JP5467026B2 - Method for evaluating delayed fracture characteristics of PC steel - Google Patents
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本発明は、各種コンクリート構造物の補強材として使用されるＰＣ鋼材の遅れ破壊特性を評価する方法に関するものである。 The present invention relates to a method for evaluating delayed fracture characteristics of PC steel used as a reinforcing material for various concrete structures.
コンクリートポールやコンクリート杭に代表されるコンクリート製品には、ＰＣ（プレストレストコンクリート）鋼材が補強材として用いられる。ＰＣ鋼材には、熱処理によって製造されるＪＩＳ Ｇ ３１３７の「細径異形ＰＣ鋼棒」、冷間加工によって製造されるＪＩＳ Ｇ ３５３８の「ＰＣ硬鋼線」がある。細径異形ＰＣ鋼棒は、引張強さが１４２０ＭＰａ以上のものが規格化されており、ＰＣ硬鋼線では、引張り強さが最大１７４０ＭＰａまでの高強度材が規格化されている。なお、本発明ではＰＣ鋼棒、ＰＣ硬鋼線を総称してＰＣ鋼材と呼ぶ。 For concrete products represented by concrete poles and concrete piles, PC (prestressed concrete) steel is used as a reinforcing material. PC steel includes JIS G 3137 “small-diameter deformed PC steel bar” manufactured by heat treatment and JIS G 3538 “PC hard steel wire” manufactured by cold working. The thin deformed PC steel bar has a standardized tensile strength of 1420 MPa or more, and the PC hard steel wire standardizes a high strength material having a maximum tensile strength of 1740 MPa. In the present invention, PC steel bars and PC hard steel wires are collectively referred to as PC steel materials.
このような高強度のＰＣ鋼材に引張り力が作用し、長期間、使用環境に晒された場合、コンクリート中であっても、いわゆる遅れ破壊が発生することがある。ＰＣ鋼材の遅れ破壊は、亀裂等からコンクリート内に雨水が浸入してＰＣ鋼材の表面の腐食が進行し、これに伴ってＰＣ鋼材中に水素が浸入し、破断に至る現象である。このようなＰＣ鋼材の遅れ破壊は、設置後数年から数十年を経て発生することがある。 When a tensile force acts on such high-strength PC steel and is exposed to a use environment for a long time, so-called delayed fracture may occur even in the concrete. Delayed fracture of PC steel is a phenomenon in which rainwater infiltrates into concrete due to cracks and the like, and corrosion of the surface of the PC steel progresses, and hydrogen infiltrates into the PC steel, leading to fracture. Such delayed fracture of PC steel may occur several years to several decades after installation.
一般に、腐食現象は環境によって大きく変化する。したがって、遅れ破壊特性を正確に評価するためには、実際に使用される環境に、使用状態と同等の応力が負荷された試験体を暴露して、破断の発生の有無を見極めることが望ましい。しかし、暴露試験では、遅れ破壊が発生するまでに、数十年も要することから、促進試験による評価が一般的である。例えば、ＰＣ鋼材の遅れ破壊特性は、ＦＩＰ（国際プレストレストコンクリート協会）の基準による評価方法（以下ＦＩＰ試験と記す）が採用されている。 In general, the corrosion phenomenon varies greatly depending on the environment. Therefore, in order to accurately evaluate the delayed fracture characteristics, it is desirable to determine whether breakage has occurred or not by exposing a test body loaded with a stress equivalent to the usage condition to the environment in which it is actually used. However, in an exposure test, it takes several decades for delayed fracture to occur, so evaluation by an accelerated test is common. For example, an evaluation method based on FIP (International Prestressed Concrete Association) standard (hereinafter referred to as FIP test) is adopted for delayed fracture characteristics of PC steel.
ＦＩＰ試験は、質量％で２０％濃度のＮＨ4ＳＣＮ水溶液を５０℃±１℃に加熱し、溶液中にサンプルを浸漬して破断荷重の０．７〜０．８倍の一定荷重を負荷し、破断時間を測定して、耐遅れ破壊特性を評価する方法である。しかし、ＦＩＰ試験では、鋼材中に浸入する水素量が短時間で数ｐｐｍにまで達するような条件を採用しており、破壊が２００時間程度で発生する。したがって、ＦＩＰ試験の腐食環境は非常に厳しく、数十年を経て、鋼材が破断に至るような水素が鋼材中に導入されるような実環境での耐遅れ破壊特性が正確に評価できるかどうか、疑問である。 In the FIP test, an NH 4 SCN aqueous solution of 20% by mass is heated to 50 ° C. ± 1 ° C., a sample is immersed in the solution, and a constant load 0.7 to 0.8 times the breaking load is applied. In this method, the fracture time is measured to evaluate the delayed fracture resistance. However, in the FIP test, a condition is adopted in which the amount of hydrogen entering the steel material reaches several ppm in a short time, and the breakdown occurs in about 200 hours. Therefore, the corrosive environment of the FIP test is very severe, and whether the delayed fracture resistance in an actual environment where hydrogen that would cause the steel material to break can be accurately evaluated after decades has passed , Doubt.
一方、遅れ破壊発生の原因と考えられている鋼材中の水素量を基準として、鋼材に水素をチャージし、一定荷重を負荷した状態で破断しない水素量を基に遅れ破壊特性を評価する方法が提案されている（例えば、非特許文献１）。しかし、この方法では、鋼材の水素測定を行うための水素分析装置が必要となる。さらに試験中に水素の散逸を防止するために鋼材表面にめっき層を形成する等の処理が必要であり、簡便に遅れ破壊特性を評価するには費用、作業の点で課題がある。 On the other hand, based on the amount of hydrogen in steel, which is considered to be the cause of delayed fracture, a method of evaluating delayed fracture characteristics based on the amount of hydrogen that does not break under a constant load when hydrogen is charged to the steel. It has been proposed (for example, Non-Patent Document 1). However, this method requires a hydrogen analyzer for measuring hydrogen in the steel material. Furthermore, treatment such as forming a plating layer on the surface of the steel material is necessary in order to prevent hydrogen dissipation during the test, and there are problems in terms of cost and work to easily evaluate delayed fracture characteristics.
特許文献１には実環境に近い条件でのボルトの遅れ破壊試験方法が示されている。この方法は使用環境と同一の条件で遅れ破壊試験を行うための治具が提案されている。しかし、このように実環境に近い状態で遅れ破壊試験を行う場合、破断時間は４０００〜７０００時間にも達し、試験結果を得るのに時間がかかり、結果を迅速に得られないという問題がある。
従来の遅れ破壊評価方法は、ＦＩＰ試験のように全く実環境と異なる条件であったり、評価するために専門の装置が必要であったり、評価時間が非常に長くなる等の問題があった。さらに、評価試験方法によって優劣が異なるという結果が得られたり、遅れ破壊の実体と評価結果が一致していないことがあるなど、評価の信頼性が低いという問題があった。そこで、実環境に晒された場合の遅れ破壊特性の評価と同等の結果が得られ、かつ短時間で評価可能な遅れ破壊評価方法の開発が要求されている。 The conventional delayed fracture evaluation method has problems such as the FIP test under completely different conditions from the actual environment, a specialized device is required for the evaluation, and the evaluation time becomes very long. Furthermore, there is a problem that the reliability of the evaluation is low, such as a result that the superiority or inferiority varies depending on the evaluation test method, or the fact that the delayed fracture entity and the evaluation result do not match. Therefore, it is required to develop a delayed fracture evaluation method capable of obtaining results equivalent to the evaluation of delayed fracture characteristics when exposed to a real environment and capable of evaluating in a short time.
本発明は、このような実情に鑑み、実際の鋼材の遅れ破壊の評価結果が実態と一致し、簡便かつ迅速に評価可能な、ＰＣ鋼材の遅れ破壊特性評価方法を提供するものである。 In view of such circumstances, the present invention provides a method for evaluating delayed fracture characteristics of PC steel, in which the evaluation results of delayed fracture of actual steel are consistent with the actual situation and can be evaluated easily and quickly.
本発明は、ＰＣ鋼材への浸入水素量と、試験溶液の成分、ｐＨ、温度、比液量の影響および試験片の形状などの破断促進条件と評価基準について詳細に検討を行い、得られた知見に基づいてなされたものであり、その要旨は以下のとおりである。
（１）一定の荷重を負荷した試験片を試験溶液に浸漬して遅れ破壊特性を評価するＰＣ鋼材の遅れ破壊特性評価方法において、前記試験溶液は、Ｃｌイオン濃度：０．１〜１．０ｇ／ｌ、ＳＯ4イオン濃度：０．５〜１０ｇ／ｌ、ＳＣＮイオン濃度：０．１〜３ｇ／ｌを含み、温度が４５〜５５℃、ｐＨが６．５〜７．２であり、表面にノッチを形成した試験片を試験溶液に浸漬し、試験溶液の容量を試験溶液に接触している試験片の表面積で除した比液量を５〜３０ｍｌ／ｃｍ2とし、試験期間中試験溶液と大気を遮断するとともに前記試験片に一定の荷重を負荷し、予め定めた限界時間まで破断が発生しない耐破断限界荷重を測定し、該耐破断限界荷重と平滑試験片の大気中での破断荷重との比を求めて限界荷重比とすることを特徴とするＰＣ鋼材の遅れ破壊特性評価方法。
（２）前記試験片のノッチの最大深さが０．２〜０．５ｍｍであることを特徴とする（１）に記載のＰＣ鋼材の遅れ破壊特性評価方法。
（３）前記予め定めた限界時間を２００時間以上とすることを特徴とする（１）又は（２）に記載のＰＣ鋼材の遅れ破壊特性評価方法。
The present invention has been obtained by examining in detail the breakage acceleration conditions and evaluation criteria such as the amount of hydrogen penetrating into PC steel, the effects of test solution components, pH, temperature, specific liquid volume, and the shape of the test piece. Based on the findings, the summary is as follows.
(1) In the method for evaluating delayed fracture characteristics of PC steel, in which a test piece loaded with a constant load is immersed in a test solution to evaluate delayed fracture characteristics, the test solution has a Cl ion concentration of 0.1 to 1.0 g. / L, SO 4 ion concentration: 0.5-10 g / l, SCN ion concentration: 0.1-3 g / l, temperature is 45-55 ° C., pH is 6.5-7.2, surface A test piece with a notch formed in the test solution is immersed in the test solution, and the volume of the test solution divided by the surface area of the test piece in contact with the test solution is 5 to 30 ml / cm 2. The test piece is loaded with a constant load, and the breakage limit load at which no breakage occurs until a predetermined limit time is measured. It is characterized by determining the ratio with the load and setting it as the limit load ratio Method for evaluating delayed fracture characteristics of PC steel.
(2) The method for evaluating delayed fracture characteristics of PC steel according to (1), wherein the maximum depth of the notch of the test piece is 0.2 to 0.5 mm.
(3) The method for evaluating delayed fracture characteristics of PC steel according to (1) or (2), wherein the predetermined limit time is 200 hours or more.
本発明によれば、実環境に近い条件の浸入水素量を鋼材に導入し、短時間で遅れ破壊特性の評価が可能で、実製品の破断実態と遅れ破壊特性の評価結果が一致し、簡便かつ短時間でＰＣ鋼材の遅れ破壊の評価が可能となり実際のコンクリート製品の破損を予測できるために産業上の貢献が極めて顕著である。 According to the present invention, the amount of intrusion hydrogen under a condition close to the actual environment is introduced into the steel material, and the delayed fracture characteristics can be evaluated in a short time. In addition, since it is possible to evaluate delayed fracture of PC steel materials in a short time and predict the breakage of actual concrete products, the industrial contribution is extremely remarkable.
ＰＣ鋼材の遅れ破壊は、コンクリート製品の補強材として使用され、緊張力が作用しているＰＣ鋼材が、一定時間を経た時点で突然破断する現象である。その原因として、コンクリート製品のひび割れ部を通して雨水が浸透し、局部的に鋼材表面に腐食が発生して、ＰＣ鋼材に水素が浸入することが挙げられる。時間の経過にともない水素量が増加すると、ＰＣ鋼材が脆化し、破断に至ると考えられる。また、ＰＣ鋼材の強度が高いほど遅れ破壊感受性は高くなる。 Delayed fracture of PC steel is a phenomenon in which PC steel, which is used as a reinforcing material for concrete products and is subjected to tension, suddenly breaks after a certain period of time. The cause is that rainwater permeates through the cracked portion of the concrete product, the steel surface is locally corroded, and hydrogen enters the PC steel. If the amount of hydrogen increases with the passage of time, it is considered that the PC steel material becomes brittle and breaks. Moreover, delayed fracture susceptibility increases as the strength of PC steel increases.
一般に、腐食が原因となる現象については、暴露試験による評価が最も現実的であり、信頼性のある方法である。しかし、暴露試験では、ＰＣ鋼材が破断するまでに数十年もかかってしまう。一方、ＦＩＰ試験に代表される促進試験では、短時間でＰＣ鋼材が破断に至るものの、実環境から侵入する水素量に比べて多量の水素が鋼中に侵入してしまう。 In general, for phenomena caused by corrosion, evaluation by an exposure test is the most realistic and reliable method. However, in the exposure test, it takes several decades for the PC steel material to break. On the other hand, in the accelerated test represented by the FIP test, although the PC steel material breaks in a short time, a larger amount of hydrogen enters the steel than the amount of hydrogen entering from the actual environment.
したがって、ＰＣ鋼材の遅れ破壊特性を精度よく、かつ効率的に評価するためには、試験片に侵入する水素量が、短時間で、実際に使用される環境から鋼中に侵入する水素量と同等になり、かつ、その後は増加しないことが必要になる。本発明では、ＰＣ鋼材に浸入する水素量が、実使用環境から侵入する水素量にほぼ近い値となるように、試験溶液の条件を適正化した。 Therefore, in order to accurately and efficiently evaluate the delayed fracture characteristics of PC steel, the amount of hydrogen that penetrates the test piece is the amount of hydrogen that penetrates into the steel from the environment where it is actually used in a short time. It is necessary to be equal and not increase thereafter. In the present invention, the conditions of the test solution were optimized so that the amount of hydrogen entering the PC steel material was a value that was approximately close to the amount of hydrogen entering from the actual use environment.
鋼材に侵入する水素量及び鋼材の腐食に大きく影響する重要な要因は、試験溶液のｐＨである。ｐＨが低い場合は鋼中への水素侵入量が増加し、ｐＨが高くなると腐食が抑制されて、鋼中への水素の侵入が抑制される。本発明者らは、Ｃｌイオン濃度：０．２ｇ／ｌ、ＳＯ4イオン濃度：３ｇ／ｌ、ＳＣＮイオン濃度：０．８ｇ／ｌとし、さらにＮａＯＨ水溶液で試験溶液のｐＨを変化させた試験溶液に鋼材を浸漬し、水素浸入量を測定した。その結果の一例を図１に示す。図１に示すように、溶液ｐＨが５程度では１００ｈ経過後もさらに鋼材中への水素の浸入が増加し、実環境での水素侵入状況を再現できないことがわかった。一方、ｐＨを８程度まで増加すると、鋼材への水素浸入が著しく減少し、鋼材が遅れ破壊せず、評価不可能となる。なお、実環境での水素侵入量は０．１〜０．４ｐｐｍ程度である。 An important factor that greatly affects the amount of hydrogen entering the steel and the corrosion of the steel is the pH of the test solution. When the pH is low, the amount of hydrogen penetrating into the steel is increased, and when the pH is high, corrosion is suppressed and the penetration of hydrogen into the steel is suppressed. The present inventors set the Cl ion concentration: 0.2 g / l, the SO 4 ion concentration: 3 g / l, the SCN ion concentration: 0.8 g / l, and further changing the pH of the test solution with an aqueous NaOH solution. The steel material was immersed in and the amount of hydrogen penetration was measured. An example of the result is shown in FIG. As shown in FIG. 1, it was found that when the solution pH was about 5, the intrusion of hydrogen into the steel material further increased after 100 hours had passed, and the hydrogen intrusion situation in the actual environment could not be reproduced. On the other hand, when the pH is increased to about 8, the hydrogen intrusion into the steel material is remarkably reduced, the steel material is not delayed and destroyed, and evaluation becomes impossible. Note that the hydrogen penetration amount in the actual environment is about 0.1 to 0.4 ppm.
以下、耐遅れ破壊評価方法を検討して図２〜５に示す評価結果を得るに際し、試験溶液として、Ｃｌイオン濃度：０．２ｇ／ｌ、ＳＯ4イオン濃度：３ｇ／ｌ、ＳＣＮイオン濃度：０．８ｇ／ｌとし、さらにＮａＯＨ水溶液でｐＨを６．９に調整した試験溶液を使用して試験を行った。 Hereinafter, when examining the delayed fracture resistance evaluation method and obtaining the evaluation results shown in FIGS. 2 to 5, as a test solution, Cl ion concentration: 0.2 g / l, SO 4 ion concentration: 3 g / l, SCN ion concentration: The test was conducted using a test solution adjusted to 0.8 g / l and adjusted to pH 6.9 with an aqueous NaOH solution.
破断促進するには負荷荷重を増すか、表面に何らかの欠陥を形成する方法が考えられる。本発明者らは、ＰＣ鋼材の遅れ破壊が、比較的、マイルドな腐食環境でも発生することから、ＰＣ鋼材の表面に何らかの欠陥が発生しており、少量の水素の侵入によってＰＣ鋼材が破断すると考えた。そこで、本発明者らは、実際にコンクリート構造物からＰＣ鋼材を取り出し、その表面を詳細に観察した。その結果、表面に孔食状の欠陥が形成され、破断に至ることが確認された。 In order to promote breakage, a method of increasing the load or forming some defect on the surface can be considered. Since the delayed fracture of the PC steel occurs even in a relatively mild corrosive environment, the present inventors have generated some defects on the surface of the PC steel, and when the PC steel breaks due to a small amount of hydrogen intrusion. Thought. Therefore, the present inventors actually took out the PC steel material from the concrete structure and observed the surface in detail. As a result, it was confirmed that pitting corrosion-like defects were formed on the surface, leading to fracture.
そこで、実環境の腐食に近い状態を模擬するため、実際の腐食の影響を再現するように、試験片の表面にノッチを形成し、応力集中により破断を促進することにした。ノッチの深さは、応力状態を変化させ、遅れ破壊が発生する水素量に影響を及ぼす重要な因子である。 Therefore, in order to simulate a state close to corrosion in an actual environment, a notch was formed on the surface of the test piece so as to reproduce the effect of actual corrosion, and the fracture was accelerated by stress concentration. The depth of the notch is an important factor that changes the stress state and affects the amount of hydrogen at which delayed fracture occurs.
機械加工で０．１〜０．６ｍｍの深さのＶノッチを試験片に形成し、負荷荷重を変えて遅れ破壊が発生するまでの時間を測定した。なお、Ｖノッチは引張り荷重に対して直角方向に形成した。破断時間とノッチ深さの関係の一例を図２に示す。図２に示すように、ノッチが深い場合は破断時間が短くなり、試験時間を短縮でき、効率的であるが、０．５ｍｍを超える深いノッチでは短時間破断するために試験条件によらず破断時間の差が小さくなるため遅れ破壊特性の評価を行う上で好ましくない。一方、ノッチ深さが０．２ｍｍ未満では破断時間が長くなり、評価に時間がかかるとともに鋼材が遅れ破壊しないケースが発生するので好ましくない。 A V-notch having a depth of 0.1 to 0.6 mm was formed on the test piece by machining, and the time until delayed fracture occurred by changing the load was measured. The V notch was formed in a direction perpendicular to the tensile load. An example of the relationship between the fracture time and the notch depth is shown in FIG. As shown in FIG. 2, when the notch is deep, the rupture time is shortened and the test time can be shortened, which is efficient. However, when the notch is deeper than 0.5 mm, it breaks for a short time regardless of the test conditions. Since the time difference is small, it is not preferable in evaluating delayed fracture characteristics. On the other hand, if the notch depth is less than 0.2 mm, the rupture time is long, and it takes time for evaluation and a case where the steel material does not break with delay occurs.
遅れ破壊特性を評価する基準としては一定荷重下での破断時間と、負荷荷重を変えて破断しない限界の荷重で評価することが考えられるが、より鋼材の遅れ破壊特性を正確に評価可能な基準について検討した。 The criteria for evaluating delayed fracture characteristics may be to evaluate the fracture time under a constant load and the limit load that does not break by changing the applied load. Was examined.
ＦＩＰ試験のように、遅れ破壊特性の評価基準を破断時間とする場合は破断時間が鋼材間で大きく異なるために、時間の経過にともなう鋼材中の水素量の変動影響を受けやすくなる。その結果、図３に示すように、ほぼ同じ限界拡散性水素量の鋼材でも破断時間が大きく変化する。この結果、コンクリート製品の破断実体とは必ずしも一致した傾向が得られない。 When the evaluation criterion of delayed fracture characteristics is the fracture time as in the FIP test, the fracture time varies greatly among the steel materials, so that it is likely to be affected by fluctuations in the amount of hydrogen in the steel material over time. As a result, as shown in FIG. 3, the rupture time varies greatly even with a steel material having substantially the same critical diffusible hydrogen content. As a result, it is not always possible to obtain a tendency that is consistent with the fracture entity of the concrete product.
そこで、本発明では、ＰＣ鋼材が水素浸入環境下で破断しない限界の荷重によって遅れ破壊特性を評価することにした。即ち、試験片を試験溶液に浸漬し、一定の荷重を負荷して予め定めた一定時間経過後の破断の有無を見極める。負荷荷重を変化させて試験を繰り返し、遅れ破壊が発生しない限界の荷重を求め、耐破断限界荷重とする。ただし、ＰＣ鋼材の高強度化とともに遅れ破壊に対する感受性が高くなる。そこで、本発明では、試験によって求めた耐破断限界荷重を、全く脆化処理を行わない平滑なＰＣ鋼材の破断荷重によって除して正規化し、限界荷重比として評価することにした。限界拡散性水素量の評価については非特許文献１に記載の方法で行った。その結果の一例を図４に示す。本発明の限界荷重比で評価した結果は、限界拡散性水素量を基準として評価した場合の遅れ破壊特性と良く一致し、コンクリート構造物の破損実態に一致する結果となることが確認された。
Therefore, in the present invention, it was decided to evaluate the delayed fracture characteristics by the limit load that does not cause the PC steel material to break in the hydrogen infiltration environment. That is, the test piece is immersed in the test solution, and a predetermined load is applied to determine whether or not there is a break after a predetermined time has elapsed. The test is repeated while changing the applied load, and the limit load at which delayed fracture does not occur is obtained and set as the fracture resistant limit load. However, the sensitivity to delayed fracture increases as the strength of PC steel increases. Therefore, in the present invention, the breaking resistance limit load obtained by the test is normalized by dividing by the breaking load of a smooth PC steel material that is not subjected to embrittlement at all, and evaluated as a limit load ratio. The evaluation of the limit diffusible hydrogen amount was performed by the method described in
さらに、本発明者らは、試験溶液の経時変化にも着目した。図５に示すように、試験溶液が大気と接触する場合は、時間の経過に伴って空気中の二酸化炭素を吸収し、１００時間を超えると、ｐＨが低下することがわかった。そのため、鋼材に浸入する水素の挙動が変化し、遅れ破壊特性が変動することがある。したがって、試験時間が１００時間を超える条件では、遅れ破壊特性を安定して評価するためには、空気中の二酸化炭素が試験溶液に溶解しないように、試験溶液を大気から遮断することが好ましい。 Furthermore, the present inventors also focused on the change with time of the test solution. As shown in FIG. 5, when the test solution was in contact with the atmosphere, it was found that the carbon dioxide in the air was absorbed with the passage of time, and the pH was lowered when it exceeded 100 hours. For this reason, the behavior of hydrogen entering the steel material changes, and the delayed fracture characteristics may change. Therefore, under conditions where the test time exceeds 100 hours, in order to stably evaluate delayed fracture characteristics, it is preferable to block the test solution from the atmosphere so that carbon dioxide in the air does not dissolve in the test solution.
以下、本発明について、詳細に説明する。 Hereinafter, the present invention will be described in detail.
Ｃｌイオン濃度：
Ｃｌイオンは鋼材の腐食促進成分である。Ｃｌイオン濃度が、０．１ｇ／ｌ未満では腐食が進行せず、水素の浸入が著しく低下し遅れ破壊が発生しないため破断に至らない。また、１．０ｇ／ｌ超のＣｌイオン濃度を添加しても腐食促進効果が飽和する。したがって、試験溶液のＣｌイオン濃度は、０．１〜１．０ｇ／ｌとする。
Cl ion concentration:
Cl ion is a corrosion promoting component of steel. When the Cl ion concentration is less than 0.1 g / l, corrosion does not proceed, hydrogen penetration is significantly reduced, and delayed fracture does not occur, so that fracture does not occur. Further, even if a Cl ion concentration exceeding 1.0 g / l is added, the corrosion promoting effect is saturated. Therefore, the Cl ion concentration of the test solution is 0.1 to 1.0 g / l.
ＳＯ4イオン濃度：
ＳＯ4イオンも鋼材の腐食促進成分であり、Ｃｌと複合添加することで、より実環境に近い状態の腐食環境となる。ＳＯ4イオン濃度が０．５ｇ／ｌ未満では鋼材の腐食が進まず水素が鋼中に侵入せず、遅れ破壊が発生しない。一方、ＳＯ4イオン濃度が１０ｇ／ｌを超えると、鋼中に侵入する水素量が多くなり、実環境からの乖離が顕著になる。したがって、試験溶液のＳＯ4濃度は０．５〜１０ｇ／ｌとする。
SO 4 ion concentration:
SO 4 ions are also a corrosion-promoting component of steel materials, and when added together with Cl, a corrosive environment closer to the actual environment is obtained. When the SO 4 ion concentration is less than 0.5 g / l, the corrosion of the steel material does not proceed and hydrogen does not enter the steel and delayed fracture does not occur. On the other hand, when the SO 4 ion concentration exceeds 10 g / l, the amount of hydrogen that penetrates into the steel increases and the deviation from the actual environment becomes remarkable. Therefore, the SO 4 concentration of the test solution is 0.5 to 10 g / l.
ＳＣＮイオン濃度：
ＳＣＮイオンは触媒的に作用し、鋼材への水素浸入を促進する。ＳＣＮイオンはコンクリート内に浸入した水溶液中から検出されることから、本発明では、実環境を再現するために試験溶液に添加する。ＳＣＮイオン濃度が０．１ｇ／ｌ未満では鋼材中への水素侵入が少なく、遅れ破壊が発生しない。一方、ＳＣＮイオン濃度が３ｇ／ｌを超えると、鋼材への水素浸入が著しく増加し、実環境と大きく異なる。したがって、ＳＣＮイオン濃度は０．１〜３ｇ／ｌとする。
SCN ion concentration:
SCN ions act catalytically and promote hydrogen penetration into the steel. Since SCN ions are detected from an aqueous solution infiltrated into the concrete, in the present invention, they are added to the test solution in order to reproduce the actual environment. When the SCN ion concentration is less than 0.1 g / l, hydrogen penetration into the steel material is small, and delayed fracture does not occur. On the other hand, when the SCN ion concentration exceeds 3 g / l, hydrogen intrusion into the steel material is remarkably increased, which is greatly different from the actual environment. Therefore, the SCN ion concentration is 0.1 to 3 g / l.
試験溶液のｐＨ：
ｐＨは、鋼材に侵入する水素量及び鋼材の腐食に大きく影響する重要な要因である。本発明者らの検討により、ｐＨを７前後に調整した溶液では約５０時間で鋼材に浸入する水素量が飽和し、一定の水素量での遅れ破壊挙動を評価できることが明らかになった。ｐＨが６．５未満では鋼材の水素侵入量が増加して、遅れ破壊特性の優劣の精度が低下する。一方、ｐＨが７．２を超えると鋼材への水素侵入量が大きく低下し、鋼材に侵入する水素量が飽和するまでに長時間を要する。したがって、本発明では、試験溶液のｐＨを６．５〜７．２とする。
PH of test solution:
The pH is an important factor that greatly affects the amount of hydrogen entering the steel and the corrosion of the steel. As a result of studies by the present inventors, it has been clarified that in a solution whose pH is adjusted to around 7, the amount of hydrogen entering the steel material is saturated in about 50 hours, and the delayed fracture behavior can be evaluated with a constant amount of hydrogen. When the pH is less than 6.5, the hydrogen penetration amount of the steel material increases, and the superiority or inferior accuracy of the delayed fracture property decreases. On the other hand, when the pH exceeds 7.2, the amount of hydrogen entering the steel material is greatly reduced, and it takes a long time until the amount of hydrogen entering the steel material is saturated. Therefore, in the present invention, the pH of the test solution is set to 6.5 to 7.2.
試験溶液の温度：
試験溶液温度が低い場合は鋼材への水素浸入が少なくなり、高いと侵入水素量が多くなるとともに試験溶液の蒸発により試験条件が変化する。また、試験溶液温度は、試験片の表面での腐食状況にも影響を及ぼすため、一定の範囲内に制御することが必要である。本発明の試験溶液では、温度が５０℃になると、実環境から侵入する水素量に近くなる。また、試験溶液温度が変化すると、評価結果のばらつきが大きくなるため、変動の範囲を１０℃以内にすることが必要である。したがって、安定した腐食環境で、一定の速度で試験片に水素を侵入させるため、本発明では、試験溶液の温度範囲を４５〜５５℃とする。
Test solution temperature:
When the test solution temperature is low, hydrogen permeation into the steel material is reduced. When the test solution temperature is high, the amount of invading hydrogen is increased and the test conditions are changed by evaporation of the test solution. Moreover, since the test solution temperature also affects the corrosion state on the surface of the test piece, it must be controlled within a certain range. In the test solution of the present invention, when the temperature reaches 50 ° C., the amount of hydrogen entering from the actual environment is close. In addition, when the test solution temperature changes, the variation in evaluation results increases, so the range of fluctuation must be within 10 ° C. Therefore, in order to allow hydrogen to enter the test piece at a constant rate in a stable corrosive environment, the temperature range of the test solution is set to 45 to 55 ° C. in the present invention.
比液量：
比液量は、試験溶液に浸漬している試験片の単位表面積あたりの試験溶液容量である。試験片及び試験槽の形状、使用する試験溶液の容量から、試験溶液に接触している試験片の表面積を算出し、使用している試験溶液の容量を除することにより、比液量を求めることができる。比液量が３０ｍｌ／ｃｍ2を超えると、長時間、連続的に試験片に水素が侵入するため、遅れ破壊特性の優劣の精度が低下する。一方、比液量が５ｍｌ／ｃｍ2未満であると、短時間で試験片に水素が侵入しなくなり、鋼材中の水素量も減少し、遅れ破壊破断が発生し難くなる。したがって、短時間で、実環境に近い侵入水素量にするためには、試験溶液の比液量を５〜３０ｍｌ／ｃｍ2とすることが必要である。
Specific liquid volume:
The specific liquid amount is the test solution volume per unit surface area of the test piece immersed in the test solution. Calculate the surface area of the test piece in contact with the test solution from the shape of the test piece and the test tank and the volume of the test solution to be used, and calculate the specific liquid volume by dividing the volume of the test solution in use. be able to. When the specific liquid amount exceeds 30 ml / cm 2 , hydrogen penetrates into the test piece continuously for a long time, so that the accuracy of delayed fracture characteristics is deteriorated. On the other hand, when the specific liquid amount is less than 5 ml / cm 2 , hydrogen does not enter the test piece in a short time, the amount of hydrogen in the steel material also decreases, and delayed fracture breakage hardly occurs. Therefore, in order to make the amount of penetrating hydrogen close to the real environment in a short time, it is necessary to set the specific liquid amount of the test solution to 5 to 30 ml / cm 2 .
試験片のノッチ深さ：
試験片のノッチ深さは、破断を促進させるために応力集中を再現するため、引張り荷重に対して直角方向に形成する。試験片の円周方向の全周に環状ノッチとしても、部分的にノッチを形成してもかまわない。ノッチ深さが０．２ｍｍ未満では、破断時間が２０００ｈ以上になること、鋼材によっては負荷荷重を高めても破断せず、遅れ破壊の評価が難しくなることがあるので、ノッチ深さの下限を０．２ｍｍとすると好ましい。一方、０．５ｍｍより深いノッチの場合は短時間で破断するものの、荷重比を変えても破断時間の変化が小さくなり、鋼材の遅れ破壊特性の優劣が判断できなくなることがあるため、０．５ｍｍをノッチ深さの上限とすると好ましい。
Notch depth of specimen:
The notch depth of the test piece is formed in a direction perpendicular to the tensile load in order to reproduce the stress concentration in order to promote breakage. An annular notch or a notch may be partially formed on the entire circumference in the circumferential direction of the test piece. If the notch depth is less than 0.2 mm, the fracture time will be 2000 h or more, and depending on the steel material, it will not break even if the load is increased, and it may be difficult to evaluate delayed fracture. 0.2 mm is preferable. On the other hand, a notch deeper than 0.5 mm breaks in a short time, but even if the load ratio is changed, the change in the fracture time becomes small, and the superiority or inferiority of the delayed fracture characteristics of the steel material may not be judged. It is preferable that 5 mm is the upper limit of the notch depth.
なお、鋼材間の遅れ破壊の比較は勿論同一ノッチ深さで行うものであるが、ノッチ深さのばらつきは０．０５ｍｍ以内とすれば試験結果のばらつきは小さくなるため、±０．０５ｍｍが深さばらつきとして好ましく、より好ましくは０．０２ｍｍである。 Of course, the comparison of delayed fracture between steel materials is performed at the same notch depth. However, if the variation in notch depth is within 0.05 mm, the variation in test results will be small. It is preferable as the thickness variation, and more preferably 0.02 mm.
遅れ破壊特性の評価基準：
本発明では、遅れ破壊特性の評価基準を破断荷重とする。これは、破断時間による評価の場合、時間の経過にともなって鋼材中の水素量が変動し、コンクリート製品の破断の実体とは必ずしも一致した傾向が得られないためである。本発明では、試験片を試験溶液に浸漬し、一定の荷重を負荷して予め定めた一定時間経過後の破断の有無を見極める。負荷荷重を変化させて試験を繰り返し、遅れ破壊が発生しない限界の荷重を求め、耐破断限界荷重とする。予め定めた一定時間を２００時間あるいはそれ以上とすれば、耐破断限界荷重を再現性よく評価することが可能である。この耐破断限界荷重を、予め求めた、ノッチを有しない平滑試験片の大気中での破断荷重で除して、限界荷重比として評価する。平滑試験片は平滑であり、大気中で破断を評価するので、全く脆化処理を行わない試験片に相当する。また平滑試験片はノッチを形成した試験片と同一径とすると好ましい。
Evaluation criteria for delayed fracture characteristics:
In the present invention, the evaluation criterion for delayed fracture characteristics is the fracture load. This is because in the case of the evaluation based on the rupture time, the amount of hydrogen in the steel material fluctuates with the passage of time, and a tendency that does not necessarily coincide with the rupture entity of the concrete product cannot be obtained. In the present invention, a test piece is immersed in a test solution, a constant load is applied, and whether or not there is a fracture after a predetermined time has elapsed is determined. The test is repeated while changing the applied load, and the limit load at which delayed fracture does not occur is obtained and set as the fracture resistant limit load. If the predetermined time is set to 200 hours or more, it is possible to evaluate the fracture limit load with good reproducibility. This breaking resistance limit load is divided by the breaking load in the air of a smooth test piece not having a notch obtained in advance, and evaluated as a limit load ratio. Since the smooth test piece is smooth and breakage is evaluated in the air, it corresponds to a test piece that is not subjected to embrittlement at all. The smooth test piece preferably has the same diameter as the test piece having a notch.
大気との遮断の影響：
本発明の試験溶液は、大気に接触すると空気中の二酸化炭素を吸収し、ｐＨが低下する。そのため、遅れ破壊特性を安定して評価するためには、大気と試験溶液を遮断することが好ましい。大気と試験溶液を遮断する方法は特に限定はされないが、試験容器内にアルゴンなどの不活性ガスを充満させる方法、試験溶液の表面をシール材で覆う方法などが挙げられる。例えば、図６に示すように、試験容器の内壁あるいは試験片が貫通可能な形状とし、大気と遮断するために試験溶液表面に浮かせる構造が好ましい。このような構造にすることにより、試験容器の形状を変えることなく、試験片のサイズによる比液量を一定に制御することが可能となるとともに、試験溶液のｐＨを安定して維持できる。
Impact of shielding from the atmosphere:
When the test solution of the present invention comes into contact with the atmosphere, it absorbs carbon dioxide in the air and the pH decreases. Therefore, in order to stably evaluate the delayed fracture characteristics, it is preferable to shut off the atmosphere and the test solution. The method for shutting off the atmosphere and the test solution is not particularly limited, and examples thereof include a method of filling the test container with an inert gas such as argon, and a method of covering the surface of the test solution with a sealing material. For example, as shown in FIG. 6, a structure in which the inner wall of the test container or the test piece can be penetrated and floated on the surface of the test solution in order to block it from the atmosphere is preferable. By adopting such a structure, it is possible to control the specific liquid amount according to the size of the test piece to be constant without changing the shape of the test container, and it is possible to stably maintain the pH of the test solution.
表１に示す成分の線径８ｍｍの熱間圧延線材を７ｍｍに伸線した後、高周波加熱によりオーステナイト域まで加熱後、水焼入れし、さらに連続して鋼材を３５０〜６５０℃に加熱して焼戻し、引張強さを１４５０ＭＰａに調整した。試験片の試験溶液に接触する部分の中心部の表面には、環状に角度６０度のＶノッチを形成した。表２に、ノッチの深さを示す。 A hot-rolled wire rod having a wire diameter of 8 mm having the components shown in Table 1 is drawn to 7 mm, heated to an austenite region by high-frequency heating, then water-quenched, and the steel material is continuously heated to 350 to 650 ° C. and tempered. The tensile strength was adjusted to 1450 MPa. A V-notch having an angle of 60 degrees was formed annularly on the surface of the central portion of the portion of the test piece that contacts the test solution. Table 2 shows the depth of the notches.
試験溶液は、ＣｌイオンとしてＫＣｌ、ＳＯ4イオンとしてＫ2ＳＯ4、ＳＣＮイオンとしてＮＨ4ＳＣＮを溶解し、その濃度を調整した。薬剤を溶解した直後の試験溶液のｐＨは４〜５と低いため、ＮａＯＨ水溶液で試験溶液のｐＨを調整した。内径が６５ｍｍ、溶液充てん部長さが２００ｍｍであり、図６に示すように、外周部に温水を循環可能な二重構造の反応容器に試験片をセットした。先に一定荷重を負荷した後に試験溶液を充てんし、二重構造容器外周部を循環させる温水の温度によって、試験溶液温度を調整した。 The test solution, KCl as Cl ions as K 2 SO 4, SCN ions as SO 4 ions by dissolving NH 4 SCN, and adjust the concentration. Since the pH of the test solution immediately after dissolving the drug was as low as 4-5, the pH of the test solution was adjusted with an aqueous NaOH solution. The inner diameter was 65 mm, the solution filling part length was 200 mm, and as shown in FIG. 6, a test piece was set in a double-structured reaction vessel capable of circulating hot water on the outer periphery. The test solution was filled with the test solution after a certain load was applied first, and the test solution temperature was adjusted by the temperature of the hot water circulating through the outer periphery of the double structure container.
試験片に負荷する荷重を変化させて試験を繰り返し行い、遅れ破壊破断しない限界の負荷荷重比を求めた。ここでは破断しない限界の試験時間を２００ｈとした。 The test was repeated by changing the load applied to the test piece, and the limit load ratio was determined so as not to cause delayed fracture. Here, the limit test time without breaking was 200 h.
Ｎｏ．１〜２０は本発明の試験条件の範囲でＰＣ鋼材の遅れ破壊特性を評価した結果であり、鋼材の遅れ破壊特性は同一鋼種間で大きな差異はなく、安定した限界荷重比が得られた。また、ノッチ深さが０．２〜０．５ｍｍの範囲では鋼種毎の限界荷重比はＢ鋼が０．８５〜０．９、Ｃ鋼が０．７、Ｅ鋼が０．６５〜０．７、Ｄ鋼が０．５〜０．６５、Ａ鋼が０．４〜０．５で、遅れ破壊特性の序列はＢ＞Ｃ〜Ｅ＞Ｄ＞Ａとなった。一方、水素基準で評価した限界拡散性水素量は表１に示すとおりであり、限界拡散性水素量での評価の序列はＢ＞Ｃ〜Ｅ＞Ｄ＞Ａであった。即ち、本発明による遅れ破壊評価の序列は水素基準で評価した限界拡散性水素量での評価の序列と概略一致し、実環境での破断実態にほぼ一致する傾向である。ノッチ深さが０．２ｍｍ未満あるいは０．５ｍｍ超でも鋼材の限界荷重比の序列はＢ＞Ｃ＞Ａでほぼノッチ深さの範囲が一定であれば遅れ破壊特性の序列は変わらない。 No. 1 to 20 are the results of evaluating the delayed fracture characteristics of PC steel materials within the range of the test conditions of the present invention. The delayed fracture characteristics of the steel materials were not significantly different between the same steel types, and a stable limit load ratio was obtained. In addition, in the range where the notch depth is 0.2 to 0.5 mm, the critical load ratio for each steel type is 0.85 to 0.9 for Steel B, 0.7 for Steel C, 0.65 to 0.00 for Steel E. 7, Steel D was 0.5 to 0.65, Steel A was 0.4 to 0.5, and the order of delayed fracture characteristics was B> C to E> D> A. On the other hand, the limit diffusible hydrogen amount evaluated on the basis of hydrogen is as shown in Table 1, and the order of evaluation based on the limit diffusible hydrogen amount was B> C to E> D> A. That is, the rank order of delayed fracture evaluation according to the present invention roughly matches the rank order of the critical diffusible hydrogen amount evaluated based on the hydrogen standard, and tends to substantially match the actual fracture condition in the actual environment. Even if the notch depth is less than 0.2 mm or more than 0.5 mm, the order of the limit load ratio of the steel material is B> C> A and if the range of the notch depth is substantially constant, the order of the delayed fracture characteristics does not change.
一方、本発明の範囲外の比較例では同一鋼種の遅れ破壊特性が大きく変化し、鋼種間の差が検出できず、精度良い評価ができていない。 On the other hand, in the comparative example outside the scope of the present invention, the delayed fracture characteristics of the same steel type change greatly, the difference between the steel types cannot be detected, and accurate evaluation cannot be performed.
比較例のＮｏ．２１はＣｌイオンが多く、腐食が進行し低い荷重比で破断した例である。Ｎｏ．２２はＣｌイオンが少なく、遅れ破壊試験での限界荷重比が高くなった例である。Ｎｏ．２３はＳＯ4イオンが多く、腐食が進行し、低い荷重比で破断した例である。Ｎｏ．２４はＳＯ4イオンが少なく、遅れ破壊試験での限界荷重比が高くなった例である。Ｎｏ．２５はＳＣＮイオンが多く、腐食が進行し、低い荷重比で破断した例である。Ｎｏ．２６はＳＣＮイオンが少なく、遅れ破壊しなかった例である。 Comparative Example No. No. 21 is an example in which there are many Cl ions, corrosion progresses and fractures at a low load ratio. No. No. 22 is an example in which Cl ions are few and the limit load ratio in the delayed fracture test is high. No. No. 23 is an example in which there are many SO 4 ions, corrosion progresses, and fracture occurs at a low load ratio. No. No. 24 is an example in which the SO 4 ions are small and the limit load ratio in the delayed fracture test is high. No. No. 25 is an example in which there are many SCN ions, corrosion progresses, and fracture occurs at a low load ratio. No. No. 26 is an example in which there were few SCN ions and the destruction was not delayed.
Ｎｏ．２７は試験溶液温度が低く、限界荷重比が高くなり、Ｎｏ．２８は試験溶液温度が高く、限界荷重比が低くなり、同一鋼種で限界荷重比が大きく変化した例である。Ｎｏ．２９は試験溶液のｐＨが高い場合で、鋼材への水素侵入が少なく、限界荷重比が高くなった例である。一方、Ｎｏ．３０はｐＨが本発明の範囲より低く、鋼中への水素侵入量が多くなり、限界荷重比が低くなった例である。Ｎｏ．３１は比液量が多く、鋼材に長時間連続して水素が侵入し、限界荷重比が低くなった例である。Ｎｏ．３２は比液量が少なく鋼材に侵入する水素量が少なくなり、荷重比が高くなった例である。 No. No. 27 has a low test solution temperature and a high limit load ratio. No. 28 is an example in which the test solution temperature is high, the limit load ratio is low, and the limit load ratio is greatly changed in the same steel type. No. No. 29 is an example in which the pH of the test solution is high, hydrogen penetration into the steel material is small, and the critical load ratio is high. On the other hand, no. No. 30 is an example in which the pH is lower than the range of the present invention, the hydrogen penetration amount into the steel is increased, and the limit load ratio is lowered. No. No. 31 is an example in which the amount of specific liquid is large, hydrogen penetrates into the steel material continuously for a long time, and the limit load ratio becomes low. No. No. 32 is an example in which the amount of hydrogen entering the steel material is small because the amount of specific liquid is small and the load ratio is high.
Ｎｏ．３３はノッチを形成しない試験片で遅れ破壊試験を実施した例であり、２００時間経過しても破断しなかった例である。Ｎｏ．３４は大気と試験溶液が接触する構造の試験容器を使用したため、遅れ破壊試験期間中の試験溶液ｐＨが低下し、限界荷重比が低下した例である。 No. No. 33 is an example in which a delayed fracture test was carried out with a test piece not forming a notch, and it was not broken even after 200 hours. No. No. 34 is an example in which the test solution pH in the delayed fracture test period was lowered and the critical load ratio was lowered because a test container having a structure in which the atmosphere and the test solution were in contact with each other was used.
本発明によれば高強度ＰＣ鋼材の遅れ破壊評価が迅速かつ簡便に実施可能となり、かつ実体により近い状態での評価が可能となることにより鋼材の遅れ破壊特性をより正確に評価可能である。コンクリート製品の破損を防止可能となることから産業上の利用可能性が極めて高い。 According to the present invention, delayed fracture evaluation of a high-strength PC steel can be performed quickly and easily, and the evaluation in a state closer to the substance can be performed, whereby the delayed fracture characteristics of the steel can be evaluated more accurately. Since it is possible to prevent the breakage of concrete products, the industrial applicability is extremely high.
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