A freeze-thaw resistant recycled concrete

Abstract

The application relates to environment-friendly building materials, and particularly discloses a freeze-thaw resistant recycled concrete, which solves the problem that the existing recycled concrete is not resistant to freeze-thaw; specifically, the recycled concrete comprises the following raw materials in mass fractions: natural aggregate 480-540 parts; recycled aggregate 460-520 parts; cement 380-480 parts; sand 350-410 parts; water absorption sepiolite powder 160-200 parts; retarder 1.5-6.6 parts; and water reducing agent 2.4-5.6 parts; the water reducing agent and the retarder are added in the application to promote the repair of the recycled aggregate in the recycled concrete and reduce the voids, meanwhile, the water absorption sepiolite powder added can be filled into the cracks of the recycled aggregate, the cracks of the recycled aggregate are blocked, the precipitation of ice crystals and the increase of the expansion stress of the recycled concrete are slowed down during freezing, and thus the freeze-thaw resistance of the recycled concrete is improved from the aspects of the recycled concrete itself and the hindering of freeze-thaw damage.

Description

Technical Field

[0001] This invention relates to environmentally friendly building materials, and more specifically, to a freeze-thaw resistant recycled concrete. Background Technology

[0002] Recycled concrete refers to new concrete made by crushing, cleaning, and grading waste concrete blocks, mixing them with graded aggregates in a certain proportion, using recycled aggregates to partially or completely replace natural aggregates, and then adding cement, water, etc.

[0003] Natural aggregates consist of coarse aggregates (natural crushed stone or pebbles) and fine aggregates (natural sand). Because waste concrete contains a large amount of original cement mortar, direct recycling of the fine aggregates from waste concrete is difficult. Therefore, the corresponding coarse and fine aggregates in recycled aggregates are generally obtained by crushing the original coarse aggregates from waste concrete blocks. However, during the crushing process of obtaining recycled aggregates, the original coarse aggregate structure is inevitably damaged, resulting in recycled aggregates having lower structural strength, more cracks, and higher water absorption compared to natural aggregates.

[0004] When recycled concrete is used, the pores in the cured recycled concrete are more than those in ordinary concrete using natural aggregates. Therefore, compared with ordinary concrete, recycled concrete has poor freeze-thaw resistance and its strength decreases faster after freeze-thaw cycles. Summary of the Invention

[0005] To address the problem that existing recycled concrete is not resistant to freeze-thaw cycles, this application provides a freeze-thaw resistant recycled concrete.

[0006] The freeze-thaw resistant recycled concrete provided in this application adopts the following technical solution:

[0007] A freeze-thaw resistant recycled concrete comprises the following raw materials in parts by weight:

[0008] 480-540 parts natural aggregate;

[0009] 460-520 parts of recycled aggregate;

[0010] 380-480 parts cement;

[0011] 350-410 parts of sand;

[0012] 160-200 parts of water-absorbing sepiolite powder;

[0013] 1.5 to 6.6 parts of retarder;

[0014] Water-reducing agent: 2.4–5.6 parts.

[0015] By adopting the above technical solution, firstly, water-reducing agent and retarder are added to the recycled concrete of this application at the same time, which prolongs the setting time of the recycled concrete. Under the same water content, the concrete has good fluidity and less slump loss over time. This allows the free water in the recycled concrete to migrate freely for a longer period of time during preparation, after pouring and before curing. This allows the free water and the cementitious material generated by the hydration reaction to fully penetrate into the cracks of the recycled aggregate to seal and repair the cracks, thereby reducing the internal voids of the recycled concrete after curing and improving the freeze-thaw resistance of the recycled concrete.

[0016] By relying on water-reducing agents to improve the free water migration rate in recycled concrete and retarder to slow down the solidification of recycled concrete, this application also adds water-absorbing sepiolite powder with a particle size of 50nm to 100nm. The particle size of the water-absorbing sepiolite powder allows it to fill larger (wider than 50nm) cracks on the surface of recycled aggregate. Thus, the water-absorbing sepiolite powder is divided into two parts.

[0017] The first part, water-absorbing sepiolite powder, fills the cracks in the recycled aggregate with the help of water-reducing agents and retarders. There are two ways it fills these cracks: during the mixing and production of recycled concrete raw materials, it seeps into the cracks of the recycled aggregate along with cement powder and water; after the recycled concrete is mixed, it continues to migrate into the cracks of the recycled aggregate with free water. The water-absorbing sepiolite absorbs more than 100 wt% of its original weight in water. Under conditions of surrounding moisture deficiency and heating from the hydration reaction, it gradually releases water, promoting the hydration reaction in the cracks of the recycled aggregate and strengthening the repair of the crack ends.

[0018] The second part, water-absorbing sea foam powder, is dispersed in the cement mortar of the recycled concrete, gradually releasing moisture to promote the hydration reaction and enhance the overall strength of the recycled concrete.

[0019] Furthermore, due to its high water absorption and softening properties after absorbing water, water-absorbing sepiolite powder actively absorbs water, converting free water into crystalline water, thus reducing ice crystal precipitation during the process of water absorption, ice crystal precipitation, increased expansion stress, cracking, and strength reduction in recycled concrete. Moreover, after ice crystals precipitate in other parts of the recycled concrete, its softened state from the previous water absorption process makes it more compressible, thereby slowing down the increase in expansion stress and reducing cracking and strength loss. After the water-absorbing sepiolite powder dries, it regains its hardness, maintaining good strength in the recycled concrete.

[0020] In summary, this application incorporates water-reducing agents and retarders to promote the repair of recycled aggregates and reduce voids in recycled concrete. Simultaneously, the water-absorbing sepiolite powder added under the action of the water-reducing agents and retarders can partially fill cracks in the recycled aggregates, thereby reinforcing and sealing the crack ends. Furthermore, it slows down ice crystal precipitation and the increase in expansion stress when the recycled concrete absorbs water and freezes. Thus, the freeze-thaw resistance of the recycled concrete is improved from both the perspective of the recycled concrete itself and by preventing freeze-thaw damage, resulting in a freeze-thaw resistant recycled concrete.

[0021] Preferably, the retarder is either glucose or sucrose.

[0022] By adopting the above technical solutions, when glucose, sucrose, or 1,2-hexanediol are used as retarder, the freezing point of ice crystal precipitation in recycled concrete can be lowered, further improving the freeze-thaw resistance of recycled concrete.

[0023] Preferably, the retarder is glucose.

[0024] By adopting the above technical solution, when glucose is used as the retarder, the initial strength and freeze-thaw resistance of recycled concrete are both superior.

[0025] Preferably, the water-reducing agent is one of sodium lignosulfonate, magnesium lignosulfonate, and potassium lignosulfonate.

[0026] By adopting the above technical solution and selecting lignin sulfonate as a water-reducing agent, the occurrence of alkali-aggregate reaction can be reduced, thereby reducing the increase in expansion stress or internal cracks caused by alkali-aggregate reaction during the curing process of recycled concrete.

[0027] Preferably, the water-reducing agent is magnesium lignosulfonate.

[0028] By adopting the above technical solution, when magnesium lignosulfonate is selected as the reducing agent, after magnesium lignosulfonate reacts with calcium ions in the free water of recycled concrete, the magnesium ions are also converted into precipitates, which seal the capillary pores in the recycled concrete, prevent water penetration, and further enhance the freeze-thaw resistance of the recycled concrete.

[0029] Preferred: It also includes 32 to 39 parts of reinforcing fiber.

[0030] By adopting the above technical solution, adding reinforcing fibers can enhance the resistance of recycled concrete to expansion stress and strengthen its freeze-thaw resistance.

[0031] Preferably, the reinforcing fiber is polyester fiber.

[0032] By adopting the above technical solution and selecting polyester fiber as the reinforcing fiber, the recycled concrete can not only strengthen its resistance to expansion stress, but also prevent water from penetrating into the recycled concrete, reduce water absorption, and improve the freeze-thaw resistance of the recycled concrete by reducing ice crystals.

[0033] Preferably, the reinforcing fiber is a hollow fiber with closed ends.

[0034] By adopting the above technical solutions, the compressibility of fibers is enhanced, the increase in expansion stress during the freezing of recycled concrete is slowed down, the possibility of cracking in recycled concrete is reduced, and thus the freeze-thaw resistance of recycled concrete is improved.

[0035] Preferred method: The preparation method of the reinforcing fiber is as follows:

[0036] Hollow polyester or carbon fibers are obtained by hot cutting.

[0037] By adopting the above technical solution, hollow, closed-end fibers of the required length can be obtained quickly and conveniently. In summary, the present invention has the following beneficial effects:

[0038] 1. In this application, water-reducing agents and retarders are added to promote the repair of recycled aggregates in recycled concrete and reduce voids. At the same time, the water-absorbing sepiolite powder added under the action of water-reducing agents and retarders can partially fill the cracks in recycled aggregates, thereby strengthening and sealing the crack ends of recycled aggregates. It also slows down the precipitation of ice crystals and the increase of expansion stress when recycled concrete absorbs water and freezes. Thus, the freeze-thaw resistance of recycled concrete is improved from both the recycled concrete itself and the prevention of freeze-thaw damage, resulting in a freeze-thaw resistant recycled concrete.

[0039] 2. Hollow, closed-end reinforcing fibers are also added to this application to improve the resistance of recycled concrete to expansion stress and to increase the expansion stress when compressed recycled concrete freezes, thereby further enhancing the freeze-thaw resistance of recycled concrete. Detailed Implementation

[0040] Raw material source:

[0041] Natural aggregate, with a particle size of 5-6cm.

[0042] Recycled aggregate with a particle size of 3-4 cm.

[0043] The cement is commercially available grade 42.5 ordinary cement.

[0044] Sand, manufactured sand with a particle size of 1-2 mm.

[0045] Sepiolite powder is obtained by grinding and sieving commercially available sepiolite, with a particle size of 50-100 nm.

[0046] Water-absorbing sepiolite powder is obtained by mixing sepiolite powder of 50-100nm with water at a mass ratio of 1:2, soaking in water for 1 day, and then draining.

[0047] Fly ash, a commercially available product of Lingshou County Jiagong Mineral Products Co., Ltd., with a fineness of 2000 mesh.

[0048] Retarder: Glucose is a commercially available product of Suzhou Jiafu Environmental Protection Technology Co., Ltd.; Sucrose is a commercially available product of Jinan Kehua New Materials Co., Ltd.; Desulfurized gypsum powder is a commercially available product of Longyao County Dongsheng Gypsum Building Materials Co., Ltd.

[0049] Water-reducing agents: Sodium lignosulfonate, magnesium lignosulfonate, potassium lignosulfonate, and calcium lignosulfonate are commercially available products from Shanghai Tingruo Lignochemicals Co., Ltd.

[0050] Reinforcing fibers: 6cm in length, including glass reinforcing fibers, polyester reinforcing fibers made from polyester fibers, and hollow reinforcing fibers made from hollow polyester fibers.

[0051] The glass reinforcing fiber was obtained by cutting glass fibers from Changzhou Meikelai Composite Materials Co., Ltd., with an average diameter of 0.85 mm.

[0052] The polyester reinforcing fiber is prepared by using an electrically heated cutter to heat-cut the polyester fiber (polyester) to obtain the desired length of fiber. The cutter temperature is 272-282℃ and the shearing pressure is 1-1.2MPa. The polyester fiber (polyester) is a product of Shaoxing Xineng Textile Technology Co., Ltd., with a thickness of 150D and an average diameter of 0.85mm.

[0053] The hollow reinforcing fiber is prepared by using an electrically heated cutter to hot-cut the hollow polyester fiber (hollow polyester) to obtain the desired length of fiber. The cutter temperature is 272-282℃ and the shearing pressure is 1-1.2MPa. The hollow polyester fiber (hollow polyester) is a product of Shaoxing Xineng Textile Technology Co., Ltd., with a thickness of 150D and an average diameter of 0.85mm.

[0054] Example 1

[0055] A freeze-thaw resistant recycled concrete, comprising the following raw materials in parts by weight:

[0056] 480 parts natural aggregate, 520 parts recycled aggregate, 480 parts cement, 350 parts sand, 200 parts water-absorbing seawater powder, 6.6 parts retarder, 5.6 parts water-reducing agent, 39 parts reinforcing fiber, and 380 parts water.

[0057] The retarder is glucose, the water-reducing agent is magnesium lignosulfonate, and the reinforcing fiber is hollow fiber.

[0058] The method for preparing freeze-thaw resistant recycled concrete is as follows:

[0059] S1: Retarder, water-reducing agent and water are premixed to form a pre-formed liquid;

[0060] S2: Add natural aggregates, recycled aggregates, cement, sand, water-absorbing spore powder, reinforcing fibers, and precast liquid to a mixer while adding and mixing until homogeneous to obtain recycled concrete.

[0061] Examples 2-11

[0062] A freeze-thaw resistant recycled concrete is similar to Example 1, except that the amount and / or selection of raw materials are different. The specific differences are shown in Table 1 below.

[0063] Table 1. Raw material parameters of recycled concrete in Examples 1-11

[0064]

[0065]

[0066] Comparative Example 1

[0067] A type of recycled concrete differs from Example 2 in that an equal mass of fly ash is used instead of water-absorbing sepiolite powder in the raw materials, and an equal mass of water is used instead of corrosion inhibitors and water-reducing agents in the raw materials.

[0068] Comparative Example 2

[0069] A type of recycled concrete differs from Comparative Example 1 in that it uses equal mass of natural aggregate with a particle size of 3-4 cm to replace recycled aggregate in the raw materials.

[0070] Comparative Example 3

[0071] A type of recycled concrete differs from Example 2 in that an equal mass of fly ash is used instead of water-absorbing sepiolite powder in the raw materials.

[0072] Comparative Example 4

[0073] A type of recycled concrete, which differs from Example 2 in that the corrosion inhibitor is replaced with an equal mass of water in the raw materials.

[0074] Comparative Example 5

[0075] A type of recycled concrete, which differs from Example 2 in that the water-reducing agent is replaced with an equal mass of water in the raw materials.

[0076] Comparative Example 6

[0077] A type of recycled concrete differs from Example 2 in that the corrosion inhibitor and water-reducing agent are replaced with an equal mass of water in the raw materials.

[0078] Comparative Example 7

[0079] A type of recycled concrete differs from Example 2 in that it uses an equal mass of sepiolite powder instead of water-absorbing sepiolite powder in the raw materials.

[0080] Comparative Example 8

[0081] A type of recycled concrete differs from Example 2 in that it uses natural aggregate with a particle size of 3-4 cm of equal mass instead of recycled aggregate in the raw materials.

[0082] Comparative Example 9

[0083] A type of recycled concrete, which differs from Example 2 in that hollow fibers are replaced with an equal mass of contrast fibers in the raw materials.

[0084] The preparation methods for the comparative fibers are as follows:

[0085] Hollow polyester fibers were chopped at room temperature to obtain control fibers of the desired length of 6 cm. The shear pressure was 1–1.2 MPa.

[0086] Hollow polyester fiber (hollow polyester) is a product of Shaoxing Xineng Textile Technology Co., Ltd., with a thickness of 150D and an average diameter of 0.85mm.

[0087] Compressive strength tests and freeze-thaw resistance tests were conducted on the recycled concrete samples prepared in Examples 1-13 and Comparative Examples 1-9, respectively. The test methods were carried out according to the slow freezing method for compressive strength test and freeze-thaw resistance test in GB / T 50082-2009.

[0088] The freeze-thaw resistance test, using the slow freezing method, involved 50 freeze-thaw cycles. The test results included pressure loss and mass loss. The test results are shown in Table 2 below.

[0089] Table 2. Results of freeze-thaw resistance tests on recycled concrete from Examples 1-11 and Comparative Examples 1-9

[0090]

[0091]

[0092] Referring to Table 2,

[0093] Comparing Comparative Example 1 and Comparative Example 2, we can see that:

[0094] Compared to Comparative Example 2, which used all natural aggregates, Comparative Example 1, which used recycled aggregates, had a lower initial compressive strength and greater pressure and mass loss under freeze-thaw cycles. Recycled concrete using recycled aggregates had poorer freeze-thaw resistance than ordinary concrete using natural aggregates.

[0095] Comparing Examples 1-3, Comparative Example 1, and Comparative Example 2, it can be seen that:

[0096] The initial strength of Examples 1-3 is better than that of Comparative Example 1. The freeze-thaw resistance of Examples 1-3 is significantly better than that of Comparative Example 1 and is close to that of ordinary concrete using natural aggregates in Comparative Example 2.

[0097] Therefore, the addition of water-absorbing sepiolite powder, retarder, and water-reducing agent to the recycled concrete in this application effectively and significantly improves the freeze-thaw resistance of the recycled concrete.

[0098] Comparative Examples 2 and 3-7 show that:

[0099] In Comparative Examples 3 to 5, the raw materials of the recycled concrete lacked the use of water-absorbing sepiolite powder, retarder, and water-reducing agent, respectively. In Comparative Example 6, the raw materials of the recycled concrete lacked both retarder and water-reducing agent. In Comparative Example 7, non-water-absorbing sepiolite powder was used to replace the water-absorbing sepiolite powder with sufficient water absorption.

[0100] The initial strength of the recycled concrete in Comparative Examples 3 to 7 was not significantly improved, and the improvement in freeze-thaw resistance was slight.

[0101] Therefore, the improvement of the freeze-thaw resistance of recycled concrete in this application relies on the synergistic effect of water-absorbing sepiolite powder that absorbs sufficient water under the action of retarders and water-reducing agents.

[0102] Comparing Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 8, it can be seen that:

[0103] In this application, under the action of retarders and water-reducing agents, water-absorbing sepiolite powder that absorbs sufficient water has a significant effect on improving the freeze-thaw resistance of recycled concrete using recycled aggregates, but has no significant effect on ordinary concrete using natural aggregates. Therefore, the improvement of the freeze-thaw resistance of concrete in this application is achieved by the synergistic effect of water-absorbing sepiolite powder that absorbs sufficient water under the action of retarders and water-reducing agents and recycled aggregates, which is an adaptive improvement based on the defects of recycled concrete.

[0104] Comparing Examples 2, 4, and 5, it can be seen that:

[0105] In addition to glucose, sucrose or desulfurized gypsum powder can also be used as a retarder in the raw materials of the recycled concrete of this application. While desulfurized gypsum powder results in higher initial strength, its effect on improving freeze-thaw resistance is weaker than that of glucose and sucrose. When glucose is used as a retarder, the initial strength is superior, and the improvement in freeze-thaw resistance is optimal.

[0106] Comparing Examples 2 and 6-8, it can be seen that:

[0107] In addition to magnesium lignosulfonate, sodium lignosulfonate, potassium lignosulfonate, and calcium lignosulfonate can also be used as retarder in the raw materials of the recycled concrete of this application. Since lignosulfonate ions can bind to calcium ions dissolved in cement, the occurrence of alkali-aggregate reaction can be reduced. Therefore, in Examples 2, 6, and 7, when magnesium lignosulfonate, sodium lignosulfonate, and potassium lignosulfonate are used as water-reducing agents, the freeze-thaw resistance of the recycled concrete is better than that in Example 8, where calcium lignosulfonate is used.

[0108] Meanwhile, in Example 2, after magnesium lignosulfonate reacts with calcium ions in the free water of recycled concrete, the magnesium ions are also converted into precipitates, which seal the capillary pores in the recycled concrete and prevent water penetration, thereby further enhancing the freeze-thaw resistance of the recycled concrete.

[0109] Comparing Examples 2 and 9-11, it can be seen that:

[0110] Compared to Example 9, Examples 2, 10, and 11 incorporate reinforcing fibers, thus improving the freeze-thaw resistance of the recycled concrete. The reinforcing fibers can be one of glass fiber, polyester reinforcing fiber, or hollow reinforcing fiber.

[0111] Comparing Example 2, Example 9, and Comparative Example 9, it can be seen that:

[0112] The comparative fiber in Comparative Example 9 is a hollow fiber with open ends. Because the comparative fiber allows free water to penetrate more easily into the recycled concrete and provides more space for ice crystal growth, the recycled concrete with the comparative fiber instead of the hollow reinforcing fiber has poor freeze-thaw resistance, even worse than the recycled concrete without reinforcing fiber in Example 9. In this application, when hollow fibers are used as reinforcing fibers, both ends of the fiber must be closed.

[0113] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A freeze-thaw resistant recycled concrete, characterized in that, The raw materials include the following parts by weight: 480-540 parts natural aggregate; 460-520 parts of recycled aggregate; 380-480 parts cement; 350-410 parts of sand; 160-200 parts of water-absorbing sepiolite powder; 3.4 to 6.6 parts of retarder; Water-reducing agent: 4-5.6 parts; 32-39 parts reinforced fiber; The reinforcing fiber is polyester fiber; The reinforcing fiber is a hollow fiber with closed ends; The natural aggregate has a particle size of 5-6 cm, and the sand is manufactured sand with a particle size of 1-2 mm.

2. The freeze-thaw resistant recycled concrete according to claim 1, characterized in that: The retarder is either glucose or sucrose.

3. The freeze-thaw resistant recycled concrete according to claim 2, characterized in that: The retarder is glucose.

4. The freeze-thaw resistant recycled concrete according to claim 1, characterized in that: The water-reducing agent is one of sodium lignosulfonate, magnesium lignosulfonate, or potassium lignosulfonate.

5. The freeze-thaw resistant recycled concrete according to claim 4, characterized in that: The water-reducing agent is magnesium lignosulfonate.

6. The freeze-thaw resistant recycled concrete according to claim 1, characterized in that, The method for preparing the reinforcing fiber is as follows: Hollow polyester fibers are obtained by hot-cutting.

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