JPH0159990B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for improving the durability of high-strength concrete. The term "high-strength concrete" as used in the present invention is a general term for mortar, glue concrete, and concrete, and refers to concrete having a design strength of 600 Kgf/cm ² or more. Conventionally, in order to produce high-strength concrete, a dispersant called a high-performance water reducer is added, which can exhibit high dispersibility without causing side effects such as excessive setting delay or air entrainment even when added in relatively large amounts. It is done by doing. However, high-strength concrete to which only a high-performance water reducing agent is added has the disadvantage that the designed strength cannot be obtained if it is cast in place, cured, and allowed to dry. In order to solve this problem, the present inventor developed various types of gypsum or high-strength admixtures mainly composed of gypsum.
It was confirmed that it is sufficient to add at least the JIS standard value for CaSO ₄ minutes, but on the other hand, cracks begin to appear during outdoor curing, and this is especially noticeable as the amount added and the age of the wood increases. I observed that it appeared over time. The present inventor has discovered that in order to improve the durability of such high-strength concrete, it is sufficient to add a small amount of calcium aluminate of oxycarboxylic acid or its salt, and has completed the present invention. . That is, in the present invention, when mixing concrete with a low water-to-cement ratio by adding a high-performance water reducing agent and a gypsum or a high-strength admixture mainly composed of gypsum, the total amount of cement and high-strength admixture is reduced. For,
This is a method for improving the durability of high-strength concrete, which is characterized by adding 0.01 to 1% by weight of oxycarboxylic acid or its salt and at most 10% by weight of calcium aluminate. 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 is broadly classified into polyalkylaryl sulfonate type and high condensate type of triazine derivative based on the chemical structural formula of its main component. These commercially available products include Kao Soap Co., Ltd.'s ``Mighty 100'' and ``Mighty 150'', all of which are trade names.
“Mighty HS”, Takemoto Yushi Co., Ltd. “Pole Huain”
510N'', Sanyo Kokusaku Pulp Co., Ltd.'s ``Sunflow PS'', Pozoris Bussan Co., Ltd.'s ``NL-1450'', ``NL-4000'', Showa Denko Co., Ltd.'s ``Melmento'', etc., and 600Kgf/
When producing high-strength concrete of cm ² or more, their active ingredients (solid content) are 0.5
Added more than 40% by weight, water-cement ratio less than 40%,
Preferably it is adjusted to 35% or less. High-strength admixtures include gypsum such as dihydrate gypsum, hemihydrate gypsum, anhydrite (type or mold), or 1 such as alum, silica, aluminum sulfate, etc. based on these gypsums.
It is made by adding seeds or two or more kinds. The fineness of the powder should be 3000 cm ² /g or more in Blaine value, but preferably the needle-shaped or hexagonal plate-shaped crystals are destroyed, and the amount added to the cement is according to the JIS standard as CaSO ₄ minutes. It is preferable that the amount exceeds this value and is up to 20% by weight. When CaSO ₄ min is below the JIS standard value, the amount of ettringite produced is small and the effect of increasing strength is small; when it exceeds 20% by weight, even if oxycarboxylic acid or its salt and calcium aluminate are added together, there is no effect. Durability cannot be improved because reactive gypsum remains. Commercially available high-strength admixtures include "Denka Σ-1000" by Denki Kagaku Kogyo Co., Ltd., "Onoda Σ-1000" by Onoda Cement Co., Ltd., and "Asano Super" by Nippon Cement Co., Ltd. Mitsukus" and Showa Mining Co., Ltd.'s product name "Daimitsukus". Oxycarboxylic acid or its salt means citric acid,
Refers to tartaric acid, malic acid, and their salts such as sodium, potassium, lithium, zinc, lead, copper, magnesium, strontium, and calcium, which are based on the total amount of cement and high-strength admixtures.
It is added in an amount of 0.01 to 1% by weight. Citric acid, tartaric acid, and their sodium and potassium salts are preferred in terms of performance, economy, and non-toxicity. The action of oxycarboxylic acid or its salt is to control the ettringite production reaction between the high-strength admixture and calcium aluminate and the hydration reaction of the calcium silicate phase to improve crack durability during outdoor curing. If the amount added is other than the above, this effect will be small or the strength will be reduced. In other words, when only high-strength admixtures are added,
The formation reaction of ettringite proceeds slowly under conditions of a low water-to-cement ratio and proceeds in parallel with the hydration reaction of the calcium silicate phase, making it easy for unreacted gypsum to remain and significantly reducing the durability described above. Deteriorate. In particular, the more the amount added exceeds the JIS standard value, the more cracks will occur. However, if oxycarboxylic acid or its salt is used in combination with this, the hydration of the silicate phase can be delayed and the generation of ettringite can be completed during that time. In other words, the ettringite generation reaction and the reaction of the silicate phase can be completely separated. Since the process can be progressed in a consistent manner, the desired objective can be achieved. In addition, the effects of oxycarboxylic acids or their salts include improving poor workability, such as large slump loss, which is a drawback of concrete with high-performance water reducing agents added, and adding large amounts of high-strength admixtures to cement. It is possible to suppress false coagulation and increase normal coagulation. In addition, in order to promote these effects of the oxycarboxylic acid or its salt, sodium, lithium, potassium carbonate or bicarbonate is added in an amount of at most 1% by weight based on the total amount of cement and high-strength admixture. This is desirable. Calcium aluminates include C ₃ A, CA,
C ₁₂ A ₇・C ₁₁ A ₇・CaaF ₂ , C ₃ A ₃・CaF ₂ , C ₄ A ₃
(C represents CaO, A represents Al ₂ O ₃ , SO ₃ ), etc., which are melted in these composition ranges and rapidly cooled to vitrify a part or most of them, and furthermore, alumina cement, etc. are used. C ₁₁ A ₇・CaF ₂ or
C ₃ A ₃ · CaF ₂ itself has the effect of retarding the hydration of calcium silicate, so when used in combination with type anhydrite or a high-strength admixture containing it as a main component, This cannot be recommended as there is a risk of deterioration. _C3A is contained in cement at a content of about 5 to 10% by weight, but by adding calcium aluminate, the formation of ettringite is made faster and separation from the hydration reaction of the silicate phase is facilitated. , which improves crack durability and at the same time promotes the development of initial strength. Calcium aluminate is added in an amount of at most 10% by weight based on the total amount of cement and high-strength admixture, and the above effect is exhibited as the amount added increases, but the quantitative balance with the high-strength admixture is 10% by weight. It is meaningless to add more than % by weight. The fineness of calcium aluminate may be at least the same level as that of cement, and it is preferable that the fineness of calcium aluminate is finer if the calcium aluminate has low hydration activity, such as CA ₂ . As described above, the present invention combines oxycarboxylic acid or its salt and calcium aluminate when adding a high-performance water reducing agent and a high-strength admixture and kneading the mixture with high-strength concrete having a low water-to-cement ratio. It is something. According to the present invention, the cracking durability of high-strength concrete can be improved, and the initial strength development and workability can also be improved at the same time. The present invention will be explained below with reference to Examples. Example 1 Cement with different gypsum contents was prepared by changing the type and amount of high-strength admixtures to ordinary Portland cement containing 3% by weight of SO ₃ . To this, the type and amount of oxycarboxylic acid or its salt and calcium aluminate were changed, and the first
Concrete was mixed using the concrete mix shown in the table, a 10 cm x 20 cm specimen was prepared, the material was cured outdoors for 1 year and 6 months, and cracks were observed. The results are shown in Table 2. High-strength admixtures include dihydrate gypsum made from flue gas desulfurization for cement, hemihydrate gypsum heat-treated at 150℃,
Furthermore, soluble gypsum heat-treated at 200°C and gypsum (・CaSO ₄ ) generated by hydrofluoric acid generation, ・CaSO ₄
The powder degree of gypsum and dihydrate was 6000 cm ² /g, and the degree of fineness of gypsum hemihydrate and soluble anhydrite was 10000 cm ² /g or more. Calcium aluminate C ₃ A and CA, C ₄ A ₃
using pure chemicals at 1450℃, C ₁₁ A ₇・CaF ₂ at 1250
They are made by firing each at ℃,
C ₁₂ A ₇ , C ₃ A ₃ / CaF ₂ is made by mixing quicklime, bauxite and fluorite, melting it at 1600℃ in an electric furnace, cooling it rapidly or gradually, and then crushing it to a powder degree of 4000±200.
It was adjusted to cm ² /g. A commercially available alumina cement was used as is.

[Table] The high-performance water reducing agent used is "Mighty 150," a polyalkylaryl sulfonate-based product manufactured by Kao Soap Co., Ltd., and the oxycarboxylic acid or its salt is dissolved in water and simply added as an external additive. , Calcium aluminate was added in place of sand. In addition, if the slump deviated from the target slump, water was simply added and the concrete was mixed while adjusting the slump.

【table】

[Table] ○ The amount of oxycarboxylic acid or its salt and calcium aluminate added is the ratio to the total of cement and high-strength admixture.
Next, the concrete from Experiment Nos. 1 to 19 was heated to 15°C.
A specimen of 10 cm x 20 cm was prepared by kneading it, and after being demolded, it was left to cure in a room at 15°C, and its compressive strength was measured on 7 and 28 days. The results are shown in Table 3.

[Table] Example 2 In the concrete formulation shown in Table 1, the high performance water reducing agent was a triazine derivative high condensate based Showa Denko K.K.
Added 5.76Kg/ ^m3 to the product name "Melment F-10", making the unit water volume 144Kg/ ^m3 (water/cement ratio 30).
%). And Experiment No. in Table 2. Using the concrete of No. 5, alkali metal carbonate was further added to the total amount of cement and high-strength admixture, and the change in slump over time was measured in a room at 15℃, and 10〓×20
28 days compressive strength with cm test piece and 1 year 6
We observed cracks in the specimens that had been cured outdoors for several months.
The results are shown in Table 4.

[Table] There was an occurrence of scratches.

Claims (1)

[Claims] 1. When mixing concrete with a low water-to-cement ratio by adding a high-performance water reducer and a gypsum or a high-strength admixture mainly composed of gypsum, the total amount of cement and high-strength admixture should be 0.01~ A method for improving the durability of high-strength concrete, characterized by adding 1% by weight of oxycarboxylic acid or its salt and at most 10% by weight of calcium aluminate.