1、Description of Concrete Durability Damage ProcessAbstract: Based on the damage mechanics, the concrete damage grade of relative stable environment in measurable spatial is constructed in this paper, and the concrete damage evolving model and corresponding failure rule is constructed based on the dam

2、age grade fore-defined. Therefore, the concrete health status and the residual life-span can be assessed according to the measured damage grade. It is propitious to drive the development of concrete durability assessment and life-span forecast. Its feasibility of concrete damage process description

3、and health assessment is validated with the example in this paper, in which the damage state is described with the ultrasound velocity attenuation, and the freeze-thaw process is regarded as the concrete durability degradation influeneing factor to reflect the concrete durability degradation process

4、.Keywords: concrete, durability damage, life-span assessment, health monitoring, ultrasonic velocity0 .IntroductionIn city infrastructures reconstruction , concrete structures are common .So it is necessary to carry out the research on the concrete structure health monitoring,structural diagnosis an

5、d life-span evaluationThe current health monitoring and structural diagnosis method of concrete structures primarily contain two major two types，one is to supervise and control them timely at service，then pass the collection of the structural dynamic displacements，velocity and acceleration，via numer

6、ical analysis to the monitor and evaluate continuously the health progress of the structure; another is to periodically or aperiodically check and measure the structure non-destructively，and to analyzethe examination data to assess the structure progressively. Each of them has its superiority and dr

7、awbacks which should be considered in the further research and development.Except the paroxysmal process，the breakage of concrete structure is a gradual process,and the structural health deterioration should be closely linked with this processThe concrete structural gradual failure exhibits mainly i

8、ts durability failure .Concretely，it includes the concrete materiaI durability deterioration ,reinforcement steel material durability deterioration，and the bond strength between concrete and reinforcement lost graduallyThe latter two factors are interrelated closely with the concrete materiaI durabi

9、lity deteriorationNo matter which one results in the concrete material durability deterioration，in the macroscopic view it exhibits as the internal structures loosen ,defects initiation， cracks propagationDetecting and catching the concrete damage，constructing the concrete damage evolving model，then

10、 the durability deterioration of concrete structure can be monitored，and the assessment on the remaining life-span of concrete structures wil1 be realizedSuppose concrete be an isotropic system including random tiny cracksTaking the tiny unit in the concrete construction as the research object，at th

11、e initial moment，the damage defects on the tiny unit are ，and the external stress on the unit is At arbitrary moment ，the damage defects in the tiny unit are ，and the outside stress on the unit is shown in Fig.1. For the concrete gradual breakage are the results of unstable crack propagation of the

12、defects in the unit which arise from the influence of various factors，we regard the dispersive defects as a uniform field，and evaluate whole the effects of all defectsSo the materia1 damage grade can be defined asWhere, is the time parameter，describes the inner resisting state of the concrete at arb

13、itrary momentis the damage state of the concrete unit at the initial momentObviously，the structura1 damage grade D reaches：Because the force field and the corresponding displacement field of the tiny unit is related to its inner resisting state，via the damage mechanics method the relationship among

14、the concrete damage grade，the leading factor and the material parameter can be establishedNamelywhere is the material parameter of element I and is the stress status of corresponding element.The material damage evolving equation reflected primarily the damage grade change with the timeUsing the dama

15、ge grade defined in the Eq(1)and the damage mechanics principle，the concrete damage evolving equation can be establishedwhere，D0，D is the damage grade at the initial moment and arbitrary moment t respectively，D is the change rate of damage gradeAlong with the developing of the damage，the degradation

16、 of the materia1 on micro structure turns worse gradually，finally results in the failure of the materialThe damage grade corresponding to this condition should meet the failure criterion of damage：where，Df is the damage grade when concrete lost its carrying capacityThe whole process and the statuses

17、 of the concrete material of damage evolving with the time up to destroy is described by Eq(3) and Eq(4)3. Damage Development Equations Conversion to the Measurable SpatialThe damage variable defined in Eq(1) is a commonly damage mechanics variable，it is necessary to convert it to the measurable spa

18、tial convenient for the application in engineering It is shown in Fig2And then，the damage evolving Eq(3)and the failure criterion of damage Eq(4)can be mapped onto the measurable spatial asEq(5) and Eq(6) are the damage evolving equation and the failure criterion of concrete damage in the measurable

19、 spatial ( Fig3)，where D ，D is the damage grade at initial moment and arbitrary moment t in measurable spatial respectively，D is the corresponding change rate of damage grade4. Concrete Health AssessmentTo monitor the structuraI health and evaluate the life-span of concrete，the homologous constructi

20、on health evaluation criterion based on Eq(5)and Eq(6)should be establishedSupposing the measured material damage grade at a certain moment is Dt* ，the corresponding failure damage grade is Df*，then the health grade H based on the damage evolving equation can be defined asThe time when concrete reac

21、hing the failure damage grade can be defined as tf，with the measured damage grade Dt* ，the corresponding time ti can be determined with damage evolving equation shown in Fig.3, then the residual life-span R is Take the concrete degradation caused by freeze-thaw as an example，using the ultrasonic vel

22、ocity as the measurable meansThe concrete ultrasonic velocity change in the freeze-thaw process is defined as the damage variable，(where v is the concrete initia1 ultrasonic velocity，v is the freeze-thaw concrete ultrasonic veloeity)，the freeze-thaw damage evolving model based on the damage mechanic

23、s can be construeted aswhere k1，k2 is the material parameter，T is the freezethaw cycle period and T =8 h according to GBJ 8285, Dc is the damage degree according to Nc，N is the freezethaw cycle numbers， is the tensile strength of concrete andThe corresponding freeze-thaw damage failure criterion is

24、defined as：D *=Df*，N=NuThe corresponding material parameter k1，k2 and Nc can be determined according to the experimentation results of common concrete(D40,D60)and high performance ( H40，H60) in the strength grade (C40，C60)Corresponding damage evolving rule is established as in Fig4According to the m

25、easured damage grade and Eq(9)，the freeze-thaw cycle number can be determined，by which the concrete freeze-thaw health grade and the residual life-span could be reflectedTheresearch results show that it is possible to evaluate the health condition and the remaining life-span of the concrete by the m

26、ethod in the textFor the interaction of multifactors the evaluation of damage grade still need further researchOn the other hand，for the concrete damage failure criterion is the key factor to determine the concrete break，how to establish the concrete failure criterion in the measurable spatial uniqu

27、ely，still need much more thorough and comprehensive research混凝土耐久性損傷過程的描述摘要：在損傷力學的基礎上，本文闡述了在可測量的范圍內相對穩(wěn)定的環(huán)境中混凝土的損傷等級，混凝土損傷演化模型和相應的失效定義根據(jù)先前明確定義的損害等級確定。因此，混凝土具體的健康狀況和殘余壽命可以根據(jù)測定的損害等級得到評定。它有利于推動混凝土耐久性評估和壽命預測的發(fā)展。本文采用實例證明混凝土破壞過程的描述和健康狀態(tài)評估是可行性的，其中的損傷狀態(tài)采用超聲波速度的衰減描述，以及冷凍解凍過程中被視為是混凝土耐久性退化影響因素，以反映混凝土耐久性的退化過程。關鍵

28、詞: 健康檢測 超聲波檢測0. 簡介在城市基礎設施的建設與重建中混凝土結構是非常常見的，因此，有必要進行這項對混凝土結構健康監(jiān)測，結構診斷與壽命評估的研究。目前混凝土結構的健康監(jiān)控和結構性診斷的方法主要包含兩大類：一類是時時的監(jiān)管和控制，然后經(jīng)過收集結構動態(tài)的位移，速度和加速度，通過數(shù)值分析，以持續(xù)的監(jiān)測和評價結構的健康發(fā)展的狀態(tài) 2-5 ;另一大類是定期或不定期的檢查和測量結構的非破壞程度，并分析檢查的數(shù)據(jù)，以逐步評估結構的健康狀態(tài) 6-10 。這兩種方法都有自己其應進一步考慮研究與發(fā)展的優(yōu)點和缺點11-12。除了在突發(fā)性過程中，混凝土建筑結構的破損都是一個漸進的過程 1 ，且建筑結構健康狀

29、態(tài)的惡化要緊密聯(lián)系這一過程。混凝土建筑結構逐漸失效的例子主要是其耐久性的耗盡。具體地說，它包括混凝土材料耐久性惡化，增強作用的鋼筋的耐久性惡化，還有混凝土和鋼筋的粘結強度的逐漸消失。其中后兩個因素是與混凝土材料耐久性惡化密切聯(lián)系的。無論哪一個原因導致混凝土材料的耐久性失效，從宏觀上看，它展示出的都是內部結構疏松，缺陷引發(fā)，裂縫發(fā)展 14，15。1. 混凝土破壞狀態(tài)通過檢測和追蹤混凝土的損害情況，構建混凝土損傷演化模型，然后就可以監(jiān)測混凝土結構的耐久性惡化狀態(tài)，并實現(xiàn)評估混凝土結構的殘余壽命的目的。假設混凝土是各向同性系統(tǒng)，包括其中的任意細小裂紋。以混凝土結構中的任一微小單元為研究對象。在最初的

30、時刻，微小單元上的缺陷是因為混凝土的逐漸斷裂是微小單元上缺陷擴展的不穩(wěn)定裂紋的結果，該單位受各種因素的影響，我們把分散的缺陷看作為一個統(tǒng)一的領域，并評估所有缺陷的影響，所以該損害等級可以被界定為 (1)其中：t 為時間參數(shù)，為任意時刻混凝土的抵抗狀態(tài)，為最初時刻混凝土單元的破壞狀態(tài)。很明顯，結構破壞等級D的范圍為：0<D<1因為微小單元的力場和相應的位移場是和其內部的抵抗狀態(tài)有關的，采用損傷力學方法就可以建立起混凝土損傷等級，主導因素和材料參數(shù)之間的關系。即： 其中：是質點i的材料參數(shù) 是相應應力狀態(tài)的元素2. 混凝土損傷演變方程和損傷破壞準則展開的材料破壞方程主要反映損害等級隨時間變化。損害等級的定義在式（ 1 ）和損傷力學