JPH0139983B2 - - Google Patents

Description

[Detailed description of the invention]

Prestressed concrete is one of the developments in concrete in recent years, and prestressed concrete is required to have little concrete creep. However, in concrete using conventional cement, even if the water-cement ratio is reduced, not much can be expected. The present inventors have completed the present invention as a result of intensive research focusing on the fact that blast furnace cement systems have slightly less creep. The chemical composition of blast furnace slag is relatively similar to Portland cement, and the water slag obtained by rapidly cooling it has latent hydraulic properties, and the addition of slaked lime or Portland cement as a stimulant accelerates the hardening reaction. It has been known since ancient times. It is also known that the addition of gypsum will cause hardening. Therefore, the present inventors attempted to reexamine a hardened material made by mixing three materials: flue gas desulfurization gypsum, ordinary Portland cement, and blast furnace slag powder.
(i) When blast furnace slag powder accounts for around 70% (weight ratio, same below) of the whole, the surface becomes powdery. (ii) If only blast furnace slag powder and gypsum are used, the surface hardness is weak and wear resistance is poor. (iii) )When gypsum accounts for more than 20% of the total,
It was confirmed that expansion cracks tend to occur when left in water for a long period of time, and (iv) large shrinkage occurs when using only blast furnace slag powder and Portland cement without the addition of gypsum. Based on the above knowledge, the present inventors conducted various studies and found that blast furnace cement (GCS), which is the most preferable blend of 60% blast furnace cement powder, 30% Portland cement, and 10% gypsum, exhibits excellent properties with less creep. It was discovered that a blast furnace cement containing 65 to 35% blast furnace slag powder, 25 to 55% Portland cement, and 5 to 15% gypsum can sufficiently exhibit the desired properties. However, the above-mentioned blast furnace cement has a large amount of breathing, and therefore, it is difficult to embed it in prestressed concrete using the same blast furnace cement.
There are disadvantages in that voids are likely to form at the lower end of the PC steel, impairing its integration with concrete, and rust is likely to occur at the lower end of the PC steel, which is a practical drawback. The present inventors have discovered that fibrous magnesium silicate has thixotropy, adsorptivity, and caking properties, is a clay mineral with the highest adsorptivity among all minerals, and has thickening and anti-settling effects. Focusing on this, we added 1 to 10% of this fibrous magnesium silicate to blast furnace cement with the above composition.
By mixing 0.05%, breathing is prevented and the above-mentioned drawbacks of blast furnace cement are eliminated, making it more practical. The blast furnace slag powder used in the present invention has a light water slag of 3,000 to 5,000 cm ² /g brane, and the Portland cement may be any of ordinary, early-strength, ultra-early-strength, and white Portland cement. Further, the gypsum may be anhydrous gypsum, hemihydrate gypsum, or dihydrate gypsum, but those containing a large amount of phosphoric acid are not preferred because setting is delayed. However, if heat curing is performed in a sealed formwork, this will not be much of a problem. It is also possible to use gypsum of considerably poor purity, for example, 25 to 35% iron-rich gypsum (commonly known as iron clay), which is discarded during titanium production. Magnesium silicate is crushed into fibers of about 10 μm, and is available in Ede Press SP and Aed Plus PP.
(Both trade names: Showa Mining Co., Ltd.) commercially available products are suitable. When using the above mixed cement without heat curing, use blast furnace slag powder of 4000 cm ² /g or more, or use calcined alumite fired at about 650°C to a particle size of at least 100 mesh. or add 1 to 15% of nitrite-based admixtures that also have anti-corrosion ability, such as Paric C (product name: manufactured by Fujisawa Pharmaceutical Co., Ltd.), NR1900 (product name: manufactured by Pozolis Bussan Co., Ltd.), and Las Nine. (Product name: manufactured by Onoda Kenzai Co., Ltd.) etc., and kneading for a slightly longer time is preferable because it accelerates the setting. It goes without saying that a general early strengthening agent may be added. The drawing is a chart showing the compression creep test results of concrete using the mixed cement GCS according to the present invention shown in Table 1 below and ordinary concrete, where A is ordinary concrete with a slump of 8 cm and B is GCS with a slump of 18 cm. concrete used,
C shows concrete using GCS with a slump of 8 cm, and as is clear from the above diagram, concrete using the mixed cement according to the present invention has small creep, so it is suitable for prestressed concrete.

[Table] Note: General port: Ordinary Portland cement Next, the performance of the mixed cement according to the present invention will be listed.

【table】

[Table] From Table 2, it can be seen that the breathing rate of concrete using the mixed cement according to the present invention was significantly reduced. In addition to prestressed concrete, the cement according to the present invention can also be used in reinforced concrete with a large span to reduce deflection due to creep. Furthermore, by utilizing the characteristics of blast furnace slag powder, it can be used in underwater or underground structures to exhibit salt resistance.

[Brief explanation of drawings]

The drawing is a chart showing the results of compression creep tests for various types of concrete.

Claims (1)

[Claims] 1 Blast furnace slag powder 65-35% (weight ratio, same below), Portland cement 25-55%, gypsum 5-15%, and fibrous magnesium silicate 1-1%
A cement for prestressed concrete that is characterized by containing 0.05%.