A kind of γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete and preparation method thereof

Abstract

The present invention discloses a γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete, the components and their contents include: cement 600-700 kg / m 3 , fly ash 100-150kg / m 3 , silica fume 150-200kg / m 3 Modified γ-C2S phosphogypsum unburned aggregate 200-400kg / m 3 , copper-plated steel fiber 80-100kg / m 3 , medium sand 300-700kg / m 3 , floating beads 40-92kg / m 3 , fine sand 260-608kg / m 3 , water reducing agent 8-15kg / m 3 , defoaming agent 0.5-2kg / m 3 , water 150-190kg / m 3 The ultra-high performance concrete has low density, low autogenous shrinkage, and can take into account excellent workability and mechanical properties, etc., which is conducive to promoting the application of industrial solid waste lightweight aggregate in UHPC, has significant environmental and economic benefits, and is suitable for promotion and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and in particular relates to a gamma-C2S phosphogypsum lightweight aggregate ultra-high performance concrete and a preparation method thereof. Background Art

[0002] As the construction industry develops toward energy conservation and emission reduction, the utilization of industrial waste and the development and optimization of calcium silicate products are receiving widespread attention. Unburned γ-C2S phosphogypsum lightweight aggregate, with phosphogypsum as its main component, can not only be used to replace non-renewable gravel resources, but also achieve the comprehensive utilization of mineral powder and solid waste, effectively solving the problems of land resource waste and environmental pollution caused by solid waste. However, phosphogypsum is porous and easily absorbs water, and its hydration product, calcium sulfate dihydrate, is easily soluble in water, which can easily lead to a significant reduction in the strength of the phosphogypsum. Existing unburned phosphogypsum ceramsite balls often have problems such as low cylinder pressure strength, high deadweight, and softening when exposed to water, which limits their promotion and application.

[0003] Currently, conventional high-performance concrete (HPC) has high density and low strength, and the large size and deadweight of precast bridge components make their transportation and installation difficult, limiting the development and application of precast assembly construction technology. There is an urgent need to develop lightweight, high-strength, high-impact toughness, and excellent volume stability ultra-high-performance concrete materials to further reduce the deadweight of bridge structures and increase bridge spans. This will also facilitate the transportation and installation of construction equipment, enabling rapid construction of precast assembled bridges to meet ever-increasing construction needs. Summary of the Invention

[0004] The main purpose of the present invention is to address the problems and shortcomings of the existing technology and provide a γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete with low density, low autogenous shrinkage, and excellent working performance and mechanical properties. It is conducive to promoting the application research of industrial solid waste lightweight aggregate in UHPC, has significant environmental and economic benefits, and is suitable for promotion and application.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete, the components and their contents include: cement 600-700kg / m 3 , fly ash 100-150kg / m 3 , silica fume 150-200kg / m 3 Modified γ-C2S phosphogypsum unburned lightweight aggregate 200-400kg / m 3 , copper-plated steel fiber 80-100kg / m 3 , medium sand 300-700kg / m 3 , floating beads 40-92kg / m 3, fine sand 260-608kg / m 3 , water reducing agent 8-15kg / m 3 , defoaming agent 0.5-2kg / m 3 , water 150-190kg / m 3 The modified γ-C2S phosphogypsum unburned lightweight aggregate is made of γ-C2S, phosphogypsum, fly ash, mineral powder, red mud powder, sodium aluminate and water as main raw materials, which are mixed, pressed and crushed to obtain γ-C2S phosphogypsum-based lightweight aggregate, and then cured with saturated lime water-graphene cement slurry.

[0007] In the above scheme, the components and their mass percentages in the saturated lime water-graphene cement include: 0.02-0.03% graphene, 35-45% cement, and 55-75% saturated lime water; the specific preparation steps include the following:

[0008] 1) mixing the weighed graphene and saturated lime water in proportion, and stirring uniformly by ultrasonication to obtain a graphene dispersion;

[0009] 2) The obtained graphene dispersion liquid and cement are uniformly mixed in proportion to obtain the saturated lime water-graphene cement slurry.

[0010] In the above solution, the maximum radial dimension of the graphene is 1-100 μm.

[0011] In the above scheme, the ultrasonic stirring time is 20-40 minutes.

[0012] In the above scheme, the curing time of the saturated lime water-graphene cement slurry is 18-24 hours.

[0013] In the above scheme, the raw materials used in the γ-C2S phosphogypsum-based lightweight aggregate and their mass percentages include: phosphogypsum 43-48%, γ-C2S 21.5-28%, fly ash 8-13%, mineral powder 5-10%, red mud powder 3-5%, sodium aluminate 1-3%, and water 5-7%.

[0014] In the above solution, the particle size of the γ-C2S is 1.5-45 μm and the purity is higher than 99%.

[0015] Furthermore, the pH value of the phosphogypsum is greater than 3.0, and the 80um sieve residue is not more than 20%; the main chemical components and their mass percentages include: CaO 37-41%, SO3 40-43%; the red mud powder is obtained by drying and grinding red mud (natural moisture content is 32-36%), and its particle size is less than 100μm, the content of fine particles less than 0.075mm accounts for ≥75.6%, and the content of sand particles greater than 0.075mm accounts for ≤24.4%, and the main chemical components include: Fe2O3 50-53%, Al2O3 21-24%; the mineral powder is S95 grade or above, and the specific surface area is 400-450m 2 / kg; the fly ash is Class I or Class II fly ash.

[0016] In the above scheme, the pressing step adopts a step-by-step vibration pressing process, the set pressure adopted is 270-320kN, and the pressure holding time is more than 15 minutes.

[0017] In the above scheme, the step-by-step vibration pressing process adopts a three-step pressing process, specifically including: vibrating on a vibration table with a frequency of 2860-3000 times / min and an amplitude of 0.3-0.6mm; first applying pressure to 170-220kN and holding the pressure for 5-10 minutes; then applying pressure to 220-270kN and holding the pressure for 5-10 minutes; and continuing to apply pressure to 270-320kN and holding the pressure for 5-10 minutes. In the above scheme, the pressing step adopts a stress rate of 0.330-0.410MPa / s.

[0018] In the above scheme, the preparation method of the modified γ-C2S phosphogypsum unburned lightweight aggregate specifically comprises the following steps:

[0019] 1) Phosphogypsum, γ-C2S, mineral powder, fly ash, red mud powder, and sodium metaaluminate weighed according to the proportion are put into a blender and mixed evenly, and then water is added and stirred evenly to obtain a mixed raw material;

[0020] 2) placing the obtained mixed raw materials into a mold and performing step-by-step vibration compaction to obtain a block green body;

[0021] 3) Using a crusher to crush the blocky green body to form coarse aggregate; then performing rounding to remove the sharp corners on the surface of the aggregate; and then screening to obtain coarse aggregate of different particle sizes;

[0022] 4) The obtained aggregate rough embryo is placed in saturated lime water-graphene cement slurry for curing to obtain the γ-C2S phosphogypsum unburned ceramsite lightweight aggregate.

[0023] Step 3) The crushing particle size is 5.5-10 mm.

[0024] In the above scheme, the inclination angle of the rounding equipment used in step 3) is 48-65°.

[0025] In the above scheme, the particle size after rounding in step 3) is 4.5-9.5 mm, and then the obtained pellets are screened, graded and graded for curing.

[0026] Furthermore, the size of the coarse aggregate after screening and grading in step 3) is 4.5-9.5 mm.

[0027] In the above scheme, the particle size of the modified γ-C2S phosphogypsum unburned lightweight aggregate is 4.5-9.5 mm.

[0028] In the above scheme, the water reducer is a polycarboxylic acid high-performance water reducer with a water reduction rate of ≥35%, a solid content of 20-25%, an air content of ≤6.0%, and a chloride ion content of ≤6.0%.

[0029] In the above solution, the defoaming agent is a polyether powder defoaming agent.

[0030] In the above solution, the cement is ordinary Portland cement with a strength grade of 52.5 or above.

[0031] In the above solution, the fly ash is Class I or Class II fly ash, wherein the CaO content is greater than 10%.

[0032] In the above scheme, the silica fume is a gray powder with a SiO2 mass fraction of ≥90% and a specific surface area of 18000-22000m 2 / kg; the particle size of the floating beads is 10-300μm.

[0033] In the above solution, the copper-plated steel fiber has a nominal length of 8-16 mm, an equivalent diameter of 0.18-0.32 mm, a yield strength ≥ 2000 MPa, a breaking strength ≥ 3000 MPa, and an elastic modulus of 200-220 GPa.

[0034] In the above scheme, the medium sand and fine sand are machine-made sand or quartz sand, the particle size of the medium sand is 0.16-0.3 mm, and the particle size of the fine sand is 0.1-0.15 mm.

[0035] Furthermore, the medium sand and fine sand are saturated with water before use, and the adsorbed water is not included in the water consumption in the formula.

[0036] The method for preparing the above-mentioned γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete comprises the following steps:

[0037] 1) Weigh the raw materials according to the proportion, including the components and their contents: cement 600-700kg / m 3 , fly ash 100-150kg / m3 , silica fume 150-200kg / m 3 Modified γ-C2S phosphogypsum unburned aggregate 200-400kg / m 3 , copper-plated steel fiber 80-100kg / m 3 , medium sand 300-700kg / m 3 , floating beads 40-92kg / m 3 , fine sand 260-608kg / m 3 , water reducing agent 8-15kg / m 3 , defoaming agent 0.5-2kg / m 3 , water 150-190kg / m 3 ;

[0038] 2) Soak medium sand and fine sand in water until saturated to obtain pre-wet sand, add pre-wet sand, modified γ-C2S phosphogypsum unburned aggregate, cement and silica fume into a concrete mixer and mix evenly, add fly ash and floating beads and continue dry mixing evenly, then pour in water and water reducer and mix evenly, evenly add copper-plated steel fiber and mix evenly, and finally add defoamer and mix evenly;

[0039] 3) After mold installation, vibration, and molding, the surface is covered with a water-impermeable film for film curing, and then the mold is removed for standard curing or steam curing to obtain the γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete.

[0040] In the above scheme, the steam curing adopts a constant temperature curing temperature of 40-90°C and a curing time of 48-72h.

[0041] The γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete prepared according to the above scheme has an apparent density of 2100-2350 kg / m 3 , 28d compressive strength is above 110MPa, 28d tensile strength is 6-12MPa, 28d flexural strength is 15-25MPa, expansion is 650-750mm, 56d drying shrinkage is less than 300×10 -6 , chloride ion diffusion coefficient 0.03-0.05×10 -12 m 2 / s, anti-seepage grade>P20.

[0042] The principle of the present invention is:

[0043] 1) The present invention uses phosphogypsum and γ-C2S as the main raw materials, supplemented by phosphogypsum, fly ash, mineral powder, red mud and other industrial waste to prepare unburned ceramsite aggregate. Under the strong alkaline conditions provided by red mud, SO4 in phosphogypsum is consumed. 2- and provide a weak alkaline environment; under weak alkaline conditions, the activity of mineral powder and fly ash is activated, and the Ca in phosphogypsum 2+A reaction occurs to generate a large amount of calcium aluminate crystals that coat the surface of the aggregate, which is beneficial to filling the tiny gaps in the phosphogypsum aggregate and making its structure denser; however, the phosphogypsum aggregate still has problems such as softening when exposed to water and low strength; the present invention further combines the saturated lime water-graphene cement slurry curing process and the saturated lime water conditions to promote the further carbonization reaction of γ-C2S to generate a layer of dense, insoluble silica gel phase material and calcite, aragonite, vaterite and other substances, forming a waterproof film on the surface of the aggregate, which can effectively solve the problems of high water absorption and softening when exposed to water, and significantly improve the strength after hardening.

[0044] In addition, calcium carbonate crystals and ettringite can form a skeleton between the uncarbonized γ-C2S and phosphogypsum, with the silica gel phase filling the skeleton voids and simultaneously coating the surface of the uncarbonized γ-C2S and phosphogypsum, further effectively improving the mechanical properties, water stability, and durability of the resulting aggregate. The simultaneous curing and coating modification of unfired ceramsite aggregate by graphene cement slurry can significantly strengthen the interface transition zone of the lightweight aggregate, which can to a certain extent compensate for the defects of the γ-C2S phosphogypsum unfired ceramsite lightweight aggregate itself, significantly improve its strength, and promote its efficient application in fields such as ultra-high performance concrete.

[0045] 2) Ultra-high performance concrete is prepared by partially replacing fine sand with the modified γ-C2S phosphogypsum unburned aggregate obtained by the present invention, which further reduces the deadweight of the concrete. The modified γ-C2S phosphogypsum can play a ball lubrication role in the ultra-high performance concrete slurry, improving the fluidity of the slurry while filling more gaps to make the slurry more dense. In addition, its water storage and water release functions can more effectively improve the fluidity of the slurry and exert good internal curing performance.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1) The invention uses phosphogypsum as the main raw material, utilizes the synergistic effect of γ-C2S and phosphogypsum, and supplements with industrial waste such as fly ash, mineral powder, and red mud to prepare unburned ceramsite aggregate, and further combines it with a saturated lime water-graphene cement slurry curing process. Under the premise of reducing the dead weight, the strength of the phosphogypsum-based aggregate can be significantly improved, and the pore structure of the phosphogypsum-based aggregate can be optimized, while taking into account good water absorption and water stability, etc., which can realize the high-value-added resource utilization of industrial waste such as phosphogypsum;

[0048] 2) The water absorption and storage properties of the modified γ-C2S phosphogypsum unburned aggregate can produce a slow-release effect, which is beneficial to promoting the hydration reaction of cement clinker, generating more CSH gel and filling the matrix pores, thereby reducing the porosity and pore size of UHPC and making the internal structure denser;

[0049] 3) Using floating beads to replace part of the fine sand as lightweight aggregate and utilizing the multi-component powder closest packing optimization design method can further reduce the density of concrete, which is conducive to promoting efficient application in structural engineering fields such as bridges and marine engineering that have higher requirements on the self-weight of the structure. DETAILED DESCRIPTION

[0050] The present invention will be further explained below with reference to the following examples, which are provided for illustrative purposes only and are not intended to limit the scope of the present invention.

[0051] In the following examples, the cement used is PO52.5 ordinary Portland cement; the fly ash is Class I fly ash, wherein the CaO content is 20%; the SiO2 content in the silica ash is 94wt% and the specific surface area is 22000m 2 The particle size of the floating beads is 10 to 300 μm. The water reducer is a high-performance polycarboxylic acid powdered water reducer with a water reduction rate of 36%. The defoamer is a white powdered polyether defoamer P803 provided by Mingling Chemical.

[0052] The copper-plated steel fiber used has a nominal length of 8-16 mm, an equivalent diameter of 0.18-0.32 mm, a yield strength of ≥2000 MPa, a breaking strength of ≥3000 MPa, and an elastic modulus of 200-220 GPa.

[0053] The medium sand and fine sand used are quartz sand, the medium sand particle size range is 0.16-0.3mm, and the fine sand particle size range is 0.1-0.15mm.

[0054] The preparation steps of the saturated lime water-graphene cement slurry are as follows:

[0055] 1) Weighed graphene (0.03%) and saturated lime water (60%) were mixed in proportion and ultrasonically stirred for 30 minutes to obtain a graphene dispersion;

[0056] 2) The obtained graphene dispersion was evenly mixed with cement (39.97%) to obtain graphene cement slurry.

[0057] In the following examples, the step-by-step vibration pressing process used is a three-step pressing process, and the specific steps include: vibrating on a vibration table with a frequency of 2860 times / min and an amplitude of 0.3 mm;

[0058] 1) First, pressurize to 170 kN at a stress rate of 0.330 MPa / s and maintain pressure for 5 minutes;

[0059] 2) Then pressurize to 220 kN at a stress rate of 0.330 MPa / s and hold the pressure for 5 minutes;

[0060] 3) Continue to pressurize at a stress rate of 0.330 MPa / s to a target pressure of 270 kN and maintain the pressure for 10 minutes.

[0061] The rounding step uses a rounding device with an inclination angle of 60°; the particle size after rounding is 4.5-9.5 mm, and then the obtained granular material is screened, graded and graded for curing; the size of the coarse aggregate after screening and grading is 4.5-9.5 mm.

[0062] Example 1

[0063] A γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete, the preparation method of which comprises the following steps:

[0064] 1) Weighing of raw materials: ordinary 52.5 silicate cement 650kg / m 3 , fly ash 100kg / m 3 , silica fume 150kg / m 3 , modified γ-C2S phosphogypsum unburned lightweight aggregate 380kg / m 3 , medium sand 300kg / m 3 , floating beads 50kg / m 3 , fine sand 333kg / m 3 , water 150kg / m 3 , copper-plated steel fiber 80kg / m 3 , water reducing agent 8.5kg / m 3 , defoaming agent 1kg / m 3 ;

[0065] The preparation method of the modified unburned γ-C2S phosphogypsum lightweight aggregate comprises the following steps:

[0066] 1-1) Phosphogypsum (45%), γ-C2S (22%), fly ash (10%), mineral powder (10%), sodium metaaluminate (3%), red mud powder (5%), and water (5%) are mixed, pressed, and crushed to obtain γ-C2S phosphogypsum-based lightweight aggregate;

[0067] 1-2) The obtained γ-C2S phosphogypsum-based light aggregate is screened and placed in a saturated lime water-graphene cement slurry for curing for 24 hours; the modified γ-C2S phosphogypsum-free light aggregate is obtained; its bulk density is 998 kg / m 3 , 1h water absorption rate is 7.2%, the size of fine interconnected pores is 0.01-100nm and only accounts for 36.5% of the total porosity, the particle size is 4.5-9.5mm, the cylinder pressure strength is 11.2MPa, and the softening coefficient is 0.98;

[0068] The particle sizes of fine sand and medium sand used are 0.1-0.15mm and 0.16-0.3mm respectively;

[0069] 2) Soaking quartz sand, medium sand and fine sand in water until saturated with water to obtain pre-wet sand, adding the pre-wet sand, modified γ-C2S phosphogypsum unburned lightweight aggregate, cement and silica fume into a concrete mixer and pre-mixing them evenly, adding fly ash and floating beads and continuing to dry-mix them evenly, then pouring water and a water reducer and stirring them evenly, then evenly adding copper-plated steel fiber and stirring them evenly, and finally adding a defoamer and stirring them evenly to obtain a mixture;

[0070] 3) The obtained mixture is molded, vibrated, and formed, and the surface is covered with a waterproof film for film curing, and then the mold is removed for steam curing. The steam curing temperature is set to 90° C. and the steam curing time is set to 48 hours. Then, standard curing is performed to the age, thereby obtaining the γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete.

[0071] After testing, the γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete obtained after curing for 28 days has a compressive strength of 128 MPa, a flexural strength of 17.3 MPa, a tensile strength of 8.0 MPa, an expansion of 670 mm, and an apparent density of 2130 kg / m 3 , 56d drying shrinkage is 290×10 -6 , chloride ion diffusion coefficient is 0.03×10 -12 m 2 / s, anti-seepage grade P30.

[0072] Example 2

[0073] A γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete, the preparation method of which comprises the following steps:

[0074] 1) Weighing of raw materials: ordinary 52.5 silicate cement 698kg / m 3 , fly ash 110kg / m 3 , silica fume 180kg / m 3 , modified γ-C2S phosphogypsum unburned lightweight aggregate 320kg / m 3 , medium sand 406kg / m 3 , floating beads 90kg / m 3 , fine sand 600kg / m 3 , water 185kg / m 3 , copper-plated steel fiber 86kg / m 3 , water reducing agent 8.5kg / m 3 , defoaming agent 1kg / m 3 ;

[0075] The preparation method of the modified γ-C2S phosphogypsum unburned lightweight aggregate is substantially the same as that of Example 1, except that the raw materials and their mass percentages are: phosphogypsum 48%, γ-C2S 28%, fly ash 8%, mineral powder 6%, sodium metaaluminate 2%, red mud powder 3%, and water 5%;

[0076] The obtained γ-C2S phosphogypsum-based light aggregate was sieved and placed in saturated lime water-graphene cement slurry for curing for 24 hours to obtain the modified γ-C2S phosphogypsum-free light aggregate; its bulk density was 945 kg / m 3 , 1h water absorption rate is 5.0%, cylinder pressure strength is 11.7MPa, the size of fine interconnected pores is 0.01-100nm and only accounts for 32.5% of the total porosity, the particle size is 4.5-9.5mm, the cylinder pressure strength is 6.5MPa, and the softening coefficient is 0.97;

[0077] The particle sizes of fine quartz sand and medium sand are 0.1-0.15mm and 0.16-0.3mm respectively; the particle size of floating beads is 10-300μm;

[0078] 2) Soaking medium sand and fine sand in water until saturated with water to obtain pre-wet sand, adding the pre-wet sand, modified unburned γ-C2S phosphogypsum lightweight aggregate, cement and silica fume into a concrete mixer and pre-mixing them evenly, adding fly ash and continuing to dry-mix them evenly, then pouring water and a water reducer and stirring evenly, then evenly adding copper-plated steel fiber and stirring evenly, and finally adding a defoamer and stirring evenly to obtain a mixture;

[0079] 3) The obtained mixture is molded, vibrated, and formed, and the surface is covered with a waterproof film for film curing, and then the mold is removed and standard curing is performed to obtain the γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete.

[0080] After testing, the compressive strength is 134MPa, the tensile strength is 8.2MPa, the flexural strength is 19.1MPa, the expansion is 660mm, and the apparent density is 2150kg / m 3 , 56d drying shrinkage is 295×10 -6 , chloride ion diffusion coefficient is 0.04×10 -12 m 2 / s, anti-seepage grade P30.

[0081] Example 3

[0082] A γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete, the preparation method of which comprises the following steps:

[0083] 1) Weighing of raw materials: ordinary 52.5 silicate cement 700kg / m 3 , fly ash 150kg / m 3, silica fume 170kg / m 3 , modified γ-C2S phosphogypsum unburned lightweight aggregate 400kg / m 3 , medium sand 300kg / m 3 , floating beads 80kg / m 3 , fine sand 453kg / m 3 , water 150kg / m 3 , copper-coated steel fiber 90kg / m 3 , water reducing agent 9.5kg / m 3 , defoaming agent 1.5kg / m 3 ;

[0084] The preparation method of the modified γ-C2S phosphogypsum unburned light aggregate is substantially the same as that of Example 1, except that: the modified γ-C2S phosphogypsum unburned light aggregate is placed in a saturated lime water-graphene cement slurry for curing for 18 h; the obtained modified unburned γ-C2S phosphogypsum light aggregate has a bulk density of 998 kg / m 3 , 1h water absorption rate is 6.1%, the size of fine interconnected pores is 0.01-100nm and only accounts for 34.7% of the total porosity, the particle size is 4.5-9.5mm, the cylinder pressure strength is 11.1MPa, and the softening coefficient is 0.98;

[0085] The particle sizes of fine sand and medium sand used are 0.1-0.15mm and 0.16-0.25mm respectively;

[0086] 2) Soaking quartz sand, medium sand and fine sand in water until saturated with water to obtain pre-wet sand, adding the pre-wet sand, modified unburned γ-C2S phosphogypsum lightweight aggregate, cement and silica fume into a concrete mixer and pre-mixing them evenly, adding fly ash and floating beads and continuing to dry-mix them evenly, then pouring water and a water reducer and stirring evenly, then evenly adding copper-plated steel fiber and stirring evenly, and finally adding a defoamer and stirring evenly to obtain a mixture;

[0087] 3) The obtained mixture is molded, vibrated, and formed, and the surface is covered with a waterproof film for film curing, and then the mold is removed for steam curing. The steam curing temperature is set to 90° C. and the steam curing time is set to 72 hours. Then, standard curing is performed to the age, thereby obtaining the γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete.

[0088] After testing, the γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete obtained after curing for 28 days has a compressive strength of 148 MPa, a flexural strength of 24.0 MPa, a tensile strength of 10.8 MPa, an expansion of 700 mm, and an apparent density of 2180 kg / m 3 , 56d drying shrinkage is 286×10 -6 , chloride ion diffusion coefficient is 0.04×10 -12 m 2 / s, anti-seepage grade P30.

[0089] Comparative Example 1

[0090] A γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete, the preparation method of which comprises the following steps:

[0091] 1) Weighing of raw materials: ordinary 52.5 silicate cement 700kg / m 3 , fly ash 150kg / m 3 , silica fume 170kg / m 3 , modified γ-C2S phosphogypsum unburned lightweight aggregate 400kg / m 3 , medium sand 300kg / m 3 , floating beads 80kg / m 3 , fine sand 453kg / m 3 , water 150kg / m 3 , copper-coated steel fiber 90kg / m 3 , water reducing agent 9.5kg / m 3 , defoaming agent 1.5kg / m 3 ;

[0092] The preparation method of the modified unburned γ-C2S phosphogypsum lightweight aggregate comprises the following steps:

[0093] 1-1) Phosphogypsum (45%), γ-C2S (22%), fly ash (10%), mineral powder (10%), sodium metaaluminate (3%), red mud powder (5%), and water (5%) are mixed, pressed, and crushed to obtain γ-C2S phosphogypsum-based lightweight aggregate;

[0094] 1-2) The obtained γ-C2S phosphogypsum light aggregate is screened and sprayed (water mist) for 24 hours to obtain the modified unburned γ-C2S phosphogypsum light aggregate; the obtained unburned γ-C2S phosphogypsum light aggregate has a bulk density of 990 kg / m 3 , 1h water absorption rate is 6.8%, the size of fine interconnected pores is 0.01-100nm and only accounts for 32.5% of the total porosity, the cylinder pressure strength is 3.4MPa, and the softening coefficient is 0.85;

[0095] The particle sizes of fine sand and medium sand used are 0.1-0.15 mm and 0.16-0.3 mm respectively;

[0096] 2) Soaking quartz sand, medium sand and fine sand in water until saturated with water to obtain pre-wet sand, adding the pre-wet sand, modified unburned γ-C2S phosphogypsum lightweight aggregate, cement and silica fume into a concrete mixer and pre-mixing them evenly, adding fly ash and floating beads and continuing to dry-mix them evenly, then pouring water and a water reducer and stirring evenly, then evenly adding copper-plated steel fiber and stirring evenly, and finally adding a defoamer and stirring evenly to obtain a mixture;

[0097] 3) The obtained mixture is molded, vibrated, and formed, and the surface is covered with a waterproof film for film curing, and then the mold is removed for steam curing. The steam curing temperature is set to 90° C. and the steam curing time is set to 72 hours. Then, standard curing is performed to the age, thereby obtaining the γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete.

[0098] After testing, the obtained γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete after curing for 28 days has a compressive strength of 93.0 MPa, a flexural strength of 12.5 MPa, a tensile strength of 6.2 MPa, an expansion of 660 mm, and an apparent density of 2230 kg / m 3 , 56d drying shrinkage is 425×10 -6 , chloride ion diffusion coefficient is 0.06×10 -12 m 2 / s, anti-seepage grade P25.

[0099] Comparative Example 2

[0100] A γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete, the preparation method of which comprises the following steps:

[0101] 1) Weighing of raw materials: ordinary 52.5 silicate cement 650kg / m 3 , fly ash 100kg / m 3 , silica fume 150kg / m 3 , modified γ-C2S phosphogypsum unburned lightweight aggregate 380kg / m 3 , medium sand 300kg / m 3 , floating beads 50kg / m 3 , fine sand 333kg / m 3 , water 150kg / m 3 , copper-plated steel fiber 80kg / m 3 , water reducing agent 8.5kg / m 3 , defoaming agent 1kg / m 3 ;

[0102] Among them, the preparation method of the modified unburned γ-C2S phosphogypsum lightweight aggregate is roughly the same as that in Example 1, except that: the components and their mass percentages include: phosphogypsum 43%, γ-C2S 27%, fly ash 13%, mineral powder 5%, water 7%, and water glass 5% (water glass replaces the sodium aluminate and red mud powder in Example 1). The raw materials are weighed in the proportion required; the water glass modulus used is 1.5, and the main chemical components and their contents are Na2O 10wt% and SiO2 24wt%; the bulk density of the obtained phosphogypsum lightweight aggregate reaches 1100kg / m 3, cylinder pressure strength 3.5Mpa, softening coefficient 0.92, water absorption rate 8.2%, crushing value 20.1%, porosity 39.1%, micro-connected pore size 0.01-100nm and accounting for 36.6% of the total porosity,

[0103] The particle sizes of fine sand and medium sand used are 0.1-0.15 mm and 0.16-0.3 mm respectively;

[0104] 2) Soaking quartz sand, medium sand, and fine sand in water until saturated with water to obtain pre-wet sand, adding the pre-wet sand, modified unburned γ-C2S phosphogypsum lightweight aggregate, cement, and silica fume into a concrete mixer and pre-mixing them evenly, adding fly ash and continuing to dry-mix them evenly, then pouring water and a water reducer into the mixture and stirring them evenly, then evenly adding copper-plated steel fiber and stirring them evenly, and finally adding a defoamer and stirring them evenly to obtain a mixture;

[0105] 3) The obtained mixture is molded, vibrated, and formed, and the surface is covered with a waterproof film for film curing, and then the mold is removed for steam curing. The steam curing temperature is set to 90° C. and the steam curing time is set to 48 hours to obtain the γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete.

[0106] After testing, the γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete obtained after curing for 28 days had a compressive strength of 94.0 MPa, a flexural strength of 14.1 MPa, a tensile strength of 6.8 MPa, an expansion of 680 mm, and an apparent density of 2223 kg / m 3 , 56d shrinkage strain is 342×10 -6 , chloride ion diffusion coefficient is 0.07×10 -12 m 2 / s, anti-seepage grade P25.

[0107] Comparative Example 3

[0108] A γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete, the preparation method of which is substantially the same as that of Example 1, except that: the γ-C2S phosphogypsum-based lightweight aggregate is placed in saturated lime water for curing for 24 hours; the obtained modified γ-C2S phosphogypsum unburned lightweight aggregate has a bulk density of 963 kg / m 3 , 1h water absorption rate is 4.9%, the size of fine interconnected pores is 0.01-100nm and accounts for 34% of the total porosity, the particle size is 4.5-9.5mm, the cylinder pressure strength is 8.6MPa, and the softening coefficient is 0.95;

[0109] The test results show that the obtained γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete has a compressive strength of 109.0 MPa, a flexural strength of 12.2 MPa, a tensile strength of 7.1 MPa, an expansion of 660 mm, and an apparent density of 2190 kg / m 3 , 56d drying shrinkage is 389×10-6 , chloride ion diffusion coefficient is 0.06×10 -12 m 2 / s, anti-seepage grade P28.

[0110] Comparative Example 4

[0111] A γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete, the preparation method of which is substantially the same as that of Example 1, except that: the γ-C2S phosphogypsum-based lightweight aggregate is set to three-stage pressing during step-by-step pressing, but the vibration condition is canceled; the obtained modified γ-C2S phosphogypsum unburned lightweight aggregate has a bulk density of 1210 kg / m 3 , 1h water absorption rate is 7.5%, the size of fine interconnected pores is 0.01-100nm and only accounts for 33.3% of the total porosity, the particle size is 4.5-9.5mm, the cylinder pressure strength is 6.6MPa, and the softening coefficient is 0.96;

[0112] The test results show that the obtained γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete has a compressive strength of 101.0 MPa, a flexural strength of 10.2 MPa, a tensile strength of 6.8 MPa, an expansion of 690 mm, and an apparent density of 2189 kg / m 3 , 56d drying shrinkage is 352×10 -6 , chloride ion diffusion coefficient is 0.06×10 -12 m 2 / s, anti-seepage grade P25.

[0113] The present invention is not limited to the above-described embodiments. Persons skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are deemed to be within the scope of protection of the present invention. Any matters not described in detail in this specification constitute prior art known to those skilled in the art.

Claims

1. A γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete, characterized in that: The components and their contents include: cement 600-700kg / m 3 , fly ash 100-150kg / m 3 , silica fume 150-200kg / m 3 Modified γ-C2S phosphogypsum unburned aggregate 200-400kg / m 3 , copper-plated steel fiber 80-100kg / m 3 , medium sand 300-700kg / m 3 , floating beads 40-92kg / m 3 , fine sand 260-608kg / m 3 , water reducing agent 8-15kg / m 3 , defoaming agent 0.5-2kg / m 3 , water 150-190kg / m 3 ; The modified γ-C2S phosphogypsum unburned lightweight aggregate is prepared by mixing, pressing and crushing γ-C2S phosphogypsum, fly ash, mineral powder, red mud powder, sodium metaaluminate and water as main raw materials, and then curing the γ-C2S phosphogypsum-based lightweight aggregate with saturated lime water-graphene cement slurry. The preparation method of the γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete comprises the following steps: 1) Weigh each raw material according to the ratio; 2) Soak medium sand and fine sand in water until saturated to obtain pre-wet sand, add pre-wet sand, modified γ-C2S phosphogypsum unburned aggregate, cement and silica fume into a concrete mixer and mix evenly, add fly ash and floating beads and continue dry mixing evenly, then pour in water and water reducer and mix evenly, evenly add copper-plated steel fiber and mix evenly, and finally add defoamer and mix evenly; 3) After the mold is filled, vibrated, and formed, the mold is removed and cured after the film is cured to obtain the γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete.

2. The γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete according to claim 1, characterized in that: The components in the saturated lime water-graphene cement slurry and their mass percentages include: 0.02-0.03% graphene, 35-45% cement, and 55-75% saturated lime water.

3. The γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete according to claim 1, characterized in that: The curing time of the saturated lime water-graphene cement slurry is 18-24 hours.

4. The γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete according to claim 1, characterized in that: The raw materials used in the gamma-C2S phosphogypsum-based lightweight aggregate and their mass percentages include: phosphogypsum 43-48%, gamma-C2S 21.5-28%, fly ash 8-13%, mineral powder 5-10%, red mud powder 3-5%, sodium metaaluminate 1-3%, and water 5-7%.

5. The γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete according to claim 1, characterized in that: The pressing conditions adopt a set pressure of 270-320 kN and a total holding time of more than 15 minutes.

6. The γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete according to claim 1, characterized in that: The particle size of the modified γ-C2S phosphogypsum unburned lightweight aggregate is 4.5-9.5 mm.

7. The γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid high performance water reducing agent, and its water reducing rate is ≥35%.

8. The γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete according to claim 1, characterized in that: The cement is ordinary Portland cement with a strength grade of 52.5 or above; the fly ash is Grade I or Grade II fly ash, wherein the CaO content is greater than 10%; and the SiO2 content in the silica ash is greater than 90wt%.

9. The γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete according to claim 1, characterized in that: The medium sand and fine sand are machine-made sand or quartz sand, the particle size of the medium sand is 0.16-0.3 mm, the particle size of the fine sand is 0.1-0.15 mm; the particle size of the floating beads is 10-300 μm.

10. The method for preparing the γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete according to any one of claims 1 to 9, characterized in that: The following steps are involved: 1) Weigh the raw materials according to the proportion, including the components and their contents: cement 600-700kg / m 3 , fly ash 100-150kg / m 3 , silica fume 150-200kg / m 3 Modified γ-C2S phosphogypsum unburned aggregate 200-400kg / m 3 , copper-plated steel fiber 80-100kg / m 3 , medium sand 300-700kg / m 3 , floating beads 40-92kg / m 3 , fine sand 260-608kg / m 3 , water reducing agent 8-15kg / m 3 , defoaming agent 0.5-2kg / m 3 , water 150-190kg / m 3 ; 2) Soak medium sand and fine sand in water until saturated to obtain pre-wet sand, add pre-wet sand, modified γ-C2S phosphogypsum unburned aggregate, cement and silica fume into a concrete mixer and mix evenly, add fly ash and floating beads and continue dry mixing evenly, then pour in water and water reducer and mix evenly, evenly add copper-plated steel fiber and mix evenly, and finally add defoamer and mix evenly; 3) After the mold is filled, vibrated, and formed, the mold is removed and cured after the film is cured to obtain the γ-C2S phosphogypsum lightweight aggregate ultra-high performance concrete.