with chloride ions [3,4]. ASCl contains KOH 0.08 mol/L, NaOH 0.02 mol/L, Ca(OH)2 0.001 mol/L and NaCl 0.3 mol/L, so that [Cl-]/[OH-]=3. The solution containing silicate ions (SSCl) incorporates Na2SiO3.5H2O 0.3 mol/L, corresponding to [inhibitor]/[Cl-]=1. The electrochemical evaluation included standard tests such as cyclic voltammograms, polarization curves, electrochemical impedance spectroscopy (EIS) and weight loss tests involving long exposure times. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to investigate the composition of the surface films. The findings for bare rebars demonstrate that the presence of silicate ions in solution may effectively prevent carbon steel corrosion, with an inhibition efficiency greater than 99% and no localized attack seen after 30 days of immersion. It has also been observed that a 24-hour pretreatment at open circuit potential (OCP) in silicate solutions (SS) improves the corrosion resistance of construction steel when tested in SSCl. The polarization curves show higher pitting potential and lower corrosion current intensities when compared to untreated electrodes. XPS spectra show that silicate ions are incorporated into the surface film. Pretreatments in SS produce passive films that are rich in Fe(II), present mainly as oxohydroxides. EIS shows that the film is more resistive and compact. In contrast, the reference pretreatment in the absence of silicates led to surface films composed mainly of Fe(III) oxides and oxohydroxoxides.Tests in mortars were carried out including reinforcement bars (rebars) in mortar prepared with water/Portland cement=0.6 and sand/cement ratio =3. Mix R (for reference) had no admixed inhibitor and mix S incorporated Na2SiO3.5H2O using a 0.3 mol/L solution to replace the water in the mix. Also, samples P contained rebars pre-treated by previous immersion in silicate ions solutions, in mortars with the same composition as mix R. Once cured for 7 days, the mortar samples were immersed in aerated 0.3 mol/L NaCl solution for 3 months. The electrochemical follow-up included periodical evaluation by EIS and Rp. The alkaline reservoir in the mortar (which is the content of insoluble Ca(OH)2) was investigated by thermogravimetric analysis. Also, a lixiviation test was designed using pH indicators to verify changes in basicity after a lixiviation process. In mortars R and S, charge transfer and polarization resistance (Rt and Rp) remained lower than 50 kΩ cm2 after the first 15 days. However, Rt and Rp higher 100 kΩ cm2 were measured for rebars P after 15 and 60 days of exposure. The differences between P and R tend to flatten after 90 days of exposure. This shows that the inhibitor effect of pretreating the rebars (P) is lost over a longer period of time. According to the results from thermogravimetric tests, silicate ions in mortar consume Ca+2 ions, producing NaOH. Since this is more soluble than Ca(OH)2 it lixiviates quicker, causing the pH to decrease. Lixiviation tests support this theory.In summary, silicate ions are very effective corrosion inhibitors when tested in alkaline solutions. When silicates are used to pretreat the rebars the beneficial effect is lost after 90 days. When solutions containing silicate ions replace water in the mortars´ preparation, the inhibitory effect is lost faster due to the consumption of portlandite and the consequent acidification of the mortars.References Gaidis, J.M., Chemistry of corrosion inhibitors. Cement & Concrete Composites, 2004. 26(3): p. 181. Elsener B., Corrosion inhibitors for steel in concrete. State of the art report. London, ed. M. Publishing. 2001. Montes, F., et al., Silicate Ions as Corrosion Inhibitors for Carbon Steel in Chloride-Contaminated Concrete Pore Simulating Solutions. Corrosion, 2020. 76(12): p. 1147-1154.Rolandi A.C. et al. Corrosion Engineering, Science and Technology 57(5) (2022) 455–463. Figure 1

A feasible re-use of an agro-industrial by-product: Hazelnut shells as high-mass bio-aggregate in boards for indoor applications

The present work investigates the feasibility of producing boards, with unconventional materials, namely hazelnut shells as a high-mass bio-aggregate and a sodium silicate solution as a no-toxic adhesive, and discusses possible applications based on an extensive characterization. The aim is to define a feasible reuse of a largely produced agro-industrial by-product to reduce the high environmental impact caused by both the construction and the agriculture sectors, by proposing a building composite that improves indoor comfort. The presented combination of aggregate-adhesive generated a product with characteristics interesting to explore. The thermal conductivity is moderated, and the composite achieved values of σmax = 0.39 N/mm² for flexural strength and σmax = 2.1 N/mm² for compressive strength, but it showed high sorption capacity with a moisture buffering value of about 3.45 g/(m² %RH), and a peak of sound absorption between 700 and 900 Hz. Therefore, the boards' most promising performance parameters seem to be their high hygroscopicity and acoustic absorption behaviour, namely in the frequency range of the human voice. Hence, the proposed composite could improve indoor comfort if applied as an internal coating board.

Performance assessment and cost analysis of slag/metakaolin based rubberized semi-lightweight geopolymers with perlite aggregate: Sustainable reuse of waste tires

Low-carbon binders or industrial waste can reduce or even eliminate the demand for Portland cement and other natural resources, which reduces environmental pollution in accordance with the principles of sustainable development. The assessment of the mechanical, durability and microstructural properties of slag/metakaolin based rubberized semi-lightweight geopolymer composites (LWGC) with perlite aggregate (PA) is the main objective of this study. Waste tires aggregates (WTA) was produced from discarded waste tires, another environmental pollutant, and used in LWGC mixtures as substitution for the fine perlite aggregate by 0%, 20%, 45%, and 60% replacement. Metakaolin (MK) and ground granulated blast furnace slag (GBFS) were used as precursors in the synthesis of LWGC. Sodium hydroxide and sodium silicate solution was used as activators. Eight mixtures were created; four of them had 100% GBFS, while the other four contained 90% GBFS slag and 10% MK. All eight mixtures were then cured for 5 h at 60 °C and 100 °C. The effects of curing temperature, WTA, and MK on the compressive, flexural strength, physical properties, and sorptivity of the LWGC were examined as well as flowability. The performance of the blends at high temperatures, freeze thaw cycles and sulfate attack was also evaluated. Microstructure analyses of the mixtures were also done using SEM. CO2 emissions and costs of the mixtures were also evaluated. The results showed that inclusion of WTA instead of PA and MK instead of GBFS decreased the flow diameter. Thermal conductivity and dry density of the mixtures also decreased considerably with the addition of WTA. The findings showed that 10%MK incorporated mixture with 60%WTA produced a compressive strength of 25.10 MPa at curing temperatures of 100 °C. The results indicated compressive strength of MK incorporated mixture with 60%WTA increased by 48.10% and 31.20% at heat curing of 60 °C and 100 °C, respectively. The mixture WT60MK0 cured at 100 °C exhibited the best high temperature resistance and the same mixture also presented the best F-T performance regardless of curing temperature. The mixture WT40MK0 cured at 60 °C and the mixture WT60MK10 cured at 100 °C performed the best sulfate resistance.

Mechanical properties of fly ash and silica fume based geopolymer concrete made with magnetized water activator

Using of magnetized water (MW) in the manufacturing of Portland cement concrete has shown promising effects in recent decades. This research investigates the effect of using alkaline activator (AA) solution prepared with MW on producing fly ash (FA) and silica fume (SF) based geopolymer concrete. The MW was prepared by passing tap water (TW) through two permanent magnetic fields of 1.4 and 1.6 Tesla intensities. Sodium hydroxide (SH), potassium hydroxide (PH), and sodium silicate (SS) solutions were the AA used. In total, 28 geopolymer concrete mixes were produced and tested in this study. Half of the mixes was made with the proposed MW (activator and added water), and compared with the other half that made with TW (activator and added water). Variables like; water type (TW or MW), SF content (10%−100%), AA type (SH+SS or PH+SS), AA concentration, AA to cementitious materials (AA/C) ratio, and water to cementitious materials (W/C) ratio were applied in this study. Physical and chemical properties of the utilized water and AA were measured. Concrete fresh and hardened mechanical properties were measured including workability, compressive strength, tensile strength, flexural strength, bond strength, and water absorption. Ultrasonic pulse velocity non-destructive testing was also conducted on the produced concrete. Scanning electronic microscope (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD) analyses were carried out on selected mixes to closely investigate the microstructure of the introduced geopolymer concrete. The results showed that compared with TW, utilizing MW in preparing the AA of geopolymer concrete caused notable increase in the concrete slump with an average of 14%, compressive strength increase by up to 64%, tensile strength increase by up to 60%, flexural strength increase by up to 41%, bond strength increase by up to 40%, and water absorption decrease by up to 38%.

Assessing the engineering properties of massive self-compacting geopolymer concretes utilising the Taguchi method

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.

Properties of flyash based wood geopolymer composite

Geopolymers are inorganic adhesive synthesized from industrial waste such as fly ash thus the development of wood geopolymer composite would be a low carbon footprint material. Geopolymers, being a non-formaldehyde adhesive can be used as an alternative binder for wood based composites where environmentally friendly and sustainability of product is important. In this study flyash as precursor is been used in the development of wood geopolymer composite product. Flyash is activated with a combination of sodium hydroxide and sodium silicate solutions at a weight ratio of 1:2.5 for geopolymer formation. The study investigated the properties of wood geopolymer composite made with ratios of wood particle to flyash percentage (23/77), (37/62), (44/55), (50/50) and (57/43). Geopolymer formation was observed by X-ray Diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Influence of wood particles in wood geopolymer composite were observed by Scanning electron microscope. The study shows that the water absorption and thickness selling properties of all the formulations of wood geopolymer composites are comparable with the medium density particle board and cement-bonded particleboard according to the IS:3087–2005 standard and IS: 12406: respectively. Highest mechanical properties and good bond strength was obtained by the composite containing 23% wood particle ratio with 77% percent flyash. However, still improvement in mechanical properties is needed to achieve the mechanical properties comparable to cement bonded particle board.

Development of super dimensional stable poplar structure with fire and mildew resistance by delignification/densification of wood with highly aligned cellulose molecules

Wood is one of the most popular materials for construction purposes because of its environmentally friendly and sustainable characteristics. However, the use of wood is constrained by the lengthy time it takes for trees to mature. Consequently, fast-growing wood species have become popular as substitute options due to their ability to rapidly reach maturity and high yields. Although the problem of low density and strength has been effectively addressed in recent years by densifying wood, the problem of large thickness swelling due to moisture and water absorption has limited its application. Therefore, we reported an effective modification strategy to overcome the thickness swelling issue of densified wood by preparing a cellulosic reinforced material through the synergistic action of alkaline chemical pretreatment, multi-step cyclic impregnation and high-temperature densification. The results showed that the alkaline chemical pretreatment was effective for removing a large amount of lignin and hemicelluloses, creating a large number of hydrogen bonds among the remaining strong celluloses. The impregnated sodium silicate solution bonded celluloses tightly, and the densification treatment contributed to the production of Si-O-Si structure, forming the shuttle hybridized structure through Si-O-C bonds. The hardness, flexural strength, elastic modulus, and compressive strength of the modified wood increased by 3.9, 6.0, 3.4 and 28.2 times, respectively. In addition, 0 % thickness swelling for 30-day moisture absorption and 1.0 % thickness swelling for 72-hour water absorption were achieved, realizing super dimensional-stable poplar structures. Furthermore, the high-performance densified wood prepared by this method has excellent fire and mildew resistance properties, which lays the foundation for the application of fast-growing wood in outdoor engineering structures.

Acoustic emission characteristics of micro-discharges in initial pulsed PEO process on 60% SiCp/Al composite

The initial discharge process of pulsed plasma electrolytic oxidation (PEO) on the 60% SiCp/2009 aluminum metal matrix composite (Al MMC) in silicate solution was monitored by acoustic emission (AE) technique. Parameters and correlations of AE signals on the Al MMC sample and under water were analyzed, and their generation mechanism was discussed. It was found that the peak amplitudes of AE signals and AE hits during the pulse time quickly increased with the increase of micro-discharge intensity, and the absolute energy of AE signals improved several orders of magnitude. Moreover, different from the peak amplitude, duration and rise time, the duration and count had a strong correlation. Elastic stress waves resulted from the microjet of plasma bubble collapse, the inner-surface friction inside discharge channel, the expansion-shrinkage process of plasma bubbles and micro-crack propagation during rapid solidification of melt are sources of AE signals on the Al MMC sample during the pulse time. However, the expansion-shrinkage process of plasma bubbles plays a key role in the generation of underwater AE signals. In the pause time of one pulse period, the bursting and moving of vapor bubbles result in weak AE signals. It is demonstrated that the AE technique can effectively characterize the features of micro-discharges within a pulse period.

Experimental investigation on trinary blended geopolymer mortar synthesized from Industrial-agro and municipal solid waste ash subjected to different acid exposure

Geopolymer binders prove to be a reliable option to avoid dependency on conventional binders, and reduce the burden on the environment. The current study assesses the durability characteristics of a developed mortar made from a combination of Granulated blast furnace slag (GBFS), Sugar cane bagasse ash (SCBA), and Municipal solid waste ash (MSWA). The Geopolymer mortar specimens were cured under ambient conditions after the ternary blended mix had been activated by a solution of sodium silicate and sodium hydroxide of 8 M (SS/SH-2.5). Mass loss and compressive strength were measured at various time regimes of acid attack studies under mild concentrations of 3% sulphuric acid, hydrochloric acid, and nitric acid. The durability, macroscopic, microscopic, and morphological, studies were carried out. The results indicated that trinary blended geopolymer mortar exposed to sulphuric acid showed less mass loss and high compressive strength retention compared to the control mortar. The nitric acid exposure exhibited comparable strength loss for the trinary blend with control mortar and hydrochloric acid showed negligible effect on mortar. Mass loss was more significant in sulfuric acid than the hydrochloric and nitric acid. RCPT and Carbonation tests revealed that geopolymer mortar exhibits moderate chlorine ion penetration and the ingress of CO2 was less in the trinary blend mix. The mineralogical studies showed the formation of gypsum, nitrate, and chloride products. The optical microscopic image revealed the ingress of sulfuric acid is more intense in the mortar compared to hydrochloric and nitric acid and microstructural studies witnessed the degradation of C-A-S-H supported by EDX.