混凝土碳化深度的BP神经网络随机预测模型

通过对混凝土的碳化机理及影响因素的分析,考虑混凝土碳化的随机性,建立了以混凝土暴露时间、混凝土抗压强度、混凝土暴露状态为输入,混凝土碳化深度平均值和标准差为输出的BP神经网络预测混凝土碳化深度的随机模型,计算结果与检测结果符合较好.采用提出的模型对相同暴露状态、不同强度的混凝土进行了随时间变化的碳化深度预测,预测结果较为理想.     

砼回弹仪弹击拉簧失效分析

砼回弹仪是利用回弹法无损检测工业与民用一般建筑物混凝土的抗压强度的一种仪器.其工作原理是用弹簧驱动弹击锤,通过弹击杆弹击试样表面所产生的瞬时弹性形变的恢复力,从而带动指针弹回并指示出回弹距离,以回弹值作为评定混凝土抗压强度的相关指标之一,其检测结果反映的是混凝土试件硬度与强度间的相关关系.     

基于模糊逻辑的舰船维修经费预测

针对多输入、单输出的复杂非线性系统，基于Takagi-Sugeno模糊规则给出了一种系统预测模型，分别用模糊C- 值聚类算法和线性回归方法导出模型参数。利用该模型对舰船维修经费进行了预测，并进行了精度分析。     

JJF1721-2018《碳化深度测量仪和测量尺校准规范》解读

正一、制定背景碳化深度测量仪和测量尺是回弹法检测混凝土抗压强度时测量混凝土碳化深度的仪器,广泛应用于混凝土以及其他建材表面碳化层深度的测量。碳化深度测量仪和测量尺的量值准确与否关系到建筑工程的质量,关系到人身安全,因此迫切要求对其进行量值溯源。JJF1721-2018《碳化深度测量仪和测量尺校准规范》已于2018年12月25日由市场监管总局批准,并于2019年3月25日实施。该规范统一了碳化深度测量仪和测量尺的计量性能、校准方法和校准项目,保证了该器具的量值溯源。     

基于成因模糊综合分析的瓦斯涌出量预测模型

瓦斯涌出量预测是一个高维非线性数据处理问题。在分析物理成因的基础上采用模糊识别、模糊聚类及优选理论等方法将高维数据一维化,以生成的模糊综合指标即优属度值作为输入变量建立瓦斯涌出量高斯函数预报模型。实例分析表明利用该方法创建的一元非线性预测模型具有较高的预测精度,预测结果好于已有的一些预测模型。     

浅谈混凝土回弹与碳化深度

回弹检测混凝土强度是以混凝土的表面硬度来推断混凝土强度的,碳化会增大混凝土表面硬度,所以回弹判定其强度时需要检测碳化深度进行修正.     

回弹法在混凝土强度检测中的应用分析

文章对在混凝土检测中常用的回弹法进行了阐述分析。回弹法作为无损检测方法之一,由于该方法对混凝土结构构件不破坏,操作简单,测试费用低,成为混凝土抗压强度的一种主要的检测方法。     

基于互信息PSO-LSSVM的SO2浓度预测

针对火电厂SO2污染物排放问题,提出了一种基于互信息的粒子群寻优(PSO)最小二乘支持向量机(LSSVM)模型预测方法,通过筛选出与SO2实测入口浓度相关性较高的辅助变量,将其作为模型的输入,实现对主导变量SO2浓度的预测。利用互信息筛选出的辅助变量相比于机理分析、皮尔逊相关性筛选出的辅助变量具有更高的相关性。利用互信息筛选出的辅助变量作为LSSVM模型的输入以及粒子群法确定LSSVM的参数,不仅缩短了计算时间,还提高了预测精度。将该方法应用到某火电厂的SO2浓度软测量中,利用现场数据进行仿真,结果表明预测精度较高,相对误差较低,预测趋势更贴近实际值,减小了实际值与预测值的误差(均方根误差为2.485,平均相对误差为0.2603%),为现场的SO2浓度提前控制提供了软件技术支持。     

如何评价混凝土回弹法测强结果

《回弹法检测混凝土抗压强度技术规程》(JGJ/T23-2001)自2001年10月1日执行以来,由于依据该规程计算而得出的混凝土抗压强度推定值多数情况下低于构件中最小的测区混凝土强度换算值,因此经常有人询问如何评价混凝土回弹法测强报告的数据,或者询问依回弹报告如何评定混凝土强度的质量。更有人认为,当回弹测强结果中的强度推定值低于设计的强度等级标准值时,就满足不了设计要求。对此,笔者谈一些自己的看法。一、回弹法测强报告不参加强度评定《混凝土结构工程施工及验收规范》(GB50204-92)第4.6.10条规定:当对混凝土试件强度的代表性有怀…     

新型半主动整星隔振平台及其模糊最优控制研究

为降低卫星在发射过程中受到的动态载荷,提出一种采用磁流变阻尼器的新型半主动整星隔振平台。建立隔振平台的动力学模型和柔性卫星隔振系统总体的动力学模型。将LQG最优控制和模糊控制技术相结合应用于半主动整星隔振系统,以卫星振动响应能量和作动器输入能量的加权和最小作为最优控制目标来确定最优控制力,并采用预测状态法进行时滞补偿。以最优控制力和磁流变阻尼器的实际出力作为输入变量,以磁流变阻尼器的控制电流作为输出变量设计模糊最优控制器。仿真分析结果表明:新型半主动整星隔振系统采用模糊最优控制时,在卫星轴向和横向方向上都可取得良好的振动控制效果,并且控制效果明显优于被动控制和限幅最优控制。     

地下工程砼结构基于碳化作用的耐久性劣化模型

碳化作用是地下混凝土结构耐久性的重要影响因素之一,由此造成的结构的劣化程度可以用结构保护层碳化的深度表示。该文设计了室内快速碳化试验,建立了混凝土在不同应力水平和不同水灰比及不同碳化龄期情形下的碳化深度模型公式,并得出结论:混凝土碳化速度系数随时间逐渐减小;拉应力对混凝土碳化有促进作用,而压应力则对碳化起到抑制作用;一定范围内,水灰比越大,则碳化速度越快。通过对耐久性评判准则的假设和建立相应的耐久性极限状态方程,可以很好地分析和预测结构的劣化程度及耐久性寿命。     

Some effects of cement and curing upon carbonation and reinforcement corrosion in concrete

Experimental data are presented to illustrate the effects of cement type and curing upon the depth of carbonation and reinforcement corrosion in cover concrete after exposure for 18 months at 20°C and 60% relative humidity. Three curing periods (1, 3 and 28-days) and 17 cements, with various proportions of granulated blastfurnace slag or limestone, were used to make concretes, at 0.59 water/cement ratio, with 28 day strengths in the range 26 to 46 MPa. The depth of carbonation after 18 months was 64% greater than after 6 months and was affected more by cement type than by curing. The depth of carbonation increased when Portland cement clinker was replaced by 19% or more of limestone or granulated blastfurnace slag. The depth of carbonation after 18 months correlated better with the air permeability of cover concrete, initial weight loss (an indicator of moisture diffusion rate in cover concrete) or the cube strength 8 days after the end of curing than it did with 28-day cube strength. The rate of reinforcement corrosion increased steeply when the carbonation front approached the reinforcing steel, and it was still increasing after the carbonation front had completely passed the reinforcement. For a given unneutralised remainder (i.e. cover depth minus the depth of carbonation), curing had little effect upon the rate of corrosion but higher rates were observed when the cement contained granulated blastfurnace slag. The results were broadly consistent with a simple engineering strategy in which the rate of carbonation was related to the air permeability of cover concrete, and the rate of any subsequent reinforcement corrosion was largely dependent upon moisture conditions, without any obvious influence of the cover depth or the permeability of the cover concrete. The results also suggested that estimation of the rate of reinforcement corrosion could be improved by taking account of the cement type and treating the unneutralised remainder as a variable.     

Carbonation in concrete infrastructure in the context of global climate change: Part 2 – Canadian urban simulations

In Part 1 of this paper, a carbonation model was developed and experimentally verified which was able to forecast carbonation depth of a concrete specimen considering varying ambient temperature, humidity and CO₂ concentrations.Part 2 of the paper applies the carbonation diffusion/reaction model developed in Part 1 to predict the effects of global climate change on the carbonation of concrete. Climate scenarios were formulated and combined with the model for two major Canadian cities, Toronto and Vancouver. Results show that for undamaged and unstressed concrete, climate change will significantly affect carbonation progress. The model showed that for unloaded, non-pozzolanic concrete, ultimate carbonation depths in Toronto and Vancouver could be up to 45% higher. For in-service structures under load, the rates of deterioration are likely to be even faster. This is a cause for concern, and much further effort must be devoted to fully understand these phenomena.     

考虑氯离子侵蚀与混凝土碳化的公路桥梁时变可靠度分析

基于国内外对氯离子侵蚀和混凝土碳化环境下钢筋锈蚀速率的最新研究成果,建立了混凝土构件在氯离子侵蚀下考虑坑蚀和在混凝土碳化下考虑平均锈蚀的弯曲抗力退化模型,用Monte Carlo方法和统计回归法编制了退化钢筋混凝土构件及系统的时变可靠度计算程序。以北京地区一座公路桥为算例,结果表明:在氯离子侵蚀下考虑坑蚀的桥梁承载能力时变可靠度在30年左右即下降到设计目标可靠度,在混凝土碳化下考虑平均锈蚀的桥梁承载能力时变可靠度在50年左右即下降到设计目标可靠度,从而需要补强,这表明考虑主筋锈蚀后我国钢筋混凝土公路桥一般达不到100年设计使用期;对因主筋锈蚀导致混凝土保护层胀裂而言,构件达到抗裂正常使用极限状态远远早于达到承载能力极限状态,建议将混凝土保护层开裂时间作为桥梁检查/维修参考点。     

碳化环境下混凝土结构耐久性模型的更新方法

碳化环境下的混凝土结构耐久性模型,是基于扩散理论、快速试验、自然暴露试验以及工程经验建立的。由于结构固有的不确定性和服役环境的复杂性,理论模型的预测结果与实际结构检测的耐久状况存在较大偏差。该文利用工程耐久性检测获得的碳化深度、检测钢筋锈蚀比例、检测混凝土开裂比例,综合先验知识,基于贝叶斯理论,提出碳化环境下的耐久性模型更新方法。结合结构实际的检测结果,经过更新的耐久性预测模型与待评估结构实际耐久状况更相符。依此模型进行相应剩余耐久寿命的概率预测和耐久性评级,为既有结构耐久性评估提供参考。     

Prediction model of carbonation depth for recycled aggregate concrete

The prediction of carbonation depth for recycled aggregate concrete (RAC) is investigated in this paper. The existing prediction models were evaluated, and it showed that the coefficient of variation (COV) of model error for the existing models is high. By introducing the weighed water absorption of aggregates, the COV of model error can be effectively decreased. Compared with the existing models, the proposed model can predict more accurate carbonation depths. For RAC specimens, compared with the fib model and Xiao and Lei's model-a, the COV of model error of the proposed model is 0.36 which is decreased by 33.3%, and when compared with Xiao and Lei's model-b and Silva et al.’s model, the corresponding decreases are 55.2% and 16.2%. Finally, the proposed model is validated by a 10-year-old carbonation experiment, which indicates that the proposed model is reasonable and can be applied to predict the carbonation depth of RAC.     

Effect of composition,environmental factors and cement-lime mortar coating on concrete carbonation

The paper describes the physicochemical processes of concrete carbonation and presents a simple mathematical model for the evolution of carbonation in time, applicable under constant relative humidity higher than 50%. The model is based on fundamental principles of chemical reaction engineering, and uses as parameters the ambient concentration of CO₂, the molar concentratrations of the carbonatable constituents, Ca(OH)₂ and CSH, in the concrete volume, and the effective diffusivity of CO₂ in carbonated concrete. The latter is given by an empirical function of the porosity of hardened cement paste and of relative humidity, derived from laboratory diffusion tests. The validity of the model for OPC or pozzolanic cement concretes and mortars is demonstrated by comparison of its predictions with accelerated carbonation test results obtained in an environment of controlled CO₂ concentration, humidity and temperature. The mathematical model is extended to cover the case of carbonation of the coating-concrete system, for concrete coated with a cement-lime mortar finish, applied either almost immediately after the end of concrete curing or with a delay of a certain time. Parametric studies are performed to show how the evolution of carbonation depth with time is affected by cement and concrete composition (water/cement or aggregate/cement ratio, percentage OPC or aggregate replacement by a pozzolan), environmental factors (relative humidity, ambient concentration of CO₂), the presence and the time of application of a lime-cement mortar coating and its composition (water/cement, aggregate/cement and lime/cement ratios of the mortar, percentage OPC or aggregate replacement by a pozzolan).     

Effect of carbonation on the rebound number and compressive strength of concrete

Experimental research was performed to clarify the influence of carbonation on the rebound number and the strength evolution of concrete for three strength levels. The results reveal that the strength level dependent influence of carbonation is a source of errors in the existing equations for the strength reduction coefficient; these equations are used to compensate for the influence of surface carbonation in the rebound number method. A new equation for the strength reduction coefficient that can consider the influence of strength level was developed based on field test data extracted from technical reports of the Korea Research Institute of Standards and Science and of four universities. Over a wide range of strength levels, the equation shows good agreement with strength reduction coefficients established experimentally.     

Moisture conditioning and transport properties of concrete test specimens

An experimental investigation is reported of drying and conditioning concrete at 50°C to obtain a uniform moisture distribution, prior to testing for air permeability and water absorption rate. The use of 100 mm cubes of concrete with a cast-in cylindrical cavity facilitated assessment of moisture distribution and measurement of air permeation through the surface layers of concrete: the moisture distribution was assessed by comparing the relative humidities measured within the cavity and at the surface of the test specimen. Partial drying followed by sealed storage at 50°C for a few days provided a rapid and convenient method of obtaining a uniform moisture distribution. The test results for a range of concretes indicated that air permeability and water absorption rate were very sensitive to the moisture content of the concrete, particularly at relative humidities above 60% and which were common for field exposure. The transport properties of the empty capillary pore system could be assessed using test specimens preconditioned at 60% relative humidity, but preconditioning at 85% relative humidity might be more appropriate for assessing field performance if there is a risk of carbonation induced corrosion.     

Performance of silica fume-calcium hydroxide mixture as a repair material

The aim of this experimental work was to investigate the performance of a special concrete repair material. The use of silica fume (SF)-Ca(OH)₂ mixture, with and without cement addition in reinforced mortars has been studied. The examination of the hydration reaction progress by X-Ray Diffraction (XRD), Differential Thermal Analysis-Thermogravimetry (DTA-TG), and Scanning Electron Microscopy (SEM) analysis of SF-Ca(OH)₂ mixture with various cement ratios, shows that calcium silicate hydrate is formed in a desired extent. Damaged specimens repaired by the above-mentioned materials also showed low carbonation depth and the lowest corrosion rate, close to of undamaged specimens. This is attributed to the formation of C–S–H compounds at the interface between these mixtures and cement mortar, resulting in the creation of good binding properties of the repair materials.