Augmented Simplex-centroid Design Research Articles

Optimizing Ultrasonic-Assisted and Microwave-Assisted Extraction Processes to Recover Phenolics and Flavonoids from Passion Fruit Peels.

This study optimized the ultrasonic-assisted extraction (UAE) and microwave-assisted extraction (MAE) processes to acquire phenolics and flavonoids from passion fruit peels using a mixture of ethanol, acetone, and water. An augmented simplex-centroid design was employed to find the suitable volume ratio among solvent ingredients to attain the highest extraction yield of phenolics and flavonoids. One-factor experiments were conducted to investigate the influence of UAE and MAE parameters on the recovery yield of phenolics and flavonoids before the two processes were optimized using Box-Behnken Design (BBD) models. The optimal UAE conditions for recovering phenolics and flavonoids from passion fruit peel powder (PFP) were 28 mL/g of liquid-to-solid ratio (LSR), 608 W of ultrasonic power, and 63 °C for 20 min to acquire total phenolic content (TPC) and total flavonoid content (TFC) at 39.38 mg of gallic acid equivalents per gram of dried basis (mg GAE/g db) and 25.79 mg of rutin equivalents per gram of dried basis (mg RE/g db), respectively. MAE conditions for attaining phenolics and flavonoids from PFP were 26 mL/g of LSR and 606 W of microwave power for 2 min to recover TPC and TFC at 17.74 mg GAE/g db and 8.11 mg RE/g db, respectively. The second-order kinetic model was employed to determine the UAE and MAE mechanism of TPC and TFC and the thermodynamic parameters of the extraction processes. The antioxidant activities of passion fruit peel extracts at optimal conditions were examined to compare the efficiency of UAE and MAE. This study establishes an effective approach for obtaining phenolics and flavonoids from passion fruit peels.

Optimisation of the anaerobic co-digestion process of Calotropis procera leaves, stems, and cow dung using a mixture design

Batch tests were carried out to evaluate the biogas production potential of the co-digestion of Calotropis Procera and cow manure. An augmented simplex centroid design was used to establish the mixture proportions for the co-digestion process. Cow dung, Calotropis procera leaves, and Calotropis procera stems were the three components that went into forming the mixtures. Before and after the digestion process, each mixture combination was analyzed for Total Solids content, Volatile Solids content, and pH. Cumulative biogas production, cumulative methane yield, and the percentage of volatile solids reduction were the responses utilized to evaluate the performance of the reactors. The Response Surface Methodology was used in order to determine the optimal combination that would result in the maximum amount of biogas and bio-methane generation. Contour, 3D surfaces and residual plots were used to locate and display the regions that showed the best performance in terms of responses. The results showed that the optimal proportions for maximum biogas yield, cumulative methane production, and percentage reduction in volatile solids were 17.17% leaves and 82.83% stems. The study has thus revealed that the co-digestion of Calotropis Procera leaves with stems is more significant than that of the mixtures containing cow dung. The findings of this study suggest that although the co-digestion of Calotropis Procera with cow dung is a viable solution for improving the biogas production, the co-digestion of Calotropis Procera leaves and stems has a higher yield.

Characteristics, microstructures, and optimization of the geopolymer paste based on three aluminosilicate materials using a mixture design methodology

This study focuses on the application of mixture design as a novel approach to developing a geopolymer paste with optimized mechanical properties. It also aims to utilize the abundance of natural or industrial aluminosilicate precursors through their combination for synthesizing high-performance geopolymers. The synthesis factors studied are kaolin (K), metakaolin (MK), and fly ash (FA) as aluminosilicate sources. Different mixture proportions were prepared by adopting an augmented simplex-centroid design. Twelve geopolymer pastes were synthesized by activating the mixtures with an alkaline solution of sodium hydroxide and sodium silicate. After 28 days of solidification under ambient conditions, the compressive strength (MPa) and bulk density (g/cm3) of the geopolymer samples were measured. The structural and microstructural properties of the raw and elaborated materials were analyzed using a range of physicochemical techniques, including X-ray Fluorescence (XRF) spectroscopy, X-ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR) spectroscopy, Scanning Electron Microscopy combined with Energy Dispersive Spectroscopy (SEM/EDS), and Transmission Electron Microscopy (TEM). The results showed that the compressive strength and bulk density of the geopolymeric pastes ranged from 7.59 to 19.48 MPa and from 1.52 to 1.82 g/cm3, respectively. According to the validated special cubic models and optimization results, the optimum mixture of FA (75 %) and MK (25 %) was found to develop the optimized geopolymer (GPO) paste with the best performance. The optimized geopolymer matrix had a non-porous structure mainly formed by a dense amorphous sodium aluminosilicate gel, which gave excellent mechanical properties (1.82 g/cm3 and 20.80 MPa). The practical application of the results of this study includes the development of an efficient geopolymer paste with excellent mechanical properties that can be employed in construction and civil engineering applications. The significance of this work lies in its potential to reduce environmental impacts and minimize waste disposal by utilizing abundant natural resources and industrial waste in the formulation of practical and efficient products. Overall, this study provides valuable insights into the development of an improved geopolymer paste through the application of a mixture design methodology, which can have a significant impact on the construction and civil engineering industries.

Optimization of antibacterial activity of essential oil mixture obtained from three medicinal plants: Evaluation of synergism with conventional antibiotics and nanoemulsion effectiveness

• Mixture design of L. maroccana, T. vulgaris and A. leucotricus were established. • Synergistic interactions were recorded and optimized EO mixture was defined. • Optimal mixture decreased the antibiotics MICs by 2- to 64-fold. • Optimized EO mixture showed high antibacterial effect in nanoemulsion. The present study aimed to optimize the antibacterial activity of essential oil (EO) mixture obtained from Ammodaucus leucotrichus Cosson, Thymus vulgaris L. and Lavandula maroccana (Murb.) against three multi-drug resistant bacteria, using augmented simplex-centroid design. GC–MS analysis showed that A. leucotrichus EO was characterized by the abundance of l -perillaldehyde (50.39%), d -limonene (21.61%) and bornyl angelate (7.09%). T. vulgaris EO was dominated by thymol (42.34%), p -cymene (19.71%) and γ-terpinene (11.50%), while carvacrol (71.62%) represents the main component of L. maroccana EO. Regarding antibacterial assays, individual EOs displayed moderate activity with MIC and MBC values ranging from 0.06% to 5.00%, while the coefficient terms of the different tested combinations revealed synergistic interactions. The results of predicted optimization showed that the optimal EOs mixture composed by 55% of T. vulgaris, 41% of L. maroccana and 4% of A. leucotrichus, significantly decreased the MICs against Staphylococcus aureus (0.0225%), Escherichia coli (0.05%) and Pseudomonas aeruginosa (0.688%). The optimal mixture exhibited a significant decrease in the MICs of gentamicin (4-fold) and amoxicillin (2- to 64-fold), and achieve the highest antibacterial effect in nanoemulsion formulation. The optimized EO mixture based on the studied plants should be considered as a potential alternative to control foodborne, and resistant bacteria.

Nutritional and Rheological Characterization of an Infant Flour Based on Parboiled Rice (Oryza sativa), Spirulina (Spirulina platensis), and Cashew Nut (Anacardium occidentale).

Protein-energy malnutrition and mineral deficiencies in children under five years are major problems in developing countries. The present study was thus carried out with the aim of proposing a weaning flour based on parboiled rice, spirulina, and cashew nut that meets the nutritional needs of children aged 06 to 24 months. To achieve this, the mixture design approach (a 9-point augmented simplex-centroid design) was used to obtain optimal blend of flour. The responses evaluated where proteins, lipids, carbohydrates, minerals (iron, calcium, phosphorus, potassium, sodium, magnesium, and zinc), carotenoids, fibers, and ash content. The rheological analyses (rapid viscosity analysis) were carried out on the optimal flour. It results that the optimal proportion of parboiled rice, spirulina, and cashew nut was, respectively, 85.80, 5.96, and 8.23. These conditions result in a protein, lipids, carbohydrates, carotenoids, ash, fibers, calcium, iron, magnesium, and zinc content of 14.15%, 9.04%, 68.46%, 8.2 mg, 3% ash, 4.98%, 510 mg, 16 mg, 65 mg, and 5 mg, respectively, and an energy value of 411.8 kcal. These optimate conditions resulted also in a peak viscosity of 60 cP and a final viscosity of 86 cP which are lower than the established value (1000 cP). Thus, the weaning flour based on parboiled rice, spirulina, and cashew nut obtained in these optimate conditions can meet the nutritional needs of children aged 06 to 24 months and is therefore an efficient weaning food to fight against child malnutrition.

Application of Augmented Simplex Centroid Design for Optimization of HPLC Mobile Phase for Estimation of Curcumin and Piperine

Application of Augmented Simplex Centroid Design for Optimization of HPLC Mobile Phase for Estimation of Curcumin and Piperine

Antimicrobial combined action of Mentha pulegium, Ormenis mixta and Mentha piperita essential oils against S. aureus, E. coli and C. tropicalis: Application of mixture design methodology

Experimental design methodology (mixture design) coupled to microdilution assay were used to study the potential interactions between several active compounds from three Moroccan essential oils (EOs) (M. pulegium, O. mixta and M. piperita) against S. aureus E. coli and C. tropicalis, to increase their sensitivity and to predict optimal formulations. EOs extraction was firstly obtained by hydrodistillation, then, their chemical composition was determined by GC/MS and their antimicrobial activity was evaluated. The optimization of antimicrobial activity of essential oils mixtures by augmented simplex-centroid design allowed us to model and validate statistically as well as to establish a prediction profile of the studied phenomena. The optimization of mixtures antimicrobial activities has highlighted the synergistic effect between M. piperita and M. pulegium essential oils. The optimal mixture predicted against E. coli, S. aureus and C. tropicalis corresponded to 54%/46%; 56%/44% and 55%/45% of M. piperita and M. pulegium essential oils, respectively. This study shows that the combination of essential oils may be applicable in the fight against emerging microbial drug resistance or useful as natural food preservatives.

Application of Simplex-Centroid Design Methodologies to Optimize the Anti-bacterial and Anti-candidal Activity of the Mixture of Mentha pulegium, Pituranthos chloranthus and Thymus algeriensis Essential Oils

This work aims to study the antimicrobial activities of the essential oils of M. pulegium, P. chloranthus and T. algeriensis and to identify the antagonistic or synergistic impacts of their combinations. Antimicrobial activities were analyzed by disc diffusion and microdilution against six foodborne microbial strains (Staphylococcus aureus, Bacillus cereus, Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa and Candida albicans). That's why, to predicate the optimal mix, we are using the Augmented Simplex Centroid Design. The chemical composition shows that the main compound of M. pulegium were pulegone (50.31%) and menthone (26.92%). For P. chloranthus EO, The major constituents were dillapiole (13.56%) and pregnane (8.47%) and the main products of T. algeriensis EO are Camphor (14.06%), β-Phellandrene (13.71%) and α-pinene (8.55%). The antimicrobial activity of the three studied EOs confirms the highest antibacterial activity of T. algeriensis and P. chloranthus EO against a lower antibacterial activity of M. pulegium EO. Moreover, the response surface analysis showed significant synergistic effects in some binary and ternary mixtures. The optimal mixture predicted against C. albicans corresponded to 12%, 35% and 53% of M. pulegium, P. chloranthus and T. algeriensis EOs, respectively. While the optimal mixture predicted against S. aureus was composed by P. chloranthus and T. algeriensis essential oils at 84% and 16%, respectively. Similarly, this binary mixture, between P. chloranthus and T. algeriensis, presented optimal antimicrobial activity against P. aeruginosa composed by essential oils at 20% and 80%, respectively. Generally, the combination between 19% M. pulegium, 41% P. chloranthus and 40% T. algeriensis consisting the optimal ternary mixture Eos. Our findings show that by the use of mixture design we can predict antibacterial interaction of essential oils. Therefore, it can be used as a natural antimicrobial agent and a food additives.

Intra-combined antioxidant activity and chemical characterization of three fractions from Rhamnus alaternus extract: Mixture design

The look for benefits antioxidant agents has attracted much attention from consumers, health and food industries. Certainly, the interactions occurring between different compounds affect the antioxidant efficiency. The current study aims the investigation of the antioxidant combined effect of Rhamnus alaternus fractions using DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate) assay. The three most active fractions were subject for binary and ternary combinations using the augmented simplex-centroid design. Two known compounds emodin (1) and kaempferol (2) were identified from the ethanolic extract of the leaves of Rhamnus alaternus. Their structures were elucidated using spectroscopy data. The antioxidant potent of the crude extract and the mixture was compared with the antioxidant activity of the fractions separately. Important synergetic effects were observed in binary mixture between the most active fractions, besides the response optimizer allowed us to optimize the mixture presenting the highest antioxidant activity at 82.54 %. The results from the present work could have interesting applications in both medical formulations and functional food design.

Anaerobic co-digestions of agro-industrial waste blends using mixture design

Batch assays were performed under a stressed condition during the anaerobic digestion process to assess the effect of component proportions on the quantity and pattern of biochemical methane yield of two sets of mixtures, consisting of poultry droppings (PD) with sugarcane bagasse (SB) and press mud (PM) for set A and PD with sugar beet roots and tops (SBRT) and PM for set B. Augmented simplex centroid design was used to design the mixture composition for the anaerobic co digestion. The reactor performances were assessed under identical conditions using cumulative methane yield (CMY) and percentage volatile solids destruction (PVSD) as the criteria. The maximum volume of methane were obtained 48.5 NL CH4 kg−1 VS at mixture proportion of 66.67% of PM, 16.665% of PD and 16.665% of SB for set A and 44 NL CH4 kg−1 VS at mixture proportion of 50% of PM and 50% of PD for set B. Synergistic effect were observed by adding a greater proportion of PM for both the sets of A and B. Antagonistic effect were obtained by adding a greater proportion of SB for set A and a higher proportion of SBRT for set B. Response surface methods and modeling were used to find out optimum mixture combinations for maximizing the methane production. From the optimization plots, the use of PD having the antagonistic effect was found for both the sets of A and set B.

Optimized Extraction of Antioxidants from Olive Leaves Using Augmented Simplex Centroid Design

ABSTRACTThe olive tree historically provided economic benefits to the countries in Mediterranean basin as a source of products contributing to health promotion. Some of the health benefits attributed to olive tree leaves are related to phenolic composition. In this study, a 10-point augmented simplex-centroid design was used to formulate a three-component mixture system using water, ethanol, and methanol, adequate for the extraction of phenolics from olive leaves. Phenolic and flavonoid content, antioxidant activity with 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), oleuropein, and luteolin7-O-glucoside concentrations were selected as responses. The optimal extraction mixture was: 12.7% water, 14.8% ethanol, and 72.5% methanol. The yields of total phenolic and flavonoid compounds, oleuropein, and luteolin-7-O-glucoside were 163.69 ± 6.35 mg gallic acid g−1, 114.69 ± 3.56 mg rutin g−1, 858.29 µg g−1, and 21.04 µg g−1 dry weight of olive leaves. The antioxidant capacity was 238.71 ± 4.35 mM equivalent Trolox per g−1 dry weight of olive leaves.

Experimental design of mixture for the anaerobic co-digestion of sewage sludge

Batch experiments were conducted for assessing the biogas generation potential of two sets of mixtures (set A and set B). Mixtures consisting of sewage sludge with cow dung and garden waste were studied with set A, whereas mixtures consisting of sewage sludge with cow dung and fruit juice wastewater were studied with set B. Augmented simplex centroid design was used to design the mixture composition for the anaerobic co-digestion. The reactor performance was assessed using cumulative methane volume and percentage volatile solids destruction as the criteria. Synergetic effect was found to be 9.71% of garden waste (GW), 20.29% of cow dung (CD) and 70% of sewage sludge (SS) in set A and 75.5% of SS and 24.5% of CD in set B. Antagonism was observed with the mixes containing garden and fruit juice wastewater (FJW) with the SS. The reason may be due to the rapid acidification of FJW which leads to the soaring of the reactor. In case of GW, the substrate was limiting and the biogas production was negligible after 10th day. Response surface methods were used to find out optimum mixture combination for maximising the biogas production.

Optimization of the fermentation media for sophorolipid production from Candida bombicola ATCC 22214 using a simplex centroid design

This article describes the use of a simplex centroid mixture experimental design to optimize the fermentation medium in the production of sophorolipids (SLs) using Candida bombicola. In the first stage, 16 media ingredients were screened for the ones that have the most positive influence on the SL production. The sixteen ingredients that were chosen are five different carbohydrates (fructose, glucose, glycerol, lactose, and sucrose), five different nitrogen sources (malt extract, peptone extract, soytone, urea, and yeast extract), two lipid sources (mineral oil and oleic acid), two phosphorus sources (K(2)HPO(4) and KH(2)PO(4)), MgSO(4), and CaCl(2). Multiple regression analysis and centroid effect analysis were carried out to find the sugar, lipid, nitrogen source, phosphorus source, and metals having the most positive influence. Sucrose, malt extract, oleic acid, K(2)HPO(4), and CaCl(2) were selected for the second stage of experiments. An augmented simplex centroid design for five ingredients requiring 16 experiments was used for the optimization stage. This produced a quadratic model developed to help understand the interaction amongst the ingredients and find the optimal media concentrations. In addition, the top three results from the optimization experiments were used to obtain constraints that identify an optimal region. The model together with the optimal region constraints predicts the maximum production of SLs when the fermentation media is composed of sucrose, 125 g/L; malt extract, 25 g/L; oleic acid, 166.67 g/L; K(2)HPO(4), 1.5 g/L; and CaCl(2), 2.5 g/L. The optimal media was validated experimentally and a yield of 177 g/L was obtained.

Mixture design as first step for improved glutaminase production in solid-state fermentation by isolatedBacillussp. RSP-GLU

Investigation of mixture-design impact on glutaminase production by isolated Bacillus sp. An augmented simplex centroid design was used to optimize a three (wheat bran, Bengal gram husk and palm seed fibre) component mixture for glutaminase production. Selected substrate materials showed impact on glutaminase production values at individual level by Bengal gram husk [2789 U gds(-1) (gram dry substrate] and in two-level combination with wheat bran and Bengal gram husk (maximum of 3300 U gds(-1)). Bengal gram husk is the most suitable substrate medium for glutaminase production by Bacillus sp. Maximum glutaminase production is achieved using solid-substrate mixture at two-level combinations in the ratio of 66 : 34 for Bengal gram husk and wheat bran, respectively. The present study has significance in large-scale production of glutaminase at commercial level with the use of multi-substrate rather than single-substrate/support material.

Monitoring of paintings under exposure to UV light by ATR-FT-IR spectroscopy and multivariate control charts

This paper concerns the improvement of a method, already applied for the conservation state monitoring of wooden and painted surfaces, to a system closely simulating a real artwork, namely a canvas painted with mixtures of three organic pigments (Alizarin, Permanent Red, Phtalocyanine Green). Ten mixtures of these pigments, according to an augmented simplex-centroid design, were prepared, mixed with linseed oil and spread on 10 cotton canvas strips. Drying ended, all the samples were analysed by ATR-FT-IR spectroscopy to describe the superficial variability in normal conditions of conservation, i.e. when no degradation is present. Successively, the samples were exposed to artificial UV light simulating the action of an aggressive portion of sunlight. The IR spectra of the surfaces were regularly acquired to monitor the superficial changes due to the UV aggression. Treatment ended, a chemometric study based on the Principal Component Analysis of the spectroscopic data collected both in normal conditions of conservation and during the artificial accelerated ageing, was performed and the multivariate Shewhart and Cusum control charts were built with the scores of the significant PCs (principal components). PCA based control charts showed to be able to identify the presence of significant changes of the painted surfaces, to identify the starting of the degradations and to provide insights about the chemical alterations induced by the UV exposure.

Multivariate calibration applied to the field of cultural heritage: Analysis of the pigments on the surface of a painting

This paper concerns a first attempt of application of multivariate calibration to the field of cultural heritage for the determination of the superficial pigments composition of a painting. For this purpose, 10 mixtures of three organic pigments (Alizarin, Permanent Red and Phtalocyanine Green) selected by an augmented simplex-centroid design were mixed with linseed oil and spread on 10 cotton canvas strips. Each sample was characterised with three genuine replicates of an ATR-IR spectrum. Three calibration models, responding to the relative concentration of each specific pigment in the mixtures, were built with the partial least squares (PLS1) algorithm, using the ATR-IR spectra of the surfaces as predictors. The three mixtures corresponding to the augmentation of the simplex-centroid design were used to validate the model predictive ability which proved to be very satisfactory, with very low root mean squared error of prediction (RMSEP). Finally the models were successfully applied to a real painting, to predict the concentrations of some unknown mixtures of the three studied pigments. This work might have possible applications in the determination of the composition of dyes in real paintings to obtain information on the execution technique and for restoration purposes.

Statistical analysis of process and composition factors affecting the leaching of heavy metals from fly ash solidified/stabilized wastes

The results of an extensive series of experimental Toxicity Characteristic Leaching Procedure (TCLP) tests on the leaching behavior of heavy-metal containing wastes solidified/stabilized by compacting the waste with pozzolanic fly ash are given. The test simulates the behavior of the waste by contacting it with an acidic media during 18 h with continuous agitation. The two heavy metals studied (chromium and cadmium) were selected based on the pH at which their minimum solubility occurred. Even though aluminum is not considered a heavy metal, it was also included in this study since its minimum solubility occurred at a lower pH than the other two metals. Six process factors were studied using a combined 2 6–3 fractional factorial design and the composition was studied using an augmented simplex-centroid design. Process factors included acid strength, acid/waste ratio, slurry pH, ash/slurry ratio, pressure, and aging time. Statistical analysis of the TCLP data obtained after 18 h of leaching showed that the factors which significantly affected the results depended on the specific response metal being studied. Only the process factor, aging time, was statistically significant for all of the responses. The composition of the waste did affect only the cadmium response. The results obtained in this study will contribute to understanding the leaching behavior of hazardous materials contained in solidified/stabilized fly ash wastes.

Determination of Optimum Ingredients for Phosphogypsum Composite Stability under Marine Conditions-Response Surface Analysis with Process Variables

The construction of mixture designs and the methods of response surface analysis of mixture data are discussed and applied for determining the optimum ingredients for stabilized phosphogypsum (PG) composites conducive to marine application. Of particular importance is the ability of the composites to maintain physical integrity when submerged. Therefore, potential indicators for the survivability of the stabilized PG composites were also screened. The triangular coordinate system was used to present the three ingredient components of the PG composites as well as their dependent variables. The augmented simplex centroid design with pseudocomponents was used in determining mixture ingredient composition. A quadratic model with two process variables was used to analyze the experimental results and predict the optimum ingredient composition. The model predicts that a series of PG: class C fly ash:portland type II cement ingredients, such as 62%:35%:3% PG:class C fly ash:portland type II cement and 65%:31%:4% ...

Stabilization of phosphogypsum using class C fly ash and lime: assessment of the potential for marine applications

Phosphogypsum (PG, CaSO 4·H 2O), a solid byproduct of phosphoric acid manufacturing, contains low levels of radium ( 266 Ra ), resulting in stackpiling as the only currently allowable disposal/storage method. PG can be stabilized with class C fly ash and lime for potential use in marine environments. An augmented simplex centroid design with pseudo-components was used to select 10 PG:class C fly ash:lime compositions. The 43 cm 3 blocks were fabricated and subjected to a field submergence test and 28 days saltwater dynamic leaching study. The dynamic leaching study yielded effective calcium diffusion coefficients ( D e) ranging from 1.15×10 −13 to 3.14×10 −13 m 2 s −1 and effective diffusion depths ( X c) ranging from 14.7 to 4.3 mm for 30 years life. The control composites exhibited diametrical expansions ranging from 2.3 to 17.1%, providing evidence of the extent of the rupture development due to ettringite formation. Scanning electron microscopy (SEM), microprobe analysis showed that the formation of a CaCO 3 on the composite surface could not protect the composites from saltwater intrusion because the ruptures developed throughout the composites were too great. When the PG:class C fly ash:lime composites were submerged, saltwater was able to intrude throughout the entire composite and dissolve the PG. The dissolution of the PG increased the concentration of sulfate ions that could react with calcium aluminum oxides in class C fly ash forming additional ettringite that accelerated rupture development. Effective diffusion coefficients and effective diffusion depths alone are not necessarily good indicators of the long-term survivability of PG:class C fly ash:lime composites. Development of the ruptures in the composites must be considered when the composites are used for aquatic applications.

Stabilized phosphogypsum: class C fly ash: Portland type II cement composites for potential marine application.

Phosphogypsum (PG, CaSO4 x H20), a byproduct of phosphoric acid manufacturing, contains low levels of Ra226. PG can be stabilized with portland type II cement and class C fly ash for use in marine environments, thus eliminating the airborne vector of transmission for radon gas. An augmented simplex centroid design with pseudocomponents was used to select 10 PG:class C fly ash:portland type II cement compositions. The 43 cm3 blocks were fabricated and subjected to a 1.5-yr field submergence test and a 28-d saltwater dynamic leaching study. All field composites survived with no signs of degradation. Dynamic leaching resulted in effective calcium diffusion coefficients ranging from 0.21 to 7.5 x 10(-14)m2 s(-1). Effective diffusion depths, calculated for t=1 and 30 yr, ranged from 0.4 to 2.2 mm and from 2.0 to 11.9 mm, respectively. Scanning electron microscopy and wavelength dispersive microprobe and X-ray diffraction analyses of the leached composites identified a 40-60-microm calcite layer that was absent in the control composites. This suggests that a reaction between the composites and the saltwater results in the precipitation of calcite onto the block surface, encapsulating the composites and protecting them from saltwater attack and dissolution.