Steel slag cement concrete accelerated curing method based on three-stage microwave control

Abstract

The invention discloses a steel slag cement concrete accelerated curing method based on three-stage microwave control, which comprises the following steps: preparing a steel slag cement concrete mixture C, pouring the prepared steel slag cement concrete mixture C out of a stirrer, and uniformly pouring the steel slag cement concrete mixture C into a test mold, putting into microwave curing equipment, and sequentially carrying out initial microwave accelerated curing, middle-stage microwave curing and later-stage microwave curing; after the later-period curing is finished, the concrete member is moved out of the microwave curing equipment for demolding, and then the concrete member is naturally cooled to the room temperature for curing; a three-stage microwave curing strategy is adopted, and parameters such as microwave frequency, power, temperature and heating rate of each stage are accurately regulated and controlled, so that rapid and uniform heating of the concrete is realized, hydration reaction of each component in the steel slag cement concrete is effectively promoted, strength development of the concrete is accelerated, and meanwhile, efficient, energy-saving and environment-friendly curing effects can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of the maintenance of civil engineering materials, and more specifically, relates to an accelerated curing method for steel slag cement concrete based on three-stage microwave control. Background Art

[0002] With the continuous development of China's construction industry, concrete has become an important part of engineering structures, and its construction efficiency and quality assurance have always been the focus of the industry. In the production process of concrete, the selection of cement and the curing process have always been important factors affecting the performance of concrete. In recent years, as a large amount of solid waste generated in the production process of the steel industry, the rational application of steel slag in the production of cement concrete can not only effectively solve the problem of steel slag stacking, reduce environmental pressure, but also reduce the production cost of concrete to a certain extent, realize the recycling of resources, and meet the current requirements of energy conservation, emission reduction and environmental protection. However, due to the low heat released during the hydration process of steel slag cement, it is difficult to ensure the curing effect, resulting in slow development of concrete strength, which restricts the wide application of steel slag cement concrete.

[0003] Traditional concrete curing methods usually include water curing, covering curing, steam curing and other methods. Water curing promotes cement hydration by keeping the concrete surface wet, usually by continuously spraying water or covering with a wet cloth. Covering curing uses plastic film or straw curtain to reduce water evaporation and maintain stable humidity. Steam curing is commonly used for precast components, and accelerates cement hydration by steam heating to shorten the curing time. Although the traditional methods have low cost and simple operation, they also have disadvantages such as difficult water control and long curing time. Traditional concrete curing methods also often have disadvantages such as high energy consumption, long cycle and strict requirements for environmental conditions.

[0004] Therefore, there is an urgent need for an efficient, energy-saving and highly adaptable steel slag cement concrete curing method. Summary of the Invention

[0005] In view of the above deficiencies or improvement requirements of the prior art, the present invention provides an accelerated curing method for steel slag cement concrete based on three-stage microwave control. Through reasonable microwave radiation design and curing time control, the early strength of steel slag cement concrete is effectively improved, and the problems existing in its curing process are solved. Through experiments and engineering applications, while ensuring the strength development of concrete, the present invention can achieve low energy consumption and a short construction period. Through microwave accelerated curing technology, the present invention not only solves the problem of insufficient early strength of steel slag cement concrete, but also achieves efficient, energy-saving and environmental protection curing effects, has significant technical and application advantages, can promote the wide application of steel slag cement concrete in practical engineering, provides a high-performance, green and sustainable concrete material and its curing method for the construction industry, achieves technical effects of high efficiency, early strength and high quality, and meets the multiple requirements of the current construction industry for construction efficiency, quality assurance and environmental protection.

[0006] To achieve the above object, the present invention provides an accelerated curing method for steel slag cement concrete based on three-stage microwave control, including the following steps:

[0007] S1: Pour ordinary Portland cement, silica fume, and steel slag-based solid waste into a planetary mixer and dry mix for 1 min to obtain mixture A;

[0008] S2: Add river sand, steel slag sand, limestone gravel, and steel slag coarse aggregate to mixture A and dry mix for 2 min to obtain mixture B;

[0009] S3: Mix the polycarboxylate superplasticizer and water and slowly add them to mixture B in two portions, and mix at a temperature of 10 - 30 °C for 2 min to obtain the steel slag cement concrete mixture C;

[0010] S4: Pour the steel slag cement concrete mixture C out of the mixer and evenly pour it into a test mold, and place it in a microwave curing device to perform initial microwave accelerated curing, intermediate microwave curing, and final microwave curing in sequence;

[0011] In step S4, the time of the initial microwave accelerated curing is 0.4 - 0.8 h, the temperature is controlled between 45 - 60 °C, the frequency used for the initial microwave curing is set at 1500 - 3000 MHz, the power is set at 1000 - 5000 W, and the heating rate is set at 10 - 20 °C / h;

[0012] In step S4, the time of the intermediate microwave curing is 0.5 - 1.0 h, the temperature is controlled between 50 - 75 °C, the frequency used for the intermediate microwave curing is set between 2450 - 5000 MHz, the power is set at 2000 - 5000 W, and the heating rate is set at 10 - 20 °C / h;

[0013] The later microwave curing time is 0.5 - 1.0 h, the temperature is controlled between 70 - 90 °C, the frequency used for later microwave curing is set at 2450 - 5000 MHz, the power is set at 3000 - 5000 W, and the heating rate is set at 15 - 20 °C / h;

[0014] S5: After the later curing is completed, remove the concrete member from the microwave curing equipment to demold it, and then let it cool naturally to room temperature to complete the curing.

[0015] Further, in step S1, the raw material composition by weight is 10.2 - 11.8 parts of ordinary Portland cement, 1.0 - 1.4 parts of silica fume, and 9.7 - 11.3 parts of steel slag-based solid waste.

[0016] Further, the steel slag-based solid waste in step S1 includes steel slag powder, slag, raw ash, desulfurized gypsum, and silica fume;

[0017] 100 parts of steel slag-based solid waste include 31.8 - 42.2 parts of steel slag powder, 19.1 - 25.9 parts of slag, 14.2 - 19.8 parts of raw ash, 13.5 - 17.5 parts of desulfurized gypsum, and 7.7 - 9.4 parts of silica fume.

[0018] Further, in step S2, the raw material composition by weight is 26.2 - 28.4 parts of fine aggregate, 18.8 - 22.9 parts of limestone gravel, and 19.9 - 24.5 parts of steel slag coarse aggregate.

[0019] Further, the fine aggregate in step S2 includes river sand and steel slag sand;

[0020] 100 parts of fine aggregate include 40 - 60 parts of river sand and 40 - 60 parts of steel slag sand.

[0021] Further, in step S3, the raw material composition by weight is 0.3 - 0.4 parts of polycarboxylate superplasticizer and 6.2 - 6.3 parts of water.

[0022] Further, the polycarboxylate superplasticizer is composed of a mixture of acrylic acid, methacrylic acid, maleic anhydride, polyoxyethylene allyl ester, polyoxyethylene methacrylate, polyoxyethylene acrylate, water, etc.

[0023] Further, the stirring speed in step S2 is 60 - 100 r / min, and after reaching the stirring time, it is cast into blocks.

[0024] Further, in step S4, the initial microwave curing adopts the continuous microwave heating curing method;

[0025] The intermediate microwave curing adopts the microwave gradient heating curing method, with a gradient of 500 W to achieve step-by-step temperature rise;

[0026] The subsequent microwave curing continues to adopt the intermittent microwave heating curing method, with a cycle of 10 minutes, heating for 5 minutes and stopping for 5 minutes in each cycle. The total cycle duration is 0.5 - 1 h, the heating rate is controlled at 15 - 20 °C / h, and the temperature is controlled at 70 - 90 °C.

[0027] Furthermore, the microwave curing equipment includes a microwave source, a waveguide, a cavity, and a control system. The microwave source can generate microwaves with a frequency of 1500 - 5000 MHz and a power of 1000 - 5000 W, and transmits the microwaves generated by the microwave source to the cavity through the waveguide. The cavity is used to place the steel slag cement concrete component; the control system can accurately control the frequency, power, and curing time of the microwaves, as well as the temperature and heating rate inside the cavity.

[0028] Generally speaking, compared with the prior art by the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0029] (1) The present invention provides an accelerated curing method for steel slag cement concrete based on three - stage microwave control. By adopting a three - stage microwave curing strategy, parameters such as the microwave frequency, power, temperature, and heating rate in each stage are accurately regulated, effectively promoting the hydration reaction of each component in the steel slag cement concrete and accelerating the development of concrete strength; the 72 - h compressive strength in Examples 2 - 6 reaches 55.4 - 57.7 MPa, and the splitting tensile strength reaches 4.2 - 4.4 MPa, far higher than those of the comparative examples of traditional curing and simplified microwave curing, indicating that this method can efficiently improve the early strength of concrete and can solve the problem of slow strength development of steel slag cement concrete.

[0030] (2) The present invention provides an accelerated curing method for steel slag cement concrete based on three - stage microwave control. The microwave radiation technology adopted utilizes microwave energy to accelerate the vibration and friction of water molecules inside the concrete, rapidly increasing the concrete temperature, thereby accelerating the hydration reaction of cement and promoting the rapid improvement of concrete strength; microwave radiation has the characteristic of selective heating, which can uniformly heat the inside of the concrete and can avoid the crack problem caused by a large temperature gradient in traditional curing methods.

[0031] (3) The present invention provides an accelerated curing method for steel slag cement concrete based on three - stage microwave control. The microwave curing equipment adopted can accurately control the curing parameters, realize rapid and uniform heating of the concrete. Compared with traditional steam curing and other methods, the curing time is significantly shortened and the energy consumption is reduced. In addition, this method is not restricted by environmental conditions and can meet the curing requirements of concrete components of different scales and shapes, providing a flexible and efficient solution for the application of steel slag cement concrete in various engineering scenarios.

[0032] (4) The present invention provides an accelerated curing method for steel slag cement concrete based on three - stage microwave control, enabling the effective application of steel slag - based solid waste in the production of cement concrete. It not only digests a large amount of steel slag, reduces environmental pressure, but also lowers production costs, realizes resource recycling, conforms to the concepts of energy conservation, emission reduction and environmental protection, provides strong technical support for the wide application of steel slag cement concrete, and promotes the sustainable development of the construction industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic flow chart of the preparation of the steel slag cement concrete mixture C in an accelerated curing method for steel slag cement concrete based on three - stage microwave control according to an embodiment of the present invention;

[0034] Figure 2 It is a schematic flow chart of an accelerated curing method for steel slag cement concrete based on three - stage microwave control according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] In order to overcome the deficiencies of traditional curing methods and meet the dual requirements of modern construction projects for construction efficiency and quality, microwave curing technology has emerged and gradually shown great application potential in the field of concrete construction.

[0037] Microwave is a high - frequency electromagnetic wave. When microwave acts on concrete, polar molecules (such as water molecules) in the concrete will vibrate violently and rub to generate heat under the action of the microwave electromagnetic field, thereby realizing the internal heating of the concrete and promoting the acceleration of the cement hydration reaction to achieve the purpose of rapid curing.

[0038] Microwave heating generates a uniform heating effect inside the material through the radiation of electromagnetic waves, realizes rapid and uniform temperature rise inside the concrete, and then accelerates the process of cement hydration reaction, effectively shortening the curing time. At the same time, the energy transfer method during microwave curing is different from traditional heating methods, with strong selectivity and pertinence, and can better regulate the hydration process of steel slag cement concrete and promote the improvement of its early strength.

[0039] Compared with traditional curing methods, microwave curing not only has a faster heating rate but also can uniformly heat the concrete, ensuring that the cement hydration reaction proceeds fully and evenly, which helps to improve key performance indicators such as the strength and density of the concrete. It has the advantages of high efficiency, good quality, energy conservation, environmental protection, flexibility, and controllability.

[0040] Example 1

[0041] One aspect of the present invention provides an accelerated curing method for steel slag cement concrete based on three-stage microwave control, comprising the following steps:

[0042] S1: Pour ordinary Portland cement, silica fume, and steel slag-based solid waste into a planetary mixer and dry mix for 1 min to obtain mixture A;

[0043] S2: Add river sand, steel slag sand, limestone gravel, and steel slag coarse aggregate to mixture A and dry mix for 2 min to obtain mixture B;

[0044] S3: Mix the polycarboxylate superplasticizer and water and slowly add them to mixture B in two portions, and mix at a temperature of 10 - 30 °C for 2 min to obtain the steel slag cement concrete mixture C;

[0045] S4: Pour the steel slag cement concrete mixture C out of the mixer and evenly pour it into a test mold, and place it in a microwave curing device to perform initial microwave accelerated curing, intermediate microwave curing, and final microwave curing in sequence;

[0046] The time of the initial microwave accelerated curing is 0.4 - 0.8 h, the temperature is controlled between 45 - 60 °C, the frequency used for the initial microwave curing is set at 1500 - 3000 MHz, the power is set at 1000 - 5000 W, and the heating rate is set at 10 - 20 °C / h;

[0047] The time of the intermediate microwave curing is 0.5 - 1.0 h, the temperature is controlled between 50 - 75 °C, the frequency used for the intermediate microwave curing is set at 2450 - 5000 MHz, the power is set at 2000 - 5000 W, and the heating rate is set at 10 - 20 °C / h;

[0048] The time of the final microwave curing is 0.5 - 1.0 h, the temperature is controlled between 70 - 90 °C, the frequency used for the final microwave curing is set at 2450 - 5000 MHz, the power is set at 3000 - 5000 W, and the heating rate is set at 15 - 20 °C / h;

[0049] S5: After the final curing is completed, remove the concrete member from the microwave curing device and then it can be demolded, and then it is naturally cooled to room temperature to complete the curing.

[0050] Further, step S1 also includes weighing ordinary Portland cement, silica fume, steel slag-based solid waste, river sand, steel slag sand, limestone gravel, steel slag coarse aggregate, polycarboxylate superplasticizer, and water by weight. The steel slag-based solid waste includes steel slag powder, slag, raw ash, desulfurized gypsum, and silica fume, and the fine aggregate includes river sand and steel slag sand;

[0051] The preparation raw materials of 100 parts of the steel slag cement concrete mixture C include 10.2 - 11.8 parts of ordinary Portland cement, 9.7 - 11.3 parts of steel slag-based solid waste, 6.2 - 6.3 parts of water, 26.2 - 28.4 parts of fine aggregate, 19.9 - 24.5 parts of steel slag coarse aggregate, 18.8 - 22.9 parts of limestone gravel, 0.3 - 0.4 parts of polycarboxylate superplasticizer, and 1.0 - 1.4 parts of silica fume;

[0052] 100 parts of steel slag-based solid waste include 31.8 - 42.2 parts of steel slag powder, 19.1 - 25.9 parts of slag, 14.2 - 19.8 parts of raw ash, 13.5 - 17.5 parts of desulfurized gypsum, and 7.7 - 9.4 parts of silica fume;

[0053] 100 parts of fine aggregate include 40 - 60 parts of river sand and 40 - 60 parts of steel slag sand.

[0054] Further, the stirring speed of the planetary mixer in step S2 is 60 - 100 r / min, and after reaching the stirring time, it is poured into blocks.

[0055] Further, the polycarboxylate superplasticizer in step S3 is composed of acrylic acid, methacrylic acid, maleic anhydride, polyoxyethylene allyl ester, polyoxyethylene methacrylate, polyoxyethylene acrylate, water, etc. The preparation process of the steel slag cement concrete mixture C in step S3 is as Figure 1 shown.

[0056] Further, the microwave curing equipment in step S4 includes a microwave heating device for heating the steel slag in stages; a temperature sensor for real-time monitoring of the steel slag temperature; and a control system for controlling the curing parameters.

[0057] The microwave heating device includes a microwave source, a waveguide, and a cavity;

[0058] The microwave source can generate microwaves with a frequency of 1500 - 5000 MHz and a power of 1000 - 5000 W, and transmit the microwaves generated by the microwave source to the cavity through the waveguide. The cavity is used to place the steel slag cement concrete component;

[0059] The control system is used to accurately control the frequency, power, and curing time of the microwave, as well as the temperature and heating rate in the cavity according to the preset parameters.

[0060] Further, in the natural cooling stage of step S6, the time required for the steel slag to cool from the temperature at the end of the later heating to room temperature is 2 to 4 hours.

[0061] Example 2

[0062] The difference between this example and Example 1 is as follows:

[0063] In the preparation of 100 parts of the steel slag cement concrete mixture C in step S3, the raw materials by weight include 11.2 parts of ordinary Portland cement, 10.2 parts of steel slag-based solid waste, 6.2 parts of water, 27.7 parts of fine aggregate, 21.6 parts of steel slag coarse aggregate, 21.7 parts of limestone gravel, 0.3 part of polycarboxylate superplasticizer, and 1.1 part of silica fume.

[0064] 100 parts of the steel slag-based solid waste include 42.5 parts of steel slag powder, 20.8 parts of slag, 14.8 parts of raw ash, 13.5 parts of desulfurized gypsum, and 8.4 parts of silica fume;

[0065] 100 parts of the fine aggregate include 50 parts of river sand and 50 parts of steel slag sand;

[0066] In step S4, the initial microwave curing adopts the continuous microwave heating curing method, with a microwave of frequency 2450 MHz and power 3000 W continuously curing for 0.5 h, the heating rate is controlled at 10 °C / h, and the temperature is controlled at 55 - 60 °C;

[0067] After the initial curing ends, intermediate microwave curing is carried out. In the intermediate microwave curing, the microwave gradient heating curing method is adopted. Microwaves with frequencies of 2450 MHz and powers of 2000 W, 2500 W, 3000 W, 3500 W, and 4000 W are used to cure for 0.2 h respectively, with a total duration of 1 h. With a gradient of 500 W, the temperature is increased step by step, the heating rate is controlled at 15 °C / h, and the temperature is controlled at 60 - 75 °C;

[0068] After the intermediate curing ends, late microwave curing is carried out. The late microwave curing adopts the intermittent microwave heating curing method, with the curing frequency set at 2450 MHz and power 5000 W. Taking 10 minutes as a cycle, heating for 5 minutes and stopping for 5 minutes in each cycle, with a total cycle duration of 1 h, the heating rate is controlled at 15 °C / h, and the temperature is controlled at 75 - 90 °C.

[0069] After the full-cycle curing ends, natural cooling to room temperature can complete the curing. The curing process is shown in Figure 2 .

[0070] Example 3

[0071] The difference between this example and Example 2 is as follows:

[0072] In the initial microwave curing described in step S4, continuous microwave heating curing method is adopted, with microwave of frequency 3000Hz and power 5000W continuously curing for 0.4h, the heating rate is controlled at 20℃ / h, and the temperature is controlled at 47 - 55℃;

[0073] After the initial curing is completed, intermediate microwave curing is carried out. The intermediate microwave curing adopts microwave gradient heating curing method, with microwave of frequency 4200MHz and powers 2500W, 3000W, 3500W, 4000W, 4500W curing for 0.2h respectively, with a total duration of 1h. With a gradient of 500W, stepwise temperature increase is achieved, the heating rate is controlled at 20℃ / h, and the temperature is controlled at 55 - 75℃;

[0074] After the intermediate curing is completed, late microwave curing is carried out. The late microwave curing continues to adopt intermittent microwave heating curing method, with microwave of frequency 2450MHz and power 5000W. Taking 10 minutes as a cycle, heating for 5 minutes and stopping for 5 minutes in each cycle, with a total cycle duration of 1h, the heating rate is controlled at 15℃ / h, and the temperature is controlled at 75 - 90℃.

[0075] After the full - cycle curing is completed, natural cooling to room temperature can complete the curing.

[0076] Example 4

[0077] The difference between this example and Example 2 is:

[0078] In the initial microwave curing described in step S4, continuous microwave heating curing method is adopted, with microwave of frequency 2450MHz and power 3000W continuously curing for 0.5h, the heating rate is controlled at 10℃ / h, and the temperature is controlled at 55 - 60℃;

[0079] After the initial curing is completed, intermediate microwave curing is carried out. The intermediate microwave curing adopts microwave gradient heating curing method, with microwave of frequency 5000MHz and powers 3000W, 3500W, 4000W, 4500W, 5000W curing for 0.1h respectively, with a total duration of 0.5h. With a gradient of 500W, stepwise temperature increase is achieved, the heating rate is controlled at 20℃ / h, and the temperature is controlled at 60 - 70℃;

[0080] After the intermediate curing is completed, late microwave curing is carried out. The late microwave curing continues to adopt intermittent microwave heating curing method, with microwave of frequency 2450MHz and power 5000W. Taking 10 minutes as a cycle, heating for 5 minutes and stopping for 5 minutes in each cycle, with a total cycle duration of 1h, the heating rate is controlled at 15℃ / h, and the temperature is controlled at 70 - 85℃.

[0081] After the full - cycle curing is completed, natural cooling to room temperature can complete the curing.

[0082] Example 5

[0083] The difference between this example and Example 2 is as follows:

[0084] In step S4, the initial microwave curing adopts the continuous microwave heating curing method, and the microwave with a frequency of 2450 MHz and a power of 1000 W is continuously cured for 0.8 h, the heating rate is controlled at 10 °C / h, and the temperature is controlled at 52 - 60 °C;

[0085] After the initial curing is completed, the intermediate microwave curing is carried out. The intermediate microwave curing adopts the microwave gradient heating curing method. The microwave with a frequency of 2450 MHz and powers of 2000 W, 2500 W, 3000 W, 3500 W, and 4000 W is cured for 0.2 h respectively, with a total duration of 1 h. With a gradient of 500 W, step-by-step heating is realized, the heating rate is controlled at 15 °C / h, and the temperature is controlled at 60 - 75 °C;

[0086] After the intermediate curing is completed, the final microwave curing is carried out. The final microwave curing adopts the intermittent microwave heating curing method. The curing frequency is set at 5000 MHz and the power is 5000 W. With a cycle of 10 minutes, it is heated for 5 minutes and stopped for 5 minutes in each cycle. The total cycle duration is 0.5 h, the heating rate is controlled at 20 °C / h, and the temperature is controlled at 75 - 85 °C.

[0087] After the full-cycle curing is completed, it is naturally cooled to room temperature to complete the curing.

[0088] Example 6

[0089] The difference between this example and Example 2 is as follows:

[0090] In step S4, the initial microwave curing adopts the continuous microwave heating curing method, and the microwave with a frequency of 1500 MHz and a power of 2000 W is continuously cured for 0.5 h, the heating rate is controlled at 10 °C / h, and the temperature is controlled at 45 - 50 °C;

[0091] After the initial curing is completed, the intermediate microwave curing is carried out. The intermediate microwave curing adopts the microwave gradient heating curing method. The microwave with a frequency of 4200 MHz and powers of 2000 W, 2500 W, 3000 W, 3500 W, and 4000 W is cured for 0.2 h respectively, with a total duration of 1 h. With a gradient of 500 W, step-by-step heating is realized, the heating rate is controlled at 20 °C / h, and the temperature is controlled at 50 - 70 °C;

[0092] After the mid-term maintenance is completed, carry out the later-stage microwave maintenance. The later-stage microwave maintenance adopts the intermittent microwave heating maintenance method. The maintenance frequency is set at 5000 MHz, the power is 3000 W, with a 10-minute cycle. Each cycle heats for 5 minutes and stops for 5 minutes. The total cycle duration is 1 h, the heating rate is controlled at 15 °C / h, and the temperature is controlled at 70 - 85 °C.

[0093] After the full-cycle maintenance is completed, naturally cool it to room temperature to complete the maintenance.

[0094] Comparative example

[0095] The difference between Comparative Example 1 and Example 2 is that in step S4, microwave maintenance is not adopted, but standard curing box is used for maintenance. The maintenance temperature is 20 °C, the humidity is 95%, and the maintenance time is 72 h.

[0096] The difference between Comparative Example 2 and Example 2 is that in step S4, three-stage microwave maintenance is not adopted, but two-stage microwave maintenance is used. The steel slag cement concrete mixture C obtained in step S3 is placed in a microwave maintenance device for primary microwave maintenance. In the primary microwave maintenance conditions, the continuous microwave heating maintenance method is adopted, and microwave with a frequency of 2450 MHz and a power of 3000 W is continuously maintained for 0.5 h. The heating rate is controlled at 10 °C / h, and the temperature is controlled at 50 - 55 °C. After the primary maintenance is completed, carry out secondary microwave maintenance. The secondary microwave maintenance adopts the microwave gradient heating maintenance method. Microwaves with frequencies of 2450 MHz and powers of 2000 W, 2500 W, 3000 W, 3500 W, and 4000 W are respectively maintained for 0.3 h, with a total duration of 1.8 h. With a 500 W gradient, gradual heating is achieved. The heating rate is controlled at 20 °C / h, and the temperature is controlled at 55 - 91 °C. After the full-cycle maintenance is completed, naturally cool it to room temperature to complete the maintenance.

[0097] The difference between Comparative Example 3 and Example 2 is that in step S4, three-stage microwave maintenance is not adopted, but two-stage microwave maintenance is used. The steel slag cement concrete mixture C obtained in step S3 is placed in a microwave maintenance device for primary microwave maintenance. In the primary microwave maintenance conditions, the continuous microwave heating maintenance method is adopted, and microwave with a frequency of 2450 MHz and a power of 3000 W is continuously maintained for 0.5 h. The heating rate is controlled at 10 °C / h, and the temperature is controlled at 50 - 55 °C. After the primary maintenance is completed, carry out secondary microwave maintenance. The secondary microwave maintenance adopts the intermittent microwave heating maintenance method. The maintenance frequency is set at 3500 MHz, the power is 5000 W, with a 10-minute cycle. Each cycle heats for 5 minutes and stops for 5 minutes. The total cycle duration is 2.5 h, and the temperature is controlled at 55 - 90 °C. After the full-cycle maintenance is completed, naturally cool it to room temperature to complete the maintenance.

[0098] The difference between Comparative Example 4 and Example 2 is that in step S4, three-stage microwave curing is not adopted, and only continuous microwave heating curing method is used. The curing time is 3 h, the frequency is set at 2450 MHz, the power is set at 3000 W, and the maximum curing temperature is maintained at 90 °C.

[0099] The difference between Comparative Example 5 and Example 2 is that in step S4, three-stage microwave curing is not adopted, and only intermittent microwave heating curing method is used. The curing time is 3 h, with a 10-minute cycle. It is heated for 5 minutes and stopped for 5 minutes in each cycle. The frequency is set at 3500 MHz, the power is set at 4000 W, and the maximum curing temperature is maintained at 90 °C.

[0100] According to the methods described in Examples 2-6 and Comparative Examples 1-5, cube specimens with dimensions of 100 mm×100 mm×100 mm were made with reference to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", and the 72-hour compressive strength and 72-hour splitting tensile strength values of the cube specimens were measured. The test results are shown in Table 1.

[0101] Table 1 Performance test results of each example and comparative example

[0102]

[0103] Examples 2-6 demonstrate the influence of different microwave curing parameter combinations on the properties of steel slag cement concrete. Each example is different in terms of microwave frequency, power, curing time, heating rate, etc., resulting in differences in the compressive strength and splitting tensile strength of the concrete. For example, the compressive strength of Example 3 is 56.2 MPa and the splitting tensile strength is 4.3 MPa; the compressive strength of Example 5 reaches 56.8 MPa and the splitting tensile strength is 4.3 MPa, indicating that under specific microwave curing conditions, the concrete performance is better.

[0104] Comparative Example 1 uses a standard curing box for curing. Although the curing time is long (72 h), the compressive strength of the concrete is only 37.2 MPa and the splitting tensile strength is 3.0 MPa, which is much lower than the performance indexes in the examples, indicating that the microwave curing method has significant advantages in improving the early strength of concrete.

[0105] Comparative Examples 2-5 adopt different microwave curing strategies, such as two-stage microwave curing, only continuous microwave heating or only intermittent microwave heating, etc. Compared with Example 2, there are also certain differences in the concrete performance. For example, the compressive strength of Comparative Example 2 is 47.6 MPa and the splitting tensile strength is 3.9 MPa; the compressive strength of Comparative Example 4 is 47.2 MPa and the splitting tensile strength is 3.9 MPa. This shows that the three-stage microwave curing method (initial stage, middle stage, later stage) is more effective in improving the comprehensive performance.

[0106] By comparing the performance test results of the examples and the comparative examples, the conclusion can be drawn that the use of the three-stage microwave curing method can significantly improve the compressive strength and splitting tensile strength of steel slag cement concrete. A reasonable combination of microwave frequency, power, curing time, and heating rate is the key factor for achieving high-performance concrete. In practical engineering applications, appropriate microwave curing parameters should be selected according to the specific concrete mix ratio, raw material characteristics, and requirements for the final performance.

[0107] Compared with the existing curing methods, the curing method of the present invention can accelerate the hydration reaction rate: by rapidly and uniformly heating the concrete with microwaves, the hydration rate of cement is significantly increased, while traditional curing methods (such as watering and steam curing) often require a long time to achieve the same hydration effect. This enables microwave curing to promote strength development in a shorter time.

[0108] Compared with the existing curing methods, the curing method of the present invention can improve the early strength of concrete: microwave curing can make the concrete reach a higher strength in a shorter time. The strength improvement of steel slag concrete under microwave curing is more obvious than that under traditional curing methods, especially in the early stage of concrete, which can significantly shorten the curing time.

[0109] Compared with the existing curing methods, the curing method of the present invention can save energy and time: microwave curing has a high energy conversion efficiency and does not require a large supply of heat and water like traditional steam curing, which can save energy and reduce the dependence on equipment and materials in traditional curing methods, improving production efficiency.

[0110] Compared with the existing curing methods, the curing method of the present invention has stronger uniformity and controllability: microwave energy can be more evenly distributed in each part of the concrete, thereby reducing temperature gradients and stress concentrations, and avoiding cracks and quality unevenness problems caused by excessive local temperature differences in traditional curing.

[0111] Compared with the existing curing methods, the curing method of the present invention is more environmentally friendly: traditional curing methods may consume a large amount of water and energy, while microwave curing reduces the dependence on water and resources, helps reduce the environmental burden, and meets the requirements of modern green building.

[0112] The implementation of the present invention not only helps to improve the performance of steel slag cement concrete, but also provides new technical support for sustainable development and the application of green building materials. In practical engineering, microwave accelerated curing of steel slag cement concrete can greatly improve construction efficiency and reduce costs, and has broad application prospects.

[0113] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An accelerated curing method for steel slag cement concrete based on three - stage microwave control, characterized in that: It includes the following steps: S1: Pour ordinary Portland cement, silica fume, and steel slag-based solid waste into a planetary mixer and dry mix for 1 min to obtain mixture A; S2: Add river sand, steel slag sand, limestone gravel, and steel slag coarse aggregate to mixture A and dry mix for 2 min to obtain mixture B; S3: Mix polycarboxylate superplasticizer and water, and slowly add them to mixture B in two portions, and mix for 2 min at a temperature of 10 - 30 °C to obtain steel slag cement concrete mixture C; S4: Pour the steel slag cement concrete mixture C out of the mixer and evenly pour it into a test mold, and place it in a microwave curing device to perform initial microwave accelerated curing, intermediate microwave curing, and final microwave curing in sequence; In step S4, the time of the initial microwave accelerated curing is 0.4 - 0.8 h, the temperature is controlled between 45 - 60 °C, the frequency used for the initial microwave curing is set at 1500 - 3000 MHz, the power is set at 1000 - 5000 W, and the heating rate is set at 10 - 20 °C / h; In step S4, the time of the intermediate microwave curing is 0.5 - 1.0 h, the temperature is controlled between 50 - 75 °C, the frequency used for the intermediate microwave curing is set at 2450 - 5000 MHz, the power is set at 2000 - 5000 W, and the heating rate is set at 10 - 20 °C / h; The time of the final microwave curing is 0.5 - 1.0 h, the temperature is controlled between 70 - 90 °C, the frequency used for the final microwave curing is set at 2450 - 5000 MHz, the power is set at 3000 - 5000 W, and the heating rate is set at 15 - 20 °C / h; S5: After the final curing is completed, remove the concrete member from the microwave curing device to demold it, and then perform natural cooling to room temperature to complete the curing.

2. The accelerated curing method of steel slag cement concrete based on three - stage microwave control according to claim 1, wherein: In step S1, the raw material composition by weight is 10.2 - 11.8 parts of ordinary Portland cement, 1.0 - 1.4 parts of silica fume, and 9.7 - 11.3 parts of steel slag-based solid waste.

3. A method for accelerating the curing of steel slag cement concrete based on three - level microwave control according to claim 2, characterized in that: In step S1, the steel slag-based solid waste includes steel slag powder, slag, raw ash, desulfurized gypsum, and silica fume; 100 parts of steel slag-based solid waste include 31.8 - 42.2 parts of steel slag powder, 19.1 - 25.9 parts of slag, 14.2 - 19.8 parts of raw ash, 13.5 - 17.5 parts of desulfurized gypsum, and 7.7 - 9.4 parts of silica fume.

4. A method for accelerating the curing of steel slag cement concrete based on three - stage microwave control according to claim 2, characterized in that: In step S2, the raw material composition by weight is 26.2 - 28.4 parts of fine aggregate, 18.8 - 22.9 parts of limestone gravel, and 19.9 - 24.5 parts of steel slag coarse aggregate.

5. A method for accelerating the curing of steel slag cement concrete based on three-stage microwave control according to claim 4, characterized in that: In step S2, the fine aggregate includes river sand and steel slag sand; 100 parts of fine aggregate include 40 - 60 parts of river sand and 40 - 60 parts of steel slag sand.

6. A method for accelerating the curing of steel slag cement concrete based on three-stage microwave control according to claim 5, characterized in that: In step S3, the raw material composition by weight is 0.3 - 0.4 parts of polycarboxylate superplasticizer and 6.2 - 6.3 parts of water.

7. A method for accelerating the curing of steel slag cement concrete based on three-stage microwave control according to any one of claims 1-6, characterized in that: The polycarboxylate superplasticizer is composed of a mixture of acrylic acid, methacrylic acid, maleic anhydride, polyoxyethylene allyl ester, polyoxyethylene methacrylate, polyoxyethylene acrylate, water, etc.

8. A method for accelerating the curing of steel slag cement concrete based on three - stage microwave control according to any one of claims 1 - 6, characterized in that: In step S2, the stirring speed is 60 - 100 r / min, and after reaching the stirring time, it is cast into blocks.

9. A method for accelerating the curing of steel slag cement concrete based on three - level microwave control according to any one of claims 1 - 6, characterized in that: In step S4, the initial microwave curing adopts the continuous microwave heating curing method; The medium-term microwave curing adopts the microwave gradient heating curing method, with 500W as a gradient to achieve step-by-step temperature increase; The late-stage microwave curing continues to adopt the intermittent microwave heating curing method, with 10 minutes as a cycle, heating for 5 minutes and stopping for 5 minutes in each cycle. The total cycle duration is 0.5 - 1h, the heating rate is controlled at 15 - 20°C / h, and the temperature is controlled at 70 - 90°C.

10. A method for accelerating the curing of steel slag cement concrete based on three-stage microwave control according to any one of claims 1-6, characterized in that: The microwave curing equipment includes a microwave source, a waveguide, a cavity, and a control system. The microwave source can generate microwaves with a frequency of 1500 - 5000MHz and a power of 1000 - 5000W, and transmits the microwaves generated by the microwave source to the cavity through the waveguide. The cavity is used to place the steel slag cement concrete components; the control system can accurately control the frequency, power, and curing time of the microwaves, as well as the temperature and heating rate in the cavity.

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