JP2008223372A - Concrete curing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a concrete curing method for performing optimum curing management for concrete after form removal, depending on the age of each concrete section. <P>SOLUTION: According to the concrete curing method, a waterproof sheet 2 is stretched so as to cover a surface of the concrete 1 from which a concrete placing form is removed, in a manner spacing a necessary interval away from the concrete 1, and a spatial portion 3 is secured between the waterproof sheet 2 and the concrete 1. Then water which has its temperature adjusted to a value almost equal to a surface temperature of the concrete 1, changing with the lapse of time due to hydration, is sprayed to the spatial portion 3 in an almost hermetically sealed state, and filled in the spatial portion 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a concrete curing method, and more particularly, to a concrete curing method in which optimal curing management is performed for each age of the concrete after deframement.

Concrete, which is the main member of tunnel structures such as roads and railways, has been limited to construction work, such as early removal of the frame and limited construction period, as well as arch-like conditions after curing the concrete. However, due to the special features of the structure such as the concrete surface facing up, nothing was done.
In the case of a tunnel structure, it is usually unframed at the age of 1 day (15 to 20 hours after placing the concrete), the concrete surface is in an unprotected state, and the surface is dried by transpiration of moisture from the surface. Water for maintaining the hydration reaction necessary for the development of the hardening strength of concrete will be insufficient.
For this reason, there are concerns about surface defects (cracking, etc.) due to insufficient curing, and deterioration of long-term durability due to reduced strength, etc., and in extreme cases, serious problems that may lead to personal injury such as peeling or collapsing of concrete pieces occur. Or deterioration of public structure assets.

  However, among civil engineering structures in general, conventional curing methods (sprinkling, covering with a sheet, placing a formwork) such as the inside of a box culvert constructed outdoors, wall structures such as a bridge pier abutment, etc. It may be difficult to cure. If curing is insufficient due to the particularity and complexity of these shapes, problems similar to those described above may occur.

On the other hand, as a conventional curing technique for tunnel structures and civil engineering structures in general, there is a method of spreading a liquid curing agent that forms a thin film on the concrete surface.
This is a means to form a film to prevent moisture from transpiration from the surface of concrete and to cure it, but there is a problem in certainty such as workability and uniformity at the time of spray coating, and it is completely transpiration of moisture. It can not prevent.

Therefore, the present applicant has proposed a concrete curing method in Patent Document 1 below.
This concrete curing method consists of assembling a supporting member at a position 100 to 300 mm away from the concrete surface immediately after removing the concrete casting form for concrete to be constructed in a continuous form such as a tunnel or box culvert. Cover concrete with a sheet.
And watering equipment is installed in the supporting member, and concrete is cured by watering the concrete surface continuously for 24 hours to 72 hours.

By the way, the heat generation temperature of the concrete during curing changes with time due to the hydration reaction. However, in the above conventional concrete curing method, the water is sprayed at a constant temperature by the sprinkler. It is difficult to carry out optimal curing management for each age.
JP 2004-285803 A

  In view of the problems of the conventional concrete curing method described above, an object of the present invention is to provide a concrete curing method in which optimum curing management is performed for each age of the concrete after deframement. .

  In order to achieve the above object, the concrete curing method of the present invention includes a waterproof sheet stretched over the concrete from which the casting form has been removed so as to cover the surface of the concrete with a required interval. A space is formed between the sheet and the concrete, and the water whose temperature is changed to the same temperature as the surface temperature is sprayed and filled in the concrete whose temperature changes over time due to a hydration reaction. And

  In this case, the average particle diameter of the sprayed water can be a fine mist of 10 to 100 μm.

  Moreover, the temperature change by the hydration reaction of concrete can be detected with a temperature sensor, and the temperature of the sprayed water can be adjusted based on the detected temperature.

  Moreover, the temperature change by the hydration reaction of concrete can be calculated | required beforehand as a theoretical value, and the temperature of the sprayed water can be adjusted based on the temperature of this theoretical value.

  In addition, the curing section can be divided into a plurality of spans, the space portion can be divided for each span, and the temperature of water sprayed for each span can be adjusted.

According to the concrete curing method of the present invention, a waterproof sheet is stretched so as to cover the surface of the concrete with a required interval on the concrete from which the casting form has been removed, and between the waterproof sheet and the concrete. In addition to forming a space in the concrete, the temperature of the concrete that changes with time due to the hydration reaction is sprayed and filled with water adjusted to approximately the same temperature as the surface temperature. Based on the theoretical value of temperature change during detection and curing, the surface can be moistened at the optimum temperature for curing the concrete by age, which makes it possible to optimize the concrete for each age of the unframed concrete. Can be managed.
In addition, by filling the space formed on the concrete surface with fog, a curing space in a uniform humidity state can be formed, thereby maintaining the hydration reaction necessary to develop the hardening strength of the concrete. By eliminating the transpiration of water and actively supplying fine particulate water, it is possible to contribute to the densification of the concrete surface and the enhancement of strength, and to reduce the occurrence of defects on the concrete surface.

  In this case, by making the average particle size of the sprayed water a fine mist of 10 to 100 μm, the curing of the complicated shape, ceiling surface, and vertical surface easily fills the mist, and the concrete surface due to the collision of water drops etc. It is possible to prevent roughening and traces of water dripping on the streaks, and furthermore, the amount of water necessary for the generation of mist is very small, and it is possible to prevent the road surface from becoming muddy.

  In addition, the temperature change due to the hydration reaction of concrete is detected by a temperature sensor, and the temperature of water sprayed is adjusted based on the detected temperature, so that the actual heat generation temperature of the concrete is detected and sprayed in real time. The water temperature can be controlled.

  In addition, the temperature change due to the hydration reaction of concrete is obtained as a theoretical value in advance, and the temperature of the sprayed water is adjusted based on the temperature of the theoretical value, thereby eliminating the trouble of arranging the temperature sensor. The temperature management of the sprayed water can be performed based on the theoretical value according to the placing conditions.

  In addition, the curing section is divided into a plurality of spans, the space is divided into spans, and the temperature of water sprayed for each span is adjusted, so that the concrete after deframed is categorized by age. More optimal curing management can be performed.

  Embodiments of the concrete curing method of the present invention will be described below with reference to the drawings.

1 to 6 show an embodiment of the concrete curing method of the present invention.
In this concrete curing method, a waterproof sheet 2 is stretched so as to cover the surface of the concrete 1 at a predetermined interval with respect to the concrete 1 from which the casting form has been removed. A substantially sealed space 3 is formed between them.
Then, the concrete 1 whose temperature changes with time due to the hydration reaction is sprayed and filled in the substantially sealed space portion 3 with water adjusted to substantially the same temperature as the surface temperature.
It should be noted that the spraying of the water into the space 3 is performed for 7 days continuously, for example, continuously at a humidity of 100%, immediately after the placement form is removed from the concrete 1.

In the case of a tunnel, the curing device 4 that forms the substantially sealed space 3 is provided, for example, as shown in FIG.
An arch frame 5 having a cross-sectional shape slightly smaller than the tunnel is framed with H steel or the like so as to be several tens of centimeters away from the concrete surface inside the tunnel, and the waterproof sheet 2 is covered so as to cover the arch frame 5.
At both ends of the arch frame 5, an air bulk 6 is provided as a partition wall that closes the gap with the concrete surface, thereby securing a substantially sealed space 3 that blocks the concrete surface and external air. This space portion is kept airtight, and heat retention and moisture retention are ensured.
A wheel 7 is provided at the lower part of the arch frame 5, and the wheel 7 can move on a rail 8 laid in the length direction on both sides of the lower part of the tunnel. The curing device 4 can move in the length direction inside the tunnel via the wheel 7.

The waterproof sheet has a thickness of 0.8 to 1.2 mm and is made of a plastic-based ethylene vinyl acetate copolymer (EVA), polyvinyl chloride (PVC), ethylene copolymer bitumen (ECB), or polypropylene copolymer ( PPC) may be used.
The installation position of the waterproof sheet covers the concrete surface so that air does not escape through a gap of 10 cm to 1 m from the concrete surface.
The reason for selecting this gap is that if it is less than 10 cm, the spray nozzle or the like is likely to come into contact with the concrete surface and be damaged. This is because when the distance is 1 m or more, the gap with the concrete surface widens, the volume amount for adjusting the temperature increases, or the heating unit for adjusting the temperature becomes large.

A large number of spray nozzles 9 are arranged in the arch frame 5 at essential points. For example, fine mist water having an average particle diameter of 10 to 100 μm, more preferably 45 to 60 μm, is provided in the substantially sealed space 3. By completely spraying and filling, a curing space in a uniform humidity state is formed.
In this way, by maintaining a uniform humidity state, there is no transpiration of water for maintaining the hydration reaction necessary for the development of the hardening strength of the concrete 1, and on the contrary, the particulate water is actively supplied. This contributes to densification of the surface and enhancement of strength, and reduces the occurrence of defects on the surface of the concrete 1.

The spray nozzle 9 is generally classified into a super fine mist of 10 μm or less, a fine mist of 10 to 100 μm, a fine mist of 100 to 300 μm, a medium mist of 0.3 to 1.0 mm, and a coarse mist of 1.0 mm or more depending on the diameter of the spraying portion.
Furthermore, it is important to select the spray nozzle 9 according to the area, volume and direction of spraying. That is, when spraying directly on concrete, it is uneconomical that the cement adheres to the surface of the concrete after the hydration reaction, causing a problem with aesthetics, and spraying more than necessary for the hydration reaction.
In the case of super fine mist, a large number of spray nozzles 9 are required in consideration of volume and area. As a result of comprehensively examining and experimenting with this, it was found that the fine fog range of 10 to 100 μm, more preferably 45 to 60 μm was most suitable.
The spray angle of the spray nozzle 9 is desirably 80 degrees as a result of considering the distance to the concrete surface, the area, the volume, and the number of spray nozzles 9. Further, the pitch of the spray nozzles 9 is optimally set at a 3 m interval when fine mist and an angle of 80 degrees are used.

Moreover, as shown in FIG. 4, the temperature of the sprayed water can be adjusted by appropriately heating the water supplied to the spray nozzle 9 by the heating unit.
In this case, as shown in FIG. 6, the surface temperature of the concrete 1 is detected and fed back, or based on the theoretical value of the temperature change during curing of the concrete 1, it is the same as the surface temperature of the concrete 1 that changes over time. The water adjusted to the temperature is sprayed and filled in the substantially sealed space 3.
The temperature of the sprayed mist drops slightly before reaching the spray nozzle, so the supplied water is heated slightly higher, but it is more preferably ± 3 ° C of the concrete surface temperature at the spraying temperature. May be within a range of ± 2 ° C., more preferably ± 1 ° C.
In addition, the temperature change due to the hydration reaction of concrete is obtained in advance as a theoretical value, and the temperature of the sprayed water is adjusted based on the temperature of the theoretical value from this experiment etc. Omitted, temperature control of the sprayed water can be performed based on the theoretical value according to the concrete placing conditions.
In addition, although FIG. 6 shows the control temperature of the sprayed water, the surface temperature of the concrete after a formwork deframement also shows the same curve. The surface temperature of the concrete also varies depending on the casting thickness, but in this example, the temperature rises from about 23 ° C. to about 35 ° C. and falls to about 20 ° C. in the two days after the frame is removed. For about 5 days, it keeps about 20 ℃.

The temperature sensor 12 that measures the surface temperature of the concrete is suitable if it has a measurement range of minus 20 ° C. to 100 ° C. Considering the spraying situation, a thermocouple type φ6.4 mm and a length of 20 cm are desirable.
As shown in FIG. 4, the heating unit includes a temperature controller 13, a water tank 14, a water temperature sensor (not shown), a heater 15, and a pump 16.
The temperature controller 13 receives the value of the temperature sensor 12, compares this value with the water temperature sensor, and heats the water supplied to the heater 15 to be supplied to this temperature.

On the other hand, the concrete in the tunnel is constructed with, for example, a length of about 10 m as one span S. In this embodiment, the curing device 4 has a plurality of span lengths such as three spans. Thus, a plurality of spans S can be cured at the same time while the curing device 4 is advanced every time the span S is unframed.
In this case, the curing device 4 is divided into the spans S, the substantially sealed space 3 is divided into the spans S, and the curing device 4 is advanced by one span for each frame removal, whereby the concrete 1 after the frame removal is performed. Each span unit can be cured in sequence at the optimum temperature and humidity for the material age.

For example, the first span S1 is a curing span immediately after the lining formwork, and is the first span that should be controlled and managed with the highest curing temperature immediately after the frame removal.
The second span S2 is an intermediate curing span, and the concrete temperature exceeds the peak temperature and shows a descending pattern. Therefore, the water temperature from the pipe at the end of the first span S1 may be available. In other cases, the heating unit is arranged in the same manner as the first span S1, but the heater does not need the heating capability as much as the first span S1.
The third span is the final span, and the concrete surface temperature is close to the tunnel tunnel temperature, but sudden changes in temperature and humidity have a detrimental effect. Continue to spray.

On the other hand, as shown in FIGS. 5 (b) to 5 (c), in the concrete structure such as the wall structure such as the bridge pier abut 10 and the concrete structure such as the culvert 11, the concrete 1 from which the casting form is removed, A waterproof sheet 2 is stretched so as to cover the surface of the concrete 1 with a required interval, and a substantially sealed space 3 is formed between the waterproof sheet 2 and the concrete 1.
The space 3 is filled with water adjusted to a temperature substantially the same as the surface temperature of the concrete 1 that changes with time.
The space 3 can be formed by stretching a waterproof sheet 2 supported by a frame along the surface of the concrete 1 to be cured.
In this case, a large number of spray nozzles 9 are arranged at important points in the frame, and fine water is sprayed evenly into the substantially sealed space 3 to form a curing space in a uniform humidity state.

For cracks caused by cement hydration, the volume change based on the temperature distribution calculated by the temperature analysis and the volume change due to self-shrinkage are obtained, and the stress analysis is performed using these changes.
At this time, if the temperature history of the surface of the concrete is obtained, and temperature management and curing are performed so that there is no difference from this temperature, no temperature difference occurs on the concrete surface, and cracking due to temperature can be prevented.
On the other hand, cracks in concrete do not occur if the tensile strength (due to temperature, drying shrinkage, etc.) is generated on the concrete surface and the concrete itself has a large tensile strength relative to the tensile strength.
Therefore, it is necessary to aim for a concrete whose cracking resistance increases as the strength of the concrete increases quickly and as the long-term strength increases.

By the way, it is generally said that crack resistance increases when the strength of concrete increases. Therefore, three types of blast furnace cement type B, ordinary Portland cement, and early strength Portland cement, water cement ratio 55%, material age 3, 7, 28, the method of spray curing and air curing without spraying A comparative experiment was carried out by the method.
As a result, the spray curing increased the compression / tensile strength by about 1.5 to 1.8 times compared to the air curing.
As a result of investigating cracks obtained by a method based on temperature analysis, it was found that such spray curing is extremely effective in preventing cracks.
Furthermore, it was found that by performing such spray curing, the initial strength and long-term strength of the blast furnace cement B type increased from 1.3 to 1.7 times that of the early strong Portland cement.
If this spray curing is carried out, the blast furnace cement type B has higher cracking resistance than the early strong Portland cement. This also shows that underwater curing and 90 to 100% humidity curing are effective for fully exhibiting the cement hydration reaction.

On the other hand, in order to confirm the curing effect of the concrete curing method of the present example for controlling the temperature of sprayed water, a full-scale test was performed.
As shown in FIGS. 3 to 4, a normal two-lane tunnel has a length of 10.5 m, a height of 7 m, and an upper cross-sectional radius of 5 m. The inside of this tunnel is covered with a waterproof sheet 2 over a 6 m length section to provide a substantially sealed space 3, and an arch frame 5 in which spray nozzles 9 are provided at eight locations in the circumferential direction in the arch frame 5. Are arranged in two rows in the length direction, and a total of 16 spray nozzles 9 are provided (partially omitted in the figure).
Further, temperature sensors 12 for measuring the surface temperature of the concrete were installed on the arch frame 5 at three locations in the circumferential direction. The thickness of the concrete 1 was 30 cm, and blast furnace cement type B was used. Under such conditions, spray curing was carried out for 7 days, and then the cover of the waterproof sheet 2 was removed.
As a result, cracks did not occur in the concrete covered with the waterproof sheet 2 and subjected to the curing method of this example.

On the other hand, cracks having a substantially linear width of 0.5 to 3.5 mm in the tunnel length direction occurred in the concrete in the 4.5 m section where curing was not performed. This crack is the same as the crack shape generated in the tunnel lining concrete currently being constructed.
As for the strength of the concrete, the compressive / tensile strength was obtained by collecting three concrete cores each of 28 days old, φ10 cm and 30 cm long from the cured concrete and the uncured concrete.
This sample was tested by the test method of compression test JISA1108 and tensile strength test JISA1113. As a result, the cured concrete core was about 1.5 times both in compressive and tensile strength compared to the uncured concrete core.
That is, in the concrete curing method of the present embodiment that controls the temperature of the sprayed water, the effect was confirmed against cracking prevention and strength increase, but this is to prevent dry shrinkage cracking to prevent cracking. This is because heat retention and wet curing were possible, and temperature stress cracking due to the heat of hydration of cement could be prevented by temperature control.

Thus, according to the concrete curing method of the present embodiment, the waterproof sheet 2 is stretched so as to cover the surface of the concrete 1 at a necessary interval with respect to the concrete 1 from which the casting mold is removed. A substantially sealed space 3 is formed between the waterproof sheet 2 and the concrete 1, and water that has been adjusted to a temperature substantially the same as its surface temperature is applied to the concrete 1 whose temperature changes over time due to a hydration reaction. 3 is sprayed and filled, based on the detection of the surface temperature of the concrete 1 and the theoretical value of the temperature change during curing, the surface can be moistened at the optimum temperature for curing the concrete 1 by age, Thereby, the optimal curing management for every age can be performed with respect to the concrete 1 after a frame removal.
Further, by filling the substantially sealed space portion 3 formed on the concrete surface with fog, a curing space in a uniform humidity state can be formed, and thereby the hydration necessary for developing the hardening strength of the concrete 1. Contribute to the densification of concrete surface and the enhancement of strength by reducing the transpiration of water to sustain the reaction and actively supplying fine particulate water, reducing the occurrence of defects on the concrete surface Can do.

  In this case, the average particle size of the sprayed water is 10 to 100 μm, more preferably 45 to 60 μm, so that the complex shape, the ceiling surface, and the curing of the vertical surface can easily fill the mist, It can prevent the surface of concrete 1 from being rough due to the impact of water droplets and the like, and the traces of water dripping on the streaks. Furthermore, the amount of water required for the generation of mist is very small. Mudification can be prevented.

  Moreover, while detecting the temperature change due to the hydration reaction of the concrete 1 with the temperature sensor 12 and adjusting the temperature of the sprayed water based on the detected temperature, It is possible to control the temperature of water sprayed in real time.

  Further, the temperature change due to the hydration reaction of the concrete 1 is obtained in advance as a theoretical value, and by adjusting the temperature of the sprayed water based on the temperature of the theoretical value, the trouble of arranging the temperature sensor 12 is omitted, The temperature management of the sprayed water can be performed based on the theoretical value according to the placing conditions of the concrete 1.

  Further, the curing section is divided into a plurality of spans S, the space portion 3 is divided into the spans S, and the temperature of the water sprayed for each span S is adjusted, so that the concrete 1 after deframed Therefore, more optimal curing management can be performed for each age.

  As mentioned above, although the concrete curing method of the present invention has been described based on the examples thereof, the present invention is not limited to the configurations described in the above examples, and the configurations are appropriately set within the scope not departing from the gist thereof. Can be changed.

  Since the concrete curing method of the present invention can perform optimum curing management for each age of the concrete after deframement, for example, tunnels, box culverts, piers, bridges, retaining walls, waterways, architectural columns, It can be suitably used for curing concrete of many structures such as walls and beams.

An example of the concrete curing method of the present invention is shown, (a) is a cross-sectional view of a tunnel to be constructed, (b) is a left half cross-sectional view of (a) B arrow, and the right half is (A) A. It is arrow sectional drawing. The curing device used in the embodiment is shown, in which (a) is a cross-sectional view of the vicinity of the ceiling, (b) is a two-side view of wheels and rails, and (c) is a three-side view of rails. It is a perspective view which shows the experimental example of the curing method of the concrete. It is a schematic diagram which shows a heating unit. The concrete curing method of the present invention is shown, (a) is a perspective view showing construction on a tunnel, (b) is a perspective view showing construction on a bridge pier, and (c) is a perspective view showing construction on a culvert. It is. It is a graph which shows the temperature of the water sprayed from a spray nozzle corresponding to the temperature of the concrete surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Concrete 2 Tarpaulin 3 Space part 4 Curing apparatus 5 Arch frame 6 Air bulk 7 Wheel 8 Rail 9 Spray nozzle 10 Bridge pier abut 11 Calvert 12 Temperature sensor 13 Temperature controller 14 Water tank 15 Heater 16 Pump

Claims (5)

  A waterproof sheet is stretched over the concrete from which the casting form has been removed so as to cover the surface of the concrete at a required interval, and a space is formed between the waterproof sheet and the concrete, and the hydration reaction A concrete curing method characterized by spraying and filling the space with water adjusted to approximately the same temperature as the surface temperature of the concrete whose temperature changes with time.   The concrete curing method according to claim 1, wherein the sprayed water has an average particle diameter of 10 to 100 μm.   The concrete curing method according to claim 1 or 2, wherein a temperature change due to a hydration reaction of the concrete is detected by a temperature sensor, and the temperature of the sprayed water is adjusted based on the detected temperature.   The concrete curing method according to claim 1 or 2, wherein a temperature change due to a hydration reaction of the concrete is obtained in advance as a theoretical value, and a temperature of water to be sprayed is adjusted based on the temperature of the theoretical value.   The concrete according to claim 1, 2, 3, or 4, wherein the curing section is divided into a plurality of spans, the space is divided into spans, and the temperature of water sprayed is adjusted for each span. Curing method.

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