JP7574012B2 - Capsule admixture - Google Patents

Description

The present invention relates to capsule admixtures, in particular capsule admixtures added to cement compositions.

Carbonation is the phenomenon in which carbon dioxide from the atmosphere penetrates concrete (hardened cement body) and causes a carbonation reaction, lowering the pH of the pore solution. This neutralization accelerates corrosion of the reinforcing steel inside the concrete, causing cracks that lead to spalling of the concrete and cross-sectional defects, which reduces its durability.

Representative countermeasures against such neutralization include the surface impregnation method, which blocks deterioration factors (reducing the intrusion of carbon dioxide, water, and oxygen into the concrete), and the re-alkalization method, which restores the neutralized area (restoring the alkalinity of already neutralized concrete). The surface impregnation method, as described in the following non-patent document 1, is a method of blocking the intrusion of deterioration factors from the outside by applying an impregnating material, such as a silicate-based material, to the concrete surface with a brush or roller and impregnating it. The re-alkalization method, as described in the following patent document 1, is a method of passing a direct current from the anode on the concrete surface to the internal reinforcing bar (cathode), and using this current to permeate the re-alkalization solution on the surface into the concrete.

JP 2015-227578 A

"Guidelines for Concrete Crack Inspection, Repair and Reinforcement - 2009", p. 140 (Japan Concrete Institute)

However, the above-mentioned re-alkalization method is large-scale and requires a long period of time, from 2 to 4 weeks, for re-alkalization by passing electricity through the concrete. Furthermore, all of these typical carbonation countermeasures are carried out after the concrete has deteriorated to an advanced stage, and require repairs to be made to large cross-sections where the concrete is exposed to the outside air.

The present invention was made in consideration of the above problems, and its purpose is to provide a capsule admixture that is added to a cement composition and is useful as a carbonation suppression measure without requiring subsequent application.

The capsule admixture of the present invention, which is intended to achieve the above object, is a capsule admixture for addition to a cement composition, and is characterized by having a shell portion that holds a re-alkalinization solution inside and retains the re-alkalinization solution at an alkaline pH equal to or higher than a predetermined value, and disintegrates in other pH ranges to leak the re-alkalinization solution.

According to this configuration, the cement composition, which is originally alkaline, is neutralized by a carbonation reaction after hardening, and when the pH falls below the above-mentioned predetermined value, the shell of the admixture added to the hardened cement product collapses and the re-alkalization solution leaks out. This causes the hardened cement product to be re-alkalized inside, preventing the hardened cement product from peeling off or losing its cross-section, and improving its durability. This re-alkalization of the hardened cement product is carried out gradually from the surface of the hardened cement product as the hardened cement product is neutralized, so it is possible to extend the period until the carbonation reaches the reinforcing bars, and it is possible to effectively improve the durability of the hardened cement product without carrying out any subsequent construction work.

Another aspect of the present invention is that the predetermined value is pH 8 to pH 10.

According to this configuration, the cement composition, which originally shows an alkalinity of more than pH 10, is neutralized by a carbonation reaction after hardening, and when the pH becomes less than pH 8 to pH 10, the shell of the admixture added to the hardened cement product collapses and the re-alkalization solution leaks out, thereby re-alkalizing the hardened concrete product. This pH value may be, for example, a constant pH of 10, or may be set at multiple values between pH 8 and pH 10. In particular, if multiple pH values for shell collapse are set, among multiple admixtures added to a certain (specific) region of the hardened cement product, for example, the shell that collapses at pH 10 collapses first and the re-alkalization solution leaks out, and then when the region becomes pH 8, the shell of the remaining admixture collapses and the re-alkalization solution leaks out. In other words, if multiple pH values for shell collapse are set, as the neutralization of the hardened cement product progresses, re-alkalization is performed multiple times each time the pH value of the hardened cement product falls below the set pH value, making it possible to effectively improve the durability of the hardened cement product.

A further configuration of the present invention is characterized in that the particle diameter of the shell portion is 0.05 mm to 0.2 mm.

According to this configuration, by setting the particle size of the shell part of the admixture to 0.05 mm to 0.2 mm, the admixture can be easily mixed into the cement composition. In addition, when added to a finishing material such as mortar, the shell part is approximately spherical, which improves the viscosity of the cement composition compared to when sand is used alone, improving adhesion and improving workability such as trowel finishing.

A further configuration of the present invention is that the thickness of the shell portion is 0.01 mm to 0.05 mm.

According to this configuration, by setting the film thickness of the shell of the mixture to 0.01 mm to 0.05 mm, it can be reliably collapsed at a specified pH value. In addition, by setting the film thickness thin, it is possible to reduce the amount of collapsed shell that becomes foreign matter in the hardened cement product after collapse, so it is possible to ensure the strength of the hardened cement product after the shell collapses.

As explained above, according to the present invention, as the carbonation of the hardened cement product progresses, re-alkalization occurs inside the hardened cement product, and this re-alkalization occurs gradually from the surface of the hardened cement product to deeper layers, so that no subsequent construction is required and carbonation suppression measures can be implemented over the long term.

FIG. 1 is a cross-sectional view showing one embodiment of a capsule admixture of the present invention.

One embodiment of the capsule admixture of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a cross-sectional view of the capsule admixture 1 of this embodiment. This capsule admixture 1 is added to a cement composition, so-called ready-mix concrete, and mixed, and the mixed cement composition is used as cement paste, mortar, and concrete. This capsule admixture 1 has a roughly spherical shell 2 with a hollow interior. This shell 2 is made of, for example, a synthetic resin or a natural polymer, and has an outer diameter (particle size) of 0.05 mm to 0.2 mm, and a film thickness of the shell 2 of 0.01 mm to 0.05 mm.

The shell 2 is filled with a re-alkalization solution 3 that allows the hardened cement material to be re-alkalized. The solute of this re-alkalization solution 3 can be a base (a substance that gives off hydroxide ions when dissolved in water) with a pH of 10 or higher, and among these, an aqueous solution of potassium carbonate or sodium carbonate, which is strongly alkaline, is preferable. When the shell 2 collapses in the hardened cement material, the re-alkalization solution 3 leaks into the hardened cement material, and the hardened cement material in the vicinity is re-alkalized.

The most characteristic feature of the capsule admixture 1 of this embodiment is that the shell 2 collapses at a predetermined pH value. For example, a pH value of pH 8 to pH 10 is considered appropriate for the collapse of the shell 2. Since the re-alkalinization solution 3 is enclosed inside the shell 2, if the shell 2 collapses at a predetermined pH value, the hardened cement product is re-alkalized as described above. The hardened cement product is generally neutralized by spraying a 1% ethanol solution of phenolphthalein onto the hardened cement product, and the part that is reddish purple (alkaline at about pH 10 or higher) is judged to be an unneutralized part, and the part that is not colored is judged to be a neutralized part. In order to conform to this judgment of the neutralization of the hardened cement product and to re-alkalize the hardened cement product that has been neutralized (or judged to be neutralized), the collapse pH value of the shell 2 is set to pH 8 to pH 10.

The pH value at which the shell 2 collapses can be set to only one specific pH value, as described above, or multiple pH values can be set. For example, if only one pH value at which the shell 2 collapses is set, the shell 2 can be reliably collapsed only when the pH value of the hardened cement product falls below the collapse pH value, and the hardened cement product can be re-alkalized, and the development and manufacturing costs of the shell 2 can be reduced. On the other hand, if multiple pH values at which the shell 2 collapses are set, different shells 2 can collapse and re-alkalize the hardened cement product every time the pH value of the hardened cement product falls below the multiple collapse pH values. That is, as an example, the first re-alkalization is performed when the pH value of the hardened cement product in a certain region becomes less than pH 10, the second re-alkalization is performed when the pH value of the hardened cement product in that region becomes less than pH 9, and finally the third re-alkalization is performed when the pH value of the hardened cement product in that region becomes less than pH 8. In this way, the neutralization of the hardened cement product can be suppressed for a long period of time, and the durability of the hardened cement product can be maintained for a long time.

The cement composition to which the capsule admixture 1 is added is a mixture of cement, water, admixtures, and various aggregates. The cement used in this cement composition is an inorganic binder that exhibits hardening when mixed with water, and in this embodiment, hydraulic cement is used. As the hydraulic cement, plain cement such as ordinary Portland cement, hydraulic lime, Roman cement, and natural cement may be used, or mixed cement such as lime-mixed cement and mixed Portland cement may be used.

For example, by adding capsule admixture 1 having a roughly spherical outer diameter to a finishing cement composition such as mortar that uses sand as fine aggregate, the viscosity of the cement composition is improved compared to a composition that does not contain capsule admixture 1, which improves adhesion during trowel finishing and improves workability.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[Design example]
The materials listed in Table 1 below can be used for the cement composition. Ordinary Portland cement is used for the cement, and water, fine aggregate, and coarse aggregate are mixed to prepare ready-mix concrete (cement composition). For the admixture, an air-entraining water-reducing agent (AD) having a cement dispersion function and an air-entraining function, and an air content regulator (AE) for adjusting the amount of air entrained are used. For the capsule admixture, two types were set: capsule admixture B1 with a particle size of 0.05 mm and a film thickness of 0.01 mm, and capsule admixture B2 with a particle size of 0.2 mm and a film thickness of 0.05 mm. Both capsule admixtures were filled with an aqueous potassium carbonate solution.

The amount of capsule admixture added is set according to Table 2 below. Here, a comparative example is one that does not use capsule admixture, Examples 1 to 3 are ones in which capsule admixture B1 is added at 0.5 Vol%, 1.0 Vol%, and 2.0 Vol% relative to the amount of cement paste (= cement + water), and Examples 4 to 6 are ones in which capsule admixture B2 is added at 0.5 Vol%, 1.0 Vol%, and 2.0 Vol%, respectively.

The physical properties of the cement composition are shown in Table 3 below. The table shows the design strength, coefficient of variation, target strength, target slump, and target air content.

The amounts and ratios of materials excluding capsule admixtures are shown in Table 4 below. The symbols in Table 4 follow those in Table 1. In addition, s/a in the table is the fine aggregate ratio (= fine aggregate amount/total bone material x 100). In addition, in Table 4, the amounts of admixtures are shown as mass % relative to the amount of cement.

The mixing conditions for the cement composition are as follows. That is, a forced twin-screw mixer with a nominal capacity of 50 L was used to mix 30 L of material to prepare the cement composition. The mixing procedure was as follows: first, cement (C), capsule admixtures (B1, B2), fine aggregate (S) and coarse aggregate (G) were added to the forced twin-screw mixer with a nominal capacity of 50 L and mixed for 15 seconds, water (W) was added and mixed for an additional 30 seconds. This mixture was scraped off, and then admixtures (AD, AE) were added and mixed for an additional 90 seconds, and then discharged to prepare the cement composition.

The properties of the cement composition and its hardened product thus obtained can be tested according to Table 5 below. As the fresh properties of the cement composition, the slump amount was measured according to JIS A 1101, and the air content was measured according to JIS A 1128. As the hardened properties of the concrete hardened product, the compressive strength was measured according to JIS A 1108, and the accelerated state of carbonation was measured according to JIS A 1152 and JIS A 1153. The specimens for compressive strength were cylindrical bodies with a diameter of 10 cm and a height of 20 cm, which were cured in standard water according to JIS A 1132, and their age was set to 28 days. For the test of the accelerated state of carbonation, the aforementioned phenolphthalein ethanol solution was used, and the accelerated period was set to 91 days.

Although the results do not show specific numerical values, it was confirmed that all of the examples, including the comparative examples, achieved the target values for slump, air content, and compressive strength. On the other hand, the carbonation depth was smaller in all of the examples in which the capsule admixture of the present invention was added than in the comparative examples in which no capsule admixture was used. In addition, a comparison between the examples showed that the greater the amount of capsule admixture added, the smaller the carbonation depth, i.e., the greater the carbonation suppression effect. In addition, a comparison between capsule admixture B1 and capsule admixture B2 showed that capsule admixture B2 had a greater carbonation suppression effect even with the same amount added. This is thought to be due to the difference in particle diameter (diameter) and film thickness of the shell, which results in a larger volume of the inclusion, i.e., the above potassium carbonate aqueous solution, in capsule admixture B2 than in capsule admixture B1.

In this way, in the cement composition containing the capsule admixture of the present invention, the cement composition, which is originally alkaline, is neutralized by a carbonation reaction after hardening, and when the pH becomes less than the above-mentioned predetermined value, the shell 2 of the capsule admixture 1 added to the hardened cement product collapses and the re-alkalization solution 3 leaks out. This is thought to re-alkalize the hardened cement product inside, preventing the hardened cement product from peeling off or losing its cross-section, and improving its durability. This re-alkalization of the hardened cement product is carried out gradually from the surface of the hardened cement product as the hardened cement product is neutralized, making it possible to extend the period until the carbonation reaches the reinforcing bars, and effectively improving the durability of the hardened cement product.

In addition, a cement composition that is originally alkaline with a pH of over 10 is neutralized by a carbonation reaction after hardening, and when the pH falls below 8 to 10, the shells 2 of the capsule admixture 1 added to the hardened cement product collapse, causing the re-alkalization solution 3 to leak out, and the hardened concrete product is re-alkalized. In particular, if multiple pH values for the collapse of the shells are set, as the neutralization of the hardened cement product progresses, re-alkalization is performed multiple times each time the pH value of the hardened cement product falls below the set pH value, making it possible to effectively improve the durability of the hardened cement product.

In addition, by setting the particle size of the shell part 2 of the admixture to 0.05 mm to 0.2 mm, the admixture can be easily mixed into the cement composition. Furthermore, when added to a finishing material such as mortar, the shell part 2 is approximately spherical, which improves the viscosity of the cement composition compared to when sand is used alone, improving adhesion and improving workability such as trowel finishing.

In addition, by setting the film thickness of the shell 2 of the mixture to 0.01 mm to 0.05 mm, it can be reliably broken down at a specified pH value. Furthermore, by setting the film thickness thin, it is possible to reduce the amount of broken down shell that becomes foreign matter in the hardened cement product after the break down, so it is possible to ensure the strength of the hardened cement product after the shell breaks down.

The above describes the capsule admixture 1 according to the embodiment, but the present invention is not limited to the configuration described in the above embodiment, and various modifications are possible within the scope of the gist of the present invention. For example, in the above example, the amount of capsule admixture 1 added was 0.5 Vol% to 2.0 Vol% relative to the amount of cement paste, but the amount of capsule admixture added according to the present invention is not limited to this range.

1 Capsule admixture 2 Shell 3 Re-alkalinization solution

Claims (3)

In an encapsulated admixture for addition to a cement composition,
A shell portion is provided inside the re-alkalized solution, and the re-alkalized solution is retained at an alkaline pH of a predetermined value or more , and the shell portion is disintegrated at other pH ranges to leak the re-alkalized solution;
A capsule admixture characterized in that the predetermined value is set in a range of pH 8 to pH 10 . The capsule admixture according to claim 1 , characterized in that the particle diameter of the shell portion is 0.05 mm to 0.2 mm. The capsule admixture according to claim 1 or 2 , characterized in that the shell has a thickness of 0.01 mm to 0.05 mm.

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