JPH0196051A - Method for casting concrete in cold season - Google Patents

Abstract

PURPOSE:To obtain a hardened composite of high quality with low cement ratio by adding specified amount of small lumps of ice to the mixture of cement and aggregate, etc., agitating and mixing in a pseudo-solid state to obtain an uniformly mixed cement composite, charging the mixture into an insulating frame, preventing the mixture from freezing by simply insulating the surface, and carrying out the curing. CONSTITUTION:Comparatively small lumps of ice of 4-6mm average particle diameter are added to the mixture of cement and aggregate, etc., so that water-cement ratio is <=45%, and agitated and mixed in a pseudo-solid state which is formed in the humid state of mixture consisting of cement, aggregate, etc., and melting water generated on the surface of small lumps of ice so as to become a macroscopic homogeneous phase, and the small lumps of ice are gradually melted to obtain a homogeneously mixed cement composite having no lumps of ice. Then, the composite is put into the insulating frame, and the exposed surface of the composite is covered by insulating material or by covering material with air layer between. By this method, the water- cement ratio is reduced without lowering workability, and the temp. rising rate is increased by the heat of hydration, and high quality concrete is allowed to be cast with simple insulating means.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for placing concrete in the cold, in which a concrete composition is placed in an atmosphere below freezing.

[Problem that the invention seeks to solve]

Cement compositions such as cement mortar or ready-mixed concrete are said to freeze at -0.5 to -2 degrees Celsius, and because of the risk of freezing when the average daily temperature is below 4 degrees Celsius, concrete is not poured. Ta. If a cement composition freezes in the early stages of setting and hardening, the hydration reaction of the cement will be delayed, and even if it is subsequently cured at an appropriate temperature, its strength will deteriorate.
Early freezing had to be avoided as it would have a negative effect on properties such as durability and watertightness.

For this reason, when placing a cement composition in an atmosphere where the temperature is below freezing, it is necessary to store the cement, aggregate, etc. so that they do not get too cold, avoid using low-temperature mixing water, transport and place, etc. Measures such as heating were required during curing.

Furthermore, a method has been proposed in which the heat of the hydration reaction of the cement is used to prevent the cement composition from freezing and to accelerate its hardening. The heat of hydration reaction generated by a cement composition is calculated by the unit amount of cement (kg
/m), and the rate at which the temperature of the cement composition increases due to the heat of hydration reaction is inversely proportional to the water-cement ratio if the unit amount of cement is the same. Therefore, a cement composition in which the unit amount of cement is large and the water-cement ratio is small has a large rate of temperature rise due to the heat of hydration reaction, and is effective in preventing freezing. However, increasing the unit cement i increases the cost of the material, and using a low water-cement ratio decreases fluidity, plasticity, etc., and the workability of the composition decreases, resulting in uniform kneading, dense filling, etc. This was an obstacle to achieving this goal.

This invention was made in view of the above circumstances. The purpose is to reduce the water-cement ratio without impairing workability, increase the rate of temperature rise due to the heat of hydration reaction in the cement composition, and enable high-quality concrete to be poured without freezing with only a slight amount of insulation. This article proposes a method for placing concrete in the cold.

[Means for solving problems]

The method of placing concrete in cold weather according to the present invention is that in the method of placing concrete in cold weather, small ice cubes are added to a mixture of cement or aggregate, etc., and the cement or aggregate etc. and the small ice cubes are moistened with melted water generated on the surface of the mixture. Stir and mix in a quasi-solid phase state to form a macroscopic homogeneous system, gradually melt small ice blocks to create a homogeneously mixed cement composition in which virtually no small ice blocks remain, and apply this composition to the formwork. The small ice cubes are added to a water-cement ratio of 45% or less, and a heat-retaining mold is used, and the exposed surface of the composition is covered with a heat-insulating material or a covering material with an air layer in between. It is characterized by curing.

In this invention, a portion of a small ice cube is melted, and cement is made into a "pseudo-solid state," which is moistened with the melted water.
Stir and mix aggregate, etc. and small ice cubes. Cement particles and fine aggregate adhere to the wet surface of the ice block, and the attached fine particles absorb a small amount of water and become sticky, forming small lumps with the ice block as a core. The pseudo-solid state is a state in which the small lumps and solid cement and aggregate coexist.

In this pseudo-solid state, even if the water-cement ratio is 45% or less and the amount of small ice blocks added is small, the small ice blocks behave as small blocks with sticky surfaces, and the surrounding cement, aggregate, etc. A macroscopically homogeneous system in which aggregates and the like are uniformly dispersed can be easily formed through short-time mixing in which convective mixing is dominant. Therefore, the main purpose of the pseudo-solid state is achieved by appearing for a relatively short period of time at the beginning of stirring and mixing the composition.

After forming a macroscopically homogeneous mixed system, the ice cubes gradually melt at ambient temperature, but this water is finely dispersed and adsorbed by particles mainly composed of cement, making the entire mixed system less than 45% Even at low water-to-cement ratios, the composition is highly homogeneous.

In the composition thus prepared, water is very uniformly dispersed and adsorbed, and the water-to-cement ratio is 45% or less, which is a relatively small amount, so free water does not aggregate and exist. Water in this state has a low freezing temperature, and even if it freezes, it will not form chunks of ice, so the damage caused by freezing is small. Furthermore, since this composition has a low water-to-cement ratio and a small unit amount of water, a small proportion of the heat of the hydration reaction of the cement is consumed to raise the temperature of the water, and a large proportion is consumed to raise the temperature of the composition. Therefore, by simply placing the cement composition into a formwork with good heat retention, such as plywood, and simply covering the exposed surface, a hydration reaction can occur even in a sub-zero atmosphere, promoting hardening. can.

The water-cement ratio of the cement composition used in this casting method is 45% or less. If the water-cement ratio exceeds 45% in the composition range of commonly used cement mortar or ready-mixed concrete, the rate of temperature rise of the composition will be small due to the heat of hydration reaction, and in order to prevent freezing, heat retention or advanced insulation equipment is required. However, the purpose of this invention cannot be satisfied. For example, in the case of a mortar with cement and sand = 172, if the water-cement ratio exceeds .45%, free water will be present, which is not preferable. Also,
In the case of cement paste, even if the water-cement ratio is the same as that of mortar, the unit water amount is large, so the water-cement ratio is preferably 20 to 25% or less.

The size of the small ice cubes used in this invention can be changed depending on conditions such as the temperature of cement, aggregate, etc., and ambient temperature, but in a low-temperature atmosphere where the outside temperature is below freezing, the average particle size is a few marks and is relatively small. The time required for melting is appropriate and is suitable for achieving homogeneous mixing.

This casting method requires the use of formwork with good heat retention. A thick wooden formwork may be used, but in cases where it is extremely cold or the number of units of pouring is small, an insulating formwork using a laminated material with a foamed resin board is preferable. The heat insulating material covering the exposed surface is a foamed resin board or relatively thick plywood, and in the case of a foamed resin board, a relatively thin material with a thickness of about 10 rM1 can provide a sufficient heat retention effect.

When using a covering material with low heat insulation performance, such as a synthetic resin sheet, the effect of heat retention can be obtained by providing an air layer between the surface of the cast composition and the surface of the cast composition, as in the examples described below.

〔Example〕

Example 1 Composition of cement composition: Cement 448 kg/rrl Fine aggregate 679 (maximum particle size 2.5) Coarse aggregate 11
63 〃 (Maximum particle size 25 cylinders) Small ice blocks 148〃 (Small ice blocks + surface water of aggregate) Admixture 1.12 〃 (AE: $i water agent Pozolith N
α70) A cement composition was prepared by stirring and mixing the above-mentioned materials, melting all the small ice cubes, and uniformly mixing them. This composition was divided into 180cm x 180cm x 20CI11 (thickness 12
mm plywood) formwork 1, and 10cmφx20c++
The sample was placed in a steel cylinder 2 (h), covered with a vinyl chloride resin sheet 3 as shown in FIG. 1, and left in an insulated air space for 3 days for curing. In Fig. 1, the formwork 1 and the cylinder 2 are respectively 5 x 5 cm square wood sticks 5 and 12 m thick placed on a concrete floor 4.
It was placed on a plywood board 6 of m.

FIG. 2 shows a graph of the relationship between the outside air temperature and the temperature of the cement composition in the formwork 1 (the temperature at the thermocouple measurement point 7 in the center of the formwork 1).

During the 45 minutes between the time when the cement composition line rises (a) and the time when it starts to be poured into the formwork, it is transported by truck agitator (2 bottles of 4 and 5 are loaded on the car), and it takes 30 minutes to pour it in (time C when the pouring is completed). did. The cement composition charged into formwork 1 was heated to 20° C. or higher even though the outside temperature was below freezing, and solidification and hardening proceeded. Even after 3 days, the temperature remained about 5°C higher than the outside temperature, and there was no freezing.

After curing for 3 days, the cured material in the formwork 1 and cylinder 2 was cut out to prepare specimens, and the compressive strength of both specimens was measured, and was found to be approximately 200 kg/c111.

Example 2 Composition of cement composition Cement 412.5 kg/rr (Fine aggregate 730 (2.5 mm or less) Coarse aggregate
1007 s (15W or less) Small ice block 165
(Small ice blocks + aggregate surface (water cement water) ratio 40%) The above homogeneously mixed cement composition was mixed as shown in Figure 3 (
It was filled into molds with different heat retention conditions shown in Toshin (C) and (d), and left in a freezer at a temperature of -10°C for 6 days to cure.

Formwork 8 has an internal dimension of 15 x 15 x 12 (height) and a thickness of 1 l.
The wooden box 9 is made of plywood and has an open top, and polystyrene foam 10 with a thickness of 50 ml is placed on the bottom and outside of the four sides.

FIG. 3(a) shows that the upper surface of the formwork 8 is covered with a polystyrene foam 10 with a thickness of 50 m, and a cement composition 11 is placed in a wooden box 9.
(Specimen Na1).

Figure 3 (b) shows the upper surface of the formwork 8 made of plywood 12 with a thickness of 11 mm.
9 wooden boxes were filled with cement composition 11 and cured (specimen Nα2).

FIG. 3(C) shows a 9-cup wooden box filled with cement composition 11, an air layer 13 with a thickness of 10 ml 11 provided on the upper surface of the form 8, and the upper surface covered with a vinyl chloride resin sheet 14 for curing. (Specimen Nα3).

FIG. 3(d) shows 9 wooden boxes filled with cement composition 11 and cured with the top surface of formwork 8 left open (
Specimen No. 4). In both cases, the joints were sealed with gummed tape 15 to ensure airtightness.

Specimen No. 1.2.3.4 cured under the above conditions
was taken out into a room at about 20°C, demolded, and left for 2 hours.
It was painted with gypsum and subjected to a compression test 24 hours later.

FIG. 4 shows the temperature change at the center of the Na 1.2.3°4 specimen and the temperature inside the freezer during the curing process. Note that the specimen temperature is the temperature at the measurement point 7 in the center.

The compressive strength of each specimen was as follows.

Nα1 258 kg/c+fl Nα2 136 kg/cI11 3 l 41 〃 Nα4 92 〃 If the water-cement ratio is relatively small at 40% and the concrete is homogeneously mixed using small ice blocks, the exposed surface can be insulated. This shows that pouring can be done in the cold by simply covering it with wood or sheets.

Example 3 Composition of cement composition Cement 471 kg/n (fine aggregate 708 horns (2.5 mm or less) coarse aggregate
980t! (15 mm or less) Small ice blocks 165〃 (Water-cement ratio 35%) The cement composition obtained by uniformly mixing the above was filled into the same mold 8 as in Example 2, and cured in a -10°C freezer for 6 days. The compressive strength of the specimen was measured after being left in a room at 20°C for 24 hours after demolding.

As a heat retention condition, for the specimens Nα5 and N016, the upper surface of the formwork 8 was covered with a polystyrene foam having a thickness of 30 mo+ and 10 mm, respectively, as shown in FIG. 3(a).

Specimens Nα7, 8, and 9 each have an air layer 13 and are covered with a resin sheet 14 in the same way as in FIG. He said.

Fig. 5 shows the specimen No. 5.6.7 during the curing process.
It shows the temperature change in the center part of 8°9 and the temperature inside the freezer.

The compressive strength of each specimen was as follows.

ikuα5 293 kg/cd Pouring in the cold is possible by means of
It was found that sufficient strength was developed in a short period of time.

〔Effect of the invention〕

The present invention is as described above, and according to this method, concrete can be placed in cold weather without freezing by simply providing simple insulation, and a high-quality hardened product made of a low water-to-cement ratio composition can be obtained. be able to.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing the curing state of the cement composition of Example 1, FIG. 2 is a graph of the relationship between the air temperature and the temperature of the cement composition in Example 1, and FIG. )
4 and 5 are graphs showing the relationship between the air temperature and the cement composition temperature in Example 2 and Example 3, respectively. l...Formwork, 2...Steel cylinder, 3...Vinyl resin sheet, 4...Earth floor concrete, 5...Wood bar piece, 6...Plywood, 7...Measurement point , 8... Formwork, 9... Wooden box, 10... Polystyrene foam, 11
... Cement composition, 12... Plywood, 13... Air layer, 14... Vinyl chloride resin sheet, 15... Gum tape, a... Cement composition line rising point, b...
- Time of input, C... Time of completion of input. Figure 2 (Temperature) Part 3 (a) 1° (C) (d)

Claims (1)

[Claims] (1) In the method of placing concrete in the cold, small ice cubes are added to a mixture with cement or aggregate, etc., and the mixture is stirred and mixed in a quasi-solid state moistened by melt water that forms on the surface of the cement or aggregate and the small ice cubes. A macroscopically homogeneous cement composition is created by gradually melting small ice blocks to create a homogeneous cement composition in which substantially no small ice blocks remain, and this composition is poured into a mold and allowed to solidify. water cement 4
A method for placing concrete in cold weather, characterized by using a heat-retaining formwork and covering and curing the exposed composition surface with a heat insulating material or a covering material with an air space in between.