JPH0222831B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing thermal cracking in large cross-section concrete, ie, mass concrete.

When constructing mass concrete, thermal stress occurs due to the hydration reaction of cement, causing cracks.

Conventional methods for preventing this type of cracking include (i) providing construction joints; (ii) Perform cooling. (iii) Reducing the amount of cement in concrete by changing the mix. Measures have been taken.

However, as shown in method (iii), it is difficult to significantly suppress the temperature rise by changing the concrete mix, and it is not possible to reduce the amount of cement haphazardly to ensure the design strength.

Furthermore, as shown in method (i), in order to completely prevent cracks depending on the purpose of construction, an unrealistically large number of joints must be provided.

The only one that can be expected to have a crack prevention effect is (ii)
However, the cost of securing cooling piping and cooling water sources is extremely high, so it is rarely applied in practice except for dam construction.

On the other hand, in contrast to the above-mentioned methods, there is a method of using expanded concrete as a method of directly compensating for the volume change of concrete to prevent cracking.

However, since the calorific value of expanded concrete is greater than that of ordinary concrete, if expanded concrete is used for the entire structure, the stress that will be generated will inevitably increase, and it will be difficult to completely eliminate this stress.

The present invention was proposed in order to eliminate such problems, and when placing mass concrete, if tensile stress becomes large in advance in response to temperature stress generated due to temperature rise due to hydration reaction of cement, Expandable concrete whose expansion start time is adjusted to coincide with the time when the temperature at the center of the mass concrete reaches its maximum point is used locally in the expected area, and the tensile stress generated in the area is reduced. The present invention relates to a method for preventing thermal cracking in mass concrete, which is characterized by offsetting.

In the present invention, thermal stress analysis is performed in advance when placing mass concrete, and expanded concrete is used locally only in areas where tensile stress is expected to be large, thereby canceling out the tensile stress and preventing temperature cracking. It is intended to prevent At this time, the expanded concrete used in the present invention is adjusted with a retardant etc. so that its expansion start time coincides with the time when the center temperature of the mass concrete reaches its lowest temperature, so that the expansion The action is capable of efficiently reducing tensile stress.

In addition, since expanded concrete is used only in small amounts locally, it is possible to prevent the increase in costs due to the use of expensive expanded concrete.In addition, by adjusting the expansion start time as described above, the hydration reaction heat of expanded concrete can be reduced. This prevents excessive temperature rise due to

The present invention will be described below with reference to the illustrated embodiments.

Figure 1 shows the construction of plate-shaped mass concrete. Tensile stress occurs near the surface of a plate-shaped member. Therefore, in the overlapping area between the reinforcing bars 1 and the formwork 2, expanded concrete is prepared using a retardant or the like so that the expansion start time coincides with the time when the temperature at the center of the ordinary concrete 3 reaches its maximum point. 4 to offset the tensile stress generated on the surface of the plate-shaped member and prevent temperature cracks. Note that when the reinforcing bars 1 are densely arranged, the viscosity of the concrete is very high, so the two types of concrete 3 and 4 will not mix. Further, if the reinforcing bars 1 are roughly arranged, a wire mesh is brought into contact with the reinforcing bars 1 to prevent the two types of concrete 3 and 4 from mixing.

Fig. 2 shows the case where the present invention is applied to the construction of an extremely large structure, and since concrete is poured in layers from below, when pouring concrete for each layer, the periphery touches the formwork 5. After pouring and pouring expanded concrete 6, ordinary concrete 7 is placed in the middle, and expanded concrete 6 is placed on the entire top layer.

Although the present invention has been described above with reference to embodiments, the present invention is, of course, not limited to such embodiments, and can be modified in various ways without departing from the spirit of the present invention. .

[Brief explanation of drawings]

FIGS. 1 and 2 are longitudinal cross-sectional views showing the implementation status of each embodiment of the method of the present invention, respectively. 1...Reinforcement, 2...Formwork, 3...Ordinary concrete, 4...Expanded concrete, 5...Formwork, 6
...Expansible concrete, 7...Ordinary concrete.

Claims (1)

[Claims] 1. When placing mass concrete, the expansion start time is determined by the temperature at the center of the mass concrete in areas where tensile stress is expected to increase in advance in response to the temperature stress generated due to the temperature rise due to the hydration reaction of cement. 1. A method for preventing thermal cracking in mass concrete, which comprises locally using expanded concrete adjusted to coincide with the time when the peak temperature reaches its maximum point to offset the tensile stress generated in the same area.