JP6813805B2 - Manufacturing method of high-strength precast concrete - Google Patents
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- 238000004519 manufacturing process Methods 0.000 title claims description 35
- 239000011178 precast concrete Substances 0.000 title claims description 20
- 239000004567 concrete Substances 0.000 claims description 54
- 239000004568 cement Substances 0.000 claims description 19
- 239000003638 chemical reducing agent Substances 0.000 claims description 16
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 16
- 239000000463 material Substances 0.000 claims description 10
- 239000000203 mixture Substances 0.000 claims description 9
- 229910021487 silica fume Inorganic materials 0.000 claims description 8
- 239000011398 Portland cement Substances 0.000 claims description 6
- 238000001816 cooling Methods 0.000 claims description 3
- 238000001723 curing Methods 0.000 description 38
- 230000000694 effects Effects 0.000 description 9
- 238000009415 formwork Methods 0.000 description 7
- 239000011230 binding agent Substances 0.000 description 6
- 238000009833 condensation Methods 0.000 description 6
- 230000005494 condensation Effects 0.000 description 6
- 238000010276 construction Methods 0.000 description 5
- 238000005266 casting Methods 0.000 description 3
- 239000011372 high-strength concrete Substances 0.000 description 3
- 238000006467 substitution reaction Methods 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 230000000977 initiatory effect Effects 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 230000035882 stress Effects 0.000 description 2
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 235000011941 Tilia x europaea Nutrition 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- JHLNERQLKQQLRZ-UHFFFAOYSA-N calcium silicate Chemical compound [Ca+2].[Ca+2].[O-][Si]([O-])([O-])[O-] JHLNERQLKQQLRZ-UHFFFAOYSA-N 0.000 description 1
- 229910052918 calcium silicate Inorganic materials 0.000 description 1
- 235000012241 calcium silicate Nutrition 0.000 description 1
- 238000005345 coagulation Methods 0.000 description 1
- 230000015271 coagulation Effects 0.000 description 1
- 238000013329 compounding Methods 0.000 description 1
- 229920001577 copolymer Polymers 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000036571 hydration Effects 0.000 description 1
- 238000006703 hydration reaction Methods 0.000 description 1
- 229910052500 inorganic mineral Inorganic materials 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- 239000004571 lime Substances 0.000 description 1
- 239000011707 mineral Substances 0.000 description 1
- 239000004570 mortar (masonry) Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000008646 thermal stress Effects 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/91—Use of waste materials as fillers for mortars or concrete
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- Devices For Post-Treatments, Processing, Supply, Discharge, And Other Processes (AREA)
- Curing Cements, Concrete, And Artificial Stone (AREA)
Description
本発明は、高強度プレキャストコンクリートの製造において、型枠の存置期間が短く、また温度ひび割れが生じ難い製造方法に関する。 The present invention relates to a production method for producing high-strength precast concrete, in which the shelf life of the formwork is short and temperature cracks are unlikely to occur.
プレキャストコンクリートを用いた工法は、予め製作したコンクリート製品を施工現場で組み立て構造体を構築する工法であり、通常、コンクリート製品は専用工場で製作されるので、天候に左右されることなく、高品質で品質の安定したコンクリート製品を製造でき、工事期間の短縮化、施工現場の省力化ができるなどの利点を有しており、広く実施されている。 The construction method using precast concrete is a construction method in which pre-made concrete products are assembled at the construction site to construct a structure. Normally, concrete products are manufactured in a dedicated factory, so high quality is not affected by the weather. It has the advantages of being able to manufacture concrete products with stable quality, shortening the construction period, and saving labor at the construction site, and is widely practiced.
プレキャストコンクリートの製造について、製造時間の短縮や製品の圧縮強度を高めるための検討がなされており、例えば、以下の製造方法が知られている。
(イ) 特開２０００−７１２３２号公報（特許文献１）には、前養生温度を４０℃にすることで蒸気養生サイクルを短縮した製造方法が記載されている。
(ロ) 特開２０１３−１４４４７号公報（特許文献２）には、シリカフューム混入セメントを結合材としたセメント組成物において、水結合材比を０.２以下にして混練、成型し、７０〜１００℃の温度範囲で２〜７２時間蒸気養生する第１の養生工程と、常圧を超え２２ＭＰａ以下の加圧条件下で１００〜４００℃の温度範囲で２〜７２時間加熱する第２の養生工程を行うことによって、圧縮強度３００Ｎ/ｍｍ２以上の高強度セメント硬化体を得ることが記載されている。
(ハ) 特開２０１１−１９５３５４号公報（特許文献３）には、低発熱型セメントとポゾラン質物質を含む結合材を用いた高強度プレキャストコンクリートの製造において、常温で２〜４時間前養生した後に、５〜１０℃/ｈの昇温勾配で最高温度６０〜９０℃まで昇温して３〜９時間保持した後に常温まで冷却する製造方法が記載されている。この製造方法は前養生時間を短縮できるので概ね２４時間以内に脱型できるとしている。
Regarding the production of precast concrete, studies have been made to shorten the production time and increase the compressive strength of the product. For example, the following production methods are known.
(B) Japanese Unexamined Patent Publication No. 2000-71232 (Patent Document 1) describes a production method in which the steam curing cycle is shortened by setting the pre-curing temperature to 40 ° C.
(B) Japanese Patent Application Laid-Open No. 2013-14447 (Patent Document 2) describes a cement composition containing silica fume-mixed cement as a binder, kneaded and molded with a water binder ratio of 0.2 or less, and 70 to 100. A first curing step of steam curing in a temperature range of ° C. for 2 to 72 hours, and a second curing step of heating in a temperature range of 100 to 400 ° C. for 2 to 72 hours under a pressurized condition exceeding normal pressure and 22 MPa or less. It is described that a high-strength cement cured product having a compressive strength of 300 N / mm 2 or more can be obtained by carrying out the above.
(C) Japanese Patent Application Laid-Open No. 2011-195354 (Patent Document 3) states that in the production of high-strength precast concrete using a binder containing a low-heat-generating cement and a pozzolanic substance, it was cured at room temperature for 2 to 4 hours. Later, a production method is described in which the temperature is raised to a maximum temperature of 60 to 90 ° C. with a temperature rise gradient of 5 to 10 ° C./h, held for 3 to 9 hours, and then cooled to room temperature. Since this manufacturing method can shorten the pre-curing time, it is said that the mold can be removed within about 24 hours.
特許文献３に開示されている製造方法は、小型の供試体レベルでは所要の強度発現をするものの、実大寸法のプレキャストコンクリートでの部材温度は、高温が数日間推移しており、型枠存置期間が長期化する傾向にある。また、特許文献１〜３の製造方法も同様であるが、一般に部材温度が十分に低下していない段階で脱型すると、特に粉体量の多い超高強度コンクリートの内部は高温になっており内部温度応力によるひび割れや、脱枠時の外気と部材表面の温度差によりヒートクラックを生じる可能性がある。 Although the manufacturing method disclosed in Patent Document 3 exhibits the required strength at the level of a small specimen, the temperature of the member in the full-scale precast concrete has remained high for several days, and the formwork is retained. The period tends to be longer. Further, the manufacturing methods of Patent Documents 1 to 3 are the same, but in general, when the member is demolded at a stage where the member temperature is not sufficiently lowered, the inside of the ultra-high strength concrete having a particularly large amount of powder becomes high. There is a possibility that cracks may occur due to internal temperature stress, or heat cracks may occur due to the temperature difference between the outside air and the surface of the member when the frame is removed.
本発明は、従来の製造方法における上記課題を解決したものであり、型枠から短時間で脱型することができ、型枠の回転率を高め、かつ温度ひび割れが生じ難い高強度プレキャストコンクリートを製造する方法を提供する。 The present invention solves the above-mentioned problems in the conventional manufacturing method, and provides a high-strength precast concrete that can be removed from the formwork in a short time, increases the rotation rate of the formwork, and is less likely to cause temperature cracks. Provide a method of manufacturing.
本発明は、以下の構成によって上記課題を解決した高強度プレキャストコンクリートの製造方法に関する。
〔１〕低熱ポルトランドセメントがベースセメントであるシリカフューム混合セメントに粗骨材、細骨材、促進型高性能減水剤を配合したコンクリート組成物を用いたプレキャストコンクリートの製造方法であって、コンクリートを型枠に打設し、３０〜５０℃で６〜９時間の前養生を行って凝結始発時間を早めた後に、引続き、昇温勾配１０〜２０℃/ｈの割合で養生温度を高め、最高温度６０〜９０℃で２時間〜４時間保持させる蒸気養生を行い、その後に自然冷却して、コンクリートの表面温度と内部温度との温度差が２０℃以下、およびコンクリートの表面温度と外気温との温度差が２０℃以下になった後に脱型する温度履歴を経ることを特徴とする高強度プレキャストコンクリートの製造方法。
〔２〕促進型高性能減水剤を結合材に対して１〜６質量％含有し、膨張材を単位量で２〜２０kg/ｍ３含有するコンクリート組成物を用いる上記[１]に記載する高強度プレキャストコンクリートの製造方法。
The present invention relates to a method for producing high-strength precast concrete that solves the above problems by the following configurations.
[1] A method for producing precast concrete using a concrete composition in which coarse aggregate, fine aggregate, and an accelerated high-performance water reducing agent are mixed with silica-fume mixed cement whose base cement is low-heat Portland cement. After placing in a frame and pre-curing at 30 to 50 ° C. for 6 to 9 hours to accelerate the settling start time, the curing temperature is continuously increased at a rate of temperature rise gradient of 10 to 20 ° C./h to the maximum temperature. Steam curing is performed by holding at 60 to 90 ° C for 2 to 4 hours, and then air cooling is performed so that the temperature difference between the concrete surface temperature and the internal temperature is 20 ° C or less, and the concrete surface temperature and the outside temperature A method for producing high-strength precast concrete, which comprises a temperature history of demolding after the temperature difference becomes 20 ° C. or less .
[2] The height according to the above [1], wherein a concrete composition containing 1 to 6% by mass of an accelerated high-performance water reducing agent and 2 to 20 kg / m 3 of an expanding material in a unit amount is used. How to make strong precast concrete.
本発明の製造方法は、コンクリートを型枠に打設した後に直ちに断熱シートで覆い、３０〜５０℃で６〜９時間前置養生を行うことによって、コンクリートの凝結始発時間が促進される。一般的な養生方法は、特許文献３に記載されている製造方法のように、凝結始発に到達後に蒸気養生を行うが、本発明の製造方法は、常温よりやや高い温度で前養生を行って凝結始発時間を早める。引続き、昇温勾配１０〜２０℃/ｈの割合で養生温度を高め、最高温度６０〜９０℃で２時間〜４時間保持させる方法であり、前養生時間（約６〜９時間）と昇温時間（約３０分〜６時間）と高温保持時間（２〜4時間）と、コンクリートの表面温度と内部温度との温度差が２０℃以下、およびコンクリートの表面温度と外気温との温度差が２０℃以下に到達するまでに要する自然冷却時間の合計養生時間は概ね４０時間〜４８時間であり、短時間に脱型することができる。 In the production method of the present invention, the concrete setting start time is promoted by immediately covering the concrete with a heat insulating sheet after placing it in a mold and performing pre-curing at 30 to 50 ° C. for 6 to 9 hours. As a general curing method, steam curing is performed after reaching the first condensation, as in the production method described in Patent Document 3, but in the production method of the present invention, pre-curing is performed at a temperature slightly higher than normal temperature. Accelerate the first settling time. Subsequently, the curing temperature is raised at a rate of a temperature rise gradient of 10 to 20 ° C./h, and the temperature is maintained at a maximum temperature of 60 to 90 ° C. for 2 hours to 4 hours. The temperature rises with the pre-curing time (about 6 to 9 hours). The time (about 30 minutes to 6 hours) and high temperature holding time (2 to 4 hours), the temperature difference between the concrete surface temperature and the internal temperature is 20 ° C or less, and the temperature difference between the concrete surface temperature and the outside air temperature. The total curing time of the natural cooling time required to reach 20 ° C. or lower is approximately 40 hours to 48 hours, and the mold can be removed in a short time.
本発明の製造方法は、コンクリートを型枠に打設後４０時間〜４８時間経過後の同一時間におけるコンクリートの表面温度と内部温度の温度差が従来の製造方法よりも小さい。また、本発明の製造方法によれば、コンクリートの表面温度と内部温度との温度差が２０℃以下、およびコンクリートの表面温度と外気温との温度差が２０℃以下になった後に脱型することによって、温度ひび割れが生じ難い高強度プレキャストコンクリートを得ることができる。
In the manufacturing method of the present invention, the temperature difference between the surface temperature and the internal temperature of the concrete at the
本発明の製造方法は、温度ひび割れやヒートクラックを抑制した高強度のプレキャストコンクリートを製造することができる。また、前養生温度を常温よりやや高くして、促進型高性能減水剤を配合したセメント組成物の凝結始発時間を早めるので、型枠からの脱型時間を短縮することができ、効率よく高強度プレキャストコンクリートを製造することができる。 The production method of the present invention can produce high-strength precast concrete in which temperature cracks and heat cracks are suppressed. In addition, the pre-curing temperature is slightly higher than room temperature to accelerate the settling start time of the cement composition containing the accelerated high-performance water reducing agent, so that the time required for demolding from the mold can be shortened, resulting in high efficiency. Strong precast concrete can be produced.
以下、本発明を実施形態に基づいて具体的に説明する。
本発明の製造方法は、低熱ポルトランドセメントがベースセメントであるシリカフューム混合セメントに、細骨材、粗骨材および促進型高性能減水剤を配合したセメント組成物を用いたプレキャストコンクリートの製造方法であって、コンクリートを型枠に打設し、３０〜５０℃で６〜９時間の前養生を行って凝結始発時間を早めた後に、引続き、昇温勾配１０〜２０℃/ｈの割合で養生温度を高め、最高温度６０〜９０℃で２時間〜４時間保持させた後に、自然冷却してコンクリートの表面温度と内部温度との温度差が２０℃以下、およびコンクリートの表面温度と外気温との温度差が２０℃以下になった後に、脱型する温度履歴を経ることを特徴とする高強度プレキャストコンクリートの製造方法である。
Hereinafter, the present invention will be specifically described based on the embodiments.
The production method of the present invention is a method for producing precast concrete using a cement composition in which fine aggregate, coarse aggregate and an accelerated high-performance water reducing agent are mixed with silica fume mixed cement based on low-heat Portorand cement. Then, concrete is placed in a mold and pre-cured at 30 to 50 ° C. for 6 to 9 hours to accelerate the settling start time, and then the curing temperature is continuously increased at a rate of 10 to 20 ° C./h. After increasing the temperature and holding it at a maximum temperature of 60 to 90 ° C for 2 to 4 hours, it is naturally cooled so that the temperature difference between the surface temperature of the concrete and the internal temperature is 20 ° C or less, and the surface temperature of the concrete and the outside temperature This is a method for producing high-strength precast concrete, which is characterized by undergoing a temperature history of demolding after the temperature difference becomes 20 ° C. or less.
本発明の製造方法は、低熱ポルトランドセメントがベースセメントであるシリカフューム混合セメントを用いたプレキャストコンクリートの製造方法である。低熱ポルトランドセメントはビーライトＣ２Ｓ量を４０質量％以上にして水和熱を抑えたセメントであり、長期強度の発現に優れ、コンクリートの低熱性、高強度性および高流動性に適している。低熱ポルトランドセメントの含有量は、好ましくは、８５.０〜９２.５質量％である。低熱ポルトランドセメントは一般的な鉱物組成を有するものでよく、例えば、Ｃ２Ｓが６０〜８０質量％、Ｃ３Ｓが２０〜３０質量％、Ｃ３Ａが６質量％以下の範囲である。 The production method of the present invention is a method for producing precast concrete using silica fume mixed cement in which low-heat Portland cement is the base cement. Low heat Portland cement is a cement with a belite C 2 S content more than 40 mass% suppressing heat of hydration, superior for expression of long strength, low heat concrete, is suitable for high strength and high fluidity .. The content of low heat Portland cement is preferably 85.0 to 92.5% by mass. Low-heat Portland cement may have a general mineral composition, for example, C 2 S is 60 to 80% by mass, C 3 S is 20 to 30% by mass, and C 3 A is 6% by mass or less.
本発明に用いるシリカフューム混合セメントは、シリカフュームの置換率は、例えば７.５〜１５質量％である。シリカフュームの置換率が７.５質量％未満では流動性および強度を高める効果が不十分であり、この置換率が１５質量％を上回ると、製造工程において多くのシリカフュームを添加する必要があり、製造効率が低下するばかりでなく、相対的にセメント量が少なくなるので強度低下を生じる場合がある。 The silica fume mixed cement used in the present invention has a silica fume substitution rate of, for example, 7.5 to 15% by mass. If the substitution rate of silica fume is less than 7.5% by mass, the effect of increasing fluidity and strength is insufficient, and if this substitution rate exceeds 15% by mass, it is necessary to add a large amount of silica fume in the manufacturing process. Not only is the efficiency reduced, but the amount of cement is relatively small, which may result in a decrease in strength.
本発明のコンクリートには、促進型高性能減水剤が添加される。促進型高性能減水剤は、例えば、ポリカルボン酸コポリマーを主成分とし、モルタルやコンクリートが一定の流動性を得るための単位水量を減少すると共にこれらの凝結を促進する効果を有する。
該促進型高性能減水剤の添加量はセメント等の結合材に対して１〜６質量％が好ましい。該促進型高性能減水剤は市販品（竹本油脂社製：チューポールSSP−104Hなど）を用いることができる。促進型高性能減水剤を上記含有量添加することにより、温度が３０〜５０℃の前養生６〜９時間の間に凝結始発時間に到達するように凝結始発時間を短縮することができる。促進型高性能減水剤の添加量が結合材に対して１質量％より少ないと、コンクリートの打設に必要な流動性を得ることができず、凝結始発時間を早める効果も十分に得られない。促進型高性能減水剤の添加量が結合材に対して６質量％より多いと、コンクリートの流動性が過剰となり材料分離を起こすばかりでなく、強度発現性が低下する。
An accelerated high-performance water reducing agent is added to the concrete of the present invention. The accelerated high-performance water reducing agent contains, for example, a polycarboxylic acid copolymer as a main component, and has an effect of reducing the unit amount of water for mortar or concrete to obtain a certain fluidity and promoting the coagulation of these.
The amount of the accelerated high-performance water reducing agent added is preferably 1 to 6% by mass with respect to the binder such as cement. As the accelerated high-performance water reducing agent, a commercially available product (Takemoto Oil & Fat Co., Ltd .: Chupole SSP-104H, etc.) can be used. By adding the above-mentioned content of the accelerated high-performance water reducing agent, the condensation initiation time can be shortened so that the condensation initiation time is reached within 6 to 9 hours of pre-curing at a temperature of 30 to 50 ° C. If the amount of the accelerated high-performance water reducing agent added is less than 1% by mass with respect to the binder, the fluidity required for concrete placement cannot be obtained, and the effect of accelerating the condensation start time cannot be sufficiently obtained. .. If the amount of the accelerated high-performance water reducing agent added is more than 6% by mass with respect to the binder, the fluidity of the concrete becomes excessive, causing not only material separation but also a decrease in strength development.
本発明のコンクリートにおいて、粗骨材および細骨材の含有量は一般的な高強度コンクリート組成物の範囲でよく、例えば、粗骨材の単位量４００〜５００kg/ｍ３、細骨材の単位量９００〜１１００kg/ｍ３であり、水セメント比は１０〜２０％が好ましい。水セメント比が１０質量％未満であると、所望の流動性を得るために減水剤の添加量を多く必要し、２０質量％を超えるとコンクリートの十分な強度が得られない。 In the concrete of the present invention, the content of coarse aggregate and fine aggregate may be in the range of a general high-strength concrete composition, for example, a unit amount of coarse aggregate 400 to 500 kg / m 3 , a unit of fine aggregate. The amount is 900 to 1100 kg / m 3 , and the water-cement ratio is preferably 10 to 20%. If the water-cement ratio is less than 10% by mass, a large amount of water reducing agent is required to obtain the desired fluidity, and if it exceeds 20% by mass, sufficient strength of concrete cannot be obtained.
本発明のコンクリートには、硬化後の収縮やひび割れなどを防止するための収縮低減剤や膨張材などを添加してもよい。これらの収縮低減剤および膨張材は市販品を用いることができる。例えば、膨張材として、太平洋マテリアル社製品の石灰系膨張材（ハイパーエクスパン）などを用いることができる。膨張材の混入量は、単位量で２〜２０kg/ｍ３の範囲が適している。膨張材の単位量が２kg/ｍ３より少ないと膨張効果が十分ではなくひび割れが発生する場合があり、２０kg/ｍ３より多いとコンクリートの強度発現性が悪くなるばかりでなく、異常膨張による膨張ひび割れが発生する場合があるので、好ましくない。 To the concrete of the present invention, a shrinkage reducing agent, an expanding material, or the like for preventing shrinkage or cracking after hardening may be added. Commercially available products can be used as these shrinkage reducing agents and expanding materials. For example, as the expansion material, a lime-based expansion material (Hyper Expand) manufactured by Pacific Materials Co., Ltd. can be used. The amount of the expanding material mixed in is preferably in the range of 2 to 20 kg / m 3 in unit amount. If the unit amount of the inflatable material is less than 2 kg / m 3 , the expansion effect is not sufficient and cracks may occur. If it is more than 20 kg / m 3 , not only the strength development of concrete deteriorates, but also expansion due to abnormal expansion It is not preferable because it may cause cracks.
練り混ぜたコンクリートは型枠に打設して養生し、凝結硬化させる。型枠は無筋でもよく、鉄筋を配筋しても良い。 The kneaded concrete is cast in a formwork, cured, and hardened by condensation. The formwork may be unreinforced or reinforced.
本発明の製造方法は、コンクリートを型枠に打設した後に、直ちに断熱シートで覆い、蒸気養生を行う。蒸気養生の温度変化を図１に示す。図示するように、蒸気を吹き込んで３０〜５０℃にし、この状態を６〜９時間保って前置養生を行う。蒸気を吹き込む代わりに、３０〜５０℃に温度が調整された蒸気養生槽内に投入してもよい。常温よりやや高い温度で前養生を行うことでコンクリートの凝結始発時間が促進される。この前養生温度が３０℃より低いと凝結始発時間を早める効果が不十分となる。効果が不十分であり、一方、前養生温度が５０℃を超えると、凝結始発時間に到達するより前に高温の温度履歴を与えることにより、コンクリートの強度発現が阻害されることになるので好ましくない。 In the manufacturing method of the present invention, concrete is cast into a mold and immediately covered with a heat insulating sheet and steam-cured. The temperature change of steam curing is shown in FIG. As shown in the figure, steam is blown into the temperature to 30 to 50 ° C., and this state is maintained for 6 to 9 hours for pre-curing. Instead of blowing steam, it may be put into a steam curing tank whose temperature is adjusted to 30 to 50 ° C. Pre-curing at a temperature slightly higher than normal temperature accelerates the time at which concrete condenses. If the pre-curing temperature is lower than 30 ° C., the effect of accelerating the settling start time becomes insufficient. On the other hand, when the pre-curing temperature exceeds 50 ° C., the effect is insufficient, and it is preferable because the strength development of concrete is hindered by giving a high temperature history before reaching the condensation start time. Absent.
上記前養生の後に、引き続き、昇温勾配１０〜２０℃/ｈの割合で最高温度６０〜９０℃まで養生温度を高める。昇温勾配が１０℃/ｈより低いと、最高温度に達する時間がかかりすぎるので好ましくない。一方、昇温勾配が２０℃/ｈを超えると、コンクリートの表面温度がコンクリート内部よりも急激に高くなり、コンクリートの表面温度と内部温度の温度差が急激に大きくなるため、温度応力によるひび割れを生じやすくなる。 After the above pre-curing, the curing temperature is subsequently raised to a maximum temperature of 60 to 90 ° C. at a rate of temperature rising gradient of 10 to 20 ° C./h. If the temperature rise gradient is lower than 10 ° C./h, it takes too much time to reach the maximum temperature, which is not preferable. On the other hand, when the temperature rise gradient exceeds 20 ° C./h, the surface temperature of the concrete becomes sharply higher than that inside the concrete, and the temperature difference between the surface temperature and the internal temperature of the concrete sharply increases, so that cracks due to thermal stress occur. It is easy to occur.
昇温後、この最高温度で２時間〜４時間保持する。最高温度が６０℃未満であり、または保持時間が２時間未満であると、十分な養生効果が得られず圧縮強度が低くなる。一方、最高温度が９０℃を超え、または保持時間が４時間を超えると、養生効果はあまり変わらず、圧縮強度の発現性も頭打ちになり、むしろ打設から脱型するまでの所要時間が長くなるので好ましくない。 After the temperature is raised, the temperature is maintained at this maximum temperature for 2 to 4 hours. If the maximum temperature is less than 60 ° C. or the holding time is less than 2 hours, a sufficient curing effect cannot be obtained and the compressive strength becomes low. On the other hand, when the maximum temperature exceeds 90 ° C. or the holding time exceeds 4 hours, the curing effect does not change much, the expression of compressive strength reaches a plateau, and the time required from casting to demolding is rather long. It is not preferable because it becomes.
上記養生後、自然冷却させ、コンクリートの表面温度と内部温度との温度差が２０℃以下、およびコンクリートの表面温度と外気温との温度差が２０℃以下になった後に脱型する。コンクリートの表面温度と内部温度との温度差が２０℃より高い状態で脱型すると、粉体量の多い超高強度コンクリートは内部応力によるひび割れが生じやすくなり、また、脱型時の外気温とコンクリート表面温度の温度差が２０℃より高いと、ヒートクラックを生じることがあるので好ましくない。 After the above curing, the concrete is naturally cooled, and the mold is removed after the temperature difference between the surface temperature of the concrete and the internal temperature becomes 20 ° C. or less and the temperature difference between the surface temperature of the concrete and the outside air temperature becomes 20 ° C. or less. If the temperature difference between the surface temperature and the internal temperature of the concrete is higher than 20 ° C, the ultra-high-strength concrete with a large amount of powder is likely to crack due to internal stress, and the outside air temperature at the time of demolding If the temperature difference between the concrete surface temperatures is higher than 20 ° C, heat cracks may occur, which is not preferable.
本発明の製造方法では、上記温度履歴の蒸気養生によって、コンクリートの表面温度と外気温との温度差が２０℃以下になる時間が短く、脱型時間を短縮することができる。 In the production method of the present invention, the time for the temperature difference between the surface temperature of concrete and the outside air temperature to be 20 ° C. or less is short and the demolding time can be shortened by the steam curing of the above temperature history.
〔実施例１〕
表１に示す材料を用い、表２に示す配合条件に従ってコンクリートを調製した。このコンクリートを練り混ぜて、寸法が９００×９００×２０００ｍｍの鋼製型枠に打設した後に、直ちに断熱シートで覆い、蒸気を吹き込んで蒸気養生を行い、養生後、脱型して状態を調べた。また、材齢7日、２８日、５６日、９１日でコンクリートの中央部と端部からコア試験体を採取し、圧縮強度を調べた。養生条件および養生効果を表３に示した。コンクリート表面の状態および圧縮強度を調べた。この結果を表４に示した。表３、表４に示すように、本発明の試料No.１〜４は何れも亀裂の無い良好なコンクリートが得られる。一方、前養生温度が３０℃より低く２０℃と常温である試料No.５は、凝結始発時間の到達に１５時間を要し、打設時間から型枠脱型時間までに５４時間を要した。
前養生温度が５０℃より高く６０℃である試料No.６は、打設時間から型枠脱型時間までに５９.４時間を要した。さらに、コンクリート表面に巣のような欠陥部が発生し、強度発現性が劣る。また、コンクリートの表面温度と内部温度の差が２８℃の試料No.７、および、外気温とコンクリートの表面温度との差が２９℃の試料No.８は何れもコンクリート表面にひび割れや亀裂が発生した。
[Example 1]
Using the materials shown in Table 1, concrete was prepared according to the compounding conditions shown in Table 2. After kneading this concrete and placing it in a steel formwork with dimensions of 900 x 900 x 2000 mm, immediately cover it with a heat insulating sheet, blow steam to perform steam curing, and after curing, remove the mold and check the condition. It was. In addition, core test specimens were collected from the central and end parts of concrete at the ages of 7, 28, 56, and 91 days, and the compressive strength was examined. Table 3 shows the curing conditions and curing effects. The condition of the concrete surface and the compressive strength were examined. The results are shown in Table 4. As shown in Tables 3 and 4, good concrete without cracks can be obtained in each of Samples Nos. 1 to 4 of the present invention. On the other hand, Sample No. 5, which has a pre-curing temperature lower than 30 ° C. and a normal temperature of 20 ° C., required 15 hours to reach the settling start time and 54 hours from the casting time to the mold removal time. ..
Sample No. 6, which had a pre-curing temperature higher than 50 ° C. and 60 ° C., required 59.4 hours from the casting time to the mold removal time. Further, defects such as nests are generated on the concrete surface, and the strength development is inferior. In addition, sample No. 7 having a difference between the concrete surface temperature and the internal temperature of 28 ° C. and sample No. 8 having a difference between the outside air temperature and the concrete surface temperature of 29 ° C. have cracks and cracks on the concrete surface. Occurred.
Claims (2)
The high-strength precast concrete according to claim 1, wherein a concrete composition containing 1 to 6% by mass of an accelerated high-performance water reducing agent and 2 to 20 kg / m 3 of an expanding material in a unit amount is used. Production method.
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