JPH0541581B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cement admixture for the purpose of reducing or preventing efflorescence of Portland cement mortar or concrete. Cement mortar or concrete is inherently susceptible to efflorescence, which often impairs the appearance of buildings and causes tiles and paint to peel off. Usually, efflorescence is said to occur due to two causes based on its components. One is the Ca released by hydrolysis of the calcium silicate phase.
(OH) ₂ is carbonated on the concrete surface and becomes _CaCO3
The second is that it becomes a white stain.
Na and K contained in cement, aggregate, mixing water, etc.
Alkali metals and sulfate radicals elute onto the surface of mortar and concrete, become alkali metal sulfates, and grow as crystals. Therefore, conventional methods for preventing efflorescence include:
If Ca(OH) ₂ is the cause, activated silica,
It has been proposed to add higher fatty acids that form salts that are insoluble with calcium, and in cases where alkali metal sulfates are the cause, barium hydroxide or the like. Although these methods all attempt to prevent efflorescence by fixing the component that causes efflorescence as an insoluble salt, sufficient effects cannot be obtained. Activated silica cannot fix sulfate groups or alkali metals, and barium hydroxide cannot
Since Ca(OH) ₂ cannot be fixed,
Although it is possible to use a mixture of these, it is not sufficient. As a result of intensive research into a method for simultaneously reducing and preventing efflorescence caused by Ca(OH) ₂ and alkali metal sulfates, the inventor has found a method that is highly effective, although the reason is not clear. This is what I found. That is, the present invention is directed to a mortar of Portland cement or concrete efflorescence, which contains molded anhydrite and a water-soluble organic polymeric substance, and which does not substantially contain calcium aluminate, polymer emulsion, and gypsum hemihydrate. is an inhibitor,
All of these were achieved by the combined use of appropriate amounts of components that, when used alone, do not have the ability to fix Ca(OH) ₂ or alkali metal sulfates as insoluble salts. The present invention will be explained in more detail below. First, molded anhydrite and water-soluble organic polymer substances have no effect when added alone, but when used together in appropriate amounts, they have become effective in preventing the occurrence of efflorescence. be. Type anhydrite is obtained by heat-treating gypsum at 350° C. or higher, or by-product type anhydrite generated by hydrofluoric acid generation, and is preferably added in an amount of 1 to 8% by weight based on the cement. If it is less than 1% by weight, the effect of addition is small, and if it exceeds 8% by weight, efflorescence will occur. The preferred range of use is 2 to 6% by weight based on cement. The powderiness of molded anhydrite does not significantly affect the efflorescence prevention effect, and a Blaine value of about 4000 cm ² /g is sufficient. Examples of gypsum include gypsum hemihydrate in addition to type anhydrite, but in the present invention, only type anhydrite exhibits an efflorescence-preventing effect. Examples of water-soluble organic polymer substances include polyvinyl acetate, polyvinyl alcohol and its modified and partially saponified products, polyethylene oxide, and cellulose ethers such as methylcellulose. The appropriate amount of the water-soluble organic polymer substance to be added varies depending on its type, degree of polymerization, average molecular weight, etc., but sufficient effects can be exhibited at an amount of 0.05 to 0.5% by weight based on cement. If it is less than 0.05% by weight, the effect of addition is small, and if it exceeds 0.5% by weight, the strength will decrease significantly and efflorescence will easily occur. None of these water-soluble organic polymer substances are specially prepared, and commercially available products may be used. In the present invention, the efflorescence prevention effect cannot be seen unless it is water-soluble, and if a water-soluble organic polymer substance such as an emulsion is mixed, the efflorescence prevention effect of the present invention can be achieved by using a combination of molded anhydrite and a water-soluble organic polymer substance. No effect seen. The product of the present invention is further effective in preventing efflorescence when combined with activated silica, which has been known to be effective. The most preferable is one that has been heat-treated at about °C, and the effect can be achieved by adding a small amount of at most 10% by weight or less to the cement. The cement that is the object of the present invention is normal, early strength,
These are a variety of mixed cements, including ultra-early strength, moderate heat, and white Portland cement, as well as silica, fly ash, and blast furnace slag cement. The present invention will be explained below with reference to Examples. Example 1 Γ-type anhydrite (・CaSO ₄ )...Gypsum by-product when hydrofluoric acid is generated (blane 4050cm ² /g) Γ Water-soluble organic polymer material Polyvinyl acetate (PVAc)... Commercial product with degree of polymerization 1700 ( (manufactured by Denki Kagaku Kogyo Co., Ltd.) Polyvinyl alcohol (PVA)...Product name: Denka PVA K-17) (manufactured by Denki Kagaku Kogyo Co., Ltd.) Modified polyvinyl alcohol (MPVA)...
…Product name: “Denka HV Polymer” (manufactured by Denki Kagaku Kogyo Co., Ltd.) Partially saponified polyvinyl alcohol (SPVA)
...Product name "Denka PVA B-17" (manufactured by Denki Kagaku Kogyo Co., Ltd.) Polyethylene oxide ...Product name "PEO"
-1" (manufactured by Steel Chemical Co., Ltd.) Polyethylene oxide...Product name: "PEO
-18'' (manufactured by Steel Chemical Co., Ltd.) Methyl cellulose (MC-25)...Product name: ``Marporose Type M25'' (manufactured by Takemoto Yushi Co., Ltd.) Methyl cellulose (MC-2000)...Product name: ``Marporose'' Type M2000 (manufactured by Takemoto Yushi Co., Ltd.) Using the above ・CaSO ₄ and water-soluble organic polymer substances, changing the mixing ratio and adding them to ordinary Portland cement, a 1:3 mortar (using FM290 natural sand) The table flow according to JIS R-5201 was mixed by adding water to 200 ± 5 mm,
A test piece of 10φ×20cm was molded. After 48 hours, cut the top 3cm of the test piece into rounds and leave it for 24 hours.
After drying at 100°C, the sides were coated with paraffin to prepare a test piece for the efflorescence test. Efflorescence occurs indoors at 5°C.
The specimen was immersed to a depth of 1.5 cm in a bath containing oil to prevent carbonation on the surface of an aqueous solution containing 2% by weight of Na ₂ SO ₄ and excess Ca(OH) ₂ , and the occurrence of efflorescence was measured. If efflorescence occurs, remove the ingredient by
Qualitative analysis was performed using line diffraction. In addition, the same mortar was molded into a 4 x 4 x 16 cm test piece, and the compressive strength after 28 days of standard curing was also measured at the same time. Table 1 shows a list of blending ratios and test results. Incidentally, the observation of the occurrence of efflorescence was carried out two weeks after immersion, and the judgment was made as follows. A lot (×)...Crystal growth on the entire surface Little (△)...Crystal growth on the outside of the specimen Slight (〇)...Slight white coloring on the outside or center None (◎)...No occurrence at all・CaSO ₄ and water-soluble organic polymer substances were added to the cement in proportion. The water-cement ratio of the mortar was 50-60%. As is clear from Table 1, no effect was observed when CaSO ₄ or a water-soluble organic polymer substance was added alone (Experiments Nos. 1 to 8), and even when both were used together, they were not added in appropriate amounts (Experiments Nos. 1 to 8). No.14, 15 and 20) The effect will be smaller. Note that Experiment No. 35 is a reference example.

【table】

[Table] Example 2 Type anhydrite made by calcining dihydrate gypsum at 400℃ for 2 hours (Blaine value 9800 cm ² /g), polyethylene oxide product name "PEO-1", blast furnace slag powder (Blaine value 4010 cm ² /g) g) and activated clay at 800℃
(Brain value 5080cm ² /g)
Mix it with the concrete shown in Table 2 by changing the amount of addition (note: the amount added to the cement) and make 10φ×20cm.
A test piece was molded. After 48 hours, the upper part was cut to a thickness of 5 cm, the sides were coated with paraffin, and then placed in the aqueous solution of Example 1 in a room at 5°C.
The material was immersed to a depth of 2.5 cm and observed for efflorescence on the 28th day of age.
The results are shown in Table 3. The 48-hour strength and the 28-day strength of the standard curing material were measured using a 10φ x 20cm test piece, and if efflorescence occurred, its components were qualitatively analyzed by X-ray diffraction.

【table】

【table】

[Table] As is clear from Table 3, there is no effect when activated silica is added alone (Experiments Nos. 36 to 40), but when it is used in combination with the product of the present invention (Experiments Nos. 41 to 46), the effect increases significantly. Example 3 The same procedure as in Example 1 was conducted except that the formulations in Table 4 were used. The results are also shown in Table 4.

[Table] *1 is hemihydrate gypsum, *2 is dihydrate gypsum.

Claims (1)

[Claims] 1. An efflorescence inhibitor for Portland cement mortar or concrete, which contains type 1 anhydrite and a water-soluble organic polymeric substance, and is substantially free of calcium aluminate, polymer emulsion, and gypsum hemihydrate.