JP5487958B2 - Construction method to improve resistance to sulfate degradation of hardened cement - Google Patents

Description

The present invention relates to a construction method for improving the resistance of a cement hardened body to sulfate deterioration.

  As an example of soil containing sulfate, marine stratum-origin soil containing pyrite produced sulfate by oxidation by air contact (see Non-Patent Document 1), landfilled by-products during coal drilling Soil, as well as soil from chemical factory sites and hot spring areas. It is known that hardened cement bodies such as concrete structures constructed on such soil deteriorate with time due to sulfate (see Non-Patent Document 2). Degradation due to sulfate in sulfate soil is roughly divided into chemical degradation and physical degradation (see Non-Patent Document 3).

Chemical degradation is a phenomenon in which concrete is expanded and destroyed when sulfate ions (SO ₄ ²⁻ ) and sodium ions (Na ⁺ ) contained in sulfate soil react with cement hydrate to produce ettringite. Physical degradation is due to the formation of sodium sulfate and sodium sulfate decahydrate by the concentration of underground sulfate and sodium ions on the concrete surface above the ground and drying. Concrete is destroyed by pressure. In a concrete structure constructed on soil containing sulfate, the deterioration is caused by a combined deterioration effect in which chemical deterioration occurs mainly in the underground and physical deterioration occurs on the ground. A part of the surface of the hardened cement body 20 shown in FIG. 2 is destroyed due to deterioration, and the ground portion 20a of the ground portion 20a and the underground portion 20b is mainly broken due to physical deterioration due to sulfate.

"Symposium on Natural Environment and Concrete Performance Evaluation", Japan Concrete Institute, 2005, pp. 301-308 “Concrete Engineering Annual Papers, Vol. 23, No. 2”, Japan Concrete Institute, 2001, pp. 673-678 “CBRC, 2003”, Japan Building Research Institute, pp. 32-38

  By the way, it is known that chemical deterioration accompanied by the formation of ettringite can be suppressed by using sulfate-resistant Portland cement (see, for example, JP 2009-120433 A). On the other hand, the present condition is not yet established about the technique which suppresses the physical degradation by the production | generation pressure of sodium sulfate or sodium sulfate decahydrate.

This invention is made | formed in view of the said situation, and it aims at providing the construction method which can fully improve the tolerance with respect to sulfate deterioration of a cement hardening body .

  The inventors of the present invention have intensively studied to solve the above problems. As a result, when water-resistant polymer cement mortar is applied to the surface of the ground part from a part of the ground part of the hardened cement body in the soil that causes sulfate degradation, the physical properties of sodium sulfate and sodium sulfate decahydrate precipitate. The present invention has been found to be able to extremely effectively suppress deterioration, and has led to the completion of the following invention.

That is, the construction method according to the present invention is for improving the resistance to sulfate deterioration of a cement hardened body including an underground part buried in the ground and an above-ground part extending from the underground part and provided on the ground. A first step of removing the soil around the cement cured body so that the surface of the ground portion of the underground portion is exposed, and of the surface of the cement cured body, the ground portion exposed by the first step A second step of forming a coating layer by applying a waterproof covering material from the portion to the ground portion side of the ground portion, and a third step of backfilling the portion from which the soil has been removed in the first step after the second step; The upper end of the range in which the coating layer is formed is 0.3 to 2.0 m high from the ground surface. Cement cured body the construction is made, the ground portion which is buried in the ground, and than ash and a ground portion provided on the ground and extends from the place middle, of the surface of the hardened cement paste, at least A covering layer is formed by applying a waterproof covering material from the ground side of the ground part to the ground part side of the ground part.

  The hardened cement according to the present invention has sufficient resistance to physical deterioration caused by sulfate. For this reason, the lifetime of the hardened cement body is extended, and further, the repair cost and the waste generated by re-construction are reduced. The hardened cement according to the present invention does not necessarily have to be the one where the entire surface of the hardened material is covered with the coating layer. As described above, the cement hardened material is coated at least from the ground part side of the ground part to the ground part side of the ground part. If the layer is formed, the above effect can be obtained.

  The main reason that the effect of preventing sulfate deterioration can be obtained by forming a coating layer on the above-mentioned predetermined part of the hardened cement body is that the waterproof coating material prevents the concentration of sulfate ions and sodium ions on the surface of the hardened cement body. This is probably because of this. That is, the sulfate solution absorbed from the portion where the hardened cement body and the soil are in direct contact rises along the relatively dry surface of the ground even in the hardened cement body, and is dried and concentrated at the portion in contact with the atmosphere. After the concentration, sodium sulfate and sodium sulfate decahydrate destroy the cement hardened body surface due to the generation pressure (see FIG. 2). In the present invention, it is presumed that by forming a coating layer on the surface of the hardened cement body in contact with the atmosphere, concentration of the sulfate solution by drying is prevented, and physical deterioration due to sulfate can be suppressed.

  In the present invention, the covering material is preferably a polymer cement mortar. The polymer cement mortar is an emulsion containing an acrylic polymer, and the mass of the acrylic polymer with respect to 100 parts by mass of the emulsion is preferably 50 to 60 parts by mass, and more preferably 54 to 57 parts by mass.

  In this invention, it is preferable that an underground part and an above-ground part consist of a hardening body of a sulfate-resistant portland cement. By using sulfate-resistant Portland cement as a raw material for the hardened body that forms the underground part and the above-ground part, resistance to chemical deterioration due to sulfate in the underground part is also increased, and the durability of the cemented hardened body is further improved. be able to.

  According to the construction method of the present invention, it is only necessary to dig up a part of the soil in the part where the structure having the cement hardened body and the ground are in contact, and to apply the covering material only on a part of the surface of the structure. There is no need to apply the entire surface of the object. For this reason, it is possible to prevent sulfate deterioration even with existing structures as well as existing structures by minor modifications.

ADVANTAGE OF THE INVENTION According to this invention, the tolerance with respect to sulfate deterioration of a cement hardening body can fully be improved.

(A)-(d) is a schematic diagram which each shows the process of the construction method which concerns on this invention. It is a schematic diagram which shows an example of the hardened cement body which the physical deterioration by the sulfate produced. (A) is a perspective view which shows the application range of the cylindrical test body and polymer cement mortar used for the test, (b) is a perspective view which shows the application range of the prism test body and polymer cement mortar used for the test. It is a photograph which shows the external appearance of the mortar test body after 26 weeks of test periods. It is a graph which shows the relationship between a test period and the compressive strength of concrete with a water cement ratio of 45%. It is a graph which shows the relationship between a test period and the compressive strength of concrete with a water cement ratio of 55%. It is a graph which shows the relationship between a test period and the mass change rate of concrete with a water cement ratio of 45%. It is a graph which shows the relationship between a test period and the mass change rate of concrete with 55% of water cement ratio. It is a figure which shows the element mapping result of the degradation site | part of the mortar test body which concerns on the comparative example 2. FIG. It is a figure which shows the element mapping result of the degradation site | part of the mortar test body which concerns on the comparative example 4. FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

<Construction method>
The construction method for preventing the sulfate deterioration of the existing concrete structure (hardened cement) will be described with reference to FIG. The construction method according to the present embodiment is preferably carried out on a concrete structure that is in contact with the ground (particularly the ground made of soil containing sulfate). FIG. 1A is a schematic view showing a state in which a columnar concrete structure 10 is erected on the ground G. FIG. As shown in the figure, the concrete structure 10 includes an underground portion 10b buried in the ground and in direct contact with the soil, and an above-ground portion 10a extending upward from the underground portion 10b and provided on the ground.

  First, the soil around the concrete structure 10 is removed from the state shown in FIG. 1A to obtain the state shown in FIG. Thereby, as shown in FIG.1 (b), the surface 10F by the side of the ground part 10a of the underground part 10b is exposed (1st process). The depth at which the soil is removed depends on the concentration of sulfate contained in the soil and the state of the concrete structure 10, but is preferably 0.1 to 1.0 m, and preferably 0.3 to 0.5 m. Is more preferable. If this depth is less than 0.1 m, the surface tends to deteriorate near the ground surface L. On the other hand, if it exceeds 1.0 m, the working efficiency tends to decrease.

  The covering layer 15 is formed by applying a waterproof covering material over a predetermined range on the ground portion 10b side of the ground portion 10a from the surface 10F exposed in the first step (second step). At this time, the covering layer 15 is preferably formed over the entire circumference of the side surface of the concrete structure 10. The upper end of the range in which the covering layer 15 is formed depends on conditions such as ambient temperature and humidity, but is preferably 0.3 to 2.0 m high from the ground surface L, 0.5 to 1. More preferably, the height is 0 m. If the height is less than 0.3 m, deterioration tends to occur at a position higher than this, and if it exceeds 2.0 m, the working efficiency tends to decrease.

  After the said 2nd process, as shown in FIG.1 (d), the part which removed the soil in the 1st process is backfilled, and construction is complete | finished (3rd process).

  Since the construction method according to the present embodiment can be performed only by digging up the soil around the concrete structure 10, it is suitable for application to the existing concrete structure 10 as described above. In addition, after digging up the soil, there is an advantage that an excellent deterioration preventing effect can be obtained only by a relatively simple operation of applying a covering material in a predetermined range.

  In addition, although the concrete structure 10 shown in FIG. 1 has a circular cross section perpendicular to the longitudinal direction, the cross-sectional shape is not limited to a circle, and may be an ellipse, a rectangle, or other shapes. Specific examples of concrete structures include piles for steam curing, concrete products such as U-shaped grooves, and foundations such as piers and piers, foundations for houses, and boulders.

<Coating material>
Next, the covering material used in this embodiment will be described. As the covering material, a material capable of forming the covering layer 15 exhibiting waterproofness on the surface of the concrete structure 10 is used. The covering layer 15 serves to prevent water from entering the concrete structure 10 and to prevent concentration of sodium sulfate and sodium sulfate decahydrate on the surface of the concrete structure 10. By reducing precipitation of sodium sulfate and sodium sulfate decahydrate on the surface of the concrete structure 10, the progress of physical deterioration of the concrete structure 10 is suppressed.

  In this embodiment, polymer cement mortar is used as the coating material. Suitable polymer cement mortar includes a mixture of an emulsion containing an acrylic polymer and cement mortar. Specific examples of suitable acrylic polymers include acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl methacrylate, acrylonitrile and methacrylonitrile. As the dispersion medium for dispersing the acrylic polymer, anionic, nonionic, cationic or amphoteric surfactants, protective colloids such as polyvinyl alcohol, and the like can be used.

  It is preferable that content of the acrylic polymer with respect to 100 mass parts of emulsion is 54-57 mass parts from a viewpoint of exhibiting the outstanding waterproofness. From the same viewpoint, the content of the acrylic polymer with respect to 100 parts by mass of the polymer cement mortar is preferably 25 to 40% by mass, and more preferably 30 to 36% by mass.

  The cement mortar preferably contains each material in the following ratio. That is, the cement mortar preferably contains 20 to 30% by mass of cement, 5 to 10% by mass of gypsum, and 50 to 70% by mass of dredged sand.

In addition, when using the liquid agent whose content rate of an acrylic polymer (compound name: (meth) acrylic acid ester copolymer) is 20 mass% or more (more preferably 25 mass% or more) as a covering material, a concrete structure It is preferable that 0.9 kg / m ² (thickness 0.45 mm) or more is applied to the surface of 10. When the coating amount of the coating material is less than 0.9 kg / m ² (thickness 0.45 mm), the effect of suppressing physical deterioration of the concrete structure 10 tends to be insufficient.

  In the present embodiment, a water absorption inhibitor may be used as the covering material. The water absorption inhibitor is preferably a solution in which a silane water repellent component is dissolved. The content of the silane-based water-repellent component in such a solution is preferably 90% by mass or more, and more preferably 95% by mass or more from the viewpoint of obtaining an excellent water absorption preventing effect.

  Specific examples of the silane-based water repellent component include triethoxyisobutylsilane, hexyltrimethoxysilane, decyltrimethoxysilane, and the like. One of these may be used alone, or two or more may be used in combination. Good. Among the above compounds, it is more preferable to use triethoxyisobutylsilane as the silane water repellent component. Triethoxyisobutylsilane has a feature of high permeability to the concrete structure forming the coated surface.

When a solution having a triethoxyisobutylsilane content of 90% by mass or more (more preferably 95% by mass or more) is used as the water absorption inhibitor, the water absorption inhibitor is added to the surface of the concrete structure 10 at 300 ml / It is preferable to apply m ² or more. When the coating amount of the water absorption inhibitor is less than 300 ml / m ² , the effect of suppressing physical deterioration of the concrete structure 10 tends to be insufficient.

<Concrete structure>
In this embodiment, in order to suppress physical deterioration of the concrete structure 10, the type of cement used as a raw material for the base concrete of the concrete structure 10 is not particularly limited. However, in order to sufficiently suppress both physical deterioration and chemical deterioration, the base concrete forming the concrete structure 10 is preferably a hardened body of sulfate-resistant Portland cement.

The sulfate-resistant polyland cement has a mineral composition of C ₃ S amount of 60 to 75 mass%, C ₃ A amount of 2 mass% or less, and C ₄ AF amount of 11 to 16 mass% in terms of Borg conversion. preferable. Here, C ₃ S is alite (3CaO · SiO ₂ ), C ₄ AF is a ferrite phase (4CaO · Al ₂ O ₃ · Fe ₂ O ₃ ), and C ₃ A is an aluminate phase (3CaO · Al ₂ O ₃ ) is shown respectively.

  The preferred embodiment of the present invention has been described in detail above, but the present invention is not limited to the above embodiment. For example, in the above-described embodiment, the case where the construction method according to the present invention is applied to an existing concrete structure 10 is illustrated, but a coating material is applied to a predetermined range of a new concrete structure, and the physical deterioration thereof is performed. It may be possible to improve the resistance to.

  Moreover, in the said embodiment, although the concrete structure was illustrated as a cement hardening body, this invention can also be applied to a mortar structure.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

<Materials used>
(1) The cement composition cement composition, mineral composition _{(C 3 S, C 2 S} , C 3 A, C 4 AF), chemical composition _{(SO 3, Na 2 O eq} ) and fineness (Blaine specific surface area ) Two different types (sulfate resistant Portland cement (SR) and ordinary Portland cement (N)) were used. Table 1 shows the chemical composition and mineral composition of these cements, and Table 2 shows the physical properties.
(2) Fine aggregate As fine aggregate, sea sand (surface dry density 2.56 g / cm ³ , water absorption 2.15%, coarse particle ratio 3.03) and crushed sand (surface dry density 2.70 g / cm ³ , water absorption 1.50%, coarse particle ratio 2.64).
(3) Coarse aggregate As the coarse aggregate, crushed stone 2005 (surface dry density 2.70 g / cm ³ , water absorption 0.50%, coarse particle ratio 6.67) was used.
(4) Admixture The admixture includes POZOLIS No. manufactured by BASF Pozzolith Co., Ltd. 70 (AE water reducing agent: complex of lignin sulfonic acid compound and polyol) was used (AD). Moreover, BASF Pozzolith Co., Ltd. micro air 404 (polyalkylene glycol derivative) was used as an antifoamer which adjusts the air quantity (AT).
(5) Polymer cement mortar (coating material)
A polymer cement mortar (Beam Protector S (trade name) manufactured by Ube Industries, Ltd.) was used as the waterproof coating.
(6) Mixing water Tap water was used as the mixing water.

<Concrete mix>
Table 3 shows the mix of concrete. The target slump was 15 cm and the target air amount was 4.5%. The water-cement ratio was 45 and 55%.

<Production of concrete and mortar>
Concrete and mortar were produced as follows. First, in a constant temperature room at 20 ° C., the cement composition, fine aggregate and coarse aggregate are put into a biaxial forced kneading mixer having a capacity of 50 L, stirred for 30 seconds, and then water containing an admixture (that is, admixture + water). ) And mixed for 90 seconds to prepare a concrete cylindrical specimen (φ100 × 200 mm). The concrete slump value is the method described in JIS A 1101: 2005 “Concrete slump test method”, and the air amount is JIS A 1128: 2005 “Test method based on air pressure of fresh concrete—air chamber pressure”. Measurement was performed by the method described in “Method”. In addition, the mortar was used as a sample from which coarse aggregate was removed by sieving concrete with a steel mesh sieve having a sieve interval of 5 mm.

<Healing conditions>
Curing of concrete and mortar specimens was carried out in accordance with JIS draft "Testing method for chemical resistance by solution immersion of concrete (draft)". The specimen was demolded at a material age of 1 day and was cured under water at 20 ° C. until the material age was 7 days (6 days), and then sealed at 20 ° C. until the material age was 21 days (14 days), the material age was 26 days. In-air curing (5 days) and underwater curing (2 days) until the age of 28 days in a constant temperature and humidity room at 20 ° C. and 60% humidity.

<Method of applying polymer cement mortar>
In the case of a concrete cylindrical specimen having a diameter of 100 × 200 mm, the polymer cement mortar was applied using a brush on the side surface except for 40 mm from the lower surface. In the case of a 40 × 40 × 160 mm mortar specimen, it was applied to the side surface using a brush except for the bottom surface up to 30 mm. The coating amount was 300 ml / m ² and left for 1 hour until the surface was dried. Degradation of concrete in actual sulfate soil occurs at a part of the ground and a rising part from the ground (see FIG. 2). Therefore, FIG. 3 shows the application range of the water absorption inhibitor, which was simulated to simulate this.

<Dry and wet repeat test using sulfate solution simulating sulfate soil>
As the immersion liquid, a sodium sulfate solution and tap water for reference were used. The concentration of the sodium sulfate solution was 10% by mass. For 7 days from the start of the test, immerse the specimen in a dipping solution from the bottom to a height of 1/4 (50 mm for concrete, 40 mm for mortar), then dry for 2 days, soak for 1 day, and dry for 3 days. Immersion was repeated for 1 day to make one cycle for 7 days. The soaking solution was changed weekly until the test period of 28 days and changed every month after the 28th day. The test was conducted in a temperature-controlled room controlled at a temperature of 20 ° C. The measurement items were compression strength, mass change and appearance observation. FIG. 4 is a photograph showing the appearance of the mortar specimen after the 26-week test period.

  The measurement of compressive strength was performed before the start of the test and at 4, 13, and 26 weeks after the start. The change in mass was measured before the start of the test and at 1 week, 4 weeks, 8 weeks, 13 weeks and 26 weeks after the start of the test. The mass change is measured before the start of the test (that is, after 2 days of underwater curing), and the precipitates in the air when switching from the last immersion (1 day immersion) to the next cycle drying (2 days drying). However, it was carried out after wiping off the moisture in the soaked part.

<Measurement method of compressive strength>
The compressive strength of concrete was measured by the method described in JIS A 1108: 2006 “Concrete Compression Test Method”.

<Analyzing method by SEM-EDX>
About the comparative example 2 and the comparative example 4, the degradation site | part was analyzed for the element distribution in the concrete using the scanning electron microscope (SEM-EDX: Hitachi S-3000H, EDAX SUTM). The sample was collected at the aerial part where the deterioration was the most significant (at a position 60 mm from the upper surface of the test body), and the sample dimensions were 40 mm × 40 mm × thickness 10 mm. After sampling, the cut surface (observation surface) of the sample was polished with sandpaper (# 4000), then D-dried for 3 days, carbon evaporated, and subjected to SEM-EDX. In addition, element mapping was implemented about S (sulfur) and Na (sodium).

<Compressive strength of concrete>
As described above, a dry and wet repeated test using a 10 mass% sodium sulfate solution was performed, and the compressive strength was measured in a predetermined test period. The relationship between the test period and the compressive strength is shown in FIGS. The compressive strength of the concrete specimens of Comparative Example 1 and Comparative Example 2 has decreased since the test period of 13 weeks, whereas the compressive strength of the mortar specimens of Examples 1 and 2 is immersed in tap water. There is no significant difference from the reference examples 1 and 2, and no decrease in compressive strength with the test period is observed.

<Mass change rate of concrete>
As described above, a wet and dry repeated test using a 10% sodium sulfate solution was performed, and a change in mass was measured in a predetermined test period. The relationship between the test period and the mass change rate is shown in FIGS. The mass change rate of the concrete specimens of Example 1 and Example 2 was smaller than the concrete specimens of Comparative Example 1 and Comparative Example 2, and was a value close to Reference Examples 1 and 2 soaked in tap water. This is because the suction of the sulfate solution to the concrete surface in the constantly dried portion was suppressed, and the precipitation of sodium sulfate and sodium sulfate decahydrate was suppressed.

<Analysis of degradation sites by SEM-EDX>
The result of having analyzed the degradation site | part of the test body of the comparative example 2 and the comparative example 4 by SEM-EDX is shown in FIG. 9 and FIG. The white part of FIGS. 9 and 10 is the part where the element concentration is high, and in both Comparative Example 2 and Comparative Example 4, S (sulfur) and Na (sodium) are concentrated on the surface portion of the specimen. It can be inferred that mortar has deteriorated due to the concentration of these substances on the surface. In Examples 1 and 2 to which the water absorption inhibitor was applied, no deterioration of the surface of the test specimen was observed, indicating that there is an effect of suppressing the concentration of such deterioration factors.

  INDUSTRIAL APPLICATION This invention is useful as a technique which suppresses sulfate deterioration of the concrete structure constructed to the soil containing a sulfate. The main uses include civil engineering structures such as bridge piers, place piles, and building structures such as fabric foundations, boulders, concrete foundations such as condominiums and factories.

  DESCRIPTION OF SYMBOLS 10 ... Concrete structure (hardened cement body), 10a ... Above-ground part of concrete structure, 10b ... Underground part of concrete structure, 10F ... Surface on the above-ground part side of underground part, 15 ... Cover layer, G ... Ground, L ... the ground surface.

Claims (6)

A ground portion which is buried in the ground, a construction method for improving the resistance to sulfate degradation of the cement hardened body having a ground portion provided on the ground and extends from the place Chubu,
A first step of removing soil around the hardened cement body so that the surface of the ground part on the ground part side is exposed;
A second step of forming a coating layer by applying a waterproof covering material from the ground portion exposed in the first step to the ground portion side of the ground portion of the surface of the hardened cement body; ,
After the second step, a third step of backfilling the portion from which the soil was removed in the first step,
Equipped with a,
The upper end of the range for forming the coating layer, construction wherein the height der Rukoto of 0.3~2.0m the ground surface. The construction method according to claim 1, wherein the underground is sulfate soil. The construction method according to claim 1, wherein the hardened cement body is a foundation or a boulder of a house. The construction method according to any one of claims 1 to 3, wherein the coating material is polymer cement mortar. The polymer cement mortar is a mixture of an emulsion containing an acrylic polymer and cement mortar, and the mass of the acrylic polymer with respect to 100 parts by mass of the emulsion is 50 to 60 parts by mass. 4. The construction method according to 4 . The construction method according to any one of claims 1 to 5 , wherein the underground part and the ground part are made of a hardened body of sulfate-resistant Portland cement.