JP7508524B2 - Methods for preventing cracks in cast-in-place concrete - Google Patents
Methods for preventing cracks in cast-in-place concrete Download PDFInfo
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- JP7508524B2 JP7508524B2 JP2022168466A JP2022168466A JP7508524B2 JP 7508524 B2 JP7508524 B2 JP 7508524B2 JP 2022168466 A JP2022168466 A JP 2022168466A JP 2022168466 A JP2022168466 A JP 2022168466A JP 7508524 B2 JP7508524 B2 JP 7508524B2
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Description
本発明は、ＰＣａ床版間の間詰め部に打設する間詰めコンクリートに代表される既設構造物により拘束を受ける場所打ちコンクリートのひび割れを抑制する場所打ちコンクリートのひび割れ抑制方法に関する。 The present invention relates to a method for suppressing cracks in cast-in-place concrete that is constrained by existing structures, such as filler concrete poured into the filler sections between PCa slabs.
従来、ＰＣａ床版（プレキャスト床版）とＰＣａ床版との間の間詰め部に現場打ちのコンクリートを打設されるが、その間詰めコンクリートには、ひび割れ生じることがある。間詰めコンクリートにひび割れが生じ易い原因としては、間詰め部は、ＰＣａ床版に両側が挟まれているため、構造的に拘束が大きく、コンクリートの特性として、体積変化により引張応力が大きく発生し易いためと考えられる。つまり、間詰め部の体積変化が起き易いのは、高強度コンクリートを使用するため、自己収縮が大きく、セメント量が多いため水和発熱温度が高く、且つ、部材の体積が小さいことから急激な温度変化となり易いためと考えられる。 Conventionally, on-site concrete is poured into the gap between PCa slabs (precast slabs), but cracks can occur in the gap-filling concrete. The reason why cracks tend to occur in the gap-filling concrete is thought to be that the gap-filling concrete is sandwiched between the PCa slabs on both sides, which means that there is a large structural constraint, and the characteristics of concrete mean that it is prone to large tensile stresses due to volumetric changes. In other words, the reason why volumetric changes tend to occur in the gap-filling concrete is thought to be because high-strength concrete is used, which causes large autogenous shrinkage, the large amount of cement means that the hydration heat temperature is high, and the small volume of the components means that the temperature is prone to sudden changes in temperature.
そこで、例示した間詰めコンクリートのようなＰＣ床版等の周囲の既設構造物に拘束される既設構造物に対して比較的小容量の場所打ちコンクリートにひび割れが発生する原因とそのメカニズムを解明することが嘱望されている。詳しくは、現場毎の施工条件に基づいた短期的及び長期的な収縮量、応力度を推定し、事前にひび割れリスクを評価した上で、ひび割れを最大限防止する配合計画及び施工計画を計画できる手法の確立が望まれていた。 Therefore, there is a need to clarify the cause and mechanism of cracking in relatively small volumes of cast-in-place concrete for existing structures that are constrained by surrounding existing structures such as PC deck slabs, such as the example of interfacial filling concrete. In particular, there is a need to establish a method to estimate short-term and long-term shrinkage and stress levels based on the construction conditions at each site, evaluate the risk of cracking in advance, and then plan mix plans and construction plans that will prevent cracking to the greatest extent possible.
例えば、特許文献１には、床版１２０のコンクリートを打設する際に、床版１２０の温度又は湿度を管理するコンクリート養生方法において、床版１２０の内部に埋め込み内部温度を測定する内部温度計測手段としての内部温度計２０、床版１２０の養生空間１４０の温度を測定する養生空間温度測定手段としての養生空間温度計３０、養生空間１４０の湿度を測定する養生空間湿度測定手段としての養生空間湿度計４０、外気温を測定する外気温測定手段としての外気温度計５０、を備え、内部温度、養生空間の温度及び湿度、外気温を用いて、ひび割れ指数Ｉｃｒ（ｔ）を算出し、床版１２０のひび割れ指数Ｉｃｒ（ｔ）を基に養生期間を定めるコンクリート養生方法が開示されている（特許文献１の特許請求の範囲の請求項１、明細書の段落［００１５］～［００２５］、図面の図１～図３等参照）。 For example, Patent Document 1 discloses a concrete curing method for controlling the temperature or humidity of the floor slab 120 when pouring concrete for the floor slab 120, which includes an internal thermometer 20 embedded inside the floor slab 120 as an internal temperature measuring means for measuring the internal temperature, a curing space thermometer 30 as a curing space temperature measuring means for measuring the temperature of the curing space 140 of the floor slab 120, a curing space hygrometer 40 as a curing space humidity measuring means for measuring the humidity of the curing space 140, and an outside air thermometer 50 as an outside air temperature measuring means for measuring the outside air temperature, and calculates a crack index Icr(t) using the internal temperature, the temperature and humidity of the curing space, and the outside air temperature, and determines the curing period based on the crack index Icr(t) of the floor slab 120 (see claim 1 in the scope of claims of Patent Document 1, paragraphs [0015] to [0025] of the specification, and Figures 1 to 3 of the drawings, etc.).
特許文献１に記載のコンクリート養生方法は、温度や湿度の履歴からひび割れ指数を予測することで、適切な養生期間を決定するので、養生期間の適切な管理が実現でき、コンクリート構造物の表面ひび割れの発生を抑制することが可能となるとされている。しかし、特許文献１に記載のコンクリート養生方法は、コンクリート床版全体を現場打ちのコンクリートで打設した場合であり、前述の間詰めコンクリートの構造的に拘束が大きいという問題や高強度コンクリートを使用するため、自己収縮が大きく、セメント量が多いため水和発熱温度が高く、且つ、部材の体積が小さいことから急激な温度変化となり易いという問題を解決できるものではなかった。 The concrete curing method described in Patent Document 1 predicts a crack index from temperature and humidity history to determine an appropriate curing period, which is said to enable appropriate management of the curing period and suppress the occurrence of surface cracks in concrete structures. However, the concrete curing method described in Patent Document 1 is for cases where the entire concrete floor slab is poured with in-situ concrete, and does not solve the problems of the aforementioned large structural constraints of the interfacial concrete, and the use of high-strength concrete, which results in large autogenous shrinkage, a high hydration heat temperature due to the large amount of cement, and a tendency for sudden temperature changes due to the small volume of the components.
また、特許文献２には、コンクリートひび割れ評価方法は、構造物の構造情報を含むＢＩＭデータを準備する工程Ｓ１０と、ＢＩＭデータを利用して、解析領域検討モデルを生成する工程Ｓ２０と、解析領域検討モデルを利用して、複数の解析モデルを生成する工程Ｓ３０と、複数の解析モデルのそれぞれについて、コンクリートを打設するときにコンクリートにひび割れが生じる可能性を評価するためのマスコンクリート解析を行う工程Ｓ４０と、を有するコンクリートひび割れ評価方法が開示されている（特許文献２の特許請求の範囲の請求項１、明細書の段落［００１６］～［００３７］、図面の図１～図４等参照）。 Patent document 2 discloses a method for evaluating cracks in concrete, which includes a step S10 of preparing BIM data including structural information of a structure, a step S20 of generating an analysis domain study model using the BIM data, a step S30 of generating multiple analysis models using the analysis domain study model, and a step S40 of performing mass concrete analysis for each of the multiple analysis models to evaluate the possibility of cracks occurring in the concrete when pouring the concrete (see claim 1 in the scope of claims of patent document 2, paragraphs [0016] to [0037] of the specification, and Figures 1 to 4 of the drawings, etc.).
特許文献２に記載のコンクリートひび割れ評価方法は、解析者の能力や経験に左右されることなく、信頼性の高い評価結果を得ることが可能とされている。しかし、特許文献２に記載のコンクリートひび割れ評価方法は、特許文献１に記載のコンクリート養生方法と同様に、前述の間詰めコンクリート等の構造的に拘束が大きいという問題や高強度コンクリートを使用するため、自己収縮が大きく、セメント量が多いため水和発熱温度が高く、且つ、部材の体積が小さいことから急激な温度変化となり易いという問題を解決できるものではなかった。 The concrete crack evaluation method described in Patent Document 2 is said to be capable of obtaining highly reliable evaluation results without being dependent on the ability or experience of the analyst. However, like the concrete curing method described in Patent Document 1, the concrete crack evaluation method described in Patent Document 2 does not solve the problems of the large structural constraints of the aforementioned interfacial concrete, the large autogenous shrinkage caused by the use of high-strength concrete, the high hydration heat temperature due to the large amount of cement, and the small volume of the components that are prone to sudden temperature changes.
そこで、本発明は、前述した問題に鑑みて案出されたものであり、その目的とするところは、周囲の既設構造物に拘束を受ける場所打ちコンクリートの諸問題を解決し、現場毎の施工条件に基づいた短期的及び長期的な収縮量、応力度を推定し、事前にひび割れリスクを評価した上で、ひび割れを最大限防止する配合計画及び施工計画を計画できる場所打ちコンクリートのひび割れ抑制方法を提供することにある。 The present invention was devised in consideration of the above-mentioned problems, and its purpose is to provide a method for preventing cracks in cast-in-place concrete that solves the various problems of cast-in-place concrete being constrained by existing surrounding structures, estimates short-term and long-term shrinkage and stress levels based on the construction conditions at each site, and can assess the risk of cracking in advance, allowing for the planning of mix plans and construction plans that will prevent cracking to the greatest extent possible.
請求項１に記載の場所打ちコンクリートのひび割れ抑制方法は、周囲の既設構造物に拘束される場所打ちコンクリートのひび割れを抑制する場所打ちコンクリートのひび割れ抑制方法であって、実際に打設する場所打ちコンクリートに使用する同種の材料で予めコンクリートを試し練りし、圧縮強度試験、静弾性係数試験、拘束膨張試験、自己収縮試験、乾燥収縮試験を含む各種試験を行って、実際に打設する前記場所打ちコンクリートの特性値として、圧縮強度の経時変化、静弾性係数の経時変化、膨張ひずみの経時変化、自己収縮ひずみの経時変化の関係式の係数、及び間詰め部の材齢６か月後の長さ変化を推定した上、推定した前記圧縮強度の経時変化から前記場所打ちコンクリートの材齢ｔ時における引張強度を算出し、推定した静弾性係数の経時変化、膨張ひずみの経時変化、自己収縮ひずみの経時変化の関係式の係数、及び間詰め部の材齢６か月後の長さ変化から前記場所打ちコンクリートの材齢ｔ時における収縮ひずみの引張応力及び前記場所打ちコンクリートの材齢ｔ時における温度変化による引張応力を、それぞれ算出し、算出した前記収縮ひずみの引張応力と算出した前記温度変化による引張応力とを合算した引張応力で算出した前記引張強度を割って前記場所打ちコンクリートの材齢ｔ時のひび割れ指数を算出し、算出した前記ひび割れ指数が目標値以上か否かでひび発生のリスクを評価することを特徴とする。 The method for suppressing cracks in cast-in-place concrete according to claim 1 is a method for suppressing cracks in cast-in-place concrete that is restrained by surrounding existing structures, and comprises the steps of: mixing concrete in advance with the same type of material as that used in the cast-in-place concrete to be actually cast; conducting various tests including a compressive strength test, a static elastic modulus test, a restrained expansion test, an autogenous shrinkage test, and a drying shrinkage test; estimating the characteristic values of the cast-in-place concrete to be actually cast , including the change in compressive strength over time, the change in static elastic modulus over time, the change in expansion strain over time, the coefficient of a relational expression for the change in autogenous shrinkage strain over time, and the change in length of the filling part after six months of age; and then calculating the change in compressive strength over time from the estimated change in compressive strength over time. The method is characterized in that the tensile strength of the cast-in-place concrete at age t is calculated, and the tensile stress of shrinkage strain of the cast-in-place concrete at age t and the tensile stress due to temperature change of the cast-in-place concrete at age t are calculated from the coefficients of the relational equations for the estimated changes in static elastic modulus over time, the changes in expansion strain over time, and the changes in length of the filling portion after 6 months of age, and a crack index of the cast-in-place concrete at age t is calculated by dividing the calculated tensile strength by the tensile stress obtained by adding up the calculated tensile stress of shrinkage strain and the calculated tensile stress due to temperature change, and the risk of crack occurrence is evaluated based on whether the calculated crack index is equal to or greater than a target value.
請求項２に記載の場所打ちコンクリートのひび割れ抑制方法は、請求項１に記載の場所打ちコンクリートのひび割れ抑制方法において、算出した前記ひび割れ指数が目標値を下回る場合、配合修正を行って再度試し練りをし、再度、圧縮強度試験、静弾性係数試験、拘束膨張試験、自己収縮試験、乾燥収縮試験を含む各種試験を行って、前記場所打ちコンクリートの材齢ｔ時における引張強度、前記場所打ちコンクリートの材齢ｔ時における 収縮ひずみの引張応力、前記場所打ちコンクリートの材齢ｔ時における温度変化による引張応力を、それぞれ算出し直して、算出し直した前記ひび割れ指数が目標値以上か否かでひび発生のリスクを再度評価することを特徴とする。 The method for suppressing cracks in cast-in-place concrete described in claim 2 is characterized in that, in the method for suppressing cracks in cast-in-place concrete described in claim 1, if the calculated crack index falls below the target value, the mix is modified and test-mixed again, and various tests including compressive strength tests, static elastic modulus tests, restrained expansion tests, autogenous shrinkage tests, and drying shrinkage tests are performed again to recalculate the tensile strength of the cast-in-place concrete at age t, the tensile stress of shrinkage strain of the cast-in-place concrete at age t, and the tensile stress due to temperature change of the cast-in-place concrete at age t, and the risk of cracking is reassessed based on whether the recalculated crack index is equal to or greater than the target value.
請求項３に記載の場所打ちコンクリートのひび割れ抑制方法は、請求項１に記載の場所打ちコンクリートのひび割れ抑制方法において、算出した前記ひび割れ指数が目標値を下回る場合、温度抑制対策を施して前記場所打ちコンクリートの温度変化を抑制した場合の前記温度変化による引張応力を算出し直して、算出し直した前記ひび割れ指数が目標値以上か否かでひび発生のリスクを再度評価することを特徴とする。 The method for suppressing cracks in cast-in-place concrete described in claim 3 is characterized in that, in the method for suppressing cracks in cast-in-place concrete described in claim 1, if the calculated crack index falls below a target value, the tensile stress caused by the temperature change when temperature suppression measures are taken to suppress the temperature change of the cast-in-place concrete is recalculated, and the risk of crack occurrence is reassessed based on whether the recalculated crack index is equal to or greater than the target value.
請求項４に記載の場所打ちコンクリートのひび割れ抑制方法は、請求項３に記載の場所打ちコンクリートのひび割れ抑制方法において、算出し直した前記ひび割れ指数が目標値を下回る場合、収縮抑制対策を施して前記場所打ちコンクリートの材齢ｔ時における収縮ひずみの引張応力を算出し直して、算出し直した前記ひび割れ指数が目標値以上か否かでひび発生のリスクを再度評価することを特徴とする。 The method for suppressing cracks in cast-in-place concrete described in claim 4 is characterized in that, in the method for suppressing cracks in cast-in-place concrete described in claim 3, if the recalculated crack index falls below the target value, shrinkage suppression measures are taken to recalculate the tensile stress of the shrinkage strain of the cast-in-place concrete at age t, and the risk of cracking is reassessed based on whether the recalculated crack index is equal to or greater than the target value.
請求項５に記載の場所打ちコンクリートのひび割れ抑制方法は、請求項１に記載の場所打ちコンクリートのひび割れ抑制方法において、前記拘束膨張試験では、材齢７日の供試体の膨張ひずみを実測し、前記実測値から膨張ひずみの経時変化を推定することを特徴とする。 The method for suppressing cracks in cast-in-place concrete described in claim 5 is the method for suppressing cracks in cast-in-place concrete described in claim 1, characterized in that in the restrained expansion test, the expansion strain of a specimen that is 7 days old is actually measured, and the change in the expansion strain over time is estimated from the measured value.
請求項６に記載の場所打ちコンクリートのひび割れ抑制方法は、請求項１に記載の場所打ちコンクリートのひび割れ抑制方法において、自己収縮試験では、材齢２８日までの供試体の自己収縮ひずみの経時変化を実測し、前記実測値から場所打ち部の寸法効果を考慮して自己収縮ひずみの経時変化の関係式の係数を推定することを特徴とする。 The method for suppressing cracks in cast-in-place concrete described in claim 6 is the method for suppressing cracks in cast-in-place concrete described in claim 1, characterized in that in the autogenous shrinkage test, the change over time in the autogenous shrinkage strain of the specimen up to an age of 28 days is actually measured, and the coefficients of the relational expression for the change over time in the autogenous shrinkage strain are estimated from the measured values, taking into account the dimensional effect of the cast-in-place part.
請求項７に記載の場所打ちコンクリートのひび割れ抑制方法は、請求項１に記載の場所打ちコンクリートのひび割れ抑制方法において、乾燥収縮試験では、乾燥材齢２８日後の供試体の長さ変化を実測して６カ月後の長さ変化を推定し、材齢７日から６カ月後まで自己収縮ひずみの実測値の増加分を差し引いて、乾燥収縮ひずみの実測値を算出し、前記乾燥収縮ひずみの実測値から場所打ち部の材齢ｔ時の長さ変化を推定することを特徴とする。 The method for suppressing cracks in cast-in-place concrete described in claim 7 is the method for suppressing cracks in cast-in-place concrete described in claim 1, characterized in that in the drying shrinkage test, the change in length of the test specimen after 28 days of drying is measured to estimate the change in length after 6 months, and the actual measured value of drying shrinkage strain is calculated by subtracting the increase in the actual measured value of autogenous shrinkage strain from 7 days to 6 months of age , and the change in length of the cast-in-place portion at age t is estimated from the measured value of drying shrinkage strain.
請求項１～７に記載の発明によれば、場所打ちコンクリートの諸問題を解決し、現場毎の施工条件に基づいた短期的及び長期的な収縮量、応力度を推定し、事前にひび割れリスクを評価した上で、ひび割れを最大限防止する配合計画及び施工計画を立案することができる。 The inventions described in claims 1 to 7 solve the various problems associated with cast-in-place concrete, estimate short-term and long-term shrinkage and stress levels based on the construction conditions at each site, and evaluate the risk of cracking in advance, allowing for the creation of mix plans and construction plans that will prevent cracking to the greatest extent possible.
特に、請求項２に記載の発明によれば、軽微な配合修正により場所打ちコンクリートのひび割れを抑制することができるか否かの判別がつき、実行が容易な施工計画を立案することができる。 In particular, according to the invention described in claim 2, it is possible to determine whether cracks in cast-in-place concrete can be suppressed by minor mix modifications, and to devise construction plans that are easy to implement.
特に、請求項３に記載の発明によれば、温度抑制対策を施して場所打ちコンクリートの温度変化を抑制した場合の温度変化による引張応力を算出し直して、算出し直したひび割れ指数が目標値以上か否かでひび発生のリスクを再度評価するので、収縮ひずみを抑制する対策より対策が取り易く効果も大きいと考えられ、且つ、材料費が嵩むこともない温度変化を抑える対策で、場所打ちコンクリートのひび割れを抑制することができる。 In particular, according to the invention described in claim 3, the tensile stress caused by temperature change when temperature suppression measures are taken to suppress temperature change in cast-in-place concrete is recalculated, and the risk of cracking is reassessed based on whether the recalculated crack index is equal to or greater than the target value. This is considered to be easier to implement and more effective than measures to suppress shrinkage strain, and it is possible to suppress cracks in cast-in-place concrete by using measures to suppress temperature change that do not increase material costs.
特に、請求項４に記載の発明によれば、収縮抑制対策を施して場所打ちコンクリートの材齢ｔ時における収縮ひずみの引張応力を算出し直して、算出し直したひび割れ指数が目標値以上か否かでひび発生のリスクを再度評価するので、温度変化を抑える対策でも抑えることができない場合でも場所打ちコンクリートのひび割れを抑制することができる。 In particular, according to the invention described in claim 4, shrinkage suppression measures are taken, the tensile stress of the shrinkage strain of cast-in-place concrete at age t is recalculated, and the risk of cracking is reassessed based on whether the recalculated crack index is equal to or greater than the target value. This makes it possible to suppress cracks in cast-in-place concrete even when measures to suppress temperature changes are not sufficient to suppress cracks.
特に、請求項５～７に記載の発明によれば、自由ひずみの算出精度が向上し、場所打ちコンクリートの事前のひび割れリスクを正確に評価することができる。 In particular, the inventions described in claims 5 to 7 improve the accuracy of calculating free strain, making it possible to accurately evaluate the risk of cracking in cast-in-place concrete in advance.
以下、本発明に係る場所打ちコンクリートのひび割れ抑制方法を実施するための一実施形態について、図面を参照しながら詳細に説明する。 Below, one embodiment of the method for suppressing cracks in cast-in-place concrete according to the present invention will be described in detail with reference to the drawings.
図１～図４を用いて、本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法について説明する。以下、周囲の既設コンクリートにより拘束を受ける場所打ちコンクリートとして、ＰＣａ床版間の間詰め部に打設する間詰めコンクリートを例示して説明する。図１は、本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法の概要を示すフロー図であり、図２は、配合設計の例を示すフローチャートである。本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法は、一のＰＣａ床版と他のＰＣａ床版との間の間詰め部に打設する間詰めコンクリートのひび割れを抑制する方法である。 A method for suppressing cracks in cast-in-place concrete according to an embodiment of the present invention will be described using Figures 1 to 4. Below, an example of filler concrete poured into the filler section between PCa slabs will be described as cast-in-place concrete that is constrained by the surrounding existing concrete. Figure 1 is a flow diagram showing an overview of a method for suppressing cracks in cast-in-place concrete according to an embodiment of the present invention, and Figure 2 is a flow chart showing an example of mix design. The method for suppressing cracks in cast-in-place concrete according to an embodiment of the present invention is a method for suppressing cracks in filler concrete poured into the filler section between one PCa slab and another PCa slab.
（配合設計）
図１に示すように、本実施形態に係る間詰めコンクリートのひび割れ抑制方法では、先ず、生コン工場等と協議し、配合設計を行う。具体的には、図２に示すように、実際に打設する間詰めコンクリートに使用する同種の材料で予めコンクリートを試し練りし、水結合材比及びセメント種類を検討し、保証材齢、水セメント比Ｃ／Ｗ曲線、変動係数などを確認する。
(Mixture design)
As shown in Fig. 1, in the method for suppressing cracks in interfacial concrete according to this embodiment, first, a mix design is carried out in consultation with a ready-mix concrete plant, etc. Specifically, as shown in Fig. 2, a test mix is made in advance using the same materials as will be used in the interfacial concrete to be actually poured, the water-binder ratio and cement type are examined, and the guaranteed age, water-cement ratio C/W curve, coefficient of variation, etc. are confirmed.
なお、水結合材比とは、フレッシュコンクリート又はフレッシュモルタルに含まれるセメントペースト中の水と結合材の重量比のことを指している。ここで、結合材とは、粉体の内、水と反応し、コンクリートの強度発現に寄与する物質を生成するものの総称で、セメント、高炉スラグ微粉末、フライアッシュ、膨張材等を含む用語である。水セメント比が結合材としてポルトランドセメントのみ、あるいは混合セメントのみを意味する用語であるのに対して、水結合材比は、セメントと混合材がプレミックスされていない結合材をも含む用語である。 The water-binder ratio refers to the weight ratio of water to binder in the cement paste contained in fresh concrete or fresh mortar. Here, binder is a general term for powder that reacts with water to produce a substance that contributes to the strength of concrete, and is a term that includes cement, ground granulated blast furnace slag, fly ash, expansive materials, etc. While the water-cement ratio is a term that refers to only Portland cement or only blended cement as a binder, the water-binder ratio is a term that also includes binders in which the cement and admixture are not premixed.
配合設計では、図２に示すように、先ず、生コン工場等において、試し練りにより単位水量を決定し、施工性を確認した上、暫定配合を決定する。そして、本実施形態に係る間詰めコンクリートのひび割れ抑制方法では、図１に示すように、ｓｔｅｐ１として圧縮強度試験、静弾性係数試験、拘束膨張試験、自己収縮試験、乾燥収縮試験を含む各種試験を行う。後述のように、試し練りの供試体の試験結果から間詰めコンクリートとして打設するまだ固まらないフレッシュコンクリートの任意の材齢時である材齢ｔ時における各種特性値を推定するためである。 In mix design, as shown in Figure 2, first, the unit water volume is determined by test mixing at a ready-mix concrete plant or the like, and after confirming workability, a provisional mix is decided. Then, in the method for suppressing cracks in interfacial concrete according to this embodiment, as shown in Figure 1, various tests are conducted in step 1, including a compressive strength test, a static elastic modulus test, a restrained expansion test, an autogenous shrinkage test, and a drying shrinkage test. As described later, this is to estimate various characteristic values at an arbitrary age, t, of the fresh, unhardened concrete to be poured as interfacial concrete from the test results of the test mix specimen.
図２に示すように、各種試験により、暫定配合の水結合材比の－３％、暫定配合の水結合材比、暫定配合の水結合材比の＋３％の圧縮強度を確認する。また、２０ｋｇ及び２５ｋｇの拘束膨張試験をそれぞれ行って膨張ひずみを確認する。 As shown in Figure 2, various tests are conducted to confirm the compressive strength at -3% of the provisional mix water-to-binder ratio, the provisional mix water-to-binder ratio, and +3% of the provisional mix water-to-binder ratio. In addition, restrained expansion tests of 20 kg and 25 kg are conducted to confirm the expansion strain.
そして、変動係数８％となる水結合材比及び膨張ひずみ２００μｍ以上となる単位膨張材量を求め、配合を決定する。 Then, determine the water-binder ratio that results in a coefficient of variation of 8% and the unit amount of expansive material that results in an expansion strain of 200 μm or more, and determine the mix.
その後、決定した配合により、例えば生コン工場でフレッシュコンクリートを練り混ぜ供試体を作成し、試験機関等に搬送し、そこで自己収縮試験や乾燥収縮試験等を実施し、後述のように、間詰めコンクリートとして打設するコンクリートの特性値を推定した上、ひび割れ照査を行う。 After that, fresh concrete is mixed using the determined mix ratio, for example at a ready-mix concrete plant, to create test specimens, which are then transported to a testing institute, where autogenous shrinkage tests and drying shrinkage tests are carried out. As described below, the characteristic values of the concrete to be poured as interfacial filling concrete are estimated, and a crack inspection is carried out.
ひび割れ照査でＯＫとなった場合は、最終試し練りを行って、供試体を作成し、強度を確認するとともに、再度、乾燥収縮試験等を行って、ひび割れ発生の評価を行う。図１に示すように、本実施形態に係る間詰めコンクリートのひび割れ抑制方法では、ｓｔｅｐ２の配合照査段階でひび割れ発生の評価において、後述のように、ひび割れ指数が所定値を上回り、ＯＫとなった場合には、通常の従来の施工方法で間詰めコンクリートを打設して施工する。 If the crack inspection is deemed OK, a final test mix is carried out to prepare a test specimen to check its strength, and a drying shrinkage test, etc. is conducted again to evaluate the occurrence of cracks. As shown in Figure 1, in the method for suppressing cracks in interfacial concrete according to this embodiment, in the evaluation of crack occurrence at the mix inspection stage in step 2, if the crack index exceeds a predetermined value and is deemed OK, as described below, the interfacial concrete is poured and constructed using the normal conventional construction method.
しかし、図１に示すように、ｓｔｅｐ２の配合照査段階でＮＧとなった場合は、最初に対策１である配合修正で解消できるように試みる。具体的には、本実施形態に係る間詰めコンクリートのひび割れ抑制方法のｓｔｅｐ３の配合修正では、単位水量や単位セメント量（単位結合材量）等を増減することで対応する。なお、ｓｔｅｐ２の配合照査は、通常行う圧縮強度と拘束膨張試験に基いた配合決定に加え、通常の配合設計では行わない静弾性係数、自己収縮や乾燥収縮を試験機関等で測定してひび割れ指数を計算して決定配合が満足するかを評価することを指している。 However, as shown in Figure 1, if the mix verification in step 2 is found to be NG, the first step is to attempt to resolve the problem by modifying the mix, which is Countermeasure 1. Specifically, in the mix verification in step 3 of the method for suppressing cracks in interfill concrete according to this embodiment, the mix is modified by increasing or decreasing the unit water content and unit cement content (unit binder content). Note that in addition to determining the mix based on the usual compressive strength and restrained expansion tests, mix verification in step 2 refers to measuring the static elastic modulus, autogenous shrinkage, and drying shrinkage at a testing institute, etc., which are not performed in normal mix designs, and calculating the crack index to evaluate whether the determined mix is satisfactory.
（ひび割れ照査）
次に、図３，図４を用いて、本実施形態に係る間詰めコンクリートのひび割れ抑制方法のひび割れ照査について説明する。図３は、収縮ひずみによる引張応力の算定方法の概要を示す図であり、図４は、コンクリート試験からひび割れ発生の評価に至るまでのひび割れ照査のフローを示すフロー図である。
(Crack inspection)
Next, the crack inspection of the crack suppression method for interfacial concrete according to the present embodiment will be described with reference to Figures 3 and 4. Figure 3 is a diagram showing an overview of the method for calculating tensile stress due to shrinkage strain, and Figure 4 is a flow diagram showing the flow of crack inspection from concrete testing to evaluation of crack occurrence.
前述のように決定したコンクリートの配合により生コン工場等で供試体を作成し、図４に示すように、圧縮強度試験及び静弾性係数試験を行い、材齢２８日の圧縮強度及び材齢２８日の静弾性係数を測定する。そして、間詰めコンクリートの特性値として圧縮強度及び静弾性係数の経時変化を推定して、材齢ｔ時の引張強度の算定やひずみに応じたクリープを考慮する際に用いる。 Test specimens are prepared at a ready-mix concrete plant or similar using the concrete mix determined as described above, and compressive strength tests and static modulus of elasticity tests are conducted as shown in Figure 4 to measure the compressive strength at age 28 days and the static modulus of elasticity at age 28 days. The changes in compressive strength and static modulus of elasticity over time are then estimated as characteristic values of the interfill concrete, and are used to calculate the tensile strength at age t and to consider creep according to strain.
（１）収縮ひずみの特性値の推定
また、図３，図４に示すように、本発明の実施形態に係る間詰めコンクリートのひび割れ抑制方法では、前述のように、生コン工場から試験機関等に搬送された供試体からコンクリートのひずみに関するコンクリート試験を行って間詰めコンクリートの収縮ひずみの特性値を推定する。つまり、本実施形態に係る間詰めコンクリートのひび割れ抑制方法では、収縮ひずみの設計上の特性値は、バラツキが大きいため、１か月程度の各種の収縮試験を行って、その試験値から特性値を推定するようにした。
(1) Estimation of characteristic value of shrinkage strain As shown in Figures 3 and 4, in the method for suppressing cracks in interfacial concrete according to the embodiment of the present invention, as described above, a concrete test on concrete strain is carried out on a test specimen transported from a ready-mix concrete plant to a testing institute or the like, and a characteristic value of shrinkage strain of interfacial concrete is estimated. In other words, in the method for suppressing cracks in interfacial concrete according to the present embodiment, since the design characteristic value of shrinkage strain varies widely, various shrinkage tests are carried out for about one month, and the characteristic value is estimated from the test values.
具体的には、配合決定した試し練りのフレッシュコンクリートから供試体を作成し、図３，図４に示すように、拘束膨張試験を行って材齢７日の膨張ひずみを実測し、膨張ひずみの実測値εｅｘ（７）を得る。そして、この実測値εｅｘ（７）から膨張ひずみの経時変化を推定する。例えば、７日の実測値εｅｘ（７）を最終値とて、日本コンクリート工学会発行のマスコンクリートのひび割れ制御指針２０１６の指数関数式（設計式）に代入して任意の材齢時である材齢ｔ時の膨張ひずみを推定する。 Specifically, a test specimen is made from freshly mixed concrete with the determined mix ratio, and a restrained expansion test is carried out to measure the expansion strain at an age of 7 days, as shown in Figures 3 and 4, to obtain the measured value of the expansion strain εex(7). The change in the expansion strain over time is then estimated from this measured value εex(7). For example, the measured value εex(7) at 7 days is taken as the final value, and substituted into the exponential function formula (design formula) of the Guidelines for Crack Control of Mass Concrete 2016 published by the Japan Concrete Institute to estimate the expansion strain at any age, t.
また、配合決定した試し練りのフレッシュコンクリートから供試体を作成し、図３，図４に示すように、供試体の自己収縮試験を行って材齢２８日までの自己収縮ひずみの経時変化を実測し、自己収縮ひずみの実測値εａｓ（ｔ）を得る。そして、この実測値εａｓ（ｔ）から直方体状の間詰め部（現場打ちコンリートを打設する部位を示す。以下同じ）の寸法効果（×０．８）を考慮して自己収縮ひずみの経時変化の関係式の係数を推定する。なお、実物大要素実験及び実現場でのひずみ測定とひび割れ観察から、自己収縮試験に用いる断面寸法１００×１００ｍｍの角柱供試体と概ね間詰部と同等となる断面寸法２００×２００ｍｍまたは２４５×２４５ｍｍの試験体との自己収縮ひずみの比率を０．８とした。 In addition, a specimen is prepared from the test mix fresh concrete after the mix ratio has been determined, and an autogenous shrinkage test is conducted on the specimen as shown in Figures 3 and 4 to measure the change in autogenous shrinkage strain over time up to 28 days, and the measured value of autogenous shrinkage strain εas(t) is obtained. From this measured value εas(t), the coefficient of the relational expression for the change in autogenous shrinkage strain over time is estimated, taking into account the size effect (×0.8) of the rectangular parallelepiped interfill section (referring to the area where the cast-in-place concrete is poured; the same applies below). From full-scale element experiments and strain measurements and crack observations at the actual site, the ratio of autogenous shrinkage strain between the rectangular column specimen with cross-sectional dimensions of 100×100 mm used in the autogenous shrinkage test and specimens with cross-sectional dimensions of 200×200 mm or 245×245 mm, which are roughly equivalent to the interfill section, was set to 0.8.
また、配合決定した試し練りのフレッシュコンクリートから供試体を作成し、供試体の乾燥収縮試験を行って乾燥材齢２８日（材齢３５日）後の供試体の長さ変化を実測し、材齢６か月（１８２日）後の長さ変化を推定し、前述の材齢７日から１８２日までの自己収縮ひずみの実測値εａｓ（ｔ）の増加分を差し引いて、乾燥収縮ひずみの実測値εｓｈ（１８２）を得る。つまり、乾燥収縮試験の実測値には、材齢７日以降の自己収縮が含まれているため、自己収縮試験の実測値を差し引くようにしてる。なお、７日というのは乾燥収縮試験は実材齢７日を起点としているため、差し引く分の自己収縮試験は７日からとしている。また、コンクリート標準示方書には、乾燥収縮に関する式が定められ、乾燥収縮は乾燥面の露出の程度や周りの湿度に影響されるため、乾燥収縮試験における１００×１００×４００ｍｍの値を実際の構造物の状態に換算するようになっている。このとき、体積表面積比（Ｖ／Ｓ）及び相対湿度を考慮して、乾燥収縮ひずみの実測値εｓｈ（１８２）を算出している In addition, a test specimen is made from the test mix fresh concrete, and a drying shrinkage test is performed on the test specimen to measure the change in length of the test specimen after 28 days of drying (35 days of drying). The change in length after 6 months (182 days) is estimated, and the increase in the measured autogenous shrinkage strain εas(t) from the 7th day of drying to the 182nd day of drying is subtracted to obtain the measured drying shrinkage strain εsh(182). In other words, the measured value of the drying shrinkage test includes the autogenous shrinkage after the 7th day of drying, so the measured value of the autogenous shrinkage test is subtracted. The 7th day is the starting point of the drying shrinkage test, so the subtracted part of the autogenous shrinkage test is from the 7th day of drying. In addition, the Standard Specifications for Concrete stipulate an equation for drying shrinkage, and since drying shrinkage is affected by the degree of exposure of the drying surface and the surrounding humidity, the value of 100 x 100 x 400 mm in the drying shrinkage test is converted to the actual state of the structure. At this time, the actual drying shrinkage strain εsh (182) is calculated taking into account the volume-surface area ratio (V/S) and relative humidity.
このように、配合決定した試し練りのフレッシュコンクリートから供試体を作成し、供試体の拘束膨張試験、自己収縮試験、及び乾燥収縮試験を行って、膨張ひずみの経時変化、自己収縮ひずみの経時変化の関係式の係数、及び間詰め部の材齢６か月後の長さ変化を推定し、間詰め部のコンクリートの自由ひずみεｍ１を算出する（図３参照）。 In this way, test specimens are made from the test-mixed fresh concrete, and restrained expansion tests, autogenous shrinkage tests, and drying shrinkage tests are conducted on the test specimens to estimate the change in expansion strain over time, the coefficients of the relational equation for the change in autogenous shrinkage strain over time, and the change in length of the filling part after six months of age, and the free strain εm1 of the concrete in the filling part is calculated (see Figure 3).
（２）鉄筋拘束及び外部拘束の考慮
次に、本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法では、場所打ちコンクリートである間詰めコンリートの鉄筋拘束度及び外部拘束度を考慮する。鉄筋拘束度及び外部拘束度は、現状の構造設計では設計上の値はなく、また、構造毎に異なるため、間詰め部とＰＣａ床版との剛性比で部材の形状による拘束ひずみを算出して考慮する。
(2) Consideration of rebar restraint and external restraint Next, in the method for suppressing cracks in cast-in-place concrete according to an embodiment of the present invention, the rebar restraint degree and external restraint degree of the interfacial concrete, which is cast-in-place concrete, are taken into consideration. Since there are no design values for the rebar restraint degree and the external restraint degree in the current structural design and they differ for each structure, the restraint strain due to the shape of the member is calculated and taken into consideration using the rigidity ratio between the interfacial concrete part and the PCa floor slab.
具体的には、前述の自由ひずみεｍ１と下記式（１）との積により鉄筋拘束及び外部拘束で拘束された状態の間詰めコンクリートの材齢ｔ時における部材の拘束ひずみεｍ２を算出する。
Ｒｓ＋（１－Ｒｓ）×Ｒｏ・・・式（１）
ここで、Ｒｓ：鉄筋拘束度
Ｒｏ：外部拘束度
なお、図４の鉄筋拘束度＝０．２７２としているのは、寸法効果と同様に、実物大要素実験及び実現場でのひずみ測定とひび割れ観察から得た値である。具体的には間詰コンクリートと同じ形状の部材で、鉄筋の有り、無しのひずみを計測して、その比率から求めたものである。
Specifically, the restraint strain εm2 of the member at age t of the interfacial concrete restrained by reinforcing bars and external restraint is calculated by multiplying the above-mentioned free strain εm1 by the following equation (1).
Rs + (1-Rs) × Ro ... formula (1)
Here, Rs: rebar restraint ratio Ro: external restraint ratio Note that the rebar restraint ratio of 0.272 in Figure 4 is a value obtained from full-scale element experiments and in-situ strain measurements and crack observations, just like the size effect. Specifically, it was calculated by measuring the strain with and without rebars in a member of the same shape as the fill concrete, and then calculating the ratio.
（３）クリープを考慮した収縮ひずみによる引張応力の算出
次に、図３，図４に示すように、本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法では、材齢ｔ－１時から材齢ｔ時に生じる収縮ひずみに応じたクリープを考慮して収縮ひずみによる引張応力を算出する。
(3) Calculation of tensile stress due to shrinkage strain taking creep into account Next, as shown in Figures 3 and 4, in the method for suppressing cracks in cast-in-place concrete according to an embodiment of the present invention, the tensile stress due to shrinkage strain is calculated taking into account creep corresponding to shrinkage strain occurring from age t-1 to age t.
具体的には、自由ひずみεｍ１×拘束ひずみεｍ２に有効ヤング係数である下記式（２）を掛け合わせて、収縮ひずみによる引張応力σｔを算出する。
Ｅ／（１+φ）・・・式（２）
ここで、Ｅ：ヤング係数
φ：クリープ係数
Specifically, the tensile stress σt due to the shrinkage strain is calculated by multiplying the free strain εm1 × the restrained strain εm2 by the effective Young's modulus given by the following formula (2).
E / (1 + φ) ... Equation (2)
Where, E: Young's modulus φ: creep modulus
（４）クリープを考慮した温度変化の拘束ひずみによる引張応力の算出
本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法では、図４に示すように、前述の収縮ひずみによる引張応力の算出と並行して、材齢ｔ－１時から材齢ｔ時に生じる温度変化による拘束ひずみに応じたクリープを考慮して拘束ひずみによる引張応力を算出する。
(4) Calculation of tensile stress due to restraint strain caused by temperature change taking creep into account In the method for suppressing cracks in cast-in-place concrete according to an embodiment of the present invention, as shown in Figure 4, in parallel with the calculation of tensile stress due to shrinkage strain described above, the tensile stress due to restraint strain is calculated taking into account creep corresponding to restraint strain caused by temperature change occurring from material age t-1 to material age t.
具体的には、施工時期の外気温の変化を継続的に計測し、温度応力解析から定めた単位セメント量（単位結合材量）と外気温による関係式から材齢ｔ時における温度変化による拘束ひずみεｔを算出し、有効ヤング係数である前記式（２）を掛け合わせて、温度変化による拘束ひずみの引張応力σｔを算出する。 Specifically, the change in outside temperature during construction is continuously measured, and the restraint strain εt due to temperature change at material age t is calculated from the relational equation between the unit cement amount (unit amount of binder) and the outside temperature determined from temperature stress analysis, and this is multiplied by the effective Young's modulus, as shown in equation (2) above, to calculate the tensile stress σt of the restraint strain due to temperature change.
ここで、温度変化による拘束ひずみを抑制する対策と収縮ひずみを抑制する対策を比べると、温度変化を抑える対策の方が、収縮ひずみを抑制する対策より対策が取りやすく効果も大きいと考えられる。よって、本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法では、ｓｔｅｐ２の配合照査段階でＮＧとなった場合、且つ、最初に対策１であるｓｔｅｐ３の配合修正でひずみの抑制ができなかった場合は、対策２のｓｔｅｐ４として、間詰めコンクリートの温度変化を抑制する温度抑制対策を試みる。 Comparing measures to suppress restraint strain caused by temperature change with measures to suppress shrinkage strain, measures to suppress temperature change are considered to be easier to implement and more effective than measures to suppress shrinkage strain. Therefore, in the method for suppressing cracks in cast-in-place concrete according to an embodiment of the present invention, if the mix verification stage in step 2 is found to be NG, and if the mix correction in step 3, which is measure 1, fails to suppress the strain initially, then step 4 of measure 2 is to attempt temperature suppression measures to suppress temperature changes in the interfill concrete.
具体的には、温度抑制対策としては、打設したフレッシュコンクリートをブルーシートや保温シートなどで被うなどして保温する保温養生や、ジェットヒーター等で暖気を供給するなどする給熱養生を行うことが挙げられる。また、打設するフレッシュコンクリート（生コン）そのものの温度を抑制する生コン温度抑制対策などを行うことも有効である。 Specific temperature control measures include insulation curing, in which poured fresh concrete is covered with a blue tarp or thermal insulation sheet to keep it warm, and heat curing, in which warm air is supplied using a jet heater or similar. It is also effective to take measures to control the temperature of the fresh concrete (ready mixed concrete) itself as it is poured.
そして、前述のクリープを考慮した収縮ひずみによる引張応力の算出で算出された引張応力と、及びクリープを考慮した温度変化の拘束ひずみによる引張応力の算出で算出された引張応力を合算し、図４に示すように、合算した引張応力と、圧縮強度試験から求めた引張強度とから、材齢ｔ時におけるひび割れ指数（引張強度／引張応力）を算出する。 Then, the tensile stress calculated by calculating the tensile stress due to shrinkage strain taking creep into account as described above and the tensile stress calculated by calculating the tensile stress due to restraint strain of temperature change taking creep into account are added together, and the crack index (tensile strength/tensile stress) at material age t is calculated from the added tensile stress and the tensile strength obtained from the compressive strength test, as shown in Figure 4.
この算出したひび割れ指数と実物大要素実験及び実現場でのひずみ測定とひび割れ観察により得た収縮ひずみの整合性を検証した。結果としては、ひび割れ指数が材齢７日までは１．５以内、材齢７日以降は１．０以内であればひび割れを防止できることが検証できた。よって、本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法では、図４に示すように、ひび割れ指数が材齢７日までは１．５以上、材齢７日以降は１．０以上を目標値として間詰めコンクリートのひび割れ発生のリスクを評価する。 The consistency of this calculated crack index with shrinkage strain obtained from full-scale element experiments and on-site strain measurements and crack observations was verified. As a result, it was verified that cracks can be prevented if the crack index is within 1.5 until the material is 7 days old, and within 1.0 after 7 days old. Therefore, in the method for suppressing cracks in cast-in-place concrete according to an embodiment of the present invention, as shown in Figure 4, the risk of cracking in fill concrete is evaluated with a target crack index of 1.5 or more until the material is 7 days old, and 1.0 or more after 7 days old.
そこで、図１に示すように、本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法では、ｓｔｅｐ５として、対策２のｓｔｅｐ４で温度抑制対策を行った場合の温度応力解析を行う。具体的には、ｓｔｅｐ５の温度応力解析では、温度抑制対策を行った場合の温度変化の拘束ひずみによる引張応力を算出し、試し練りのコンクリートから求められた前述のクリープを考慮した収縮ひずみによる引張応力を合算して、ひび割れ指数が前述の目標値以上であればＯＫとしてｓｔｅｐ４の温度抑制対策に適合した養生を工夫した施工方法により間詰めコンクリートを打設して施工する。 As shown in Figure 1, in the method for suppressing cracks in cast-in-place concrete according to an embodiment of the present invention, in step 5, a temperature stress analysis is performed when temperature suppression measures are taken in step 4 of measure 2. Specifically, in the temperature stress analysis in step 5, the tensile stress due to restraint strain of temperature change when temperature suppression measures are taken is calculated, and the tensile stress due to shrinkage strain considering the above-mentioned creep obtained from the test mix concrete is added. If the crack index is equal to or greater than the above-mentioned target value, it is deemed OK, and the filling concrete is poured and constructed using a construction method that devises curing suitable for the temperature suppression measures in step 4.
この温度応力解析は、市販の表計算ソフトを利用して関係式を予め打ち込んで解析ソフトを構築し、圧縮強度試験、静弾性係数試験、拘束膨張試験、自己収縮試験、乾燥収縮試験を含む各種試験で得られた実測値を入力することにより、自動で評価できるようにすることが好ましい。専門知識がなくても誰でも簡単に間詰めコンクリートのひび割れの発生リスクを評価して対応策をとることが容易となるからである。 It is preferable to use commercially available spreadsheet software to construct the analysis software by inputting the relational equations in advance, and then inputting the actual measured values obtained from various tests, including compressive strength tests, static elastic modulus tests, restrained expansion tests, autogenous shrinkage tests, and drying shrinkage tests, so that this temperature stress analysis can be performed automatically. This is because anyone, even without specialist knowledge, can easily evaluate the risk of cracking in interfacial concrete and take appropriate measures.
また、図１に示すように、ｓｔｅｐ５の温度応力解析でＮＧとなった場合は、対策３としてｓｔｅｐ６の収縮抑制対策を行う。ｓｔｅｐ６の収縮抑制対策では、収縮低減剤の使用や、膨張材の増量を検討して収縮ひずみによる引張応力の低減を試みる。 Also, as shown in Figure 1, if the temperature stress analysis in step 5 is NG, shrinkage suppression measures in step 6 are implemented as countermeasure 3. In shrinkage suppression measures in step 6, attempts are made to reduce the tensile stress caused by shrinkage strain by considering the use of shrinkage reducing agents and increasing the amount of expansive material.
具体的には、収縮低減剤の使用、膨張材の増量等で収縮抑制対策を施した配合で再度試し練りを行い、その配合により生コン工場でフレッシュコンクリートを練り混ぜ供試体を作成し、試験機関等に搬送し、そこで自己収縮試験や乾燥収縮試験等を実施し、再度、ｓｔｅｐ２の配合照査、ｓｔｅｐ５の温度応力解析をやり直してＯＫとなるまで繰り返す。 Specifically, a test mix is run again using a mix that has shrinkage-suppressing measures in place, such as using a shrinkage-reducing agent and increasing the amount of expansive material, and fresh concrete is mixed using this mix at a ready-mix concrete plant to create a test specimen, which is then transported to a testing institute, etc., where autogenous shrinkage tests and drying shrinkage tests are conducted, and the mix verification in step 2 and the temperature stress analysis in step 5 are repeated until the specimen is deemed acceptable.
以上説明した本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法によれば、ＰＣａ床版に両側が挟まれているため、構造的に拘束が大きく、且つ、自己収縮が大きく、セメント量が多いため水和発熱温度が高いとともに、部材の体積が小さいことから急激な温度変化となり易いという間詰めコンクリート（周囲の既設構造物に拘束を受ける場所打ちコンクリート）特有の諸問題を解決することができる。 The above-described method for suppressing cracks in cast-in-place concrete according to the embodiment of the present invention can solve the problems specific to filler concrete (cast-in-place concrete that is constrained by existing surrounding structures), such as the large structural constraints due to the PCa deck sandwiched between the two sides, the large autogenous shrinkage, the high hydration heat temperature due to the large amount of cement, and the small volume of the components that make it susceptible to sudden temperature changes.
また、本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法によれば、現場毎の施工条件に基づいた短期的及び長期的な収縮量、応力度を推定し、事前にひび割れリスクを評価できるので、ひび割れを最大限防止する配合計画及び施工計画を立案することが容易となる。 In addition, the method for suppressing cracks in cast-in-place concrete according to an embodiment of the present invention makes it possible to estimate short-term and long-term shrinkage and stress levels based on the construction conditions at each site and evaluate the risk of cracking in advance, making it easy to devise mix plans and construction plans that will prevent cracking to the greatest extent possible.
そして、本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法によれば、ひび割れ指数が目標値を下回る場合、配合修正を行って再度試し練りをし、算出し直したひび割れ指数でひび発生のリスクを再度評価するので、軽微な配合修正により間詰めコンクリートのひび割れを抑制することができるか否かの判別がつき、実行が容易な施工計画を立案することができる。 In addition, according to the method for suppressing cracks in cast-in-place concrete according to an embodiment of the present invention, if the crack index falls below the target value, the mix is modified and test mixed again, and the risk of cracks is reassessed using the recalculated crack index. This makes it possible to determine whether cracks in the interfill concrete can be suppressed by minor mix modifications, and allows the creation of a construction plan that is easy to execute.
さらに、本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法によれば、温度抑制対策を施して間詰めコンクリートの温度変化を抑制した場合の温度変化による引張応力を算出し直して、算出し直したひび割れ指数が目標値以上か否かでひび発生のリスクを再度評価するので、収縮ひずみを抑制する対策より対策が取り易く効果も大きいと考えられ、且つ、材料費が嵩むこともない温度変化を抑える対策で、間詰めコンクリートのひび割れを抑制することができる。 Furthermore, according to the method for suppressing cracks in cast-in-place concrete of an embodiment of the present invention, the tensile stress caused by temperature change when temperature suppression measures are taken to suppress temperature change in the interfacial concrete is recalculated, and the risk of cracking is reassessed based on whether the recalculated crack index is equal to or greater than the target value. This is considered to be easier to implement and more effective than measures to suppress shrinkage strain, and it is possible to suppress cracks in interfacial concrete by using measures to suppress temperature change that do not increase material costs.
また、本発明の実施形態に係る間詰めコンクリートのひび割れ抑制方法によれば、収縮抑制対策を施して間詰めコンクリートの材齢ｔ時における収縮ひずみの引張応力を算出し直して、算出し直したひび割れ指数が目標値以上か否かでひび発生のリスクを再度評価するので、温度変化を抑える対策でも抑えることができない場合でも間詰めコンクリートのひび割れを抑制することができる。 In addition, according to the method for suppressing cracks in interfacial concrete according to an embodiment of the present invention, shrinkage suppression measures are taken to recalculate the tensile stress of the shrinkage strain of the interfacial concrete at age t, and the risk of cracking is reassessed based on whether the recalculated crack index is equal to or greater than the target value. This makes it possible to suppress cracks in interfacial concrete even when measures to suppress temperature changes are not sufficient to suppress cracks.
それに加え、本発明の実施形態に係る間詰めコンクリートのひび割れ抑制方法によれば、拘束膨張試験では、材齢７日の供試体の膨張ひずみを実測し、実測値から膨張ひずみの経時変化を推定し、自己収縮試験では、材齢２８日までの供試体の自己収縮ひずみの経時変化を実測し、実測値から間詰め部（現場打ちコンリートを打設する部位）の寸法効果を考慮して自己収縮ひずみの経時変化の関係式の係数を推定し、乾燥収縮試験では、乾燥材齢２８日後の供試体の長さ変化を実測して６カ月後の長さ変化を推定し、自己収縮ひずみの実測値を差し引いて、乾燥収縮ひずみの実測値を算出し、乾燥収縮ひずみの実測値から間詰め部の材齢６か月後の長さ変化を推定する。このため、自由ひずみの算出精度が向上し、間詰めコンクリートの事前のひび割れリスクを正確に評価することができる。 In addition, according to the method for suppressing cracks in interfacial concrete according to the embodiment of the present invention, in the restrained expansion test, the expansion strain of a specimen with an age of 7 days is actually measured, and the change in the expansion strain over time is estimated from the measured value. In the autogenous shrinkage test, the change in the autogenous shrinkage strain of a specimen with an age of 28 days is actually measured, and the coefficient of the relational expression for the change in autogenous shrinkage strain over time is estimated from the measured value, taking into account the size effect of the interfacial filling part (the part where the cast-in-place concrete is poured). In the drying shrinkage test, the change in length of the specimen after 28 days of drying is actually measured, and the change in length after 6 months is estimated, and the measured value of the autogenous shrinkage strain is subtracted to calculate the measured value of the drying shrinkage strain, and the change in length of the interfacial filling part after 6 months is estimated from the measured value of the drying shrinkage strain. This improves the accuracy of the calculation of the free strain, and allows for accurate assessment of the risk of cracking in advance of interfacial concrete.
以上、本発明の実施形態に係る場所打ちコンクリートのひび割れ抑制方法について詳細に説明した。しかし、前述した又は図示した実施形態は、いずれも本発明を実施するにあたって具体化した一実施形態を示したものに過ぎず、これらによって本発明の技術的範囲が限定的に解釈されてはならないものである。特に、本発明に係る場所打ちコンクリートのひび割れ抑制方法は、間詰め部に打設される間詰めコンリートに限られず、既設構造物により拘束を受ける場所打ちコンクリートには適用することができる。 Above, a method for suppressing cracks in cast-in-place concrete according to an embodiment of the present invention has been described in detail. However, the above-mentioned and illustrated embodiments are merely examples of concrete embodiments for carrying out the present invention, and the technical scope of the present invention should not be interpreted in a limiting manner based on these. In particular, the method for suppressing cracks in cast-in-place concrete according to the present invention is not limited to concrete filled in gaps, but can be applied to cast-in-place concrete that is restrained by existing structures.
Claims (7)
実際に打設する場所打ちコンクリートに使用する同種の材料で予めコンクリートを試し練りし、圧縮強度試験、静弾性係数試験、拘束膨張試験、自己収縮試験、乾燥収縮試験を含む各種試験を行って、実際に打設する前記場所打ちコンクリートの特性値として、圧縮強度の経時変化、静弾性係数の経時変化、膨張ひずみの経時変化、自己収縮ひずみの経時変化の関係式の係数、及び間詰め部の材齢６か月後の長さ変化を推定した上、
推定した前記圧縮強度の経時変化から前記場所打ちコンクリートの材齢ｔ時における引張強度を算出し、推定した静弾性係数の経時変化、膨張ひずみの経時変化、自己収縮ひずみの経時変化の関係式の係数、及び間詰め部の材齢６か月後の長さ変化から前記場所打ちコンクリートの材齢ｔ時における収縮ひずみの引張応力及び前記場所打ちコンクリートの材齢ｔ時における温度変化による引張応力を、それぞれ算出し、
算出した前記収縮ひずみの引張応力と算出した前記温度変化による引張応力とを合算した引張応力で算出した前記引張強度を割って前記場所打ちコンクリートの材齢ｔ時のひび割れ指数を算出し、算出した前記ひび割れ指数が目標値以上か否かでひび発生のリスクを評価すること
を特徴とする場所打ちコンクリートのひび割れ抑制方法。 A method for suppressing cracks in cast-in-place concrete that suppresses cracks in cast-in-place concrete that is constrained by surrounding existing structures, comprising:
Concrete is test-mixed in advance using the same materials as will be used for the cast-in-place concrete that will actually be poured, and various tests including compressive strength tests, static elastic modulus tests, restrained expansion tests, autogenous shrinkage tests, and drying shrinkage tests are conducted to estimate the characteristic values of the cast-in-place concrete that will actually be poured, including the coefficients of the relational expressions for the change in compressive strength over time, the change in static elastic modulus over time, the change in expansion strain over time, and the change in length of the filling part after six months of age .
The tensile strength of the cast-in-place concrete at age t is calculated from the estimated change in compressive strength over time, and the tensile stress of shrinkage strain of the cast-in-place concrete at age t and the tensile stress due to temperature change of the cast-in-place concrete at age t are calculated from the estimated change in static elastic modulus over time, the change in expansion strain over time, and the coefficient of the relational expression of the change in autogenous shrinkage strain over time, and the change in length of the filling portion after 6 months of age, respectively;
A method for suppressing cracks in cast-in-place concrete, comprising: dividing the calculated tensile strength by the combined tensile stress of the calculated shrinkage strain and the calculated tensile stress due to the temperature change to calculate a crack index of the cast-in-place concrete at age t; and evaluating the risk of crack occurrence based on whether the calculated crack index is equal to or greater than a target value.
を特徴とする請求項１に記載の場所打ちコンクリートのひび割れ抑制方法。 2. A method for suppressing cracks in cast-in-place concrete as described in claim 1, characterized in that if the calculated crack index is below the target value, the mix is modified and test mixing is performed again, and various tests including compressive strength tests, static elastic modulus tests, restrained expansion tests, autogenous shrinkage tests, and drying shrinkage tests are performed again to recalculate the tensile strength of the cast-in-place concrete at age t, the tensile stress of the shrinkage strain of the cast-in-place concrete at age t, and the tensile stress due to temperature change of the cast-in-place concrete at age t, and the risk of cracks occurring is re-evaluated based on whether the recalculated crack index is equal to or greater than the target value.
を特徴とする請求項１に記載の場所打ちコンクリートのひび割れ抑制方法。 A method for suppressing cracks in cast-in-place concrete as described in claim 1, characterized in that if the calculated crack index falls below the target value, the tensile stress caused by the temperature change when temperature suppression measures are taken to suppress the temperature change of the cast-in-place concrete is recalculated, and the risk of crack occurrence is re-evaluated based on whether the recalculated crack index is above the target value.
を特徴とする請求項３に記載の場所打ちコンクリートのひび割れ抑制方法。 A method for suppressing cracks in cast-in-place concrete as described in claim 3, characterized in that if the recalculated crack index falls below the target value, shrinkage suppression measures are taken to recalculate the tensile stress of the shrinkage strain of the cast-in-place concrete at age t, and the risk of crack occurrence is re-evaluated based on whether the recalculated crack index is equal to or greater than the target value.
を特徴とする請求項１に記載の場所打ちコンクリートのひび割れ抑制方法。 2. The method for suppressing cracks in cast-in-place concrete according to claim 1, wherein in the restrained expansion test, the expansion strain of a specimen aged 7 days is actually measured, and the change in the expansion strain over time is estimated from the measured value.
を特徴とする請求項１に記載の場所打ちコンクリートのひび割れ抑制方法。 The method for suppressing cracks in cast-in-place concrete described in claim 1, characterized in that in the autogenous shrinkage test, the change in the autogenous shrinkage strain of the test specimen over time is measured up to 28 days after the material age, and the coefficients of the relational equation for the change in the autogenous shrinkage strain over time are estimated from the measured values, taking into account the dimensional effect of the cast-in-place part.
を特徴とする請求項１に記載の場所打ちコンクリートのひび割れ抑制方法。 2. The method for suppressing cracks in cast-in-place concrete according to claim 1, characterized in that in the drying shrinkage test, the change in length of the test specimen after 28 days of drying is measured to estimate the change in length after 6 months, the increase in the actual measured value of autogenous shrinkage strain from 7 days to 6 months of age is subtracted to calculate the actual measured value of drying shrinkage strain, and the change in length of the cast-in-place portion at age t is estimated from the measured value of drying shrinkage strain.
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Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2002048690A (en) | 2000-08-01 | 2002-02-15 | Okumura Corp | Cracking judgment method in premature age of member using high strength concrete and judging apparatus using the same and casting method of high strength concrete |
| JP2012107941A (en) | 2010-11-16 | 2012-06-07 | Taiheiyo Cement Corp | Method for determining compounding amount of shrinkage reducing agent |
| JP2012154125A (en) | 2011-01-27 | 2012-08-16 | Ihi Infrastructure Systems Co Ltd | Method of suppressing crack of temperature prestress introducing concrete |
| JP2013002904A (en) | 2011-06-15 | 2013-01-07 | Japan Concrete Institute | Method of preventing cracks in concrete |
| JP2013231656A (en) | 2012-04-27 | 2013-11-14 | Sumitomo Osaka Cement Co Ltd | Method of evaluating cracking resistance of concrete |
| JP2013231598A (en) | 2012-04-27 | 2013-11-14 | Taiheiyo Cement Corp | Quantitative evaluation method of crack reduction effect by shrinkage-reducing material, and selection method of shrinkage-reducing material |
-
2022
- 2022-10-20 JP JP2022168466A patent/JP7508524B2/en active Active
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2002048690A (en) | 2000-08-01 | 2002-02-15 | Okumura Corp | Cracking judgment method in premature age of member using high strength concrete and judging apparatus using the same and casting method of high strength concrete |
| JP2012107941A (en) | 2010-11-16 | 2012-06-07 | Taiheiyo Cement Corp | Method for determining compounding amount of shrinkage reducing agent |
| JP2012154125A (en) | 2011-01-27 | 2012-08-16 | Ihi Infrastructure Systems Co Ltd | Method of suppressing crack of temperature prestress introducing concrete |
| JP2013002904A (en) | 2011-06-15 | 2013-01-07 | Japan Concrete Institute | Method of preventing cracks in concrete |
| JP2013231656A (en) | 2012-04-27 | 2013-11-14 | Sumitomo Osaka Cement Co Ltd | Method of evaluating cracking resistance of concrete |
| JP2013231598A (en) | 2012-04-27 | 2013-11-14 | Taiheiyo Cement Corp | Quantitative evaluation method of crack reduction effect by shrinkage-reducing material, and selection method of shrinkage-reducing material |
Non-Patent Citations (3)
| Title |
|---|
| 中村 秀明，コンクリートの収縮ひび割れ対策 （１）ひび割れ（温度応力）解析の基礎，コンクリート工学，50(2)，pp.207-212 |
| 吉川 信二郎，第3回温度応力解析のいろは 一解析概要編一，プレストレストコンクリート，44(5)，pp.65-75 |
| 飯田 眞理，（２）硬化コンクリートの性質，新 セメント・コンクリート用混和材料 ，技術書院，2013年，pp.97-102 |
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