JPH0325324B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing concrete by mechanically mixing concrete materials using a batch mixer.

To illustrate the conventional mechanical mixing process, as shown in Figure 1, cement, sand, gravel, water, and an admixture are put into a rotating mixer almost simultaneously and mixed, and the mixed concrete is mixed. The process of taking it out from the mixer is common.

Various experiments have been attempted regarding the order in which concrete materials are added; some methods include making cement paste first, then adding sand and gravel in that order; Alternatively, cement is mixed with sand whose moisture content has been kept constant in advance to make mortar, and then gravel and gravel are added. It is also known to mix it into concrete by adding water. Another known method is to first mix cement, sand, and gravel, perform dry mixing, then add water and an admixture, and then mix and stir again. It is not clear how this affects the strength of the material.

Therefore, this invention succeeded in elucidating the dry kneading time, etc., which can be expected to improve slump and compressive strength. It is characterized by kneading, and then adding coarse aggregate, water, and an admixture, and mixing and stirring again. The dry kneading time is preferably about 0.5 to 3 minutes, and the admixture is So-called high-performance water reducing agents such as those based on polyalkylaryl sulfonates or those based on high condensates of triazine derivatives are preferable, and dry kneading and final mixing and stirring should be performed in different mixers. is preferable.

Examples using the method of the present invention and experimental examples using the conventional method will be shown below.

The materials used are Γ cement... Ordinary Portland cement made by Company 0, specific gravity 3.17 Γ Fine aggregate... Natural sand from Kinugawa, specific gravity 2.60 Γ Coarse aggregate... Crushed boulder from Kinugawa, specific gravity 2.61 In addition, the The slump range is
This shows the range when no dry kneading is performed.

Next, the compressive strength is measured by outer diameter 20cm x inner diameter 12cm x
A centrifugal specimen with a length of 30 cm was steam-cured and then treated with high-temperature, high-pressure steam curing at a maximum temperature of 180°C and a pressure of 10 atm for 3 hours.

Test results The slump for the formulations shown in Table 1 is as shown in Figure 3. (1) By performing dry kneading, higher water reduction is achieved than with the current kneading method that does not perform dry kneading. The slump when using the agent is significantly larger.

In other words, as shown in Table 1, the slump without dry kneading is 3.0 to 7 cm, whereas in the case of using a high performance water reducing agent and dry kneading for 1 minute, the slump is 13.5 cm.
~19.5cm, and 18.5cm in 3 minutes of dry kneading.
~21.5cm, and by performing dry kneading for 1 minute and using a high-performance water reducer, the slump is almost 21.5cm compared to that without dry kneading and using a normal water reducer. The value is 6 times to 6 times, and it is considered that the synergistic effect of dry kneading and the use of a high performance water reducing agent has a particularly large effect on the increase in slump.

(2) As the dry kneading time increases, the slump also increases, but this increasing trend ends around 3 minutes.

Next, we investigated the effect of dry kneading on the compressive strength of the formulations shown in Table 2.
As shown in Figure 4, (3) When the water-cement ratio is within the same range, the compressive strength hardly changes even if dry kneading is performed.

(4) Even when dry mixing is performed, the compressive strength of concrete increases as the water-cement ratio decreases.

(5) Therefore, it can be inferred from these facts that by performing dry mixing, concrete with the same level of slump can be obtained even if the unit water volume is reduced compared to when dry mixing is not performed. Therefore, if the unit amount of water can be reduced in this way, the water-cement ratio will also be reduced, and the compressive strength of concrete will increase as shown in FIG. 4.

(6) Therefore, when dealing with the predetermined compressive strength required by concrete products, the amount of cement per unit can be reduced by adopting the dry mixing method of this invention compared to the current method that does not perform dry mixing. It is.

In other words, it was found that by employing dry mixing, it was possible to produce inexpensive concrete with a small amount of cement per unit.

(7) Water reducing agents that are generally used as admixtures are broadly classified into ordinary water reducing agents and high performance water reducing agents.General water reducing agents include Γlignin sulfonate type (NM Company Product C Test No. 17~ Two types of Γ-hydroxycarboxylic acids are known.

In addition, high-performance water reducing agents include Γ polyalkylaryl sulfonate type (product A of K company, used for test numbers 1 to 12 and 21 to 28), high condensate system of Γ triazine derivatives (product B of NM company, test number 13) There are two known types:

Then, when a normal water reducing agent or a high performance water reducing agent was added to the formulation shown in Table 1 and dry kneading was carried out, whether or not there was an increase in slump was investigated, as shown in Figure 3. (a) Even if a normal water reducing agent is added, an increase in slump due to dry mixing cannot be expected, but if a high performance water reducing agent is used, the increase in slump due to dry mixing is significant.

In addition, those belonging to the above polyalkylaryl sulfonate type mainly contain formalin high condensates of naphthalene sulfonic acid or its derivatives or related substances, and those belonging to the above high condensates of triazine derivatives have melamine as the main component. The main component is formalin resin sulfonate, and most of the commercially available products belong to the polyalkylaryl sulfonate type.
The chemical structures of these main components are shown on the next page.

In addition, these high-performance water reducing agents greatly increase their water reducing properties as the amount of Γ used increases, compared to ordinary water reducing agents.

Γ Air entrainment is small.

Has little Γ setting retardation effect.

Most of them are characterized by
It is sold as a liquid product of 1.15 to 1.25.
The amount used varies widely, from 0.5 to 4% of the weight of cement, depending on the brand and purpose of use.

Recently, there are also types that have been given setting retarding properties by adding a retarder.

(b) For the formulations shown in Table 1, the relationship between the addition ratio of high performance water reducing agent (relative to cement) and the increase in slump was investigated for each dry kneading time. As shown in the figure, the increasing tendency of slump reaches a saturated state when the addition rate is around 2%.

(8) Considering the above test results, (a) It is most preferable to set the dry kneading time to approximately 0.5 to 3 minutes; if it is shorter than this, the materials may not be mixed evenly. In practice, this is difficult, and even if the length is longer than this, the slump will hardly increase, resulting in inefficiency.

(a) As an admixture, it is effective to use a high performance water reducing agent to increase slump.

In addition, it is possible to use an additive rate of about 0.2 to about 7.5% by weight relative to cement, but a small amount will not be effective as a water reducer, and an excessive amount will increase the viscosity of the concrete and impede the pumping performance. The addition rate of the water reducing agent is the same as that of the K company A product mainly used in the above experiments, i.e., the high performance water reducing agent based on polyallylalkyl sulfonate. The rate is approx.
When using a water reducing agent based on a high condensate of triazine derivatives, which is considered to have a preferable value of 0.5 to about 2%, and is said to have about half the performance of this polyallylalkyl sulfonate based water reducing agent, About 1 to about 4% is considered a preferred addition rate.

In addition, it is said that powdered products have about twice the performance as liquid ones, so taking this into consideration, we developed the method of this invention using currently commercially available high-performance water reducing agents. Preferred addition rates for carrying out the above are shown in Table 3.

(c) The total weight of the cement and fine aggregate that is added in the dry mixing operation that is the first step is calculated based on the total weight of the coarse aggregate that is added to the mixing and stirring operation of the second step. Since the total weight of water and admixture is approximately equal, when repeating concrete production work, first perform dry mixing in the first mixer, then mix from this first mixer to the second mixer. If the dry mixed cement and fine aggregate are transferred and the coarse aggregate, water, and admixture are added to this second mixer and mixed and stirred, the raw materials can be mixed in the first mixer as well. We will be processing approximately 1/2 the weight of the product, and since the first mixer performs dry kneading before adding water, the mixing resistance is small, so the first mixer has a small capacity. Next, in the second mixer, the mixing and stirring work is performed after the dry kneading is completed, so the mixing time is shortened, and since the mixing resistance in each mixer can be divided in this way, each It is economical because a small mixer is sufficient.

(9) From the above considerations, ``By dry-mixing concrete material to which a high-performance water-reducing agent has been added, a predetermined slump (12 ± 2 cm) can be secured, and the unit water volume can be adjusted according to the dry-mixing time. As shown in Figure 6, they confirmed the assumption that "if the amount of concrete is reduced and the concrete is mixed, the compressive strength of the concrete will be higher than that of the current method that does not include dry mixing."

That is, in the same figure, the method of the present invention is used to
As shown in the mixing table in the table, the amount of cement per unit was reduced compared to the conventional method, and the slump was maintained within the range of 15 ± 2.5 cm as shown in the table. As a result, if we calculate the unit amount of cement to obtain the same compressive strength as the current method, that is, 800 kg/cm ² from Figure 6, it will be 368 kg as shown by the arrow.
Kg/m ³ , so compared to the case without dry kneading, by performing dry kneading, 430Kg/m ³ −368
It was found that the amount of cement per unit could be reduced by Kg/m ³ = 62Kg/m ³ .

As described above, the method for producing concrete of the present invention involves adding cement and fine aggregate to a mixer, mixing and stirring the dry mixing operation for about 0.5 minutes to about 3 minutes.
After that, the coarse aggregate, water, and a high-performance water reducer as an admixture are added and mixed and stirred again.
Dry kneading for about 5 minutes to about 3 minutes will ensure sufficient mixing and improve slump.
Moreover, the slump was further increased by using the high performance water reducing agent, and the synergistic effect of dry kneading and the use of the high performance water reducing agent resulted in a significant increase in the slump.

Then, the unit amount of water can be reduced in accordance with this increase in slump, and the unit amount of cement can be reduced in accordance with the improvement in compressive strength due to the decrease in unit water amount.
In this way, after performing the dry kneading operation for less than a few minutes,
By adding a small amount of high-performance water reducer, the amount of cement used could be reduced compared to conventional methods, and manufacturing costs could be lowered.

Furthermore, since the dry mixing operation is carried out by mixing cement and fine aggregate without introducing coarse aggregate, there is also the advantage that wear on the mixer due to coarse aggregate can be reduced.

[Brief explanation of drawings]

Fig. 1 is a process diagram showing the conventional manufacturing method, Fig. 2 is a process diagram showing the manufacturing method of the present invention, and Figs. 3 to 6 are experimental data showing the results of the manufacturing method of the present invention. It is a diagram.

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Claims (1)

[Claims] 1. Put cement and fine aggregate into a mixer, mix and stir them for about 0.5 to 3 minutes, and then add coarse aggregate, water, and a high-performance water reducer. A method for producing concrete characterized by mixing and stirring again.