A durable recycled aggregate concrete and its preparation method

Abstract

The present application discloses a durable recycled aggregate concrete and a preparation method thereof. The durable recycled aggregate concrete comprises the following raw materials in parts by mass: 110-130 parts of modified recycled coarse aggregate, 48-60 parts of fine aggregate, 12-15 parts of ultra-fine admixture, 27-34 parts of cement, 12-15 parts of fly ash, 1-1.5 parts of water reducer, 4-8 parts of chloride ion adsorbent, and 16-19 parts of water; the chloride ion adsorbent contains polypyrrole / titanium dioxide, and carboxyl groups are attached to the surface of the modified recycled coarse aggregate. The recycled aggregate concrete of the present application has good strength and chloride ion adsorption capacity.

Description

Technical Field

[0001] The present application relates to the field of concrete, and in particular to a durable recycled aggregate concrete and a preparation method thereof. Background Art

[0002] The construction industry is developing rapidly, and a large number of obsolete buildings are being demolished. The demolition of buildings is accompanied by the generation of a large amount of construction waste, among which waste concrete accounts for the largest proportion of construction waste. As the concept of energy conservation and environmental protection is deeply rooted in people's hearts, recycling waste concrete has become the focus of research on the recycling of construction waste.

[0003] Recycled concrete refers to the waste concrete that has been crushed, cleaned, and graded, and then partially or completely replaced with natural aggregates such as sand and gravel to form recycled aggregate concrete. Recycled aggregate concrete can not only save natural aggregates, but also further solve the problem of recycling construction waste.

[0004] However, due to the large pores and many gaps in recycled aggregates, the strength of recycled concrete is lower and the porosity is larger than that of concrete made from natural aggregates. This also causes recycled concrete to be easily corroded by chloride ions in the external environment during use, and the internal steel structure is corroded, resulting in a shortened service life of the concrete and reduced durability. Summary of the invention

[0005] In order to solve the problem that recycled aggregate concrete has low strength and is susceptible to chloride ion corrosion, the present application provides a durable recycled aggregate concrete and a preparation method thereof.

[0006] In a first aspect, the present application provides a durable recycled aggregate concrete, comprising the following raw materials in parts by weight: 110 to 130 parts of modified recycled coarse aggregate, 48 to 60 parts of fine aggregate, 12 to 15 parts of ultrafine admixture stone, 27 to 34 parts of cement, 12 to 15 parts of fly ash, 1 to 1.5 parts of water reducer, 4 to 8 parts of chloride ion adsorbent, and 16 to 19 parts of water; the chloride ion adsorbent contains polypyrrole / titanium dioxide, and carboxyl groups are attached to the surface of the modified recycled coarse aggregate.

[0007] Preferably, the raw material of polypyrrole / titanium dioxide comprises pyrrole monomer and nano-titanium dioxide in a mass ratio of (1.2-1.8):1.

[0008] By adopting the above technical solution, due to the porosity of recycled aggregate, it is easier to be penetrated and corroded by chloride ions in concrete, and a large number of chloride ion free radicals accumulate inside the concrete. The polypyrrole in the polypyrrole / titanium dioxide loses electrons through oxidation reaction, and the positively charged polypyrrole / titanium dioxide can adsorb the chloride ion free radicals in the concrete, thereby avoiding the problem of steel corrosion caused by the large accumulation of chloride ion free radicals in the concrete, and effectively improving the durability of the concrete.

[0009] Preferably, the chloride ion adsorbent is a microcapsule structure with polypyrrole / titanium dioxide as the core and a chitosan-calcium alginate complex coacervation layer as the coating layer.

[0010] By adopting the above technical solution, the chitosan-calcium alginate complex coacervation layer contains carboxyl groups, which can effectively oxidize the polypyrrole component in the polypyrrole / titanium dioxide, so that the polypyrrole loses electrons and the positively charged polypyrrole / titanium dioxide can adsorb chloride radicals, achieving the effect of reducing chloride radicals. At the same time, there are a large number of positive charges on the surface of chitosan-calcium alginate, which can attract chloride radicals to chitosan-calcium alginate. At the same time, the polypyrrole / titanium dioxide adsorbs the attracted chloride radicals, achieving the effect of adsorbing and reducing chloride radicals.

[0011] Moreover, the chitosan-calcium alginate complex coacervation layer can protect the properties of the internal polypyrrole / titanium dioxide from the influence of the external environment, making the polypyrrole / titanium dioxide not easily inactivated and losing its ability to adsorb chloride ions.

[0012] In addition, there are also a large number of primary amino groups on the surface of the chitosan-calcium alginate complex coacervation layer, and the primary amino groups can react and crosslink with the carboxyl groups on the modified recycled coarse aggregate, enabling the chloride ion adsorbent to crosslink on the modified recycled coarse aggregate through bonding, promoting the uniform dispersion of the chloride ion adsorbent, and being more beneficial to the adsorption of chloride ions.

[0013] Preferably, the particle size of the chloride ion adsorbent is 0.5 mm to 1.5 mm.

[0014] By adopting the above technical solution, the chloride ion adsorbent is sieved, and the millimeter-sized chloride ion adsorbent selected is easier to disperse and has a large specific surface area, and can effectively adsorb chloride ions to a large extent.

[0015] Preferably, the preparation steps of the chloride ion adsorbent are as follows:

[0016] Preparation of polypyrrole / titanium dioxide: Add nano-titanium dioxide to an acidic solution and disperse it evenly, then add pyrrole monomer and stir to obtain solution A; add a ferric salt catalyst to the acidic solution and stir and mix to obtain solution B; mix solution A and solution B in an ice-water bath and stir, and then obtain polypyrrole / titanium dioxide through washing, drying, and grinding.

[0017] Preparation of chloride ion adsorbent: The obtained polypyrrole / titanium dioxide nanoparticles and sodium alginate solution are added to a calcium ion solution together. At a temperature of 8 - 15 °C, they are stirred and mixed for 15 - 25 min. After stirring, a chitosan solution is added and stirring continues for the composite gel reaction. After the reaction, a dialdehyde cross-linking agent is added, the temperature is raised to 20 - 30 °C, and stirring and curing are carried out for 40 - 80 min. After curing, it is left standing, filtered, dried, and sieved to obtain the chloride ion adsorbent;

[0018] Preferably, the mass fractions of the sodium alginate solution and the chitosan solution are 0.5% - 2%.

[0019] More preferably, the mass fractions of the sodium alginate solution and the chitosan solution are 1%.

[0020] Preferably, the ratio of the mass of the polypyrrole / titanium dioxide nanoparticles to the volume of the sodium alginate solution is 1 g:(3.5 - 4.5) ml; the volume ratio of the sodium alginate solution to the chitosan solution is 1:(1.1 - 1.4).

[0021] Preferably, the acidic solution has a concentration of 1 mol / L and is one of hydrochloric acid solution, nitric acid solution, and sulfuric acid solution.

[0022] More preferably, the acidic solution is a hydrochloric acid solution with a concentration of 1 mol / L.

[0023] Preferably, the ferric salt catalyst is one or more of ferric chloride hexahydrate, ferric nitrate nonahydrate, and ferric sulfate nonahydrate.

[0024] More preferably, the ferric salt catalyst is ferric chloride hexahydrate.

[0025] Preferably, the ratio of the mass of nano-titanium dioxide to the volume of the acidic solution is 1 g:(4.8 - 5.2) ml, and the ratio of the ferric salt catalyst to the acidic solution is 1:(9.7 - 10.2).

[0026] More preferably, the ratio of the mass of nano-titanium dioxide to the volume of the acidic solution is 1 g:5 ml, and the ratio of the ferric salt catalyst to the acidic solution is 1:10.

[0027] Preferably, the calcium ion solution is one of a calcium nitrate aqueous solution with a mass fraction of 20% and an anhydrous calcium chloride aqueous solution with a mass fraction of 20%.

[0028] More preferably, the calcium ion solution is a calcium nitrate aqueous solution with a mass fraction of 20%.

[0029] Preferably, the dialdehyde cross-linking agent includes one or more of glutaraldehyde, genipin, and glyoxal.

[0030] More preferably, the dialdehyde cross-linking agent is glutaraldehyde.

[0031] Preferably, the mass ratio of the dialdehyde crosslinking agent to chitosan is (0.8 - 1.2):1.

[0032] By adopting the above technical solution, a gel mainly produced by chelation reaction occurs between sodium alginate and calcium ions in the calcium ion solution, forming calcium alginate gel beads with polypyrrole / titanium dioxide as the core. The calcium alginate gel beads are added to the chitosan solution, and through a re-gel reaction, a chitosan-calcium alginate re-coagulation layer is formed. A three-dimensional network structure is formed between the molecular chains of alginic acid, enabling the obtained chloride ion adsorbent to have good mechanical properties and being not easily broken. Then, the dialdehyde crosslinking agent is used to crosslink and solidify the re-coagulation layer, further strengthening the chitosan-calcium alginate polypyrrole / titanium dioxide microcapsules, enabling the chloride ion adsorbent to effectively adsorb chloride ions for a long time. At the same time, through crosslinking and solidification, the agglomeration or bonding phenomenon between the chitosan-calcium alginate polypyrrole / titanium dioxide microcapsules can be effectively reduced, increasing the effectiveness of the chloride ion adsorbent.

[0033] Preferably, the raw materials of the modified recycled coarse aggregate include recycled coarse aggregate, an amino-silane coupling agent, and an organic acid anhydride with a mass ratio of 100:(3 - 6):(3.5 - 7).

[0034] Preferably, the organic acid anhydride is one or more of succinic anhydride, ethyl propionic anhydride, propionic anhydride, and maleic anhydride.

[0035] More preferably, the organic acid anhydride is maleic anhydride

[0036] Preferably, the amino-silane coupling agent is one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β(aminoethyl)-γ-aminopropyltriethoxysilane, and phenylaminomethyltriethoxysilane.

[0037] More preferably, the amino-silane coupling agent is γ-aminopropyltriethoxysilane.

[0038] By adopting the above technical solution, the recycled coarse aggregate is stirred and mixed with the amino-silane coupling agent, making the surface of the recycled coarse aggregate contain amino groups; then the organic acid anhydride is added, and the anhydride group in the organic acid anhydride reacts with the amino groups on the surface of the recycled coarse aggregate, making the surface of the recycled coarse aggregate adhere to carboxyl groups. The carboxyl groups can react and crosslink with the primary amino groups on the surface of the chitosan-calcium alginate re-coagulation layer, enabling the chloride ion adsorbent to be uniformly dispersed and crosslinked on the modified recycled coarse aggregate, which is more beneficial to the adsorption of chloride ions.

[0039] Preferably, the D50 particle size of the ultra-fine admixture is 3 μm - 8 μm, and it is a composition of one or more of silicon carbide and silicon dioxide.

[0040] By adopting the above technical solution, the ultra-fine admixture can fill the gaps in the recycled coarse aggregate, reduce the porosity, improve the structure of the interfacial transition zone, reduce the cracks in the interfacial zone, increase the compactness of the concrete, strengthen the bonding force between the modified recycled coarse aggregate and cement and fly ash, and enhance the strength of the recycled aggregate concrete.

[0041] Secondly, the present application provides a method for preparing durable recycled aggregate concrete, comprising the following steps:

[0042] Step 1: Uniformly dry-mix the modified recycled coarse aggregate, fine aggregate and ultra-fine admixture, and then pour in cement and fly ash and stir to obtain a crude mixture;

[0043] Step 2: Add a water reducer and a chloride ion adsorbent to the crude mixture, stir and mix, and finally add water and continue to stir to obtain durable recycled aggregate concrete.

[0044] Preferably, the water reducer is a polycarboxylate graft copolymerization type water reducer, and the grafting raw materials of the polycarboxylate graft copolymerization type water reducer include one or more of acrylic acid, maleic anhydride, methacrylic acid, and hydroxyethyl acrylate.

[0045] By adopting the above technical solution, the molecular structure of the water reducer contains one or more of carboxyl groups, sulfonic acid groups, and hydroxyl groups. Among them, the carboxylate ions formed by the carboxyl groups can combine with calcium ions in the recycled aggregate concrete, slow down the decrease in the concentration of the water reducer, and enhance the strength of the recycled aggregate concrete.

[0046] In summary, the present application has the following beneficial effects:

[0047] 1. The chloride ion adsorbent in the durable recycled aggregate concrete of the present application contains polypyrrole / titanium dioxide. Polypyrrole / titanium dioxide carries a positive charge under the oxidation of carboxyl groups in the chitosan-alginate calcium complex coagulation layer, achieving the effect of adsorbing chloride ions.

[0048] 2. The chloride ion adsorbent is a microcapsule structure with polypyrrole / titanium dioxide as the core and a chitosan-alginate calcium complex coagulation layer as the coating layer. On the one hand, the chitosan-alginate calcium complex coagulation layer can protect the internal polypyrrole / titanium dioxide from the external environment. On the other hand, the positive charge on the surface of the chitosan-alginate calcium complex coagulation layer can be used to attract chloride ions, accelerating the adsorption of chloride ion free radicals by the chloride ion adsorbent. In addition, the chitosan-alginate calcium complex coagulation layer can also form a three-dimensional network structure, and through cross-linking and curing, the mechanical properties of the chloride ion adsorbent can be strengthened, avoiding agglomeration and bonding between chloride ion adsorbents, so that the chloride ion adsorbent can effectively adsorb chloride ions for a long time.

[0049] 3. The modified recycled coarse aggregate in the durable recycled aggregate concrete of the present application has carboxyl groups on its surface. The primary amino groups on the surface of the chitosan-calcium alginate double coagulation layer can crosslink with the carboxyl groups on the surface of the modified recycled coarse aggregate, strengthening the binding of the chloride ion adsorbent to the modified recycled coarse aggregate, facilitating the uniform dispersion of the chloride ion adsorbent, and making it easier to adsorb chloride ion free radicals.

[0050] 4. The durable recycled aggregate concrete of the present application contains ultra-fine admixtures. The ultra-fine admixtures can fill the pores in the recycled aggregate concrete, strengthen the compactness of the recycled aggregate concrete, and improve the strength of the concrete. Detailed implementation manners

[0051] Preparation examples of chloride ion adsorbents

[0052] Preparation Example 1-1, a chloride ion adsorbent, is prepared by the following method:

[0053] Take 20 g of nano-titanium dioxide powder and add it to 100 ml of hydrochloric acid solution with a concentration of 1 mol / L. Ultrasonically disperse for 5 min, then add 30 g of pyrrole monomer, and stir and mix for 30 min to make the mixture uniform to obtain Solution A; take 10 g of ferric chloride hexahydrate and add it to 100 ml of hydrochloric acid solution with a concentration of 1 mol / L, and stir to fully dissolve the ferric chloride hexahydrate to obtain Solution B; mix Solution A and Solution B and stir in an ice-water bath. After stirring for 30 min, let it stand, wash the product to remove the residual chloride ions on the surface, dry it to constant weight in an oven at 70 °C, and grind it thoroughly to obtain polypyrrole / titanium dioxide powder.

[0054] Take 20 g of the prepared polypyrrole / titanium dioxide powder and 80 ml of sodium alginate solution with a mass fraction of 1% and add them to 250 ml of calcium nitrate aqueous solution with a mass fraction of 20%. At a temperature of 10 °C, stir and mix. After stirring for 20 min, calcium alginate gel beads with polypyrrole / titanium dioxide as the core are formed. Then add 100 ml of chitosan solution with a mass fraction of 1%, and continue to stir for the double gel reaction. After reacting for 20 min, raise the temperature to 30 °C, add 10 ml of glutaraldehyde solution with a mass fraction of 10%, and crosslink and cure the formed chitosan-calcium alginate double coagulation layer. Stir and cure for 60 min. After the curing is completed, let the solution stand for 40 min to settle and precipitate, and then filter, dry, and sieve to obtain chloride ion adsorbents with a particle size of 0.8 mm to 1.2 mm.

[0055] Preparation Example 1-2, a chloride ion adsorbent, is different from Preparation Example 1-1 only in that the addition amount of pyrrole monomer is 24 g, the addition amount of sodium alginate solution with a mass fraction of 1% is 70 ml, and the addition amount of chitosan solution with a mass fraction of 1% is 88 ml.

[0056] Preparation Example 1-3, a chloride ion adsorbent, which is different from Preparation Example 1-1 only in that the addition amount of pyrrole monomer is 36 g, the addition amount of 1% sodium alginate solution is 90 ml, and the addition amount of 1% chitosan solution is 126 ml.

[0057] Preparation Example 1-4, a chloride ion adsorbent, which is different from Preparation Example 1-1 only in that the addition amount of pyrrole monomer is 20 g, the addition amount of 1% sodium alginate solution is 60 ml, and the addition amount of 1% chitosan solution is 60 ml.

[0058] Preparation Example 1-5, a chloride ion adsorbent, which is different from Preparation Example 1-1 only in that the addition amount of pyrrole monomer is 40 g, the addition amount of 1% sodium alginate solution is 100 ml, and the addition amount of 1% chitosan solution is 150 ml.

[0059] Preparation Example 1-6, a chloride ion adsorbent, which is different from Preparation Example 1-1 only in that 10% glutaraldehyde solution is not added.

[0060] Preparation Example 1-7, a chloride ion adsorbent, which is different from Preparation Example 1-1 only in that sieving treatment is not carried out after drying, and the particle size distribution of the chloride ion adsorbent is 0.5 - 3.5 mm.

[0061] Preparation Example 1-8, a chloride ion adsorbent, which is different from Preparation Example 1-1 only in that polypyrrole / titanium dioxide is not coated with a chitosan-calcium alginate complex coagulation layer.

[0062] Preparation Example 1-9, a chloride ion adsorbent, which is different from Preparation Example 1-1 only in that polypyrrole / titanium dioxide is not added.

[0063] Preparation Examples of Modified Recycled Coarse Aggregates

[0064] Preparation Example 2-1, a modified recycled coarse aggregate, is prepared by the following method:

[0065] Perform pre-crushing treatment on 70 kg of recycled coarse aggregate, and remove internal impurities such as steel bars during the crushing process. Stir the pretreated recycled coarse aggregate evenly with 2.8 kg of γ-aminopropyltriethoxysilane to obtain a premix; then add 3.15 kg of maleic anhydride to the premix and stir until evenly mixed, and then obtain the modified recycled coarse aggregate through washing and drying.

[0066] Preparation Example 2-2, a modified recycled coarse aggregate, which is different from Preparation Example 2-1 only in that the addition amount of γ-aminopropyltriethoxysilane is 3.5 kg and the addition amount of maleic anhydride is 4.2 kg.

[0067] Preparation Example 2-3, a modified recycled coarse aggregate, which is different from Preparation Example 2-1 only in that the addition amount of γ-aminopropyltriethoxysilane is 2.1 kg and the addition amount of maleic anhydride is 2.45 kg

[0068] Example

[0069] Example 1, a durable recycled aggregate concrete, is prepared according to the following method:

[0070] 120 kg of the modified recycled coarse aggregate prepared in Preparation Example 2-1, 52 kg of fine aggregate, and 13 kg of ultrafine admixture are uniformly dry-mixed, and then 30 kg of cement and 13 kg of fly ash are added and stirred to obtain a coarse mixture; 1.2 kg of polycarboxylate water reducer and 6 kg of the chloride ion adsorbent prepared in Preparation Example 1-1 are added to the coarse mixture, stirred and mixed, and finally 18 kg of water is added and stirred continuously to obtain the durable recycled aggregate concrete.

[0071] Among them, the fine aggregate is fine sand with a fineness modulus of 2.2 to 1.6 and an average particle size of 0.25 to 0.35 mm; the ultrafine admixture is silicon carbide with a particle size of 4 to 6 μm, the type of polycarboxylate water reducer is VS-F type; the cement is ordinary Portland 42.5 cement.

[0072] Example 2, a durable recycled aggregate concrete, which is different from Example 1 only in that the modified recycled coarse aggregate prepared in Preparation Example 2-2 is used to replace the modified recycled coarse aggregate prepared in Preparation Example 2-1 in equal amount; the chloride ion adsorbent prepared in Preparation Example 1-2 is used to replace the chloride ion adsorbent prepared in Preparation Example 1-1 in equal amount.

[0073] Example 3, a durable recycled aggregate concrete, which is different from Example 1 only in that the modified recycled coarse aggregate prepared in Preparation Example 2-3 is used to replace the modified recycled coarse aggregate prepared in Preparation Example 2-1 in equal amount; the chloride ion adsorbent prepared in Preparation Example 1-3 is used to replace the chloride ion adsorbent prepared in Preparation Example 1-1 in equal amount.

[0074] Example 4, a durable recycled aggregate concrete, which is different from Example 1 only in that the addition amount of the modified recycled coarse aggregate prepared in Preparation Example 2-1 is 130 kg, the addition amount of fine aggregate is 60 kg, the addition amount of ultrafine admixture is 15 kg, the addition amount of cement is 27 kg, and the addition amount of fly ash is 12 kg.

[0075] Example 5, a durable recycled aggregate concrete, which is different from Example 1 only in that the addition amount of the modified recycled coarse aggregate prepared in Preparation Example 2-1 is 112 kg, the addition amount of fine aggregate is 48 kg, the addition amount of ultrafine admixture is 12 g, the addition amount of cement is 34 kg, and the addition amount of fly ash is 15 kg.

[0076] Example 6. A durable recycled aggregate concrete, which is different from Example 1 only in that the addition amount of polycarboxylate water reducer is 1.5 kg, and the addition amount of the chloride ion adsorbent prepared in Preparation Example 1-1 is 4 kg.

[0077] Example 7. A durable recycled aggregate concrete, which is different from Example 1 only in that the addition amount of ultra-fine admixture is 20 kg.

[0078] Example 8. A durable recycled aggregate concrete, which is different from Example 1 only in that the chloride ion adsorbent prepared in Preparation Example 1-1 is replaced with the chloride ion adsorbent prepared in Preparation Example 1-4 in equal amount.

[0079] Example 9. A durable recycled aggregate concrete, which is different from Example 1 only in that the chloride ion adsorbent prepared in Preparation Example 1-1 is replaced with the chloride ion adsorbent prepared in Preparation Example 1-5 in equal amount.

[0080] Example 10. A durable recycled aggregate concrete, which is different from Example 1 only in that the chloride ion adsorbent prepared in Preparation Example 1-1 is replaced with the chloride ion adsorbent prepared in Preparation Example 1-6 in equal amount.

[0081] Example 11. A durable recycled aggregate concrete, which is different from Example 1 only in that the chloride ion adsorbent prepared in Preparation Example 1-1 is replaced with the chloride ion adsorbent prepared in Preparation Example 1-7 in equal amount.

[0082] Example 12. A durable recycled aggregate concrete, which is different from Example 1 only in that the VS-F type polycarboxylate water reducer is replaced with an equal amount of lignosulfonate water reducer.

[0083] Example 13. A durable recycled aggregate concrete, which is different from Example 1 only in that the silicon carbide with a particle size of 4-6 μm is replaced with an equal amount of silicon carbide with a particle size of 10-12 μm.

[0084] Example 14. A durable recycled aggregate concrete, which is different from Example 1 only in that the chloride ion adsorbent prepared in Preparation Example 1-1 is replaced with the chloride ion adsorbent prepared in Preparation Example 1-8 in equal amount.

[0085] Comparative Example

[0086] Comparative Example 1. A durable recycled aggregate concrete, which is different from Example 1 only in that the modified recycled coarse aggregate prepared in Preparation Example 2-1 is replaced with an equal amount of unmodified recycled coarse aggregate.

[0087] Comparative Example 2. A durable recycled aggregate concrete, which is different from Example 14 only in that the modified recycled coarse aggregate prepared in Preparation Example 2-1 is replaced with an equal amount of unmodified recycled coarse aggregate.

[0088] Comparative Example 3, a durable recycled aggregate concrete, which is different from Example 1 only in that the chloride ion adsorbent prepared in Preparation Examples 1-9 is used in equal amount to replace the chloride ion adsorbent prepared in Preparation Example 1-1.

[0089] Comparative Example 4, a durable recycled aggregate concrete, which is different from Example 1 only in that no chloride ion adsorbent is added.

[0090] Comparative Example 5, a durable recycled aggregate concrete, which is different from Example 14 only in that the addition amount of fine aggregate is 65 kg and no ultra-fine admixture is added.

[0091] Performance detection test

[0092] 1. The strength of the concrete was tested according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", and the 28-day compressive strength and splitting tensile strength of the concrete specimens were measured.

[0093] 2. The chloride ion adsorption capacity of the concrete was tested according to GB / T 50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete". The electric flux method was adopted to measure the electric flux passing through the concrete specimens. The smaller the electric flux, the stronger the chloride ion adsorption capacity.

[0094] The specific test results are shown in Table 1:

[0095] Table 1 Test results of examples and comparative examples

[0096]

[0097]

[0098] According to Table 1, in combination with Example 1 and Example 14, it can be seen that the 28-day compressive strength and 28-day splitting strength of Example 14 change little compared with Example 1, and the electric flux increases compared with Example 1, indicating that the chloride ion penetration resistance of Example 14 is lower than that of Example 1. The reason may be that the polypyrrole / titanium dioxide in Example 14 is not coated by the chitosan-calcium alginate composite coagulation layer, the oxidation degree in the concrete is low, the effective ions capable of adsorbing chloride ions are reduced, and at the same time, lacking the protection of the chitosan-calcium alginate composite coagulation layer, the polypyrrole / titanium dioxide is prone to agglomeration and even inactivation, reducing or gradually losing the ability to adsorb chloride free radicals.

[0099] Combined with Example 1, Example 14, Comparative Example 1 and Comparative Example 2, it can be seen that the 28-day compressive strength and 28-day splitting tensile strength of Comparative Example 1 and Comparative Example 2 are both lower than those of Example 1 and Example 14, and the electric flux increases compared with Example 1, and the increase in Comparative Example 2 is more obvious. This shows that the strength and chloride ion adsorption capacity of Comparative Example 1 and Comparative Example 14 are lower than those of Example 14, that is, the chloride ion penetration resistance performance decreases. The reason may be that the recycled coarse aggregate used in Comparative Example 1 is not modified, and its surface does not contain carboxyl groups, so it cannot react and crosslink with the primary amino groups on the surface of the chloride ion adsorbent. As a result, the chloride ion adsorbent cannot be well dispersed in the concrete, leading to a decrease in the efficiency of chloride ion adsorption, a reduction in the amount, and a decline in the chloride ion penetration resistance performance. At the same time, the lack of carboxyl groups on the recycled coarse aggregate makes it impossible to bond with other substances, resulting in a decrease in the compactness of the concrete and a decline in strength. In Comparative Example 2, the recycled coarse aggregate used is still not modified, resulting in a decrease in strength and a decrease in the ability of the concrete to adsorb chloride ion free radicals due to the lack of the synergistic effect of the chitosan-alginate double coagulation layer.

[0100] Combined with Example 1, Comparative Example 3 and Comparative Example 4, it can be seen that the electric fluxes of Comparative Example 3 and Comparative Example 4 are very different from that of Example 1. The electric flux of Comparative Example 4 is even higher than that of Comparative Example 3. At the same time, the 28-day compressive strength and 28-day splitting tensile strength of Comparative Example 3 and Comparative Example 4 are lower than those of Example 1. This shows that the chloride ion adsorption capacities of Comparative Example 3 and Comparative Example 4 are very poor compared with Example 1, and their chloride ion penetration resistance performances are very poor. The chloride ion penetration resistance performance of Comparative Example 4 is worse than that of Comparative Example 3.

[0101] The reason may be that the chloride ion adsorbent in Comparative Example 3 lacks polypyrrole / titanium dioxide, and no chloride ion adsorbent is added in Comparative Example 4. This shows that the chloride ion adsorbent can effectively adsorb chloride ions in the concrete and reduce the content of chloride ion free radicals in the concrete. The main part that adsorbs chloride ions is polypyrrole / titanium dioxide. When the chloride ion adsorbent lacking polypyrrole / titanium dioxide is added to the concrete, its chloride ion adsorption capacity will be greatly reduced. However, since there are also a large number of positive charges on the surface of the chitosan-alginate double coagulation layer, a small part of the chloride ion free radicals are attracted into the chitosan-alginate double coagulation layer. Therefore, Comparative Example 3 still retains partial chloride ion penetration resistance performance.

[0102] Combined with Example 1, Example 14 and Comparative Example 5, it can be seen that the 28-day compressive strength and 28-day splitting tensile strength of Comparative Example 5 are significantly lower than those of Example 1 and also lower than those of Example 14. The electric flux increases compared with Example 1, indicating that the strength of Comparative Example 5 is significantly lower than that of Example 1, and the chloride ion adsorption capacity decreases compared with Example 1. The reason may be that no ultra-fine admixture is added in Comparative Example 5. The gaps between recycled coarse aggregates are larger and the porosity is higher compared with natural coarse aggregates. Without ultra-fine admixture for filling, the compactness of the concrete is poor, and the bonding force between the recycled coarse aggregates, cement and fly ash is low, resulting in a significant decrease in the strength of recycled aggregate concrete.

[0103] Combined with Example 1, Example 2 and Example 3, it can be seen that the 28-day compressive strength, 28-day splitting tensile strength and electric flux of Example 2 and Example 3 have no obvious change compared with Example 1, indicating that changing the mass fraction of the raw materials of the modified recycled coarse aggregate and chloride ion adsorbent within the required range has no obvious effect on the strength of the concrete and the chloride ion adsorption capacity.

[0104] Combined with Example 1 and Examples 4-6, it can be seen that the 28-day compressive strength, 28-day splitting tensile strength and electric flux of Examples 4-6 have no obvious change compared with Example 1, indicating that changing the mass fraction of the raw materials of the durable recycled aggregate concrete within the required range has no obvious effect on the strength of the concrete and the adsorption capacity for chloride free radicals.

[0105] Combined with Example 1 and Example 7, it can be seen that the 28-day compressive strength and 28-day splitting tensile strength of Example 7 are lower than those of Example 1, and the electric flux has no obvious change compared with Example 1, indicating that the strength of Example 7 is lower than that of Example 1, and the chloride ion adsorption capacity is similar. The reason may be that an excessive amount of ultra-fine admixture is added in Example 7, resulting in agglomeration of the ultra-fine admixture and a decrease in the strength of the recycled aggregate concrete.

[0106] Combined with Example 1 and Example 8, it can be seen that the electric flux of Example 8 increases compared with Example 1, indicating that the chloride ion adsorption capacity of Example 8 decreases compared with Example 1. The reason may be that the addition amount of polypyrrole / titanium dioxide in the chloride ion adsorbent in Example 8 is lower than the required addition amount during preparation, resulting in a decrease in the concentration of polypyrrole / titanium dioxide in the prepared chloride ion adsorbent and a decrease in the chloride ion adsorption capacity.

[0107] Combining Example 1 and Example 9, it can be seen that the electric flux of Example 9 has increased compared to Example 1, indicating that the chloride ion adsorption capacity of Example 9 has decreased compared to Example 1. The reason may be that during the preparation of the chloride ion adsorbent in Example 9, the addition amounts of the sodium alginate solution and the chitosan solution have increased, the proportion of the chitosan-calcium alginate complex coagulation layer in the chloride ion adsorbent has become larger, and the concentration of polypyrrole / titanium dioxide has decreased, resulting in a reduced ability to adsorb chloride ions.

[0108] Combining Example 1 and Example 10, it can be seen that the electric flux of Example 10 has increased compared to Example 1, indicating that the chloride ion adsorption capacity of Example 10 has decreased compared to Example 1. The reason may be that no dialdehyde cross-linking agent was added during the preparation of the chloride ion adsorbent in Example 10. On the one hand, without the curing and cross-linking effect of the dialdehyde cross-linking agent, the formed chloride ion adsorbent solution agglomerates and adheres, reducing the specific surface area and the ability to adsorb chloride ions. On the other hand, without the cross-linking and curing of the dialdehyde cross-linking agent, the strength of the chitosan-calcium alginate complex coagulation layer has decreased, resulting in increased losses during the preparation of concrete and a decrease in the ability to adsorb chloride ions.

[0109] Combining Example 1 and Example 11, it can be seen that the electric flux of Example 11 has increased compared to Example 1, indicating that the chloride ion adsorption capacity of Example 11 has decreased compared to Example 1. The reason may be that the chloride ion adsorbent in Example 11 was not sieved after drying, resulting in an increase in the average particle size of the chloride ion adsorbent and a reduction in the specific surface area, making it impossible to capture and adsorb chloride ions to the maximum extent, and thus reducing the ability to adsorb chloride ions.

[0110] Combining Example 1 and Example 12, it can be seen that the 28-day compressive strength and 28-day splitting tensile strength of Example 12 have also decreased compared to Example 1, indicating that the water-reducing effect of the water reducer used in Example 12 is lower than that of the water reducer used in Example 1, resulting in a reduction in strength. The reason may be that the lignosulfonate water reducer was used in Example 12, and the water reducer does not contain carboxyl groups, while the polycarboxylate graft copolymerization type water reducer was used in Example 1, which is a high-efficiency water reducer and contains carboxyl groups. The carboxylate ions formed by the carboxyl groups can not only combine with calcium ions in the recycled aggregate concrete, slow down the decrease in the water reducer concentration, significantly increase the water reduction rate, but also enhance the strength of the recycled aggregate concrete.

[0111] Combined with Example 1 and Example 13, it can be seen that the 28-day compressive strength and 28-day splitting tensile strength of Example 13 are lower than those of Example 1, indicating that the strength of Example 13 is lower than that of Example 1. The reason may be that the ultra-fine aggregate used in Example 13 has a larger particle size, and there are many tiny gaps in the recycled coarse aggregate. The aggregate with a large particle size cannot well fill the gaps in the recycled coarse aggregate, resulting in a poor effect on reducing the porosity of the concrete, leading to a decrease in the compactness of the concrete and a decrease in the strength of the concrete.

[0112] This specific embodiment is only an interpretation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment that do not contribute creatively as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A durable recycled aggregate concrete, characterized in that, It includes raw materials in the following parts by mass: 110 - 130 parts of modified recycled coarse aggregate, 48 - 60 parts of fine aggregate, 12 - 15 parts of ultra-fine admixture, 27 - 34 parts of cement, 12 - 15 parts of fly ash, 1 - 1.5 parts of water reducer, 4 - 8 parts of chloride ion adsorbent, and 16 - 19 parts of water; the chloride ion adsorbent is a microcapsule structure with polypyrrole / titanium dioxide nanometer as the core and a chitosan-calcium alginate composite coagulation layer as the coating layer; carboxyl groups are attached to the surface of the modified recycled coarse aggregate; the preparation steps of the chloride ion adsorbent are as follows: Preparation of polypyrrole / titanium dioxide nanometer: Add nanometer titanium dioxide into an acidic solution and disperse it evenly, then add pyrrole monomer and stir to obtain solution A; Add a ferric salt catalyst into the acidic solution, stir and mix to obtain solution B; Stir and mix solution A and solution B in an ice-water bath, then wash, dry, and grind to obtain polypyrrole / titanium dioxide nanometer; Preparation of chloride ion adsorbent: Add the obtained polypyrrole / titanium dioxide nanometer and sodium alginate solution into a calcium ion solution, stir and mix at a temperature of 8 - 15 °C for 15 - 25 min. After stirring, add chitosan solution and continue stirring for a composite gel reaction. After the reaction, add a dialdehyde cross-linking agent, raise the temperature to 20 - 30 °C, stir and cure for 40 - 80 min. After curing, let it stand, filter, dry, and sieve to obtain the chloride ion adsorbent; The raw materials of the modified recycled coarse aggregate include recycled coarse aggregate, amino silane coupling agent, and organic anhydride in a mass ratio of 100:(3 - 6):(3.5 - 7).

2. A durable recycled aggregate concrete according to claim 1, characterized in that, The raw materials of the polypyrrole / titanium dioxide nanometer include pyrrole monomer and nanometer titanium dioxide in a mass ratio of (1.2 - 1.8):

1.

3. A durable recycled aggregate concrete according to claim 1, characterized in that, The particle size of the chloride ion adsorbent is 0.5 mm - 1.5 mm.

4. A durable recycled aggregate concrete according to claim 1, characterized in that, The mass fractions of the sodium alginate solution and the chitosan solution are 0.5% - 2%.

5. A durable recycled aggregate concrete according to claim 4, characterized in that, The ratio of the mass of the polypyrrole / titanium dioxide nanometer to the volume of the sodium alginate solution is 1 g:(3.5 - 4.5) ml; the volume ratio of the sodium alginate solution to the chitosan solution is 1:(1.1 - 1.4).

6. A durable recycled aggregate concrete according to claim 1, characterized in that, The organic anhydride is one or more of succinic anhydride, ethyl propionic anhydride, propionic anhydride, and maleic anhydride.

7. A durable recycled aggregate concrete according to claim 1, characterized in that, The D50 particle size of the ultra-fine admixture is 3 μm - 8 μm, and it is a composition of one or more of silicon carbide and silicon dioxide.

8. A method for preparing durable recycled aggregate concrete according to any one of claims 1 to 7, characterized in that, It includes the following steps: Step 1: Uniformly dry-mix the modified recycled coarse aggregate, fine aggregate, and ultra-fine admixture, then pour in cement and fly ash and stir to obtain a rough mixture; Step 2: Add a water reducer and a chloride ion adsorbent to the rough mixture, stir and mix, and finally add water and continue stirring to obtain durable recycled aggregate concrete.

Images