JP5652820B2 - Unreinforced concrete, crack control method, and construction method - Google Patents

Description

  The present invention relates to unreinforced concrete.

  Unreinforced concrete is generally used in a finishing sense. For example, it is placed as finishing / adjustment of the concrete cover thickness (thickness from the reinforcing bar surface to the concrete surface) or finishing / adjustment of the surface thickening. By the way, basically, unreinforced concrete is easily cracked. As a method for preventing this crack, use of non-shrink mortar (concrete), curing well, etc. have been proposed. That said, cracking in unreinforced concrete was very difficult. And when a crack arises in the mortar (concrete) of a cover thickness part, a water | moisture content will infiltrate from this crack location and a water | moisture content will adhere to the reinforcing bar surface. As a result, the reinforcing bars are rusted and the durability of the concrete is reduced.

  The methods for dealing with the above-described cracks are roughly classified into “a technique for preventing the occurrence of cracks” and “a technique for controlling (suppressing) the crack width”.

  The former “prevention of cracking” is appropriate measures, for example, when it is necessary to ensure watertightness and airtightness only with concrete, or when there is a risk of seriously damaging the aesthetics and value of concrete structures. Is required. This may be technically possible, for example by the use of low heat cement, expansion materials, shrinkage reducing agents and the like. However, it can be fully expected that the degree of freedom of the composition of the concrete composition is extremely small and that the cost will increase due to other reasons.

  The latter “control (inhibition) of crack width” can be said to be substantially free from the problem of strength reduction in concrete if the crack is small if the problem of landscape degradation is set aside. And unlike the former, since it does not eliminate a crack, it is very advantageous in terms of cost. In this technique, there are known a technique of applying cracking induction joints and concentrating the cracks at the joints, and a technique of dispersing cracks using a fiber reinforced sheet or the like (a method of controlling the crack width).

  By the way, the former method for concentrating cracks by applying induced joints has not yet reached the stage of practical use because the control technology using induced joints is not yet complete and the accumulation of technologies is small.

  On the other hand, “the latter method of controlling the crack width” allows the generation of cracks. However, with appropriate management, it is possible to specify the crack site and reduce the crack width. In other words, by setting the crack within an appropriate range, the cracked part can be easily identified, repaired easily, and a fatal crack in concrete (crack width requiring repair is 0.05 mm or more). Is suppressed. Therefore, it is very economical. And generally, installing a fiber reinforced sheet etc. is performed for the purpose of controlling the crack width.

  By the way, on the surface of the poured ready-mixed concrete for the purpose of slowing the evaporation rate of moisture contained in the ready-mixed concrete and reducing the evaporation amount, suppressing the shrinkage action of the ready-made concrete and preventing cracking of the concrete, A plurality of thin long bands and short bands made of synthetic resin, etc. are crossed perpendicularly and knitted into a rough mesh shape, and the predetermined contact surfaces of the intersecting long and short bands are fused and bonded together Cover the surface of the ready-mixed concrete on the surface of the ready-mixed concrete, and press it with a pressing machine from above, so that at least a slight sink from the surface of the ready-mixed concrete does not appear above the surface of the ready-mixed concrete A concrete cracking prevention method using a sheet that is laid in a state and solidifies the ready-mixed concrete under the state is proposed (Japanese Patent Laid-open No. Hei 8- 20927 JP) are.

JP-A-8-120927

  However, in the technique of Patent Document 1, a sense of unity with concrete is poor. For example, when the sheet is submerged and the length (embedding depth) is shallow, the integrity of the concrete is greatly impaired. For example, it can be easily understood that the upper layer (surface layer) concrete on the upper side of the sheet is easily peeled off. In particular, the sheet in Patent Document 1 is for slowing the evaporation of moisture in fresh concrete. Therefore, even if the sheet is formed by crossing the long band and the short band, as can be seen from FIG. 2 of Patent Document 1, the area of the opening surrounded by the long band and the short band is small. . This is because if the area of the opening is large, the evaporation of moisture in the ready-mixed concrete cannot be slowed down, and the effect intended by Patent Document 1 cannot be achieved. However, if the area of the opening is small, the integrity of the lower concrete on the lower side of the sheet and the upper (surface) concrete on the upper side is lacking. In particular, the thinner the upper layer (surface layer) concrete, the easier it is for the surface layer concrete to peel off. Furthermore, in patent document 1, the sheet | seat is sunk inside from the surface of ready-mixed concrete by pressing with a pressing machine. For this reason, it is no exaggeration to say that it is almost impossible to sink the sheet to a certain depth. That is, the embedding depth of the sheet must be shallow. Also from such a thing, in the thing of patent document 1, surface concrete will peel easily. Further, when the technique of Patent Document 1 is adopted, the workability is poor. Further, when the sheet is submerged from the surface of the ready-mixed concrete by pressing with a pressing machine, the sheet is uneven and inferior in flatness. In addition, since the sheet is depressed by pressing with a pressing machine, the position of the sheet is unlikely to be as designed.

  Therefore, the problem to be solved by the present invention is to solve the above-mentioned problems. In particular, it is to provide unreinforced concrete that can be performed with good workability, can be embedded at a desired position, and can effectively suppress cracking.

The above issues are
A method for suppressing cracks in unreinforced concrete,
It solves by the crack suppression method in unreinforced concrete characterized by arrange | positioning an alkali-resistant glass fiber net so that following formula (1) may be satisfied.

The above issues are
Unreinforced concrete,
This is solved by unreinforced concrete, wherein the alkali-resistant glass fiber net is arranged so as to satisfy the following formula (1).

The above issues are
A method for constructing unreinforced concrete,
A first concrete filling process in which concrete is filled into a mold;
After the first concrete filling step, an alkali resistant glass fiber net placement step in which an alkali resistant glass fiber net is placed on the surface of the concrete layer;
After the alkali-resistant glass fiber net placement step, the second concrete filling step in which concrete is filled on the alkali-resistant glass fiber net to form an unreinforced concrete layer satisfying the following formula (1): This is solved by a method for constructing unreinforced concrete, characterized by:

Formula (1)
1 ≦ T / G ≦ 12.5
T = Cover thickness of the alkali-resistant glass fiber net G = Maximum aggregate size in the concrete constituting the unreinforced concrete layer

  In the present invention, preferably, an alkali-resistant glass fiber net is provided with an interval of 75 cm or less.

  In the present invention, preferably, the alkali-resistant glass fiber net has a width of 10 cm to 50 cm.

  In the present invention, preferably, the alkali-resistant glass fiber net is configured in a net shape using a first yarn and a second yarn having a longer length than the first yarn. (Tensile stiffness of the first yarn) / (Tensile stiffness of the second yarn) = 1.5-30.

  In the present invention described above, the alkali-resistant glass fiber net is preferably (total area of the opening having a size of 10 mm or more in the opening and having a size of 10 mm or more in the opening) / (total area of the net). 0.2-0.9.

  In the present invention, preferably, the unreinforced concrete is provided on the surface layer of the reinforced concrete.

  Cracks in unreinforced concrete were greatly suppressed. Moreover, the workability for that is very good.

Partial plan view of net Plan and cross section of unreinforced concrete

  The first aspect of the present invention is a crack suppression method for unreinforced concrete. In this method, the alkali-resistant glass fiber net is arranged so as to satisfy the following formula (1).

  The second present invention is unreinforced concrete. The unreinforced concrete has an alkali-resistant glass fiber net. This alkali-resistant glass fiber net is arranged so as to satisfy the following formula (1).

  The third aspect of the present invention is a method for constructing unreinforced concrete. This construction method includes a first concrete filling step in which concrete (fresh concrete) is placed in a mold. The construction method includes an alkali-resistant glass fiber net placement step in which an alkali-resistant glass fiber net is placed on the surface of the concrete layer after the first concrete filling step. This net placement step is preferably performed before the ready-mixed concrete placed in the first concrete filling step is solidified. In the present construction method, after the step of placing the alkali-resistant glass fiber net, concrete is placed on the alkali-resistant glass fiber net to form an unreinforced concrete layer that satisfies the following formula (1). A concrete filling process is provided. This second concrete filling step is preferably performed before the ready-mixed concrete cast in the first concrete filling step is solidified.

Formula (1)
1 ≦ T / G ≦ 12.5
T = Cover thickness of the alkali-resistant glass fiber net G = Maximum aggregate size in the concrete constituting the unreinforced concrete layer

  T / G was preferably 7.5 or less. Furthermore, it was 5 or less.

  Even if the alkali-resistant glass fiber net provided (embedded) in the present invention is only one layer, a sufficient crack suppressing effect is exhibited. However, although workability is lowered, it does not prevent the alkali-resistant glass fiber net from being provided in a plurality of layers such as two layers or three layers.

  The alkali-resistant glass fiber net used (embedded) in the present invention may be provided over the entire surface of the concrete layer. However, even if an alkali-resistant glass fiber net was not provided over the entire surface of the concrete layer, the effect of suppressing cracking was sufficiently achieved. For example, a plurality of alkali-resistant glass fiber nets may be provided at intervals. Preferably, the gap (the gap in the horizontal direction) is preferably arranged on the concrete surface with a gap of 75 cm or less (preferably 20 cm or more). The reason is that if the interval is too wide, the crack suppressing effect is reduced.

  The alkali-resistant glass fiber net used in the present invention has a width of 10 cm to 50 cm. If the net width is too short, the crack suppression effect is small unless so many nets are used. If a large number of nets must be used, the workability is reduced accordingly. On the contrary, when the net width is too long, the filling property at the time of placing the concrete is lowered. For this reason, an alkali-resistant glass fiber net having the above-described size was preferred.

  The alkali-resistant glass fiber net used in the present invention is preferably configured in a net shape using a first yarn and a second yarn having a longer length than the first yarn. And (tensile stiffness of the first yarn) / (tensile stiffness of the second yarn) = 1.5-30. The net is a yarn existing in at least two directions (simply referred to as a yarn, but this is a fiber itself, a plurality of fibers twisted, or a plurality of fibers twisted). The twisted one is a twisted one, or a string or a narrow sheet-like one) is a crossed net-like one. The shape surrounded by this intersection (intersection) (opening shape: window shape) is, for example, a square, a rhombus, or a rectangle. Of course, not only the quadrangle as described above, but also other polygons may be used. However, if a net having a shape other than the quadrangle is to be manufactured, the cost increases. It is a square (square or rectangular, in particular rectangular) net. Yarn existing in the first direction (first yarn) and yarn existing in the second direction (second yarn: second yarn having a shorter length than the first yarn) ) Preferably has the following relationship: The two directions are, for example, a vertical direction and a horizontal direction. When an attempt is made to produce a net, generally, the yarn in the longitudinal direction is the warp and the yarn in the short direction is the weft. (Tensile stiffness of first yarn (for example, longitudinal yarn: warp)) / (Tension stiffness of second yarn (for example, lateral yarn: weft)) = 1.5-30. More preferably, the value is 1.8 or more. More preferably, the value was 5 or more. More preferably, the value was 25 or less. More preferably, the value was 20 or less. That is, the crack suppression effect of unreinforced concrete by the net constructed so that (tensile stiffness of the first yarn) / (tensile stiffness of the second yarn) becomes the above value was great. Moreover, the yarn amount can be reduced. The tensile rigidity of the yarn is obtained by (yarn elastic coefficient) × (yarn cross-sectional area). When several fibers are twisted to form a thread, if the cross section is taken, there is a gap between the fibers in the cross section. However, in the case of (tensile stiffness of warp) / (tensile stiffness of weft), there is almost no problem even if the gap is neglected in the cross-sectional area of the yarn. Therefore, the cross-sectional area of the yarn is an area determined by the outer shape in the cross-section. This is the value obtained in. In order to configure the net so that (the tensile stiffness of the first yarn) / (the tensile stiffness of the second yarn) becomes the above value, each of the yarns whose tensile stiffness ratio becomes the above value should be selected. However, this can be achieved by considering the width of the yarn and the number of yarns when using an equivalent yarn. For example, when substantially the same yarn is used, this can be achieved by using a plurality of first yarns. That is, it can be achieved by knitting the net with a ratio of N (N is an integer of 2 or more) of the first yarn to one second yarn.

  The alkali-resistant glass fiber net used in the present invention is preferably (total area of the opening having a size of 10 mm or more in the opening and 10 mm or more in the opening in the net) / (total area of the net). .2 to 0.9. That is, from the viewpoint of the crack suppression effect, the net is preferably (total area of the opening having a size of 10 mm or more and 10 mm or more in the opening in the net) / (total area of the net). .2 to 0.9. More preferably, the value is 0.4 or more. The value was 0.8 or less. The size of the opening (rectangular conversion area) having a length of 10 mm or more and a width of 10 mm or more was preferably 100 mm 2 to 10,000 mm 2. In particular, when converted into a rectangular shape, the long side was preferably 10 mm or more. And it was 400 mm or less. More preferably, it was 15 mm or more. And it was 300 mm or less. Especially preferably, it was 20 mm or more. And it was 200 mm or less. From the viewpoint of the effect of suppressing cracks, the net is preferably a net having four or more intersections between the first yarn and the second yarn per 10 cm square. More preferably, it was 20 or more. And it was 500 or less. Most preferably, it was 40 or more. And it was 300 or less. This is because when the opening is as described above, it is difficult to adversely affect the filling of concrete or the like. Moreover, the width of the yarn was preferably about 0.1 to 30 mm. More preferably, it was 1 mm or more. And it was 10 mm or less. That is, the strength of a thread that is too small is poor, and conversely, in the case of a thread that is too wide, the integrity of the concrete located on both sides of the crack suppression material is reduced so much. A width yarn was preferred. Since the second yarn (weft yarn) having a short length is waved at the intersection point and positioned above and below the first yarn (warp yarn) having a long length, the first yarn (warp yarn) is also provided. It was preferable to make the thickness of the first yarn (warp yarn) thicker than the thickness of the second yarn (weft yarn). In addition, it was preferable to make the width of the first yarn (warp yarn) wider than the width of the second yarn (weft yarn).

The net is composed of synthetic fibers such as aramid fibers, carbon fibers, glass fibers, and the like. Preferably, a fiber having a high elastic modulus is used. In view of the affinity with the cement and the cost, a net made of glass fiber yarn was preferred. Among them, a net made of alkali-resistant glass fiber (for example, glass fiber containing 14% by mass or more of zirconium oxide (ZrO ₂ )) was preferable.

  And according to invention of the said embodiment, the crack width was able to be suppressed economically and efficiently. And since the operation | work for crack suppression is performed before concrete placement, the problem in the case of performing the post-operation said to cover with a curing sheet after placement is improved. In particular, the above-mentioned problem of Patent Document 1 is greatly solved. Furthermore, the alkali-resistant glass fiber net of the above embodiment is a uniaxially arranged continuous fiber, has extremely high reinforcement efficiency, and has the effect of suppressing crack width by suppressing cracks by improving tensile resistance and the effect of uniformly dispersing stress. It was expensive. For example, the reinforcement efficiency is five times higher than that of fiber reinforced concrete having a three-dimensional random arrangement. And the crack suppression effect in unreinforced concrete was remarkable. In particular, in the present invention in which the alkali-resistant glass fiber net is disposed relatively flat, the crack suppressing effect is remarkable. And even if the crack generate | occur | produced, it was suppressed to the crack width (within 0.05 mm) which does not need repair. Furthermore, the integrity of the concrete on both sides of the alkali-resistant glass fiber net is high. Therefore, peeling of the surface concrete is difficult to occur. Moreover, it was excellent in workability, workability, and economy.

  Hereinafter, the present invention will be described with specific examples. However, the present invention is not limited to the embodiments.

  FIG. 1 is a plan view of a part of the net 1. FIGS. 2A and 2B are a plan view and a cross-sectional view of unreinforced concrete. The plan view shown in FIG. 2A is a plan view in a state where the net is arranged but no unreinforced concrete is placed on the net.

First, the net (alkali resistant glass fiber net) used in this example will be described in detail.
1 is the net. The net 1 has a length (width) in the short direction (left-right direction in FIG. 1) of 10 to 50 cm, for example, about 25 cm. As can be seen from FIG. 1, the net 1 is made of three hardened (three bundled together) glass fibers (alkali-resistant glass fibers) in the longitudinal direction (vertical direction in FIG. 1). (Thread width: about 3 mm, thread thickness: about 0.7 mm) are provided with an interval of about 17-19 mm (FIG. 1, an interval of about 17-19 mm in the left-right direction). The three yarns that are provided tightly may be in contact with each other. Therefore, instead of using three yarns having a yarn width of about 3 mm, a yarn having a yarn width of 9 mm may be used. However, in this embodiment, as can be seen from FIG. 1, since three yarns having a yarn width of about 3 mm were used, although the three yarns are solidified, in reality, between the warp yarns, A slight gap, for example, a gap of about 1 mm is provided. Such a slight gap and a gap are preferred from the viewpoint of crack suppression because the cement compositions on both sides of the crack suppression material are integrated through the gap. In FIG. 1, the first, second and third yarns from the left side are solidified and provided in the vertical direction, and the fourth yarn is provided in the vertical direction with an interval of about 17 to 19 mm from the third yarn, and The fourth, fifth, and sixth yarns are similarly set in the longitudinal direction, and the seventh yarn is provided in the longitudinal direction with an interval of about 17 to 19 mm from the sixth yarn. The seventh, eighth and ninth yarns were also set in the longitudinal direction in the same manner. Furthermore, the thread | yarn was similarly arrange | positioned on the right side in FIG. In the lateral direction (left and right direction in FIG. 1), one glass fiber (alkali-resistant glass fiber) thread (thread width: about 2.3 mm, thread thickness: about 0.5 mm, thread length: about 155 mm) Are provided with an interval of about 30 to 32 mm (in FIG. 1, an interval of about 30 to 32 mm in the vertical direction). The lateral yarns are arranged so as to be the back and front in order with respect to the longitudinal yarns (three yarns). That is, if weft is arranged on the first, second and third warps from the left (on the surface), the weft is arranged under the fourth, fifth and sixth warps from the left (under the back), The weft yarn is arranged above the seventh, eighth and ninth warp yarns (on the surface) from the left, and the weft yarn is arranged under the tenth, eleventh and twelfth warp yarns (under the back surface). The same applies hereinafter. Also, the weft adjacent to the above-mentioned weft is assumed to be above the first, second, third warp from the left (under the back), and above the fourth, fifth, sixth warp from the left ( Weft yarn is arranged on the top surface, and the weft yarn is arranged below the seventh, eighth and ninth warp yarns from the left (bottom of the back surface), and the weft yarn is placed on the next tenth, eleventh and twelfth warp yarns (on the surface) Is arranged. The same applies hereinafter. The above vertical relationship may be such that the three yarns are not one lump but each one is alternately in order. The warp and the weft are made of a plurality of fibers. Therefore, at the intersection of the warp and the weft, the weft can come out between the warps. That is, the warp and the weft are knitted so that the weft can be removed between the fibers of the warp. The intersection of the warp and the weft is impregnated with resin, and the warp and the weft are bonded to each other so that no deviation occurs at the intersection. Since the warp and weft are knitted as described above, the shape of the opening (window) formed by the four intersections of the warp and weft is substantially rectangular (longitudinal dimension: 30 to 30). 32 mm, short direction dimension: about 17 to 19 mm). And (tensile stiffness of the first yarn) / (tensile stiffness of the second yarn) was about 5.5.

  Reference numerals 2a and 2b denote mold frames. In addition, 2a is a wooden frame and 2b is an iron mold.

  3 is an unreinforced concrete layer. The unreinforced concrete layer 3 is provided on the surface of the reinforced concrete layer. In FIG. 2, the portion indicated by reference numeral 4 may be an unreinforced concrete layer or a reinforced concrete layer. That is, a net 1 is arranged on the surface of a concrete layer (an unreinforced concrete layer or a reinforced concrete layer) 4 that has not been solidified immediately after placement, and the concrete is placed immediately after this to place the unreinforced concrete layer 3. Is configured. The unreinforced concrete layer 3 had a thickness of 2 cm. The diameter of the maximum aggregate contained in the concrete constituting the unreinforced concrete layer 3 was 2 cm. Therefore, T (cover thickness of the alkali-resistant glass fiber net) / G (maximum aggregate size of the aggregate in the concrete constituting the unreinforced concrete layer 3) was 1.

Next, the construction method will be described.
First, although not shown, a predetermined bar arrangement was performed. Moreover, the formwork 2a, 2b was provided. Thereafter, concrete was placed in the formwork of the reinforcing bar arrangement portion in the formwork 2a, 2b. Thereby, although not solidified, the reinforced concrete layer 4 was comprised.

  When the reinforced concrete layer 4 was not solidified, two nets 1 and 1 were arranged in a predetermined pattern on the surface of the reinforced concrete layer 4 as shown in FIG. That is, the dimension (inner dimension) between the net 1 having a width of 25 cm and the net 1 having a width of 25 cm is 50 cm, and the dimension between the outer edge of the net 1 having a width of 25 cm and the inner edge of the wooden frame 2a is 25 cm. Arranged.

  After this, that is, in a state where the concrete of the reinforced concrete layer 4 is not solidified, the concrete is cast to form the unreinforced concrete layer 3. After the concrete placement, compaction was performed by a vibrator. The cover thickness T at this time was 2 cm. The maximum aggregate size of the aggregate in the concrete constituting the unreinforced concrete layer 3 used at this time (dimension in the vertical direction of the maximum aggregate in the cast concrete layer 3: when the maximum aggregate is spherical, The dimension was 2 cm in diameter in the spherical shape. That is, the unreinforced concrete layer 3 is constructed by placing concrete using the maximum aggregate having a size of 2 cm.

  It carried out according to the said Example 1. In Example 1 above, the cover thickness T of the net 1 was 2 cm (T / G = 1), but in Example 2 the cover thickness T was 10 cm (T / G = 5). The procedure was the same except that the cover thickness was different.

  It carried out according to the said Example 1. In Example 1 above, the cover thickness T of the net 1 was 2 cm (T / G = 1), but in Example 3 the cover thickness T was 15 cm (T / G = 7.5). The procedure was the same except that the cover thickness was different.

  It carried out according to the said Example 1. In Example 1 above, the cover thickness T of the net 1 was 2 cm (T / G = 1), but in Example 4 the cover thickness T was 25 cm (T / G = 12.5). The procedure was the same except that the cover thickness was different.

  It carried out according to the said Example 1. In Example 5, the cover thickness T of the net 1 was 2 cm, but the maximum aggregate size of the aggregate constituting the unreinforced concrete layer 3 was 1.5 cm. Therefore, T / G = 1.33.

  It carried out according to the said Example 1. In Example 6, the cover thickness T of the net 1 was 15 cm, but the maximum aggregate size of the aggregate in the concrete constituting the unreinforced concrete layer 3 was 1.5 cm. Therefore, T / G = 10.

  In Example 7, the dimension (inner dimension) between the net 1 having a width of 25 cm and the net 1 having a width of 25 cm is 75 cm, and the dimension between the outer edge of the net 1 having a width of 25 cm and the inner edge of the wooden frame 2a is 12. It was performed according to Example 1 except that it was arranged to be 0.5 cm.

  It carried out according to the said Example 1. In Example 1 above, the cover thickness T of the net 1 was 2 cm (T / G = 1), but in Comparative Example 1, the cover thickness T was 28 cm (T / G = 14). The procedure was the same except that the cover thickness was different.

  It carried out according to the said Example 1. In Example 1 above, the cover thickness T of the net 1 was 2 cm (T / G = 1), but in Comparative Example 2, the cover thickness T was 1.6 cm (T / G = 0.8). The procedure was the same except that the cover thickness was different.

  It carried out according to the said Example 1. However, Comparative Example 3 is an example in which the net 1 was not used at all.

  Various characteristics of the unreinforced concrete structures obtained in Examples 1 to 8 and the unreinforced concrete structures obtained in Comparative Examples 1 to 3 were examined. It is shown in Table 1. The cracks were observed after 6 months of placing unreinforced concrete.

Table 1
T / G Workability Crack characteristics
Crack Maximum crack width Number of cracks Example 1 1 Excellent None − 0
Example 2 5 Excellent 0.01 mm 1 Example 3 7.5 Excellent 0.02 mm 1 Example 4 12.5 Excellent 0.05 mm 1 Example 5 1.33 Excellent None 0
Example 6 10 Excellent 0.04 mm 1 Example 7 1 Excellent None −0
Comparative Example 1 14 Excellent 0.10 mm 1 Comparative Example 2 0.8 Poor Yes 0.06 mm 1 Comparative Example 3-Excellent 0.30 mm 1 * Workability: Concrete filling * The cracked part is net 1 and net It was the central part between 1.

  From Table 1, it can be seen that in the present invention, cracking is greatly suppressed. In particular, since T (cover thickness of the alkali-resistant glass fiber net) / G (maximum aggregate size of the aggregate in the concrete constituting the unreinforced concrete layer 3) is 1 to 12.5, The cracking characteristics could be greatly improved. It can also be seen that the improvement in cracking properties is even greater when T / G is 7.5 or less.

  On the other hand, as can be seen from Comparative Example 1, when T / G exceeded 12.5, even when the net 1 was provided, the degree of improvement in cracking characteristics was small. This is presumed to be because the embedding depth of the net 1 was too deep, and the effect of suppressing the concrete shrinkage strain at the surface layer portion of the unreinforced concrete layer 3 by the net 1 was small.

  Then, when we asked if the burial depth of net 1 should be shallow, it was not so. That is, when the embedding depth of the net 1 is too shallow, as can be seen from the comparative example 2, the embedded net 1 becomes as if it was partially pushed by the aggregate existing on the net 1, and the net 1 is arranged. It was inferred that the effect of suppressing the concrete shrinkage strain due to the net 1 was reduced as a result of the unevenness of the net 1 being formed and the flatness (levelness) of the net 1 being lost.

  Further, when the net 1 of the present invention is used, the opening area of the net 1 is large, so that the concrete filling property is good. And the integrity of the upper and lower concrete of the net 1 is high. For example, when a sheet like Patent Document 1 is used, it is considered that the concrete filling property is poor.

  Moreover, in this invention, after arrange | positioning the net | network 1, since only the ready-mixed concrete for comprising unreinforced concrete is poured in, workability | operativity is very high.

1 Alkali-resistant glass fiber net 3 Unreinforced concrete layer

Claims (10)

A method for suppressing cracks in unreinforced concrete,
A method for suppressing cracking in unreinforced concrete, wherein the alkali-resistant glass fiber net is disposed so as to satisfy the following formula (1).
Formula (1)
1 ≦ T / G ≦ 12.5
T = Cover thickness of the alkali-resistant glass fiber net G = Maximum aggregate size in the concrete constituting the unreinforced concrete layer 2. The method for suppressing cracks in unreinforced concrete according to claim 1, wherein the alkali-resistant glass fiber net is provided with an interval of 75 cm or less. The method for suppressing cracks in unreinforced concrete according to claim 1 or 2, wherein the alkali-resistant glass fiber net has a width of 10 cm to 50 cm. The alkali-resistant glass fiber net is formed into a net shape using a first yarn and a second yarn having a length longer than that of the first yarn (the tension of the first yarn). Rigidity) / (Tensile rigidity of the second yarn) = 1.5-30. The method for suppressing cracks in unreinforced concrete according to any one of claims 1 to 3. Unreinforced concrete,
An unreinforced concrete in which an alkali-resistant glass fiber net is disposed so as to satisfy the following formula (1).
Formula (1)
1 ≦ T / G ≦ 12.5
T = Cover thickness of the alkali-resistant glass fiber net G = Maximum aggregate size in the concrete constituting the unreinforced concrete layer 6. The unreinforced concrete according to claim 5, which is an unreinforced concrete provided on a surface layer of reinforced concrete. 7. The unreinforced concrete according to claim 5 or 6, wherein the alkali-resistant glass fiber net is provided with an interval of 75 cm or less. The unreinforced concrete according to any one of claims 5 to 7, wherein the alkali-resistant glass fiber net has a width of 10 cm to 50 cm. The alkali-resistant glass fiber net is formed into a net shape using a first yarn and a second yarn having a length longer than that of the first yarn (the tension of the first yarn). Rigidity) / (Tensile rigidity of the second yarn) = 1.5-30 The unreinforced concrete according to any one of claims 5-8. A construction method of unreinforced concrete according to any one of claims 5 to 9,
A first concrete filling process in which concrete is filled into a mold;
After the first concrete filling step, an alkali resistant glass fiber net placement step in which an alkali resistant glass fiber net is placed on the surface of the concrete layer;
After the alkali-resistant glass fiber net placement step, the second concrete filling step in which concrete is filled on the alkali-resistant glass fiber net to form an unreinforced concrete layer satisfying the following formula (1): A method for constructing unreinforced concrete, characterized by:
Formula (1)
1 ≦ T / G ≦ 12.5
T = Cover thickness of the alkali-resistant glass fiber net G = Maximum aggregate size in the concrete constituting the unreinforced concrete layer