JPH0154296B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing high strength concrete with improved durability. The term "high-strength concrete" as used in the present invention is a general term for mortar, concrete, and glue concrete, and means concrete having a design strength of 600 Kgf/cm ² or more. Conventionally, to increase the strength of concrete, high-performance water reducers have been used, which have minimal side effects such as excessive setting delay or air entrainment even when added in relatively large amounts, and have high dispersibility without adversely affecting the hardening of concrete. This is done by adding a dispersant that can exhibit this effect and a larger amount of dihydrate gypsum than the JIS standard value to create concrete with a low water-cement ratio. However, concrete with a low water-to-cement ratio containing such a high-performance water reducer and a large amount of dihydrate gypsum cracks when exposed to outdoor curing, and expands when cured in water. The disadvantage was that the durability was significantly reduced. The present inventors have discovered that in order to solve these drawbacks, it is sufficient to add a small amount of specific oxycarboxylic acids, and have completed the present invention. That is, the first invention of the present invention provides that when producing concrete with a low water-cement ratio to which a high performance water reducing agent and a large amount of dihydrate gypsum are added, , 0.05~
The second invention adds 0.7% by weight of one or more selected from citric acid, tartaric acid, malic acid, and salts of these acids (hereinafter simply referred to as citric acid, etc.). This is a method for producing high-strength concrete with improved durability, characterized by further adding at most 1% by weight of alkali metal carbonate. The present invention will be explained in detail below. The high-performance water reducing agent in the present invention has the above-mentioned properties, and from the chemical structure of its main component, it can be used as a polyalkylaryl sulfone such as a high condensate salt of naphthalene sulfonic acid or its derivatives and formalin. It is roughly divided into acid salt type and high condensate type of triazine derivatives such as melamine formalin resin sulfonate.
These commercially available products are all trade names, but Kao Soap Co., Ltd.'s ``Mighty 100'' and ``Mighty
150'', Takemoto Yushi Co., Ltd. ``Pole Fine 510N'', Sanyo Kokusaku Pulp Co., Ltd. ``Sunflow PS'', Pozoris Bussan Co., Ltd.
These include "NL-1450", "NL-4000", and Showa Denko's "Melmento". Normally, these high performance water reducers are 600Kgf/cm ²
When manufacturing concrete with the above amount, the active ingredients (in terms of solid content) are calculated based on the amount of cement in the concrete.
0.5% by weight or more is added, and the water-cement ratio is 35.
% or less. However, with concrete to which only a high performance water reducer has been added, not only does the drop in slump significantly increase, making it difficult to work, but when cast-in-place concrete is used, it is cured as it is poured and cannot be sufficiently cured. Therefore, depending on the weather conditions, the strength is often much lower than the design strength. Further, even when steam curing is performed, the initial hydration is promoted, so that subsequent strength growth becomes small and high strength cannot be obtained. Therefore, in the present invention, in order to solve the drawbacks of concrete in which such a high-performance water reducing agent is simply added, a larger amount of dihydrate gypsum than the JIS standard value is mixed. The dihydrate gypsum used is that which is normally used as gypsum for cement, and its fineness is sufficient if it has a Blaine value of about 3000 cm ² /g, but it is preferably acicular or hexagonal plate-shaped crystals. is being destroyed. To add it to concrete, it can be crushed simultaneously with cement clinker, crushed separately with cement clinker and then mixed, or further blended with Portland cement.
Alternatively, this can be done by adding it during mixing of concrete. The blending amount of dihydrate gypsum is preferably about 17% by weight at most, exceeding the JIS standard value, based on CaSO ₄ equivalent of the total dihydrate gypsum in the cement. If the amount of dihydrate gypsum added is less than the JIS standard value, the amount of ettringite produced will be small and the effect of increasing strength will be small, and the amount of ₁₇
If it exceeds % by weight, unreacted gypsum will remain even if citric acid or the like described later is added, which is not preferable. However, gypsum dihydrate normally reacts with the aluminate phase in cement to produce ettringite, but the reaction proceeds slowly under conditions of a low water-cement ratio, so if the amount added is increased, It began to proceed in combination with the reaction of the silicate phase,
Unreacted plaster tends to remain. Therefore, the above-mentioned durability problem arises. According to the inventor's experiments, when added in excess of the JIS standard value,
Due to outdoor exposure and curing, cracks are more likely to form.
It was observed that when the content exceeded 100% by weight in terms of CaSO ₄ , significant expansion occurred and the strength decreased. In order to solve such durability problems, the present invention further adds citric acid or the like to delay the hydration of the silicate phase, and during this time, the reaction between the dihydrate gypsum and the aluminate phase (the reaction of ettringite) is carried out. In other words, the objective is to complete the reaction between the aluminate phase and the silicate phase, allowing the reaction between the aluminate phase and the silicate phase to proceed separately, so that no unreacted gypsum remains. Ettringite produced through such a reaction promotes the compaction of the structure by filling the voids in the concrete that has not yet hardened, and at the same time, the water in the silicate phase that is subsequently generated The sums are added together to obtain high intensity. Furthermore, since the formation of ettringite incorporates a large amount of crystallization water, this ettringite itself produces an effect similar to the pressurized dehydration effect that is generally used to increase the strength of concrete. Examples of citric acid include citric acid, tartaric acid, malic acid, and their salts such as sodium, potassium, lithium, calcium, strontium, magnesium, zinc, iron, copper, and lead, and one or more of them Citric acid, tartaric acid and their sodium and potassium salts, malic acid and sodium malate are preferred, but the most preferred are citric acid and their sodium and potassium salts. It's salt. These citric acids and the like have the effect of preventing slump loss (workability) in concrete to which a high performance water reducing agent is added, but improve the durability of concrete in which a large amount of dihydrate gypsum is mixed. The amount added is 0.05 to 0.7% by weight, preferably 0.1 to 0.7% by weight, based on the total amount of cement and dihydrate gypsum in concrete.
It is 0.5% by weight. If it is less than 0.05% by weight, it will be difficult to adjust the hydration pattern, and if it is less than 0.7% by weight, it will be difficult to adjust the hydration pattern.
If it exceeds % by weight, the hydration of the silicate phase will be significantly delayed, which is not preferable. As described above, the first invention is to add a specific amount of citric acid, etc. to concrete containing a high performance water reducing agent and a large amount of dihydrate gypsum, thereby improving workability and exposure curing. It is possible to obtain highly durable, high-strength concrete that prevents cracking and expansion in water. In the second invention, an alkali metal carbonate is added in order to promote the slump loss prevention effect of citric acid, etc. without impairing the expression of such effects, and to improve the rise of the silicate phase after it starts to hydrate. The amount added is 1% by weight based on the total amount of cement and dihydrate gypsum in concrete.
If this value is exceeded, the strength will decrease or efflorescence will occur. Alkali metal carbonates include potassium, sodium,
One or more selected from lithium carbonates and bicarbonates are used. The components according to the present invention described above may be added to cement in advance, or may be added at the time of mixing concrete. The types of cement used in this case are various portland cements and mixed cements, and in the case of mixed cements, it is the same as before that the amount of cement per unit must be increased to obtain the same strength. The addition of appropriate amounts of fly ash, activated silica, and blast furnace slag, especially in coexistence with alkali carbonates, increases pozzolanic activity and contributes to strength development. Further, various polymers, sulfur, fibers, etc. may be mixed. The present invention is applicable to general concrete work and applications requiring abrasion resistance and durability, such as dam excavation road aprons, sabo dams, coasts, river revetments, airport runways, etc.
It is highly effective in road construction, and can also be applied to the manufacture of concrete products such as piles and poles that require steam curing. Hereinafter, the present invention will be explained in more detail with reference to examples. Example 1 Mighty 150, a commercially available high-performance water reducer containing polyalkylaryl sulfonate as its main ingredient (Kao Soap Co., Ltd.)
Co., Ltd. product name) at 7.2Kg/ ^m3 , sodium citrate at 0.2% by weight relative to the total amount of cement and dihydrate gypsum, and the amount of dihydrate gypsum added was changed. Concrete was mixed according to the mixture shown in Table 1. Slump loss of concrete and 20℃, R.H65%
Table 2 shows the measurement results of compressive strength at 28 days old and the observation of cracking after 6 months of outdoor exposure and curing. Experiment Nos. 1, 2, 6, and 7 are comparative examples, and Experiments No. 3 to 5 are examples of the present invention. The cement used was ordinary Portland cement with an SO ₃ value of 2.0%, the dihydrate gypsum was a by-product from flue gas desulfurization and was crushed in a vibrating pot mill for 5 minutes, and the gravel was completely crushed stone. Sodium citrate was used dissolved in kneading water. Fine adjustments to the slump were made visually by adjusting the amount of water.

【table】

【table】

[Table] Yes.
As shown in Table 2, the comparative examples of Experiment Nos. 1 and 2 both exhibited small strength development, indicating that there was a significant decrease in strength due to air-dry curing. In the comparative example of Experiment No. 6, gypsum was added beyond the scope of the present invention, and it can be seen that it is inferior to the inventive example in terms of strength development and durability. In the comparative example of Experiment No. 7, the slump was significantly reduced and the durability was not improved. Example 2 Mixture of Experiment No. 4 (total dihydrate gypsum converted to CaSO ₄ 10
The same test as in Example 1 was conducted by changing the type and amount (external division) of citric acid etc. (adjusted to weight %). The results are shown in Table 3. Experiment Nos. 8 and 15 are comparative examples, and the others are examples of the present invention.

【table】

[Table] As shown in Table 3, in the comparative examples of Experiments No. 8 and 15, citric acid, etc. was added in a different range from the present invention, and in that case, the durability could not be improved or Strength decreases. Example 3 Using a commercially available high performance water reducing agent "Melment F-10" (trade name of Showa Denko Co., Ltd.) containing a high condensate of triazine derivatives as the main component, dihydrate gypsum was dissolved in CaSO ₄ min.
10% by weight, potassium citrate is calculated as 0.2% by weight based on the total amount of cement and dihydrate gypsum, and the type and amount of alkali carbonate added (total amount of cement and dihydrate gypsum) is determined according to the concrete mix in Table 4. Tests were conducted by changing the amount added (external addition amount). The results are shown in Table 5. Experiment No. 42 is a comparative example, and the others are examples of the present invention.

【table】

【table】

Claims (1)

[Claims] 1. When producing concrete with a low water-to-cement ratio by adding a high-performance water reducer and a large amount of dihydrate gypsum, the total amount of cement and dihydrate gypsum in the concrete should be 0.05 to 0.7% by weight citric acid, tartaric acid,
A method for producing high-strength concrete with improved durability, characterized by adding one or more selected from malic acid and salts of these acids. 2. When producing concrete with a low water-cement ratio by adding a high performance water reducer and a large amount of dihydrate gypsum, 0.05 to 0.7% by weight of citric acid is added to the total amount of cement and dihydrate gypsum in the concrete. , tartaric acid,
A method for producing high-strength concrete with improved durability, characterized by adding one or more selected from malic acid and salts of these acids, and at most 1% by weight of an alkali metal carbonate. .