JPH01282171A - Production of precast concrete member - Google Patents

Abstract

PURPOSE:To increase the rate of operation of equipment and to improve the quality of the title concrete member by regulating the consistency of a cement compsn. according to the amt. of cement milk to maintain a low water cement ratio and by keeping the cement compsn. warm in a mold without heating from the outside to carry out precuring and to shorten the time elapsed before the resulting member is released from the mold. CONSTITUTION:The consistency of a cement compsn. is regulated according to the amt. of cement milk to maintain a low water cement ratio of <=40%. The heat of hydration of cement in a stage for precuring the cement compsn. is utilized for heating the compsn. charged into a mold, so the hardening of the compsn. is accelerated without heating from the outside and the resulting precast concrete member is released from the mold after the lapse of a short precuring time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing precast concrete members, such as concrete panels, blocks, etc., in a factory or the like.

[Problem 8 to be solved by the invention] When producing precast concrete members in a factory, conventionally, the process consisting of pouring a cement composition into a mold, initial curing, and demolding is generally repeated on a daily or half-day basis. We are working to improve the operating rate of formwork and associated factory equipment. In the conventional manufacturing method of such precast concrete parts, the water-cement ratio is usually 45 to 55%.
In some cases, early-strengthening cement is actively heated by steam curing, etc., and maintained at 50 to 60°C for initial curing to achieve a compressive strength of 120 to 150 kg/d and a bending strength of 20 to 30 kg/cili. It had good demolding strength. Usually, in this process, a mold made of steel with high thermal conductivity is used, and the initial curing time from pouring to demolding requires about 18 hours or 8 hours (for small molds).

That is, the conventional manufacturing method of precast concrete members uses steam for initial curing to promote hardening. Therefore, the burden of equipment costs and energy costs required for curing was small.

This invention was made in view of the above circumstances. The purpose of this is to create precast concrete parts that can be demolded in a short curing time equivalent to that of steam curing without using steam for the initial curing, reducing equipment and energy costs, and offering superior product quality. We are proposing a manufacturing method.

[Means to solve the problem]

This method of manufacturing a precast concrete member is a method of manufacturing a precast concrete member in which a process consisting of injecting a cement composition into a formwork, initial curing, and demolding is repeated in units of time within one day. The consistency is adjusted by adjusting the amount of cement milk to keep the water-cement ratio below 40%, and the initial curing is carried out by keeping warm without actively heating from the outside.

This invention utilizes the heat of the hydration reaction of cement during mechanical casting during the initial curing process of the cement composition to increase the temperature of the cement composition press-fitted into the mold, thereby promoting hardening without actively heating it from the outside. , which enabled demolding with a short initial curing time.

The consistency of cement compositions such as concrete and mortar is related to its shear resistance and flow rate, and is usually expressed by slump, and is generally adjusted by the amount of water per unit. However, in this manufacturing method, the consistency is adjusted by increasing or decreasing cement milk with the water-cement ratio set at a predetermined ratio, and the water-cement ratio is adjusted to 40%.
Keep below. When the water-cement ratio exceeds 40%, in cement compositions such as concrete with a normal mixing ratio,
The heat of the hydration reaction of the cement is insufficient, and the temperature of the cement composition injected into the mold is insufficient, which makes it difficult to accelerate hardening and remove the mold at an early stage, which is undesirable.

Conventionally, when steam heating is used during initial curing, a steel formwork is used to increase the conductivity of heat from outside the formwork. This manufacturing method uses low thermal conductivity formwork, such as wooden or plastic formwork, or formwork with laminated insulation layers.
Alternatively, it can be cured without external heating by keeping it warm by covering it with a heat-insulating sheet or storing the formwork in an insulated box.

To prepare a cement composition with a low water-to-cement ratio, where the water-to-cement ratio is 40% or less, it is preferable to form the blended water into granular ice, add it to a mixture of cement or cement aggregate, and mix with stirring.

When granular ice is added to a mixture of cement or cement aggregate, etc. and stirred, a portion of the ice melts, and cement or cement and aggregate, etc., is sprinkled around the wet granular ice, which easily becomes macroscopic. It is possible to obtain a uniformly mixed system, and then, as the granular ice melts, a homogeneously mixed system composition in which substantially no granular ice remains can be obtained. Moreover, compared to a composition kneaded using water, this composition has a high slump value because the hydration reaction is suppressed due to the low temperature during preparation, and high workability can be obtained at the same water-cement ratio.

〔Example〕

Test conditions Concrete mixture: Concrete with the composition shown in Table 1
00! ! , Using a PAN type turbo mixer, mix the (cement + sand, gravel) mixture for 2 minutes, add the mixture (blended water (ice or water) and mixer) and mix for 2 minutes, and the amount of mixing at one time is 301. concrete was made. The room temperature during the preparation was 20''C.

Formwork: Specimen for compression test is diameter 10CIIIX height 20
A cylindrical formwork with a diameter of 1 cm was used, and the specimen for the splitting tensile test had a diameter of 1 cm.
A cylindrical formwork of 0 cm x height 10 cm was used.

Initial curing: The upper opening of the formwork injected with concrete having the composition shown in Table 1 is covered with a vinylidene chloride resin film, and the example is stored in an insulating box made of polystyrene foam with a thickness of 5 cm, and the comparative example is placed at the ambient temperature. It was left in a room at 10-15°C.

The mold was removed after 17 hours, and the resulting specimen was subjected to strength measurement after 20 minutes. At the end of the 17-hour initial curing, the temperature in the insulated box was about 30°C.

The strength measurement results for each specimen are shown in Table 2.
Table Composition of concrete (unit: kg/bo) Table 2 Physical properties of cured product after curing (initial 3 tJ) (17 hours) [Function] This invention consists of the above configuration. This manufacturing method uses steam to cure the cement composition without heating it from the outside of the mold, which accelerates the hardening of the cement composition in the same way as steam curing, allowing early removal from the mold once or twice a day. It becomes possible to operate the formwork and auxiliary equipment in units of cycles. Although the amount of cement used increases slightly, this increase in cost does not involve labor costs and is lower than the cost of steam curing. Decreasing the water-cement ratio significantly contributes to improving product quality, such as increasing product strength and reducing shrinkage.

Furthermore, if granular ice is used in the mixing water of the cement composition, even if the water-cement ratio is low (40% or less), a uniform composition can be easily made and a good consistency can be obtained. It is possible and suitable.

〔Effect of the invention〕

This invention is as described above. According to this manufacturing method, it is possible to shorten the time required to demold the precast concrete member and improve the equipment operating rate without consuming external thermal energy. At the same time, it is possible to improve the quality of precast concrete members.

Claims (1)

[Claims] (1) In a method for manufacturing precast concrete members in which the steps of pouring a cement composition into a formwork, initial curing, and demolding are repeated in units of one day or less, the consistency of the cement composition is A method for producing precast concrete members characterized by adjusting the amount of milk to maintain a water-cement ratio of 40% or less, and performing initial curing by keeping warm without actively heating from the outside.