JPS61162303A - Method of kneading concrete - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for mixing concrete.

(Prior Art) Ordinary concrete using natural aggregates is manufactured by charging aggregates such as cement, sand, crushed stone, water, and admixtures into a mixer at the same time and kneading them.

Lightweight concrete using lightweight aggregate is manufactured by allowing the lightweight aggregate to absorb water (prewetting) in advance and then kneading it in the same manner as ordinary concrete.

Prewetting of lightweight aggregates is carried out to prevent deterioration of workability of concrete due to water absorption by aggregates during mixing and to control strength.

(Problems to be Solved by the Invention) Lightweight concrete produced by the conventional method has the following disadvantages compared to ordinary concrete.

In other words, pre-wetting absorbs moisture into the aggregate that has no bearing on the strength or workability of the concrete.
The durability of concrete after hardening, especially its resistance to freezing and thawing, deteriorates significantly.

Furthermore, when lightweight concrete is pumped, water in the concrete permeates into the lightweight aggregate due to the pressure, which reduces the workability of the concrete and causes blockage of the pumping pipe.

(Means for Solving the Problems) The present invention was proposed to solve these problems, and involves kneading the entire amount of aggregate, cement, water, and a portion of the water reducer under reduced pressure. The present invention relates to a method for kneading concrete, which is characterized in that the remaining amounts of cement, water, and a water reducing agent are then added to the kneaded material under atmospheric pressure and kneaded.

(Function) According to the present invention, as described above, by kneading the entire amount of aggregate, cement, water, and a portion of the water reducing agent under reduced pressure, the surface of the aggregate is coated with cement 6-st. Since atmospheric pressure is introduced to mix the kneaded material with the remaining amount of cement, water, and water reducing agent, the cement yeast is press-fitted into the voids on the surface of the aggregate by the atmospheric pressure, forming a dense cement matrix. - A dry layer is formed, which prevents absorption of moisture during secondary kneading.

(Effects of the Invention) According to the method of the present invention, water added during secondary kneading is prevented from being absorbed into the aggregate, thereby preventing a decrease in workability due to water absorption.

Furthermore, since unnecessary moisture is not contained within the aggregate, the durability of concrete, especially its freeze-thaw properties, is improved.

Furthermore, when concrete is pumped using a concrete pump, absorption of water into the aggregate due to pressure is prevented, thereby preventing accidents of clogging of pumping pipes.

(Example) The present invention will be described below with reference to Examples.

1) - Human kneading Into a mixer that can maintain a reduced pressure state, put the total amount of bone-dry aggregate, part of the cement, part of the water, and part of the water reducing agent, immediately reduce the pressure and mix thoroughly, Cover the surface of the aggregate with cement.

I) Secondary kneading - After the manual kneading work is completed, the inside of the mixer is returned to atmospheric pressure, and the remaining cement, water, water reducer, and various additives are added and kneaded further to achieve the desired workability. After that, drain it.

In addition, in the above-mentioned manual kneading, it is desirable to dry the aggregate and cement in advance in order to prevent the aggregate from absorbing water due to capillary action. Also, the lower the pressure is, the better the decompression state is.
200m1cH,! 9 or less is sufficient and high vacuum is not necessary.

Further, the amounts of cement and water to be added to the secondary mixing vary depending on the strength and workability of the concrete to be manufactured.

Next, an experimental example of this method will be given.

Table 1 (200) (60) (561X451) (1,0
) Note (1) The lightweight aggregate of specimen shop 1 is surface dry (2) The lightweight aggregate of specimen 42 and 43 is bone dry (lightweight aggregate is mesalite) (3) () indicates primary kneading The composition is shown below.

Specimens 41 and 2 were mixed in a forced wire mixer, and specimen 3 was first kneaded separately under a reduced pressure of 5 to 10 mHJF, and then secondary kneading was performed in a forced kneading mixer.

Table 2 shows the change in concrete slump over time immediately after mixing and the results of a rapid underwater freeze-thaw test.

Table 2 Note: The durability index of the varnish lamp after 2 hours of mixing is 4.4C~- according to the test method for concrete freezing and thawing resistance specified by ASTMK.
17,8C is repeated for 2 to 4 hours per cycle until the relative modulus of elasticity of the specimen decreases by 40%.

From the above test results, the durability index DF (%) is calculated from the following formula.

P: Relative modulus of elasticity in N cycles (%) N: Number of cycles at the end of the test Ns: Number of cycles to end the test determined by the purpose (usually 300 cycles) According to the above results, the material kneaded by this method Compared to concrete mixed using conventional methods, the slump fluctuations of concrete are the same as those using aggregates that have absorbed sufficient water, and the durability index is lower than that of concrete that uses bone-dry aggregates. It turns out that it is also excellent.

Although the present invention has been described above with reference to embodiments, the present invention is of course not limited to these embodiments, and can be modified in various ways without departing from the spirit of the invention. In addition to kneading concrete materials, other materials such as phenol,
It is also possible to coat by first kneading an organic substance such as an epoxy resin, and it is also possible to knead the thermoplastic resin while heating it during kneading.

Claims (1)

[Claims] The total amount of aggregate, cement, water, and part of the water reducing agent are kneaded under reduced pressure, and then cement, water,
A concrete mixing method characterized by adding and mixing the remaining amount of a water reducing agent.