Gelling material for coal-fired slag-based concrete and preparation process of cementing material

Abstract

The invention relates to the technical field of building materials, and discloses a cementing material for coal-fired furnace slag-based concrete and a preparation process thereof.The cementing material is premixed dry powder and comprises the following components: coal-fired furnace slag subjected to mechanical force-chemical composite activation, a core-shell structure slow-release early strength agent, an instantaneous alkaline nanocrystal nucleating agent and an auxiliary exciting agent, and zwitterionic functionalized graphene. The preparation process comprises the following steps: mixing the components by a dry method to obtain premixed dry powder; the dry powder and water are mixed to form slurry, and then the slurry is subjected to phonochemical construction treatment in stages; and finally, performing low-temperature thermal cycle curing on the formed body. According to the invention, through the synergistic effect of a chemical excitation system and a physical field process, the dynamic regulation and control of the rheological property of the slurry and the accurate control of the hydration process are realized, and the prepared cementing material has the characteristics of high early strength, good working performance and high utilization rate of the coal-fired slag.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, in particular to a cementitious material for coal-fired slag-based concrete and a preparation process thereof. BACKGROUND

[0002] As the main solid waste in the process of thermal power generation, coal-fired slag is not only occupying land resources, but also may pose a potential threat to the environment. Utilizing coal-fired slag in the field of building materials, such as a component of cementitious material, is an important way to achieve its high value-added utilization and promote sustainable development.

[0003] However, untreated coal-fired slag is mainly composed of inert glass phase, and its own hydration activity is very low. If it is simply partially replaced by cement as an inert admixture, it will lead to a significant decrease in the early mechanical properties of concrete or mortar, and the proportion of slag is strictly limited, which cannot achieve large-scale effective disposal.

[0004] In order to stimulate the potential activity of coal-fired slag, the existing technology usually adopts the method of chemical activation. One of the mainstream technical routes is to use high-concentration alkaline solution, such as sodium silicate (commonly known as water glass) or sodium hydroxide, as an activator. Although this kind of strong alkali activation system can effectively decompose the glass network of slag, its inherent technical defects are also very prominent. Liquid strong alkali activator has high corrosiveness and high viscosity, which brings safety hazards and operational inconvenience to site construction. At the same time, a large amount of alkali metal ions introduced into the hardened material can easily cause harmful alkali-aggregate reaction, and may lead to durability problems such as shrinkage cracking and surface efflorescence in the later period. In addition, the hydration reaction process of this kind of system is often too violent and difficult to control, resulting in a short working performance window period, fast loss of fluidity, and is not conducive to practical engineering application.

[0005] Another technical route is to use sulfate as the main activator. Although this method avoids some of the drawbacks of strong alkali systems to some extent, the activation process is usually relatively mild, resulting in slow early hydration reaction rate of slag, too long setting time, and insufficient early strength development of hardened body. This defect seriously restricts its application in projects that require rapid construction and mold turnover.

[0006] Therefore, while realizing high proportion utilization of coal-fired slag, the existing technology is difficult to balance the early mechanical properties, long-term durability, working performance of slurry, and safety and convenience of production and use of the material, and there is an urgent need for a technical solution that can systematically solve the above problems. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application provides a cementitious material for coal-fired slag-based concrete and a preparation process thereof, and solves the problems of low early strength, poor paste workability and limited utilization rate of slag caused by the insufficient activation efficiency and uncontrollable hydration process of the existing coal-fired slag-based cementitious material.

[0008] To achieve the above object, the present application provides a cementitious material for coal-fired slag-based concrete and a preparation process thereof.

[0009] The present application provides a cementitious material for coal-fired slag-based concrete, which is a premixed dry powder, and the components thereof comprise, in parts by weight: 60-80 parts of activated coal-fired slag; 5-15 parts of a core-shell structure slow-release early strength agent; 2-8 parts of a transient alkaline nanocrystalline core agent; 5-10 parts of an auxiliary activator; and 0.03-0.08 parts of a zwitterionic functionalized graphene.

[0010] Preferably, the core-shell structure slow-release early strength agent has a specific physical structure, the core phase of which is calcium sulphoaluminate or anhydrous calcium sulphite, and the shell phase of which is a layer of hydrophobic polymer material. The shell plays a physical isolation role for the core phase in the dry powder state and the initial stage of mixing with water, and hinders the contact of the core phase with water.

[0011] Preferably, the transient alkaline nanocrystalline core agent is nanosilica with amino functional groups grafted on the surface. When this component contacts with water, the amino functional groups on the surface undergo hydrolysis reaction to generate hydroxyl ions in the micro-environment around the particles, thereby locally increasing the pH value. At the same time, the nanosilica particles themselves can act as heterogeneous nucleation sites for the generation of hydration products.

[0012] Preferably, the zwitterionic functionalized graphene has positively charged quaternary ammonium salt functional groups and negatively charged carboxylate functional groups covalently connected to the surface of the two-dimensional sheet structure thereof. This structure makes the graphene sheet exhibit ion concentration response behavior in the paste: in the initial stage of paste formation, due to the low ion concentration, the electrostatic repulsion between the graphene sheets is dominant, and the graphene sheets are in a good dispersed state; as other components in the cementitious material dissolve, the ion concentration in the paste increases, and the carboxylate functional groups on the surface of the graphene sheets form ionic bonds with high-valence cations and the quaternary ammonium salt functional groups form ionic bonds with anions, thereby establishing a three-dimensional physical cross-linking network between the graphene sheets. 2+ , Al 3+ , SO4 2- , etc.

[0013] The present application provides a preparation method of the above-mentioned cementitious material for coal-fired slag-based concrete, which comprises the following steps:

[0014] S1. performing mechanical force-chemical complex activation treatment on the coal-fired slag raw material;

[0015] S2. Dry-mixing the activated coal-fired slag obtained in step S1 with the core-shell structure slow-release early strength agent, the instant alkaline nanocrystal core agent, the auxiliary activator and the zwitterion functionalized graphene to obtain the premixed dry powder;

[0016] S3. Mixing the premixed dry powder with water to form a slurry, and performing a staged sonochemical construction treatment on the slurry; and

[0017] S4. Performing low-temperature thermal cycle curing on the shaped slurry.

[0018] Preferably, the mechanical force-chemical complex activation treatment of step S1 specifically refers to co-milling the coal-fired slag and the industrial by-product gypsum as the auxiliary activator by high-energy ball milling. This process introduces defects and active sites in the lattice structure of the coal-fired slag particles by high-frequency mechanical force impact and shearing while increasing the specific surface area of the material.

[0019] Preferably, the staged sonochemical construction treatment of step S3 is specifically performed as follows: first, a first-stage sonochemical treatment is applied at the initial stage of slurry mixing. The ultrasonic waves applied in this stage have the characteristics of high power and low frequency (for example, 20-25 kHz). The cavitation effect generated by the ultrasonic waves can destroy the hydrophobic shell of the core-shell structure slow-release early strength agent, exposing the core phase to the water environment; at the same time, the energy input in this stage can promote the uniform dispersion of the nanoscale components in the slurry. Subsequently, the rheological parameters (such as viscosity or acoustic impedance) of the slurry are obtained by an online monitoring device. When the parameter reaches a preset threshold value (for example, the viscosity of the slurry reaches 3-5 times its initial minimum value), it indicates that a certain structural network has been formed inside the slurry due to ionic crosslinking and preliminary hydration reactions. At this time, the control system switches the sonochemical treatment to the second stage. The ultrasonic waves applied in the second stage have the characteristics of low power and high frequency (for example, 40-50 kHz). The micro-vibration in this stage provides energy for the ordered growth of hydration products and helps to expel the small bubbles wrapped in the structural network of the slurry.

[0020] Preferably, the low-temperature thermal cycle curing of step S4 specifically refers to placing the shaped slurry in an environment with a temperature of 40-50℃ and a relative humidity of not less than 95% for 6-8 hours, and then moving it to a standard room temperature environment for further curing.

[0021] The present application provides a coal-fired slag-based cementitious material for concrete and a preparation process thereof. The present application has the following beneficial effects:

[0022] 1. The invention is realized by the synergistic effect of transient alkaline nanocrystalline nucleating agent and core-shell structure slow-release early strength agent. The former forms high alkaline microzones in situ on the surface of slag particles at the initial stage of water addition and provides nucleation sites to trigger preliminary hydration; the latter releases aluminate components through sonochemical action, which rapidly reacts with gypsum and calcium ions in the system to generate a large amount of needle-like ettringite, forming a stable structural framework in the early stage. Combined with low-temperature thermal cycle curing, the kinetics of the above reactions is further accelerated.

[0023] 2. The invention introduces a large number of lattice defects on the surface of slag particles by high-energy ball milling co-milling of coal-fired slag and gypsum, improving the reactivity of the slag itself. At the same time, the chemical activation system (especially the transient alkaline nanocrystalline nucleating agent) acts on the surface of the activated slag in a local and high-concentration manner, promoting the decomposition of the glassy structure and the dissolution of active substances, thereby achieving effective utilization of slag without relying on a large amount of cement clinker.

[0024] 3. The prepared paste has dynamic self-regulating rheological properties, improving the workability of the paste. This is due to the addition of zwitterionic functionalized graphene. In the initial stage of stirring, the graphene exists in a dispersed state in the paste, giving the paste a low initial viscosity and good flowability; as the hydration reaction proceeds, the ion concentration in the paste increases, and the graphene forms a three-dimensional physical network through the bridging of its surface anion and cation functional groups with the ions in the paste, causing the paste viscosity to increase in time, thereby improving the paste's segregation resistance and bleeding resistance.

[0025] 4. The preparation method of the invention helps to form a more compact hardened body microstructure. In the second stage of the phased sonochemical construction process, low-power, high-frequency ultrasound is applied to the paste that has formed a preliminary structure. This energy input provides favorable conditions for the ordered growth and arrangement of hydration products (such as hydrated calcium silicate gel and ettringite crystals), while also helping to expel the small bubbles trapped in the paste network, reducing the number of harmful pores in the final hardened body and improving the homogeneity and compactness of the matrix.

[0026] 5. The scheme of the invention improves the safety, standardization, and controllability of the production process. The cementitious material is provided in the form of a fully solid pre-mixed dry powder, avoiding direct handling of high-concentration, corrosive liquid alkali activators at the production or use site, reducing safety risks. At the same time, the design of automatically triggering the sonochemical process stage switching based on online monitoring of rheological parameters introduces a closed-loop feedback control, reducing the dependence on operator experience, ensuring the consistency of different batches of products in key preparation steps, and improving the stability of the process and the uniformity of the product quality. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0028] The main raw materials and reagents used in the following examples and comparative examples are as follows, and the reagents not specifically described are commercially available analytical pure or higher grade products.

[0029] Coal-fired furnace slag: coal-fired boiler bottom slag from a certain thermal power plant of China Huaneng Group, which is crushed and sieved to have a particle size of less than 4.75 mm. Its main chemical components (mass percentage) are: SiO240% to 50%, Al2O320% to 30%, CaO 8% to 15%, Fe2O35% to 10%.

[0030] Desulfurization gypsum: a by-product of a flue gas desulfurization system of a certain coal-fired power plant, which mainly contains calcium sulfate dihydrate (CaSO4·2H2O) with a content of not less than 95%.

[0031] CAS No.: 10101-41-4

[0032] Nano-silicon dioxide (SiO2): hydrophilic fumed silica with an average primary particle size of 15 to 20 nm and a BET specific surface area of 180 to 220 m 2 / g.

[0033] CAS No.: 7631-86-9

[0034] Calcium sulfoaluminate clinker: industrial-grade sulfoaluminate cement clinker, whose main mineral phase is calcium sulfoaluminate (Ca4Al6SO 16 ).

[0035] Graphene oxide (GO): single-layer graphene oxide aqueous dispersion prepared by improving the Hummers method, with a concentration of 5 mg / mL.

[0036] (3-aminopropyl)triethoxysilane (APTES): purity ≥98%.

[0037] CAS No.: 919-30-2

[0038] Polystyrene (PS): average molecular weight (Mw) is 35,000 g / mol.

[0039] CAS No.: 9003-53-6

[0040] Sodium hydroxide (NaOH): granular, purity ≥98%.

[0041] CAS No.: 1310-73-2

[0042] Chloroacetic acid (ClCH2COOH): purity ≥ 99%.

[0043] CAS No.: 79-11-8

[0044] (3-Chloro-2-hydroxypropyl)trimethylammonium chloride (CHPTAC): 69 wt.% aqueous solution.

[0045] CAS No.: 3327-22-8

[0046] Other chemical reagents:

[0047] Dichloromethane (CH2Cl2), CAS No.: 75-09-2

[0048] Polyvinyl alcohol (PVA), type 1788 (polymerization degree about 1700, alcoholysis degree about 88%), CAS No.: 9002-89-5

[0049] Anhydrous ethanol (C2H5OH), CAS No.: 64-17-5

[0050] Standard sand: Xiamen ISO standard sand meeting the requirements of GB / T 17671-1999 “Cement mortar strength test method (ISO method)”.

[0051] Water for experiment: deionized water.

[0052] In order to more clearly illustrate the content of the present application, the following will be described through specific examples. It should be understood that these examples are only used to illustrate the present application, and are not used to limit the protection scope of the present application.

[0053] Example 1

[0054] The present example provides a coal-fired slag-based cementitious material and a preparation method thereof.

[0055] S1. Mechanical force-chemical composite activation treatment is performed on the coal-fired slag raw material;

[0056] 70 parts by weight of the coal-fired slag and 5 parts by weight of the desulfurization gypsum heat-treated at 180°C for 2 hours are placed in a planetary ball mill, the ball-to-material mass ratio is set to 15:1, the rotation speed of the ball mill is 400 rpm, and the grinding is performed for a total of 60 minutes.

[0057] S2. The activated coal-fired slag obtained in step S1 is dry mixed with the core-shell structure slow-release early strength agent, the instantaneous alkaline nanocrystalline core agent, the auxiliary excitation agent and the zwitterionic functionalized graphene to obtain the premixed dry powder.

[0058] (1) Preparation of the premixed dry powder

[0059] a. Preparation of transient alkaline nanocrystalline nucleating agent: 10 g of nanosilica powder was added into 500 mL of absolute ethanol and ultrasonically dispersed for 30 min at a power of 300 W and a frequency of 40 kHz. Under mechanical stirring, 2 g of (3- aminopropyl)triethoxysilane was slowly added dropwise into the suspension. After the addition was completed, the mixture was heated to 75 °C and continuously stirred at this temperature for 18 h. After the reaction was completed, the product was separated by centrifugation and washed with deionized water and absolute ethanol three times in turn. The washed solid was dried in a vacuum drying oven at 70 °C for 12 h to obtain a white powdery transient alkaline nanocrystalline nucleating agent.

[0060] b. Preparation of core-shell structure slow-release early strength agent: 10 g of polystyrene was completely dissolved in 100 mL of dichloromethane to form an oil phase solution. 100 g of calcium sulfoaluminate clinker powder with an average particle size of 10 μm was added into the solution and uniformly dispersed in the oil phase by mechanical stirring to form an oil phase suspension. 1 g of polyvinyl alcohol (PVA) was dissolved in 1000 mL of deionized water to form an aqueous phase solution. The above oil phase suspension was added into the aqueous phase solution, and a high-speed shearing emulsifier was used to shear at a speed of 5000 rpm for 10 min to form an O / W emulsion. The emulsion was transferred into a reaction kettle with a stirrer, and continuously stirred at 35 °C to completely evaporate dichloromethane. After the product was solidified, it was filtered, washed with deionized water, and dried at 60 °C for 24 h to obtain a core-shell structure slow-release early strength agent.

[0061] c. Preparation of zwitterionic functionalized graphene (Z-GO): 200 mL of graphene oxide aqueous dispersion with a concentration of 5 mg / mL was taken, and 4 g of sodium hydroxide was added and ultrasonically treated to dissolve it. The system was heated to 90 °C, and 4 g of chloroacetic acid was added, and reacted at this temperature for 3 h. After the reaction was completed, the carboxylated graphene oxide was purified by dialysis. The product was dispersed in water, and 8 g of (3-chloro-2-hydroxypropyl)trimethylammonium chloride (CHPTAC) aqueous solution was added, and reacted at 65 °C for 6 h. After the reaction was completed, the system was dialyzed to be neutral again, and finally freeze-dried to obtain a powdery zwitterionic functionalized graphene.

[0062] d. Activation and blending: the co-milling product was placed in a V-type mixer with 10 parts by weight of the core-shell structure slow-release early strength agent prepared in step b), 5 parts by weight of the transient alkaline nanocrystalline nucleating agent prepared in step a), and 0.05 parts by weight of the zwitterionic functionalized graphene prepared in step c), and low-speed mixed at a speed of 30 rpm for 20 min to obtain a premixed dry powder of Example 1.

[0063] S3. Mix the premixed dry powder with water to form a slurry, and perform a staged sonochemical construction process on the slurry.

[0064] According to the ratio of 450 g of the premixed dry powder of Example 1, 1350 g of standard sand, and 180 g of water (water-binder ratio of 0.40), the premixed dry powder and the standard sand were poured into a stirring pot and stirred slowly for 30 seconds, and then water was added while stirring, and the addition was completed within 60 seconds.

[0065] After the water was added, the sonochemical construction process was immediately started. In the first stage, ultrasonic waves with a frequency of 22 kHz and a sound power density of 1.0 W / cm3were applied, and at the same time, the online viscometer began to monitor the viscosity of the slurry. The trigger threshold T1 was set to 8 Pa·s. When the monitored viscosity of the slurry reached T1, the control system automatically switched the ultrasonic wave parameters to the second stage, with a frequency of 45 kHz and a sound power density of 0.2 W / cm3, and this stage lasted for 120 seconds. 3

[0066] S4. Low-temperature thermal cycle curing of the formed slurry:

[0067] After the sonochemical process was completed, the cement mortar slurry was immediately cast into a 40 mm x 40 mm x 160 mm test mold and vibrated on a vibrating table to form a test piece. The formed test piece was immediately moved into a curing box with a temperature of 45°C and a relative humidity of 98% for 7 hours. Then the test piece was removed, demolded, and transferred to a standard curing room with a temperature of 20±2°C and a relative humidity of not less than 95% for curing until the specified age.

[0068] Example 2

[0069] The preparation method of this example is the same as that of Example 1, except that the composition ratio is different. The composition formula of the premixed dry powder of this example (in parts by weight) is:

[0070] Co-milling product of coal-fired slag and desulfurization gypsum (after heat treatment): 88 parts (of which coal-fired slag 80 parts, desulfurization gypsum 8 parts);

[0071] Core-shell structure slow-release early strength agent: 6 parts;

[0072] Instantaneous alkaline nanocrystalline core agent: 2 parts;

[0073] Zwitterionic functionalized graphene (Z-GO): 0.03 parts.

[0074] Example 3

[0075] The composition formula of this example is exactly the same as that of Example 1. The preparation method is the same as that of Example 1, except that the parameters of the sonochemical construction process and the curing system are different. In this example, the specific parameters of the sonochemical construction process and the curing system are as follows:​

[0076] First stage sonochemical treatment: frequency of 25 kHz, acoustic power density of 1.2 W / cm 3 .

[0077] Trigger threshold T1: set at 10 Pa·s.

[0078] Second stage sonochemical treatment: frequency of 40 kHz, acoustic power density of 0.4 W / cm 3 , duration of 180 seconds.

[0079] Low temperature thermal cycling curing: curing in an environment with temperature of 50℃ and relative humidity of 98% for 6 hours.

[0080] Part III: Comparative Examples

[0081] Comparative Example 1: This comparative example aims to simulate a conventional slag-based cementitious material which does not contain the core technical features of the present invention. The pre-mixed dry powder is composed of 70 parts of un-complexed and un-activated coal combustion slag and 30 parts of ordinary Portland cement (P.O 42.5) by weight fraction. During the preparation of the mortar test piece, the conventional mechanical stirring method is adopted without applying any sonochemical treatment, and the test piece is continuously cured in a standard curing room (temperature of 20±2℃ and relative humidity no less than 95%) until the specified curing age.

[0082] Comparative Example 2: Compared with Example 1, the only difference is that 0.05 parts by weight of ordinary graphene oxide (GO) which is not zwitterionically functionalized is used to replace the same weight of the zwitterionically functionalized graphene (Z-GO). All other component formulations, preparation steps and process parameters are exactly the same as Example 1.

[0083] Comparative Example 3: Compared with Example 1, the only difference is that the step-by-step sonochemical construction process is not adopted during the preparation of the mortar test piece. After adding water, the slurry is only stirred by the same conventional mechanical stirring method as Comparative Example 1, and the total stirring time is the same as the total stirring and sonochemical treatment time of Example 1. All other component formulations, raw material preparation steps and curing regimes are exactly the same as Example 1.

[0084] Part IV: Performance Test Examples

[0085] 4.1 Mechanical property test

[0086] (1) Test method

[0087] This test aims to determine the mechanical properties of the hardened cementitious materials prepared in Examples 1-3 and Comparative Examples 1-3 at different curing ages. The test is strictly conducted in accordance with GB / T 17671-1999 “Cement mortar strength test method (ISO method)”.

[0088] The prism specimens of each group prepared and cured to the specified age (1 day, 3 days, 28 days) were taken out of the curing room. First, the flexural strength test was carried out, and each prism specimen was folded into two sections using the three-point bending method. Subsequently, the two half prism specimens after fracture (each size is about 40mm x 40mm x 80mm) were subjected to compressive strength test. The test results of three specimens were taken for each group of data, and the arithmetic mean was calculated as the final strength value.

[0089] (2) Test results

[0090] The test results of the mechanical properties of the specimens of each group at different ages are summarized in Table 1.

[0091] Table 1: Test results of the mechanical properties of the specimens of each group

[0092]

[0093]

[0094] (3) Summary

[0095] The test data in Table 1 show that the hardened body prepared in Examples 1-3 has significantly higher mechanical properties at early age (1 day, 3 days) and later age (28 days) than Comparative Examples 1-3. This is due to the synergistic effect between the composition and the preparation process of the present application. The local high alkaline environment and nucleation sites provided by the transient alkaline nanocrystalline core agent at the initial water addition stage, combined with the immediate wall-breaking effect of the nucleated shell structure slow-release early strength agent by the first stage sonochemical treatment, together provide the necessary material and energy conditions for early hydration reaction, forming an initial strength framework mainly composed of ettringite, which is the direct reason for the higher early strength values of the examples relative to Comparative Example 1 and Comparative Example 3.

[0096] Comparing the data of Example 1 and Comparative Example 3 can reveal the effect of the phased sonochemical construction process on the final mechanical properties. In Comparative Example 3, although the same chemical components are used, the dispersion efficiency and activation degree of each functional component are lower due to the lack of sonochemical treatment. In contrast, the first stage high-power ultrasound in Example 1 ensures the uniform dispersion of nanomaterials and the effective release of slow-release agents; the second stage low-power, high-frequency ultrasound provides favorable conditions for the ordered deposition of hydration products and the densification of the network structure, which reduces the internal structural defects of the hardened body, thus showing higher mechanical strength at all test ages.

[0097] By comparing the results of Example 1 and Comparative Example 2, the influence of the structure of zwitterionic functionalized graphene on its performance can be explained. In Example 1, due to the unique anionic and cationic functional groups on the surface of the graphene, a uniform three-dimensional physical crosslinking network can be formed when the ion concentration inside the paste increases, which not only improves the workability of the paste, but also provides a uniform template for the growth of hydration products and effectively transmits stress as a nano-enhanced phase. The ordinary graphene oxide used in Comparative Example 2 does not have this ion response characteristic, and it is prone to agglomeration in the paste, resulting in stress concentration points and weak areas inside the hardened body, which is reflected in the fact that all mechanical strength indicators are lower than those of Example 1.

[0098] 4.2 Paste workability test

[0099] (1) Test method

[0100] This test aims to determine the workability of the cementitious material paste prepared in Examples 1-3 and Comparative Examples 1-3, mainly including fluidity and setting time.

[0101] The fluidity test refers to GB / T2419-2005 "Cement mortar fluidity test method". The mortar paste prepared according to the formulation of each group (without standard sand) is loaded into a truncated cone round mold, and after the mold is lifted, the diameters of the paste spreading in two perpendicular directions on the glass plate are measured, and their average value is taken as the fluidity. The initial fluidity of the paste is tested immediately after the water is added and stirred, and the fluidity of the paste is tested again after the paste is left to stand in a sealed container for 30 minutes.

[0102] The setting time test refers to GB / T1346-2011 "Cement standard consistency water consumption, setting time, and stability test method". A Vicat apparatus is used to test the neat paste prepared in each group, and the time when the test needle sinks into the neat paste to a distance of 4±1mm from the bottom plate is recorded as the initial setting time, and the time when the test needle sinks into the neat paste not more than 0.5mm is recorded as the final setting time.

[0103] (2) Test results

[0104] The workability test results of the paste in each group are summarized in Table 2.

[0105] Table 2: Workability test results of paste in each group

[0106]

[0107]

[0108] (3) Summary

[0109] The data in Table 2 show that the pastes of Examples 1-3 have higher initial fluidity and controllable fluidity loss, as well as moderate setting time. Comparing Example 1 with Comparative Example 2, the former has higher initial fluidity and also higher fluidity retention after 30 minutes. The reason is that the zwitterionic functionalized graphene adopted in Example 1 has both positive and negative charge functional groups on its surface, which generate electrostatic repulsion in the initial low ionic concentration water environment, promoting the highly dispersed graphene sheets and thus giving the paste high fluidity. As hydration proceeds, the ionic concentration in the paste increases, and these functional groups form physical cross-linking between the sheets through ionic bonding, leading to a smooth increase in viscosity. The ordinary graphene oxide in Comparative Example 2 does not have this property, and it easily flocculates unevenly in the ionic environment, resulting in faster and uncontrollable loss of paste fluidity.

[0110] Comparing Example 1 with Comparative Examples 1 and 3 can illustrate the effect of the chemical activation system and the preparation process of the present application on the setting time. In Example 1, the transient alkaline nanocrystalline core agent and the slow-release early strength agent released by sonication at a certain time work together to make the start and acceleration stages of the hydration reaction proceed in an orderly manner, thus obtaining a shorter and more concentrated setting time than Comparative Example 1 (conventional cement hydration) and Comparative Example 3 (poor dispersion of functional components and low activation efficiency). This shows that the composition design of the present application can effectively regulate the progress of the hydration kinetics.

[0111] By comparing the data of Example 1 and Comparative Example 3, the effect of the sonication construction process on the workability of the paste can be determined. The higher initial fluidity of the paste of Example 1 is directly due to the high-efficiency deagglomeration and dispersion of all powder components, especially nanoscale materials, in the system by the high-power sonication in the first stage. In Comparative Example 3, the materials are not sufficiently dispersed due to the lack of this process, resulting in a significantly lower initial fluidity than Example 1. This difference in the initial state also affects the uniformity of the subsequent hydration reaction, which is one of the reasons why the setting time is longer than that of Example 1.

Claims

1. A cementitious material for coal-fired slag-based concrete, characterized by, The cementing material is a premixed dry powder, and its components include, by weight fraction: activated coal-fired slag: 60-80 parts; core-shell structure slow-release early strength agent: 5-15 parts; instant alkaline nanocrystalline nucleating agent: 2-8 parts; auxiliary activator: 5-10 parts; zwitterionic functionalized graphene: 0.03-0.08 parts.

2. A cementitious material for coal-fired slag-based concrete according to claim 1, characterized in that, The core-shell structure slow-release early strength agent has a core of calcium sulfoaluminate or anhydrous calcium sulfite and a shell of a hydrophobic polymer material.

3. A cementitious material for coal-fired slag-based concrete according to claim 1, characterized in that, The instant alkaline nanocrystalline nucleating agent is nanosilica with amino groups grafted on the surface.

4. A cementitious material for coal-fired slag-based concrete according to claim 1, characterized in that, The surface of the zwitterionic functionalized graphene is simultaneously grafted with positively charged quaternary ammonium salt functional groups and negatively charged carboxylate functional groups.

5. A process for the preparation of a cementitious material for coal-fired slag-based concrete, characterized in that, A cementing material for coal-fired slag-based concrete according to any one of claims 1-4, comprising the following steps: S1. mechanically-chemically compound activating the coal-fired slag raw material; S2. dry mixing the activated coal-fired slag obtained in step S1 with the core-shell structure slow-release early strength agent, the instant alkaline nanocrystalline nucleating agent, the auxiliary activator, and the zwitterionic functionalized graphene to obtain a premixed dry powder; S3. mixing the premixed dry powder with water to form a slurry, and performing phased sonication-chemical construction treatment on the slurry; and S4. low-temperature thermal cycle curing the formed slurry.

6. A process for the preparation of a cementitious material for coal-fired slag-based concrete according to claim 5, characterized in that, In step S1, the mechanically-chemically compound activation treatment refers to co-milling the coal-fired slag with industrial by-product gypsum as the auxiliary activator.

7. A process for the preparation of a cementitious material for coal-fired slag-based concrete as claimed in claim 5, wherein the process further comprises the step of: The phased sonication-chemical construction treatment in step S3 includes: ​ applying first-stage sonication-chemical treatment in the initial stage of slurry mixing, characterized by high power and low frequency; when the monitored rheological parameter of the slurry reaches a preset threshold value, switching to second-stage sonication-chemical treatment, characterized by low power and high frequency.

8. A process for the preparation of a cementitious material for coal-fired slag-based concrete according to claim 7, characterized in that, The frequency of the first stage is 20-25 kHz, and the frequency of the second stage is 40-50 kHz.

9. A process for the preparation of a cementitious material for coal-fired slag-based concrete according to claim 7, characterized in that, The rheological parameter is the viscosity or acoustic impedance of the slurry, and the preset threshold value is 3-5 times the initial minimum value of the viscosity of the slurry.

10. A process for the preparation of a cementitious material for coal-fired slag-based concrete as claimed in claim 5, wherein, The low-temperature thermal cycle curing in step S4 refers to curing at 40-50℃ and a relative humidity greater than 95% for 6-8 hours, followed by standard room temperature curing.

Images