JP7560017B2 - Treatment agent for ready-mixed concrete, method for producing treatment agent for ready-mixed concrete, and method for treating ready-mixed concrete - Google Patents

Description

The present invention relates to a treatment agent for ready-mixed concrete, a manufacturing method for the treatment agent for ready-mixed concrete, and a method for treating ready-mixed concrete. More specifically, the present invention relates to a treatment agent for ready-mixed concrete that can recycle remaining ready-mixed concrete in a low-cost and simple manner, a manufacturing method for the treatment agent for ready-mixed concrete, and a method for treating ready-mixed concrete.

Most of the concrete used at construction sites is transported from a concrete manufacturing plant to the site as ready mixed concrete by an agitator truck (also called a mixer truck, ready mixed concrete truck, truck mixer, etc.), and poured using equipment such as a concrete pump. However, for the convenience of managing ready mixed concrete, construction sites generally order more than the required amount, so some of the ready mixed concrete transported to the site becomes surplus and is returned to the factory (remaining concrete). In addition, ready mixed concrete that does not meet quality standards or is an inappropriate mix due to an ordering error and fails the unloading inspection is also returned unused to the factory (returned concrete).

As described above, at construction sites where ready-mixed concrete is used, there is a constant production of surplus leftover concrete, or returned concrete, which is returned to the factory. Furthermore, some ready-mixed concrete produced at concrete manufacturing plants is not shipped and remains unused. This type of leftover ready-mixed concrete is usually discharged from the drum of an agitator truck or the mixer at a concrete manufacturing plant before hardening, and is disposed of as industrial waste. For ready-mixed concrete providers, the cost of disposing of this leftover ready-mixed concrete is a significant burden.

In recent years, therefore, from the perspective of effective resource utilization, there has been a demand for technology to recycle this remaining ready-mix concrete and recycle it as raw material for concrete blocks or recycled aggregate. However, a large amount of water is added to the remaining concrete when it is discharged from the agitator truck, so it becomes a highly fluid slurry and there is a risk that it will not set properly as ready-mix concrete. In addition, when the cause of poor quality is an abnormal slump or an excessive unit water content, the returned concrete also has an excess of water, which also causes the problem of it becoming a slurry and being difficult to harden.

To address the above problems, for example, Patent Document 1 proposes a method of treating ready-mixed concrete in which a water-absorbent polymer is added to and mixed with slurry-like ready-mixed concrete, and the slurry-like ready-mixed concrete is granulated by the water-absorbing action of the water-absorbent polymer.

JP 2011-62943 A

However, when a polymer flocculant is used to treat ready-mix concrete, as in the technology disclosed in Patent Document 1, it has poor dispersibility in the ready-mix concrete, it takes a long time for the ready-mix concrete to harden, and a large amount of the polymer flocculant must be used, which creates problems in terms of economy.

Meanwhile, after extensive research, the inventors of the present invention have discovered that the reason the remaining ready-mixed concrete does not harden normally is because the remaining ready-mixed concrete has a high unit water content, which reduces the separation resistance of the ready-mixed concrete, causing the aggregate and cement paste in the ready-mixed concrete to separate during hardening, and causing only the cement paste to harden, turning the aggregate into sludge. Based on this knowledge, they have developed a treatment agent whose main component is paper sludge ash, which can restore the separation resistance and moldability of the remaining ready-mixed concrete to a certain degree.

The present invention was devised in light of the above points, and relates to a treatment agent for ready-mixed concrete that can recycle remaining ready-mixed concrete in a low-cost and simple manner, a manufacturing method for the treatment agent for ready-mixed concrete, and a method for treating ready-mixed concrete.

To achieve the above objective, the treatment agent for ready-mix concrete of the present invention is a porous material containing calcium carbonate, calcium hydroxide, and silica as main components, and talc as a trace component.

The components of the treatment agent for ready-mixed concrete are porous bodies containing calcium carbonate, calcium hydroxide, and silica as the main components, which increases water absorption and allows it to absorb water from leftover fresh concrete, such as leftover concrete that has had water added, or from returned concrete, thereby restoring the separation resistance and moldability of the ready-mixed concrete to a certain degree. Calcium carbonate and calcium hydroxide are also found in large amounts in cement reactants and limestone, which is their raw material, and can actively react with unreacted cement in the remaining ready-mixed concrete, promoting that reaction.

In addition, by including talc as a trace component in the treatment agent for ready-mixed concrete, the talc can improve smoothness and tribological properties between aggregates, so that the properties of ready-mixed concrete to which the treatment agent has been added can be improved, for example, in terms of self-leveling properties.

In addition, when the content of calcium (Ca), silicon (Si), and magnesium (Mg) in the paper sludge ash satisfies the numerical range of 65-85% by weight of Ca as CaO, 5-15% by weight of Si as _SiO2 , and 0.5% by weight or more of Mg as MgO, calculated as oxide equivalent with the total weight of the following oxides being 100% by weight, the paper sludge ash can absorb the moisture contained in the remaining ready-mixed concrete to restore the separation resistance and moldability of the ready-mixed concrete. In addition, since Ca and Mg each have a high affinity with cement, the presence of a certain amount of these components promotes the hydration reaction of cement and ensures the strength of the ready-mixed concrete.

Here, the treatment agent absorbs the water in the fresh concrete, thereby restoring the water-cement ratio of the fresh concrete and at the same time contributing as fine aggregate. The strength of concrete is affected by the water-cement if the aggregate is the same, and depends on the strength of the aggregate used if the water-cement ratio is the same. Therefore, treatment agents are required to have high water absorption and high strength as an aggregate.

The water absorbency in the treatment agent is generated during the manufacturing process of the agent by the combustion of cellulose at around 500°C and the thermal decomposition (decarbonation) of calcium carbonate contained in paper sludge at around 825°C. Also, at around 500°C, the cellulose, which accounts for around 40% by volume of the paper sludge, spontaneously combusts, causing the paper sludge aggregate particles to turn into a porous body. After that, at around 825°C, the calcium carbonate in the residue thermally decomposes, forming even finer pores in the porous body, improving water absorption performance due to capillary action, and the cellulose components are completely insulated, so the higher the calcium content, the higher the water absorbency tends to be.

However, calcium carbonate and calcium oxide (or calcium hydroxide that absorbs water at room temperature) are weak as aggregates, so considering the physical properties of hardened concrete, it is necessary to include an appropriate amount of silica ( _SiO2 ) (around 10%). The magnesium in the treatment agent is derived from talc. After the treatment agent is added, the ready-mix concrete becomes concrete with a very high fine aggregate ratio, which makes it highly thixotropic, but the fluidity between the aggregates can be maintained by including 0.5% or more talc calculated as MgO.

Furthermore, when the density of paper sludge ash is 1.9 to 2.3 g/ ^cm3 and the water absorption rate is 45% or more, adding a treatment agent made of such paper sludge ash to ready-mix concrete with added water effectively absorbs the water in the ready-mix concrete, improving the separation resistance and moldability of the ready-mix concrete.

To achieve the above-mentioned objective, the manufacturing method of the present invention for a treatment agent for ready-mix concrete comprises the steps of: adding a predetermined amount of coagulant to wastewater discharged during the waste paper recycling process to produce paper sludge; and calcining the paper sludge at a temperature of 800°C to 900°C to produce paper sludge ash that contains calcium carbonate, calcium hydroxide, and silica as main components, and talc as a trace component.

Here, by providing a process for generating papermaking sludge by adding a predetermined amount of coagulant to the wastewater discharged during the wastepaper recycling process, it is possible to generate papermaking sludge by coagulating colloidal particles contained in the wastewater discharged during the wastepaper recycling process. More specifically, the coagulant generates papermaking sludge consisting of pulp (cellulose), talc, calcium hydroxide, and calcium carbonate contained in the wastepaper.

In addition, by providing a process for burning the paper sludge at temperatures between 800°C and 900°C to produce paper sludge ash made of porous materials containing calcium carbonate, calcium hydroxide, and silica as the main components, the cellulose in the paper sludge, which has a low melting point, is burned to form paper sludge ash made of porous materials including calcium carbonate. In this way, the paper sludge ash made of porous materials has high water absorption, and by adding it to residual concrete, which is water-added ready-mix concrete, or to remaining ready-mix concrete such as returned concrete, it is possible to effectively absorb the water in the remaining ready-mix concrete and restore the separation resistance and moldability of the ready-mix concrete to a certain degree.

Furthermore, by burning paper sludge, in addition to the main components mentioned above, it is possible to include talc as a minor component. This talc has a high affinity with cement and can improve the properties of ready-mix concrete when water is added.

If the firing temperature of the paper sludge is less than 500°C, the oxidation reaction does not proceed, so the cellulose contained in the paper sludge does not burn completely, and the treatment agent does not form a porous body, which may result in poor water absorption. On the other hand, the upper limit of the firing temperature is not particularly limited, but when the firing temperature exceeds approximately 825°C, calcium carbonate gradually changes to calcium oxide, and when it exceeds 850°C, it changes completely to calcium oxide. However, during the cooling process of the paper sludge ash, some of the calcium oxide absorbs moisture in the air and changes to calcium hydroxide. Therefore, when the firing temperature exceeds approximately 850°C, the content ratio of calcium carbonate and calcium hydroxide may change, but in either case, a treatment agent with high water absorption can be achieved.

In order to achieve the above-mentioned objective, the method for treating ready-mixed concrete of the present invention involves adding a prescribed amount of a treatment agent consisting of a porous material whose main components are calcium carbonate, calcium hydroxide, and silica, with talc as a minor component, to the remaining ready-mixed concrete to which water has been added.

The components of the treatment agent are porous bodies whose main components are calcium carbonate, calcium hydroxide, and silica, and these have the property of being highly water absorbent. By adding a certain amount of this treatment agent to the remaining concrete that has had water added to it, or to the remaining ready-mixed concrete that is the returned concrete, it is possible to absorb the moisture contained in the remaining ready-mixed concrete and restore the separation resistance and moldability of the remaining ready-mixed concrete to a certain degree.

In addition, when the amount of treatment agent to be added (M _PS ) is calculated based on the formula shown in the following equation 1, where M (kg) is the mass of the remaining fresh concrete, _W0 (kg/m ³ ) is the unit water content of the remaining fresh concrete before adding water, _W1 (kg/m ³ ) is the estimated unit water content of the remaining fresh concrete after adding water, ρ (kg/m ³ ) is the unit volume mass of the base concrete calculated from the designated mix proportion, and α is a proportionality constant according to the type of cement, the optimal treatment agent can be calculated based on various parameters such as the amount of water contained in the remaining fresh concrete, and the separation resistance and formability of the remaining fresh concrete can be more effectively restored.

In addition, if an amount of treatment agent equivalent to the amount calculated based on the formula shown in equation 1 is poured into the drum of an agitator vehicle containing remaining ready-mixed concrete and the drum is stirred for a specified period of time, the treatment agent can be mixed uniformly throughout the remaining ready-mixed concrete remaining in the drum, thereby maintaining a consistent quality of the ready-mixed concrete.

The treatment agent for ready-mixed concrete, the manufacturing method of the treatment agent for ready-mixed concrete, and the method for treating ready-mixed concrete according to the present invention are low-cost and simple methods for recycling remaining ready-mixed concrete.

1A to 1C are process diagrams illustrating a method for producing a treatment agent according to an embodiment of the present invention. 1 is a process diagram showing a method of using a treatment agent according to an embodiment of the present invention. FIG. 4 is a diagram showing the results of an analysis of components contained in a treatment agent according to an embodiment of the present invention. FIG. 2 is a diagram showing the results of an X-ray analysis of ready-mix concrete before the addition of a treatment agent according to an embodiment of the present invention. FIG. 1 is a diagram showing the results of an X-ray analysis of ready-mix concrete after adding a treatment agent according to an embodiment of the present invention.

The treatment agent for ready-mixed concrete, the manufacturing method of the treatment agent for ready-mixed concrete, and the treatment method for ready-mixed concrete according to the embodiments of the present invention will be described in detail below with reference to drawings and the like to facilitate understanding of the present invention.

Figure 1 shows a process diagram for manufacturing a treatment agent for ready-mix concrete according to an embodiment of the present invention. In the manufacturing method for a treatment agent for ready-mix concrete, waste paper to be recycled is first brought into a waste paper recycling processing plant, where it undergoes well-known recycling processes such as disintegration, dust removal, deinking, and bleaching (step 11). A flocculant is then added to the wastewater generated by the recycling process in step 11, producing paper sludge as a precipitate (step 12). The paper sludge is then fired at temperatures of approximately 800°C to 900°C to produce paper sludge ash made of a porous body (step 13).

The paper sludge ash obtained by the above process is a treatment agent for ready-mixed concrete according to an embodiment of the present invention. The treatment agent is individually packaged, for example, in a water-soluble packaging material, and as described below, the required amount can be added to the remaining ready-mixed concrete to restore the slump of the remaining ready-mixed concrete and improve the properties of the ready-mixed concrete to meet specified standards.

Here, the paper sludge ash does not necessarily have to be produced by burning paper sludge produced from wastewater discharged from the recycling process of waste paper. For example, the raw material can be paper sludge made from wastewater generated during the process of making paper from new pulp (virgin pulp) made from wood.

However, when virgin pulp is used, the main components of the treatment agent, such as calcium carbonate, silica, and talc, are not contained in the wood chips, and the amount of chemicals added after the wood chips are produced for the purpose of strengthening the paper is unintentionally discharged as papermaking sludge. As a result, the wastewater discharged from the virgin pulp papermaking process may contain only a small amount of the components that make up the treatment agent of the present invention, making it difficult to actively and consistently expect the separation resistance and moldability of the remaining ready-mixed concrete to be effectively restored.

More specifically, the elements contained in paper sludge ash resulting from wastewater discharged from virgin pulp are relatively high in silicon, aluminum, and iron, while calcium and magnesium components are decreased, so there is a risk that the specified performance of the treatment agent of the present invention will not be fully achieved.

The flocculant added to the wastewater to produce the papermaking sludge used in step 12 is an inorganic flocculant whose main components are polyaluminum chloride and polyiron chloride. However, it is also possible to use other inorganic flocculants or polymer flocculants.

The conditions for burning the paper sludge in step 13 are not limited to the temperature conditions of approximately 800°C to 900°C. However, if the burning temperature is less than approximately 800°C, the calcium carbonate component contained in the paper sludge will not undergo a sufficient decarbonation reaction, making it impossible to produce paper sludge ash made of a porous body, and there is a risk that a certain level of water absorption will not be secured. However, if the burning temperature is less than 500°C, the cellulose will not be decomposed, making it impossible to obtain the desired performance.

The upper limit of the firing temperature is not particularly limited, and can be set appropriately taking into account firing costs, etc. If the firing temperature is within the range of approximately 800°C to 850°C, the paper sludge ash after firing will contain calcium carbonate, calcium hydroxide, and silica as the main components.

When paper sludge is fired at approximately 825°C or higher, the calcium carbonate contained in the paper sludge is converted to calcium oxide. Meanwhile, calcium oxide absorbs moisture in the air and converts to calcium hydroxide during the cooling process of the paper sludge ash. Therefore, when the firing temperature exceeds approximately 850°C, the content ratio of calcium carbonate and calcium hydroxide may change, but in either case, a highly water-absorbent treatment agent can be achieved. When the firing temperature exceeds 900°C, the talc component gradually begins to dehydrate and pyrolyze. Therefore, it is preferable to set the firing temperature to less than approximately 900°C.

Next, the method of using the treatment agent (paper sludge ash) obtained by the above-mentioned manufacturing process will be explained with reference to Figure 2.

First, the mass M (kg) of the remaining ready-mix concrete remaining in the drum of the agitator truck that has returned to the concrete manufacturing plant is measured (step 21). The mass of the remaining ready-mix concrete can be measured using a large weighing device such as a truck scale.

Next, a certain amount (e.g., 10 L) of the remaining fresh concrete is sampled from the drum, the mass of the sample is measured, the density is calculated, and the calculated density is input into a unit water meter to measure the unit water content _W0 (kg/ ^m3 ) of the remaining fresh concrete before water is added (step 22). Note that the density may be measured by calculation or may be measured using a density meter.

The unit water content before adding water obtained in step 22 is divided by a correction coefficient set for each model of unit water meter used for measurement to calculate an estimated unit water content _W1 (kg/ ^m3 ) of the remaining ready-mixed concrete after adding water (step 23).

Furthermore, the unit volume mass ρ (kg/m ³ ) of the base concrete (basecon) calculated from the designated mix proportion is calculated (step 24 ).

Once the parameters have been obtained in steps 21 to 24, the appropriate amount M _PS (kg/m ³ ) of the treatment agent to be added to the drum of the agitator car is calculated (step 25) based on the formula shown in the above equation 1. Here, α in the formula is a proportionality coefficient for each cement, and for example, for ordinary Portland cement (N cement), α is approximately 0.8.

When the proper amount _MPS of the treatment agent to be added is obtained in step 25, the corresponding amount of treatment agent is measured with a scale and poured into the drum of the agitator car (step 26). At this time, if the treatment agent is prepared in small portions in water-soluble packages for each predetermined unit amount as described above, it is possible to pour the number of treatment agents corresponding to the proper amount into the drum, thereby eliminating the need to measure the treatment agent with a scale.

Once the treatment agent has been poured into the drum, the drum is rotated to mix the treatment agent with the remaining ready-mixed concrete until it is uniform. The time the drum is rotated depends on the rotation speed and the amount of remaining ready-mixed concrete, but rotating it at high speed for approximately three minutes is sufficient.

<Example>
Next, an example will be described. The remaining ready mixed concrete used in the example was ordinary Portland cement (N cement), and had a nominal strength, slump, and coarse aggregate size of "24-18-20N."

First, 500 L (0.5 ^m3 ) of the remaining ready-mixed concrete in the drum was taken as a sample. Based on the density of the sample, the unit water content ( _W0 ) of the remaining ready-mixed concrete before adding water was calculated using a unit water meter (KEYTEC Corporation SONO-WZ) and was 184 kg/ ^m3 . The estimated unit water content ( _W1 ) after adding water was calculated by dividing the estimated unit water content by the correction coefficient of the unit water meter used for the measurement (0.95 in the case of the unit water meter described above), and was found to be 251.6 kg/ ^m3 .

Based on the above parameters, the appropriate amount of the treating agent (M _PS ) was calculated to be approximately 35 kg using the formula shown in Equation 1. Based on this calculation result, 35 kg of the treating agent was poured into the drum, and the drum was rotated at high speed until the treating agent and the remaining fresh concrete were uniformly mixed.

The ready-mixed concrete obtained in this way had an extremely good surface appearance and self-leveling properties due to the talc contained as a trace component in the treatment agent. Furthermore, when the slump of the ready-mixed concrete was measured before and after the addition of the treatment agent, it was confirmed that while the slump of the ready-mixed concrete before the addition of the treatment agent was 65 cm, the slump of the ready-mixed concrete after the addition of the treatment agent improved to 19 cm.

Furthermore, a strength test was conducted on the ready mixed concrete immediately after the addition of the treatment agent. The test concrete used in the strength test was cured using standard curing, ^with a one-week strength of 15.3 N/mm2 and a two-week strength of 18.5 N/ ^mm2 . From these, the estimated four-week strength was approximately 21 N, and while the ready mixed concrete before the addition of the treatment agent was "24-18-20 N," the ready mixed concrete after the addition of the treatment agent was "18-18-20 N," confirming that a certain level of strength was achieved.

Next, the results of component analysis of the treatment agent using an X-ray diffraction device (Shimadzu Corporation) are shown in Figure 3. The measurement was performed three times, and the respective measurement results are indicated as PS1, PS2, and PS3. As shown in Figure 3, the main components of the treatment agent are calcium (Ca), silicon (Si), and magnesium (Mg), and the content of Ca as CaO is 65 to 85 wt %, Si as _SiO2 is 5 to 15 wt %, and Mg as MgO is 0.5 wt % or more, calculated as oxides with the total weight of the oxides being 100 wt %.

The results of analyzing the composition of the ready-mixed concrete before and after the addition of the treatment agent using a wavelength dispersive X-ray fluorescence analyzer (ZSX Primus II, Rigaku Corporation) are shown in Figures 4 and 5. Figure 4 shows the results of the X-ray analysis of the ready-mixed concrete before the addition of the treatment agent, and Figure 5 shows the results of the X-ray analysis of the ready-mixed concrete after the addition of the treatment agent.

As shown in Figures 4 and 5, it can be confirmed that the magnesium (Mg), aluminum (Al), and calcium (Ca) contents in the fresh concrete after the addition of the treatment agent are increased compared to before the treatment agent was added. Of these, magnesium is derived from talc, which is contained as a trace component in the treatment agent. On the other hand, aluminum is derived from polyaluminum chloride and polyferric chloride contained in the coagulant added to the paper sludge. Calcium is derived from calcium carbonate, calcium hydroxide, or calcium oxide contained in the paper sludge.

The content of silicon (Si) derived from the aggregate in the ready-mix concrete is lower after the addition of the treatment agent compared to before, but this is presumably due to a relative decrease in content caused by an increase in the content of other elemental components.

As described above, the treatment agent for ready-mixed concrete, the manufacturing method for the treatment agent for ready-mixed concrete, and the method for treating ready-mixed concrete according to the present invention can recycle remaining ready-mixed concrete in a low-cost and simple manner.

Claims (7)

A treatment agent for ready-mix concrete, consisting of a porous material whose main components are calcium carbonate, calcium hydroxide, and silica, with talc as a trace component. The contents of calcium (Ca), silicon (Si), and magnesium (Mg) in the porous body are expressed as oxide equivalents with the total weight of the following oxides being 100% by weight:
65 to 85% by weight of Ca as CaO,
5 to 15% by weight of Si as _SiO2 ,
2. The treatment agent for ready-mixed concrete according to claim 1, wherein Mg is 0.5% by weight or more as calculated as MgO. 3. The treatment agent for ready mixed concrete according to claim 1, wherein the porous body has a density of 1.9 to 2.3 g/cm ³ and a water absorption rate of 45% or more. A step of generating papermaking sludge by adding a predetermined amount of coagulant to wastewater discharged during the waste paper recycling process;
and a step of calcining the papermaking sludge under a temperature condition of 800°C to 900°C to produce papermaking sludge ash consisting of a porous body containing calcium carbonate, calcium hydroxide, and silica as main components, and talc as a trace component. A method for treating ready-mixed concrete, comprising adding a prescribed amount of a treatment agent made of a porous material containing calcium carbonate, calcium hydroxide, and silica as main components and talc as a trace component to the remaining ready-mixed concrete to which water has been added. The method for treating ready-mixed concrete according to claim 5, wherein the amount of treatment agent to be added (M _PS ) is calculated based on the following formula, where M (kg) is the mass of the remaining ready-mixed concrete, W ₀ (kg/m ³ ) is the unit water content of the remaining ready-mixed concrete before water is added, W ₁ (kg/m ³ ) is the estimated unit water content of the remaining ready-mixed concrete after water is added, ρ (kg/m ³ ) is the unit volume data of base concrete calculated from the designated mix proportion, and α is a proportionality constant according to the type of cement.
The method for treating ready-mixed concrete according to claim 6, further comprising the steps of: pouring the treatment agent in an amount equivalent to the amount calculated based on the formula into a drum of an agitator vehicle in which the remaining ready-mixed concrete remains, and agitating the drum for a predetermined period of time.

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