A method for reducing shrinkage and cracking of slag-based geopolymer based on humidity control and phase regulation
By adding diatomaceous earth and gypsum-kaolin to slag-based aggregates to generate ettringite crystals and form a micro-framework structure, the shrinkage and early cracking problems caused by moisture loss in slag-based aggregates were solved, achieving significant shrinkage reduction and crack resistance effects and good mechanical properties.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUAZHONG UNIV OF SCI & TECH
- Filing Date
- 2026-04-15
- Publication Date
- 2026-06-26
AI Technical Summary
The significant shrinkage and early cracking of slag aggregates during hydration due to water loss are problems that existing improvement methods are complicated to operate or difficult to match with the expansion reaction rate, which can easily lead to secondary cracking or strength reduction.
By adding a specific proportion of diatomaceous earth to the slag base polymer to construct an internal curing mechanism, and combining gypsum and metakaolin to react in a strongly alkaline environment to generate ettringite crystals, forming a micro-framework structure, controllable expansion is achieved to compensate for shrinkage stress, and a novel eccentric ring test method is used to accurately characterize cracking characteristics.
It significantly reduces drying shrinkage, prolongs cracking time, reduces crack width, and maintains good mechanical properties, avoiding problems caused by delayed expansion reaction or excessive expansion, and has a significant shrinkage reduction and crack resistance effect.
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Figure CN122277205A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of building materials technology, specifically relating to a method for reducing shrinkage and cracking of slag-based polymers based on humidity control and phase regulation. Background Technology
[0002] Slag-based polymers, as an environmentally friendly inorganic cementitious material, are considered an ideal alternative to traditional cement due to their low energy consumption and low carbon dioxide emissions. However, in practical applications, slag-based polymers face challenges such as rapid hydration rates, significant autogenous shrinkage, and substantial drying shrinkage. Without adequate external curing, capillary water rapidly escapes, leading to a sharp drop in internal humidity and generating significant capillary tension, thus triggering substantial shrinkage strain. When this shrinkage strain exceeds the material's early tensile strength, it results in premature cracking, severely impacting the structure's durability, aesthetics, and mechanical properties.
[0003] Existing methods for improving shrinkage cracking in slag-based polymers mainly include enhanced external wet curing and the addition of expansion agents. The former is complex to implement and difficult to implement effectively on-site; the latter suffers from the problem of the expansion reaction rate not matching the matrix shrinkage, easily leading to insufficient or excessive expansion, and may even cause secondary cracking or strength reduction. Therefore, there is an urgent need to develop a novel composite modification method that can autonomously achieve moisture supply within the material and simultaneously generate controllable and moderate expansion to compensate for shrinkage. Summary of the Invention
[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for reducing shrinkage and preventing cracking in slag-based polymers based on humidity control and phase regulation. This application achieves the goal of reducing shrinkage and preventing cracking in slag-based polymers through a diatomaceous earth internal curing mechanism and a gypsum-metakaolin phase regulation mechanism. Furthermore, a novel eccentric ring test method is employed to accurately characterize the cracking characteristics of slag-based polymers, thereby significantly reducing the drying shrinkage rate of the slag-based polymers and greatly delaying the cracking time.
[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for reducing shrinkage and cracking of slag-based polymers based on humidity control and phase regulation involves mixing the following raw materials by mass percentage: 85%–94% slag, 3%–7.5% diatomaceous earth, 2%–5% gypsum, and 1%–2.5% metakaolin to obtain a solid mixture. A composite alkaline activator with a total alkali equivalent of 3–7% is added and stirred into a slurry. After pouring, standard curing, static setting and demolding, the mixture is further cured to the specified age.
[0006] This application constructs an internal curing mechanism by adding a specific proportion of diatomaceous earth (3%–7.5% by mass) to the slag in a slag-based polymer system. Diatomaceous earth has a high specific surface area and strong water absorption, enabling it to absorb and store a large amount of mixing water during the mixing stage. As the slurry hardens and the environment dries, the diatomaceous earth slowly releases the stored water, forming a continuous internal curing effect. This effectively delays the decrease in internal humidity, weakens capillary tension, and physically inhibits drying shrinkage. Experimental results show that this method can significantly reduce the 28-day drying shrinkage value, with a maximum reduction of 39.41%. Simultaneously, the introduction of a specific proportion of gypsum (2%–5% by mass) and metakaolin (1%–2.5% by mass) into the slag-based polymer system, through their interaction with Ca in the system under a strongly alkaline environment… 2+ The reaction produces needle-like ettringite crystals (AFt). The formation of ettringite crystals is accompanied by the binding of a large amount of water of crystallization, resulting in a significant increase in the solid phase volume and controllable early micro-expansion, which effectively offsets part of the shrinkage tensile stress in the slag geopolymer matrix. In addition, the interwoven ettringite crystals form a robust micro-framework structure within the slurry, enhancing the material's resistance to deformation and improving its density.
[0007] Furthermore, the specific surface area of the diatomaceous earth is 20-30 m². 2 / g, with a porosity of 30%~45%.
[0008] Furthermore, the mass ratio of gypsum to metakaolin is 2:1. Metakaolin and gypsum react in situ under a strong alkaline environment to generate ettringite crystals, resulting in controllable micro-expansion and forming a micro-skeleton structure, which compensates for shrinkage stress and ensures the optimal realization of chemical expansion effect.
[0009] Furthermore, the gypsum is dihydrate gypsum or hemihydrate gypsum; the total content of active SiO2 and Al2O3 in the metakaolin is not less than 90 wt.%.
[0010] Furthermore, the composite alkaline activator is prepared by dissolving solid strong sodium oxide in deionized water and then mixing it with a water glass solution; wherein, the total alkaline equivalent (calculated as Na2O) of the composite alkaline activator is 4%, and the modulus of the water glass solution is Ms=1.5.
[0011] Furthermore, the standard maintenance conditions are as follows: temperature 20±2℃, relative humidity RH≥95%.
[0012] Furthermore, the settling time is 24 hours.
[0013] Furthermore, the specified age period is 7 days or 28 days.
[0014] Furthermore, the slag is industrial by-product granulated blast furnace slag dried to constant weight; the diatomaceous earth, gypsum, or metakaolin is a powder raw material dried to constant weight.
[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention constructs an efficient internal curing system by incorporating diatomaceous earth with a mass fraction of 3%–7.5%, which significantly reduces the drying shrinkage of slag-based aggregates caused by moisture loss. The 28-day drying shrinkage value can be reduced by up to 39.41%, effectively suppressing the shrinkage driving force from a physical perspective. At the same time, by introducing gypsum with a mass fraction of 2%–5% and metakaolinite with a mass fraction of 1%–2.5% for phase regulation, gypsum and metakaolinite generate ettringite crystals in situ, producing a controllable micro-expansion effect and forming a micro-skeleton structure. This mechanism not only compensates for shrinkage stress but also enhances the density of the slag-based aggregate matrix. With the synergistic effect of the internal curing provided by diatomaceous earth continuously supplying moisture, the expansion reaction rate and the matrix shrinkage process are dynamically matched, effectively avoiding problems such as insufficient compensation, excessive expansion, secondary cracking, or strength reduction caused by lag or advance of the expansion reaction. Finally, this synergistic mechanism extends the cracking time of slag-based aggregates by 3.8 times and ultimately stabilizes the crack width of slag-based aggregates at 0.03 mm. The level is extremely low (mm). Moreover, the diatomaceous earth, gypsum, and metakaolin used in this invention are all common industrial raw materials or solid wastes. The preparation process is simple, requires no special equipment, and combines technological advancement with good engineering application prospects.
[0016] (2) While achieving excellent volume stability, the mechanical property loss of the present invention is controllable. The 28-day compressive strength of the slag-based polymer with a partial ratio of diatomite, gypsum and metakaolin can be maintained at more than 75% of the benchmark group (slag-based polymer without diatomite, gypsum and metakaolin). Attached Figure Description
[0017] Figure 1 The graphs show the 28-day drying shrinkage displacement curves of the slag-based polymers in Examples 1-4 and Comparative Examples 1-3 of this invention.
[0018] Figure 2 The image shows the XRD pattern of ettringite in Comparative Example 3 of this invention.
[0019] Figure 3 This is a diagram of the eccentric ring mold used in the eccentric ring test to measure the cracking time according to the present invention.
[0020] Figure 4 This is a dimensional diagram of the eccentric ring specimen used in the eccentric ring test to measure the cracking time according to the present invention.
[0021] Figure 5 This is a diagram of the crack penetration time measurement device for testing crack initiation time in the eccentric ring test of the present invention. Detailed Implementation
[0022] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings.
[0023] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as any smaller range between any other stated value or intermediate value within said range, are also included in this invention, and the upper and lower limits of these smaller ranges may be independently included or excluded from the range.
[0024] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.
[0025] Unless otherwise specified, all reagents used in this invention are commercially available, and all methods used are conventional techniques in the art.
[0026] Example 1 A method for reducing shrinkage and resisting cracking in slag-based aggregates based on humidity control and phase regulation includes the following steps: (1) Place the dried granulated blast furnace slag to constant weight with diatomaceous earth, gypsum, and metakaolin in a mixer and stir for at least 1 minute to obtain a solid mixture; wherein, the content of granulated blast furnace slag is 94%; the content of diatomaceous earth is 3%; the content of gypsum is 2%; and the content of metakaolin is 1%. (2) A composite alkaline activator prepared by mixing water glass solution with modulus Ms=1.5 and sodium hydroxide aqueous solution is added to solid mixture A and stirred until the slurry is uniform to obtain mixture B; wherein, the total alkaline equivalent (calculated as Na2O) of the composite alkaline activator is 4%; (3) Pour mixture B into a 40×40×40mm grout. 3 Vibration compaction occurs in cubic or eccentric ring molds. (4) After standing in a standard curing room (curing temperature of 20℃ and curing humidity of 95%) for 24 hours, the product was demolded and then tested for drying shrinkage, cracking time and crack width under the conditions of (temperature of 20℃ and humidity of 60%).
[0027] The slag-based polymer prepared in this embodiment had a 28-day drying shrinkage value of 777 με, a cracking time of 371 minutes, a crack width of 0.29 mm, and a 28-day compressive strength of 93.23% of the baseline group.
[0028] Example 2 A method for reducing shrinkage and resisting cracking in slag-based aggregates based on humidity control and phase regulation includes the following steps: (1) Place the dried granulated blast furnace slag to constant weight, diatomaceous earth, gypsum and metakaolin in a mixer and stir for at least 1 minute to obtain a solid mixture; wherein, the content of granulated blast furnace slag is 91%; the content of diatomaceous earth is 4.5%; the content of gypsum is 3%; and the content of metakaolin is 1.5%.
[0029] (2) A composite alkaline activator prepared by mixing water glass solution with modulus Ms=1.5 and sodium hydroxide aqueous solution is added to solid mixture A and stirred until the slurry is uniform to obtain mixture B; wherein, the total alkaline equivalent (calculated as Na2O) of the composite alkaline activator is 4%; (3) Pour mixture B into a 40×40×40mm grout. 3 Vibration compacts the material in cubic or eccentric ring molds. (4) After standing in a standard curing room (curing temperature of 20℃ and curing humidity of 95%) for 24 hours, the product was demolded and then tested for drying shrinkage, cracking time and crack width under the conditions of (temperature of 20℃ and humidity of 60%).
[0030] The slag-based polymer prepared in this embodiment had a 28-day drying shrinkage value of 708 με, a cracking time of 701 minutes, a crack width of 0.25 mm, and a 28-day compressive strength of 89.22% of the baseline group.
[0031] Example 3 A method for reducing shrinkage and resisting cracking in slag-based aggregates based on humidity control and phase regulation includes the following steps: (1) Place the dried granulated blast furnace slag to constant weight, diatomaceous earth, gypsum and metakaolin in a mixer and stir for at least 1 minute to obtain a solid mixture; wherein, the granulated blast furnace slag content is 88%; the diatomaceous earth content is 6%; the gypsum content is 4%; and the metakaolin content is 2%.
[0032] (2) A composite alkaline activator prepared by mixing water glass solution with modulus Ms=1.5 and sodium hydroxide aqueous solution is added to solid mixture A and stirred until the slurry is uniform to obtain mixture B; wherein, the total alkaline equivalent (calculated as Na2O) of the composite alkaline activator is 4%; (3) Pour mixture B into a 40×40×40mm grout. 3 Vibration compacts the material in cubic or eccentric ring molds.
[0033] (4) After standing in a standard curing room (curing temperature of 20℃ and curing humidity of 95%) for 24 hours, the product was demolded and then tested for drying shrinkage, cracking time and crack width under the conditions of (temperature of 20℃ and humidity of 60%).
[0034] The slag-based polymer prepared in this embodiment had a 28-day drying shrinkage of 669 με, a cracking time of 869 minutes, a crack width of 0.10 mm, and a 28-day compressive strength of 75.31% of the baseline group.
[0035] Example 4 A method for reducing shrinkage and resisting cracking in slag-based aggregates based on humidity control and phase regulation includes the following steps: (1) Place the dried granulated blast furnace slag to constant weight, diatomaceous earth, gypsum and metakaolin in a mixer and stir for at least 1 minute to obtain a solid mixture; wherein, the granulated blast furnace slag content is 85%; the diatomaceous earth content is 7.5%; the gypsum content is 5%; and the metakaolin content is 2.5%.
[0036] (2) A composite alkaline activator prepared by mixing water glass solution with modulus Ms=1.5 and sodium hydroxide aqueous solution is added to solid mixture A and stirred until the slurry is uniform to obtain mixture B; wherein, the total alkaline equivalent (calculated as Na2O) of the composite alkaline activator is 4%; (3) Pour mixture B into a 40×40×40mm grout. 3 Vibration compacts the material in cubic or eccentric ring molds.
[0037] (4) After standing in a standard curing room (curing temperature of 20℃ and curing humidity of 95%) for 24 hours, the product was demolded and then tested for drying shrinkage, cracking time and crack width under the conditions of (temperature of 20℃ and humidity of 60%).
[0038] The slag-based polymer prepared in this embodiment had a 28-day drying shrinkage value of 512 με, a cracking time of 996 minutes, a crack width of 0.03 mm, and a 28-day compressive strength of 69.97% of the baseline group.
[0039] Comparative Example 1 A method for reducing shrinkage and resisting cracking in slag-based polymers includes the following steps: (1) Place the dried granulated blast furnace slag to constant weight in a mixer and stir for at least 1 minute; (2) Add the composite alkaline activator prepared by water glass solution with modulus Ms=1.5 and sodium hydroxide aqueous solution to the slag after stirring in step (1), and stir until the slurry is uniform; wherein, the total alkali equivalent (calculated as Na2O) of the composite alkaline activator is 4%; (3) Pour the grout into a 40×40×40mm slab. 3 Vibration compacts the material in cubic or eccentric ring molds. (4) After standing in a standard curing room (curing temperature of 20℃ and curing humidity of 95%) for 24 hours, the product was demolded and then tested for drying shrinkage, cracking time and crack width under the conditions of (temperature of 20℃ and humidity of 60%).
[0040] The slag-based polymer prepared in this comparative example had a 28-day drying shrinkage of 845 με, a cracking time of 263 minutes, a crack width of 0.63 mm, and a 28-day compressive strength of 69.79 MPa.
[0041] Comparative Example 2 A method for reducing shrinkage and cracking in slag-based aggregates based on humidity control includes the following steps: (1) Place the dried granulated blast furnace slag and diatomaceous earth in a mixer and stir for at least 3 minutes to obtain solid mixture A; wherein the granulated blast furnace slag content is 94% and the diatomaceous earth content is 6%.
[0042] (2) A composite alkaline activator prepared by mixing water glass solution with modulus Ms=1.5 and sodium hydroxide aqueous solution is added to solid mixture A and stirred until the slurry is uniform to obtain mixture B; wherein, the total alkaline equivalent (calculated as Na2O) of the composite alkaline activator is 4%; (3) Pour mixture B into a 40×40×40mm grout. 3 Vibration compacts the material in cubic or eccentric ring molds.
[0043] (4) After standing in a standard curing room (curing temperature of 20℃ and curing humidity of 95%) for 24 hours, the product was demolded and then tested for drying shrinkage, cracking time and crack width under the conditions of (temperature of 20℃ and humidity of 60%).
[0044] The slag-based polymer prepared in this comparative example had a 28-day drying shrinkage of 690 με, a cracking time of 776 minutes, a crack width of 0.10 mm, and a 28-day compressive strength of 78.89% of the baseline group.
[0045] Comparative Example 3 A method for reducing shrinkage and resisting cracking in slag-based aggregates based on phase regulation includes the following steps: (1) Place the dried granulated blast furnace slag to constant weight, gypsum, and metakaolin in a mixer and stir for at least 3 minutes to obtain solid mixture A; wherein, the content of granulated blast furnace slag is 94%; the content of gypsum is 4%; and the content of metakaolin is 2%. (2) A composite alkaline activator prepared by mixing water glass solution with modulus Ms=1.5 and sodium hydroxide aqueous solution is added to solid mixture A and stirred until the slurry is uniform to obtain mixture B; wherein, the total alkaline equivalent (calculated as Na2O) of the composite alkaline activator is 4%; (3) Pour mixture B into a 40×40×40mm grout. 3 Vibration compacts the material in cubic or eccentric ring molds.
[0046] (4) After standing in a standard curing room (curing temperature of 20℃ and curing humidity of 95%) for 24 hours, the product was demolded and then tested for drying shrinkage, cracking time and crack width under the conditions of (temperature of 20℃ and humidity of 60%).
[0047] The slag-based polymer prepared in this comparative example had a 28-day drying shrinkage of 763 με, a cracking time of 524 minutes, a crack width of 0.26 mm, and a 28-day compressive strength that was 97.42% of the baseline group. Figure 2 It can be seen that ettringite was formed after phase regulation.
[0048] The mass percentage ratios of each component in the slag-based polymers of Examples 1-4 and Comparative Examples 1-3 are shown in Table 1.
[0049] Table 1. Proportions of components in the slag-based polymers of Examples 1-4 and Comparative Examples 1-3 Drying shrinkage, compressive strength, and cracking characteristics tests were conducted on the slag-based polymers from Examples 1-4 and Comparative Examples 1-3. The drying shrinkage curves are shown in the attached figure. Figure 1 As shown in Table 2, the results regarding cracking time and crack width are as follows. The drying shrinkage test was conducted according to GB / T 29417-2012 "Test Method for Drying Shrinkage and Cracking Performance of Cement Mortar and Concrete"; the compressive strength test was conducted according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)"; and the cracking characteristics were tested using the eccentric ring method (see attached table). Figures 3-5 As shown, the eccentric ring specimen has a height of 50 mm, a thickness of 25.5 mm at its thickest point, and a thickness of 8.5 mm at its thinnest point. The inner and outer rings are eccentric by 8.5 mm. During the drying and shrinkage process, due to the geometric eccentricity, the tensile stress on the thinner side of the specimen is greater than that on the thicker side, thus inducing cracks to appear first on the thinner side. The cracking time is measured by fixing a sensitive displacement meter above the specimen. When the displacement meter reading changes abruptly, it is recorded as the crack penetration time. The crack width is measured by a 100x reading microscope. During measurement, the objective lens is placed directly above the crack, and the crack width value is read directly through the scale on the eyepiece.
[0050] Table 2. Test results of slag-based polymers in Examples 1-4 and Comparative Examples 1-3 Note: "-" in the table indicates that there is no data for this item.
[0051] As shown in Table 2, Examples 1-4 of the present invention all exhibited varying degrees of shrinkage reduction and crack resistance compared to Comparative Examples 1-3. In Example 4, the slag-based polymer showed the highest reduction in 28-day drying shrinkage rate (39.41%), with the cracking time extended to 3.8 times that of the baseline group (Comparative Example 1), and the crack width controlled at an extremely low level of 0.03 mm. While Comparative Example 2 (containing only diatomaceous earth) and Comparative Example 3 (containing only gypsum and metakaolinite) showed some improvement in shrinkage reduction and crack resistance compared to Comparative Example 1 (containing no components), their synergistic effect was significantly weaker than that of the present invention examples. This further verifies the effectiveness of the proposed dual mechanism of "physical internal curing of diatomaceous earth + chemical phase regulation by gypsum and metakaolinite."
[0052] In this embodiment of the invention, the internal curing effect of diatomaceous earth maintains a high humidity environment inside the slurry, creating favorable conditions for the continuous and stable in-situ reaction of gypsum and metakaolin to form ettringite. Conversely, the skeletal strengthening effect of ettringite enhances the overall integrity of the material, allowing the internal curing moisture to function more effectively. The two elements form a significant synergistic effect mechanism. The method for preparing slag-based polymers provided in this embodiment of the invention, compared to traditional methods, significantly reduces drying shrinkage, greatly extends cracking time, and significantly reduces crack width, while maintaining good mechanical properties. This demonstrates advanced technology and significant application prospects.
[0053] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If such modifications and variations fall within the scope of equivalents of this invention, then this invention also intends to include these modifications and variations.
Claims
1. A method for reducing shrinkage and preventing cracking in slag-based polymers based on humidity control and phase regulation, characterized in that, The following raw materials are mixed evenly according to the following mass percentages: 85%~94% slag, 3%~7.5% diatomaceous earth, 2%~5% gypsum and 1%~2.5% metakaolin to obtain a solid mixture. Then, a composite alkaline activator with a total alkali equivalent of 3~7% is added and stirred into a slurry. After pouring, standard curing, static setting and demolding, it is further cured until the specified age.
2. The method for reducing shrinkage and cracking of slag-based polymers based on humidity control and phase regulation according to claim 1, characterized in that, The specific surface area of the diatomaceous earth is 20~30m². 2 / g, with a porosity of 30%~45%.
3. The method for reducing shrinkage and resisting cracking of slag-based polymers based on humidity control and phase regulation according to claim 1, characterized in that, The mass ratio of gypsum to metakaolin is 2:
1.
4. The method for reducing shrinkage and cracking of slag-based polymers based on humidity control and phase regulation according to claim 1, characterized in that, The gypsum is dihydrate gypsum or hemihydrate gypsum; the total content of active SiO2 and Al2O3 in the metakaolin is not less than 90 wt.%.
5. The method for reducing shrinkage and resisting cracking of slag-based polymers based on humidity control and phase regulation according to claim 1, characterized in that, The composite alkaline activator is prepared by dissolving solid strong sodium oxide in deionized water and then mixing it with a water glass solution; wherein, the total alkaline equivalent of the composite alkaline activator is 4% (based on Na2O), and the modulus of the water glass solution is Ms=1.
5.
6. The method for reducing shrinkage and resisting cracking of slag-based polymers based on humidity control and phase regulation according to claim 1, characterized in that, The standard curing conditions are as follows: temperature 20±2℃, relative humidity RH≥95%.
7. The method for reducing shrinkage and resisting cracking of slag-based polymers based on humidity control and phase regulation according to claim 1, characterized in that, The settling time is 24 hours.
8. The method for reducing shrinkage and cracking of slag-based polymers based on humidity control and phase regulation according to claim 1, characterized in that, The specified age period is 7 days or 28 days.
9. The method for reducing shrinkage and resisting cracking of slag-based polymers based on humidity control and phase regulation according to claim 1, characterized in that, The slag is granulated blast furnace slag, an industrial by-product, dried to constant weight; the diatomaceous earth, gypsum, or metakaolin is a powder raw material, dried to constant weight.