C30 prefabricated concrete component prepared by using grade iv recycled aggregate and preparation method thereof

Abstract

The application relates to the technical field of building materials, in particular to a C30 prefabricated concrete component prepared from IV-grade recycled aggregate and a preparation method thereof. The method comprises the following steps: uniformly mixing IV-grade recycled aggregate, cement, water and a water reducing agent to prepare dry-hard recycled concrete with a slump of less than 10 mm and a Veeb consistency of 17-25 s, shaping and curing, and thus obtaining the C30 prefabricated concrete component; wherein the IV-grade recycled aggregate accounts for 70-75% of the total raw material in terms of mass percentage, the cement accounts for 16-20% of the total raw material in terms of mass percentage, the water reducing agent accounts for 1-3% of the cement in terms of mass percentage, and the balance is water. The prefabricated concrete component prepared by the method meets the C30 requirement in strength.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, in particular to a C30 prefabricated concrete component prepared from IV-grade recycled aggregate and a preparation method thereof. BACKGROUND

[0002] Construction solid waste refers to the general term of muck, waste concrete, waste brick and other waste produced in the production activities of building industry such as demolition, construction, decoration, repair and natural disasters such as floods and earthquakes.

[0003] Construction solid waste is a resource that is placed in the wrong place and has recycling value. Recycled aggregate is divided into I-III grades according to performance requirements. According to the requirements of water absorption and crushing index, the main component is recycled aggregate of waste concrete crushed into concrete. The resourceization research and application of this kind of recycled aggregate are relatively mature. However, under the classification degree of the present construction solid waste, most of them are mixed solid waste of bricks and concrete. The recycled aggregate obtained by resourceization is a brick-concrete mixed aggregate with complex composition, which does not meet the performance requirements of I-III grade recycled aggregate. Therefore, after a large number of experimental verification, Beijing landmark adds IV-grade recycled aggregate outside I-III grade recycled aggregate. Part of the good quality brick-concrete aggregate can meet the performance requirements of IV-grade recycled aggregate. The following will refer to this kind of brick-concrete aggregate as IV-grade recycled aggregate.

[0004] At present, the existing recycled concrete is mainly prepared by mixing I-grade-III-grade recycled aggregate with natural sand and stone. The latest Beijing landmark expands the application range of recycled concrete aggregate, but still limits the application of IV-grade recycled aggregate to concrete below C25, and the total mixing ratio is not more than 30%. This greatly limits the resourceization application of brick-concrete aggregate. Therefore, it is of great significance to provide a method for preparing C30 prefabricated concrete components using IV-grade recycled aggregate for the resourceization application of brick-concrete aggregate.

[0005] Therefore, the present application is proposed. SUMMARY

[0006] The first object of the present application is to provide a method for preparing C30 prefabricated concrete components using IV-grade recycled aggregate. The method of the present application prepares dry hard recycled concrete with IV-grade recycled aggregate and cement, which has no pumping flow workability, so that the strength is enhanced. At the same time, the quality of the concrete is controlled by forming prefabricated concrete components, so as to avoid the quality risk of cast-in-place concrete caused by the quality fluctuation of recycled aggregate. The prefabricated components prepared by the method of the present application using IV-grade recycled aggregate meet the requirements of C30.

[0007] The second object of the present application is to provide a C30 prefabricated concrete component prepared from IV-grade recycled aggregate, which is prepared by the method as described above.

[0008] In order to achieve the above object of the present application, the following technical solutions are adopted:

[0009] A method for preparing C30 prefabricated concrete components by using IV-grade recycled aggregate, comprising the following steps:

[0010] IV-grade recycled aggregate, cement, water and water reducing agent are mixed uniformly to prepare dry hard recycled concrete with a slump of less than 10 mm and a Vibe consistency of 17-25 s, and then the dry hard recycled concrete is shaped and maintained to obtain the C30 prefabricated concrete components.

[0011] Preferably, the IV-grade recycled aggregate accounts for 70-75% of the total raw materials, the cement accounts for 16-20% of the total raw materials, the water reducing agent accounts for 1-3% of the cement, and the rest is water.

[0012] Preferably, the IV-grade recycled aggregate comprises recycled coarse aggregate with a particle size of 10-25 mm and recycled fine aggregate with a particle size of 0-5 mm, and the recycled coarse aggregate with a particle size of 10-25 mm accounts for 40-50% of the IV-grade recycled aggregate.

[0013] More preferably, in the recycled fine aggregate, the sieve residue of 2.36 mm accounts for 20-30% by mass, the sieve residue of 4.75 mm accounts for 5-15% by mass, and the recycled fine aggregate accounts for 50-60% of the IV-grade recycled aggregate.

[0014] Preferably, the IV-grade recycled aggregate further comprises medium-grit recycled aggregate with a particle size of 5-10 mm, the recycled fine aggregate with a particle size of 0-5 mm accounts for 20-30% of the IV-grade recycled aggregate by mass, and the medium-grit recycled aggregate with a particle size of 5-10 mm accounts for 20-30% of the IV-grade recycled aggregate.

[0015] Preferably, the cement comprises ordinary Portland cement with a strength grade of P.O42.5 or P.O52.5.

[0016] Preferably, the water reducing agent is a polycarboxylic acid water reducing agent.

[0017] Preferably, the preparation method of the dry hard recycled concrete comprises the following steps: the IV-grade recycled aggregate and the cement are first stirred and mixed uniformly, then the water is added, and after being stirred and mixed uniformly, the water reducing agent is added, and then the mixture is stirred and mixed uniformly.

[0018] Preferably, the stirring is forced stirring, the stirring speed is 20-40 r / min, the IV-grade recycled aggregate and the cement are stirred and mixed for 60-90 s, the stirring and mixing time after the water is added is 20-30 s, and the stirring and mixing time after the water reducing agent is added is 30-60 s.

[0019] Preferably, the forming process is: the prepared dry hard recycled concrete is poured into a mold sprayed with a release agent and vibrated, and negative pressure vibration is carried out at the same time.

[0020] Preferably, the release agent is a water-based release agent.

[0021] Preferably, the vibration power is 3-4kw, the vibration frequency is 40-50Hz, and the vibration time is 60-90s per layer.

[0022] Preferably, the vibration power of the negative pressure vibration is 1-2kw, and the vibration time of the negative pressure vibration is 60-90s per layer.

[0023] Preferably, the internal air pressure of the negative pressure vibration is 40-60kPa.

[0024] A C30 prefabricated concrete component prepared by using IV grade recycled aggregate is prepared by the method described above.

[0025] Compared with the prior art, the beneficial effects of the present application are:

[0026] (1) The method of the present application enhances the strength of the dry hard recycled concrete prepared by mixing IV grade recycled aggregate with cement, controls the quality of the concrete by forming prefabricated concrete components, avoids the quality risk of cast-in-place concrete caused by the quality fluctuation of recycled aggregate, and to some extent, gets rid of the application limitation of recycled aggregate caused by quality risk.

[0027] (2) The prefabricated component prepared by using IV grade recycled aggregate has a dense and beautiful surface, small water absorption, good frost resistance, and compressive strength meeting the C30 requirement. DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be described clearly and completely in combination with specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application. The specific conditions are not specified in the embodiments, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0029] The first aspect of the present application provides a method for preparing a C30 prefabricated concrete component by using IV grade recycled aggregate, comprising the following steps:

[0030] The IV-grade recycled aggregate, cement, water and water reducing agent are uniformly mixed to prepare dry hard recycled concrete with a slump of less than 10 mm and a Vibe consistency of 17-25 s, and the C30 prefabricated concrete member is obtained through molding and curing.

[0031] The IV-grade recycled aggregate accounts for 70-75 % of the total raw materials, the cement accounts for 16-20 % of the total raw materials, the water reducing agent accounts for 1-3 % of the cement, and the balance is water.

[0032] The method of the application uses 100 % IV-grade recycled aggregate to replace natural sand and stone, reduces the water-cement ratio, and reduces the water addition amount by adding water reducing agent, to prepare dry hard recycled concrete with cement, so as to improve the strength, and to control the quality of the concrete by molding prefabricated concrete members, to avoid the quality risk of cast-in-place concrete caused by the quality fluctuation of the recycled aggregate, and to a certain extent, to get rid of the application limitation of the recycled aggregate caused by the quality risk.

[0033] In different embodiments, the Vibe consistency of the dry hard recycled concrete can be any one value or a range value composed of two point values among 17 s, 18 s, 19 s, 20 s, 21 s, 22 s, 23 s, 24 s and 25 s; the IV-grade recycled aggregate can account for any one value or a range value composed of two point values among 70 %, 71 %, 72 %, 73 %, 74 % and 75 % of the total raw materials; the cement can account for any one value or a range value composed of two point values among 16 %, 16.5 %, 17 %, 17.5 %, 18 %, 18.5 %, 19 %, 19.5 % and 20 % of the total raw materials; the water reducing agent can account for any one value or a range value composed of two point values among 1 %, 2 % and 3 % of the cement, and the amount of water can be adjusted according to the Vibe consistency.

[0034] The cement is used to improve the strength, and too little cement will significantly reduce the strength, but too much cement will not significantly increase the strength and will significantly increase the cost, so the amount of cement needs to be reasonably controlled to balance the strength and cost.

[0035] The water reducing agent is used to reduce the water addition amount to increase the density and improve the strength while keeping the state of the recycled concrete, and too little water reducing agent cannot achieve the ideal water reducing effect, and the cost of the water reducing agent is relatively high, so the amount of the water reducing agent needs to be reasonably controlled.

[0036] In some embodiments of the present application, the IV-grade recycled aggregate is a brick-concrete aggregate meeting the requirements of the IV-grade recycled aggregate.

[0037] In some embodiments of the present application, the IV-grade recycled aggregate comprises recycled coarse aggregate with a particle size of 10-25 mm and recycled fine aggregate with a particle size of 0-5 mm (0 < particle size ≤ 5 mm), and the recycled coarse aggregate with a particle size of 10-25 mm accounts for 40-50% of the IV-grade recycled aggregate by mass ratio, for example, any one value or a range value formed by any two values selected from 40%, 42%, 45%, 46%, 46.7%, 48%, and 50%. In the present application, the recycled coarse aggregate with a particle size of 10-25 mm is used as a skeleton structure, and the recycled fine aggregate with a particle size of 0-5 mm and cement are used as gap fillers. Through grading design, a skeleton dense structure is formed inside the recycled concrete, and the density and compressive strength inside the prefabricated concrete member are improved.

[0038] In some embodiments of the present application, in the recycled fine aggregate, the sieve residue of 2.36 mm accounts for 20-30% by mass ratio, for example, any one value or a range value formed by any two values selected from 20%, 22%, 24%, 25%, 26%, 28%, and 30%; the sieve residue of 4.75 mm accounts for 5-15%, for example, any one value or a range value formed by any two values selected from 5%, 7%, 9%, 10%, 11%, 13%, and 15%; and the recycled fine aggregate accounts for 50-60% of the IV-grade recycled aggregate, for example, any one value or a range value formed by any two values selected from 50%, 52%, 53%, 53.3%, 55%, 58%, and 60%.

[0039] By reasonably controlling the particle size distribution of the recycled fine aggregate, only two types of recycled aggregate, i.e., the recycled fine aggregate with a particle size of 0-5 mm and the recycled coarse aggregate with a particle size of 10-25 mm, can achieve an ideal grading close to a close-packed state, so that the strength of the prefabricated concrete member meets the requirement of C30, and only two bins of ingredients are needed in production, which can reduce the cost.

[0040] In some other embodiments of the present application, the IV-grade recycled aggregate further comprises recycled aggregate with a medium particle size of 5-10 mm, and the recycled fine aggregate with a particle size of 0-5 mm accounts for 20-30% of the IV-grade recycled aggregate by mass ratio, for example, any one value or a range value formed by any two values selected from 20%, 22%, 24%, 26.7%, 28%, and 30%; and the recycled aggregate with a medium particle size of 5-10 mm accounts for 20-30% of the IV-grade recycled aggregate, for example, any one value or a range value formed by any two values selected from 20%, 22%, 24%, 26.7%, 28%, and 30%.

[0041] When the particle size distribution of the recycled fine aggregate meets the requirements, the addition of the medium particle size recycled aggregate of 5-10 mm has little effect on the strength; but when the recycled fine aggregate is too fine (in the actual building waste resourceization process, there are often fine aggregates that do not meet the above particle size requirements), for example, when the 3 mm sieve residue is 0, that is, the particle size of the recycled fine aggregate is 0-3 mm, the two-grade batching of only using the recycled fine aggregate and the recycled coarse aggregate will cause the gradation to be broken, and then the strength of the precast concrete member is reduced, at this time, the addition of the medium particle size recycled aggregate of 5-10 mm can avoid the reduction of the strength of the precast concrete member caused by the too fine particle size of the recycled fine aggregate, and ensure the quality of the product.

[0042] In some embodiments of the application, the cement includes ordinary Portland cement, and the strength grade is P.O42.5 or P.O52.5.

[0043] In some embodiments of the application, the water reducing agent is a polycarboxylic acid water reducing agent, which functions to reduce the water addition amount and reduce the water-cement ratio of the recycled concrete, and the water-cement ratio directly affects the strength of the concrete, and reducing the water-cement ratio can improve the strength of the precast concrete member.

[0044] In some embodiments of the application, the preparation method of the dry hard recycled concrete is: first, the IV-grade recycled aggregate and the cement are stirred and mixed uniformly, then the water is added, and after stirring and mixing uniformly, the water reducing agent is added, and stirring and mixing uniformly are obtained.

[0045] In the application, the dry materials are first stirred and then water is added to avoid too much water on the surface of the pre-saturated recycled aggregate, and the cement is added later to avoid uneven mixing of the cement; and the water reducing agent is added at the end instead of being mixed with the water first, to avoid the waste of the water reducing agent mixed in the water due to the absorption of the recycled aggregate system, and to achieve better water reducing effect in the early stage of stirring if the water reducing agent is mixed with the water and added together, which will cause more consumption of the water reducing agent.

[0046] In some embodiments of the present application, the stirring is forced stirring, the stirring speed is 20-40 r / min, for example, any one value or a range value formed by any two values selected from 20 r / min, 25 r / min, 30 r / min, 35 r / min and 40 r / min; the mixing time of the IV-grade recycled aggregate and the cement is 60-90 s, for example, any one value or a range value formed by any two values selected from 60 s, 70 s, 80 s and 90 s; the mixing time after adding the water is 20-30 s, for example, any one value or a range value formed by any two values selected from 20 s, 25 s and 30 s; the mixing time after adding the water reducing agent is 30-60 s, for example, any one value or a range value formed by any two values selected from 30 s, 40 s, 50 s and 60 s. The mixing time after adding the water reducing agent should not be too long, because the materials have been uniformly mixed in the early stage, and the mixing for too long time will cause the water reducing agent to be adsorbed by the recycled aggregate, and the water reducing effect will be poor.

[0047] In some embodiments of the present application, the forming process is as follows: the prepared dry hard recycled concrete is layered and poured into a mold sprayed with a release agent and vibrated, and at the same time, negative pressure vibration is performed, and the mold is demolded after film covering and natural curing for 18-24 h.

[0048] The dry hard recycled concrete has low water-cement ratio and poor fluidity, and is difficult to form. The traditional vibration forming method cannot guarantee the quality such as appearance and strength durability of the product, and the recycled fine aggregate has high clay content and high viscosity under the condition of low water-cement ratio, which seriously affects the discharge of internal bubbles. The surface of the recycled coarse aggregate is rough, and has many pores and strong bubble adsorption, which makes it difficult to discharge internal bubbles. The mechanical vibration and pressure forming requires large equipment investment and high mold cost in the early stage, and the production is not flexible. In view of the above problems, the method of the present application first accelerates the sinking and densification and liquefaction of the dry hard concrete by the vibration table, which can not only accelerate the loading speed of the recycled concrete, but also guarantee the smooth and dense surface of the small component, and then the internal component is vibrated and densified by negative pressure vibration, and the bubbles in the internal component are accelerated to be discharged by negative pressure, and the internal densification of the recycled concrete is accelerated. The component formed by the method has smooth appearance, high strength, small equipment investment and flexible production.

[0049] The production and forming method of the dry hard concrete makes the recycled concrete component meet the strength quality requirements of the traditional wet-formed concrete component, and the internal structure of the concrete component is compacted by grading adjustment and negative pressure vibration technology. The water in the IV-grade recycled aggregate can become the internal curing water source during the curing period, and further strengthens the internal hydration degree. Compared with the dry-formed cement products by vibration and pressure at the present stage, the surface of the recycled concrete component prepared by the method is compact and beautiful, and the water absorption and frost resistance and other durability are better.

[0050] In some embodiments of the present application, the release agent is a water-based release agent.

[0051] The dry hard recycled concrete has many bubbles in the molding process. The water-based release agent disperses the organic component through the emulsifier, and the contact angle and polarity are greater than those of the oil-based release agent. Therefore, the water-based release agent can accelerate the discharge of surface bubbles, greatly reduce the bubble size and bubble density on the surface of small components, and improve the smoothness and compactness of the surface of the dry hard recycled concrete component. As an example, the water-based release agent is Xibei XB-2610 water-based release agent or Japan Kawako water-based release agent.

[0052] In some embodiments of the present application, the power of the vibration is 3-4 kw, for example, any one value or a range value composed of two point values selected from 3 kw, 3.2 kw, 3.4 kw, 3.5 kw, 3.6 kw, 3.8 kw, and 4 kw; the frequency of the vibration is 40-50 Hz, for example, any one value or a range value composed of two point values selected from 40 Hz, 42 Hz, 44 Hz, 45 Hz, 46 Hz, 48 Hz, and 50 Hz; and the vibration time is 60-90 s for each layer, for example, any one value or a range value composed of two point values selected from 60 s, 65 s, 70 s, 75 s, 80 s, 85 s, and 90 s.

[0053] In some embodiments of the present application, the vibration power of the negative pressure vibration is 1-2 kw, for example, any one value or a range value composed of two point values selected from 1 kw, 1.2 kw, 1.4 kw, 1.5 kw, 1.6 kw, 1.8 kw, and 2 kw; and the vibration time of the negative pressure vibration is 60-90 s for each layer, for example, any one value or a range value composed of two point values selected from 60 s, 65 s, 70 s, 75 s, 80 s, 85 s, and 90 s.

[0054] In some embodiments of the present application, the internal air pressure of the negative pressure vibration is 40-60 kPa, for example, any one value or a range value composed of two point values selected from 40 kPa, 45 kPa, 50 kPa, 55 kPa, and 60 kPa. The negative pressure can accelerate the discharge of bubbles inside the recycled concrete, improve the compactness of the recycled concrete component, and improve the strength of the component. The size of the negative pressure affects the bubble removal effect, and the negative pressure range needs to be reasonably controlled.

[0055] In some embodiments of the present application, the curing is standard curing, and the conditions of the standard curing are temperature 20±2℃ and humidity ≥95%.

[0056] The second aspect of the present application provides a C30 prefabricated concrete component prepared from Grade IV recycled aggregate, which is prepared by the method for preparing a C30 prefabricated concrete component from Grade IV recycled aggregate according to any one of the preceding embodiments.

[0057] Some embodiments of the present application will be described in detail below with reference to specific examples. The raw materials used in the examples, unless otherwise specified, can be purchased on the market.

[0058] Example 1

[0059] 10-25mm brick-mixed recycled coarse aggregate 700 parts, 0-5mm brick-mixed recycled fine aggregate (2.36mm sieve residue accounts for 25%, 4.75mm sieve residue accounts for 10%) 800 parts, P.O42.5 cement 350 parts, added to a forced mixer (speed 30r / min) and stirred for 60s; 250 parts of mixing water is added to the forced mixer and stirred for 30s; 7 parts of polycarboxylic acid water reducer is added to the forced mixer and stirred for 30s to obtain a uniform dry hard concrete, the measured slump is less than 10mm, the slump index is not applicable, and the vibritity is 18s.

[0060] The dry hard recycled concrete is formed into a curbstone sample by a mechanical vibration compaction and negative pressure vibration process. The specific forming process is as follows: the mold sprayed with Xixi XB-2610 water-based release agent is placed on a 3kw vibration table, the dry hard recycled concrete is poured into the mold in two layers, a negative pressure vibrator is used to assist the vibration of the internal structure center to uniformity, the negative pressure vibration and the vibration table vibration are synchronous, the vibration frequency is 45Hz, the vibration power of the negative pressure vibration is 1.5kw, the vibration and compaction time of each layer is 60s, and the internal air pressure of the negative pressure vibration is 50kPa; after the forming is completed, the upper part is scraped flat, and the film is naturally cured for 24h. ， The demolding obtains a recycled curbstone sample with smooth and compact surface; the standard curing is 28 days, the standard curing temperature is 20℃, and the air humidity is 95%.

[0061] The obtained curbstone sample has smooth and compact surface, the measured 28-day compressive strength is 32.7MPa, which meets the requirement of C30. The water absorption is 4.3%, the frost resistance D50 mass loss rate is 1.3%, which all meet the index requirements.

[0062] Example 2

[0063] 10-25mm brick-mixed recycled coarse aggregate 700 parts, 0-3mm brick-mixed recycled fine aggregate (the fine aggregate is too fine due to insufficient disposal screening capacity) 400 parts, 5-10mm brick-mixed recycled aggregate 400 parts, P.O42.5 cement 350 parts, water 250 parts, polycarboxylic acid water reducer 7 parts, the concrete mixing method and small component forming method are consistent with example 1.

[0064] The obtained curbstone sample has smooth and dense surface, and the 28-day compressive strength after standard curing is 31.1 MPa, meeting the strength requirement.

[0065] Example 3

[0066] Example 3 is different from Example 1 in that the amount of 10-25 mm brick-concrete recycled coarse aggregate is 600 parts, the amount of 0-5 mm brick-concrete recycled fine aggregate is 900 parts, and the remaining conditions are the same as those in Example 1.

[0067] The obtained curbstone sample has smooth and dense surface, and the 28-day compressive strength after standard curing is 31.1 MPa, meeting the strength requirement.

[0068] Comparative Example 1

[0069] In Comparative Example 1, 10-25 mm brick-concrete recycled coarse aggregate is 700 parts, 0-3 mm brick-concrete recycled fine aggregate (the fine aggregate is too fine due to insufficient disposal and screening capacity) is 800 parts, P.O 42.5 cement is 350 parts, mixing water is 250 parts, polycarboxylic acid water reducer is 7 parts, and the concrete mixing method and small component molding method are the same as those in Example 1.

[0070] The obtained curbstone sample has smooth and dense surface, and the 28-day compressive strength after standard curing is 31.1 MPa, meeting the strength requirement.

[0071] Comparative Example 2

[0072] In Comparative Example 2, the raw materials and amounts of 10-25 mm brick-concrete recycled coarse aggregate, 0-5 mm brick-concrete recycled fine aggregate and P.O 42.5 cement, and the molding method are the same as those in Example 1, and the mixing process is as follows: the brick-concrete recycled aggregate and cement are added to a forced mixer and stirred for 60 s; mixing water 250 parts and polycarboxylic acid water reducer 14 parts are stirred uniformly, and then added to the forced mixer and stirred for 30 s to obtain uniform dry concrete. The molding is difficult and the internal structure is not dense. After demolding, the obtained product is in the form of water-permeable concrete, and the 28-day compressive strength after standard curing is 22.8 MPa, which does not meet the strength requirement.

[0073] Comparative Example 3

[0074] Comparative Example 3 is different from Example 1 in that the amount of 10-25 mm brick-concrete recycled coarse aggregate is 800 parts, and the amount of 0-5 mm brick-concrete recycled fine aggregate is 700 parts, and the remaining conditions are the same as those in Example 1.

[0075] The obtained curbstone sample has smooth and dense surface, and the 28-day compressive strength after standard curing is 31.1 MPa, meeting the strength requirement.

[0076] Comparative Example 4

[0077] The difference between Comparative Example 4 and Example 1 is that the amount of 10-25 mm brick-mixed recycled coarse aggregate is 500 parts, the amount of 0-5 mm brick-mixed recycled fine aggregate is 1000 parts, and the rest is the same as Example 1.

[0078] The obtained curbstone sample has a dense surface, and the compressive strength after 28 days of standard curing is 26.8 MPa, which does not meet the strength requirement.

[0079] Comparative Example 5

[0080] The dry hard recycled concrete is prepared and molded on a brick molding machine, which is a five-type machine, and the molding height can only mold a flat curbstone with a height of 200 mm. The recycled concrete is prepared with the same raw material sources as in Example 1, and the mixing ratio composition is 10-25 mm brick-mixed recycled coarse aggregate 700 parts, 0-5 mm brick-mixed recycled fine aggregate 800 parts, P.O42.5 cement 350 parts, and mixing water 200 parts, which is drier than Example 1. After vibration and pressure molding by the brick machine, a flat curbstone sample is obtained.

[0081] The compressive strength is 32.5 MPa after 28 days of standard curing, which meets the C30 requirement. However, the side surface has a clear grainy feeling, the visual effect is not good, the water absorption rate is 5.8%, the frost resistance D50 mass loss rate is 2.9%, which all meet the index requirements, but are inferior to Example 1.

[0082] Comparative Example 6

[0083] The recycled concrete is prepared according to the traditional wet molding method: the raw material sources are the same as in Example 1, the mixing ratio composition is 10-25 mm brick-mixed recycled coarse aggregate 700 parts, 0-5 mm brick-mixed recycled fine aggregate 800 parts, P.O42.5 cement 350 parts, and mixing water 350 parts, which are uniformly stirred by a forced mixer, and the measured slump is 150 mm. The mold sprayed with a release agent is placed on a vibration table, and the recycled concrete is poured and vibrated. After demolding, the appearance is good, the compressive strength is 17.2 MPa after 28 days of standard curing, which does not meet the strength requirement of curbstone. The concrete state can be pumped for construction, but its strength is low, the application direction is few, and it seriously affects the application of brick-mixed recycled aggregate in concrete products.

[0084] Although the present application has been illustrated and described with reference to specific embodiments, it is realized that the above examples are merely used to illustrate the technical solutions of the present application, and are not limiting thereof; it is understood by those skilled in the art that the technical solutions recorded in the foregoing examples can be modified, or some or all of the technical features can be replaced equivalently without departing from the spirit and scope of the present application; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solutions of the embodiments of the present application; therefore, this means that all these replacements and modifications within the scope of the present application are included in the appended claims.

Claims

1. A method for preparing C30 precast concrete members using Grade IV recycled aggregates, characterized in that, The method comprises the following steps: The IV-grade recycled aggregate, cement, water and water reducing agent are uniformly mixed to prepare dry hard recycled concrete with a slump of less than 10 mm and a Vibe consistency of 17-25 s, and the dry hard recycled concrete is molded and maintained to obtain the C30 prefabricated concrete member; the molding process is that the prepared dry hard recycled concrete is poured into a mold sprayed with a release agent in layers and vibrated, and meanwhile, negative pressure vibration is performed; The IV-grade recycled aggregate accounts for 70-75% of the total raw material in terms of mass percentage, the cement accounts for 16-20% of the total raw material in terms of mass percentage, the water reducing agent accounts for 1-3% of the cement in terms of mass percentage, and the balance is water; The IV-grade recycled aggregate comprises recycled coarse aggregate with a particle size of 10-25 mm and recycled fine aggregate with a particle size of 0-5 mm, the recycled coarse aggregate with a particle size of 10-25 mm accounts for 40-50% of the IV-grade recycled aggregate in terms of mass ratio, in the recycled fine aggregate, 2.36 mm sieve residue accounts for 20-30% in terms of mass ratio, 4.75 mm sieve residue accounts for 5-15% in terms of mass ratio, and the recycled fine aggregate accounts for 50-60% of the IV-grade recycled aggregate in terms of mass ratio; Alternatively, the IV-grade recycled aggregate comprises recycled coarse aggregate with a particle size of 10-25 mm and recycled fine aggregate with a particle size of 0-5 mm, the recycled coarse aggregate with a particle size of 10-25 mm accounts for 40-50% of the IV-grade recycled aggregate in terms of mass ratio, and the IV-grade recycled aggregate further comprises medium-grit recycled aggregate with a particle size of 5-10 mm, the recycled fine aggregate with a particle size of 0-5 mm accounts for 20-30% of the IV-grade recycled aggregate in terms of mass ratio, and the medium-grit recycled aggregate with a particle size of 5-10 mm accounts for 20-30% of the IV-grade recycled aggregate in terms of mass ratio.

2. The method for preparing C30 precast concrete members using Grade IV recycled aggregates according to claim 1, characterized in that, The method comprises at least one of the following features (1) to (2): (1) The cement comprises ordinary portland cement, and the strength grade is P.O42.5 or P.O52.5; (2) The water reducing agent is a polycarboxylic acid water reducing agent.

3. The method for preparing C30 precast concrete members using Grade IV recycled aggregates according to claim 1, characterized in that, The preparation method of the dry hard recycled concrete is as follows: the IV-grade recycled aggregate and the cement are uniformly mixed, then the water is added, and after uniform mixing, the water reducing agent is added, and uniform mixing is performed to obtain the dry hard recycled concrete.

4. The method for preparing C30 precast concrete members using Grade IV recycled aggregates according to claim 3, characterized in that, The stirring is forced stirring, the stirring speed is 20-40 r / min, the IV-grade recycled aggregate and the cement are uniformly mixed for 60-90 s, the stirring and mixing time after the water is added is 20-30 s, and the stirring and mixing time after the water reducing agent is added is 30-60 s.

5. The method for preparing C30 precast concrete members using Grade IV recycled aggregates according to claim 1, characterized in that, The method comprises at least one of the following features (1) to (4): (1) The release agent is a water-based release agent; (2) The vibration power is 3-4 kw, the vibration frequency is 40-50 Hz, and the vibration time is 60-90 s for each layer; (3) The vibration power of the negative pressure vibration is 1-2 kw, and the vibration time of the negative pressure vibration is 60-90 s for each layer; (4) The internal air pressure of the negative pressure vibration is 40-60 kPa.

6. A C30 precast concrete member prepared using Grade IV recycled aggregate, characterized in that, The method for preparing a C30 prefabricated concrete member by using IV-grade recycled aggregate is prepared by the method in any one of claims 1-5.