Low-temperature-resistant mortar doped with fly ash and preparation process thereof

Abstract

The application belongs to the technical field of building materials, and particularly relates to fly ash doped low-temperature-resistant mortar and a preparation process thereof. The fly ash doped low-temperature-resistant mortar comprises, in terms of mass fractions, 28-52 parts of desulfurization gypsum, 30-45 parts of fly ash, 15-30 parts of cement, 100-500 parts of fine aggregate, 0.7-2.5 parts of a water reducing agent, 0.5-2 parts of ordinary polyvinyl alcohol fiber, 0.2-0.5 parts of water-soluble polyvinyl alcohol fiber, 0.2-0.5 parts of a defoaming agent, and 26-38 parts of water. The application uses desulfurization gypsum and fly ash as main cementitious admixtures, greatly reduces the cement dosage, reduces the production cost, solves the problems of fly ash and desulfurization gypsum accumulation and pollution, and solves the defects of slow low-temperature strength development and easy structure damage of traditional mortar.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a fly ash-doped low-temperature resistant mortar and its preparation process. Background Technology

[0002] Mortar is a widely used material in construction engineering, mainly used for masonry, plastering, and bonding. In cold regions and during low-temperature construction in winter, traditional mortar faces severe challenges. Low temperatures cause the moisture in the mortar to freeze, expanding in volume and damaging its internal structure during solidification. This leads to problems such as reduced concrete strength, cracking, and spalling, seriously affecting the quality and durability of construction projects. Furthermore, traditional mortar typically uses cement as the main binder, resulting in high production costs and the consumption of large amounts of limestone resources, which does not meet the requirements of current green building and sustainable development.

[0003] Fly ash is an industrial waste emitted by thermal power plants. Large-scale accumulation not only occupies land resources but also causes environmental pollution. Adding fly ash as an admixture to mortar can reduce cement usage, lower production costs, and achieve resource utilization of industrial waste. It can also improve the workability of mortar and reduce the heat of hydration. However, mortar with fly ash added alone still cannot meet engineering requirements in low-temperature environments.

[0004] Therefore, developing a mortar product that uses desulfurized gypsum and fly ash as the main admixtures and has both high solid waste utilization rate and low temperature resistance is of great significance for promoting the resource utilization of industrial solid waste and solving the problem of mortar application in low temperature environments. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a fly ash-doped low-temperature resistant mortar and its preparation process. Using desulfurized gypsum and fly ash as the main cementitious admixtures, it significantly reduces cement usage, lowers production costs, solves the problem of fly ash and desulfurized gypsum accumulation and pollution, and overcomes the shortcomings of traditional mortars, such as slow strength development and easy structural damage in low-temperature environments.

[0006] The specific technical solution adopted in this invention is as follows:

[0007] A fly ash-mixed low-temperature resistant mortar, comprising, by weight, 28-52 parts desulfurized gypsum, 30-45 parts fly ash, 15-30 parts cement, 100-500 parts fine aggregate, 0.7-2.5 parts water-reducing agent, 0.5-2 parts ordinary polyvinyl alcohol fiber, 0.2-0.5 parts water-soluble polyvinyl alcohol fiber, 0.2-0.5 parts defoamer, and 26-38 parts water.

[0008] By weight, the low-temperature resistant mortar also includes 5-10 parts of low-temperature resistant modifier, which is a mixture of ethylene-vinyl acetate copolymer emulsion, propylene glycol and nano silica in a weight ratio of 5-8:2-4:1.

[0009] The fine aggregate has a particle size of 1.6-2.5 mm.

[0010] A process for preparing low-temperature resistant mortar mixed with fly ash includes the following steps:

[0011] S1. Weigh 20-30% of the total amount of fly ash and 20-30% of the total amount of desulfurized gypsum according to the formula, mix them evenly to obtain a powder mixture for later use.

[0012] S2. Weigh out all the water-soluble polyvinyl alcohol fiber and low-temperature resistant modifier according to the formula, and then take 6-10 parts of water, put them into a mixing container and stir evenly to form a composite binder for later use.

[0013] S3. Add 30-50% of the total amount of powdered mixture to the vibrating tank, and spread the powdered mixture evenly with the help of the vibration of the vibrating tank.

[0014] S4. Evenly spray 30-50% of the total amount of composite adhesive into the vibration trough;

[0015] S5. Add all the fine aggregate to the vibrating trough. The fine aggregate adheres to the powdery mixture on the surface of the fine aggregate by means of the vibration of the vibrating trough and the bonding effect of the composite binder, thus obtaining modified fine aggregate.

[0016] S6. The modified fine aggregate is fed into the vibrating screen. The vibration of the vibrating screen separates the agglomerated modified fine aggregate and passes it through the screen holes. The modified fine aggregate that has passed through the screen holes is fed back into the vibrating trough. Then, 5-10% of the total amount of powder mixture and 5-10% of the total amount of composite binder are added. The powder mixture adheres to the surface of the modified fine aggregate again.

[0017] S7. Repeat step S6 until the powder mixture and composite binder are used up to obtain modified fine aggregate with a uniform film layer on the surface. After sieving and drying the modified fine aggregate again, low-temperature resistant modified particles are obtained.

[0018] S8. Mix and stir the low-temperature resistant modified particles, cement, ordinary polyvinyl alcohol fiber, water-reducing agent, defoamer, water, and the remaining mass of fly ash and desulfurized gypsum to obtain fly ash-doped low-temperature resistant mortar.

[0019] The particle size of the powder mixture is 0.045-0.075 mm.

[0020] In step S6, the aperture of the sieve is 2.75-3.0 mm.

[0021] The preparation process utilizes a mortar production line, which includes a modified particle preparation unit, a raw material supply unit, a water supply unit, and a mortar mixing tank. The discharge end of the modified particle preparation unit is connected to the inlet end of the mortar mixing tank via a modified particle conveyor belt. The discharge end of the raw material supply unit is connected to the inlet end of the mortar mixing tank via a raw material conveyor belt. The water outlet end of the water supply unit is connected to the inlet end of the mortar mixing tank via a water pipe.

[0022] The modified particle preparation unit includes a frame and a vibrating tank and a liquid spray gun mounted on the frame. The vibrating tank has a degree of freedom of vibration by means of a drive assembly. A lead screw is provided above the vibrating tank. The liquid spray gun slides with the lead screw by means of a moving seat and has a degree of freedom of reciprocating horizontally above the vibrating tank.

[0023] The vibrating trough is also equipped with a disturbance comb, and multiple sets of disturbance combs are arranged at intervals along the discharge direction of the modified particles. The material in the vibrating trough is fully mixed by the disturbance of the disturbance comb.

[0024] The driving assembly includes a vibration motor, a swing rod, and an eccentric rod. The swing rod is connected to the lower part of the vibration groove. The output end of the vibration motor is eccentrically hinged to the swing rod via the eccentric rod. The swing rod reciprocates and drives the vibration groove to vibrate via the vibration motor.

[0025] The beneficial effects of this invention are:

[0026] 1. The mortar of this invention uses desulfurized gypsum and fly ash as the main cementitious admixtures, significantly reducing cement usage, lowering production costs, and solving the pollution problem caused by the accumulation of fly ash and desulfurized gypsum. Simultaneously, the synergistic effect of fly ash and desulfurized gypsum, with the desulfurized gypsum acting as an activation agent, can still stimulate the potential activity of fly ash at low temperatures, solving the problem of slow low-temperature reaction of fly ash. This ensures that the mortar maintains good performance in low-temperature environments, inhibiting frost heave cracking and spalling, and overcoming the shortcomings of traditional mortars such as slow low-temperature strength development and easy structural damage.

[0027] In addition, additives such as polyvinyl alcohol fiber, water-reducing agent, and defoamer can further improve the frost resistance of mortar.

[0028] 2. Traditional mortar preparation methods typically involve directly mixing powdered mixtures such as fly ash, desulfurized gypsum, and modifiers with cement and water. However, this relatively coarse method leads to uneven distribution of the powdered mixture in the mortar, making it prone to agglomeration. Weak areas easily form around agglomerated regions, where water accumulates. Furthermore, the fine aggregate particles have numerous microscopic gaps, and the poor fluidity of the cement colloid prevents it from fully penetrating the gaps between the fine aggregate particles to displace water, also leading to water accumulation. If the fine aggregate particles are pushed apart due to internal freezing, it can cause damage to the surrounding concrete structure and expand the frost damage area, affecting the final strength of the concrete.

[0029] The membrane layer prepared in this application fills the surface gaps of the fine aggregate, forming a water barrier to prevent moisture from accumulating in the gaps of the fine aggregate and to prevent the fine aggregate from cracking due to internal freezing.

[0030] 3. The layered preparation method in this invention allows the powdered mixture to adhere to the surface of the fine aggregates and completely coat them. During the process of attaching the powdered mixture, the fine aggregates may agglomerate under the action of the composite binder. In this invention, the vibration of a vibrating screen and the cutting action of the screen mesh are used to separate the agglomerates, forming independent modified fine aggregates that conform to the particle size. However, the surface of the separated modified fine aggregates may still have exposed areas. Therefore, the modified fine aggregates are fed back into the vibrating trough by a circulating conveyor belt and a screw feeder for re-coating. By forcibly separating the agglomerated modified fine aggregates, the slurry layer formed by the composite binder and the powdered mixture produces a rough surface structure, providing good support for subsequent mortar. The above-mentioned process of coating the fine aggregates is repeated multiple times, ultimately forming low-temperature resistant modified particles without agglomerates and with a uniformly adhered surface of the powdered mixture.

[0031] 4. The fine aggregate in this invention forms a film layer containing fly ash, desulfurized gypsum and binder through the preparation process. During the subsequent mortar mixing process, due to the presence of cement in the mortar, the fly ash on the surface of the aggregate particles reacts with the desulfurized gypsum and cement to form a pozzolanic reaction. The resulting cement colloid fully grips and compacts the rough surface, and after drying, it forms a strengthening effect, improving the strength of the concrete after the mortar solidifies. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the mortar production line in this invention;

[0033] Figure 2 A top view of the modified particle preparation unit;

[0034] Figure 3 A schematic diagram of the front structure of the modified particle preparation unit;

[0035] In the attached diagram, 1 is the modified particle preparation unit, 2 is the raw material supply unit, 3 is the water supply unit, 4 is the mortar mixing tank, 5 is the frame, 6 is the vibrating tank, 7 is the liquid spray gun, 8 is the lead screw, 9 is the moving seat, 10 is the disturbance comb, 11 is the vibration motor, 12 is the swing rod, 13 is the eccentric rod, 14 is the moving motor, and 15 is the limit rod. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0037] The present invention provides a mortar production line, which includes a modified particle preparation unit 1, a raw material supply unit 2, a water supply unit 3, and a mortar mixing tank 4. The discharge end of the modified particle preparation unit 1 is connected to the inlet end of the mortar mixing tank 4 via a modified particle conveyor belt. The discharge end of the raw material supply unit 2 is connected to the inlet end of the mortar mixing tank 4 via a raw material conveyor belt. The water outlet end of the water supply unit 3 is connected to the inlet end of the mortar mixing tank 4 via a water pipe.

[0038] This invention utilizes a mortar production line to achieve the preparation of low-temperature resistant modified particles and the continuous production of mortar, thereby improving mortar production efficiency. Furthermore, through the mortar mixing ratios and production line processes described in this invention, mortar can be directly produced, eliminating the need for customers to prepare their own mixes.

[0039] The modified particle preparation unit 1 includes a frame 5 and a vibrating tank 6 and a liquid spray gun 7 mounted on the frame 5. The vibrating tank 6 has a degree of freedom of vibration by means of a drive assembly. A lead screw 8 is provided above the vibrating tank 6. The liquid spray gun 7 slides with the lead screw 8 by means of a moving seat 9 and has a degree of freedom of reciprocating horizontally above the vibrating tank 6.

[0040] In this invention, the powdered mixture and fine aggregate can be directly poured into the vibrating trough 6. During the spreading of dry materials, the liquid spray gun 7 is constantly moving back and forth, which is also conducive to the full mixing of different materials.

[0041] The vibrating trough 6 is also provided with a disturbance comb 10. Multiple sets of disturbance comb 10 are arranged at intervals along the discharge direction of the modified particles. The material in the vibrating trough 6 is fully mixed by the disturbance and agitation of the disturbance comb 10 during the movement process.

[0042] The agitation comb 10 is used to cooperate with the vibration groove 6 to form a thorough mixing of materials. Compared with the traditional stirring method, the friction and collision of the stirring method in this invention are relatively mild, which is conducive to the powder mixture adhering to the surface of fine aggregate to form a film layer.

[0043] In addition, the disturbance comb 10 is set in the vertical plane between adjacent liquid spray guns 7 to avoid the composite adhesive sprayed by the liquid spray guns 7.

[0044] The driving assembly includes a vibration motor 11, a swing rod 12, and an eccentric rod 13. The swing rod 12 is connected to the lower part of the vibration groove 6. The output end of the vibration motor 11 is eccentrically hinged to the swing rod 12 via the eccentric rod 13. The swing rod 12 reciprocates and drives the vibration groove 6 to vibrate via the vibration motor 11.

[0045] The drive assembly also includes a limit rod 15 and a moving motor 14. The moving seat 9 is sleeved with the limit rod 15 and threaded with the lead screw 8. The lead screw 8 has a degree of freedom of rotation with the help of the moving motor 14, and the moving seat 9 has a degree of freedom of reciprocating above the vibration groove 6 with the help of the rotation of the lead screw 8.

[0046] The modified granule preparation unit 1 also includes a vibrating screen, a circulating conveyor belt, and a screw feeder. The output end of the modified granule preparation unit 1 is connected to the feed end of the vibrating screen, the discharge end of the vibrating screen is connected to the feed end of the circulating conveyor belt, the discharge end of the circulating conveyor belt is connected to the feed end of the screw feeder, and the discharge end of the screw feeder is connected to the feed end of the vibrating trough 6.

[0047] The reverse direction of the circulating conveyor belt is provided with an extended drying conveyor belt or a drying chamber. After the preparation of the low-temperature resistant modified particles is completed, the low-temperature resistant modified particles are sent to the drying process by reversing the circulating conveyor belt. After drying, the particles are fed into the mortar mixing tank 4.

[0048] During the process of attaching the fine aggregate to the powdery mixture, the fine aggregate may agglomerate under the action of the composite binder. Therefore, in this invention, the vibration and sieving action of a vibrating screen is used to separate the agglomerates, forming independent modified fine aggregates that conform to the particle size. However, the surface of the separated modified fine aggregates may still have exposed areas. Therefore, the modified fine aggregates are fed back into the vibrating trough 6 by a circulating conveyor belt and a screw feeder for re-coating. The above steps are repeated multiple times to finally form low-temperature resistant modified particles without agglomerates and with a uniform surface coating of the powdery mixture.

[0049] In addition, the vibrating trough 6 is set at an inclination, and the discharge port side of the vibrating trough 6 is slightly lower than the closed side. As the vibrating trough 6 vibrates, the mixed material in the vibrating trough 6 will be shaken down to a lower position and fall into the vibrating screen along the discharge port. I. Specific Implementation Methods

[0051] The water used in the preparation of the composite adhesive in this invention is obtained separately and is not included in the formulation of the low-temperature resistant mortar.

[0052] Example 1

[0053] S1. Weigh 10 parts fly ash and 12 parts desulfurized gypsum by mass, add them to a mixing tank, stir evenly and then sieve to obtain a powdery mixture.

[0054] S2. Weigh 0.3 parts of water-soluble polyvinyl alcohol fiber, 8 parts of low-temperature resistant modifier and 8 parts of water by mass, put them into a mixing container and stir evenly to form a composite binder for later use. The low-temperature resistant modifier is composed of ethylene-vinyl acetate copolymer emulsion, propylene glycol and nano silica in a mass ratio of 6:3:1.

[0055] S3. Add 40% of the total amount of powder mixture to the vibrating tank and spread the powder mixture evenly with the help of the vibration of the vibrating tank.

[0056] S4. Spray 40% of the total amount of composite adhesive into the vibration trough evenly.

[0057] S5. Add 300 parts of fine aggregate to the vibrating trough. The fine aggregate adheres to the powdered mixture on its surface by means of the vibration of the vibrating trough and the bonding effect of the composite binder.

[0058] S6. The modified fine aggregate is fed into the vibrating screen. The vibration of the vibrating screen separates the agglomerated modified fine aggregate and passes it through the screen holes. The modified fine aggregate that has passed through the screen holes is fed back into the vibrating trough. Then, 6% of the total amount of powder mixture and 6% of the total amount of composite binder are added. The powder mixture adheres to the surface of the modified fine aggregate again.

[0059] S7. Repeat step S6 until the powder mixture and composite binder are used up to obtain modified fine aggregate with a uniform film layer on the surface. After sieving and drying the modified fine aggregate again, low-temperature resistant modified particles are obtained.

[0060] S8. The obtained low-temperature resistant modified particles are mixed with 25 parts cement, 1.5 parts ordinary polyvinyl alcohol fiber, 1.2 parts water-reducing agent, 0.3 parts defoamer, 28 parts fly ash, 30 parts desulfurized gypsum and 32 parts water and stirred evenly to obtain fly ash-doped low-temperature resistant mortar.

[0061] Example 2

[0062] S1. Weigh 6 parts fly ash and 7 parts desulfurized gypsum by mass, add them to a mixing tank, stir evenly and then sieve to obtain a powdery mixture.

[0063] S2. Weigh 0.2 parts of water-soluble polyvinyl alcohol fiber, 5 parts of low-temperature resistant modifier and 6 parts of water by mass, put them into a mixing container and stir evenly to form a composite binder for later use. The low-temperature resistant modifier is composed of ethylene-vinyl acetate copolymer emulsion, propylene glycol and nano silica in a mass ratio of 5:2:1.

[0064] S3. Add 30% of the total amount of powder mixture to the vibrating tank and spread the powder mixture evenly with the help of the vibration of the vibrating tank.

[0065] S4. Spray 30% of the total amount of composite adhesive into the vibration trough evenly.

[0066] S5. Add 100 parts of fine aggregate to the vibrating trough. The fine aggregate adheres to the powdered mixture on its surface by means of the vibration of the vibrating trough and the bonding effect of the composite binder.

[0067] S6. The modified fine aggregate is fed into the vibrating screen. The vibration of the vibrating screen separates the agglomerated modified fine aggregate and passes it through the screen holes. The modified fine aggregate that has passed through the screen holes is fed back into the vibrating trough. Then, 5% of the total amount of powder mixture and 5% of the total amount of composite binder are added. The powder mixture adheres to the surface of the modified fine aggregate again.

[0068] S7. Repeat step S6 until the powder mixture and composite binder are used up to obtain modified fine aggregate with a uniform film layer on the surface. After sieving and drying the modified fine aggregate again, low-temperature resistant modified particles are obtained.

[0069] S8. When using, mix the prepared low-temperature resistant modified particles with 15 parts cement, 0.5 parts ordinary polyvinyl alcohol fiber, 0.7 parts water-reducing agent, 0.2 parts defoamer, 24 parts fly ash, 21 parts desulfurized gypsum and 26 parts water and stir evenly to obtain fly ash-doped low-temperature resistant mortar.

[0070] Example 3

[0071] S1. Weigh 12 parts fly ash and 15 parts desulfurized gypsum by mass, add them to a mixing tank, stir evenly and then sieve to obtain a powdery mixture.

[0072] S2. Weigh 0.5 parts of water-soluble polyvinyl alcohol fiber, 10 parts of low-temperature resistant modifier and 10 parts of water by mass, put them into a mixing container and stir evenly to form a viscous composite adhesive for later use. The low-temperature resistant modifier is composed of ethylene-vinyl acetate copolymer emulsion, propylene glycol and nano silica in a mass ratio of 8:4:1.

[0073] S3. Add 50% of the total amount of powder mixture to the vibrating tank and spread the powder mixture evenly with the help of the vibration of the vibrating tank.

[0074] S4. Spray 50% of the total amount of composite adhesive into the vibration trough evenly.

[0075] S5. Add 500 parts of fine aggregate to the vibrating trough. The fine aggregate adheres to the powder mixture on the surface of the vibrating trough with the help of vibration and the bonding effect of composite binder.

[0076] S6. The modified fine aggregate is fed into the vibrating screen. The vibration of the vibrating screen separates the agglomerated modified fine aggregate and passes it through the screen holes. The modified fine aggregate that has passed through the screen holes is fed back into the vibrating trough. Then, 10% of the total amount of powder mixture and 10% of the total amount of composite binder are added. The powder mixture adheres to the surface of the modified fine aggregate again.

[0077] S7. Repeat step S6 until the powder mixture and composite binder are used up to obtain modified fine aggregate with a uniform film layer on the surface. After sieving and drying the modified fine aggregate again, low-temperature resistant modified particles are obtained.

[0078] S8. When using, mix the prepared low-temperature resistant modified particles with 30 parts cement, 2 parts ordinary polyvinyl alcohol fiber, 2.5 parts water-reducing agent, 0.5 parts defoamer, 33 parts fly ash, 37 parts desulfurized gypsum and 38 parts water and stir evenly to obtain fly ash-doped low-temperature resistant mortar.

[0079] Example 4

[0080] S1. Weigh out 9 parts fly ash and 10 parts desulfurized gypsum by mass, add them to a mixing tank, stir evenly and then sieve to obtain a powdery mixture.

[0081] S2. Weigh 0.4 parts of water-soluble polyvinyl alcohol fiber, 7 parts of low-temperature resistant modifier and 8 parts of water by mass, put them into a mixing container and stir evenly to form a viscous composite adhesive for later use. The low-temperature resistant modifier is composed of ethylene-vinyl acetate copolymer emulsion, propylene glycol and nano silica in a mass ratio of 7:3:1.

[0082] S3. Add 45% of the total amount of powder mixture to the vibrating tank and spread the powder mixture evenly with the help of the vibration of the vibrating tank.

[0083] S4. Spray 45% of the total amount of composite adhesive into the vibration trough evenly.

[0084] S5. Add 400 parts of fine aggregate to the vibrating trough. The fine aggregate adheres to the powdered mixture on its surface by means of the vibration of the vibrating trough and the bonding effect of the composite binder.

[0085] S6. The modified fine aggregate is fed into the vibrating screen. The vibration of the vibrating screen separates the agglomerated modified fine aggregate and passes it through the screen holes. The modified fine aggregate that has passed through the screen holes is fed back into the vibrating trough. Then, 5% of the total amount of powder mixture and 5% of the total amount of composite binder are added. The powder mixture adheres to the surface of the modified fine aggregate again.

[0086] S7. Repeat step S6 until the powder mixture and composite binder are used up to obtain modified fine aggregate with a uniform film layer on the surface. After sieving and drying the modified fine aggregate again, low-temperature resistant modified particles are obtained.

[0087] S8. When using, mix the prepared low-temperature resistant modified particles with 22 parts cement, 1.2 parts ordinary polyvinyl alcohol fiber, 1.6 parts water-reducing agent, 0.35 parts defoamer, 29 parts fly ash, 30 parts desulfurized gypsum and 30 parts water and stir evenly to obtain fly ash-doped low-temperature resistant mortar.

[0088] Comparative Example 1

[0089] The only difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, the components were directly mixed evenly to obtain mortar. The specific steps are as follows:

[0090] S1. Weigh out 38 parts fly ash, 42 parts desulfurized gypsum, 25 parts cement, 1.2 parts water-reducing agent, 0.3 parts defoamer, 1.5 parts ordinary polyvinyl alcohol fiber, 0.3 parts water-soluble polyvinyl alcohol fiber, 8 parts low-temperature resistant modifier, and 32 parts water by weight. The low-temperature resistant modifier is composed of ethylene-vinyl acetate copolymer emulsion, propylene glycol, and nano silica in a mass ratio of 6:3:1.

[0091] S2. When using, mix and stir all components to obtain mortar.

[0092] Comparative Example 2

[0093] The only difference between Comparative Example 2 and Example 1 is that the preparation method of the low-temperature resistant modified particles in Comparative Example 2 is different. The specific steps are as follows:

[0094] S1. Weigh 10 parts fly ash and 12 parts desulfurized gypsum by mass, add them to a mixing tank, stir evenly and then sieve to obtain a powdery mixture.

[0095] S2. Weigh 0.3 parts of water-soluble polyvinyl alcohol fiber, 8 parts of low-temperature resistant modifier and 8 parts of water by mass, put them into a mixing container and stir evenly to form a composite binder for later use. The low-temperature resistant modifier is composed of ethylene-vinyl acetate copolymer emulsion, propylene glycol and nano silica in a mass ratio of 6:3:1.

[0096] S3. Add all the powdered mixture into the vibrating tank and spread the powdered mixture evenly with the help of the vibration of the vibrating tank.

[0097] S4. Spray all the composite adhesive evenly into the vibration trough;

[0098] S5. Add 300 parts of fine aggregate to the vibrating trough. The fine aggregate adheres to the powder mixture on the surface of the vibrating trough and the bonding effect of the composite binder. After sieving, low-temperature resistant modified granules are obtained for later use.

[0099] S6. Mix the prepared low-temperature resistant modified particles with 25 parts cement, 1.5 parts ordinary polyvinyl alcohol fiber, 1.2 parts water-reducing agent, 0.3 parts defoamer, 28 parts fly ash, 30 parts desulfurized gypsum and 32 parts water and stir evenly to obtain mortar.

[0100] II. Performance Testing

[0101] The mortars prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to performance testing. The testing methods and results are as follows:

[0102] 1. Mortar spread at -18℃

[0103] Test method: According to JGJ / T 70-2009 "Standard for Test Method of Basic Performance of Building Mortar", the prepared mortar sample was placed in a -18℃ low temperature constant temperature chamber for 2 hours, and then the spread of the mortar was measured.

[0104] 2. Water retention rate

[0105] According to JGJ / T 70-2009 "Standard for Test Methods of Basic Performance of Building Mortar", the filter paper water absorption method was used for testing.

[0106] 3. Compressive strength

[0107] According to JGJ / T 70-2009 "Standard for Test Methods of Basic Performance of Building Mortar", mortar was made into cubic test blocks of 70.7mm×70.7mm×70.7mm, cured for 7 days and 28 days under standard curing conditions, and the compressive strength was tested using a pressure testing machine.

[0108] 4. Bond strength

[0109] According to JGJ / T 70-2009 "Standard for Test Methods of Basic Performance of Building Mortar", the tensile bond method was used to test the tensile bond strength of mortar after 28 days of standard curing.

[0110] 5.50 freeze-thaw cycles, 28 days later, compressive strength loss rate

[0111] According to GB / T 50082-2009 "Standard Test Methods for Long-Term Performance and Durability of Ordinary Concrete", 28-day standard-cured test blocks were placed at -18℃ for freeze-thaw cycle testing. After 50 cycles, the compressive strength was tested, and the strength loss rate was calculated.

[0112] Compressive strength loss rate = (compressive strength 28 days before freeze-thaw - compressive strength 28 days after freeze-thaw) / compressive strength 28 days before freeze-thaw × 100%.

[0113] The test results for each test item are shown in Table 1.

[0114] Table 1

[0115]

[0116] As can be seen from Table 1, the synergistic effect of the preparation process and the low-temperature modifier in this invention improves the water retention, low-temperature workability, mechanical properties and low-temperature freeze resistance of the mortar from both structural and component perspectives. All properties are significantly better than those of the mortars prepared in Comparative Examples 1-2.

[0117] In Comparative Example 1, fly ash, desulfurized gypsum, water-reducing agent, and defoamer were directly mixed without fine aggregate as a carrier for dispersion, resulting in a large amount of powder agglomeration. Weak gaps formed around the agglomerated areas, allowing moisture to accumulate. Upon freezing at low temperatures, the moisture expanded, directly damaging the internal structure of the mortar during solidification. Simultaneously, the gaps on the surface of the fine aggregate were not filled, and the poor fluidity of the cement colloid prevented it from fully filling the gaps. Water accumulated in these gaps, froze, and cracked the fine aggregate, further expanding the internal frost damage area and leading to low concrete strength.

[0118] Although a coating was applied to the surface of the fine aggregate in Comparative Example 2, the coating process was relatively rough, and many surfaces of the fine aggregate were still exposed, making it impossible to form a complete water barrier. Some moisture remained in the gaps of the fine aggregate. Therefore, the concrete performance formed by the mortar in Comparative Example 2 was still lower than that of the concrete in Example 1.

Claims

1. A low-temperature resistant mortar mixed with fly ash, characterized in that, By weight, it includes 28-52 parts desulfurized gypsum, 30-45 parts fly ash, 15-30 parts cement, 100-500 parts fine aggregate, 0.7-2.5 parts water-reducing agent, 0.5-2 parts ordinary polyvinyl alcohol fiber, 0.2-0.5 parts water-soluble polyvinyl alcohol fiber, 0.2-0.5 parts defoamer, and 26-38 parts water.

2. The low-temperature resistant mortar with fly ash admixture according to claim 1, characterized in that, By weight, the low-temperature resistant mortar also includes 5-10 parts of low-temperature resistant modifier, which is a mixture of ethylene-vinyl acetate copolymer emulsion, propylene glycol and nano silica in a weight ratio of 5-8:2-4:

1.

3. The low-temperature resistant mortar with fly ash admixture according to claim 1, characterized in that, The fine aggregate has a particle size of 1.6-2.5 mm.

4. A process for preparing low-temperature resistant mortar doped with fly ash, used to prepare the low-temperature resistant mortar doped with fly ash as described in claim 2, characterized in that, Includes the following steps: S1. Weigh 20-30% of the total amount of fly ash and 20-30% of the total amount of desulfurized gypsum according to the formula, mix them evenly to obtain a powder mixture for later use. S2. Weigh out all the water-soluble polyvinyl alcohol fiber and low-temperature resistant modifier according to the formula, and then take 6-10 parts of water, put them into a mixing container and stir evenly to form a composite binder for later use. S3. Add 30-50% of the total amount of powder mixture to the vibrating tank (6) and spread the powder mixture evenly by means of the vibration of the vibrating tank (6); S4. Evenly spray 30-50% of the total amount of composite adhesive into the vibration groove (6); S5. Add all the fine aggregate to the vibrating trough (6). The fine aggregate adheres to the powdered mixture on the surface of the fine aggregate by means of the vibration of the vibrating trough (6) and the bonding effect of the composite binder, and thus obtains modified fine aggregate. S6. The modified fine aggregate is fed into the vibrating screen. The vibration of the vibrating screen separates the agglomerated modified fine aggregate and passes it through the screen holes of the vibrating screen. The modified fine aggregate that passes through the screen holes is fed into the vibrating trough (6) in a cycle. Then, 5-10% of the total amount of powder mixture and 5-10% of the total amount of composite binder are added. The powder mixture adheres to the surface of the modified fine aggregate again. S7. Repeat step S6 until the powder mixture and composite binder are used up to obtain modified fine aggregate with a uniform film layer on the surface. After sieving and drying the modified fine aggregate again, low-temperature resistant modified particles are obtained. S8. Mix and stir the low-temperature resistant modified particles, cement, ordinary polyvinyl alcohol fiber, water-reducing agent, defoamer, water, and the remaining mass of fly ash and desulfurized gypsum to obtain fly ash-doped low-temperature resistant mortar.

5. The preparation process of a fly ash-doped low-temperature resistant mortar according to claim 4, characterized in that, The particle size of the powder mixture is 0.045-0.075 mm.

6. The preparation process of a low-temperature resistant mortar mixed with fly ash according to claim 4, characterized in that, In step S6, the aperture of the sieve is 2.75-3.0 mm.

7. The preparation process of a low-temperature resistant mortar mixed with fly ash according to claim 4, characterized in that, The preparation process is carried out using a mortar production line, which includes a modified particle preparation unit (1), a raw material supply unit (2), a water supply unit (3), and a mortar mixing tank (4). The discharge end of the modified particle preparation unit (1) is connected to the inlet end of the mortar mixing tank (4) via a modified particle conveyor belt. The discharge end of the raw material supply unit (2) is connected to the inlet end of the mortar mixing tank (4) via a raw material conveyor belt. The water outlet end of the water supply unit (3) is connected to the inlet end of the mortar mixing tank (4) via a water pipe.

8. The preparation process of a low-temperature resistant mortar mixed with fly ash according to claim 7, characterized in that, The modified particle preparation unit (1) includes a frame (5) and a vibration groove (6) and a liquid spray gun (7) arranged on the frame (5). The vibration groove (6) has a degree of freedom of vibration by means of a drive assembly. A lead screw (8) is arranged above the vibration groove (6). The liquid spray gun (7) slides with the lead screw (8) by means of a moving seat (9) and has a degree of freedom of reciprocating translation in the horizontal direction above the vibration groove (6).

9. The preparation process of a fly ash-doped low-temperature resistant mortar according to claim 8, characterized in that, The vibrating trough (6) is also provided with a disturbance comb (10). Multiple sets of disturbance combs (10) are arranged at intervals along the discharge direction of the modified particles. The material in the vibrating trough (6) is fully mixed by the disturbance of the disturbance combs (10).

10. The preparation process of a low-temperature resistant mortar doped with fly ash according to claim 8, characterized in that, The drive assembly includes a vibration motor (11), a swing rod (12), and an eccentric rod (13). The swing rod (12) is connected to the bottom of the vibration groove (6). The output end of the vibration motor (11) is eccentrically hinged to the swing rod (12) via the eccentric rod (13). The swing rod (12) reciprocates and drives the vibration groove (6) to vibrate via the vibration motor (11).

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