JPH0613794B2 - Method for forming a dense layer on the surface of a cured concrete - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a dense layer on the surface of hardened concrete when constructing a reinforced concrete structure and producing a concrete product using cement as a raw material. is there.

Conventional technology When concrete is poured, there are many small voids inside and on the surface of the concrete. As a method of eliminating the voids and making the concrete more solid, (1) increasing the fluidity of the concrete Method to add additives to suppress the generation of air bubbles and additives (2) Insert a vibrator into concrete or vibrate the form, (3) After ultrasonic vibration to the cement paste ,
A method in which aggregate is added and mixed or stirred, or concrete is stirred while applying ultrasonic vibration (Japanese Patent Application Laid-Open No. 51-1271).
(See Japanese Patent Publication No. 13), (4) A method of applying ultrasonic waves to concrete that does not solidify, or applying ultrasonic waves during or after the concrete mixing step in the mixer of the concrete mixer truck (Japanese Patent Laid-Open No. 56-129687). (See Japanese Patent Publication).

Problems to be Solved by the Invention In the above conventional method, the method (1) can improve the fluidity of cocrete to fill an unfilled portion and remove a relatively large air pool, The method (1) can temporarily increase the fluidity of concrete by vibration, and can improve the solidity of concrete by discharging air bubbles scattered in the concrete, (3)
The method (1) can increase the compactness and strength of the entire concrete without changing the particle size distribution, and the method (4) can shorten the solidification time and increase the strength of the concrete. None of these methods locally changes the particle size distribution of concrete constituent particles to agglomerate particles having a particle size of cement particles at a specific portion, and therefore forms a dense layer only on the surface of concrete. Therefore, there is a problem that the air permeability is reduced and the smoothness of the surface cannot be obtained.

Means for Solving the Problems Means of the present invention for solving the above problems are as follows: After ultrasonic vibration is applied to the surface of concrete that is not yet solidified, particles having a particle size of about cement particles are aggregated. The method comprises forming a dense layer on the surface of hardened concrete which is allowed to stand and harden.

When ultrasonic vibration is applied to the surface of concrete that has not solidified yet, only minute cement particles agglomerate on the surface, and not only aggregates in concrete but also minute particles of sand are contained in a thin layer. Are formed.

In this case, the optimum frequencies of ultrasonic waves corresponding to various particle sizes are as shown in Table 1.

The dense layer formed according to the present invention has a cement particle size of 2 to 50 μm, and therefore, the frequency of ultrasonic waves used for this is 0.8 to 500 KHz, and its amplitude is 0.5. ~ 15 μm is used.

It should be noted that fine particles can be aggregated on the surface of a gypsum or the like that does not use an aggregate to form a dense layer.

Embodiment An embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, a Langevin type ultrasonic transducer (1) is attached to a steel plate (2) having a plate thickness of 2.3 mm, a mortar (3) having a thickness of 8 mm is placed on the steel plate (2), and 4 28KHz frequency with no breathing water left for hours
Ultrasonic vibration was applied for 30 seconds. After the mortar (3) hardened, peeling the mortar (3) from the steel plate (2) and observing the bottom surface, a circular part with a diameter of 12 cm centering on the vibrator (1) exhibited a dark green color and a gray part on the outer periphery thereof. And formed a clearly distinguishable borderline.

When observing the central part with a microscope, no sand particles were seen at all, only cement particles formed a dense surface, and the outer periphery was covered with white solids with scattered sand particles. .

Next, as shown in FIG. 2, a container (4) filled with water.
Insert the sample piece (5) cut out from the mortar (3) into the sample piece, attach the air collection bottle (6) to the sample piece (5) with the mouth down, and press the compressed air on the back surface of the sample piece (5). Pipes of the (7)
When the air permeability of the sample piece (5) was measured by fixing the end portion (8) of the sample (3) in close contact, the results shown in Table 2 were obtained.

As is clear from Table 2, the mortar ultrasonically vibrated has an air permeability of 1 compared to a mortar of the same composition without vibration.
It is shown that it is reduced to / 10 or less.

Next, as shown in FIG. 3, the Langevin type ultrasonic transducer (9) was attached to the 2.3 mm steel plate (10), and the steel plate (1
The concrete frame (12) having a composition of Table 3 and having a thickness of 150 mm was placed on 0), and immediately vibrated with ultrasonic waves of 28 KHz for 30 seconds.

When this concrete specimen (12) was cured and its bottom surface was observed, a dark green circular portion (13) with a diameter of 10 cm was found just above the vibration specimen (9), just like the mortar. The surface of the circular part (13) was so smooth that it could not be felt by touching with a finger, and it took 15 minutes to penetrate even if a water drop was dropped.

Next, an example of application of the precast concrete slab to the manufacturing process is shown in FIG. In FIG. 4, a precast concrete plate frame (15) having a bed steel plate (14) with a wall thickness of 4.5 mm is placed on a support stand (16), and 200
The W Langevin type ultrasonic transducer (17) was attached to the lower surface of the bed steel plate (14) and the distance between the adjacent transducer (17) was set to 20 cm, and the concrete (1
8) is cast into the mold (15) and the bed steel plate (14)
A precast concrete slab was manufactured by operating an ultrasonic transducer (17) from the lower surface of the machine and vibrating it and then curing it. In this precast concrete slab, a dense layer was formed up to a depth of 8 mm from the surface, and the air permeation rate on the surface was significantly lower than that of ordinary concrete.

EFFECTS OF THE INVENTION The present invention, which comprises the above-mentioned means, has a remarkably smooth and dense layer on the surface of concrete, and has a very low air permeation rate on the surface, so that the progress of concrete by permeation of carbon dioxide in the air It is effective as a finishing surface because the resistance to neutralization increases dramatically and it can greatly contribute to the extension of the life of concrete structures, and the abrasion resistance of the concrete surface improves and the surface smoothness is remarkable.

[Brief description of drawings]

FIGS. 1, 3, and 4 show an embodiment of the present invention. FIG. 1 is a longitudinal sectional front view, and FIG. 2 is a longitudinal sectional front view of an apparatus for measuring air permeability, FIG. 3 and FIG. FIG. 4 is a vertical sectional front view.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumio Oshida 2-5-14 Minamisuna, Koto-ku, Tokyo Inside Takenaka Corporation Technical Research Institute (56) References JP-A-56-129687 (JP, A) JP-A-51-127113 (JP, A)

Claims (1)

[Claims] 1. A dense layer is formed on the surface of hardened concrete, which is subjected to ultrasonic vibration so that particles having a particle size of cement particles are aggregated on the surface of concrete that has not yet solidified, and then allowed to stand and harden. how to.