CN110698120A - Precast concrete and curing method thereof - Google Patents
Precast concrete and curing method thereof Download PDFInfo
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- CN110698120A CN110698120A CN201911049227.4A CN201911049227A CN110698120A CN 110698120 A CN110698120 A CN 110698120A CN 201911049227 A CN201911049227 A CN 201911049227A CN 110698120 A CN110698120 A CN 110698120A
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B28—WORKING CEMENT, CLAY, OR STONE
- B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
- B28B11/00—Apparatus or processes for treating or working the shaped or preshaped articles
- B28B11/24—Apparatus or processes for treating or working the shaped or preshaped articles for curing, setting or hardening
- B28B11/245—Curing concrete articles
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B40/00—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability
- C04B40/0028—Aspects relating to the mixing step of the mortar preparation
- C04B40/0039—Premixtures of ingredients
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2103/00—Function or property of ingredients for mortars, concrete or artificial stone
- C04B2103/10—Accelerators; Activators
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/20—Resistance against chemical, physical or biological attack
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2201/00—Mortars, concrete or artificial stone characterised by specific physical values
- C04B2201/50—Mortars, concrete or artificial stone characterised by specific physical values for the mechanical strength
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Abstract
The invention discloses precast concrete, which comprises a crystal nucleus early-strength type composite additive, and comprises the following components in parts by weight: 30-60 parts of cement nanometer suspension concrete early strength agent, 20-30 parts of early strength type polycarboxylate superplasticizer, 10-20 parts of viscosity reduction and reduction type polycarboxylate superplasticizer and 20-30 parts of water reduction and slump retention type polycarboxylate superplasticizer. The compound type crystal nucleus early strength agent used in the invention has excellent early strength, viscosity reduction, shrinkage reduction and slump loss prevention functions, ensures the workability and slump of concrete during the distribution period (usually 30-50min), is easy for distribution construction, ensures the uniformity and compactness of the concrete, improves the compressive strength and durability of the concrete, reduces the shrinkage and cracking of the concrete, has the compressive strength higher than the tacit removal degree within 6-8 h under the natural curing condition, can realize the steam curing-free process of a prefabricated part, and is an excellent additive which is very suitable for the production of the concrete prefabricated part.
Description
Technical Field
The invention relates to concrete, in particular to precast member concrete and a curing method thereof.
Background
For the precast concrete, the most important is that the concrete quickly reaches the form removal strength, the form removal time is shortened, and the turnover rate of the mould is improved. Improving the early strength of concrete generally comprises: 1. adding early strength agent, inorganic salt early strength agent, such as calcium chloride, calcium nitrate, sulfate, etc.; organic early strength agents such as triethanolamine, triisoethanolamine, and the like; polycarboxylic acid early strength agent. 2. Adding nucleating agent, such as suspension early strength admixture of nanometer calcium silicate hydrate, nanometer silicon dioxide, etc. into concrete. 3. The fineness of the cement is improved, the surface area is increased, the hydration speed of the cement is improved, and the early strength is improved. However, the inorganic salt early strength agent has influence on the later strength and durability of the concrete, the organic early strength agent is sensitive to the mixing amount, the later strength of the concrete is reduced, and the polycarboxylic acid early strength agent is sensitive to soil.
Disclosure of Invention
Based on this, the invention aims to overcome the defects of the prior art and provide precast concrete. The invention utilizes nano Portland cement, polycarboxylic acid dispersant and polyvinylpyrrolidone (PVP) to prepare suspension through a special process to be used as a crystal nucleus type early strength agent, and an early strength type polycarboxylate water reducing agent compounded with an early strength type polycarboxylate water reducing agent, a viscosity reduction and shrinkage reduction type polycarboxylate water reducing agent, a water reduction and slump loss prevention type polycarboxylate water reducing agent and the like is used as an additive of a prefabricated part, the additive integrates early strength, viscosity reduction and shrinkage reduction into a whole, can effectively accelerate cement hydration, quickly improve the early strength of concrete, has the strength of more than 15MPa within 6-8 h, meets the requirement of the die removal strength of the prefabricated part, shortens the turnover period of a die, reduces the production cost, and is a concrete early strength agent with low cost and excellent performance. And meanwhile, the workability of the concrete is improved, the compressive strength and durability of the hardened concrete are improved, and the shrinkage and cracking of the concrete are reduced.
In order to achieve the purpose, the invention adopts the technical scheme that: the precast concrete comprises a crystal nucleus early-strength composite additive, wherein the crystal nucleus early-strength composite additive comprises the following components in parts by weight: 30-60 parts of cement nanometer suspension concrete early strength agent, 20-30 parts of early strength type polycarboxylate superplasticizer, 10-20 parts of viscosity reduction and reduction type polycarboxylate superplasticizer and 20-30 parts of water reduction and slump retention type polycarboxylate superplasticizer.
Preferably, the crystal nucleus early-strength type composite additive also comprises an antifoaming agent, and the content of the antifoaming agent is 0.2-0.6 kg/1000kg of the crystal nucleus early-strength type composite additive.
Preferably, the cement nanometer suspension concrete early strength agent comprises the following components in parts by weight: 2-6 parts of nano Portland cement, 25-40 parts of polycarboxylic acid dispersant and 10-16 parts of polyvinylpyrrolidone.
The cement nanometer suspension concrete early strength agent belongs to a crystal nucleus type early strength agent, has good stability and obvious early strength effect, is used in combination with a polycarboxylic acid water reducing agent, has good compatibility, is not layered, does not precipitate or segregate, has good homogeneity, is convenient to use, and is economical and applicable. Wherein:
the nano silicate cement is used as the hydrated calcium silicate crystal nucleus early strength agent, so that cement hydration can be obviously accelerated, the early strength of concrete is improved, the early strength of the concrete is quickly increased, outdoor natural maintenance is performed, the mold stripping strength can be achieved within 6-8 hours, the mold period is shortened, and the production cost is reduced.
The molecular structure design and early strength function of the polycarboxylic acid dispersant used for synthesizing the crystal nucleus early strength agent are as follows: by utilizing the principle of macromolecular structure design, a certain amount of sulfonic acid groups and amide groups are introduced into the molecular structure, so that the content of carboxylic acid groups is reduced, the molecular weight of the polymer is controlled, and a comb-shaped structure with long side chains and short main chains is formed. Reducing the carboxyl content of the main chain and weakening the carboxyl content and Ca2+Thereby reducing its complexation to C3The hydration inhibition of S achieves the aim of improving the early strength. The introduced sulfonic group can improve the dispersing performance of the polycarboxylic acid dispersing agent, so that the cement particles have more contact points with water, the hydration active points are increased, the cement hydration is accelerated, and the early strength is improved.
PVP (polyvinyl pyrrolidone) used for synthesizing the crystal nucleus early strength agent: PVP is a non-ionic water-soluble polymer, also named N-vinyl butyrolactam, the main chain is a hydrophobic C-C structure, but the side group part of each structural unit in the molecule is butyrolactam group with strong polarity, and the PVP has the functions of suspending, dispersing, complexing and the like, and has positive effects of improving the workability of concrete and reducing the shrinkage and cracking of the concrete.
Preferably, the polycarboxylic acid dispersant has a structural formula shown in formula (I):
wherein a is an integer of 50-80, b is an integer of 15-30, c is an integer of 10-20, and m is an integer of 100-200; r is H or CH3；
The structural formula of the viscosity-reducing shrinkage-reducing polycarboxylate superplasticizer is shown as a formula (I):
wherein a is an integer of 40-100, b is an integer of 10-40, c is an integer of 15-30, n is an integer of 25-80, y1Is an integer of 10 to 80, y2Is an integer of 10 to 80; r is H or CH3。
The molecular structure design and the viscosity reduction and shrinkage reduction function of the viscosity reduction and shrinkage reduction type polycarboxylate superplasticizer are as follows:
compared with common commercial concrete, the precast concrete cementing material has high dosage, small concrete slump and high concrete viscosity, and is not easy to distribute and construct, so that the concrete viscosity is an important index for the precast concrete besides the requirement of early strength, and the viscosity-reducing shrinkage-reducing polycarboxylic acid water reducing agent (formula II) is selected from the composite components of the composite crystal core type early strength admixture used in the invention, and the action mechanism is as follows: in the cement paste, water reducing agent molecules form an aggregation entanglement structure with exposed anions and are adsorbed on cement particles, the conformation is reversed to form a side chain collapse structure, associated water of PEG side chains is squeezed, free water is released to the maximum extent, and the consistency of concrete is reduced. Well-interrupted C side chain collapse3The collision probability of A hydration product gel has good collapse-protecting performance and is easy to distributeAnd the workability of concrete is good. Along with molecular adsorption, the air entraining performance of the water reducing agent is greatly reduced, which is different from that of the conventional polycarboxylic acid water reducing agent, and is beneficial to the development of concrete strength.
The main component of the nano silicate cement clinker is calcium silicate crystals, and after the calcium silicate crystals and the polycarboxylic acid dispersant form suspension, calcium silicate hydrate crystal nuclei are formed, and the crystal nuclei have the effects of remarkably promoting cement hydration and improving the early strength of concrete.
The portland cement clinker is a fine-grained artificial stone composed of a multi-mineral composition mainly comprising calcium silicate, and the grain size is generally 30-60 μm. The particle size of the nano Portland cement used in the invention is 400-900 nm, the particle size of the ordinary cement is 100 times of that of the nano cement, and the nano cement generates lattice defects in the grinding process, and the defects and the number of the lattices are main factors for determining the hydration induction period of the cement. Therefore, on one hand, the fineness and lattice defects of the nano cement enable the nano cement to have the advantages of promoting hydration and improving early strength, on the other hand, in the process that the nano cement, the polycarboxylic acid dispersant and the PVP are stirred at a high speed to form a suspension, calcium silicate nano-hydrate is formed as the main component of clinker, the nano-hydrate calcium silicate is used as a crystal nucleus, when the nano-hydrate calcium silicate is added into cement concrete, the cement hydration speed can be quickly improved, calcium silicate hydrate is formed, the calcium silicate hydrate is a main contributor to the cement strength, the induction period of cement hydration is greatly shortened, and the early strength of the concrete is further improved.
Preferably, the preparation method of the cement nanometer suspension concrete early strength agent comprises the following steps:
(1) mixing and stirring a polycarboxylic acid dispersant and polyvinylpyrrolidone, fully dissolving the polyvinylpyrrolidone to obtain a reaction flask base material, and adjusting the pH value to 8-12 by using alkali;
(2) slowly adding the nano Portland cement into a reaction bottle with the added base material in a screening and leaking mode within 2-4 hours; and then adding alkali to adjust the pH value to 9-12, and continuously stirring for 2-5 hours to obtain the cement nanometer suspension concrete early strength agent.
More preferably, in the step (2), the stirring speed is 800-1500 rpm.
Preferably, in the step (2), the addition amount of the nano portland cement is 2-6 g/100ml of the suspension.
Preferably, the mass percentage of the crystal nucleus early-strength type composite additive is 0.9-1.4% of the total mass of the cement, the fly ash and the mineral powder; more preferably, the mass percentage of the crystal nucleus early-strength type composite additive is 0.95-1.35% of the total mass of the cement, the fly ash and the mineral powder; more preferably, the mass percentage of the crystal nucleus early-strength type composite additive is 0.95-1.25% of the total mass of the cement, the fly ash and the mineral powder.
Preferably, the precast concrete further comprises cement, fly ash, water, sand and stones, and the mass ratio of the cement to the fly ash to the water to the sand to the stones is cement: fly ash: water: sand: stone (280-320): (80-110): (145-160): (750-780): (1080-1160); preferably, the mass ratio of the cement to the fly ash to the water to the sand to the stones is cement: fly ash: water: sand: stone (290-310): (80-100): (148-158): (755-70): (1090 to 1150); more preferably, the mass ratio of the cement to the fly ash to the water to the sand to the stones is cement: fly ash: water: sand: stone (295-308): (85-95): (148-155): (760 to 770): (1095 to 1145).
The invention also discloses an application of the cement nanometer suspension concrete early strength agent in precast member concrete, wherein the cement nanometer suspension concrete early strength agent comprises the following components in parts by weight: 2-6 parts of nano Portland cement, 25-40 parts of a polycarboxylate water reducing agent and 10-16 parts of polyvinylpyrrolidone.
In addition, the invention also discloses a maintenance method of the precast concrete, which comprises the following steps: and (3) performing outdoor natural maintenance, removing the mold within 6-8 hours, wherein the mold removal strength requirement is more than 15MPa, the strength is stable, and the mean square error is 3.5-4.6.
Meanwhile, the machine slump (generally 120 +/-30) and the slump protection time (generally half an hour from machine-out to pouring) are determined by comprehensively considering construction requirements, strength requirements and cost requirements according to actual production requirements, and the minimum slump is more than or equal to 80mm before pouring is finished.
Compared with the prior art, the invention has the beneficial effects that:
the compound crystal nucleus early strength agent, the viscosity-reducing shrinkage-reducing type and water-reducing slump-retaining type polycarboxylate superplasticizer used in the invention has excellent early strength, viscosity-reducing, shrinkage-reducing and slump-retaining functions, especially slump-retaining functions, ensures the workability and slump of concrete during material distribution (usually 20-40 min), is easy for material distribution construction, ensures the uniformity and compactness of the concrete, improves the compressive strength and durability of the concrete, reduces the shrinkage and cracking of the concrete, and is an excellent admixture which is very suitable for producing precast concrete members. Meanwhile, the composite early-strength admixture provided by the invention has the advantages of stable concrete strength and small mean square error.
Detailed Description
To better illustrate the objects, aspects and advantages of the present invention, the present invention will be further described with reference to specific examples.
Example 1
According to an embodiment of the precast concrete provided by the invention, in the precast concrete provided by the embodiment, the mass percentage of the crystal nucleus early-strength type composite additive is 0.9% of the total mass of cement, fly ash and mineral powder; the precast concrete also comprises cement, fly ash, water, mineral powder, sand and stones, and the mass ratio of the cement to the fly ash to the water to the mineral powder to the sand to the stones is as follows: fly ash: water: mineral powder: sand: 280 parts of stones: 80: 145: 750: 1080;
the crystal nucleus early-strength type composite additive comprises the following components in parts by weight: 30 parts of cement nanometer suspension concrete early strength agent, 20 parts of early strength type polycarboxylate superplasticizer, 20 parts of viscosity-reducing shrinkage-reducing polycarboxylate superplasticizer and 30 parts of water-reducing slump-retaining polycarboxylate superplasticizer;
the cement nanometer suspension concrete early strength agent comprises the following components in parts by weight: 2 parts of nano Portland cement, 25 parts of polycarboxylic acid dispersant and 10 parts of polyvinylpyrrolidone (PVP); the solid content of the polycarboxylate superplasticizer is 25%; the nano silicate cement is mainly calcium silicate crystals; the structural formula of the polycarboxylic acid dispersant is shown as the formula (I):
wherein a is an integer of 50-80, b is an integer of 15-30, c is an integer of 10-20, and m is an integer of 100-200; r is H or CH3；
The structural formula of the viscosity-reducing shrinkage-reducing polycarboxylate superplasticizer is shown as a formula (I):
wherein a is an integer of 40-100, b is an integer of 10-40, c is an integer of 15-30, n is an integer of 25-80, y1Is an integer of 10 to 80, y2Is an integer of 10 to 80; r is H or CH3。
The preparation method of the cement nanometer suspension concrete early strength agent comprises the following steps:
(1) adding a metered polycarboxylic acid dispersant and a metered PVP into a 500ml three-neck flask, stirring to fully dissolve the PVP, and adjusting the pH to 8 by using sodium hydroxide (or calcium hydroxide, triethylamine, triethanolamine and triisoethanolamine) as a flask bottom material;
(2) at room temperature, adding the Portland cement into a 500ml three-neck flask with the added base material, stirring at the speed of 800 r/min under the condition of intense stirring, and slowly adding the Portland cement for 2 hours in a screening and leaking mode, wherein the adding amount of the Portland cement is 2g/100ml of suspension; and after the addition is finished, adding sodium hydroxide (or calcium hydroxide, triethylamine, triethanolamine and triisoethanolamine) to adjust the pH value to 9, and continuing stirring for 2 hours to obtain the nano portland cement concrete early strength additive.
Example 2
According to one embodiment of the precast concrete, in the precast concrete of the embodiment, the mass percentage of the crystal nucleus early-strength type composite additive is 1.4% of the total mass of cement, fly ash and mineral powder; the precast concrete also comprises cement, fly ash, water, mineral powder, sand and stones, and the mass ratio of the cement to the fly ash to the water to the mineral powder to the sand to the stones is as follows: fly ash: water: mineral powder: sand: stone 320: 110: 160: 780: 1160;
the crystal nucleus early-strength type composite additive comprises the following components in parts by weight: 60 parts of cement nanometer suspension concrete early strength agent, 20 parts of early strength type polycarboxylate superplasticizer, 10 parts of viscosity-reducing and shrinkage-reducing polycarboxylate superplasticizer and 20 parts of water-reducing and slump-retaining polycarboxylate superplasticizer;
the cement nanometer suspension concrete early strength agent comprises the following components in parts by weight: 6 parts of nano Portland cement, 40 parts of polycarboxylic acid dispersant and 16 parts of polyvinylpyrrolidone (PVP); the solid content of the polycarboxylate superplasticizer is 40%; the nano silicate cement is mainly calcium silicate crystals; the structural formula of the polycarboxylic acid dispersant is shown as the formula (I):
wherein a is an integer of 50-80, b is an integer of 15-30, c is an integer of 10-20, and m is an integer of 100-200; r is H or CH3；
The structural formula of the viscosity-reducing shrinkage-reducing polycarboxylate superplasticizer is shown as a formula (I):
wherein a is an integer of 40-100, b is an integer of 10-40, c is an integer of 15-30, n is an integer of 25-80, y1Is an integer of 10 to 80, y2Is an integer of 10 to 80; r is H or CH3。
The preparation method of the cement nanometer suspension concrete early strength agent comprises the following steps:
(1) adding a metered polycarboxylic acid dispersant PCE and a metered PVP into a 500ml three-neck flask, stirring to fully dissolve the PVP, and adjusting the pH to 12 by using sodium hydroxide (or calcium hydroxide, triethylamine, triethanolamine and triisoethanolamine) as a flask bottom material;
(2) at room temperature, adding Portland cement into a 500ml three-neck flask with a bottom material, stirring at 1500 rpm under vigorous stirring for 4 hours in a sieving and leaking mode, wherein the adding amount of the Portland cement is 6g/100ml of suspension; and after the addition is finished, adding sodium hydroxide (or calcium hydroxide, triethylamine, triethanolamine and triisoethanolamine) to adjust the pH value to 12, and continuing stirring for 5 hours to obtain the nano portland cement concrete early strength additive.
Example 3
According to an embodiment of the precast concrete provided by the invention, in the precast concrete provided by the embodiment, the mass percentage of the crystal nucleus early-strength type composite additive is 1.25% of the total mass of cement, fly ash and mineral powder; the precast concrete also comprises cement, fly ash, water, mineral powder, sand and stones, and the mass ratio of the cement to the fly ash to the water to the mineral powder to the sand to the stones is as follows: fly ash: water: mineral powder: sand: stone 295: 85: 148: 760: 1095;
the crystal nucleus early-strength type composite additive comprises the following components in parts by weight: 45 parts of cement nanometer suspension concrete early strength agent, 25 parts of early strength type polycarboxylate superplasticizer, 15 parts of viscosity-reducing shrinkage-reducing polycarboxylate superplasticizer and 25 parts of water-reducing slump-retaining polycarboxylate superplasticizer;
the cement nanometer suspension concrete early strength agent comprises the following components in parts by weight: 4 parts of nano Portland cement, 32 parts of polycarboxylic acid dispersant and 13 parts of polyvinylpyrrolidone (PVP); the solid content of the polycarboxylate superplasticizer is 32%; the nano silicate cement is mainly calcium silicate crystals; the structural formula of the polycarboxylic acid dispersant is shown as the formula (I):
wherein a is an integer of 50-80, b is an integer of 15-30, c is an integer of 10-20, and m is an integer of 100-200; r is H or CH3；
The structural formula of the viscosity-reducing shrinkage-reducing polycarboxylate superplasticizer is shown as a formula (I):
wherein a is an integer of 40-100, b is an integer of 10-40, c is an integer of 15-30, n is an integer of 25-80, y1Is an integer of 10 to 80, y2Is an integer of 10 to 80; r is H or CH3。
The preparation method of the cement nanometer suspension concrete early strength agent comprises the following steps:
(1) adding a metered polycarboxylic acid dispersant and a metered PVP into a 500ml three-neck flask, stirring to fully dissolve the PVP, and adjusting the pH to 10 by using sodium hydroxide (or calcium hydroxide, triethylamine, triethanolamine and triisoethanolamine) as a flask bottom material;
(2) at room temperature, adding Portland cement into a 500ml three-neck flask with a bottom material, stirring at 1200 r/min under the condition of intense stirring, and slowly adding the Portland cement for 3 hours in a screening and leaking mode, wherein the adding amount of the Portland cement is 4g/100ml of suspension; after the addition is finished, adding sodium hydroxide (or calcium hydroxide, triethylamine, triethanolamine and triisoethanolamine) to adjust the pH value to 10, and continuing stirring for 3 hours to obtain the nano portland cement concrete early strength additive.
The maintenance method of the precast concrete in the embodiments 1 to 3 of the invention comprises the following steps: and (3) performing outdoor natural maintenance, removing the mold within 6-8 hours, wherein the mold removal strength requirement is more than 15MPa, the strength is stable, and the mean square error is 3.5-4.6. Meanwhile, the machine slump (generally 120 +/-30) and the slump protection time (generally half an hour from machine-out to pouring) are determined by comprehensively considering construction requirements, strength requirements and cost requirements according to actual production requirements, and the minimum slump is more than or equal to 80mm before pouring is finished.
And the production steam curing procedure of the common prefabricated part is as follows: 1. the pre-curing period, also called the resting period, mainly has the functions of enabling bubbles in the concrete to diffuse outwards and enabling the cement to have certain initial structural strength; 2. in the heating period, in order to prevent the destructive influence caused by thermal expansion due to excessive temperature difference on the surface of the concrete, the heating period is generally carried out in stages, namely, the temperature is slowly increased firstly, and then the temperature is accelerated little by little; 3. in the constant temperature period, the important stage of concrete strength increase; 4. and in the cooling period, the cooling speed is reasonably controlled, and the concrete is prevented from generating shrinkage cracks due to the excessively high cooling speed.
Setting experimental groups 1-12 and comparison groups 1-2, wherein the comparison group 1 is a blank comparison group and does not contain an additive; the control group 2 is precast concrete containing common additives; the experimental groups 1 to 3 are the precast concrete in the embodiments 1 to 3, except that the mass percentage of the crystal nucleus early strength type composite admixture to the total mass of cement, fly ash and mineral powder in the experimental groups 4 to 12 is different, the other experimental groups are the same as the embodiment 2, the early strength of the concrete in the experimental groups 1 to 12 and the control groups 1 to 2 is researched and analyzed according to the method, and the test mold manufacturing and compressive strength detection method refers to the national standard GB8076-2008, and is specifically shown as the data in the table 1:
TABLE 1 precast concrete early Strength
As can be seen from the data in Table 1, when the crystal nucleus early-strength type composite admixture is added, the early strength of the concrete develops rapidly, 8h is basically higher than the stripping strength by 15MPa, when the admixture addition amount is 0.9% -1.4%, the early strength of the concrete increases along with the increase of the admixture addition amount, when the early strength of the concrete is lower than the range value, the concrete strength is reduced to some extent, but the requirement of the stripping strength is also met, and when the early strength of the concrete exceeds the range value, the early strength of the concrete is in a trend of reducing along with the increase of the admixture amount, because the admixture is too high, the concrete has segregation or bleeding in different degrees, the internal structure of the concrete is not uniform, and the strength development is influenced.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Claims (10)
1. The precast member concrete is characterized by comprising a crystal nucleus early-strength composite additive, wherein the crystal nucleus early-strength composite additive comprises the following components in parts by weight: 30-60 parts of cement nanometer suspension concrete early strength agent, 20-30 parts of early strength type polycarboxylate superplasticizer, 10-20 parts of viscosity reduction and reduction type polycarboxylate superplasticizer and 20-30 parts of water reduction and slump retention type polycarboxylate superplasticizer.
2. The precast member concrete according to claim 1, wherein the nuclear early strength type compound admixture further comprises an antifoaming agent, and the content of the antifoaming agent is 0.2-0.6 kg/1000kg of the nuclear early strength type compound admixture.
3. The precast member concrete of claim 1, wherein the cement nano suspension concrete early strength agent comprises the following components in parts by weight: 2-6 parts of nano Portland cement, 25-40 parts of polycarboxylic acid dispersant and 10-16 parts of polyvinylpyrrolidone.
4. The precast concrete according to claim 3, wherein the polycarboxylic acid dispersant has a structural formula shown in formula (I):
wherein a is an integer of 50-80, b is an integer of 15-30, c is an integer of 10-20, and m is an integer of 100-200; r is H or CH3；
The structural formula of the viscosity-reducing shrinkage-reducing polycarboxylate superplasticizer is shown as a formula (I):
wherein a is an integer of 40 to 100, and b is an integer of 10 to 40A number, c is an integer of 15 to 30, n is an integer of 25 to 80, y1Is an integer of 10 to 80, y2Is an integer of 10 to 80; r is H or CH3。
5. The precast member concrete of claim 4, wherein the preparation method of the cement nanosuspension concrete early strength agent is as follows:
(1) mixing and stirring a polycarboxylic acid dispersant shown in the formula (I) and polyvinylpyrrolidone, fully dissolving the polyvinylpyrrolidone to obtain a reaction flask bottom material, and adjusting the pH value to 8-12 by using alkali;
(2) slowly adding the nano Portland cement into a reaction bottle with the added base material in a screening and leaking mode within 2-4 hours; and then adding alkali to adjust the pH value to 9-12, and continuously stirring for 2-5 hours to obtain the cement nanometer suspension concrete early strength agent.
6. The precast member concrete according to claim 5, wherein in the step (2), the stirring rate is 800 to 1500 rpm.
7. The precast member concrete according to claim 5, wherein in the step (2), the nano portland cement is added in an amount of 2 to 6g/100ml of suspension.
8. The precast concrete according to claim 1, wherein the mass percentage of the crystal nucleus early-strength type composite additive is 0.9-1.4% of the total mass of cement, fly ash and mineral powder; preferably, the mass percentage of the crystal nucleus early-strength type composite additive is 0.95-1.35% of the total mass of the cement, the fly ash and the mineral powder; more preferably, the mass percentage of the crystal nucleus early-strength type composite additive is 0.95-1.25% of the total mass of the cement, the fly ash and the mineral powder.
9. The precast member concrete according to any one of claims 1 to 8, further comprising cement, fly ash, water, sand and stones, wherein the mass ratio of the cement to the fly ash to the water to the sand to the stones is cement: fly ash: water: sand: stone (280-320): (80-110): (145-160): (750-780): (1080-1160); preferably, the mass ratio of the cement to the fly ash to the water to the sand to the stones is cement: fly ash: water: sand: stone (290-310): (80-100): (148-158): (755-70): (1090 to 1150); more preferably, the mass ratio of the cement to the fly ash to the water to the sand to the stones is cement: fly ash: water: sand: stone (295-308): (85-95): (148-155): (760 to 770): (1095 to 1145).
10. A maintenance method of precast concrete according to claims 1 to 9, characterized by comprising: and (3) performing outdoor natural maintenance, removing the mold within 6-8 hours, wherein the mold removal strength requirement is more than 15MPa, the strength is stable, and the mean square error is 3.5-4.6.
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