Robust optimization of concrete strength estimation using response surface methodology and Monte Carlo simulation

A new approach is proposed for the robust optimization of concrete strength estimation using response surface methodology and Monte Carlo simulation. The essence of the suggested procedure lies in the reliable prediction of concrete strength as a simple function of unit mass, water/cement ratio, age and superplasticizer content. The derived model provides sufficiently accurate results for the calibration and verification phases, the latter of which is conducted using data that were not used for model development. The results of additional analysis indicate that residuals in the calibration and verification stages have a normal distribution. Is its also shown that the uncertainty of estimated coefficient values has a statistically insignificant effect on concrete strength, confirming the reliability of the proposed model. Moreover, analysis of the effect of laboratory measurement errors indicates the robustness of concrete compressive strength against the variation in measured parameter values.     

Models for strength prediction of foam concrete

There are several strength prediction relations developed for plain cement paste, mortar and concrete. In concrete where air voids contribute significantly to volume of voids (like aerated and foam concrete), more general expressions including the volume of air voids is to be developed as the better alternative. The objective of this paper is to propose prediction relations for the compressive strength of foam concrete by extending two of the well-known relations available for cement paste, mortar and normal concrete, viz., Balshin’s strength-porosity model and Power’s gel-space ratio equation. For this, theoretical equations were derived for porosity and gel-space ratio relating it to the density, proportion of ingredients in the mix and material characteristics like specific gravity. Foam concrete with fly ash showed lesser dependency on pore parameters than cement-sand mixes. As both the prediction relations developed in this study consider the effect of composition on the strength, it can serve as a simple tool for predicting the strength of foam concrete. But strength-porosity model stands out compared to gel-space model as it correlates well with the measured strength and also because of its ease in application since it employs the composition of constituents and easily measurable parameters.     

Optimization of concrete mixture with hybrid blends of metakaolin and fly ash using response surface method

This paper presents the experimental results of a research carried out on the strength and permeability related properties of high performance concretes made with binary and ternary cementitious blends of fly ash (FA) and metakaolin (MK). The replacement ratios for FA were 10% and 20% by weight of Portland cement and those for MK were 5% and 10%. Compressive strength, chloride permeability, water sorptivity, and water absorption properties of concretes were obtained in this study for different testing ages up to 90 days. The influences of fly ash, metakaolin, and testing age on the properties of concretes have been identified using the analysis of variance. The statistical based regression models and the response surface method with the backward stepwise techniques were employed in the multi-objective optimization analysis. That is carried out by maximizing compressive strength while minimizing chloride permeability, water sorptivity, and water absorption. It was observed that fly ash and especially metakaolin were very effective on the aforementioned properties of the concretes, depending mainly on replacement levels and duration of curing. The results indicated that the ternary use of fly ash and metakaolin with the approximate cement replacement values of 13.3% and 10% respectively has provided the best results for the testing age of 90 days, when the optimized strength and permeability based durability properties of the concretes are concerned.     

Eco-efficient ultra-high performance concrete development by means of response surface methodology

The research described in this paper represents a statistically based model with the help of response surface methodology (RSM) aiming to study the applicability of this method to ultra-high performance concrete (UHPC) mixture design and its optimization. Besides, the effects of silica fume, ultra-fine fly ash (UFFA) and sand as three main variable constituents of UHPC on workability and compressive strength as the main performance criteria and responses of this high-tech material were investigated. The models proposed here demonstrate a perfect correlation among variables and responses. Furthermore, through performing a multi-objective optimization, cement and silica fume, as two main constituents of UHPC affecting its eco-efficiency and cost, were substituted by UFFA and sand as much as possible. Finally, an eco-efficient UHPC with cement and silica fume content of 640 kg/m³ and 56.3 kg/m³ respectively and compressive strength and flow diameter of 160.3 MPa and 19 cm was developed.     

Optimizing energy harvesting parameters using response surface methodology

Energy harvesting is a process in which energy that would otherwise be wasted is stored and then used to power a system. Due to their unique properties piezoelectric materials are ideal for energy harvesting applications. In this study a pre-stressed piezoelectric composite was pressure loaded dynamically to harvest energy. The objective of this study was to optimize, using piezoelectric diaphragms, relevant parameters that have an effect on the energy harvesting process. Parameters considered were temperature, pressure, resistance and frequency. Response surface methodology was used to develop models to identify optimal parameter ranges and also to predict power conversion capabilities for specific parameter levels. Power densities of approximately 24.27 muW/mm³ were measured at optimal conditions. The model identified an optimal temperature of 12degC and a pressure of 240 kPa, which are in agreement with experimental results.     

Synthesis of high tap density spherical micro-size silver particles by liquid-phase reduction using response surface methodology

Mono-disperse and spherical micro-size silver particles with high tap density were prepared by using silver nitrate as metal source, ascorbic acid as reductant, sulfuric acid as dispersant and polyethylene glycol 4000 (PEG4000) as surfactant. The aim of this paper was to study the simultaneous effects of surfactant dosage (PEG4000/AgNO₃ mass ratio), silver nitrate concentration [AgNO₃], deionized water dosage in reductant solution, stirring rate and their interactions on properties of silver particles. For optimizing these parameters, irregular fractional factorial design of experiments was used. As-prepared silver particles were characterized by X-ray diffraction, scanning electron microscopy, laser particle size analyzer and tap density (tap density refers to the stacking density of particles after vibration compaction) meter. The results showed that silver particles were spherical, mono-disperse and with high tap density (>5.0 g/mL), average particle size of about 2–3 μm and narrow particle size distribution. By surveying the experiment results and analysis of variance, two mathematical models were obtained and optimized parameters were determined. Analysis of the variance demonstrated that the interaction of [AgNO₃] and stirring rate were the most significant factor affecting particle size and PEG4000/AgNO₃ mass ratio and [AgNO₃] were main significant factors affecting tap density. The predicted particle size and tap density were respectively 2.5 μm and 5.065 g/mL while the experimental results were 2.52 μm and 5.108 g/mL, which indicated that the models were in good agreement with the experimental data.     

Formulation of insulin-loaded polymeric nanoparticles using response surface methodology

The objective of this work was to formulate new oral insulin-loaded nanoparticules using the response surface methodology. The insulin nanoparticles were prepared by a water-in-oil-in-water emulsification and evaporation method. The polymers used for the encapsulation were blends of biodegradable poly-epsilon-caprolactone (PCL) and of positively-charged, nonbiodegradable polymer (Eudragis RS®). A central composite design has been built to investigate the effects of three controlled variables: ratio of polymers (PCL/RS ratio), volume, and pH of the aqueous solution of polyvinyl alcohol. The nanoparticles were characterized by measuring the amount of entrapped insulin, the particle size, the polydispersity of the obtained particles, the zeta potential, and the amount of insulin released after 7 hours. A second-order model was evaluated by multiple regression and was statistically tested for each of the studied controlled variable. The obtained polynomials proved efficient to localize an optimal operating area highlighted by the use of three-dimensional response surfaces and their corresponding isoresponse curves. An interesting formulation given by the models was selected, prepared, and evaluated. The corresponding quantity of entrapped insulin was 25 IU per 100 mg of polymer, and the particle size was 350 nm with a polydispersity of 0.21. The quantity of released insulin was 4.8 IU per 100 mg of polymer after 7 hours and the zeta potential was + 44 mV. All these collected values were in perfect accordance with values estimated by the models. Finally, the results suggested that PCL/RS 50/50 nanoparticles might represent a promising formulation for oral delivery of insulin.     

Optimization of A-TIG process parameters using response surface methodology

In the present work, the influence of process parameters such as welding current (I), welding speed (S), and flux coating density (F) on different aspects of weld bead geometry for example depth of penetration (DOP), bead width (BW), depth to width ratio (D/W), and weld fusion zone area (WA) were investigated by using the central composite design (CCD). 9–12% Cr ferritic stainless steel (FSS) plates were welded using A-TIG welding. It was observed that all input variables have a direct influence on the DOP, BW, and D/W. However, flux coating density has no significant effect on WA. Mathematical models were generated from the obtained responses to predict the weld bead geometry. An optimized DOP, BW, D/W, and WA of 6.95?mm, 8.76?mm, 0.80, and 41.99?mm², respectively, were predicted at the welding current of 213.78 A, the welding speed of 96.22?mm/min, and the flux coating density of 1.99?mg/cm². Conformity test was done to check the practicability of the developed models. The conformity test results were in good agreement with the predicted values. Arc constriction and reversal in Marangoni convection were considered as major mechanisms for the deep and narrow weld bead during A-TIG welding.     

Enhancing the strength of pre-made foams for foam concrete applications

Chemical and mechanical foaming techniques are commonly used in foam concrete technology for developing lightweight construction materials. The characteristics of the foam before the lightweight structure sets and maintains its shape has a great impact on the properties of foamed concretes. The tendency of the foams to coalesce and collapse during the preparation process brings some challenges in controlling the properties of cellular structures. Consequently, it is critical to improve the stability of fresh foams in order to produce high quality cellular structures using a predictable and reliable approach. Aggregating the liquid film around bubbles is known to be effective in improving the stability of foams, but the impact of this stabilizing method has not been investigated for foam concrete applications. In this paper, Xanthan gum (with a thickening capacity) has been utilized as the foam stabilizer to aggregate the liquid film. This stabilizing method is shown to significantly enhance the pore size distribution of foam concretes. The resulting pre-made foams are remarkably more stable than the control foam, and the mechanical properties of the final cellular structure are considerably improved (about 34% in mechanical foaming and 20% in the chemical foaming technique).     

Preparation and optimization of doxorubicin-loaded albumin nanoparticles using response surface methodology

Background: The objective of this work was to optimize the preparation of doxorubicin-loaded albumin nanoparticles (Dox-A-Nps) through desolvation procedures using response surface methodology (RSM). A central composite design (CCD) for four factors at five levels was used in this study.

Method: Albumin nanoparticles were prepared through a desolvation method and were optimized in the aid of CCD. Albumin concentration, amount of doxorubicin, pH values, and percentage of glutaraldehyde were selected as independent variables, particle size, zeta potential, drug loading, encapsulation efficiency, and nanoparticles yield were chosen as response variables. RSM and multiple response optimizations utilizing a quadratic polynomial equation were used to obtain an optimal formulation.

Results: The optimal formulation for Dox-A-Nps was composed of albumin concentration of 17?mg/ml, amount of doxorubicin of 2?mg/ml, pH value is 9 and percentage of glutaraldehyde of 125% of the theoretic amount, under which the optimized conditions gave rise to the actual average value of mean particle size (151?±?0.43?nm), zeta potential (?18.8?±?0.21 mV), drug loading efficiency (21.4?±?0.70%), drug entrapment efficiency (76.9?±?0.21%) and nanoparticles yield (82.0?±?0.34%). The storage stability experiments proved that Dox-A-Nps stable in 4°C over the period of 4 months. The in vitro experiments showed a burst release at the initial stage and followed by a prolonged release of Dox from albumin nanoparticles up to 60?h.

Conclusions: This study showed that the RSM-CCD method could efficiently be applied for the modeling of nanoparticles, which laid the foundation of the further research of immuno nanoparticles.     

响应曲面法对银型无机抗菌材料干燥条件的优化

采用溶胶-凝胶法制备银型无机抗菌材料,并通过响应曲面法对干燥过程进行优化,研究表明:当干燥温度为126.62℃,干燥时间为143.72min时,样品的相对失重率可达88.6004%。经实验检测在优化条件下,样品相对失重率平均值为87.8332%,接近预测值,表明所得模型可以反映参数之间的真实关系,可以用此模型对样品的相对失重率进行分析和预测。抗菌实验表明产品对大肠杆菌杀菌效果很好,杀菌率为96.2%。     

Optimization of a surfactant-free antioxidant formulation using response surface methodology

Topical application of natural antioxidants has proven to be effective in protecting the skin against ultraviolet radiation-mediated oxidative damage. In previous studies, a Castanea sativa leaf ethanol:water (7:3) extract exhibited scavenging activity against different reactive oxygen species that are thought to contribute to oxidative damage in the skin. Its stability was shown to be enhanced in the presence of glycerine, and therefore a glycerine-based formulation with Carbopol 940 and liquid paraffin (LP) was developed as base. In this work, the influence of the glycerine and LP contents on the textural properties of the topical base and on the antioxidant activity of the formulation with C. sativa extract was evaluated using response surface methodology after 30?d storage at 20?°C and 40?°C. The textural analysis was performed in a texturometer, by carrying out a spreadability test. Paretto charts showed that both glycerine and LP contents significantly influenced the textural properties of the formulations (p?C. sativa extract leading to the conclusion that the selection of these ingredients contents can be guided exclusively by the desirable textural properties.     

Composition optimization of extruded starch foams using response surface methodology

Response surface methodology (RSM) was used to analyse the effect of polyvinyl alcohol (PVA) and calcium carbonate (CaCO₃) on the objective attributes (shipping bulk density, radial expansion ratio, compressibility and spring index) of a biodegradable cushioning extrudate. A rotatable central composite design (CCD) was used to develop models for the objective responses. The experiments were run at 105°C with a feed rate of 27.8 l/h, screw speed 500 r.p.m. and die diameter 3.92 mm. Responses were most affected by changes in polyvinyl alcohol (PVA) levels and to a lesser extent by calcium carbonate (CaCO₃) levels. Individual contour plots of the different responses were overlaid, and regions meeting the optimum shipping bulk density of 6.00 kg/m³, radial expansion ratio of 3.30, compressibility of 43.71 N, and spring index of 0.91 were identified at the PVA level of 20.23% and the CaCO₃ level of 7.89%, respectively. Copyright © 2004 John Wiley & Sons, Ltd.     

Optimising photoelectrocatalytic oxidation of fulvic acid using response surface methodology

In this paper, statistics-based experimental design with response surface methodology (RSM) was employed to investigate the effect of operation conditions on photoelectrocatalytic oxidation of fulvic acid (FA) using a Ti/TiO(2) electrode in a photoreactor. Initially, the Box-Behnken design was employed including the three key variables (initial pH, potassium peroxodisulphate (K(2)S(2)O(8)) and bias potential). Thereafter, the mutual interaction and effects between these parameters and optimum conditions were obtained in greater detail by means of SAS and Matlab software. The results of this investigation reveal that: (1) the regression analysis with R(2) value of 0.9754 shows a close fit between the experimental results and the model predictions; (2) three-dimension response surface plot can provide a good manner for visualizing the parameter interactions; (3) the optimum pH, K(2)S(2)O(8) and bias potential is found to be 3.8, 88.40 mg/L, 0.88 V, respectively, and the highest FA removal efficiency of 57.06% can be achieved.     

响应曲面法优化优先透乙醇渗透汽化复合膜的操作条件

采用自制的硅橡胶-沸石杂化优先透乙醇渗透汽化复合膜,利用响应曲面法研究原料液温度和循环流速两个参数对乙醇质量分数为4.05%的乙醇-水体系渗透汽化分离过程的影响.试验表明,温度对膜的通量和分离因子都有显著的影响,温度升高通量增加,而在50℃以下分离因子随温度升高而增加,此后分离因子随温度升高而下降.循环流速的增加会导致通量和分离因子的下降.综合考虑分离因子和通量这两个响应值,利用回归方程求得本试验所采用的渗透汽化复合膜在乙醇一水体系中最优操作条件是:温度59.8℃,循环流速30 L/h,此时总通量和乙醇分离因子分别达到242.8 g/(m2·h)和20.6.     

泡沫混凝土的组成、性能与应用研究

本文通过介绍泡沫混凝土的组成及其原材料的选择,论述泡沫混凝土的性能特点,指出国内泡沫混凝土生产应用中存在的一些问题,同时讨论泡沫混凝土的生产施工工艺及应用前景。     

High strength concrete response to hard projectile impact

High strength concrete (HSC) becomes more common in practice and may have advantageous implementations. According to existing penetration formulae HSC is expected to enhance the performance of structural elements that are designed to resist projectile impacts. However, scabbing at the rear face is expected to be more severe in elements that are made of HSC, because of the relatively high material brittleness. Therefore, it is important to enhance the ductility of HSC elements, and one possible direction is to use fibers or wire mesh reinforcement. In order to study the influence of the concrete strength and of the reinforcement type on the elements response, penetration tests were conducted on regular strength concrete (RSC) and on HSC plates, with the following types of reinforcement: 5 mm steel mesh, steel fibers, small diameter steel wire mesh, and woven steel fence mesh of various diameters. The plates were subjected to an impact of a cylindrical hard steel projectile, weighing 120 g, with a conical nose and a 1.5 aspect ration. The projectiles were accelerated by a laboratory gas gun to velocities that ranged between 85 and 230 m/sec, which were measured by an electro-optical device. By comparing the response of these plates to an impacting projectile, the effects of concrete strength and of the reinforcement were studied. Major trends of the elements behavior were studied, their responses were compared and are described herein.     

Optimizing the bake hardening behavior of Al7075 using response surface methodology

In the present work, the bake hardening behavior of Al7075 was investigated using the response surface methodology (RSM). The optimal conditions to attain the maximum bake hardening (BH) amounts and maximum yield stress (FYS) after baking were predicted by RSM. The combination of central composite design (CCD) and response surface methodology (RSM) was also used to predict the maximum bake hardenability of Al7075. This was done by recognizing the most important baking parameters, the significance of baking parameters, and the importance of interactions among process parameters. The bake hardening tests were carried out using the values predicted by the model. The results predicted by the developed model are in a very good agreement with the measured ones. The contour plots are also obtained in order to determine the significance of variables interaction. The correlation coefficient (R²) of the regression models, regarding the bake hardening and final yield stress (FYS), was about 0.99 and 0.976, respectively which confirming the excellent accuracy of the model. The results also showed that the optimum conditions to attain the maximum bake hardenability and final yield stress are met when baking is carried out at 200 °C for 23 min with the pre-straining of 6%. Under these conditions, the BH and FYS amount predicted by the developed model was about 92 and 579 MPa, respectively, whereas the measured BH and FYS was about 90 and 570 MPa, indicating a very good agreement between the predicted and measured values.     

Optimization of process parameters for transalkylation of toluene to xylene using response surface methodology

ABSTRACT

H-beta zeolite was modified by the ion exchange method to replace its H⁺ ions with Ce⁴⁺ ions. The catalytic performance of this cerium exchanged beta zeolite was evaluated for vapor phase transalkylation of 1,2,4 TMB (1,2,4 trimethylbenzene) with toluene for the production of xylene in a fixed bed, down-flow reactor. The modified zeolite was found to be highly active for this transalkylation reaction. The response surface methodology (RSM) is used for designing the experiments. The effect of three important reaction parameters viz. temperature, reactant ratio, and space time on response variables (toluene conversion and xylene selectivity) is studied and discussed. All the three selected reaction parameters were found to be significant for the toluene conversion; whereas, xylene selectivity was not much influenced by the temperature. The optimum values of the reaction parameters predicted by the model (temperature: 409.7°C, reactant ratio: 2.024, and space time: 4.451) were validated by an experimental run. The results of the experimental run were in close agreement with the model predicted results.