Preparation method of geopolymer cementing material excited by solid alkali one-step method

Abstract

The invention provides a preparation method of a geopolymer cementing material excited by a solid alkali one-step method, belongs to the technical field of geopolymer cementing materials, and solves the problems of high cost, high carbon emission and environmental pollution caused by use of cement in road maintenance engineering, high transportation cost of a liquid alkali activator, difficulty in low-temperature construction in winter and the like. The preparation method comprises the following steps: firstly, uniformly mixing fly ash, blast furnace slag, boric acid powder and mold-adjusted solid sodium silicate powder in a stirring pot, adding a certain amount of tap water, quickly stirring to form geopolymer neat paste, slowly adding polypropylene fibers into the geopolymer neat paste, and slowly stirring to uniformly distribute, so as to prepare a geopolymer cementing material; the optimal boric acid and polypropylene fiber mixing amount is comprehensively evaluated by measuring the setting time, fluidity, compressive strength and breaking strength of the geopolymer cementing material. According to the technical scheme provided by the invention, the geopolymer cementing material which is excellent in mechanical property, convenient to construct, small in low-temperature influence, economical and environment-friendly can be prepared, and the economic and social benefits are remarkable.

Description

Technical Field

[0001] The present application discloses a method for preparing a geopolymer gelling material by one-step activation of a solid alkali, and belongs to the technical field of geopolymer gelling materials. Background Art

[0002] The steady economic growth in my country has led to the continuous expansion of highway construction. By the end of 2023, the total mileage of highways in my country has reached 5.4368 million kilometers, and the highway maintenance rate is as high as 99.90%. my country's highway network is entering a large-scale maintenance and repair stage. Therefore, it is particularly important to carry out timely maintenance and repair of sections with aging and serious damage.

[0003] In my country, road construction mainly relies on cement as a binder. However, the production process of cement involves high-temperature calcination of limestone, which not only consumes a lot of energy, but also produces a lot of CO2. The CO2 emissions generated by the cement production stage in the entire construction process in my country are about 1.23 billion tons, accounting for 44% of the total emissions of building materials production, second only to the steel industry. As the greenhouse effect intensifies, the global climate faces severe challenges. As one of the main greenhouse gases, the reduction of CO2 emissions is crucial to mitigating climate change.

[0004] In order to reduce climate pollution, a new type of cementitious material - geopolymer, has become a hot topic of research. It uses industrial solid waste as the main raw material, and under the action of stimulants such as water glass, through depolymerization, polymerization, and condensation reactions, an inorganic high molecular polymer with a three-dimensional network structure is formed. This material has the characteristics of high early strength, good fluidity, and excellent impermeability. In addition, geopolymer cementitious materials do not require clinker burning, and the production process has low energy consumption. The carbon emissions in the geopolymer synthesis process are only 1 / 10 to 1 / 5 of the production of cement, and it is considered to be a "green" alternative to cement materials.

[0005] At present, domestic and foreign scholars generally use liquid water glass and hydroxide as activators for geopolymer gelling materials. Research on alkaline activators mainly focuses on the types and concentrations of alkaline activators. Studies have found that when the sodium hydroxide (potassium hydroxide) solution contains soluble silicates such as water glass, it is beneficial to increase the silicon-aluminum ratio of the material. At the same time, compared with the use of hydroxide as an activator alone, the reaction rate is faster and the formed geopolymer has better performance. The modulus of the activator is adjusted by adding sodium hydroxide (potassium hydroxide). The more hydroxide is added, the lower the modulus and the stronger the alkalinity of the activator. Therefore, if the modulus is too high, the alkalinity of the activator will be weakened, which will affect the progress of the polycondensation reaction. However, when the modulus is lower than 1.2, the concentration of the activator becomes too large, which may eventually lead to the formation of insoluble white SiO2 gel, which will reduce the effect of alkali excitation.

[0006] However, whether in production or construction, the configuration of liquid alkali activators poses operational safety risks and is not conducive to long-distance transportation. Especially in the cold winter, low temperatures have a significant impact on liquid alkali activators, which can seriously damage the performance of geopolymer cementitious materials. In contrast, solid alkali activators can be mixed and stirred with precursor powders. When used, only water needs to be added to mix, which is more convenient to operate. In addition, the heat generated by the reaction of the activator and water can effectively offset the negative impact of cold winter weather on geopolymer condensation.

[0007] Therefore, the present application provides a method for preparing a solid alkali one-step activated geopolymer cementitious material. First, the geopolymer precursor fly ash, blast furnace slag and solid sodium silicate adjusted with potassium hydroxide are placed in a stirring pot, stirred at 125 rpm for 1 minute to mix the various powders in the stirring pot evenly, and then a certain amount of tap water is added to the stirring pot, and stirred at 285 rpm for 6 minutes to obtain a solid alkali one-step activated geopolymer cementitious material. After measuring the setting time, fluidity, compressive strength and flexural strength of the geopolymer, the above steps are repeated, and a certain amount of boric acid powder and polypropylene fiber are added to make the performance of the geopolymer cementitious material meet the requirements of relevant standard technologies. The application of the present application can not only effectively replace cement as a binder for road construction and reduce CO2 emissions, but also solve the inconvenience of liquid activators during transportation and low-temperature construction in winter, reduce the transportation cost of construction, and improve the convenience of construction. Summary of the invention

[0008] (1) Technical issues

[0009] The purpose of the present application is to provide a method for preparing a solid alkali one-step activated geopolymer cementitious material. The geopolymer cementitious material prepared by the method can effectively replace cement as a binder for road projects, reduce CO2 emissions, and solve the problems of high cost, high carbon emissions, and environmental pollution caused by the use of cement in road maintenance and repair projects, as well as high transportation costs of liquid alkali activators and difficulties in construction at low temperatures in winter, thereby preparing a green cementitious material that can replace cement.

[0010] (2) Technical solution

[0011] In order to solve the problems of high cost, high carbon emissions, environmental pollution caused by the use of cement in road maintenance and repair projects, high transportation cost of liquid alkali activators, and difficulty in low-temperature construction in winter. The technical solution of this application is as follows: First, the fly ash, blast furnace slag and solid sodium silicate powder of the same quality as the precursor of the geopolymer are placed in a stirring pot, and stirred at 125 rpm for 1 minute to mix the various powders in the stirring pot evenly. Then, a certain amount of tap water is added to the stirring pot, and stirred at 285 rpm for 6 minutes to react the precursor powder with the activator to form a stable geopolymer slurry, and the setting time and fluidity of the geopolymer slurry are measured. Then, the prepared geopolymer slurry is poured into a test mold, poured and vibrated, and maintained at a constant temperature and humidity, and its compressive strength and flexural strength are tested after 3 days, 7 days and 28 days respectively. Finally, the above steps were repeated to further optimize the preparation method by adjusting the setting time, fluidity, flexural strength and compressive strength of the geopolymer cementitious material by adding a certain amount of boric acid powder and polypropylene fiber.

[0012] (3) Beneficial effects

[0013] With the rapid growth of my country's economy, as one of the infrastructures for economic development, the scale of the highway network is also expanding continuously. Every year, about 100,000 kilometers of roads need to be repaired. Most road repairs use cement as a binder. However, cement production not only consumes a lot of energy, but also produces a lot of CO2, which pollutes the environment and violates the concept of sustainable green development. At present, some scholars have used geopolymers to replace cement as a binder and have made corresponding progress. However, there are still some problems on how to apply it to road construction more efficiently and conveniently.

[0014] The present application provides a method for preparing a solid alkali one-step excited geopolymer cementitious material. First, fly ash, blast furnace slag, boric acid powder and sodium silicate powder after mold adjustment are evenly mixed in a stirring pot, a certain amount of tap water is added and quickly stirred to form a geopolymer slurry, polypropylene fiber is slowly added to the geopolymer slurry and slowly stirred to make the polypropylene fiber evenly distributed in the geopolymer slurry, and a geopolymer cementitious material is prepared. Compared with liquid water glass alkali excited geopolymer, this construction method is simpler to operate and more suitable for road construction. In addition, the reaction process releases a certain amount of heat, which can offset the negative impact of low temperatures in winter on road construction. This method can prepare a geopolymer cementitious material with excellent performance. When applied to road construction, it can effectively replace cement as a binder in road construction, thereby reducing CO2 emissions, helping to achieve dual carbon goals, and solving the problems of environmental pollution caused by road construction, high transportation costs of liquid alkali activators, and difficulties in low-temperature construction in winter, with significant economic, social and environmental benefits. DETAILED DESCRIPTION

[0015] The present application provides a one-step solid alkali-activated geopolymer gelling material preparation method, the specific implementation steps are as follows:

[0016] (1) Weigh 600 g of fly ash and blast furnace slag, two geopolymer precursor raw materials, respectively, and pour them into a stirring pot. Then weigh 160 g of solid sodium silicate powder whose modulus is adjusted to 1.2 by potassium hydroxide as an activator. Add the activator into the stirring pot containing the geopolymer precursor, and stir at 125 rpm for 1 minute to evenly mix the various powders in the stirring pot.

[0017] (2) adding 453 g of tap water to the stirring pot of step (1) according to the water-binder ratio of the geopolymer slurry of 0.32, stirring at 125 rpm for 30 seconds, and then stirring at 285 rpm for 6 minutes to allow the precursor powder and the activator to fully react to form a stable geopolymer slurry, and measuring the setting time and fluidity of the geopolymer slurry;

[0018] (3) pouring the geopolymer slurry prepared in step (2) into a test mold with a size of 40×40×160 mm, vibrating it on a vibration table for 1 minute to fully eliminate bubbles in the geopolymer slurry, leaving it to stand for 24 hours, then demolding it and curing it in a standard curing box at a temperature of 20° C. and a relative humidity of 95%, and measuring the compressive strength and flexural strength after 3 days, 7 days and 28 days, respectively, to verify the mechanical properties of the geopolymer cementitious material stimulated by the solid alkali one-step method;

[0019] (4) adding boric acid powder to a stirring pot, repeating the operations of step (1) and step (2) to form a geopolymer slurry, slowly adding polypropylene fibers to the geopolymer slurry, and stirring at 125 rpm for 2 minutes to uniformly distribute the polypropylene fibers in the geopolymer slurry, thereby obtaining a geopolymer cementitious material having a slow setting and toughening effect, and measuring the fluidity and setting time of the geopolymer cementitious material;

[0020] (5) Repeat the method of step (3) to measure the compressive strength and flexural strength of the geopolymer cementitious material prepared in step (4), comprehensively evaluate the effects of adding boric acid powder and polypropylene fiber on the setting time, fluidity, compressive strength and flexural strength of the geopolymer cementitious material, determine the optimal boric acid content and polypropylene fiber content, and determine the preparation method of the solid alkali one-step activated geopolymer cementitious material so that the solid alkali one-step activated geopolymer cementitious material meets the requirements of road construction specifications.

Claims

1. A method for preparing a geopolymer gelling material by a solid alkali one-step method, characterized in that The specific steps of this method are as follows: (1) Weigh 600 g of fly ash and blast furnace slag, two geopolymer precursor raw materials, respectively, and pour them into a stirring pot. Then weigh 160 g of solid sodium silicate powder whose modulus is adjusted to 1.2 by potassium hydroxide as an activator. Add the activator into the stirring pot containing the geopolymer precursor, and stir at 125 rpm for 1 minute to evenly mix the various powders in the stirring pot. (2) adding 453 g of tap water to the stirring pot of step (1) according to the water-binder ratio of the geopolymer slurry of 0.32, stirring at 125 rpm for 30 seconds, and then stirring at 285 rpm for 6 minutes to allow the precursor powder and the activator to fully react to form a stable geopolymer slurry, and measuring the setting time and fluidity of the geopolymer slurry; (3) pouring the geopolymer slurry prepared in step (2) into a test mold with a size of 40×40×160 mm, vibrating it on a vibration table for 1 minute to fully eliminate bubbles in the geopolymer slurry, leaving it to stand for 24 hours, then demolding it and curing it in a standard curing box at a temperature of 20° C. and a relative humidity of 95%, and measuring the compressive strength and flexural strength after 3 days, 7 days and 28 days, respectively, to verify the mechanical properties of the geopolymer cementitious material stimulated by the solid alkali one-step method; (4) adding boric acid powder to a stirring pot, repeating the operations of step (1) and step (2) to form a geopolymer slurry, slowly adding polypropylene fibers to the geopolymer slurry, and stirring at 125 rpm for 2 minutes to uniformly distribute the polypropylene fibers in the geopolymer slurry, thereby obtaining a geopolymer cementitious material having a slow setting and toughening effect, and measuring the fluidity and setting time of the geopolymer cementitious material; (5) Repeat the method of step (3) to measure the compressive strength and flexural strength of the geopolymer cementitious material prepared in step (4), comprehensively evaluate the effects of adding boric acid powder and polypropylene fiber on the setting time, fluidity, compressive strength and flexural strength of the geopolymer cementitious material, determine the optimal boric acid content and polypropylene fiber content, and determine the preparation method of the solid alkali one-step activated geopolymer cementitious material so that the solid alkali one-step activated geopolymer cementitious material meets the requirements of road construction specifications.