JPS5811378B2 - Method for producing ready-mixed concrete - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing ready-mixed concrete for concrete products, which involves centrifugal force forming and subsequent steam curing, and more particularly, to a method for producing ready-mixed concrete with little reduction in fluidity.

In general, "unhardened concrete" (herein referred to as ready-mixed concrete), which is made by mixing cement, sand (fine aggregate), gravel (coarse aggregate), etc. with water, creates gaps between reinforcing bars and formwork. It is necessary to maintain sufficient fluidity for pouring.

One way to increase the fluidity of fresh concrete is to increase the amount of mixing water, but this method deteriorates the strength and other qualities of concrete after hardening.

Therefore, concrete water reducers (also referred to as dispersants) have traditionally been used.

When a concrete water reducer is added during mixing, the concrete water reducer adsorbs to the surface of fine particles such as cement and disperses the fine particles, reducing the amount of water required to provide the same fluidity.In this case, the same amount of cement If so, the strength of concrete can be increased, and if the target strength is the same, the amount of cement can be decreased.

However, if a concrete water reducer is added to the concrete mix from the beginning of mixing, the concrete water reducer will be adsorbed onto the surface of unhydrated cement particles, and then covered with cement hydrates formed on the surface. Some do not contribute to the dispersion effect, and some do not contribute to the dispersion effect because even if they are adsorbed to the surface of the hydrate, further hydrates are formed on top of it and cover it, and the cast special particles are not sufficiently dispersed. A large amount of water reducing agent is required to maintain sufficient fluidity of fresh concrete.

Therefore, in order to use the water reducing agent effectively, a method has been proposed in which the water reducing agent is added (post-added) after the initial hydration of cement is completed. According to this method, unhydrated cement particles or It is possible to save the water reducing agent that is wasted by being incorporated into the surface of the hydrate inside.

Also, in addition to adding the main amount of water reducing agent when the initial hydration of the cement is completed, if some water reducing agent is added even at the beginning of crosstalk, it is necessary to add the water reducing agent in the main amount until the main amount of water reducing agent is added. Fluidity during kneading is also improved.

Next, an example of manufacturing a concrete pipe using centrifugal force will be described.

The method of forming concrete pipes using centrifugal force is widely used in the production of secondary concrete products such as concrete pipes and concrete piles.

The quality of such secondary concrete products depends on the centrifugal formability of fresh concrete during compaction using centrifugal force,
In particular, fluidity is greatly affected, and if centrifugal formability is insufficient, it will not only reduce the strength of the concrete pipe, but also cause voids to form in the concrete pipe body and a separated layer of fine particles to form on the inner wall of the pipe. A significantly uneven surface appears,
This causes a significant deterioration in the quality of concrete pipes.

That is, in a pipe body with voids, rusting of reinforcing bars embedded in concrete is promoted, and at the same time, watertightness and strength are poor.

In addition, a pipe inner wall with significant irregularities can cause damage to the excavation blade in the so-called hollow excavation method, in which the excavation blade is inserted into the concrete pipe and the concrete pipe is buried in the ground while rotating the excavation blade.

The quality of centrifugal force formability is greatly influenced by the magnitude of centrifugal force during centrifugal force forming, rotation time, and time distribution of low, medium, and high speed rotation, as well as the properties of the ready-mixed concrete used. .

In other words, when the amount of fine powder contained in the concrete mix is large (cement, admixtures, sand, etc.), when the particles of the cement used are very fine, or when the fluidity of fresh concrete is poor (in general, the slump value If the slump value is small, the centrifugal formability deteriorates.

In general, regular concrete products with a cement content of 450 kg/m3 or less (approximately, the compressive strength at 28 days is 5
00 kgf/cm2 or less), the conditions of appropriate centrifugal force size, rotation time, and time distribution of low speed, medium speed, and high speed rotation (hereinafter referred to as centrifugal force compaction conditions),
If centrifugal compaction is performed, the quality of the concrete pipe is unlikely to be impaired, especially as long as the fluidity of the fresh concrete does not deteriorate during the period from the end of mixing the concrete mixture to the start of centrifugal compaction.

However, in order to increase the strength of concrete pipes, high-strength concrete containing a rich mixture of cement (roughly
If the compressive strength at 28 days is about 700 kgf/cm2 or more), the fluidity in centrifugal force forming is poor, and even if appropriate centrifugal compaction conditions are used, the centrifugal formability of fresh concrete will be poor. It's worse than the regular product above.

Therefore, when manufacturing concrete pipes using such rich mix high-strength concrete, it is conventional to increase the amount of concrete water reducer used to increase the slump of fresh concrete, or to increase the mixing of concrete. Measures are being taken to shorten the period from the end of centrifugal compaction to the start of centrifugal compaction as much as possible.

However, in the production process using the filling method, if the slump of the ready-mixed concrete is too large, the ready-mixed concrete poured into the formwork will flow out of the formwork and the formwork cannot be assembled, so there is a limit to increasing the slump. , its adjustment is difficult.

In addition, when taking the latter measure, if a problem occurs in the manufacturing process, the time until centrifugal force compaction starts will be extended, and the already mixed ready-mixed concrete will be affected by centrifugal force compaction. The drawback is that the fluidity that allows for sufficient molding is lost, and the centrifugal formability of fresh concrete is impaired.

The use of fresh concrete whose slump has been increased by post-addition of a concrete water reducing agent for the production of concrete pipes is somewhat effective in improving its centrifugal formability.

However, in this case, it is necessary to add a concrete water reducer and knead the concrete mixture immediately before centrifugal compaction, so it cannot be practically applied to the production of concrete pipes using centrifugal compaction.

In addition, even if a concrete water reducing agent is added after mixing in a mixer, the slump only increases temporarily, and the rate of decrease in slump over time after mixing is not improved, and the centrifugal force The effect of improving moldability is small.

Ready-mixed concrete with truly excellent centrifugal formability has fluidity that allows it to be compacted easily during centrifugal compaction.
In addition, it is a ready-mixed concrete whose fluidity decreases little with time.

An object of the present invention is to provide a method for producing ready-mixed concrete that eliminates the drawbacks of the conventional methods described above, retains fluidity, and exhibits less deterioration in fluidity over time.

In addition, we provide a method for producing ready-mixed concrete that makes it possible to form dense, high-quality concrete products with excellent strength, watertightness, and appearance, and furthermore, we aim to improve the centrifugal formability of concrete products. It is also an object of the present invention to provide a method for producing ready-mixed concrete.

The present inventors have discovered that when mixing concrete, by first kneading a concrete mixture containing cement and water, and then adding a concrete water reducer and zinc oxide and kneading again, the desired result can be achieved without the drawbacks of conventional methods. It was discovered that the desired ready-mixed concrete could be obtained.

In particular, according to this kneading method, it is possible to obtain fresh concrete that has fluidity that makes it easy to perform centrifugal compaction and sufficiently compaction compared to the method of adding a concrete water reducer afterward, and the fluidity It has been found that unexpected and remarkable effects such as an extended shelf life and a good quality after curing are achieved.

The present invention comprises the steps of kneading a concrete mix containing cement and water, and then adding and kneading a concrete water reducer and zinc oxide to the concrete mix, so that the amount of zinc oxide is The present invention provides a method for producing ready-mixed concrete for concrete products, which involves centrifugal molding and subsequent steam curing, characterized in that the amount is 0.03 to 0.15% by weight based on the cement contained in the product.

The reason why concrete having fluidity suitable for centrifugal compaction can be obtained by the method of the present invention is not clear, but one possible reason is as follows.

When cement and water come into contact, aqueous phase products accumulate on the surface of the cement particles, increasing the viscosity of the concrete.

After this, when a concrete water reducer and zinc oxide are added and kneaded, the concrete water reducer and zinc oxide cover the hydration product, and the dispersion effect of the concrete water reducer causes gaps between the cement particles covered by the hydration product. At the same time, zinc oxide's water use reaction inhibiting action inhibits the subsequent hydration reaction of C3S, which accounts for most of the cement particles. It is thought that this method is more stable than the method of adding only a concrete water reducer and kneading afterward, and has fluidity that allows it to be easily compacted by centrifugal compaction.

According to the present invention, concrete having fluidity that can be easily compacted by centrifugal compaction can be obtained, and
Because the fluidity retention period is extended, there is no need to increase the slump of fresh concrete after mixing, and even if a problem occurs in the concrete pipe manufacturing process and the time required to start centrifugal compaction is extended. There is little risk that the centrifugal formability of the concrete pipe will be impaired.

Therefore, if the fresh concrete according to the present invention is centrifugally formed, the centrifugal formability of the concrete pipe is improved, and a dense, high-quality concrete pipe with excellent strength, watertightness, and appearance can be obtained.

The cement used in the present invention is not only ordinary Portland cement, but also early strength Portland cement, blast furnace cement, fly ash cement, silica cement, and the like.

The concrete water reducing agent used in the present invention is one normally used when mixing concrete, such as EVA, lignin sulfonic acid type, oxycarboxylic acid type, naphthalene sulfonic acid formalin condensate, polycyclic aromatic sulfonic acid, high It is a concrete water reducing agent whose main component is condensed triazine, etc., and is not particularly limited.

Next, the amount of zinc oxide added to the weight of cement contained in the concrete mixture varies depending on the fluidity of fresh concrete, the working temperature, and the required setting time, but the hydration reaction of cement is slow at low temperatures and slow at high temperatures. Since it will be faster, it will be determined appropriately considering the temperature at the time of work, but
When using steam curing in curing concrete, the content is preferably 0.03 to 0.15% by weight.

If the amount added is less than 0.03% by weight, the effects of the present invention will not be noticeable, and if it exceeds 0.15% by weight, the strength of the concrete will decrease, which is not preferable.

As described above, the method for producing ready-mixed concrete of the present invention provides ready-mixed concrete that has effective fluidity in centrifugal force forming and has a long retention period of fluidity, and has a high strength and rich blend with a large amount of cement. The effect is particularly strong on concrete.

Next, examples of the present invention will be described, but the present invention is not limited to these examples.

In the example, the cement used was early strength Portland cement manufactured by Mitsubishi Mining Cement ■, and the fine aggregate was Fujishucho River Sand (
Specific gravity: 2.63, water absorption rate 1.60%, FM: 2.81)
Crushed stone for phase electrode (specific gravity: 2.69, absorption rate 1.
37%, maximum dimension: 20 mm), and as a concrete water reducing agent, a concrete water reducing agent manufactured by Kao Soap (trade name Mighty 150) containing β-naphthalene sulfonic acid formalin condensate as an active ingredient was used.

Using the above-mentioned materials with the addition amounts and compounding amounts shown in Table 1,
Fresh concrete was prepared using the following mixing methods.

Note that Experiments 5 to 7 are of the present invention, and the other experiments are comparative examples.

Experiment 1: Cement, water, concrete water reducer, and aggregate were simultaneously put into a mixer and mixed for 2 minutes.

Experiment 2: Cement, water, and aggregate were put into a mixer at the same time and kneaded for 1 minute, then a concrete water reducer was added and kneaded again for 1 minute.

Experiment 3: Cement, water, zinc oxide, and aggregate were put into the mixer at the same time and mixed for 1 minute, then a concrete water reducer was added and mixed for 1 minute again.

Experiments 4 to 9: Cement, water, and aggregate were placed in a mixer at the same time and kneaded for 1 minute, and then concrete water reducer and zinc oxide were added and kneaded again for 1 minute.

Note: (1), (2) Addition amount, weight% relative to cement (
3) W/C; water cement ratio %, S/a; fine aggregate ratio %, C
: Unit amount of cement kg/m, W; Unit amount of water kg/m3 To compact concrete using centrifugal force, 15 kg of fresh concrete after cross-conducting is made into pipes with the dimensions of the specimen having an outer diameter of 20 cm and a length of 30 cm. Inserted into the machine, initial speed 170r
pm for 3 minutes, medium speed 365 rpm for 1 minute, high speed 600 rpm
rpm for 4 minutes to produce concrete pipes and compare centrifugal formability.

In addition, fresh concrete from the same lot as the fresh concrete used for the centrifugal compaction was poured into a formwork with a diameter of 10 m and a height of 20 cm, and a table pipe plate (vibration frequency of 6000
rpm, amplitude 4 mm) for 20 seconds to compact the specimen, and produce a specimen for compressive strength testing.

All of these specimens were subjected to normal pressure steam curing under the conditions of 5 hours of pre-incubation time, 5 hours of temperature rise gradient and 80 degrees Celsius of H1 maximum temperature, and decomposition after 24 hours had passed from the end of fresh concrete mixing. It was molded and left in a room at 20°C until it reached the age of strength testing.

Table 2 shows the properties of ready-mixed concrete obtained by the above-mentioned various cross-conducting methods and the performance and properties of concrete pipes obtained from these ready-mixed concretes.

Note: (1) Value based on elapsed time from the end of kneading (2) Compressive strength at 28 days after steam curing (3) Diameter 10
Compaction was started immediately after the completion of kneading, using a compressive strength of a specimen with a height of 20 cm and a height of 20 cm.

(4) Compressive strength of a cylindrical specimen with an outer diameter of 20 cm and a height of 30 cm (5) Elapsed time from the end of crosstalk to the start of centrifugal compaction, which is the start time of compaction of a cylindrical specimen with an outer diameter of 20 cm and a height of 30 cm Hail.

(6) Crosstalk, slump measurement, and compaction temperature: 20°C In the concrete pipe of Experiment 1, the pipe body was not compacted uniformly, and the presence of numerous voids was observed throughout the cylindrical surface and end face of the pipe. The compressive strength of force-compacted specimens is significantly lower than that of vibration-compacted specimens.

In the concrete pipes of Experiments 2 to 4, a separation layer with significant unevenness was observed on the inner wall of the pipe, and the presence of voids was observed on the end face of the pipe body.

Experiments 5 to 9 (Experiments 5 to 7 were conducted using the method of the present invention)
were made using the method of the present invention, and all of the concrete pipes are concretes with excellent centrifugal formability, in which the entire pipe is densely compacted, and there is no uneven separation layer on the inner wall of the pipe. It was a tube.

The effect of improving centrifugal formability in the present invention can be easily estimated not only from the observation of the above-mentioned appearance, but also from a comparison of the compressive strengths of the vibration-compacted specimen and the centrifugal-compacted specimen.

That is, as shown in Table 2, when comparing the compressive strength of centrifugal compaction test specimens with that of vibration compaction test specimens, it is found that the increase in compressive strength of the centrifugal compaction test specimens is at most is 0.90, whereas that of ready-mixed concrete produced by the method of the present invention (Experiments 5 to 7) is 1.1.
The values range from 2 to 1.17, indicating that the fresh concrete produced by the method of the present invention has a remarkable centrifugal compaction effect.

In addition, as shown in Table 2, the slump at the start of centrifugal compaction of fresh concrete according to the method of the present invention (Experiment 5 to
7) is in the range of 1.6 to 2.0 cm, and the slump of fresh concrete other than the present invention (Experiments 1 to 4) is 1.8 to 2.3.
cm range and there is no significant difference between the two, and the period from the end of mixing the fresh concrete to the start of centrifugal compaction is 45 minutes in the method of the present invention and 30 minutes in the method other than the present invention (Experiments 1 to 4). The clear difference in centrifugal force formability of the fresh concrete produced by the method of the present invention is that the fresh concrete produced by the method of the present invention has fluidity suitable for compaction using centrifugal force, and This conflict stems from the long holding period.

Specifically, when comparing Experiment 3 and Experiment 6, in which the amounts of the compositions were exactly the same, Experiment 6, which is the method of the present invention, shows a smaller rate of decrease in slump over time.

In addition, in Experiment 6, the centrifugal compaction start time was delayed by 15 minutes compared to Experiment 3, and even though the slump at the centrifugal compaction start time was 0.3 mm lower, the compressive strength was lower than that in the case of vibration compaction. Not only does this increase, but it also increases significantly in the case of centrifugal compaction, and the appearance of centrifugal compaction becomes denser, resulting in ready-mixed concrete with excellent centrifugal formability.

In addition, the amount of decrease in slump 45 minutes after the end of kneading in Experiments 5 to 9 was in the range of 3.4 to 4.9 times, which was 5.4 cm in Experiment 3 or 5.9 cm in Experiment 2. few.

Therefore, it goes without saying that the method of the present invention has a remarkable effect in the concrete field where centrifugal force is used to compact the concrete, but it is also useful as a countermeasure against the decline in slump due to aging in other concrete fields.

In addition, when curing concrete pipes using steam, if the amount of zinc oxide added is larger than necessary, as shown in Experiments 8 and 9, even if the pipe body has excellent centrifugal formability, its compression will deteriorate. It is preferred that the amount of zinc oxide added does not exceed 0.15% based on the weight of cement contained in the concrete mix, as strength may be compromised.

Claims (1)

[Claims] 1 Consists of a step of kneading a concrete mix containing cement and water, and then a step of adding a concrete water reducer and zinc oxide to the concrete mix and kneading, so that the amount of zinc oxide is added to the concrete mix. A method for producing ready-mixed concrete for concrete products, which comprises centrifugal force forming and subsequent steam curing, characterized in that the content is 0.03 to 0.15% by weight based on the cement contained.