JP6575991B2 - Method for measuring crack initiation strength of ultra high strength fiber reinforced concrete - Google Patents
Method for measuring crack initiation strength of ultra high strength fiber reinforced concrete Download PDFInfo
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本発明は、超高強度繊維補強コンクリートのひび割れ発生強度を高い精度で測定する方法と、該方法に用いる超高強度繊維補強コンクリートの供試体に関する。 The present invention relates to a method for measuring the cracking strength of ultra-high-strength fiber reinforced concrete with high accuracy and a specimen of ultra-high-strength fiber reinforced concrete used in the method.
超高強度繊維補強コンクリートが一軸引張力を受ける場合、荷重が小さい初期の段階では線形弾性が成立するが、さらに荷重が大きくなってひび割れが発生すると、線形弾性は成立しない。そこで、非特許文献１では、引張応力（荷重）とひずみの関係を示すグラフ上で、線形弾性が不成立となる点の応力を、ひび割れ発生強度と定め、ひび割れ発生後の最大応力である引張強度と区別している。ちなみに、非特許文献１では、超高強度繊維補強コンクリートのひび割れ発生強度（設計値）は８Ｎ／ｍｍ２、引張強度（設計値）は８．８Ｎ／ｍｍ２と規定している。
前記ひび割れ発生強度の測定方法には、直接引張強度試験、割裂引張強度試験（図１、非特許文献１の図３．２．４）、および曲げ強度試験がある。そして、該測定方法は、原則として、測定対象の構造物に想定されている引張応力の状況を考慮して、これらの試験方法から選択する。しかし、前記直接引張強度試験は、一般性があるものの、その試験方法は標準化されていない。また、割裂引張強度試験は、望ましくはコンクリートの試験方法であるＪＩＳ Ａ １１１３「コンクリートの割裂引張強度試験方法」に準拠して行うとされている。
When the ultra high strength fiber reinforced concrete receives a uniaxial tensile force, linear elasticity is established at the initial stage where the load is small, but when the load is further increased and cracking occurs, the linear elasticity is not established. Therefore, in Non-Patent Document 1, on the graph showing the relationship between tensile stress (load) and strain, the stress at the point where linear elasticity is not established is defined as the crack initiation strength, and the tensile strength which is the maximum stress after the crack has occurred. It is distinguished from. Incidentally, Non-Patent Document 1 stipulates that the cracking strength (design value) of the ultra-high-strength fiber reinforced concrete is 8 N / mm 2 and the tensile strength (design value) is 8.8 N / mm 2 .
The cracking strength measurement method includes a direct tensile strength test, a split tensile strength test (FIG. 1, FIG. 3.2.4 of Non-Patent Document 1), and a bending strength test. In principle, the measurement method is selected from these test methods in consideration of the state of tensile stress assumed for the structure to be measured. However, although the direct tensile strength test is general, the test method has not been standardized. The split tensile strength test is desirably performed in accordance with JIS A 1113 “Concrete split tensile strength test method” which is a concrete test method.
しかし、引張強度が３Ｎ／ｍｍ２程度のコンクリートの割裂引張強度試験を、引張強度が８．８Ｎ／ｍｍ２と格段に高い超高強度繊維補強コンクリートのひび割れ発生強度の測定に用いると、ひび割れ発生強度のバラツキが大きくなり測定精度が低下する。 However, when the split tensile strength test of concrete with a tensile strength of about 3 N / mm 2 is used to measure the crack initiation strength of ultra-high-strength fiber reinforced concrete with a tensile strength of 8.8 N / mm 2, which is extremely high, Intensity variation increases and measurement accuracy decreases.
そこで、本発明は、超高強度繊維補強コンクリートのひび割れ発生強度を高い精度で測定する方法と、該方法に用いる超高強度繊維補強コンクリートの供試体を提供することを目的とする。 Therefore, an object of the present invention is to provide a method for measuring the cracking strength of ultra high strength fiber reinforced concrete with high accuracy and a specimen of ultra high strength fiber reinforced concrete used in the method.
本発明者は、超高強度繊維補強コンクリートのひび割れ発生強度のバラツキを小さくするための手段を種々検討した結果、（i）ひび割れ発生強度測定用供試体として用いる円柱供試体の両端面が平滑で、（ii）試験機の上下の加圧板と供試体との接触部分に隙間がなければ、ひび割れ発生強度の測定値のバラツキを小さくできることを見出し、本発明を完成させた。
すなわち、本発明は、以下の構成を有する超高強度繊維補強コンクリートのひび割れ発生強度の測定方法と、超高強度繊維補強コンクリートの供試体である。
As a result of studying various means for reducing the variation in crack generation strength of ultra-high-strength fiber reinforced concrete, the present inventor has found that (i) both end surfaces of a cylindrical specimen used as a specimen for measuring crack generation strength are smooth. (Ii) The present invention has been completed by finding that if there is no gap in the contact portion between the upper and lower pressure plates of the testing machine and the specimen, the variation in the measured value of cracking strength can be reduced.
That is, the present invention is a method for measuring crack occurrence strength of ultrahigh strength fiber reinforced concrete having the following configuration, and a specimen of ultrahigh strength fiber reinforced concrete.
［１］下記（Ａ）〜（Ｄ）工程を経た状態の円柱供試体に載荷して、荷重とひずみの関係を求め、該荷重とひずみの関係において線形弾性が不成立となる点の荷重に対応する引張応力を、ひび割れ発生強度と定めて測定する、超高強度繊維補強コンクリートのひび割れ発生強度の測定方法。
（Ａ）超高強度繊維補強コンクリートの円柱供試体の二つの端面における凹凸の高低差の平均値が、一端面あたり１．５ｍｍ以下になるように研磨する、円柱供試体の研磨工程
（Ｂ）平板の上に、前記研磨した円柱供試体を横向きに載置し、平板と該円柱供試体の側面が接触する部分に、隙間が生じていないか否か確認する第一の確認作業と、隙間が生じていないと確認した場合は、該円柱供試体の側面から１８０°回転した位置にある円柱供試体の側面を、再度、平板の上に載置して、平板と該円柱供試体の側面が接触する部分に、隙間が生じていないか否か確認する第二の確認作業を行い、いずれの確認作業においても隙間が生じていないことを確認できた円柱供試体を、ひび割れ発生強度の測定対象として選別する、測定対象の選別工程
（Ｃ）前記隙間が生じていないと確認した二つの側面を結ぶ面と直交するように、前記選別した円柱供試体の二つの端面の中心にひずみゲージを貼付する、ひずみゲージの貼付工程
（Ｄ）前記隙間が生じていないと確認した二つの側面が、圧縮試験機の上下の加圧板とそれぞれ接触するように、前記円柱供試体を圧縮試験機に載置する、円柱供試体の載置工程
ただし、
荷重が５０ｋＮまでの範囲内において、
(i)前記二つの端面のひずみが正と負の逆（非対称）になる場合、
(ii)一つの端面においてひずみが生じない場合、
(iii)一つの端面のひずみが、他の端面のひずみの１．５倍以上になる場合
のいずれかの場合が生じたとき、
下記（ａ）および（ｂ）工程を経て選別された特性値が、閾値を超えたとき、
のいずれのときも、載荷を中断して除荷した後、前記（Ｂ）〜（Ｄ）工程を再実施して、再度、載荷を行う。
（ａ）ひずみが１００×１０−６までの範囲内において、荷重と二つの端面のひずみの実測値を用いて、各端面ごとに、荷重（説明変数）とひずみ（目的変数）の比例関係を表す二つの単回帰式を求める、単回帰分析工程
（ｂ）前記二つの単回帰式中の傾きの値を比較して、大きい方の値を特性値として選別する、特性値の選別工程
［２］ひび割れ発生強度が５Ｎ／ｍｍ２以上の超高強度繊維補強コンクリートを、ひび割れ発生強度の測定対象とする、前記［１］に記載の超高強度繊維補強コンクリートのひび割れ発生強度の測定方法。
[1] Loaded on a cylindrical specimen in the following steps (A) to (D) to obtain the relationship between the load and strain, corresponding to the load at which linear elasticity is not established in the relationship between the load and strain A method for measuring the cracking strength of ultra-high strength fiber reinforced concrete, in which the tensile stress to be measured is determined as cracking strength.
(A) Polishing process of cylindrical specimen (B), wherein the average value of the unevenness of the unevenness on the two end faces of the cylindrical specimen of ultra high strength fiber reinforced concrete is 1.5 mm or less per one end face (B) The polished cylindrical specimen is placed sideways on a flat plate, and a first confirmation operation for checking whether or not a gap has occurred in a portion where the flat plate and the side surface of the cylindrical specimen are in contact with each other, and a gap If it is confirmed that the side surface of the cylindrical specimen is rotated 180 ° from the side face of the cylindrical specimen, the side face of the cylindrical specimen is placed again on the flat board, and the side face of the flat specimen and the cylindrical specimen Measure the cracking strength of the cylindrical specimen that was confirmed to be free of any gaps in any of the confirmation operations. Sorting target to be measured (C) A strain gauge application step (D) in which a strain gauge is attached to the center of the two end faces of the selected cylindrical specimen so as to be orthogonal to the surface connecting the two side surfaces that have been confirmed not to have the gap. ) Placement step of the columnar specimen on the compression tester so that the two side surfaces confirmed that the gap does not occur are in contact with the upper and lower pressure plates of the compression tester, respectively. However,
Within the load range up to 50kN,
(i) When the strains of the two end faces are opposite to each other (asymmetric),
(ii) If there is no distortion at one end face,
(iii) When any of the cases where the strain of one end face is 1.5 times or more of the strain of the other end face occurs ,
When the characteristic value selected through the following steps (a) and (b) exceeds a threshold value ,
In any case, after the loading is interrupted and unloaded, the steps (B) to (D) are performed again, and the loading is performed again.
(A) Within the range of strain up to 100 × 10 −6 , the proportional relationship between load (explanatory variable) and strain (target variable) is obtained for each end surface using the measured values of load and strain at the two end surfaces. A single regression analysis step for obtaining two single regression equations to be expressed (b) A characteristic value selection step [2] of comparing the slope values in the two single regression equations and selecting the larger value as a characteristic value [2 ] The method for measuring the cracking strength of ultrahigh-strength fiber reinforced concrete according to [1] above, wherein the cracking strength is an ultrahigh-strength fiber-reinforced concrete having cracking strength of 5 N / mm 2 or more.
本発明の超高強度繊維補強コンクリートのひび割れ発生強度の測定方法は、測定効率が高く、また、ひび割れ発生強度の測定値のバラツキを小さくできるため、測定精度が高い。 The method for measuring the crack occurrence strength of the ultra-high strength fiber reinforced concrete of the present invention has high measurement efficiency and high measurement accuracy because the variation in the measurement value of crack occurrence strength can be reduced.
１．超高強度繊維補強コンクリートのひび割れ発生強度の測定方法
本発明の超高強度繊維補強コンクリートのひび割れ発生強度の測定方法は、前記のとおり、（Ａ）円柱供試体の研磨工程、（Ｂ）測定対象の選別工程、（Ｃ）ひずみゲージの貼付工程、および（Ｄ）円柱供試体の載置工程を経た状態の円柱供試体に載荷して、荷重とひずみの関係を求め、該荷重とひずみの関係において線形弾性が不成立となる点の荷重に対応する引張応力を、ひび割れ発生強度と定めて測定する方法である。なお、本発明において、超高強度繊維補強コンクリートは、コンクリートの他に超高強度繊維補強モルタルも含む概念である。
以下、本発明について、前記各工程に分け、図２〜図１１を用いて詳細に説明する。
1. Method for measuring crack generation strength of ultra high strength fiber reinforced concrete As described above, the method for measuring the crack generation strength of ultra high strength fiber reinforced concrete is (A) polishing process of cylindrical specimen, (B) measurement target Loading process, (C) strain gauge attaching process, and (D) loading the cylindrical specimen in a state where the cylindrical specimen was placed, obtaining the relation between the load and the strain, and the relation between the load and the strain In this method, the tensile stress corresponding to the load at the point where linear elasticity is not established is determined as the crack generation strength. In the present invention, ultra high strength fiber reinforced concrete is a concept that includes ultra high strength fiber reinforced mortar in addition to concrete.
Hereinafter, the present invention will be described in detail with reference to FIGS.
（Ａ）円柱供試体の研磨工程
該工程は、超高強度繊維補強コンクリートの円柱供試体の二つの端面における凹凸の高低差の平均値が、一端面あたり１．５ｍｍ以下になるように研磨する工程である。
超高強度繊維補強コンクリートの円柱供試体の上面（打ち込み面）および下面（底面）は、凹凸があるため荷重が不均一になり易く、ひび割れ発生強度のバラツキが大きくなる。したがって、該端面を平滑にするため、二つの端面を研磨する。上面の鋼繊維や余盛りがバリになっている場合があること、特に上面には気泡が多くみられること（図２）、また下面は型枠底面付近に歪みがある場合があることを考慮すると、研磨する厚さ（長さ）は、一端面あたり、好ましくは５〜１０ｍｍである。また、該研磨した二つの端面における凹凸の高低差の平均値は、一端面あたり、好ましくは１．５ｍｍ以下である。なお、前記高低差の平均値は、一端面あたり、より好ましくは１．０ｍｍ以下、さらに好ましくは０．５ｍｍ以下である。前記高低差はノギス等を用いて測定できる。また、研磨装置としてはコンクリート端面成形機が挙げられる。
なお、超高強度繊維補強コンクリートの円柱供試体の作製は、前記ＪＩＳ Ａ １１１３「コンクリートの割裂引張強度試験方法」に準拠して行うとよい。該供試体の作製時において、型枠面のエントラップトエアの低減を目的として行う、木槌等を用いた型枠面の打撃や加振は、コンクリート中の繊維が沈降しないように最小限に留める。
(A) Polishing process of cylindrical specimen This process is performed so that the average value of the height difference of the irregularities on the two end faces of the cylindrical specimen of ultra high strength fiber reinforced concrete is 1.5 mm or less per one end face. It is a process.
Since the upper surface (driving surface) and the lower surface (bottom surface) of the cylindrical specimen of ultra-high-strength fiber reinforced concrete are uneven, the load is likely to be uneven, and the variation in cracking strength increases. Therefore, in order to smooth the end face, the two end faces are polished. Considering that the upper surface of the steel fiber and the excess may be burred, especially that there are many bubbles on the upper surface (Fig. 2), and that the lower surface may be distorted near the bottom of the formwork Then, the thickness (length) to be polished is preferably 5 to 10 mm per one end face. Moreover, the average value of the level difference of the unevenness | corrugation in these two grind | polished end surfaces is 1.5 mm or less per end surface. In addition, the average value of the height difference is more preferably 1.0 mm or less, and further preferably 0.5 mm or less per one end face. The height difference can be measured using a caliper or the like. Moreover, a concrete end surface molding machine is mentioned as a grinding | polishing apparatus.
The cylindrical specimen of ultra high strength fiber reinforced concrete may be prepared in accordance with the above JIS A 1113 “Concrete split tensile strength test method”. When making the specimen, strike and vibration of the mold surface using a wooden mallet, etc., for the purpose of reducing entrapment air on the mold surface, should be minimized so that the fibers in the concrete do not settle. stop.
（Ｂ）測定対象の選別工程
該工程は、平板の上に、前記研磨した円柱供試体を横向きに載置し、平板と該円柱供試体の側面が線接触する部分（以下「接触線」という。）に隙間が生じないか否か確認する第一の確認作業と、隙間が生じていないと確認した場合は、該円柱供試体の側面から１８０°回転した位置にある円柱供試体の側面を、再度、平板の上に載置して、接触線に隙間が生じないか否か確認する第二の確認作業を行い、いずれの確認作業においても隙間が生じないことを確認できた円柱供試体を、ひび割れ発生強度の測定対象として選別する工程である。
平板の上に、前記研磨した円柱供試体を横向きに載置すると、接触線に隙間が生じている場合がある（図３）。この隙間の存在は、平板と円柱供試体の側面との間に、光をあてるか（図４）、隙間ゲージを挿入するか（図５）、または、平板上に敷いた紙ヤスリの上に円柱供試体を横向きに置き、円柱供試体の長さ方向に沿って前後に移動したときに生じる紙ヤスリ上の擦過線の連続性の有無により確認できる。すなわち、光が漏れていないか、隙間ゲージが挿入できないか、紙ヤスリ上の擦過線に連続性があれば（図６）、接触線に隙間がないことが確認できる（図７）。
隙間が確認された場合は、隙間が確認されない側面を見い出すまで、円柱供試体を少し回転して、別の側面について前記隙間の確認作業（第一の確認作業）を繰り返し行う。
隙間が確認されない側面を見い出した場合は、円柱供試体を該側面から１８０°回転した位置にある側面について、前記隙間の確認作業（第二の確認作業）を行う。そして、第一および第二の確認作業のいずれにおいても、隙間が確認されない側面を見い出すまでは、前記第一および第二の確認作業を繰り返す。なお、継目が長さ方向にある型枠を用いて作製した円柱供試体では、該供試体の継目に当たる側面部分は隙間が大きくかつ多いため、好ましくは、該側面部分は前記確認作業の対象から除く。
そして、第一および第二の確認作業おいて、隙間が確認されない側面を見い出したときは、該円柱供試体をひび割れ発生強度の測定対象として選別し、例えば、後工程である（Ｃ）工程において、ひずみゲージを貼付する位置と方向を明確に表示するために、該円柱供試体の端面の中心を通って隙間が確認されない二つの側面（図８）を結ぶ直線と、該直線に直交する直線の二つの直線を記入する（図９）。
(B) Selection process of measurement object In this process, the polished cylindrical specimen is placed sideways on a flat plate, and the flat plate and the side surface of the cylindrical specimen are in line contact (hereinafter referred to as “contact line”). )) To confirm whether or not there is a gap, and if it is confirmed that there is no gap, the side surface of the cylindrical specimen at a position rotated 180 ° from the side face of the cylindrical specimen The cylinder specimen that was placed on the flat plate again and confirmed whether or not there was a gap in the contact line, and confirmed that there was no gap in any of the confirmation operations. Is selected as a measurement target of cracking strength.
When the polished cylindrical specimen is placed sideways on a flat plate, there may be a gap in the contact line (FIG. 3). The existence of this gap is that light is applied between the flat plate and the side surface of the cylindrical specimen (Fig. 4), a gap gauge is inserted (Fig. 5), or on a paper file laid on the flat plate. This can be confirmed by the presence / absence of continuity of the rubbing line on the paper file generated when the cylindrical specimen is placed sideways and moved back and forth along the length direction of the cylindrical specimen. That is, if there is no light leakage, a gap gauge cannot be inserted, or if there is continuity in the rubbing line on the paper file (FIG. 6), it can be confirmed that there is no gap in the contact line (FIG. 7).
When the gap is confirmed, the cylindrical specimen is rotated a little until the side face where the gap is not found is found, and the gap confirmation work (first confirmation work) is repeated for another side face.
When a side surface in which no gap is confirmed is found, the gap confirmation operation (second confirmation operation) is performed on the side surface at a position where the cylindrical specimen is rotated 180 ° from the side surface. Then, in both the first and second confirmation operations, the first and second confirmation operations are repeated until a side surface where no gap is confirmed is found. In addition, in the cylindrical specimen prepared using the mold having the seam in the length direction, the side part corresponding to the joint of the specimen has a large and large gap. except.
And in the 1st and 2nd confirmation work, when the side surface in which a gap is not confirmed is found, the cylindrical specimen is selected as a measurement object of crack generation strength, for example, in the (C) process which is a post process In order to clearly display the position and direction of applying the strain gauge, a straight line connecting two side faces (FIG. 8) where no gap is confirmed through the center of the end face of the cylindrical specimen, and a straight line orthogonal to the straight line The two straight lines are entered (FIG. 9).
（Ｃ）ひずみゲージの貼付工程
該工程は、前記隙間が生じていないと確認した二つの側面を結ぶ面と直交するように、前記選別した円柱供試体の二つの端面の中心にひずみゲージを貼付する工程である（図１０）。
(C) Strain gauge affixing step In this step, a strain gage is affixed at the center of the two end surfaces of the selected cylindrical specimen so as to be orthogonal to the surface connecting the two side surfaces that are confirmed to have no gap. (FIG. 10).
（Ｄ）円柱供試体の載置工程
該工程は、前記隙間が生じていないと確認した二つの側面が、圧縮試験機の上下の加圧板とそれぞれ接触するように、前記円柱供試体を圧縮試験機に載置する工程である（図１１）。
次に、本発明において、ひび割れ発生強度のバラツキを、さらに抑制する二種類の方法について詳細に説明する。
(D) Cylindrical specimen mounting step This step is a compression test of the cylindrical specimen so that the two side surfaces confirmed to have no gap are in contact with the upper and lower pressure plates of the compression tester, respectively. This is a process of placing on the machine (FIG. 11).
Next, in the present invention, two methods for further suppressing the variation in cracking strength will be described in detail.
２．ひび割れ発生強度のバラツキの抑制（その１）
前記（Ａ）〜（Ｄ）工程を経た後に、前記円柱供試体に載荷して荷重とひずみを測定し、荷重が５０ｋＮまでの範囲内において、
(i)前記二つの端面のひずみが正と負の逆（非対称）になる場合、
(ii)一つの端面においてひずみが生じない場合、
(iii)一つの端面のひずみが、他の端面のひずみの１．５倍以上になる場合
のいずれかが生じたときは、ひび割れ発生強度の測定値のバラツキが大きくなるため、好ましくは、載荷を中断して除荷した後、前記（Ｂ）〜（Ｄ）工程を再実施して、再度、載荷を行う。荷重が５０ｋＮまでの範囲内では、載荷を繰り返しても、得られるひび割れ発生強度の値には影響しない。
なお、超高強度繊維補強コンクリートの円柱供試体への載荷は、ＪＩＳ Ａ １１１３「コンクリートの割裂引張強度試験方法」に準拠して行うとよい。また、荷重とひずみを連続的に測定すれば、ひび割れの発生により線形弾性が不成立になる点が明確に把握できるから好ましい。
2. Suppression of variation in cracking strength (Part 1)
After passing through the steps (A) to (D), the load was applied to the cylindrical specimen, and the load and strain were measured. Within the range of the load up to 50 kN,
(i) When the strains of the two end faces are opposite to each other (asymmetric),
(ii) If there is no distortion at one end face,
(iii) When any one of the cases where the strain of one end face is 1.5 times or more of the strain of the other end face, the variation in the measured value of cracking strength becomes large. After unloading and unloading, the steps (B) to (D) are performed again, and loading is performed again. Within the range of the load up to 50 kN, repeated cracking does not affect the cracking strength value obtained.
The loading of the ultra high strength fiber reinforced concrete onto the columnar specimen may be performed in accordance with JIS A 1113 “Method for testing split tensile strength of concrete”. Further, it is preferable to continuously measure the load and strain because it is possible to clearly grasp the point where linear elasticity is not established due to the occurrence of cracks.
３．ひび割れ発生強度のバラツキの抑制（その２）
さらに、本発明において、ひび割れ発生強度のバラツキを抑制するために、例えば、図１２の（１）に示すように、下記（ａ）および（ｂ）工程を経て選別された特性値が、閾値を超えたときは、載荷を中断して除荷した後、前記（Ｂ）〜（Ｄ）工程を再実施して、再度、載荷を行う。
（ａ）ひずみが１００×１０−６までの範囲内において、荷重と二つの端面のひずみの実測値を用いて、各端面ごとに、荷重（説明変数）とひずみ（目的変数）の比例関係を表す二つの単回帰式を求める、単回帰分析工程（図１２）
ここで、荷重を説明変数（横軸）に、ひずみを目的変数（縦軸）にとるのは、載荷しながらひずみを計測するため、荷重を横軸にとるとグラフが見やすくなるからである。
（ｂ）前記二つの単回帰式中の傾きの値を比較して、大きい方の値を特性値として選別する、特性値の選別工程
ここで、傾きの大きい方の値を、特性値として選別する理由は、経験上、傾きが大きい（引張ヤング係数が小さい）方が、ひび割れ発生強度をより低く（すなわち、安全側で）評価できるからである。
なお、ひずみが１００×１０−６までの範囲では、載荷を繰り返しても、得られるひび割れ発生強度の値には影響しない。
3. Suppression of variation in cracking strength (Part 2)
Furthermore, in the present invention, in order to suppress the variation in crack generation strength, for example, as shown in (1) of FIG. 12, the characteristic value selected through the following steps (a) and (b) has a threshold value. When it exceeds it, after loading is interrupted and unloaded, the steps (B) to (D) are performed again, and loading is performed again.
(A) Within the range of strain up to 100 × 10 −6 , the proportional relationship between load (explanatory variable) and strain (target variable) is obtained for each end surface using the measured values of load and strain at the two end surfaces. Single regression analysis process to obtain two simple regression equations (Fig. 12)
Here, the load is taken as an explanatory variable (horizontal axis) and the strain is taken as an objective variable (vertical axis) because the strain is measured while being loaded.
(B) A characteristic value selection step of comparing the slope values in the two single regression equations and selecting the larger value as the characteristic value. Here, selecting the larger slope value as the characteristic value. The reason for this is that, based on experience, it is possible to evaluate crack generation strength lower (that is, on the safe side) when the slope is larger (the tensile Young's modulus is smaller).
In the range of strain up to 100 × 10 −6 , repeated cracking does not affect the cracking strength value obtained.
次に、前記閾値について説明する。
（１）閾値の考え方
超高強度繊維補強コンクリートのひび割れ発生強度は、すでに述べたように、荷重（引張応力）とひずみの関係において、線形弾性が不成立となる点の荷重（限界応力）である。
そもそも、十分な強度が発現したコンクリートは、弾性体に近い力学的挙動を示すため、鋼材と同様に、荷重とひずみの関係は線形になる。
ここで、コンクリートが完全な弾性体であれば、圧縮応力や引張応力に対するひずみの挙動は、いずれも同じになる。しかし、コンクリートは完全な弾性体ではないため、同一の応力に対し圧縮ひずみと引張ひずみは同じにならず、引張ヤング係数は圧縮ヤング係数より小さくなる（このことは、硬化して十分に強度が発現したコンクリートにおいて一般的に確認されている。ただし、若材齢時の現象は除く。）。例えば、水結合材比が１９〜２５％の高強度コンクリートでは、引張ヤング係数は圧縮ヤング係数の０．８倍程度である。
そこで、本発明で用いる閾値を定めるために、以下の仮定をする。
（i）標準熱養生を行なった超高強度繊維補強コンクリート（ＦＭ）および超高強度繊維補強コンクリート（ＦＯ）の圧縮ヤング係数（Ｅｃ）は、それぞれ、５０ｋＮ／ｍｍ２および４５ｋＮ／ｍｍ２と仮定する。なお、前記ＦＭおよびＦＯは、後記する超強高度繊維補強コンクリート「ダクタル」（登録商標）の品番である。
（ii）引張ヤング係数（Ｅｔ）は、圧縮ヤング係数の０．８倍と仮定する。
（iii）部材安全係数（γ）は１．３と仮定する。
Next, the threshold value will be described.
(1) Concept of threshold The crack initiation strength of ultra-high-strength fiber reinforced concrete is the load (limit stress) at which linear elasticity is not established in the relationship between load (tensile stress) and strain, as described above. .
In the first place, concrete that exhibits sufficient strength exhibits a mechanical behavior close to that of an elastic body, and therefore, the relationship between load and strain is linear, similar to steel.
Here, if the concrete is a perfect elastic body, the behavior of the strain with respect to the compressive stress and the tensile stress is the same. However, since concrete is not a perfect elastic body, the compressive strain and tensile strain are not the same for the same stress, and the tensile Young's modulus is smaller than the compressive Young's modulus. It is generally confirmed in the developed concrete, except for the phenomenon at the young age). For example, in high-strength concrete with a water binder ratio of 19-25%, the tensile Young's modulus is about 0.8 times the compressive Young's modulus.
Therefore, the following assumptions are made to determine the threshold value used in the present invention.
(I) compression Young's modulus of the ultra high strength fiber reinforced concrete was subjected to standard heat curing (FM) and ultra high strength fiber-reinforced concrete (FO) (Ec), respectively, assuming 50 kN / mm 2 and 45 kN / mm 2 To do. The FM and FO are part numbers of “DACTAL” (registered trademark), which will be described later.
(Ii) The tensile Young's modulus (Et) is assumed to be 0.8 times the compressive Young's modulus.
(Iii) The member safety factor (γ) is assumed to be 1.3.
（ｃ２）閾値の決定
これらの仮定に基づき、圧縮ヤング係数（Ｅｃ）と引張ヤング係数（Ｅｔ）の関係式（１）を導出すると、
Ｅｔ＝０．８×Ｅｃ／γ＝０．６１５×Ｅｃ ・・・（１）
一方、引張応力（σ）とひずみ（ε）の関係式（２）は、
σ＝Ｅｔ×ε ・・・（２）
また、引張応力（σ）と荷重（Ｐ）の関係式（３）は、
σ＝２Ｐ／（π×ｄ×Ｌ） ・・・（３）
ただし、（３）式中、ｄは円柱供試体の端面の直径、Ｌは研磨した二つの端面間の距離（長さ）を表す。
よって、前記（１）〜（３）式から、ひずみと荷重の関係式（４）が求まる。
ε＝２／（０．６１５×Ｅｃ×π×ｄ×Ｌ）×Ｐ ・・・（４）
前記（４）式の係数（傾き）である２／（０．６１５×Ｅｃ×π×ｄ×Ｌ）に、Ｅｃ＝５０ｋＮ／ｍｍ２または４５ｋＮ／ｍｍ２、ｄ＝１００ｍｍ、およびＬ＝２００ｍｍを代入すると、超高強度繊維補強コンクリート（ＦＭ）では１．０４、超高強度繊維補強コンクリート（ＦＯ）では１．１７となる。ここで、前記のとおり、経験上、傾きが大きい方が、ひび割れ発生強度をより低く（すなわち、安全側で）評価できるから、小数点以下第二位を切り上げて、それぞれ１．１および１．２を閾値として採用する。
(C2) Determination of threshold value Based on these assumptions, when the relational expression (1) between the compression Young's modulus (Ec) and the tensile Young's modulus (Et) is derived,
Et = 0.8 × Ec / γ = 0.615 × Ec (1)
On the other hand, the relational expression (2) between tensile stress (σ) and strain (ε) is
σ = Et × ε (2)
The relational expression (3) between the tensile stress (σ) and the load (P) is
σ = 2P / (π × d × L) (3)
In the formula (3), d represents the diameter of the end face of the cylindrical specimen, and L represents the distance (length) between the two polished end faces.
Therefore, the relational expression (4) between the strain and the load is obtained from the expressions (1) to (3).
ε = 2 / (0.615 × Ec × π × d × L) × P (4)
Wherein (4) the coefficient a (slope) 2 / (0.615 × Ec × π × d × L) of formula, Ec = 50kN / mm 2 or 45kN / mm 2, d = 100mm , and L = 200 mm When substituted, it is 1.04 for ultra high strength fiber reinforced concrete (FM) and 1.17 for ultra high strength fiber reinforced concrete (FO). Here, as described above, from experience, it can be evaluated that cracking strength is lower (that is, on the safe side) when the slope is larger, so that the second decimal place is rounded up to 1.1 and 1.2, respectively. Is adopted as a threshold value.
３．荷重とひずみの関係に基づくひび割れ発生強度の決定
そして、図１２の（２）に示すように、前記（ａ）および（ｂ）工程を経て選別された特性値が閾値以下の場合には、該（ａ）工程でその一部を使用した荷重とひずみの全載荷期間の実測値を用いて、例えば、荷重を縦軸に、ひずみを横軸にしてグラフ（図１３）を作成し、該グラフから線形弾性が不成立になる点の荷重（Ｐ）の値を読み取り、前記（３）式に代入して、線形弾性が不成立となる点の荷重に対応する引張応力（σ）であるひび割れ発生強度を得る。
3. Determination of cracking strength based on the relationship between load and strain And, as shown in (2) of FIG. 12, when the characteristic value selected through the steps (a) and (b) is below a threshold value, (A) A graph (FIG. 13) is created by using the measured values of the entire loading period of the load and strain using a part of the load in the step, for example, with the load on the vertical axis and the strain on the horizontal axis. Read the value of the load (P) at the point where linear elasticity is not established, and substitute it into the equation (3) above, and the crack initiation strength which is the tensile stress (σ) corresponding to the load at the point where linear elasticity is not established Get.
２．超高強度繊維補強コンクリートの供試体
該供試体は、供試体の二つの端面における凹凸の高低差の平均値が、一端面あたり１．５ｍｍ以下である円柱供試体である。凹凸の高低差の平均値が１．５ｍｍ以下であれば、ひび割れ発生強度のバラツキを小さくできる。なお、前記高低差の平均値は、前記のとおり、好ましくは１．０ｍｍ以下、より好ましくは０．５ｍｍ以下である。
また、超高強度繊維補強コンクリートの円柱供試体は、打設時においてコンクリートの１層打ちを行う以外は、非特許文献１の８０頁に記載の「参考資料２ 強度試験用供試体の作り方」に従い作製する。
2. Specimen of Ultra High Strength Fiber Reinforced Concrete The specimen is a cylindrical specimen having an average height difference of 1.5 mm or less per one end face on the two end faces of the specimen. If the average value of the height difference of the unevenness is 1.5 mm or less, the variation in cracking strength can be reduced. In addition, as above-mentioned, the average value of the said height difference becomes like this. Preferably it is 1.0 mm or less, More preferably, it is 0.5 mm or less.
In addition, the column specimen of ultra-high strength fiber reinforced concrete is “Reference Material 2 How to make a specimen for strength test” described on page 80 of Non-Patent Document 1 except that one layer of concrete is cast at the time of placing. Prepare according to the following.
以下、本発明を実施例により説明するが、本発明はこれらの実施例に限定されない。
１．使用材料とコンクリート配合
使用した超強高度繊維補強コンクリートは、ダクタルＦＭとダクタルＦＯ（登録商標、太平洋セメント社製）であり、単位水量はダクタルＦＭが１８０ｋｇ／ｍ３、ダクタルＦＯが１８５ｋｇ／ｍ３とした。
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
1. Superstrong Advanced Fiber Reinforced Concrete Using the materials used and the concrete mix is Ductal FM and Ductal FO (registered trademark, Pacific Ocean manufactured Cement Co.), and the unit quantity of water is Ductal FM 180 kg / m 3, Ductal FO is 185 kg / m 3 It was.
２．超高強度繊維補強コンクリートのひび割れ発生強度の測定
（１）ダクタルＦＭを用いた供試体の作製
該供試体は、打設時においてコンクリートの１層打ちを行なった以外は、非特許文献１の８０頁に記載の「参考資料２ 強度試験用供試体の作り方」に従い、鋼製型枠を用いて、直径１００ｍｍ、長さ２００ｍｍの円柱供試体を作製した。
なお、エントラップトエアをできる限り巻き込まないように、コンクリートを１層で連続的に前記型枠へ流し込み、振動締固めは行わなかった。また、該コンクリートは、２４時間、気中養生した後に脱型し、さらに９０℃で４８時間、蒸気養生して円柱供試体を作製した（図２）。
2. Measurement of cracking strength of ultra-high-strength fiber reinforced concrete (1) Preparation of specimen using ductal FM The specimen is 80 of Non-Patent Document 1 except that one layer of concrete is cast at the time of placing. A cylindrical specimen having a diameter of 100 mm and a length of 200 mm was produced using a steel mold according to “Reference Material 2 How to Make Specimens for Strength Test” described on page.
In order to prevent entrapment air from being involved as much as possible, concrete was poured continuously into the mold in one layer, and vibration compaction was not performed. The concrete was cured in the air for 24 hours and then demolded, and further steam cured at 90 ° C. for 48 hours to prepare a cylindrical specimen (FIG. 2).
（２）円柱供試体の研磨
次に、該供試体の二つの端面を、コンクリート端面成形機を用いて、両端面ともに５ｍｍ程度研磨して、二つの端面における凹凸の高低差の平均値を、一端面あたり１ｍｍにした。
(2) Polishing of cylindrical specimen Next, the two end faces of the specimen are polished by about 5 mm on both end faces using a concrete end face molding machine, and the average value of the height difference of the irregularities on the two end faces is determined. It was 1 mm per one end face.
（３）測定対象の選別
該研磨した円柱供試体を横向きに載置し、反対側から光をあてて接触線に隙間が生じていないか否か確認した（図４）。隙間が生じていないと確認した後は、該円柱供試体の側面から１８０°回転した位置にある円柱供試体の側面を、再度、平板の上に載置して、接触線に隙間が生じないか否か光をあてて確認した。そして、いずれの確認作業においても隙間が生じないことを確認した円柱供試体を、ひび割れ発生強度の測定対象として選別した（図７）。
(3) Selection of measurement object The polished cylindrical specimen was placed sideways, and light was applied from the opposite side to confirm whether there was a gap in the contact line (FIG. 4). After confirming that there is no gap, place the side face of the cylindrical specimen at a position rotated 180 ° from the side face of the cylindrical specimen again on the flat plate, so that no gap occurs in the contact line. It was confirmed whether it was exposed to light. And the cylindrical specimen which confirmed that a clearance gap does not arise in any confirmation work was selected as a measuring object of crack generation intensity (Drawing 7).
（４）ひずみゲージの貼付
さらに、該円柱供試体の端面の中心を通って隙間が確認されない二つの側面を結ぶ直線と、該直線に直交する直線の二つの直線を記入した（図９）。そして、前記選別した円柱供試体の二つの端面の中心において、前記直交する直線に平行に、ひずみゲージ１とひずみゲージ２を貼付した（図１０）。
(4) Affixing the strain gauge Furthermore, two straight lines were entered, a straight line connecting two side faces through which the gap is not confirmed through the center of the end face of the cylindrical specimen, and a straight line perpendicular to the straight line (FIG. 9). And the strain gauge 1 and the strain gauge 2 were affixed in parallel with the orthogonal straight line at the center of the two end faces of the selected cylindrical specimen (FIG. 10).
（５）円柱供試体の載置
前記隙間が生じていないと確認した二つの側面が、圧縮試験機の上下の加圧板とそれぞれ接触するように、前記円柱供試体を圧縮試験機（型番：ＡＣＡ−１００Ａ、前川試験機製作所社製）に載置した（図１１）。
(5) Placement of the cylindrical specimen The cylindrical specimen is placed on the compression tester (model number: ACA) so that the two side surfaces confirmed to have no gap are in contact with the upper and lower pressure plates of the compression tester, respectively. -100A, manufactured by Maekawa Tester Manufacturing Co., Ltd.) (FIG. 11).
（６）ひび割れ発生強度の測定
ＪＩＳ Ａ １１１３「コンクリートの割裂引張強度試験方法」に準拠して、圧縮試験機に載置した円柱供試体に載荷して、荷重とひずみの関係を求め、該荷重とひずみの関係において線形弾性が不成立となる点の荷重に対応する引張応力からひび割れ発生強度を求めた。
なお、荷重が５０ｋＮまでの範囲内において、(i)二つの端面のひずみが正と負の逆（非対称）になった場合、(ii)一つの端面においてひずみが生じなかった場合、または(iii)一つの端面のひずみが、他の端面のひずみの１．５倍以上になった場合は、載荷を中断して除荷した後、前記（３）〜（５）の工程を再実施して、再度、載荷を行った（再実施１）。
また、１００×１０−６までの範囲のひずみの測定において求めた特性値が、段落００１８において採用した閾値（１．１）を超えた場合も、載荷を中断して除荷した後、前記（３）〜（５）の工程を再実施して、再度、載荷を行った（再実施２）。
ダクタルＦＭの各円柱供試体のひび割れ発生強度の値を表１に示す。また、前記再実施１または再実施２の実施の有無も表１に併記する。
(6) Measurement of cracking strength In accordance with JIS A 1113 “Test method for split tensile strength of concrete”, the test piece was loaded on a cylindrical specimen placed on a compression tester, and the relationship between load and strain was determined. The crack initiation strength was obtained from the tensile stress corresponding to the load at the point where linear elasticity was not established in the relationship between the strain and strain.
It should be noted that within the range of load up to 50 kN, (i) when the distortion of the two end faces is opposite to the positive and negative (asymmetric), (ii) when no distortion occurs at one end face, or (iii ) If the strain of one end face is 1.5 times or more of the strain of the other end face, stop loading and unload, then re-execute the steps (3) to (5). The loading was performed again (re-execution 1).
Further, when the characteristic value obtained in the measurement of the strain in the range of up to 100 × 10 −6 exceeds the threshold (1.1) adopted in paragraph 0018, after the loading is interrupted and the unloading is performed, The steps 3) to (5) were performed again, and loading was performed again (re-execution 2).
Table 1 shows the value of the crack initiation strength of each cylindrical specimen of Ductal FM. In addition, Table 1 also shows whether the re-execution 1 or the re-execution 2 is performed.
比較として、前記段落００２２で作製した円柱供試体を非特許文献１に記載の方法（従来の方法）に準拠して、単回帰式の傾きとひび割れ発生強度を求めた。得られたひび割れ発生強度を表２に示す。また、荷重が５０ｋＮまでの範囲内において、下記(i)〜(iii)のうちのいずれかの発生の有無を表２に示す。
(i)二つの端面のひずみが正と負の逆（非対称）になった。
(ii)一つの端面においてひずみが生じなかった。
(iii)一つの端面のひずみが、他の端面のひずみの１．５倍以上になった。
さらに、１００×１０−６までの範囲のひずみの測定において求めた特性値の値と再実施２の必要性の判定も表２に示す。
As a comparison, the slope of the single regression equation and the crack generation strength were determined for the cylindrical specimen prepared in paragraph 0022 in accordance with the method described in Non-Patent Document 1 (conventional method). Table 2 shows the obtained crack initiation strength. In addition, Table 2 shows whether or not any of the following (i) to (iii) occurs within a load range up to 50 kN.
(i) The strains on the two end faces are opposite to each other (asymmetric).
(ii) No distortion occurred on one end face.
(iii) The strain of one end face was 1.5 times or more of the strain of the other end face.
Furthermore, Table 2 also shows the values of characteristic values obtained in the measurement of strain in the range of up to 100 × 10 −6 and the necessity of re-execution 2.
次に、表１と表２のデータに基づいて算出した、ひび割れ発生強度の平均値、標準偏差、および変動係数を表３に示す。 Next, Table 3 shows the average value, standard deviation, and coefficient of variation of the crack occurrence strength calculated based on the data in Tables 1 and 2.
ダクタルＦＭに代えて、ダクタルＦＯを用いた以外は、前記と同様の試験方法により、単回帰式の傾きとひび割れ発生強度を求めた。ひび割れ発生強度の測定結果を表４と表５に示す。また、表４と表５のデータに基づいて算出した、ひび割れ発生強度の平均値、標準偏差、および変動係数を表６に示す。 The slope of the single regression equation and the crack generation strength were determined by the same test method as described above except that the fractal FM was used instead of the fractal FM. Tables 4 and 5 show the results of measurement of cracking strength. Table 6 shows the average value, standard deviation, and coefficient of variation of crack initiation strength calculated based on the data in Tables 4 and 5.
（７）ひび割れ発生強度のバラツキについて
表３と表６に示すように、ダクタルＦＭおよびダクタルＦＯともに、変動係数は、すべての実施例において、比較例と比べ１／７〜２／３と小さい。したがって、本発明のひび割れ発生強度の測定方法は、従来の方法と比べ、ひび割れ発生強度のバラツキが顕著に小さい。
以上のことから、本発明は、超高強度繊維補強コンクリートのひび割れ発生強度を、高い精度で、効率よく測定することができる。
(7) Variation in cracking strength As shown in Tables 3 and 6, the fluctuation coefficient of both the fractal FM and fractal FO is as small as 1/7 to 2/3 in all examples compared to the comparative example. Therefore, the crack generation strength variation method of the present invention has significantly less variation in crack generation strength than the conventional method.
From the above, the present invention can efficiently measure the cracking strength of ultra high strength fiber reinforced concrete with high accuracy.
Claims (2)
（Ａ）超高強度繊維補強コンクリートの円柱供試体の二つの端面における凹凸の高低差の平均値が、一端面あたり１．５ｍｍ以下になるように研磨する、円柱供試体の研磨工程
（Ｂ）平板の上に、前記研磨した円柱供試体を横向きに載置し、平板と該円柱供試体の側面が接触する部分に、隙間が生じていないか否か確認する第一の確認作業と、隙間が生じていないと確認した場合は、該円柱供試体の側面から１８０°回転した位置にある円柱供試体の側面を、再度、平板の上に載置して、平板と該円柱供試体の側面が接触する部分に、隙間が生じていないか否か確認する第二の確認作業を行い、いずれの確認作業においても隙間が生じていないことを確認できた円柱供試体を、ひび割れ発生強度の測定対象として選別する、測定対象の選別工程
（Ｃ）前記隙間が生じていないと確認した二つの側面を結ぶ面と直交するように、前記選別した円柱供試体の二つの端面の中心にひずみゲージを貼付する、ひずみゲージの貼付工程
（Ｄ）前記隙間が生じていないと確認した二つの側面が、圧縮試験機の上下の加圧板とそれぞれ接触するように、前記円柱供試体を圧縮試験機に載置する、円柱供試体の載置工程
ただし、
荷重が５０ｋＮまでの範囲内において、
(i)前記二つの端面のひずみが正と負の逆（非対称）になる場合、
(ii)一つの端面においてひずみが生じない場合、
(iii)一つの端面のひずみが、他の端面のひずみの１．５倍以上になる場合
のいずれかの場合が生じたとき、
下記（ａ）および（ｂ）工程を経て選別された特性値が、閾値を超えたとき、
のいずれのときも、載荷を中断して除荷した後、前記（Ｂ）〜（Ｄ）工程を再実施して、再度、載荷を行う。
（ａ）ひずみが１００×１０−６までの範囲内において、荷重と二つの端面のひずみの実測値を用いて、各端面ごとに、荷重（説明変数）とひずみ（目的変数）の比例関係を表す二つの単回帰式を求める、単回帰分析工程
（ｂ）前記二つの単回帰式中の傾きの値を比較して、大きい方の値を特性値として選別する、特性値の選別工程 The test piece is loaded on a cylindrical specimen that has undergone the following steps (A) to (D), the relationship between the load and strain is obtained, and the tensile stress corresponding to the load at which linear elasticity is not established in the relationship between the load and strain. Is determined as cracking strength, and the cracking strength measurement method of ultra-high strength fiber reinforced concrete is measured.
(A) Polishing process of cylindrical specimen (B), wherein the average value of the unevenness of the unevenness on the two end faces of the cylindrical specimen of ultra high strength fiber reinforced concrete is 1.5 mm or less per one end face (B) The polished cylindrical specimen is placed sideways on a flat plate, and a first confirmation operation for checking whether or not a gap has occurred in a portion where the flat plate and the side surface of the cylindrical specimen are in contact with each other, and a gap If it is confirmed that the side surface of the cylindrical specimen is rotated 180 ° from the side face of the cylindrical specimen, the side face of the cylindrical specimen is placed again on the flat board, and the side face of the flat specimen and the cylindrical specimen Measure the cracking strength of the cylindrical specimen that was confirmed to be free of any gaps in any of the confirmation operations. Sorting target to be measured (C) A strain gauge application step (D) in which a strain gauge is attached to the center of the two end faces of the selected cylindrical specimen so as to be orthogonal to the surface connecting the two side surfaces that have been confirmed not to have the gap. ) Placement step of the columnar specimen on the compression tester so that the two side surfaces confirmed that the gap does not occur are in contact with the upper and lower pressure plates of the compression tester, respectively. However,
Within the load range up to 50kN,
(i) When the strains of the two end faces are opposite to each other (asymmetric),
(ii) If there is no distortion at one end face,
(iii) When any of the cases where the strain of one end face is 1.5 times or more of the strain of the other end face occurs ,
When the characteristic value selected through the following steps (a) and (b) exceeds a threshold value ,
In any case, after the loading is interrupted and unloaded, the steps (B) to (D) are performed again, and the loading is performed again.
(A) Within the range of strain up to 100 × 10 −6 , the proportional relationship between load (explanatory variable) and strain (target variable) is obtained for each end surface using the measured values of load and strain at the two end surfaces. A single regression analysis step for obtaining two single regression equations to be expressed (b) A characteristic value selection step of comparing the slope values in the two single regression equations and selecting the larger value as a characteristic value
The method for measuring crack occurrence strength of ultra-high-strength fiber reinforced concrete according to claim 1, wherein an ultra-high-strength fiber reinforced concrete having a crack occurrence strength of 5 N / mm 2 or more is an object to be measured for crack occurrence strength.
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