Soluble Silica Research Articles

PMA-Zeolite: Chemistry and Diverse Medical Applications.

Numerous scientific studies have been conducted in recent decades with the aim to study targeted application of zeolites in various industries, ecology, agronomy and medicine. The biggest advances, however, have been documented in medical and veterinary research of the natural zeolite, clinoptilolite. Although the exact biological mechanisms of action of the zeolite clinoptilolite are not completely elucidated, obtained results point to its antioxidative, immunomodulatory and detoxifying effects, the latter partially based on release of soluble and bioavailable silica forms from the surface material. The studied zeolite clinoptilolite materials have different geographical origins which confer to the physicochemical differences in the material. In addition, the production process of the material for oral applications differs between different producers which also accounts for different properties of the surface upon mechanical activation. Recently, a well-characterized zeolite clinoptilolite material, namely the PMA-zeolite, has been tested in different clinical applications and has shown potential as supportive therapy in inflammatory conditions, osteoporosis as well as during tumor chemotherapy. We accordingly present a comprehensive review of the PMA-zeolite effects in the clinical applications and discuss its probable mechanisms of effect in vivo.

A clean approach to high-strength fly ash-based geopolymers: Multi-granular screening with NaAlO2 enhancement

The limited application of fly ash-based geopolymers in large-scale construction is primarily due to the slow evolution of compressive strength and low early-stage compressive strength. Our research counters this by introducing a method that harnesses the innate reactivity of finer fly ash (FF), significantly enhancing the compressive strength. Experimental and characterization results suggest that the superior performance of FF-based geopolymer is attributable to its higher content of reactive silica-alumina components, an optimal ratio of soluble silica to alumina, and a greater specific surface area, which collectively facilitate the geopolymerization process. Adding just 15 wt% NaOH, the FF-based geopolymer attains a compressive strength of 58.81 MPa after 14 d and an additional 10 wt% NaAlO2 can increase compressive strength to 70.5 MPa, showcasing a method that circumvents the need for energy-intensive milling or activation treatments. For the coarser fractions, thermal activation at 550 °C for an hour markedly improves strength to 39.40 MPa, aligning it with traditionally processed fly ash. This breakthrough paves the way for cleaner, more energy-efficient, and more substantial geopolymer materials in modern construction.

Valorization of aplite in alkali-activated materials

Geopolymers belong to the broad family of alkali-activated materials that are considered to have much smaller carbon dioxide (CO2) footprint than traditional Portland cements. A wide range of metallurgical wastes are utilized as silicious sources to produce geopolymer components with a prospect of numerous applications in the construction field. At the same time, efforts have been also made to the valorization of aplite rock, which is found to be abundant in Finnvolldalen of Norway and consists mainly of quartz and alkali feldspar, resembling the composition of Na-rich pozzolans. In this framework, the current study focuses on the synthesis of inorganic polymers made of aplite and metakaolin as precursors. In addition, the production of synthetic Na-waterglass is also tested as candidate soluble silica donor in geopolymer systems, through the hydrothermal treatment of aplite. The obtained results confirm that inorganic polymers produced by hydrothermally treated aplite (HTA) and metakaolin (MK) lead to materials with enhanced compressive strength values compared to specimens produced by untreated aplite and MK. At the same time, sodium silicate solution from aplite and commercially available waterglass present similar properties, indicating that aplite can be used as alternative raw material in the production of sodium silicates.

Unraveling Parent Rock and Mineral Influences in Tropical Weathering Profiles: REE, Nd and Sr Isotopic Geochemistry

This study aims to investigate the effects of parent rock and minerals on lateritic weathering. The study presents X-ray diffraction (XRD), whole-rock geochemistry, and Nd-Sr isotopic data for examining two profiles, 10 and 12 m thick, respectively, that illustrate the regional tropical weathering status in the Midwest of Brazil. The profiles, developed from metasedimentary and sedimentary rocks, are constituted by saprolite, mottled horizon, lateritic duricrust, and oxisol. Across the profiles, the minerals controlling the weathering geochemistry are muscovite, microcline, quartz, kaolinite, hematite, goethite, and gibbsite. Red and yellow zones in the saprolite and mottled horizon as well as the lateritic duricrust with breccia/fragmental, pisolitic, and oolitic textures make profile 1 more complex. In contrast, profile 2 has an oxisol that mantles the homogeneous vermiform lateritic duricrust. Fe2O3, accumulated during surface weathering, is a potent element in the geochemical profile control since it forms the harder goethite to hematite lateritic duricrust, bearing most of the trace elements (As, Cu, Cs, Pb, Sc, Sr, Th, U, V, and Zn) with similar ionic radii and electrovalence. The LREE have affinity for the elements of the Fe2O3 group of the lateritic duricrust. On the other hand, the K2O group together with Zr and TiO2 e in the phyllite, saprolite, and mottled horizon of profile 1, are associated with the HREE. Additionally, in profile 2, the HREE are mostly associated with the Al2O3 group and the residual minerals in the oxisol. The indication that REE is associated with phosphates, zircon, rutile/anatase, cereanite, and muscovite/illite, which have variable weathering behavior, caused the REE fractionation to occur across and between the profiles. Despite the REE fractionation, the ƐNd(0) values along the profiles consistently maintain the signature of the parent rock. Muscovite and microcline weathering, in profiles 1 and 2, respectively, control the decrease in 87Sr/86Sr signatures of both profiles and the distinct radiogenic ratios. The development of lateritic duricrust in both profiles indicates a similar weathering intensity, although the gibbsite–kaolinite predominance in the oxisol of profile 2 highlights a geochemical reorganization under humid conditions, as well as near-intense soluble silica leaching.

Nutrient dynamics in wetland systems associated with hydrological and anthropogenic variations in the south of Samborombón Bay, Argentina

Wetlands provide numerous ecosystem services to the environment, such as nutrient removal and storage. The aim of this work is to evaluate the nutrient dynamics in different sectors within wetland systems in the south of the Samborombón Bay (Argentina) based on hydrological and/or anthropogenic variations. For this purpose, the hydrological features of the wetland were defined through the analysis of satellite images, precipitation and tidal data, and field surveys. Three sectors were identified in the wetland: one with tidal influence, another which is dependent on rainfall, and another that receives inputs from rainfall and from a sewage effluent treatment plant. In order to analyze the nutrient dynamics, samples of surface water, groundwater, and sediments were collected from these sectors. Measurements of pH and electrical conductivity were determined in situ in water samples, while the concentration of inorganic forms of phosphorus and nitrogen, soluble reactive silica, and organic carbon were determined through laboratory analysis. Also, bioavailable phosphorus, organic matter, pH, and electrical conductivity were determined in the sediment samples collected. Statistical analysis of the data reveals differences between the sectors and allows the interpretation of the dynamics of the studied components in the wetland. Electrical conductivity distinguishes the intertidal sectors of the wetland while components associated with P and N discriminate the sectors with inputs from the sewage effluent treatment plant. On the other hand, soluble reactive silica, organic carbon, and organic matter do not seem to be influenced by the tide or effluent discharge. This study demonstrates that the studied wetland works as a nutrient retention area, providing ecosystem services to local inhabitants. Although these services can be utilized, they require a continuous monitoring over time to provide an early warning in case the variations in P and N cycles could lead to eutrophication or wetland degradation.

Acceleration of Early Strength Development in Mortars Containing Soluble Silica Extracted from Palm Oil Clinker

Soluble silica from palm oil clinker was extracted using Laine’s method. It involved two major steps, namely water reflux and distillation. The use of 480 g of POCP and 12 hours of distillation in the extraction experiment resulted in 53.50% of dissolved silica, which was the highest gain among the trial experiments and was chosen as an optimum parameter for the subsequent characterisation analysis. In addition, its effect on cement hydration was studied by including it as a filler in mortar mixtures. Mortar with 7.50% of extracted silica gained high strength in the early days of curing and performed well throughout the maturing age. The rapid hardening properties of soluble silica-based mortar would promote the potential of soluble silica as an additive for rapid hardening.

Durability, Long-Term, and Environmental Evaluation of Alkali-Activated Alternative Soluble Silica Source for Recycled Asphalt Pavement Stabilization

Durability, Long-Term, and Environmental Evaluation of Alkali-Activated Alternative Soluble Silica Source for Recycled Asphalt Pavement Stabilization

Temporal phytoplankton dynamics and environmental variables in four Ethiopian soda lakes

We investigated the spatio-temporal dynamics of phytoplankton composition, chlorophyll-a as a proxy for algal biomass, and abundance in relation to environmental parameters in four Ethiopian soda lakes: Arenguade, Beseka, Chittu, and Shala. Triplicate water samples were collected from each lake from January to December 2020, four times in different seasons. Lake Chittu had the highest chlorophyll-a concentration, followed by Lake Arenguade, Beseka and Shala. Chlorophyll-a concentrations generally increased during the post rainy and dry season. The results of LR models are high for lakes Arengude, Beseka and Chittu. Lakes Shala and Beseka had the highest number of phytoplankton taxa, with both taxa composition and abundance dominated by Bacillariophyceae. Cyanoprokaryota, particularly Limnospira fusiformis, predominated in the abundance of Lakes Arenguade and Chittu. Water temperature, Secchi depth, turbidity, electrical conductivity, soluble reactive phosphorus, nitrate and silica significantly influenced the phytoplankton community structure. Long-term trend analysis revealed changes in phytoplankton biomass and lake taxonomic composition. The alteration in phytoplankton biomass and species composition of the lakes could be attributed to three factors: (1) frequent high-velocity explosions conducted for seismological studies in the past. This impact caused a dramatic increase in lake level in the case of Lake Beseka leading to a drop in nutrient concentration; (2) climate change and (3) salt content. Overall, our findings suggest that phytoplankton composition, biomass, and abundance varied according to seasonal fluctuations, emphasizing the possible effects of anthropogenic and natural causes on their community structure.

Silica Scaling Inhibition in Water Treatment Process Using Fibrous Al2O3-Nylon 6 Adsorbents

This study describes a novel approach using fibrous Al2O3-Nylon 6 composites to induce inhibition behavior in silica scaling systems. The composite fibers were fabricated with a wet-spinning process using the coagulation of a methanolic Nylon-CaCl2 solution with Al2O3 powder after immersing the thread-like solution in water. The mesoporous nylon fibers composed of Al2O3 powders ranging from 10 to 30 wt% loading demonstrated superior adsorption capabilities to silica in water, behaving with the Freundlich model and exhibiting effective multilayer adsorption onto the Al2O3 sites embedded in the fiber. Furthermore, the composite fibers inhibited silica scaling, even at high concentrations, due to a substantially efficient reduction in soluble silica when the composite fiber was present in the system. The utilization of 15 g of composite fibers resulted in a rapid drop to approximately 30 mg/L within the initial 10 h, which is a considerable improvement compared to the 300 mg/L observed in the fiber-free control sample. Notably, the presence of an elevated fiber content exceeding 7.5 g demonstrated the complete inhibition of silica precipitation. An analysis of the pore volume using nitrogen adsorption experiments before and after silica adsorption showed that silica adsorption resulted in a significant decrease in mesoporous properties at the alumina sites. This indicated an efficient adsorption of silica onto the alumina site, effectively removing silica from the system.

Modulation of growth and chemical element accumulation in <i>Fragaria × ananassa</i> plants <i>in vivo</i> under the effect of silicon chelates

Due to the protective role played by silicon in plants against unfavorable environmental conditions, siliconcontaining preparations are of considerable interest as biostimulants. In this work, a mechanical composite of rice husk and green tea containing soluble silica chelate complexes was used as the source of silicon. The study aims to examine the effect of silicon chelates on the growth and physiological parameters and the chemical composition of Fragaria × ananassa plants (Solnechnaya Polyanka variety) under greenhouse conditions. The plants were watered using water without a mechanical composite (control) or an aqueous solution containing 0.3 g/L of mechanical composite twice per period. Sampling was carried out one week after the last treatment. In order to determine the concentration of chemical elements (Si, P, S, Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, and Mo) in the roots and shoots of garden strawberry, it was proposed to use synchrotron X-ray fluorescence analysis. The use of the mechanical composite was shown to increase the amount of chlorophyll a, chlorophylls a and b, and carotenoids; decrease the amount of hydrogen peroxide; and increase the activity of the main antioxidant enzymes (superoxide dismutase, catalase, and peroxidase). It was determined that under the effect of the preparation, silicon accumulates primarily in shoots, affecting the accumulation of micro- and macroelements in the shoots and roots of plants. The obtained results substantiate the use of silicon-containing “green chemistry” as a means of controlling the growth and development of garden strawberry plants under in vivo conditions.

Relationship between Cyanobacterial Abundance and Physicochemical Variables in the Ebro Basin Reservoirs (Spain)

One of the main problems arising in inland waterbodies is nutrient enrichment that accelerates eutrophication, causing massive cyanobacteria blooms and degrading aquatic ecosystems. This study focused on physical/chemical factors that affect cyanobacteria of 30 reservoirs in the Ebro River basin within the Iberian Peninsula of northeastern Spain. The abundance of cyanobacteria was assessed as total cell number, total biovolume, and the indicator pigment, total phycocyanin (PC). In addition, empirical measurements for PC were compared to PC estimated from remote sensing. Variables assessed for correlation with cyanobacteria abundance included temperature, pH, light availability inferred from Secchi depth, water residence time, total nitrogen, dissolved inorganic nitrogen, total phosphorus, soluble reactive phosphorus, silica, and total phytoplankton biomass as chlorophyll a. These variables were also assessed with a multi-statistical principal component analysis for relationships with cyanobacteria abundance. Cyanobacteria cell number and biovolume were positively correlated with temperature, total nitrogen, total phosphorus, and water residence time, and negatively correlated with silica. High PC concentrations were documented in the reservoirs, and satellite images from remote sensing showed the PC spatial distribution and heterogeneity in the reservoirs. The PCA results show that some variables, such as nitrogen and phosphorus, are closely related to the abundance of cyanobacteria, while other variables such as silica do not show a clear relationship. This study contributes to the knowledge base about inland waterbodies from a physical/chemical perspective, which had not been done before in the Ebro Basin, including the application of analytic tools such as remote sensing.

Seawater used to Metakaolinite-based geopolymer preparation

The use of seawater (SW) to prepare geopolymers has attracted increasing attention, for its potential to save fresh water and reduce carbon dioxide emission. However, the ions in SW influence the geopolymers. This study investigated the effects of SW concentration on the microstructure and mechanical properties of metakaolinite (MK)-based geopolymers with different Si/Al molar ratios (1.3, 1.6, and 2.0). The compositions and structures of the obtained geopolymers were characterized via several techniques, including X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and mercury intrusion porosimetry.With an increasing Si/Al molar ratio, the high soluble silica content promoted geopolymer formation, further increasing the microstructure density and compressive strength of the geopolymer. The reaction between MK and alkaline solution with an Si/Al ratio of 1.3 resulted in the formation of a zeolite A-containing geopolymer, which exhibited a 28-day compressive strength of only 12.7 MPa. SW addition did not significantly influence the geopolymer microstructure and mechanical properties, but zeolite formation was inhibited with increasing SW concentration.In contrast, geopolymers with Si/Al ratios of 1.6 and 2.0 exhibited a dense microstructure, with 28-day compressive strengths of 35.0 and 57.5 MPa, respectively. The SW-mixed geopolymers exhibited a lower compressive strength than the pure water-mixed geopolymers. With increasing SW concentration (artificial SW), the geopolymer compressive strengths gradually decreased, but to a limited extent. The ions in SW altered the geopolymer composition, resulting in the formation of some salts. The formation of these salts negatively influenced the microstructure and pore size distribution of the geopolymer, thereby reducing its compressive strength. In addition, Cl- was distributed in the geopolymer matrix, but SO42- underwent precipitation at a high concentration of artificial SW.Overall, the results showed that the ions in SW reduced the compressive strength slightly by changing the microstructure and composition of the MK-based geopolymer. These findings suggest that SW-mixed MK-based geopolymers can be suitably used as building materials in the marine environment.

Ophthalmic glass lens waste as an alternative soluble silica source for alkali-activation reactions

This research study was aimed at assessing the potential use of glass powder (GW), from the production of optical lenses, as a substitute of commercial sodium silicate (SS), to produce fly ash-based alkaline cements. The dissolution of the GW and the subsequent activation were achieved either with a cleaning solution (CS) from the aluminium casting industry, and a commercial sodium hydroxide solution (SH) so as to. Firstly, GW dissolution with CS and SH was evaluated at different time and temperatures, i.e.,16 h, 3, 7 and 28 days at 20 °C and 16 h at 20, 40, 60 and 80 °C, to find the best dissolution rate, which an optimum point was observed when CS was the dissolving agent. Then, several pastes were synthesized and cured for 7 days at 50 °C to assess their mechanical behaviour and alkaline-activated gel formation by compressive strength test. Furthermore, reaction products were characterized by X-ray diffraction (XRD) and electron microscopy (SEM/EDX). The observations reveal that although SH solution acted well to dissolve GW, so that the compressive strength was close to that of SS, CS also showed reasonable potential to be used as a dissolving agent for GW, rendering a cheap and environmentally friendly alternative activator. Microstructural analysis also illustrated the rise in the crystallinity of the reaction products obtained from industrial by-products, i.e., GW and CS.

Preparation of Artificial Aggregates from Marine Dredged Material: CO2 Uptake and Performance Regulation

A continuous treatment process using steel slag powder including foam drying and carbonation processes (termed the SSFD-C method) is a novel technology previously developed in our laboratory. It has achieved the first application of carbonation solidification technology to recycle marine dredged material with high moisture content. The aim of this study is to investigate CO2 uptake and performance regulation in the preparation of carbonated eco-aggregates (CEAs) from dredged soils processed using the SSFD-C method. Steel slag and lime hydrate independently contribute to the strength of CEAs. However, the influence they exert on CO2 uptake, along with other properties, such as pH values and water absorption of CEAs, remains unclear. Furthermore, it is important to clarify whether the soluble silica in a CEA originates from dredged soil or steel slag, as a CEA has the potential to provide silica nutrients to plants. The findings indicated that within the initial three hours of carbonation, the strength of CEAs could approximate 65% of the ultimate stable strength. The moisture absorption for CEAs was noted to be in the 26–30% range. Carbonation over a 24 h period can lower the pH of the CEA to less than 10, and the carbonation reaction can penetrate the core of the 10–15 mm CEA pellets. Carbonation of the lime hydrate fraction was more favorable to increase the CO2 uptake of the CEA, and carbonation of the steel slag fraction was more favorable to decrease the pH value and water absorption of the CEA. The water-soluble silicon of the CEA was found to have been mainly derived from steel slag, while it was established that carbonation could increase the water-soluble silicon content of the CEA by 5–8 times. The result of this study could provide theoretical guidance for regulating the performance of CEAs.

Utilizing Robust Design to Optimize Composite Bioadhesive for Promoting Dermal Wound Repair.

Catechol-modified bioadhesives generate hydrogen peroxide (H2O2) during the process of curing. A robust design experiment was utilized to tune the H2O2 release profile and adhesive performance of a catechol-modified polyethylene glycol (PEG) containing silica particles (SiP). An L9 orthogonal array was used to determine the relative contributions of four factors (the PEG architecture, PEG concentration, phosphate-buffered saline (PBS) concentration, and SiP concentration) at three factor levels to the performance of the composite adhesive. The PEG architecture and SiP wt% contributed the most to the variation in the results associated with the H2O2 release profile, as both factors affected the crosslinking of the adhesive matrix and SiP actively degraded the H2O2. The predicted values from this robust design experiment were used to select the adhesive formulations that released 40-80 µM of H2O2 and evaluate their ability to promote wound healing in a full-thickness murine dermal wound model. The treatment with the composite adhesive drastically increased the rate of the wound healing when compared to the untreated controls, while minimizing the epidermal hyperplasia. The release of H2O2 from the catechol and soluble silica from the SiP contributed to the recruitment of keratinocytes to the wound site and effectively promoted the wound healing.

Silica-Coated Micrometer-Sized Latex Particles.

A series of silica-coated micrometer-sized poly(methyl methacrylate) latex particles are prepared using a Stöber silica deposition protocol that employs tetraethyl orthosilicate (TEOS) as a soluble silica precursor. Given the relatively low specific surface area of the latex particles, silica deposition is best conducted at relatively high solids to ensure a sufficiently high surface area. Such conditions aid process intensification. Importantly, physical adsorption of chitosan onto the latex particles prior to silica deposition minimizes secondary nucleation and promotes the formation of silica shells: in the absence of chitosan, well-defined silica overlayers cannot be obtained. Thermogravimetry studies indicate that silica formation is complete within a few hours at 20 °C regardless of the presence or absence of chitosan. Kinetic data obtained using this technique suggest that the adsorbed chitosan chains promote surface deposition of silica onto the latex particles but do not catalyze its formation. Systematic variation of the TEOS/latex mass ratio enables the mean silica shell thickness to be tuned from 45 to 144 nm. Scanning electron microscopy (SEM) studies of silica-coated latex particles after calcination at 400 °C confirm the presence of hollow silica particles, which indicates the formation of relatively smooth (albeit brittle) silica shells under optimized conditions. Aqueous electrophoresis and X-ray photoelectron spectroscopy studies are also consistent with latex particles coated in a uniform silica overlayer. The silica deposition formulation reported herein is expected to be a useful generic strategy for the efficient coating of micrometer-sized particles at relatively high solids.

A New Method to Predict Final Products of Red Mud-Slag-Based Alkali-Activated Materials Using Complete Phase Analysis of Precursors

This paper presents a new method for predicting the final products of red mud-slag-based alkali-activated materials (RM-AAMs) using comprehensive phase analysis. As the first step, a quantitative method by X-ray diffraction (XRD) was used to analyze six different types of red mud and ground-granulated blast-furnace slag (GGBS). Secondly, X-ray fluorescence (XRF) was employed to determine the bulk elemental oxide contents of the precursors. A procedure combining XRD and XRF was then used to quantify both the crystalline and amorphous components of the precursors. In addition to investigating precursors, soluble silica from sodium silicate has been considered in calculating reactive silica. The research includes forty sets of alkali-activated samples using various activators with different concentrations. The XRD results of hardened paste samples revealed that the method could successfully predict the final products of RM-AAMs. By predicting the final products of the alkali-activation process, the optimization of raw material types and contents will be more efficient. For example, in the case of having C-S-H as the final product, adding substances with high reactive alumina would be unnecessary.

Unusual yield stress behaviour of silica suspensions in the presence of maleic and fumaric acids: Composite precipitate bridging

There are many instances of unusual colloidal suspension behaviour being reported. This study provided a new approach to finding the cause of one such behaviour helping to alleviate biofouling and scaling problems. The yield stress-pH behaviour of silica suspensions in the presence of maleate and fumarate is different depending upon the direction of the step change in the pH employed. In the direction from high to low pH, i.e. 11–2, the suspension displayed a continuous yield stress behaviour down to pH 6. In the opposite direction, the yield stress was small at pH 4–5, absent at pH 8.5 and increased sharply from pH ∼ 9.5. Precipitate bridging is responsible for the yield stress behaviour. At high pH, the precipitates were already well-formed to bridge particles. This was not the case in the low to high pH direction. The precipitates were composite formed by soluble silica, organic acid anion and positively charged metal ions hydrolysis products. Yield stress was observed under the conditions of i) high silica solubility, i.e. at pH > 9 and ii) fumaric or maleic acids being present in significant concentration. The Al(III), Fe(III) and Fe(II) impurities already present in relatively important quantity formed the hydrolysis products upon leaching or solubilisation of the silica. The composite precipitates bridged the silica particles via heterogeneous charge and van der Waals attraction. Their formation is limited by the amount of Al(III), Fe(III) and Fe(II) present and they must be small enough to be in sufficient number to have all the particles in the network bridged. Fumarate played a role in forming and stabilising the small precipitate particles, and enhancing the yield stress. Biofouling and scaling in processes involving this type of composite materials can be mitigated by making sure that a high pH operating environment is avoided.

Rice husk ash as an alternative soluble silica source for alkali-activated metakaolin systems applied to recycled asphalt pavement stabilization

Alkali-activated binders have been shown as a viable alternative do ordinary Portland cement. However, the development of lower carbon emission activators for this process is still a research-gap. The goal of this research was to analyze the stabilization of recycled asphalt pavement (RAP) mixtures with a metakaolin-based binder, alkali-activated by rice husk ash synthetized sodium silicate. Compaction, unconfined compressive strength (UCS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests were conducted in stabilized RAP mixtures, submitted to different curing periods and temperatures. Also, results were correlated with the porosity/binder content index. Compaction results showed a reduction in dry unit weight as the RAP content increased for non-stabilized mixtures and a non-linear behavior for stabilized ones. For the UCS tests, the increase in binder content led to an increase in strength for all mixtures. High curing temperatures prevented the efflorescence phenomenon, however reduced strength due to crack formation. XRD analyzes showed the formation of minerals rich in silica and alumina, indicating the formation of geopolymerization products. Finally, the porosity/binder index was shown to be a viable dosage method to predict the strength of stabilized RAP mixtures.

Design of Online Detection System of Boiler Water Quality Based on STM32

Industrial boilers have strict requirements for water quality. It is necessary to adjust water treatment measures and regular blowdown according to the monitoring of phosphate and soluble silica content in boiler water to avoid boiler scaling, corrosion, and deterioration of steam quality, and prevent major accidents. The traditional boiler water quality detection technology has a strong lag and long detection time, which cannot meet real-time online detection. Aiming at the requirement of detection of phosphate radical and soluble silica content in boiler water quality, a portable and low-cost online detection system of boiler water quality based on STM32 was studied. The pump valve flow path is constructed with a syringe pump equipped with a syringe and a distribution valve, LED and silicon photocell are used for the light source and detector of the system respectively, and the photoelectric detection part is composed of a designed Z-shaped flow cell, which reduces the experimental cost; Design a data acquisition circuit based on STM32 microcontroller and a 16-bit high-precision analogy-to-digital converter, as well as a constant-current drive circuit for driving LED light sources, to improve the stability and high precision of the automatic measuring instrument. The system test results show that the boiler water quality online detection system based on STM32 can accurately detect the phosphate and soluble silica concentrations in boiler water quality.