Floor structure and construction method of floor structure

Abstract

This will suppress cracking and reduce costs. [Solution] A floor structure having a lower floor slab and an upper floor slab provided on the lower floor slab, wherein the lower floor slab is made of unreinforced concrete or reinforced concrete using first concrete, and the upper floor slab is made of reinforced concrete using second concrete, and the shrinkage strain of the second concrete is smaller than the shrinkage strain of the first concrete.

Description

Technical Field

[0001] The present invention relates to a floor structure and a method for constructing the floor structure.

Background Art

[0002] In a floor slab (floor structure) such as a reinforced concrete floor slab, cracks may occur due to the drying shrinkage of concrete. (For example, see Patent Document 1). As one measure against such cracks, for example, using low-shrinkage concrete can be mentioned.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, since low-shrinkage concrete is more costly than ordinary concrete, it is expensive to apply it to the entire floor slab. In particular, the greater the cross-sectional thickness of the floor slab, the higher the cost.

[0005] The present invention has been made in view of the above problems, and its object is to suppress cracks and reduce costs.

Means for Solving the Problems

[0006] The main invention for achieving the above object is a floor structure having a lower floor slab and an upper floor slab provided on the lower floor slab, wherein the lower floor slab is a plain concrete or reinforced concrete using a first concrete, the upper floor slab is a reinforced concrete using a second concrete, and the shrinkage strain of the second concrete is smaller than the shrinkage strain of the first concrete.

[0007] Other features of the present invention will be revealed in the specification and drawings described below. [Effects of the Invention]

[0008] According to the present invention, cracking can be suppressed and costs can be reduced. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic perspective view of the floor structure 10 of this embodiment. [Figure 2] This is a schematic cross-sectional view of the floor structure 10 of this embodiment. [Figure 3] This figure shows the relationship between the depth from the slab surface and the moisture content. [Figure 4] This is a flowchart showing an example of a construction method for the floor structure 10 of this embodiment. [Figure 5] This is a schematic diagram showing the level of the simulated member test specimen in the example. [Figure 6] This diagram shows the details of the materials used. [Figure 7] This diagram shows the mix design conditions for various types of concrete. [Figure 8] Figures 8A to 8C show the results of strain measurement tests. [Modes for carrying out the invention]

[0010] The following information will become clear from the description in the specification and drawings described later.

[0011] (Aspect 1) A floor structure comprising a lower floor slab and an upper floor slab provided on the lower floor slab, wherein the lower floor slab is made of unreinforced concrete or reinforced concrete using a first concrete, and the upper floor slab is made of reinforced concrete using a second concrete, characterized in that the shrinkage strain of the second concrete is smaller than the shrinkage strain of the first concrete.

[0012] According to the floor structure of Aspect 1, cracking can be suppressed and costs can be reduced.

[0013] (Aspect 2) The floor structure according to Aspect 1, wherein the first concrete is preferably ordinary concrete.

[0014] According to the floor structure of Aspect 2, the cost can be reduced by using ordinary concrete for the first concrete. Also, since the first concrete is placed below the upper floor slab (a part away from the surface layer), it is less affected by drying (less likely to crack).

[0015] (Aspect 3) The floor structure according to Aspect 1, wherein the first concrete may be concrete having coarse aggregate of limestone.

[0016] According to the floor structure of Aspect 3, even when concrete having coarse aggregate of limestone is used for the first concrete, cracking can be suppressed and costs can be reduced.

[0017] (Aspect 4) The floor structure according to any one of Aspects 1 to 3, wherein the second concrete preferably contains limestone as coarse aggregate.

[0018] According to the floor structure of Aspect 4, the shrinkage strain of the second concrete can be reduced and cracking can be suppressed.

[0019] (Aspect 5) The floor structure according to any one of Aspects 1 to 4, wherein the second concrete preferably contains an expansion agent.

[0020] According to the floor structure of Aspect 5, the shrinkage strain of the second concrete can be reduced and cracking can be suppressed.

[0021] (Aspect 6) A floor structure according to any of embodiments 1 to 5 is provided, wherein the second concrete preferably contains a shrinkage reducing agent.

[0022] According to the floor structure of embodiment 6, the shrinkage strain of the second concrete can be reduced, and cracking can be suppressed.

[0023] (Aspect 7) A floor structure according to any of embodiments 1 to 6, wherein the second concrete preferably contains moderate-heat Portland cement or low-heat Portland cement.

[0024] According to the floor structure of embodiment 7, the shrinkage strain of the second concrete can be reduced, and cracking can be suppressed.

[0025] (Pattern 8) The floor structure according to any of embodiments 1 to 7 is preferably wherein the second concrete contains, for example, a shrinkage-reducing water-reducing agent, a shrinkage-reducing high-performance water-reducing agent, a shrinkage-reducing AE water-reducing agent, or a shrinkage-reducing high-performance AE water-reducing agent as a chemical admixture that provides shrinkage reduction.

[0026] According to the floor structure of embodiment 8, the shrinkage strain of the second concrete can be reduced, and cracking can be suppressed.

[0027] (Aspect 9) In the floor structure described in any of embodiments 1 to 8, it is desirable that the sum of the thickness of the lower floor slab and the thickness of the upper floor slab be 30 cm or more.

[0028] According to the floor structure of embodiment 9, the cost reduction effect is greater.

[0029] (Aspect 10) In any of the floor structures described in Embodiments 1 to 9, it is desirable that the thickness of the upper floor slab be 10 cm or more.

[0030] According to the floor structure of embodiment 10, the area affected by drying is approximately 10 cm from the surface, so cracking can be effectively suppressed by using the second concrete in this area.

[0031] (Aspect 11) A method for constructing a floor structure according to any of embodiments 1 to 10, characterized in that the pouring of the first concrete for the lower floor slab and the pouring of the second concrete for the upper floor slab are performed on the same day.

[0032] According to the floor structure of embodiment 11, the second concrete can be prevented from being restrained by the first concrete (hardened concrete), and cracking can be suppressed.

[0033] ===Implementation Method=== <Regarding floor structure> Figure 1 is a schematic perspective view of the floor structure 10 of this embodiment, and Figure 2 is a schematic cross-sectional view of the floor structure 10. The vertical direction shown in the figures is the direction along the vertical direction, with the upper side in the vertical direction being referred to as "up" and the lower side as "down".

[0034] As shown in Figures 1 and 2, the floor structure 10 of this embodiment has a lower section 12 (corresponding to a lower floor slab) and an upper section 14 (corresponding to an upper floor slab) provided on top of the lower section 12. The lower section 12 and the upper section 14 are each made of reinforced concrete floor slabs, as will be described later. The cross-sectional thickness (length in the vertical direction) of the floor structure 10 of this embodiment is 1 m.

[0035] Incidentally, cracks can occur in reinforced concrete floor slabs due to drying shrinkage of the concrete. One measure to prevent concrete cracking is to use low-shrinkage concrete, which has a small shrinkage strain. However, low-shrinkage concrete is generally more expensive than ordinary concrete, so applying it to the entire structure becomes costly. In particular, the greater the cross-sectional thickness of the floor slab, the higher the cost.

[0036] Therefore, in the floor structure 10 of this embodiment, concrete with low shrinkage strain (details will be described later) is used in the upper layer 14, which is prone to cracking due to drying. This suppresses cracking and reduces costs.

[0037] The lower layer 12 is a reinforced concrete slab and is equipped with concrete C1 (corresponding to the first concrete) and reinforcing bars 22. In this embodiment, concrete C1 is ordinary concrete. The reinforcing bars 22 are arranged in a grid pattern vertically and horizontally near the bottom end of the lower layer 12 (slightly above the bottom end).

[0038] The upper layer 14 is also a reinforced concrete slab, and is equipped with concrete C2 (corresponding to the second concrete) and reinforcing bars 24. Concrete C2 is concrete with smaller shrinkage strain than concrete C1. The reinforcing bars 24 are arranged in a grid pattern vertically and horizontally near the top of the upper layer 14 (slightly below the top). In addition, reinforcing bars not shown may be provided between the reinforcing bars 22 of the lower layer 12 and the reinforcing bars 24 of the upper layer 14 (for example, reinforcing bars may be provided at the center in the vertical direction).

[0039] As mentioned above, the shrinkage strain of concrete C2 in the upper layer 14 is smaller than the shrinkage strain of concrete C1 in the lower layer 12. Furthermore, low-shrinkage concrete is specified in the "Standard Specifications for Building Construction and Commentary JASS5 Reinforced Concrete Construction (hereinafter referred to as JASS5)" as concrete with low shrinkage strain. For details, low-shrinkage concrete is defined as concrete whose shrinkage strain is reduced to 650 × 10 by the use of admixtures and the selection of aggregates. -6 The concrete is as follows. However, the concrete C2 in this embodiment is not limited to such low-shrinkage concrete, but is acceptable as long as its shrinkage strain is smaller than that of the concrete C1 (in this case, ordinary concrete) of the lower layer 12. For example, if the shrinkage strain of concrete C1 is 800 × 10 -6 In this case, the shrinkage strain is 750 × 10 -6 It may also be something else.

[0040] (Method for measuring shrinkage strain) The shrinkage strain shall be a value that takes into account the drying shrinkage rate and the expected reduction in shrinkage when using an expanding material.

[0041] The drying shrinkage rate is the rate of change in length of a 10 × 10 × 40 cm concrete specimen that has been cured to standard age 7 days, as specified in JASS5, when dried for 6 months (26 weeks) under conditions of a temperature of 20 ± 2°C and a relative humidity of 60 ± 5%. The rate of change in length can be determined according to JIS A 1129. There are three methods for measuring the change in length: the comparator method (JIS A 1129-1), the contact gauge method (JIS A 1129-2), and the dial gauge method (JIS A 1129-3). Measurement can be performed using any of these three methods.

[0042] The expected reduction in shrinkage when using an expansive material is 150 × 10 -6 If this is taken into account, the constrained expansion rate is 150 × 10 -6 The above is the end of the procedure. The confined expansion rate shall be measured according to JIS A 6202 Annex B (Reference) (Test method for confined expansion and shrinkage of expansive concrete), and shall be the confined expansion rate at 7 days of age. However, since the confined expansion rate is affected by the amount of expansive agent used, depending on the amount of expansive agent used, the shrinkage reduction amount may be 150 × 10 -6 It is not limited to that.

[0043] (Regarding common conditions for concrete) For both the lower layer 12 and the upper layer 14, concrete conforming to JIS A 5308 or concrete certified by the Minister of Land, Infrastructure, Transport and Tourism may be used.

[0044] (Regarding concrete C2 in the upper layer 14) In the upper layer 14, concrete (concrete C2) that has been treated to reduce drying shrinkage in terms of material properties will be applied. The material treatment will be one of the following (1) to (5), or a combination of several of the following (1) to (5).

[0045] (1) Use an expanding agent (compliant with JIS A 6202 or JASS 5M-403). (2) Limestone aggregate (crushed stone) is used as coarse aggregate. (3) Use a shrinkage reducing agent (compliant with JIS A 6211). (4) Use moderate-heat Portland cement or low-heat Portland cement (conforming to JIS R 5210). (5) Chemical admixtures (conforming to JIS A 6204) that provide shrinkage reduction. For example, shrinkage-reducing water-reducing agents, shrinkage-reducing high-performance water-reducing agents, shrinkage-reducing AE water-reducing agents, shrinkage-reducing high-performance AE water-reducing agents, etc. may be used.

[0046] In the examples described later, (1) and (2) above are applied, but the method is not limited to these; (3) to (5) may also be applied, or a combination of these may be used. In these cases as well, shrinkage strain can be reduced.

[0047] <Relationship between depth from the surface and moisture content> Figure 3 shows the relationship between depth from the slab surface and moisture content. The horizontal axis of Figure 3 represents the volumetric moisture content (%), and the vertical axis represents the depth from the surface (mm). Note that 0 (zero) on the vertical axis represents the slab surface (surface layer), and as the value increases, the distance from the surface (depth) increases.

[0048] This evaluation was performed using a method (hereinafter referred to as cured PS7D) in which test specimens were prepared using ordinary concrete, demolded after 7 days of age, and then sealed with aluminum tape on all sides except the cast surface, allowing one side to dry. The drying periods were evaluated at 7 days, 21 days, 49 days, 91 days, and 175 days.

[0049] The volumetric moisture content was determined for each depth from the surface by cutting the cured PS7D specimen into 20mm thick sections at each measurement point.

[0050] In Figure 3, there is a significant difference in moisture content up to about 70 mm from the surface, but no significant difference in moisture content is observed at deeper depths. From these results, it can be concluded that the effects of drying (where cracking is likely to occur) are concentrated in the area from the surface down to about 100 mm (10 cm).

[0051] Therefore, in the floor structure 10 of this embodiment, concrete C2 with low shrinkage strain is used for the upper layer 14 on the surface side. This makes it possible to reduce costs and suppress cracking compared to when the entire floor structure 10 is made of concrete C2.

[0052] <Construction method for floor structure 10> Figure 4 is a flowchart showing an example of a construction method for the floor structure 10 of this embodiment.

[0053] First, preparations are made, such as arranging the formwork (not shown) and placing the reinforcing bars (reinforcing bars 22 and 24) (S01).

[0054] Next, concrete C1 (in this case, ordinary concrete) is poured to form the lower layer 12 (S02). For example, in the case of a slab thickness of 1 m (= 100 cm) as in this embodiment, concrete C1 is poured into the first 50 cm thickness.

[0055] Next, on the same day that the concrete C1 for the lower layer 12 is poured, concrete C2 with low shrinkage strain is poured on top of the lower layer 12 to form the upper layer 14 (reinforced concrete slab). For example, if the slab thickness is 1 m (= 100 cm) as described above, and concrete C1 is poured to the first 50 cm thickness, then concrete C2 is poured to the 50 cm above it.

[0056] The reason for pouring the concrete C1 of the lower layer 12 and the concrete C2 of the upper layer 14 on the same day is that if concrete C2 were poured after concrete C1 had hardened, concrete C2 would be constrained by the hardened concrete C1, potentially causing cracks to occur at the interface. Pouring them on the same day prevents concrete C2 from being constrained by concrete C1.

[0057] However, the above is not an exhaustive list, and the composition may be modified as appropriate. For example, the first 70 cm thickness may be filled with regular concrete C1, and the next 30 cm with concrete C2, which has low shrinkage strain. However, since the upper layer 14 is a reinforced concrete slab, the concrete C2 should be in contact with the upper reinforcement bars (reinforcement bars 24 in this case) of the slab reinforcement. For this reason, it is desirable that the area occupied by concrete C2 be at least 15 cm thick from the surface.

[0058] Since concrete members begin to dry from the parts exposed to the outside air, cracking of the floor slab can be effectively suppressed by placing concrete C2, which has low shrinkage strain, on the surface side (a range of 10 cm or more from the surface, preferably 15 cm or more). Furthermore, the floor structure 10 of this embodiment can reduce costs compared to using concrete C2 with low shrinkage strain throughout. Thus, it is possible to suppress cracking and reduce costs. In particular, this embodiment is more effective when the thickness of the floor structure 10 is large (30 cm or more), as the cost reduction effect becomes greater.

[0059] <<Examples>> A simulated member test specimen of floor structure 10 was prepared, and the strain and other properties were evaluated when different types of concrete were used for the upper and lower sections. The thickness of the test specimen was 1 m (50 cm for the upper section and 50 cm for the lower section).

[0060] (Level, composition, etc.) Figure 5 is a schematic diagram showing the level of the simulated member test specimen in the embodiment. The notation in Figure 5 is as follows:

[0061] Ordinary concrete: Ordinary concrete Limestone: Concrete using limestone aggregate (crushed stone) as coarse aggregate. Expansion concrete: Concrete using an expansion agent.

[0062] For example, in Example 1, ordinary concrete is used as the concrete C1 of the lower layer 12, and expansive concrete is used as the concrete C2 of the upper layer 14. In Example 3, a combination of limestone and an expansive agent is used as the concrete C2 of the upper layer 14.

[0063] Furthermore, as a reference example, a model in which the entire structure (lower layer 12 and upper layer 14) was formed from expanded concrete was fabricated and evaluated.

[0064] Figure 6 shows details of the materials used, and Figure 7 shows the mix design conditions for each concrete.

[0065] In Figure 6, W represents water, C represents cement, EX represents expansive agent, S1 and S2 represent fine aggregate, G1 to G3 represent coarse aggregate (G3 is crushed limestone), and Ad represents chemical admixture.

[0066] (Strain measurement test method) Before concrete pouring, strain gauges (concrete strain gauges) were attached to the upper reinforcement bars (reinforcement bar 22 in Figure 1), the lower reinforcement bars (reinforcement bar 24 in Figure 1) at each level, and to the central reinforcement bar in the thickness direction (not shown in Figure 1). The strain gauges were installed near the center of the plane at each location, in both the vertical and horizontal directions along the orientation of the grid-like reinforcement bars.

[0067] Then, concrete was poured for the first layer (lower layer 12) and the second layer (upper layer 14) to create test specimens, and the amount of strain at each position was measured over time. The average value of the measurement results from the longitudinal and transverse strain measuring instruments was used as the amount of strain.

[0068] (Strain measurement test results) Figures 8A to 8C show the results of strain measurement tests. In each figure, the horizontal axis represents the number of days elapsed, and the vertical axis represents the amount of strain. Figure 8A shows the test results (average value) for the upper section (location of rebar 24), Figure 8B shows the test results (average value) for the central section, and Figure 8C shows the test results for the lower section (location of rebar 22).

[0069] As shown in Figure 8A, the amount of strain in the upper part (near reinforcing bar 24) was almost the same in Examples 1-3 and the reference example. Furthermore, although not shown here, no decrease in strength was observed in the concrete overlapping section (the boundary between the lower and upper layers).

[0070] These results confirm that even without using concrete with low shrinkage strain throughout the entire structure, using concrete with low shrinkage strain in the upper layer can effectively suppress cracking and reduce costs.

[0071] ===Other=== The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention can be modified and improved without departing from its spirit, and it goes without saying that the present invention includes equivalents thereof.

[0072] In the embodiment described above, both the lower layer 12 and the upper layer 14 are made of reinforced concrete slabs, but this is not the only option. For example, in the case of a concrete floor, the lower layer 12 may be an unreinforced concrete slab that does not use reinforcing bars.

[0073] In the above-described embodiment, ordinary concrete was used as the concrete C1 of the lower layer 12, but it is not limited to ordinary concrete. For example, concrete containing limestone coarse aggregate may be used as concrete C1. In that case, the concrete C2 of the upper layer 14 should be made of concrete with a smaller shrinkage strain than concrete C1 (concrete containing limestone coarse aggregate) by combining it with the drying shrinkage reduction measures described in (1) to (5) above. Alternatively, if concrete containing an expansive agent is used as concrete C1, the concrete C2 of the upper layer 14 should be made of concrete containing both an expansive agent and a shrinkage reducing agent that has a smaller shrinkage strain than concrete C1. [Explanation of Symbols]

[0074] 10 Floor structure 12 Lower part (lower floor slab) 14 Upper floor (upper floor slab) 22, 24 Reinforcement bars C1 Concrete (First Concrete) C2 Concrete (Second Concrete)

Claims

1. A floor structure comprising a lower floor slab and an upper floor slab provided on the lower floor slab, The aforementioned lower floor slab is made of unreinforced concrete or reinforced concrete using the first concrete, The aforementioned upper floor slab is reinforced concrete using the second concrete, The shrinkage strain of the second concrete is smaller than the shrinkage strain of the first concrete. A floor structure characterized by the following features.

2. The floor structure according to claim 1, The first concrete is ordinary concrete. A floor structure characterized by the following features.

3. The floor structure according to claim 1, The first concrete is concrete having limestone coarse aggregate. A floor structure characterized by the following features.

4. A floor structure according to any one of claims 1 to 3, The second concrete contains limestone as coarse aggregate. A floor structure characterized by the following features.

5. A floor structure according to any one of claims 1 to 3, The second concrete contains an expansive agent. A floor structure characterized by the following features.

6. A floor structure according to any one of claims 1 to 3, The second concrete contains a shrinkage reducing agent. A floor structure characterized by the following features.

7. A floor structure according to any one of claims 1 to 3, The second concrete contains moderate-heat Portland cement or low-heat Portland cement. A floor structure characterized by the following features.

8. A floor structure according to any one of claims 1 to 3, The second concrete contains, for example, a shrinkage-reducing water-reducing agent, a shrinkage-reducing high-performance water-reducing agent, a shrinkage-reducing AE water-reducing agent, or a shrinkage-reducing high-performance AE water-reducing agent, as a chemical admixture that provides shrinkage reduction. A floor structure characterized by the following features.

9. A floor structure according to any one of claims 1 to 3, The sum of the thickness of the lower floor slab and the thickness of the upper floor slab is 30 cm or more. A floor structure characterized by the following features.

10. A floor structure according to any one of claims 1 to 3, The thickness of the aforementioned upper floor slab is 10 cm or more. A floor structure characterized by the following features.

11. A method for constructing a floor structure according to any one of claims 1 to 3, The pouring of the first concrete for the lower floor slab and the pouring of the second concrete for the upper floor slab are performed on the same day. A construction method for a floor structure characterized by the following features.

Images