A high-performance repair cement based on alkali-activated cementitious materials and its preparation method

Abstract

This invention provides a high-performance repair cement based on alkali-activated cementitious materials and its preparation method, relating to the field of cement technology. The repair cement of this invention is composed of the following raw materials by mass percentage: 70%~80% composite precursor, 13%~14% composite activator, and 8%~9% admixtures; the sum of the mass percentages of the above raw materials is 100%; the composite precursor is composed of slag, steel slag, fly ash, and grinding aid; the composite activator is composed of sodium silicate, sodium carbonate, and calcium oxide; and the admixtures are composed of desulfurized gypsum and water-reducing agent. The high-performance repair cement of this invention has the characteristics of high early strength, low shrinkage, and good crack resistance, and can meet the requirements of conventional engineering for rapid repair cement.

Description

Technical Field

[0001] This invention provides a high-performance repair cement based on alkali-activated cementitious materials and its preparation method, belonging to the field of cement technology. Background Technology

[0002] Alkali-activated cementitious materials are a new type of cementitious material produced by activating waste residues (such as slag, fly ash, steel slag, and metakaolin) with pozzolanic activity using an alkaline activator. Through fracture depolymerization and condensation reactions, they exhibit a certain strength. Alkali-activated cementitious materials offer advantages such as rapid hardening and early strength, high bond strength, strong corrosion resistance, high impermeability, and environmental friendliness, meeting some of the requirements for rapid repair cement.

[0003] Chinese invention patent CN111646740A discloses a novel rapid repair cement based on magnesium oxysulfate cementitious material and its preparation method, using lightly calcined magnesium oxide powder, magnesium sulfate solution, and aluminate cement clinker. Compared with this patent, its production cost is higher, its environmental performance is worse, and the large amount of magnesium oxide added in this patent easily causes problems such as poor stability. Patent CN106699037A discloses a geopolymer grouting material, using stone powder, fly ash, slag, and microsilica as precursors, and water glass and sodium hydroxide as alkali activators to prepare the geopolymer grouting material. This patent has the advantages of stable and adjustable performance, wide applicability, and simple operation. However, its early strength is significantly insufficient (1-day compressive strength is less than 30 MPa), and the problems of large shrinkage, easy cracking, and efflorescence of alkali-activated cementitious materials are not solved.

[0004] Chinese invention patent CN111646740A discloses a basalt fiber reinforced geopolymer composite grout and its preparation method. This composite grout uses fly ash, slag, and clay as precursors, and water glass and sodium hydroxide as alkaline activators. Because these three precursors are untreated and have low inherent activity, the patent uses a large amount of activator (40-80 parts water glass and 5-10 parts sodium hydroxide), which not only increases the cost of the grout but may also lead to problems such as severe efflorescence later on.

[0005] Therefore, current alkali-activated cementitious materials still have shortcomings, such as unstable precursor sources, large shrinkage, poor crack resistance, and severe efflorescence, which significantly limit their application in the field of rapid repair. Therefore, developing cement suitable for rapid repair applications to address these shortcomings of alkali-activated cementitious materials has broad application prospects. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a high-performance repair cement based on alkali-activated cementitious materials and its preparation method. The present invention is achieved by the following technical solution:

[0007] A high-performance repair cement based on alkali-activated cementitious materials, composed of the following raw materials by mass percentage:

[0008] Composite precursor 70%–80%,

[0009] Composite activator 13%–14%,

[0010] Additives 8%–9%; the sum of the mass percentages of the above raw materials is 100%;

[0011] The composite precursor is composed of slag, steel slag, fly ash and grinding aid;

[0012] The composite activator is composed of sodium silicate, sodium carbonate and calcium oxide;

[0013] The additive consists of desulfurized gypsum and a water-reducing agent.

[0014] Preferably, the mass ratio of slag, steel slag, fly ash and grinding aid in the composite precursor is 4:3:1.5 to 2:0.3.

[0015] Preferably, the mass ratio of sodium silicate, sodium carbonate, and calcium oxide in the composite activator is 2:1:1.

[0016] Preferably, the mass ratio of desulfurized gypsum to water-reducing agent in the admixture is 6:4.

[0017] Preferably, the slag is a highly active S105 grade granulated blast furnace slag powder, wherein the slag contains SiO2 ≥ 30 wt% and CaO ≥ 40 wt%.

[0018] The fly ash contains CaO ≥ 10 wt%, SiO2 ≥ 45 wt%, and Al2O3 ≥ 35 wt%.

[0019] The steel slag has a particle size of 0.1–0.3 μm, and the steel slag contains ≥30% SiO2 and ≥40% CaO.

[0020] Preferably, the sodium silicate has a modulus of 1.3 to 1.8; and the calcium oxide has a particle size of 20 nm to 40 nm.

[0021] Preferably, the water-reducing agent is one of naphthalene-based water-reducing agents or calcium lignosulfonate; the grinding aid is one or a mixture of several of sodium sulfate, sodium chloride, sodium nitrite, and triethanolamine.

[0022] Another object of the present invention is to provide a method for preparing the high-performance repair cement based on alkali-activated cementitious materials, comprising the following steps:

[0023] (1) Weigh the raw materials according to the proportion, mix the slag, steel slag and grinding aid and add them to the ball mill, grind until the particle size is less than 30μm to obtain composite powder;

[0024] (2) Mix the composite powder with fly ash evenly, then calcine at 300℃~400℃ for 30min, cool to room temperature and hold for 10min, then heat to 600℃~800℃ and calcine for 20min, then cool to room temperature to obtain the composite precursor;

[0025] (3) Sodium silicate, sodium carbonate and calcium oxide are mixed evenly in proportion and ground for 15 min to obtain a composite activator. The composite activator has a particle size of less than 1 μm.

[0026] (4) Mix the composite precursor and the composite activator in proportion, then add desulfurized gypsum and water-reducing agent in proportion, and mix well to obtain high-performance repair cement.

[0027] Compared with existing technologies, this invention utilizes the early strength, rapid hardening, high adhesion, and strong erosion resistance of alkali-activated cementitious materials to prepare a high-performance repair cement. This invention makes full use of industrial solid waste, reducing costs while achieving the rational utilization of resources.

[0028] This invention effectively solves the problem of insufficient early strength caused by the low activity of industrial solid waste by leveraging the synergistic effect of composite precursors and composite activators. Similarly, the addition of desulfurized gypsum and water-reducing additives addresses the problems of large shrinkage, poor crack resistance, and potential strength reduction and efflorescence in existing alkali-activated gel materials.

[0029] This invention utilizes the expansion of ettringite generated through the hydration reaction of desulfurized gypsum to partially offset chemical shrinkage. Simultaneously, the prismatic crystals of the unhydrated desulfurized gypsum limit the shrinkage of the C-(A)-SH gel, thus improving the crack resistance of the matrix. Nano-calcium oxide not only reacts with sodium carbonate to form nano-sized calcium carbonate, filling smaller pores and improving crack resistance, but some calcium oxide also reacts with water to form calcium hydroxide, which also has an expansion effect, reducing shrinkage. Furthermore, this invention utilizes the micro-aggregate effect of fly ash, which can also significantly reduce shrinkage.

[0030] This invention significantly increases the activity of the composite precursor through calcination treatment. In the early stages of hydration, the sodium silicate in the composite activator reacts with the hydration reaction of slag and steel slag to rapidly generate CSH gel, providing strength. Simultaneously, sodium carbonate reacts with the active calcium oxide in the precursor to generate calcium carbonate, refining the pore structure and achieving higher early strength, with a 24-hour compressive strength ≥30 MPa. As the hydration reaction progresses, the dissolution of active CaO, SiO2, and Al2O3 in the precursor leads to the generation of more CASH gel and calcium carbonate in the matrix. Furthermore, the addition of desulfurized gypsum results in the formation of ettringite, making the matrix even denser. Therefore, the high-performance repair cement of this invention does not exhibit strength reduction under autoclaving-free conditions, with a 28-day compressive strength exceeding 100 MPa.

[0031] The high-performance repair cement of this invention can still maintain good workability under low water-cement ratio conditions.

[0032] This invention utilizes a powdered composite activator to prepare high-performance repair cement. On one hand, compared to liquid activators, the powdered composite activator increases the dissolution time, thus slowing down the hydration reaction rate. On the other hand, the use of a combination of sodium silicate and sodium carbonate, compared to using either sodium silicate or sodium carbonate alone, also slows down the hydration reaction rate. Therefore, without affecting the final setting time, the initial setting time of this invention's high-performance repair cement is ≥30 minutes, providing convenience for construction.

[0033] The high-performance repair cement prepared by this invention is in powder form, which is convenient for packaging and transportation. When using it, the construction process can be referenced from that of ordinary silicate cement. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in further detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0035] The slag used in the following embodiments and comparative examples of this invention is high-activity S105 grade granulated blast furnace slag powder, wherein the SiO2 content is 33wt%, the CaO content is 45wt%, and the Al2O3 content is 22wt%; the fly ash is Class C, with a CaO content of 15wt%, a SiO2 content of 45wt%, and an Al2O3 content of 40wt%; the steel slag is obtained by fully grinding large-particle steel slag into powder using a ball mill, with a SiO2 content of 30wt%, a CaO content of 60wt%, and a MnO content of 10wt%. The sodium silicate is fast-dissolving powdered sodium silicate with a modulus of 1.5; the sodium carbonate is powdered anhydrous sodium carbonate; and the average grain size of calcium oxide is 30nm.

[0036] Example 1

[0037] This embodiment provides a method for preparing high-performance repair cement based on alkali-activated cementitious materials, the specific steps of which are as follows:

[0038] (1) Weigh the following parts by weight of raw materials:

[0039] 40 parts slag, 30 parts steel slag, 15 parts fly ash, 6 parts desulfurized gypsum, 8 parts sodium silicate, 4 parts sodium carbonate, 4 parts calcium oxide, 4 parts water-reducing agent, and 3 parts grinding aid.

[0040] Among them, the water-reducing agent is a naphthalene-based water-reducing agent and the grinding aid is triethanolamine.

[0041] (2) Weigh out the slag, steel slag and grinding aid, mix them and add them into a ball mill, grind until the particle size is less than 30 μm, and obtain composite powder;

[0042] (3) Mix the composite powder with fly ash evenly, then calcine at 300℃ for 30 min, cool to room temperature and hold for 10 min, then heat to 600℃ and calcine for 20 min, then cool to room temperature to obtain the composite precursor;

[0043] (4) Weigh out sodium silicate, sodium carbonate and calcium oxide and mix them evenly in proportion. Grind for 15 min to obtain a composite activator with a particle size of 0.5 μm.

[0044] (5) The composite precursor and the composite activator are mixed, and then desulfurized gypsum and water-reducing agent are added. After mixing evenly, a high-performance repair cement is obtained.

[0045] Example 2

[0046] This embodiment provides a method for preparing high-performance repair cement based on alkali-activated cementitious materials, the specific steps of which are as follows:

[0047] (1) Weigh the following parts by weight of raw materials:

[0048] 40 parts slag, 30 parts steel slag, 20 parts fly ash, 6 parts desulfurized gypsum, 8 parts sodium silicate, 4 parts sodium carbonate, 4 parts calcium oxide, 4 parts water-reducing agent, and 3 parts grinding aid.

[0049] The water-reducing agent is a naphthalene-based water-reducing agent; the grinding aid is triethanolamine.

[0050] (2) Weigh out the slag, steel slag and grinding aid, mix them and add them into a ball mill, grind until the particle size is less than 30 μm, and obtain composite powder;

[0051] (3) Mix the composite powder with fly ash evenly, then calcine at 400°C for 30 min, cool to room temperature and hold for 10 min, then heat to 700°C and calcine for 20 min, then cool to room temperature to obtain the composite precursor;

[0052] (4) Weigh out sodium silicate, sodium carbonate and calcium oxide and mix them evenly in proportion. After grinding for 15 min, a composite activator with a particle size of 0.5 μm is obtained.

[0053] (5) The composite precursor and the composite activator are mixed, and then desulfurized gypsum and water-reducing agent are added. After mixing evenly, a high-performance repair cement is obtained.

[0054] The high-performance repair cement prepared in Example 2 was tested according to the "Test Method for Crack Resistance of Cement Mortar" (JC / T951-2005), and the results are as follows:

[0055] Comparative Example 1

[0056] A method for preparing repair cement, the specific steps of which are as follows:

[0057] (1) Weigh the following parts by weight of raw materials:

[0058] The composition includes 40 parts slag, 30 parts steel slag, 15 parts fly ash, 6 parts desulfurized gypsum, 8 parts sodium silicate, 4 parts sodium carbonate, 4 parts calcium oxide, and 4 parts water-reducing agent. The water-reducing agent is a naphthalene-based water-reducing agent.

[0059] (2) Weigh out the slag, steel slag and fly ash and mix them evenly to obtain a composite precursor;

[0060] (3) Mix sodium silicate, sodium carbonate and calcium oxide evenly, and grind for 15 minutes to obtain a composite activator;

[0061] The composite precursor, composite activator, desulfurized gypsum, and water-reducing agent are thoroughly mixed and stirred evenly to obtain a repair cement.

[0062] Comparative Example 2

[0063] A method for preparing repair cement, the specific steps of which are as follows:

[0064] (1) Weigh the following parts by weight of raw materials:

[0065] The composition includes 40 parts slag, 30 parts steel slag, 5 parts fly ash, 8 parts sodium silicate, 4 parts sodium carbonate, 4 parts water-reducing agent, and 3 parts grinding aid. The water-reducing agent is a naphthalene-based water-reducing agent. The grinding aid is triethanolamine.

[0066] (2) Weigh out the slag, steel slag and grinding aid, mix them and add them into a ball mill, grind until the particle size is less than 30 μm, and obtain composite powder;

[0067] (3) Mix the composite powder with fly ash evenly, then calcine at 300°C for 30 min, cool to room temperature and hold for 10 min, then heat to 600°C and calcine for 20 min, then cool to room temperature to obtain the composite precursor;

[0068] (4) Sodium silicate and sodium carbonate are mixed evenly and ground for 15 min to obtain a composite activator with a particle size of 0.5 μm;

[0069] (5) Mix the composite precursor, composite activator and water-reducing agent thoroughly and stir evenly to obtain a repair cement.

[0070] The repair cements prepared in Examples 1-2 and Comparative Examples 1-2 were subjected to the following tests:

[0071] I. Initial setting time and final setting time

[0072] Test method: "Test methods for standard consistency water requirement, setting time and soundness of cement" (GB / T1346-2011). The results are shown in Table 1.

[0073] Table 1

[0074] Initial setting time Final freezing time Example 1 32min 45min Example 2 35min 48min Comparative Example 1 38min 55min Comparative Example 2 34min 48min

[0075] II. Compressive Strength

[0076] Test method: "Test methods for standard consistency water requirement, setting time and soundness of cement" (GB / T1346-2011). The results are shown in Table 2.

[0077] Table 2

[0078]

[0079]

[0080] As can be seen from Table 2, the repair cement prepared in Examples 1-2 of the present invention meets the requirements of "Rapid Repair Materials for Cement Concrete Pavement" (JT / T1211.1-2018), while the repair cement prepared in Comparative Examples 1-2 does not meet the requirements of "Rapid Repair Materials for Cement Concrete Pavement" (JT / T1211.1-2018).

[0081] III. 28-day systolic value

[0082] Test method: Cement mortar drying shrinkage test method (JC / T603-2004), the test results are shown in Table 3.

[0083] Table 3

[0084] Shrinkage value Example 1 308με Example 2 295με Comparative Example 1 580με Comparative Example 2 270με

[0085] IV. Time of Initial Crack Appearance

[0086] Test method: According to the "Test Method for Crack Resistance of Cement Mortar" (JC / T951-2005), the results are shown in Table 4.

[0087] Table 4

[0088] Initial crack appearance time Example 1 380min Example 2 405min Comparative Example 1 385min Comparative Example 2 175min

[0089] The test results of Examples 1 and 2 show that the high-performance repair cement of the present invention, composed of composite precursor, composite activator and admixture, has the characteristics of high early strength, low shrinkage and good crack resistance, and can meet the requirements of conventional engineering for rapid repair cement.

[0090] A comparison of Example 1 and Comparative Example 1 shows that Comparative Example 1, due to the lack of grinding and calcination treatment of the composite precursor, resulted in a significant reduction in the early strength of the prepared repair cement, even failing to meet the strength requirements for rapid repair cement. This is mainly attributed to the low activity of the composite precursor, especially steel slag and fly ash, under untreated conditions. With the same amount of alkali activator, the alkali dissolves the precursor more slowly, leading to a reduction in the amount of gel formed during hydration, thus hindering the achievement of rapid hardening and early strength. However, the composite precursor, after grinding and calcination, exhibits increased specific surface area, increasing contact with the alkali activator and accelerating dissolution. Furthermore, grinding and calcination enhance its activity, primarily through the decomposition of calcium carbonate in the precursor to calcium oxide and the increase in amorphous active glassy substances in the system. Therefore, this patent achieves rapid hardening and early strength under the action of the composite activator.

[0091] A comparison of Example 1 and Comparative Example 2 shows that Comparative Example 2, which did not add desulfurized gypsum and nano-calcium oxide and also reduced the amount of fly ash, resulted in a significant increase in the shrinkage and a decrease in the crack resistance of the repair cement. This is mainly due to the following factors: 1. The addition of calcium oxide can react with sodium carbonate to generate nano-sized calcite crystals, which can effectively facilitate the sliding of C-(A)-SH gel. Furthermore, unreacted calcium oxide absorbs water to generate calcium hydroxide, which expands and can offset some of the shrinkage. 2. The addition of desulfurized gypsum reacts with calcium oxide and alumina (present in fly ash and slag) in the system to generate ettringite. As columnar crystals, ettringite not only acts as an expansion agent but also restricts the sliding of C-(A)-SH gel. Unreacted desulfurized gypsum also has an expansion effect. 3. The addition of fly ash allows its micro-aggregate effect to act as a skeleton, limiting gel shrinkage. Moreover, fly ash has high activity, which not only provides a micro-aggregate effect and increases the workability of cement but also has little impact on the early strength of cement. Therefore, this invention optimizes the shrinkage of cement from the nanoscale to the microscale without affecting its strength, thereby enabling the application of alkali-activated cementitious materials in the field of rapid repair.

[0092] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A high-performance repair cement based on alkali-activated cementitious materials, characterized in that, Composed of the following raw materials by mass percentage: Composite precursor 70%~80%, Composite activator 13%~14%, Additives 8%~9%; the sum of the mass percentages of the above raw materials is 100%; The composite precursor is composed of slag, steel slag, fly ash and grinding aid; The composite activator is composed of sodium silicate, sodium carbonate and calcium oxide, and the mass ratio of sodium silicate, sodium carbonate and calcium oxide in the composite activator is 2:1:

1. The admixture is composed of desulfurized gypsum and water-reducing agent, and the mass ratio of desulfurized gypsum to water-reducing agent in the admixture is 6:

4. A method for preparing high-performance repair cement based on alkali-activated cementitious materials includes the following steps: (1) Weigh the raw materials according to the proportion, mix the slag, steel slag and grinding aid and add them into the ball mill, grind until the particle size is less than 30μm to obtain composite powder; (2) The composite powder is mixed evenly with fly ash, then calcined at 300℃~400℃ for 30 min, cooled to room temperature and held for 10 min, then heated to 600℃~800℃ and calcined for 20 min, and cooled to room temperature to obtain the composite precursor; (3) Sodium silicate, sodium carbonate and calcium oxide are mixed evenly in proportion and ground for 15 min to obtain a composite activator. The particle size of the composite activator is less than 1 μm. (4) Mix the composite precursor and the composite activator in proportion, then add desulfurized gypsum and water-reducing agent in proportion, and mix evenly to obtain high-performance repair cement.

2. The high-performance repair cement based on alkali-activated cementitious materials as described in claim 1, characterized in that, The mass ratio of slag, steel slag, fly ash and grinding aid in the composite precursor is 4:3:1.5~2:0.

3.

3. The high-performance repair cement based on alkali-activated cementitious materials as described in claim 1, characterized in that, The slag is a highly active S105 grade granulated blast furnace slag powder, wherein the slag contains SiO2 ≥ 30 wt% and CaO ≥ 40 wt%. The fly ash contains CaO ≥ 10 wt%, SiO2 ≥ 45 wt%, and Al2O3 ≥ 35 wt%. The steel slag has a particle size of 0.1~0.3 μm, and the steel slag contains ≥30% SiO2 and ≥40% CaO.

4. The high-performance repair cement based on alkali-activated cementitious materials as described in claim 1, characterized in that, The sodium silicate has a modulus of 1.3 to 1.8; the calcium oxide has a particle size of 20 nm to 40 nm.

5. The high-performance repair cement based on alkali-activated cementitious materials as described in claim 1, characterized in that, The water-reducing agent is one of naphthalene-based water-reducing agents or calcium lignosulfonate; the grinding aid is one or a mixture of several of sodium sulfate, sodium chloride, sodium nitrite, and triethanolamine.

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