JP2612885B2 - Manufacturing method of precast concrete products - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a precast concrete product which has been subjected to a smooth surface finish using an early-curing self-leveling material instead of a plaster finish.

[Prior Art] Conventionally, precast concrete products have been subjected to surface finishing by plastering work such as gold troweling, brush finishing, etc. after casting hot concrete in a predetermined formwork.
This surface finish is a complex task that requires a subtle sensation and is done only by skilled workers.

However, in recent years, an increase in the production of precast concrete products has led to a shortage of skilled workers, and a chronic shortage of skilled workers has required an alternative method. In addition, there is a need for a solution in which a reduction in manufacturing cost due to a reduction in surface finishing time and labor saving is also an issue.

[Problems to be Solved by the Invention] An object of the present invention is to provide a method for producing a precast concrete product having a smooth surface finish in a large amount, inexpensively, and in a short time without the need for skilled workers. Furthermore,
An object of the present invention is to provide a method for producing a precast concrete product excellent in workability and stability in production.

[Constitution of the Invention] [Means for Solving the Problems] The gist of the present invention is that the surface of hot concrete, which has not yet solidified yet, has been cast into a predetermined formwork and is kept within 7 hours at room temperature. This is a method for producing a precast concrete product having a smooth surface, characterized by pouring a slurry of a self-curing self-leveling material at an early stage of hardening, integrally hardening and molding. The above-mentioned early curing self-leveling material is based on a composition containing a cement, a calcium aluminate compound and gypsum, and further contains a water reducing agent, a thickening agent, a defoaming agent, a reaction controlling agent, an admixture. It is preferable to use a mixture obtained by combining and combining the aggregates. Then, as its calcium aluminate-based compounds, a _{3CaO · 3Al 2 O 3 · CaSO} 4 or 12CaO · 7Al ₂ O ₃ by each alone or in combination, are preferred those containing in a total amount of 50 wt% or more.

In the method for manufacturing a precast concrete product according to the present invention, the present inventors poured a predetermined fluid self-leveling material slurry into the surface of hot concrete cast in a predetermined formwork, and after steam curing, The external appearance was observed, and the adhesive strength with the underlying concrete was measured.
As a result, it was found that the curing speed significantly affects the smoothness of the finished surface, the occurrence of cracks, etc., as well as the fluidity of the self-leveling material. From the research, in the production of the precast concrete product of the present invention, the study was conducted on the curing time of the constituent self-leveling material itself and its composition. As a result, JIS R 5201
It has been found that when the curing speed is as slow as about 6 to 7 hours, the smoothness of the finished surface deteriorates and cracks occur. Therefore, according to the production method of the present invention, the starting time for curing must be within 7 hours at room temperature, more preferably within 6 hours.

In addition, in order to impart early curing property to the self-leveling material used according to the present invention, 3CaO
_{2 O 3, CaO · Al 2} O 3, 12CaO · 7Al 2 O 3, 11CaO · 7Al 2 O 3 · CaF
_2, it is necessary to formulate a series of calcium aluminate compounds and gypsum, such as _{3CaO · 3Al 2 O 3 · CaSO} 4. At that time, it was found that if the compounding ratio of the calcium aluminate compound was less than 10% by weight based on the compounding cement, the early curing property was insufficient and cracking and peeling occurred. If it exceeds 50% by weight, the curing time is too early,
Workability and adhesive strength deteriorate. Accordingly, the range of the outer mixing ratio of the calcium aluminate compound to the compounded cement is 10 to 50% by weight, more preferably 15 to 30% by weight.
% By weight.

On the other hand, if the proportion of gypsum to the early-setting self-leveling material is less than 5% by weight of the blended cement, the strength is poorly expressed, and if it exceeds 50% by weight, the stability is poor due to delayed expansion. . Therefore, the ratio of the gypsum to the compounded cement is from 5 to 50% by weight, more preferably from 10 to 40% by weight. The gypsum to be used may be any of gypsum dihydrate, gypsum hemihydrate and gypsum anhydrous. However, anhydrous gypsum is more preferred from the viewpoint of helping to develop strength.

Determine the composition of the composition of the self-leveling material base as described above, and further, as a constituent material of the self-leveling material in the prior art, a known water reducing agent, thickener, defoaming agent, reaction control agent, admixture It was confirmed that the proper function of the self-leveling material such as workability, fluidity, stability, etc., as well as the early curing property, can be improved by combining and blending the appropriate aggregates. The invention has been completed.

Next, the results of the experiments performed will be described. Table 1 shows the blending ratio of the self-leveling material used in the experiment.

In Table 1, calcium aluminate is 3CaO.
Using clinker powder containing 72 wt% in the total amount of 3Al ₂ O ₃ · CaSO ₄ and 12CaO · 7Al ₂ O _3.

Further, a melamine resin was used as a water reducing agent, methyl cellulose was used as an adhesive, a silicon resin was used as a defoaming agent, oxycarboxylic acid was used as a reaction control agent, and No. 5 silica sand was used as an aggregate.

Observation of the flow value at 20 ° C, the setting time, the strength of the cured product, the flow value at 35 ° C, the strength of the cured product, and the surface condition of the kneaded product of self-leveling material and commercially available products listed in Table 1 with water The surface condition after the deposition curing was observed. Table 2 shows the results.

In Table 2, the flow value was obtained by placing a pipe (volume = 100 cm ³ ) having an inner diameter of 50 mm and a height of 51 mm on a glass plate, putting the kneaded material into the glass plate, and then pulling up the pipe to obtain a circular kneaded material. It is a value obtained by measuring the diameter. The setting time and compressive strength were in accordance with JIS R 5201, and the curing was air curing. The surface condition after curing was poured into a 30 mm × 30 cm slate mold at a thickness of 5 mm, and after curing, cracks were visually observed.

From the results shown in Table 2, it is clear that the surface condition of the precast concrete product according to the invention at 20 ° C. and at 35 ° C. and after steam curing was good without cracking. In addition, a sufficiently satisfactory result was obtained in terms of strength. Sample 1 and a commercially available product (Sample 4) had cracking and swelling after steam curing due to low curing speed. In addition, the steam curing treatment is performed at 20 ° C for 3 hours and then at 20 ° C.
/ Hour and rise to 65 ° C and hold at 65 ° C for 3 hours.
It was left to cool.

Next, the method for producing a precast concrete product according to the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[Example 1] Hot concrete of about 50 ° C was poured into a 1 m × 2 m formwork having a depth of 15 cm with an upper end of 5 mm, and the slurry of sample 3 was poured thereon. In this case, the crack occurrence after steam curing was zero as shown in FIG. 1A,
For comparison with this, a commercial product was similarly constructed,
As shown in FIG. 1B, many cracks occurred.

Further, a test of the adhesion strength of the substrate after steam curing was performed. The test method is 4 cm x 4 cm of self-leveling material constructed on site
The specimens were cut to the ground with a size of, and the specimens were tested on the 7th and 28th days by the Kenken-type tensile test method with 6 specimens at each age. The result is shown in FIG.

In FIG. 2, a solid line indicates a precast concrete product of the present invention (sample No. 3), and a broken line indicates a commercially available product. According to FIG. 2, the precast concrete product of the present invention is slightly inferior in adhesive strength as compared with a commercially available product, but is 5 kgf / cm ² or more, which is a criterion for determining the adhesive strength to the self-leveling material substrate of the Housing and Urban Development Corporation. And it was confirmed that it was suitable as a self-leveling material for the production of precast concrete products from the viewpoint of finishing accuracy.

[Effects of the Invention] By the method for producing a precast concrete product of the present invention, firstly, a method for producing a precast concrete product having a smooth surface at a low cost is provided. Remarkable technology, such as being able to provide inexpensively as having characteristics, and thirdly, being able to provide a method for producing a precast concrete product which is excellent in workability and stability in production and can be produced in a short time. Effect was obtained.

[Brief description of the drawings]

FIGS. 1A and 1B show the state of occurrence of cracks when a precast concrete product according to the present invention and a commercial product are constructed, respectively. FIG. 2 shows the test results of the bond strength between the precast concrete product according to the present invention and a commercial product.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenkichi Nakajima 3-13-18 Sendagaya, Shibuya-ku, Tokyo Inside Fujita Industries Co., Ltd. (72) Inventor Masao Sato 651-2 Owada 2, Yachiyo-shi, Chiba Prefecture Mitsuo Toyoda 3-27-2-503, Shintakane, Funabashi City, Chiba Prefecture (72) Inventor Toshikazu Minematsu 3-7-1, Tsudanuma, Narashino City, Chiba Prefecture (56) References JP-A-57-71880 (JP, A)

Claims (3)

(57) [Claims] 1. A slurry of an early-hardening self-leveling material having a hardening start time of 7 hours or less at room temperature is poured onto a surface of hot concrete that has not yet solidified and is cast on a predetermined formwork, and is integrally hardened. A method for producing a precast concrete product having a smooth surface, characterized by molding. 2. The above-mentioned early-curing self-leveling material,
Cement, a composition containing a calcium aluminate compound and gypsum as a base material, further, a water reducing agent, a thickener,
2. The method for producing a precast concrete product having a smooth surface according to claim 1, wherein an antifoaming agent, a reaction controlling agent, an admixture, and an aggregate are combined and mixed. As claimed in claim 3, wherein the calcium aluminate-based compounds, and characterized in that it contains _{3CaO · 3Al 2 O 3 · CaSO} 4 or 12CaO · 7Al ₂ O ₃ by each alone or in combination, in a total amount of 50 wt% or more 3. A method for producing a precast concrete product having a smooth surface according to claim 2.