Analysis of carbonation behavior in concrete using neural network algorithm and carbonation modeling

Carbonation on concrete structures in underground sites or metropolitan cities is one of the major causes of steel corrosion in RC (Reinforced Concrete) structures. For quantitative evaluation of carbonation, physico-chemo modeling for reaction with dissolved CO₂ and hydrates is necessary. Amount of hydrates and CO₂ diffusion coefficient play an important role in evaluation of carbonation behavior, however, it is difficult to obtain a various CO₂ diffusion coefficient from experiments due to limited time and cost.In this paper, a numerical technique for carbonation behavior using neural network algorithm and carbonation modeling is developed. To obtain the comparable data set of CO₂ diffusion coefficient, experimental results which were performed previously are analyzed. Mix design components such as cement content, water to cement ratio, and volume of aggregate including exposure condition of relative humidity are selected as neurons. Training of learning for neural network is carried out using back propagation algorithm. The diffusion coefficient of CO₂ from neural network are in good agreement with experimental data considering various conditions such as water to cement ratios (w/c: 0.42, 0.50, and 0.58) and relative humidities (R.H.: 10%, 45%, 75%, and 90%). Furthermore, mercury intrusion porosimetry (MIP) test is also performed to evaluate the change in porosity under carbonation. Finally, the numerical technique which is based on behavior in early-aged concrete such as hydration and pore structure is developed considering CO₂ diffusion coefficient from neural network and changing effect on porosity under carbonation.     

Influence of traversing crack on chloride diffusion into concrete

This study examined the effects of traversing cracks of concrete on chloride diffusion. Three different concretes were tested: one ordinary concrete (OC) and two high performance concretes with two different mix designs (HPC and HPCSF, with silica fume) to show the influence of the water/cement ratio and silica fume addition. Cracks with average widths ranging from 30 to 250 μm, were induced using a splitting tensile test. Chloride diffusion coefficients of concrete were evaluated using a steady-state migration test. The results showed that the diffusion coefficient of uncracked HPCSF was less than HPC and OC, but the cracking changed the material behavior in terms of chloride diffusion. The diffusion coefficient increased with the increasing crack width, and this trend was present for all three concretes. The diffusion coefficient through the crack D_cr was not dependent of material parameters and becomes constant when the crack width is higher than  80 μm, where the value obtained was the diffusion coefficient in free solution.     

Experimental investigation and numerical modeling of chloride penetration and calcium dissolution in saturated concrete

Chloride penetration and calcium dissolution have been investigated for a saturated concrete after exposure to a 0.5 mol/L NaCl solution for a period of up to 3150 days. Simultaneous ion transport model (SiTraM) that allows the transport of chloride and calcium ions to be simultaneously simulated in a hydrated cement system has been used to verify the experimental results.Self-compacting concrete (SCC) with a water to cement ratio of 0.3 resulted in a limited chloride penetration depth while the calcium dissolution was also reduced within the near surface zone. Increased unit water content for normal concrete resulted in higher chloride penetration depth and larger dissolution front of Ca(OH)₂ regardless of having the same water to cement ratio.It was revealed that the SiTraM can predict the profiles of chloride and calcium for self-compacting concrete. It was also found that the primary factor to control chloride penetration front and the dissolution front of Ca(OH)₂ was the pore structure characteristic of concrete.     

Cover cracking of reinforced concrete due to rebar corrosion induced by chloride penetration

Cracking of concrete cover due to corrosion induced expansion of steel rebar is one of the major causes of the deterioration of reinforced concrete (RC) structures exposed to marine environments and de-icing salts.This paper presents two models that deal with the chloride-induced corrosion and subsequent cracking of concrete cover in RC structures. The former analyses the chloride diffusion within partially saturated concrete. A comprehensive model is developed through the governing equations of moisture, heat and chloride-ion flow. Nonlinearity of diffusion coefficients, chloride binding isotherms and convection phenomena are also highlighted. The latter describes the internal cracking around the bar due to expansive pressures as corrosion of the reinforcing bar progresses. Once a certain chloride concentration threshold is reached in the area surrounding the bar, oxidation of steel begins and oxide products are generated, which occupy much greater volume than the original steel consumed by corrosion. An embedded cohesive crack model is applied for cracking simulation.Both models are incorporated in the same finite element program. The models are chained, though not explicitly coupled, at first instance. Comparisons with experimental results are carried out, with reasonably good agreements being obtained. The work is a step forward for the integration of the two traditional phases (initiation and propagation) widely used in the literature and usually analysed separately. The estimation of the service life of the structure needs to evaluate the associated time for each one.     

Compared imbibitions of ordinary and high performance concrete with null or positive water pressure head

A method to simultaneously measure the moisture diffusion coefficient, D_θ, of unsaturated concrete, and the saturated concrete hydraulic conductivity, K_l, was developed for cylindrical specimens placed on a container filled with water that could be maintained at a given hydraulic pressure. Ordinary Portland cement Concrete (OPC) with a moderate and High Performance Concrete (HPC) with a low water to cement ratio were tested. The time dependent distribution of water content in the specimens was measured using a non-intrusive method based on gamma-ray attenuation. The measurements were conducted with varying hydraulic head (positive or null). Boltzmann's transformation was used to analyze the experimental results obtained at different hydraulic pressures and the difference between the null (or atmospheric) and positive pressure results is used to accurately determine K_l and also D_θ . This paper will present the results obtained using this original method, possible interpretations and future research.     

Influence of high-temperature and low-humidity curing on chloride penetration in blended cement concrete

The influence of high-temperature and low-humidity curing on chloride penetration in concrete containing cement replacement materials was investigated. Three different mixes were studied: a control mix in which no cement replacement materials were added and two mixes where cement was partially replaced by 20% fly ash and 9% silica fume (by weight), respectively, at a constant water-to-binder ratio of 0.45. High-temperature curing was employed to simulate concrete temperature in hot climate. The results show that at early periods of exposure, initial curing has a substantial influence on chloride penetration in concrete. The effect of initial curing is much reduced after a long period of exposure. The chloride penetration at early ages of exposure is directly related to the porosity of the binder phase and the absorption of concrete. Higher chloride penetration resistance was observed when cement is partially replaced with either fly ash or silica fume.     

Study of chloride binding and diffusion in GGBS concrete

Ordinary Portland cement (OPC) and OPC/ground granulated blastfurnace slag (GGBS) 70%, with or without 5% sulfates, were widely investigated in respect to their pore structures, chloride diffusion coefficients, internal and external chloride-binding capabilities by expression method and leaching method and the microstructure analysis on Friedel's salt such as differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It can be concluded that GGBS can improve the pore structure of OPC and decrease the chloride diffusion coefficient greatly, and that sulfates do not do good for the pore structure and chloride diffusion for GGBS. GGBS increases the chloride-binding capability greatly without reference to the internal or external chloride and sulfates decrease the chloride-binding capability of GGBS greatly. It can be also found that the maximum intensity peak corresponding to Friedel's salt appears at about 8.0 Å, its endothermic effect appears at about 360 °C, its morphology is hexagonal slice whose size is about 2-3 μm; that the output of Friedel's salt formed by GGBS is much more than OPC; and that sulfates influence the output of Friedel's salt greatly. The corresponding mechanism was also analyzed.     

Hydration and microstructure of ultra high performance concrete incorporating rice husk ash

Rice husk ash (RHA) and silica fume (SF) have a similar chemical composition and a very high specific surface area, but RHA is not an ultra-fine material like SF. The high specific surface area of RHA originates from its internal porosity. For this reason RHA can be expected to behave differently from SF in terms of the hydration and the resulting microstructure of concrete. This still remains unclear in Ultra High Performance Concrete (UHPC). The objective of this research was to study the effect of RHA on the hydration and microstructure development of UHPC. The results are compared to those obtained with a control sample and a sample made with SF.The results show that the addition of RHA can increase the degree of cement hydration in UHPC at later ages. RHA can also refine the pore structure of UHPC and reduce the Ca(OH)₂ content, but less significantly than SF. The thickness of the interface transition zone (ITZ) between sand particles and cement matrix of all samples is very small at the age of 28 days. The compressive strength of the sample made with RHA after 7 days was higher than that of the control sample and the sample made with SF. It is suggested that the porous structure of RHA and the uptake of water in this porous structure results in a kind of is attributable to the internal water curing of the RHA modified mixture.     

Transport properties of water and glycol in an ultra high performance fiber reinforced concrete (UHPFRC) under high tensile deformation

Ultra High Performance Fiber Reinforced Concretes (UHPFRC) present outstanding mechanical properties and a very low permeability. Those characteristics make them very attractive for the rehabilitation of existing structures and the conception of new structures. To define the range of admissible tensile deformation in those materials, the influence of imposed tensile deformation and subsequent cracking on permeability and absorption was studied. The transport properties of water and glycol were assessed in order to estimate the effect of the interaction of water with a specific UHPFRC. The experimental results demonstrate that permeability and absorption increase steadily until a residual tensile deformation of 0.13% is reached in the material, then water seeping rises distinctly. During experiments, the interaction of water with the UHPFRC decreases by 1 to 3 orders of magnitude the permeability and reduces absorption by approximately 50 to 85%. Test results reveal the high capability of the material to seal cracks and improve its water-tightness with time.     

Comparison of two processes for treating rice husk ash for use in high performance concrete

Rice husk ashes (RHA) have been used as pozzolanic admixtures for high performance concrete (HPC). This study reports on a chemical treatment before burning that improves the effectiveness of the RHA. The resulting ash (ChRHA) was compared to ash produced by conventional incineration (TRHA). The digestive chemical treatment before burning produced an RHA with properties comparable to silica fume. The ChRHA was highly amorphous, white in color, presented higher specific surface area and exhibited greater pozzolanic activity. The fresh and hardened properties of HPC made with different percentages of these RHAs were compared. The hardened concrete testing included the determination of the modulus of elasticity and the compressive and flexural properties. It was shown that ChRHA and TRHA were effective supplementary cementing materials, although concrete mixes required higher dosages of superplasticizer compared to the control concrete mix.     

Prediction of moisture content in pre-osmosed and ultrasounded dried banana using genetic algorithm and neural network

In this study, application of a versatile approach for estimation moisture content of dried banana using neural network and genetic algorithm has been presented. The banana samples were dehydrated using two non-thermal processes namely osmotic and ultrasound pretreatments, at different solution concentrations and dehydration times and were then subjected to air drying at 60 and 80 °C for 4, 5 and 6 h. The processing conditions were considered as inputs of neural network to predict final moisture content of banana. Network structure and learning parameters were optimized using genetic algorithm. It was found that the designed networks containing 7 and 10 neurons in first and second hidden layers, respectively, give the best fitting to experimental data. This configuration could predict moisture content of dried banana with correlation coefficient of 0.94. In addition, sensitivity analysis showed that the two most sensitive input variables towards such prediction were drying time and temperature.     

Performance of spalling resistance of high performance concrete with polypropylene fiber contents and lateral confinement

This paper presents an experimental study on the spalling resistance of high performance concrete with polypropylene (PP) fibers and fabric or sheet material for lateral confinement subjected to fire. According to the test results, spalling occurred on all specimens that did not contain PP fiber in the concrete mixture. However, spalling did not occur on specimens containing PP fibers above 0.05% by volume. A metal fabric showed beneficial effect on spalling resistance, but glass or carbon fiber fabrics do not show the same effect on the spalling resistance due to reduction of bond strength at high temperatures. Spalling did not occur on all specimens in which PP fibers and metal fabric were applied at the same time, and hence spalling resistance performance was significantly improved. The residual compressive strength was maintained at about 90% of its original strength, and this can be considered as an improved performance against fire damage.     

Effect of incorporating PVC waste as aggregate on the physical,mechanical, and chloride ion penetration behavior of concrete

With the growing needs for resource materials and the environmental protection requirements associated with sustainable development, it has become necessary to study all the possibilities of reusing and recycling industrial wastes and by-products, especially in the field of civil engineering. In the work presented here, non-biodegradable plastic aggregates made of polyvinylchloride (PVC) waste, obtained from scrapped PVC pipes, were used in partial replacement of conventional aggregates in concrete. For this purpose, a number of laboratory prepared concrete mixes were tested, in which natural sand and coarse aggregates were partially replaced by PVC plastic waste aggregates in the proportions of 30, 50, and 70% by volume (granular classes 0/3 and 3/8). Fresh concrete mixtures were tested for workability and density, and hardened concrete specimens were used to investigate compressive strength, ultrasonic wave velocity, and resistance to chloride ion penetration. The results of the laboratory study showed that concrete made with 50 and 70% of recycled PVC aggregates fell into the category of structural lightweight concrete in terms of unit weight and strength properties. This study gave quite encouraging results and opened up a new way of recycling PVC waste as a lightweight aggregate in concrete.     

Strength, durability and micro-structural aspects of high performance volcanic ash concrete

This paper presents the results of investigations to assess the suitability of using volcanic ash (VA) as a cement replacement material to produce high performance concrete. Tests were conducted on concrete mixtures replacing 0 to 20% by mass of ordinary Portland cement (OPC) by VA. The performance of high performance volcanic ash concrete (HPVAC) mixtures was evaluated by conducting comprehensive series of tests on fresh and hardened properties as well as durability. The mechanical properties were assessed by compressive strength, while durability characteristics were investigated by rapid chloride permeability (RCP), drying shrinkage (DS), mercury intrusion porosimetry (MIP), differential scanning calorimetry (DSC) and microhardness tests. HPVACs showed better durability properties compared to control concrete with 0% VA. The improved performance of HPVACs was attributed to the refinement of pore structure, and pozzolanic action of VA. HPVAC having a minimum 28-day compressive strength of 60 MPa can be obtained by replacing up to 20% (by mass) of cement by VA. Development of non-expensive and environmentally friendly HPVAC with acceptable strength and durability characteristics (as illustrated in this study) is extremely helpful for the sustainable development and rehabilitation of volcanic disaster areas around the world.     

Thermal and mechanical properties of fiber reinforced high performance self-consolidating concrete at elevated temperatures

This paper presents the effect of temperature on thermal and mechanical properties of self-consolidating concrete (SCC) and fiber reinforced SCC (FRSCC). For thermal properties specific heat, thermal conductivity, and thermal expansion were measured, whereas for mechanical properties compressive strength, tensile strength and elastic modulus were measured in the temperature range of 20–800 °C. Four SCC mixes, plain SCC, steel, polypropylene, and hybrid fiber reinforced SCC were considered in the test program. Data from mechanical property tests show that the presence of steel fibers enhances high temperature splitting tensile strength and elastic modulus of SCC. Also the thermal expansion of FRSCC is slightly higher than that of SCC in 20–1000 °C range. Data generated from these tests was utilized to develop simplified relations for expressing thermal and mechanical properties of SCC and FRSCC as a function of temperature.     

高效液相色谱法测定重组人干扰素α1b滴眼液中苯扎氯铵的含量

目的采用高效液相色谱法(high performance liquid chromatography,HPLC)测定重组人干扰素α1b(recombi-nant human interferonα1b,rhIFNα1b)滴眼液中苯扎氯铵(benzalkonium chloride)的含量。方法采用HPLC法测定rhIFNα1b滴眼液中苯扎氯铵含量,色谱条件:流动相:乙腈:5 mmol/L醋酸铵[含1%三乙胺,用冰醋酸调节pH值至(5.0±0.2)]体积比为65∶35;流速:1.0 ml/min;检测波长:262 nm;进样量20μl;柱温:室温。对该方法进行验证,并应用该方法检测3批rhIFNα1b滴眼液中苯扎氯铵的含量。结果该方法检测苯扎氯铵专属性和系统适应性良好;最低检测限和定量限分别为0.53μg/ml和1.48μg/ml;苯扎氯铵在10～50μg/ml浓度范围内,标准曲线的线性关系良好,R2=0.999 1;连续6次进样,峰面积的RSD=1.78%;苯扎氯铵理论浓度为22、24、26μg/ml的加样回收率平均为97.90%,RSD=0.96%。3批rhIFNα1b滴眼液中苯扎氯铵的相对含量分别为19.27、19.89和19.76μg/ml,分别为标示量的96.34%、94.46%和98.80%。结论 HPLC法简便、灵敏、准确,可用于测定rhIFNα1b滴眼液中苯扎氯铵的含量。     

高效液相色谱质谱联用鉴别口服疫苗中硫柳汞降解产物

目的采用高效液相色谱质谱联用的方法鉴别口服疫苗中硫柳汞的降解产物。方法采用C18色谱柱,甲醇-醋酸铵缓冲溶液(pH 4.5)梯度洗脱,以紫外和质谱检测器进行检测,对某口服疫苗中的未知色谱峰进行鉴别。结果疫苗样品中两个色谱峰的保留时间及其一级二级质谱图与硫柳汞的降解产物硫代水杨酸以及2,2’-二硫代二苯甲酸基本一致。结论高效液相色谱质谱联用可鉴别口服疫苗中的硫柳汞降解产物。     

Experimental characterization of the self-healing of cracks in an ultra high performance cementitious material: Mechanical tests and acoustic emission analysis

Self-healing of cracks in an ultra high performance concrete, considered as a model material, is investigated in this paper. An experimental program is carried out in order to quantify the phenomenon, which has been mainly highlighted by means of water permeability tests until now. Mechanical behaviour of self-healed concrete under three points bending, and acoustic emission analysis of the cracking mechanisms are reported. The mechanical tests demonstrate a recovery of the global stiffness, depending on the time of healing, for specimens initially cracked and then self-healed, and a slow improvement of structural strength. The acoustic emission (AE) analysis is performed in order to show that the mechanical response is due to new crystals precipitating in the crack. The microcracking of these products during three points bending tests is highlighted and an energy analysis provides insights about the cracking process of healed concrete, including damage of the newly formed crystals and continuation of the crack propagation.     

基于遗传BP神经网络预测硫在高含硫气体中溶解度

为更精确地关联预测硫在高含硫气体中的溶解度,提出将遗传算法(GA)和LM-反向传播神经网络(LM-BP ANN)相结合的预测模型。设计了该模型的计算过程,讨论了模型参数的设置。以温度、压力和气体组分作为BP神经网络预测模型的输入变量,利用GA优化了BP神经网络的初始权值和阈值,采用遗传算法优化后的BP神经网络计算了元素硫在高含硫气体中的溶解度。结果表明,该模型训练结果与实测值之间的平均相对误差为5.90%,测试结果与实测值的平均相对误差为5.54%;该方法较BP神经网络模型具有预测精度高、收敛速度快的优点;该模型具有较好的模拟及内推、外推功能。