CN114573262A

CN114573262A - Steam curing-free agent for precast concrete member and preparation method thereof

Info

Publication number: CN114573262A
Application number: CN202210302801.8A
Authority: CN
Inventors: 汪智勇; 齐冬有; 张钰; 何昌毓; 宁靖华; 徐笃军
Original assignee: Technical Supervision & Res Ct For China Building Materials Industry; INSTITUTE OF TECHNICAL INFORMATION FOR BUILDING MATERIALS INDUSTRY OF CHINA; PowerChina Shandong Pipeline Engineering Corp Ltd
Current assignee: Technical Supervision & Res Ct For China Building Materials Industry; INSTITUTE OF TECHNICAL INFORMATION FOR BUILDING MATERIALS INDUSTRY OF CHINA; PowerChina Shandong Pipeline Engineering Corp Ltd
Priority date: 2022-03-24
Filing date: 2022-03-24
Publication date: 2022-06-03

Abstract

The invention relates to a steam-curing-free agent for a precast concrete member and a preparation method thereof, belonging to the technical field of additives. The steam curing-free agent for the precast concrete member is prepared from the following raw materials in percentage by mass: 50-90% of active mineral material containing aluminum and 10-50% of gypsum. The invention also discloses a preparation method of the steam curing-free agent for the precast concrete member. The steam curing-free agent for the precast concrete member can greatly accelerate the hydration hardening speed of the concrete after the precast concrete member is put into a mold, so that the precast concrete can achieve the demolding strength after being cured for 6-12 hours at normal temperature, and the time is equivalent to the time of steam curing; and the compactness of the concrete is increased, and the later strength and the durability, particularly the shrinkage performance, are obviously improved.

Description

Steam curing-free agent for precast concrete member and preparation method thereof

Technical Field

The invention relates to a steam-curing-free agent for a precast concrete member and a preparation method thereof, belonging to the technical field of additives.

Background

The fabricated building has the advantages of high construction efficiency, short construction period, high quality, environmental friendliness and the like, and is a building mode which encourages popularization and application in China and various places. A precast concrete member (PC) is a main constituent element of an assembly type building, and plays a central role in the development of the assembly type building. The novel construction mode such as tunnel shield method construction, open caisson method construction, jacking method construction and box culvert method construction also need prefabricated section of jurisdiction, prefabricated open caisson, prefabricated push pipe, prefabricated box culvert etc. as main supporting component, and the precast concrete component is used more and more extensively, and the demand also lasts the increase.

The precast concrete member may be produced on site or in a factory. The field production is mainly used for preparing oversized members which are oversized, overweight and difficult to carry, such as open caisson, box culvert and the like. Most prefabricated parts are produced in a factory in a flow line mode, have the advantages of good production conditions, good product quality and the like, and are the most main mode for producing the prefabricated concrete parts. The factory production is that concrete mixing is carried out in a factory mixing station, then pouring forming is carried out in a mold preset in a factory, demolding is carried out, and the factory is transported to a construction site for assembly construction after curing to a specified age. The used dies are usually set metal dies with fixed specifications, have the advantages of accurate size, high automation degree (such as automatic vibration), flow line production and the like, but are high in price and limited by factors such as factory areas, the number of die sets in production is usually fixed during factory design, and the turnover rate of the dies becomes a main factor for restricting the production efficiency. Therefore, in order to accelerate the turnover rate of the mold and the site and improve the production efficiency in the factory production process, the hardening of the concrete is accelerated by adopting hot steam curing, so that the demolding time is shortened, and the purpose of producing two or even three prefabricated concrete members every day is achieved. The steam curing link is the link with the highest energy consumption in the precast concrete production. Therefore, the method cancels the steam curing link and realizes the steam curing-free production, thereby being an important technical approach for carbon emission reduction and carbon neutralization.

At present, the precast concrete non-autoclave technology is realized mainly by improving the early strength of the concrete through early strength type chemical additives, but the method has limited effect on improving the early strength and can cause the problems of increased shrinkage, easy cracking and the like, the precast concrete non-autoclave technology can be used in summer when the temperature is high, and steam curing is still needed in other seasons with low temperature.

In view of the above, there is a need to provide a new steam curing-free agent for precast concrete members and a preparation method thereof, so as to solve the deficiencies of the prior art.

Disclosure of Invention

The invention aims to provide a steam-curing-free agent for precast concrete members.

The technical scheme for solving the technical problems is as follows: a steam curing-free agent for precast concrete members is prepared from the following raw materials in percentage by mass: 50-90% of active mineral material containing aluminum and 10-50% of gypsum.

The principle of the steam curing agent for precast concrete members of the present invention is illustrated:

the invention relates to a steam-curing-free agent for precast concrete members, which takes an aluminum-containing active mineral material and gypsum as raw materials. According to the research, the aluminum-containing active mineral material contains raw materials such as calcium, aluminum, iron, sulfur and the like after being calcined at high temperature, the hydration activity is high, a framework structure can be quickly built up by a crystal product generated after hydration, and the generated gel product, silicate cement mineral and other hydration products can be filled in the framework structure, so that a compact slurry structure is formed, and the early performance of the concrete is rapidly increased. In addition, the aluminum-containing active mineral material has large hydration heat release in the hydration process, so that the temperature of the cast precast concrete can be raised to generate the self-heating curing effect, thereby accelerating the hydration reaction and promoting the development of the early performance of the concrete.

The invention selects the aluminum-containing active mineral material to be compounded with the gypsum, and the prepared curing-free agent can be quickly hydrated and hardened in the concrete, and simultaneously can greatly promote the early hydration of the silicate cement mineral and increase the compactness of a hardened body, thereby greatly improving the early strength of the concrete.

Tests prove that the steam curing-free agent for the precast concrete member can greatly accelerate the hydration hardening speed of the concrete after the precast concrete member is put into a mold, so that the precast concrete can achieve the demolding strength after being cured for 6-12 hours at normal temperature, and the time is equivalent to the steam curing time; in addition, the compactness of the concrete is increased, and the later strength and the durability, particularly the shrinkage performance, are obviously improved.

The steam curing-free agent for the precast concrete member has the beneficial effects that:

1. the steam curing-free agent for the precast concrete member can be mixed into concrete in an additive form, and the development of the early performance of the concrete is improved, so that the steam curing link is cancelled in the production of the precast concrete member.

2. The steam curing-free agent for the precast concrete member can greatly accelerate the hydration hardening speed of the concrete after the precast concrete member is put into a mold, so that the precast concrete can achieve the demolding strength after being cured for 6-12 hours at normal temperature, and the time is equivalent to the time of steam curing; and the compactness of the concrete is increased, and the later strength and the durability, particularly the shrinkage performance, are obviously improved.

On the basis of the technical scheme, the invention can be further improved as follows.

Further, the steam curing-free agent for the precast concrete member is prepared from the following raw materials in percentage by mass: 50 to 89.8 percent of aluminum-containing active mineral material, 10 to 40 percent of gypsum, 0.1 to 15 percent of mineral admixture and 0.1 to 5 percent of chemical additive.

The adoption of the further beneficial effects is as follows: according to the invention, through research, the technical effect of the steam curing-free agent for the precast concrete member is better after the mineral admixture and the chemical additive are added in addition to the aluminum-containing active mineral material and the gypsum. Wherein the mineral admixture mainly acts to increase the fluidity of the concrete mixture; the chemical additive regulates the time of the reinforcing effect and maintains the working performance of the fresh concrete.

Further, the preparation method of the active mineral material containing aluminum comprises the following steps: respectively weighing the following raw materials in percentage by mass: 40-80% of calcareous raw material, 10-40% of aluminium or aluminium-iron raw material, 0-15% of iron raw material and 0-35% of sulfur raw material, mixing, grinding, and processing by adopting one of the following three modes: the first method is as follows: drying after balling, and then calcining at high temperature; the second method comprises the following steps: tabletting, drying and then calcining at high temperature; the third method comprises the following steps: directly adopting an industrial kiln for high-temperature calcination; then quickly cooling to be less than or equal to 100 ℃ to obtain the product.

The adoption of the further beneficial effects is as follows: the active mineral material containing aluminum is prepared by high-temperature calcination, and contains raw materials such as calcium, aluminum, iron, sulfur and the like. Detected by chemical analysis, contains Al₂O₃ 20％-80％、CaO 15-50％、SiO₂ 0-20％、Fe₂O₃0-18% and SO₃ 0-20％。

Wherein, the rapid cooling can furthest keep the activity of the active mineral material containing aluminum and simultaneously can increase the internal stress of the calcined material particles or blocks, thereby leading the material to be more easily ground. For example, the grate cooler can be used for rapid cooling.

Furthermore, the calcareous raw material is limestone, the aluminum or aluminum-iron raw material is bauxite or high-iron bauxite, the iron raw material is any one of iron ore, iron tailings and sulfuric acid slag, and the sulfur raw material is any one or a mixture of more than two of natural hydrated gypsum, natural anhydrous gypsum, byproduct hydrated gypsum and byproduct anhydrous gypsum.

Further, the grinding is to grind the raw material to 80 μm with 0% -30% of the residue on the sieve.

The adoption of the further beneficial effects is as follows: by adopting the parameters, the raw materials can be ensured to fully react at high temperature to generate the active aluminum-containing mineral.

Furthermore, the high-temperature calcination is performed by staying at the calcination temperature of 1200-1400 ℃ for 10-60 min.

The adoption of the method has the further beneficial effects that: through high-temperature calcination, the materials can fully undergo chemical reaction to form active minerals and grow to a certain crystal size.

Further, the gypsum is natural anhydrous gypsum or a mixture of natural anhydrous gypsum and hydrous gypsum, and the mass percentage of the anhydrous gypsum in the mixture is more than or equal to 50%.

Adopt above-mentioned further beneficial effect to be: the gypsum and the aluminum-containing active mineral material quickly form a hardened body skeleton structure in the cement hydration process.

Further, the mineral admixture is any one or a mixture of more than two of fly ash, silica fume and vitrified micro bubbles.

The adoption of the further beneficial effects is as follows: the above can be used as mineral admixture, can increase the fluidity of concrete mixture, and is beneficial to the pouring of concrete mixture.

Further, the chemical additive is any one or a mixture of more than two of boric acid, citric acid, sodium lignosulphonate, calcium lignosulphonate, sodium gluconate, calcium gluconate, tartaric acid, lithium carbonate, sodium sulfate and calcium nitrite.

The adoption of the further beneficial effects is as follows: the above can be used as chemical additive, and the main function is to assist in regulating hydration of active mineral containing aluminum.

The second object of the present invention is to provide a method for preparing the steam curing-free agent for precast concrete members.

The technical scheme for solving the technical problems is as follows: the preparation method of the steam curing-free agent for the precast concrete member comprises the following steps:

respectively weighing the following raw materials in percentage by mass: 50-90% of aluminum-containing active mineral material and 10-50% of gypsum are uniformly mixed and ground to obtain the steam-curing-free agent for the precast concrete member.

The preparation method of the steam curing-free agent for the precast concrete member has the beneficial effects that:

the preparation method of the steam curing-free agent for the precast concrete member is simple, easy to operate, low in cost and suitable for large-scale popularization and application.

Further, the specific surface area of the steam curing agent-free precast concrete member is 350m²/kg-550m²/kg。

Adopt above-mentioned further beneficial effect to be: by adopting the parameters, the performance of the steam curing agent for the precast concrete member is improved.

Detailed Description

The principles and features of this invention are described below in conjunction with embodiments, which are included to explain the invention and not to limit the scope of the invention.

Example 1

The preparation method of the steam curing-free agent for the precast concrete member of the embodiment comprises the following steps:

step 1: respectively weighing the following raw materials in percentage by mass: 50 percent of limestone, 40 percent of bauxite and 10 percent of anhydrite are mixed and ground to raw material with 80 mu m of screen residue of 8 to 12 percent, the raw material is evenly mixed with water accounting for 6 percent of the mass of the raw material and then pressed into raw material cakes, and then the raw material cakes are dried in an oven. And (3) putting the dried raw meal cake into a high-temperature electric furnace, heating the electric furnace from room temperature to 1350 ℃, preserving the heat for 60min, taking out, and cooling in the air to room temperature to obtain the aluminum-containing active mineral material. The components of the active mineral material containing aluminum are shown in table 1 by chemical analysis detection.

TABLE 1 chemical composition of active mineral material containing aluminum (%)

Name (R)	Loss on ignition	SiO₂	Al₂O₃	Fe₂O₃	CaO	MgO	K₂O	Na₂O	TiO₂	SO₃	Is totaled
												Limestone	43.2	0.33	0.23	0.12	54.01	0.53	0.21	0.23	-	-	98.86
Bauxite	14.05	17.51	55.43	5.38	2.16	0.42	0.09	0.33	3.12	-	98.49
												Anhydrite	5.15	0.46	0.43	0.12	39.46	1.42	-	-	-	51.59	98.63
Active mineral material containing aluminium	-	9.98	30.90	3.08	44.03	0.80	0.20	0.34	1.73	7.14	98.19

Step 2: respectively weighing the following raw materials in percentage by mass: 70.0 percent of aluminum-containing active mineral material, 25 percent of anhydrite, 4.5 percent of mineral admixture and 0.5 percent of chemical additive are evenly mixed and ground to the specific surface area of 420 +/-20 m²And/kg, namely obtaining the steam curing-free agent for the precast concrete member. Wherein the mineral admixture is second-grade fly ash; the chemical additive is a mixture of boric acid with the mass percent of 5%, lithium carbonate with the mass percent of 5% and sodium sulfate with the mass percent of 90%.

Example 2

step 1: respectively weighing the following raw materials in percentage by mass: 58 percent of limestone, 32 percent of bauxite and 10 percent of anhydrite are mixed and ground into raw material with 80 mu m screen residue of 16 to 18 percent, the raw material is calcined to 1350 +/-50 ℃ by a rotary kiln, the retention time of the material in the rotary kiln is about 30min to form uniform granular or blocky material with consistent inside and outside, the fuel used by the rotary kiln is fire coal, and the coal ash generated after the fire coal is combusted is 2.6 percent of the weight of the material before calcination. And (4) cooling the calcined material in a cooler after the calcined material comes out of the rotary kiln to obtain the active mineral material containing aluminum. The components of the active mineral material containing aluminum are shown in table 2 by chemical analysis detection.

TABLE 2 chemical composition of active mineral material containing aluminum (%)

Name (R)	Loss on ignition	SiO₂	Al₂O₃	Fe₂O₃	CaO	MgO	K₂O	Na₂O	TiO₂	SO₃	Total up to
												Limestone	43.2	0.33	0.23	0.12	54.01	0.53	0.21	0.23	-	-	98.86
Bauxite	11.2	12.68	65.13	3.44	2.52	0.5	0.13	0.23	2.18	-	98.01
												Anhydrite (hard plaster)	5.05	0.33	0.43	0.12	40.02	1.22	-	-	-	51.59	98.76
Coal ash	-	49.87	30.81	6.87	8.1	1.63	-	-	0.62	-	97.90
												Active mineral material containing aluminium	-	6.62	32.74	1.82	47.24	0.82	0.22	0.29	1.09	7.15	97.98

Step 2: respectively weighing the following raw materials in percentage by mass: 70.0 percent of the aluminum-containing active mineral material, 29 percent of anhydrite and 1 percent of chemical additive are evenly mixed and ground to the specific surface area of 500 +/-20 m²And/kg, namely obtaining the steam curing-free agent for the precast concrete member. Wherein the chemical additive is sodium gluconate.

Example 3

step 1: respectively weighing the following raw materials in percentage by mass: limestone 44%, bauxite 35.65%, mixed gypsum 13.15% and iron ore waste residue 7.2%, grinding to obtain raw material with 80 μm screen residue of 8% -12%, mixing the raw material with water 8% of the raw material, pressing into raw material cake, and oven drying in oven. And (3) putting the dried raw meal cake into a high-temperature electric furnace, heating the electric furnace from room temperature to 1300 ℃, preserving the heat for 40min, taking out, and cooling in the air to room temperature to obtain the aluminum-containing active mineral material. The composition of the aluminum-containing active mineral material is shown in table 3 by chemical analysis.

TABLE 3 chemical composition of active mineral material containing aluminum (%)

Step 2: respectively weighing the following raw materials in percentage by mass: 70.0 percent of aluminum-containing active mineral material, 28 percent of mixed gypsum, 2 percent of mineral admixture and 0.2 percent of chemical additive are evenly mixed and ground to the specific surface area of 420m²/kg-450m²And/kg, namely obtaining the steam curing-free agent for the precast concrete member. Wherein the mineral admixture is vitrified micro bubbles.

Example 4

step 1: respectively weighing the following raw materials in percentage by mass: 44.75 percent of limestone, 34.20 percent of bauxite, 13.85 percent of anhydrite and 7.2 percent of iron ore waste residue, grinding the mixture to powder with the particle size of 80 mu m and the screen residue of 20 to 22 percent, calcining the powder to 1350 +/-50 ℃ by a tunnel kiln, calcining the powder to uniform granular or blocky materials with consistent inside and outside, taking out the materials, and cooling the materials in the air to room temperature to obtain the active mineral material containing aluminum. The composition of the aluminum-containing active mineral material is shown in table 4 by chemical analysis.

TABLE 4 chemical composition of active mineral material containing aluminum (%)

Step 2: respectively weighing the following raw materials in percentage by mass: 60.0 percent of the aluminum-containing active mineral material, 28 percent of anhydrite, 10 percent of mineral admixture and 2 percent of chemical additive are evenly mixed and ground to the specific surface area of 380m²/kg-420m²And/kg, namely obtaining the steam curing-free agent for the precast concrete member. Wherein the mineral admixture is a mixture of fly ash and silica fume in a mass ratio of 1: 1. The chemical additive is a substanceA mixture of 80% by weight of calcium lignosulfonate, 10% by weight of citric acid and 10% by weight of lithium carbonate.

Example 5

step 1: respectively weighing the following raw materials in percentage by mass: limestone 35%, bauxite 60.06% and fly ash 4.94%, mixing, grinding to obtain raw material with 80 μm screen residue of 6% -18%, mixing the raw material with water 8% of raw material mass, pressing into raw material cake, and oven drying in oven. And (3) putting the dried raw meal cake into a high-temperature electric furnace, heating the electric furnace from room temperature to 1350-1400 ℃, preserving the heat for 30min, taking out, and cooling in the air to room temperature to obtain the aluminum-containing active mineral material. The composition of the aluminum-containing active mineral material is shown in table 5 by chemical analysis.

TABLE 5 chemical composition of active mineral material containing aluminum (%)

Step 2: respectively weighing the following raw materials in percentage by mass: 67 percent of aluminum-containing active mineral material, 25 percent of anhydrite, 5 percent of mineral admixture and 3 percent of chemical additive are evenly mixed and ground to the specific surface area of 350m²/kg-400m²And/kg, namely obtaining the steam curing-free agent for the precast concrete member. The mineral admixture is a mixture of fly ash, silica fume and vitrified micro bubbles according to a mass ratio of 1:1: 1. The chemical additive is a mixture of 70% by mass of calcium gluconate and 30% by mass of sodium sulfate.

Example 6

step 1: respectively weighing the following raw materials in percentage by mass: 50 percent of limestone, 40 percent of bauxite and 10 percent of anhydrite are mixed and ground to raw material with 80 mu m of screen residue of 8 to 12 percent, the raw material is evenly mixed with water accounting for 6 percent of the mass of the raw material and then pressed into raw material cakes, and then the raw material cakes are dried in an oven. And (3) putting the dried raw meal cake into a high-temperature electric furnace, heating the electric furnace from room temperature to 1350 ℃, preserving the heat for 60min, taking out, and cooling in the air to room temperature to obtain the aluminum-containing active mineral material. The composition of the aluminum-containing active mineral material is shown in table 6 by chemical analysis.

TABLE 6 chemical composition of active mineral material containing aluminum (%)

Name(s)	Loss on ignition	SiO₂	Al₂O₃	Fe₂O₃	CaO	MgO	K₂O	Na₂O	TiO₂	SO₃	Total up to
												Limestone	43.2	0.33	0.23	0.12	54.01	0.53	0.21	0.23	-	-	98.86
Bauxite	14.05	17.51	55.43	5.38	2.16	0.42	0.09	0.33	3.12	-	98.49
												Anhydrite	5.15	0.46	0.43	0.12	39.46	1.42	-	-	-	51.59	98.63
Active mineral material containing aluminium	-	9.98	30.90	3.08	44.03	0.80	0.20	0.34	1.73	7.14	98.19

Step 2: respectively weighing the following raw materials in percentage by mass: mixing 70.0% of the above aluminum-containing active mineral material and 30% of anhydrite uniformly, and grinding to specific surface area of 450 + -20 m²And/kg, namely obtaining the steam curing-free agent for the precast concrete member.

Examples of the experiments

The steam-curing-free agent for the precast concrete members, which is prepared in the embodiments 1-6 of the invention, can replace a cementing material by 2% -12% of the cement amount according to actual requirements during concrete mixing, so that the purposes of shortening the cement setting time, improving the early strength increase of concrete and realizing the production of the precast members to two or three times a day without steam curing are achieved.

Using the non-curing agent for precast concrete unit prepared in examples 1 to 6 of the present invention, cement paste and C₅₀The concrete mix replaced 7% of the cement (P.O 52.5.5 grade), and the cement setting time and concrete strength performance test results are shown in table 6. Meanwhile, concrete to which no steam curing agent was added was used as a comparative example.

TABLE 6 Cement setting time and concrete compressive Strength before and after addition of steam curing agent

From the results, the steam-curing-free agent for the precast concrete members prepared in the embodiments 1 to 6 of the invention has the advantages that the setting time is obviously shortened, the early demoulding strength (8h) of the concrete is greatly improved, the improvement range can reach more than 10MPa, and the hoisting and demoulding requirements of the precast members can be met. Meanwhile, the strength of the concrete 28d doped with the non-curing agent is greatly increased, and the shrinkage rate of the concrete 28d is greatly reduced and is only 1/4-1/5 which is not doped.

The steam curing-free agent for the precast concrete member can greatly accelerate the hydration hardening speed of the concrete after the precast concrete member is molded, so that the precast concrete can achieve the demolding strength after being cured for 6-12 hours at normal temperature, and the time is equivalent to the steam curing time; in addition, the compactness of the concrete is increased, and the later strength and the durability, particularly the shrinkage performance, are obviously improved.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. The steam-curing-free agent for the precast concrete member is characterized by being prepared from the following raw materials in percentage by mass: 50-90% of active mineral material containing aluminum and 10-50% of gypsum.

2. The steam-curing-free agent for the precast concrete unit as claimed in claim 1, which is prepared from the following raw materials in percentage by mass: 50 to 90 percent of aluminum-containing active mineral material, 10 to 50 percent of gypsum, 0.1 to 15 percent of mineral admixture and 0.1 to 5 percent of chemical additive.

3. The non-curing agent for precast concrete member according to claim 1 or 2, characterized in that the preparation method of the active mineral material containing aluminum is: respectively weighing the following raw materials in percentage by mass: 40-80% of calcareous raw material, 10-40% of aluminium or aluminium-iron raw material, 0-15% of iron raw material and 0-35% of sulfur raw material, mixing, grinding, and processing by adopting one of the following three modes: the first method is as follows: drying after balling, and then calcining at high temperature; the second method comprises the following steps: tabletting, drying and then calcining at high temperature; the third method comprises the following steps: directly calcining at high temperature by using an industrial kiln; then quickly cooling to be less than or equal to 100 ℃ to obtain the product.

4. The non-autoclaved agent for precast concrete members according to claim 3, wherein the calcareous material is limestone, the aluminous or aluminoferrite material is bauxite or high-iron bauxite, the irony material is any one of iron ore, iron tailings and sulfuric acid sludge, and the sulfurous material is any one or a mixture of two or more of natural hydrous gypsum, natural anhydrous gypsum, byproduct hydrous gypsum and byproduct anhydrous gypsum.

5. The non-autoclaved for precast concrete member as set forth in claim 3, wherein said grinding is to grind raw material with a screen residue of 0% -30% of 80 μm, and said high temperature calcination is to stay at a calcination temperature of 1200 ℃ -1400 ℃ for 10min-60 min.

6. The steam-curing-free agent for the precast concrete member as recited in claim 1 or 2, wherein the gypsum is natural anhydrous gypsum, or a mixture of natural anhydrous gypsum and hydrous gypsum, and the mass percentage of the anhydrous gypsum in the mixture is not less than 50%.

7. The steam-curing-free agent for the precast concrete unit according to claim 2, wherein the mineral admixture is any one or a mixture of two or more of fly ash, silica fume and vitrified micro bubbles.

8. The non-autoclaved agent for precast concrete members according to claim 2, wherein the chemical additive is any one or a mixture of two or more of boric acid, citric acid, sodium lignosulfonate, calcium lignosulfonate, sodium gluconate, calcium gluconate, tartaric acid, lithium carbonate, sodium sulfate and calcium nitrite.

9. The method for preparing the steam curing free agent for precast concrete member as set forth in any one of claims 1 to 8, characterized by comprising the steps of:

10. The method for preparing a steam curing free agent for precast concrete unit according to claim 9, wherein the steam curing free agent for precast concrete unit has a specific surface area of 350m²/kg-550m²/kg。