A hydration heat regulating type calcium-magnesium composite expansive agent for concrete and a preparation method thereof

Abstract

The application discloses a hydration heat regulating type calcium-magnesium composite expansive agent for concrete and a preparation method thereof. The hydration heat regulating type calcium-magnesium composite expansive agent for concrete comprises the following components: a magnesia expansive component, a calcium expansive component, a hydration heat regulating component, a humidity control component and a plasticizing component. The hydration heat regulating type calcium-magnesium composite expansive agent has high expansion capacity, long expansion period and good temperature inhibition effect, can well adapt to internal temperature and humidity changes of a concrete structure, reduce water loss in the structure, match temperature changes to compensate shrinkage, effectively reduce the generation of concrete shrinkage cracks, and the hydration heat regulating component can reduce the internal temperature of the concrete structure, reduce temperature shrinkage, and further promote the effect of late-stage compensation shrinkage of low-activity magnesium oxide. Meanwhile, the material has good adaptability to cement, has no negative influence on the workability and mechanical properties of concrete, and has good batch engineering application prospect.

Description

Technical Field

[0001] This invention relates to the field of concrete admixtures in building materials, and in particular to a calcium-magnesium composite expansion agent for concrete with hydration heat regulation and its preparation method. Background Technology

[0002] Concrete is the largest and most widely used engineering material, playing a crucial role in the construction of public utilities, civil engineering, transportation, water conservancy, municipal engineering, nuclear power, and other projects. Cement, as the main binder in concrete, releases heat and shrinks during hydration. Influenced by various shrinkage factors and constraints, this can lead to cracks in concrete structures. Cracks adversely affect the safety, aesthetics, and durability of structures; therefore, effectively reducing the risk of cracking in concrete structures is a hot topic of concern in the industry.

[0003] Expansive agents are commonly used shrinkage compensation materials in concrete. They utilize the volume expansion that occurs during hydration to effectively compensate for concrete shrinkage, thereby reducing the risk of structural cracking. However, several shortcomings have been identified in their crack-resistant applications. For example, calcium oxide-based expansive agents hydrate rapidly and are highly temperature-sensitive, only compensating for early autogenous shrinkage of concrete at lower ambient temperatures, but not for temperature shrinkage and later drying shrinkage. Calcium oxide-calcium sulfoaluminate dual-expansion-source expansive agents require a large amount of water during hydration, making it difficult to compensate for the shrinkage of ultra-long and ultra-thick concrete structures with low water-cement ratios. Magnesium oxide expansive agents have delayed expansion characteristics, but their hydration activity is low at low temperatures, primarily used to compensate for temperature-induced shrinkage in large-volume hydraulic concrete structures. Calcium-magnesium composite expansive agents combine the early expansion characteristics of calcium oxide and the delayed expansion characteristics of magnesium oxide, effectively compensating for the autogenous shrinkage of ultra-long and ultra-thick concrete structures with low water-cement ratios, but their effectiveness against temperature shrinkage and drying shrinkage is limited. Chinese patent document CN102092976A discloses an ecological large-volume concrete expansive agent and its preparation method. The method involves uniformly mixing magnesite tailings and dolomite tailings to form raw materials, calcining them at 850℃~1200℃ for 60~120 min, holding at that temperature for 60~90 min, and then cooling them in air. After sieving, a calcium-magnesium composite expansive agent is obtained. However, the expansive agent prepared by this method still suffers from excessively rapid calcium oxide hydration and significant loss of expansion energy during the plastic stage of cement-based materials, failing to effectively compensate for later shrinkage and reduce temperature shrinkage. Chinese patent document CN115180866A discloses a hydration heat-regulating magnesium-based high-efficiency crack-resistant agent and its preparation method. This method mainly involves compounding an expansive component with a temperature-controlling component. The expansive component is primarily a magnesium oxide expansive agent, which has a slow hydration reaction and low expansion energy. It only achieves good crack resistance under high-temperature service conditions and cannot effectively compensate for early shrinkage and later drying shrinkage of concrete. Chinese patent document CN113603388B discloses a concrete strengthening, densifying, and temperature-regulating crack-resistant agent and its preparation method. The agent is composed of a modified calcium-magnesium composite expansion component, an ultrafine component, a waterproof component, a temperature-controlling component, and a shrinkage-reducing component. The modified calcium-magnesium composite is prepared by carbonation modification. However, at modification reaction temperatures of 100–150°C, the calcium carbonate on the surface of calcium oxide particles is difficult to maintain stability, making it difficult to guarantee the modification effect on calcareous clinker. Therefore, the expansion agent prepared by this method cannot overcome the problem of excessively rapid expansion rate of calcareous clinker under high-temperature conditions. Furthermore, the mass production process of carbonation modification is difficult to achieve, making it impossible to guarantee the large-scale application of the product.

[0004] Based on the above problems, there is an urgent need to develop a temperature-controlled calcium-magnesium composite expansion agent that has good environmental temperature adaptability, significant shrinkage compensation effect, matching expansion process, and inhibits the hydration heat release rate of concrete structures. Starting from reducing temperature shrinkage, compensating for shrinkage, reducing drying shrinkage, and improving the density of concrete, it can effectively solve the defects of concrete structure cracks caused by shrinkage. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and propose a calcium-magnesium composite expansion agent for concrete with hydration heat regulation and its preparation method, thereby solving the technical problem that existing concrete expansion agents cannot simultaneously address the cracking caused by temperature shrinkage, compensating shrinkage, early shrinkage, chemical shrinkage, carbonation shrinkage, and drying shrinkage.

[0006] In a first aspect, the present invention provides a hydration heat-regulating calcium-magnesium composite expansion agent for concrete, comprising the following components by mass percentage: 35%–50% magnesium expansion component, 40%–60% calcium expansion component, 1%–4% hydration heat regulating component, 1%–5% moisture-controlling component, and 0.5%–2% plasticizing component; wherein, the magnesium expansion component is a low-activity magnesium oxide expansion agent with an MgO content ≥90% and a reaction time of 400s–600s; the calcium expansion component is a calcium oxide-calcium sulfoaluminate expanded clinker with dual modification by ion doping and physical coating; the hydration heat regulating component includes starch derivatives and nano-regulating materials; the moisture-controlling component is porous carbon material; and the plasticizing component is a slump-preserving superplasticizer.

[0007] Secondly, the present invention provides a method for preparing a hydration heat-regulated calcium-magnesium composite expansion agent, comprising the following steps: mixing magnesium expansion component, calcium expansion component, hydration heat-regulated component, moisture-controlling component and plasticizing component evenly to obtain a hydration heat-regulated calcium-magnesium composite expansion agent.

[0008] Compared with the prior art, the beneficial effects of the present invention include:

[0009] The hydration heat-regulated calcium-magnesium composite expansive agent of this invention not only has high expansion energy, long expansion cycle, and good temperature suppression effect, but also adapts well to changes in internal temperature and humidity of concrete structures, reduces internal moisture loss, and compensates for shrinkage by matching temperature changes, effectively reducing the generation of shrinkage cracks in concrete. At the same time, the hydration heat-regulated component can reduce the internal temperature of the concrete structure, reduce temperature shrinkage, and further promote the effect of low-activity magnesium oxide in compensating for shrinkage in the later stage. The components have a significant synergistic effect under reasonable proportions, solving the shrinkage cracking problem of concrete structures from the aspects of compensating for shrinkage, reducing autogenous shrinkage, and temperature shrinkage. In addition, the material has good compatibility with cement and has no negative impact on the workability and mechanical properties of concrete, showing good prospects for mass engineering applications. Attached Figure Description

[0010] Figure 1 The limited expansion rate of mortar prepared by the water-heat-regulated calcium-magnesium composite expansion agent for concrete in Example 1 of this invention at different curing temperatures. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0012] In a first aspect, the present invention provides a hydration heat-regulating calcium-magnesium composite expansion agent for concrete, comprising the following components by mass percentage: 35%–50% magnesium expansion component, 40%–60% calcium expansion component, 1%–4% hydration heat regulating component, 1%–5% moisture-controlling component, and 0.5%–2% plasticizing component. The magnesium expansion component is a low-activity magnesium oxide expansion agent with an MgO content ≥90% and a reaction time of 400–600 s; the calcium expansion component is a calcium oxide-calcium sulfoaluminate expanded clinker with dual modification through ion doping and physical coating; the hydration heat regulating component includes starch derivatives and nano-regulating materials; the moisture-controlling component is a porous carbon material; and the plasticizing component is a slump-retaining superplasticizer.

[0013] This invention relates to a hydration heat-regulated calcium-magnesium composite expansive agent. It achieves long-term shrinkage compensation by modifying multi-source expansion components to match engineering conditions; the hydration heat-regulated component reduces temperature shrinkage and further enhances the shrinkage compensation effect; the moisture-controlling component reduces drying shrinkage and promotes the effect of the expansion components; and the plasticizing component weakens the negative impact of the product on concrete workability while improving the uniformity of key component distribution in concrete. This comprehensively improves the crack resistance of concrete structures. The magnesium expansion component is low-activity magnesium oxide. Unlike the existing standard CBMF19-2017 "Magnesium Oxide Expansive Agent for Concrete" which specifies a MgO reaction time of <300s, this invention controls the MgO reaction time to 400s–600s to match the high-temperature environment inside the concrete structure under engineering conditions, extending the shrinkage compensation time and enhancing the later expansion. However, the reaction time should not be too long, as an excessively long reaction time will cause the magnesium oxide to react too slowly under engineering conditions, failing to compensate for shrinkage. The calcium-based expansion component is a dual-modified calcium oxide-calcium sulfoaluminate expanded clinker with both ion doping and physical coating. Compared with pure calcium oxide clinker and calcium oxide-calcium sulfoaluminate clinker, this clinker has advantages such as extended hydration cycle, significantly reduced temperature sensitivity, reduced hydration heat release rate, and weakened negative impact on the effect of temperature control materials. The hydration heat regulation component includes a temperature control component (starch derivative) and nano-regulating materials. The nano-regulating materials have adsorption-dispersion effects, which can adjust the action time of the temperature control component to match the heat release of cement hydration and optimize the temperature suppression effect. At the same time, the starch derivative (polyhydroxy organic matter) can promote the hydration reaction of magnesium components and better stimulate the release of its later expansion energy. The moisture control component is a porous carbon material with high porosity, which can generate many adsorption sites, thereby playing a good role in water retention and release. It can not only maintain the internal humidity of concrete and reduce its own shrinkage, but also provide a better hydration environment for the expansion component and promote the shrinkage compensation effect. This invention, through the optimal selection of low-activity magnesium-based expanding components, dual modification of calcium-based expanding components, and optimization of particle size distribution, results in a material with high expansion energy and a long expansion cycle, better matching engineering temperatures and effectively compensating for shrinkage in high-temperature environments. Simultaneously, the synergistic and activating effects among the components of the expanding agent effectively compensate for shrinkage, reduce drying shrinkage and autogenous shrinkage, and improve the density of concrete, comprehensively solving the shrinkage cracking problem in concrete structures.

[0014] In this embodiment, the low-activity magnesium oxide expanding agent is prepared by the following steps: calcining magnesite at 1100–1200°C for 30–60 min, followed by grinding to a specific surface area of ​​300–400 kg / m³. 2 This yields a low-activity magnesium oxide expanding agent.

[0015] In this embodiment, the calcium oxide-calcium sulfoaluminate expanded clinker, which is modified by both ion doping and physical coating, is prepared through the following steps:

[0016] Weigh out limestone, anhydrite, bauxite, iron slag, and zinc oxide, mix them thoroughly, add water and shake until they form balls, then dry them to obtain raw material;

[0017] Raw materials are calcined and then naturally cooled to room temperature to obtain clinker;

[0018] The clinker was mixed with modified polyethylene wax powder and ball-milled. The powder was then passed through a 0.2 mm standard sieve to collect the undersize powder. The undersize powder was then passed through a 0.08 mm sieve, with the residue on the 0.08 mm sieve controlled to be 5% to 15%. The powder on the sieve and the powder undersize after passing through the 0.08 mm sieve were combined to obtain ion-doped and physically coated double-modified calcium oxide-calcium sulfoaluminate expanded clinker.

[0019] This invention achieves the required particle size through two sieving processes. Specifically, the first sieving through a 0.2mm sieve removes larger particles, which have low hydration activity and are prone to causing poor concrete stability and localized bursting. The subsequent sieving through a 0.08mm sieve further optimizes the clinker particle size. If the residue on the 0.08mm sieve is too small, the modified clinker hydrates too quickly, hindering its shrinkage compensation during the concrete hardening stage; if the residue is too large, the specimens are prone to cracking under high-temperature curing conditions.

[0020] The raw materials for preparing the raw meal, by weight percentage, include: 80%–90% limestone, 5%–10% anhydrite, 1%–5% bauxite, 0.5%–2% iron slag, and 1%–5% zinc oxide. Furthermore, the specific surface area of ​​the limestone, anhydrite, bauxite, and iron slag is 300–500 kg / m². 2 Zinc oxide is of analytical grade; limestone contains ≥50% CaO; anhydrite contains ≥48% SO3; bauxite contains ≥40% Al2O3; and iron slag contains ≥30% Fe2O3.

[0021] Among them, the water-to-solid ratio of the raw materials used to prepare the raw meal is (0.1-0.2):1.

[0022] In the clinker preparation process, the calcination temperature is 1300-1350℃ and the calcination time is 30-60 minutes.

[0023] The mass ratio of clinker to modified polyethylene wax powder is 100:(0.5-2). If the proportion of modified polyethylene wax powder is too low, it will not have a modifying effect; if the proportion of modified polyethylene wax powder is too high, it will not only be detrimental to product cost but also affect the flowability of concrete. A further ratio of 100:1 is recommended.

[0024] In this embodiment, the specific surface area of ​​the ion-doped and physically coated calcium oxide-calcium sulfoaluminate expanded clinker is 200–300 kg / m². 2 .

[0025] In this embodiment, the mass ratio of starch derivative to nano-regulating material in the hydration heat regulating component is 20-25:1. The nano-regulating component mainly enables the hydration heat regulating material to have an adsorption-dispersion effect, regulates the action time of the temperature control component, matches the heat release during cement hydration, and optimizes the temperature suppression effect. If the proportion of the nano-regulating component is too low, the matching with the cement hydration heat will be poor; if the proportion of the nano-regulating component is too high, it will excessively inhibit the release of the hydration heat regulating component and fail to achieve the effect of inhibiting the heat of hydration.

[0026] In this embodiment, the starch derivative includes at least one of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and maltodextrin; the nano-modifying material includes at least one of nano-calcium carbonate, nano-silica, nano-titanium dioxide, and nano-iron oxide.

[0027] In this embodiment, the porous carbon material is prepared through the following steps: rice husks are mixed and soaked in an ammonium chloride solution, followed by filtration, drying, and calcination to obtain the porous carbon material. The concentration of the ammonium chloride solution is 0.5–2 mol / L, more preferably 1 mol / L; the mass ratio of rice husks to ammonium chloride solution is 1:(5–20), more preferably 1:10; the soaking temperature is room temperature, and the soaking time is at least 12 hours, specifically 24 hours; the calcination temperature is 400–600℃, and the calcination time is 30–60 minutes. During this preparation process, ammonium chloride is dispersed in the rice husks. Upon high-temperature calcination, the ammonium chloride decomposes into ammonia and chlorine, which increases the porosity of the rice husk ash, giving the resulting porous material more adsorption sites and further improving its moisture retention effect.

[0028] In this embodiment, the slump-retaining superplasticizer has a slump-retaining time of ≥2h and a water reduction rate of ≥20%.

[0029] Secondly, the present invention provides a method for preparing a hydration heat-regulated calcium-magnesium composite expansion agent, comprising the following steps: mixing magnesium expansion component, calcium expansion component, hydration heat-regulated component, moisture-controlling component and plasticizing component evenly to obtain a hydration heat-regulated calcium-magnesium composite expansion agent.

[0030] Example 1

[0031] The hydration heat-regulating calcium-magnesium composite expander provided in this embodiment has the following formulation by mass percentage: 40% magnesium expander, 50% calcium expander, 4 wt% hydration heat-regulating component, 5 wt% moisture-controlling component, and 1 wt% plasticizer.

[0032] Magnesium-based expanded components were prepared by the following steps: magnesite was calcined at 1100°C for 60 min, and then ground to a specific surface area of ​​350 kg / m³. 2 The obtained magnesium-expanded component contained 91.3% MgO and the reaction time was 580 s.

[0033] The calcium-expanded component was prepared through the following steps: 85% limestone, 8% anhydrite, 3% bauxite, 1% iron slag, and 3% zinc oxide were weighed out by mass percentage, thoroughly mixed, and then 15% water (based on the total powder volume) was added. The mixture was shaken until it formed pellets and then placed in a 105℃ oven for 2 hours. The raw material was then placed in an electric furnace and calcined at 1350℃ for 30 minutes, followed by natural cooling to room temperature. The clinker and modified polyethylene wax powder (Ceridust 3251) were weighed out at a mass ratio of 100:1, and ground in a ball mill for 45 minutes. The undersize powder was then passed through a 0.2mm standard sieve. The powder was then passed through a 0.08mm sieve, with the residue controlled to be 10%. Finally, the powders above and below the 0.08mm sieve were combined to obtain the calcium-expanded component. The specific surface areas of the limestone, anhydrite, bauxite, and iron slag were 480 kg / m². 2 420kg / m 2 390kg / m 2 and 310kg / m 2 Zinc oxide was of analytical grade; limestone contained 51.2% CaO; anhydrite contained 48.6% SO3; bauxite contained 41.3% Al2O3; and iron slag contained 32.5% Fe2O3.

[0034] Hydration heat regulating component: composed of α-cyclodextrin and nano-calcium carbonate in a mass ratio of 20:1.

[0035] The moisture-controlled component was prepared by the following steps: rice husks were mixed with 1 mol / L ammonium chloride solution at a mass ratio of 1:10 and soaked at room temperature for 24 hours; the rice husk ash was filtered, dried and then calcined at 520℃ for 60 minutes and naturally cooled to room temperature to obtain porous rice husk ash.

[0036] Plasticizing component: from Suzhou Fuke Technology Co., Ltd., model C900.

[0037] Example 2

[0038] This embodiment is basically the same as Example 1, except that the hydration heat regulating component is composed of α-cyclodextrin and nano-calcium carbonate mixed at a mass percentage of 25:1.

[0039] Example 3

[0040] This embodiment is basically the same as Embodiment 1, except that it contains 50% magnesium expansion component, 40% calcium expansion component, 3 wt% hydration heat regulating component, 5 wt% moisture controlling component and 2 wt% plasticizing component.

[0041] Example 4

[0042] This embodiment is basically the same as Embodiment 1, except that it contains 35% magnesium expansion component, 60% calcium expansion component, 2.5% hydration heat regulating component, 2% moisture controlling component and 0.5% plasticizing component.

[0043] Comparative Example 1

[0044] This comparative example is basically the same as Example 1, except that the magnesium oxide meets the S-type magnesium oxide specified in the standard CBMF19-2017 "Magnesium Oxide Expansion Agent for Concrete", with an activity time of 220s.

[0045] Comparative Example 2

[0046] This comparative example is basically the same as Example 1, except that zinc oxide was not added during the preparation of the calcium-expanded component, and an equal amount of iron slag was used instead.

[0047] Comparative Example 3

[0048] This comparative example is basically the same as Example 1, except that the calcium-expanded component was not subjected to physical coating modification during preparation.

[0049] Comparative Example 4

[0050] This comparative example is basically the same as Example 1, except that zinc oxide was not added during the preparation of the calcium-expanded component, but was replaced by an equal amount of iron slag, and no subsequent physical coating modification was performed.

[0051] Comparative Example 5

[0052] This comparative example is basically the same as Example 1, except that the calcium-expanded component was controlled to have a sieve residue of 25% when passing through a 0.08 mm sieve during preparation.

[0053] Comparative Example 6

[0054] This comparative example is basically the same as Example 1, except that the inert material limestone powder is used instead of the hydration heat control component.

[0055] Comparative Example 7

[0056] This comparative example is basically the same as Example 1, except that the heat of hydration regulating component is only a starch derivative, and the content of the heat of hydration regulating component is the same as that in Example 1.

[0057] Comparative Example 8

[0058] This comparative example is basically the same as Example 1, except that the moisture-controlling component is prepared by directly calcining rice husk ash at high temperature without soaking in ammonium chloride solution.

[0059] Test case

[0060] The performance of the hydration heat-regulated calcium-magnesium composite expansion agents prepared in Examples 1-4 and Comparative Examples 1-8 was tested.

[0061] ①The hydration heat reduction rate of mortar at different pouring temperatures was determined by referring to the industry standard JC / T2608-2021 "Inhibitors of Concrete Hydration Temperature Rise". The hydration heat regulating calcium-magnesium composite expansion agent was added at 10% (internal admixture) of the total mass fraction of cementitious materials. The test results of the hydration heat reduction rate of mortar in each embodiment and comparative example are shown in Table 1.

[0062] Table 1. Test results of hydration heat reduction rate of mortar with hydration heat-regulating calcium-magnesium composite expansion agent.

[0063]

[0064]

[0065] The test results in Table 1 above show that the hydration heat reduction rate of mortar after incorporating the hydration heat-regulating calcium-magnesium composite expansive agent of this invention can exceed 50%, which is far higher than the technical indicator of ≥30% hydration heat reduction rate of mortar at a placement temperature of 20±1℃ specified in standard JC / T2608-2021 "Inhibitors of Concrete Hydration Temperature Rise"). Comparative Examples 2, 3, and 4 show that the hydration heat reduction rate is significantly improved by dual modification of calcium clinker compared to single modification and unmodified clinker. After dual modification, the hydration heat reduction rate can be increased from 35.4% to 61.2%. Meanwhile, Example 2 shows that the hydration heat regulating component has a significant effect on the 24-hour hydration heat reduction rate, but little effect on the 7-day hydration heat reduction rate, showing a slight improvement compared to the baseline group. On the other hand, the temperature suppression effect of this expansive agent is greatly affected by the ambient temperature; the higher the temperature, the lower the temperature suppression effect to some extent. This ensures that concrete does not exhibit excessively slow setting or even permanent non-setting in high-temperature environments, thus guaranteeing structural safety.

[0066] ② The test results of the restricted expansion performance of mortar under different curing temperatures were based on the industry standard group standard T / CECS 10082-2020 "Calcium-magnesium composite expansion agent for concrete". The hydration heat-regulating calcium-magnesium composite expansion agent was added at 10% (internal admixture) of the total mass fraction of cementitious materials. The results of the restricted expansion rate of mortar under different curing temperatures are shown in Tables 2, 3 and 4.

[0067] Table 2. Test results of limited expansion rate of mortar with hydrated heat-regulated calcium-magnesium composite expansion agent under water curing conditions at 20℃.

[0068]

[0069]

[0070] Table 2 above shows that after incorporating the hydration heat-regulating calcium-magnesium composite expansion agent of the present invention, the mortar specimens exhibited a relatively large restricted expansion rate under water curing conditions at 20℃, and continued to expand even after 60 days of curing. Comparative Examples 2, 3, and 4 show that the modified calcareous clinker increases the expansion energy. The main mechanism is that the modification significantly reduces the expansion loss during the plastic stage, thereby improving the compensation shrinkage effect in the later stages. Comparative Example 6 shows that without the addition of the hydration heat-regulating component, the restricted expansion rate was reduced, indicating that the temperature-controlled component has a certain activating effect under these curing conditions. Comparative Example 8 shows that modified rice husk ash can better promote the release of expansion energy.

[0071] Table 3. Test results of limited expansion rate of mortar with hydrated heat-regulated calcium-magnesium composite expansion agent under water curing conditions at 40℃.

[0072]

[0073] Table 3 above shows that under 40℃ water curing conditions, the restricted expansion rate of mortar specimens with hydration heat-regulated calcium-magnesium composite expansion agent exhibits continuous expansion. Example 1 shows that the expansion rate gradually decreases with increasing curing age, indicating that early expansion energy growth is driven by the hydration of the calcium expansion component, manifested in a rapid increase in the restricted expansion rate before 14 days of curing, while later expansion rate growth is mainly influenced by the magnesium component. Comparative Examples 2, 3, and 4 show that clinker modification can significantly improve the loss of expansion energy during the plastic stage, with dual modification showing a better effect. Comparative Example 6 shows that without the addition of the hydration heat-regulated component, the restricted expansion rate is reduced, indicating that under this curing condition, the temperature-controlled component has a certain stimulating effect on expansion energy, consistent with the conclusion under 20℃ curing conditions. Comparative Example 8 shows that modified rice husk ash is more effective in synergistically stimulating the development of the expansion rate.

[0074] Table 4. Test results of the limited expansion rate of mortar with hydration heat regulation calcium-magnesium composite expansion agent under water curing conditions at 60℃.

[0075]

[0076] As shown in Table 4 above, under water curing conditions at 60℃, the restricted expansion rate of mortar specimens with hydration heat-controlled calcium-magnesium composite expansion agent still showed continuous expansion, with the restricted expansion rate increasing by more than 0.03% from 3 days to 60 days of curing. The higher the proportion of magnesium component, the greater the increase. Comparative Example 1 shows that the activity time of magnesium oxide has a significant impact on the later expansion; the lower the activity value, the greater the later expansion. Comparative Examples 2, 3, and 4 show that the modification of calcium clinker has a significant effect on the expansion energy, mainly because modification can reduce its ineffective expansion in the plastic stage. Comparative Example 5 shows that particle size control has a significant impact on the stability of the specimen test; if the particle size is too large, the specimen is prone to cracking, making it impossible to generate effective data for detection. Comparative Example 6 shows that without the addition of hydration heat-controlled components, the restricted expansion rate is reduced, and this reduction is more significant compared to 20℃ and 40℃, indicating that under high-temperature conditions, the temperature-controlled components have a more obvious activating effect on the expansion energy. Comparative Example 8 shows that the modified rice husk ash can further promote the release of expansion energy.

[0077] ③ Concrete performance testing

[0078] The expansive agent of this invention was incorporated into C40 concrete with the following proportions: 280 parts of P·O42.5 ordinary Portland cement, 70 parts of S95 mineral powder, 60 parts of Grade II fly ash, 760 parts of river sand, 1030 parts of crushed stone, 7 parts of polycarboxylate superplasticizer, 170 parts of mixing water, and 30 parts of hydration heat-regulating calcium-magnesium composite expansive agent. The flowability of the mixture was tested according to national standard GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures", the compressive strength of concrete was tested according to national standard GB / T 50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", the shrinkage rate of concrete was tested according to national standard GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete", and the penetration height of concrete was tested according to industry standard JC / T 474-2008 "Mortar and Concrete Waterproofing Agents". The test water pressure was 1.2 MPa, and the test was conducted under constant pressure for 72 hours. The test results are shown in Table 5.

[0079] Table 5. Test results of concrete performance with hydration heat-regulated calcium-magnesium composite expansive agent.

[0080]

[0081] As shown in Table 5, the flowability of concrete was significantly enhanced after incorporating the hydration heat-regulating calcium-magnesium composite expansive agent in the examples, and the slump loss was significantly reduced after standing for 1 hour. The compressive strength of concrete specimens at all ages was higher than that of the baseline group, indicating that the expansive agent can improve the compactness of concrete and is beneficial to long-term mechanical properties. It can reduce the drying shrinkage of concrete, and the shrinkage rate can be reduced by more than 20% compared with the blank group. In particular, it can be seen from Comparative Example 8 that the shrinkage rate is significantly improved by modifying rice husk ash. The penetration height data shows that the expansive agent can improve the compactness of concrete, and the penetration height ratio is <50% compared with the baseline group.

[0082] Figure 1 The limited expansion rate of mortar prepared by the water-heat-regulated calcium-magnesium composite expansion agent for concrete in Example 1 of this invention is shown at different curing temperatures. Figure 1 It can be seen that the expanding agent has high expansion energy and a long expansion process at different curing temperatures. Even after 120 days of curing, the restricted expansion rate still shows an increase, indicating that the material has good temperature matching characteristics and a long compensation shrinkage window period at different ambient temperatures.

[0083] Based on the above test results, the hydration heat-regulating calcium-magnesium composite expansive agent of the present invention can simultaneously meet the key technical requirements of the standard JC / T2608-2021 "Inhibitors of Temperature Rise in Concrete Hydration" (hydration heat reduction rate ≥30%) and the group standard T / CECS10082-2020 "Calcium-Magnesium Composite Expansive Agent for Concrete" (limited expansion rate ≥0.05% after 7 days of water curing at 20℃, and the difference between the limited expansion rate and the 28-3 days of water curing at 60℃ is between 0.015% and 0.06%). Furthermore, all components exhibit good synergistic effects, have a long compensation shrinkage time, and are adaptable to temperature changes.

[0084] The present invention overcomes the problems of rapid hydration reaction, large loss of expansion energy in the plastic stage, and poor temperature adaptability of calcium-based expansive agents. It also solves the problems of slow hydration reaction rate and small expansion energy of magnesium-based expansive agents. Furthermore, it effectively inhibits the early hydration heat release of concrete, which can effectively avoid temperature shrinkage caused by a rapid rise in internal temperature of the structure. In this way, it reduces temperature shrinkage, matches temperature compensation shrinkage, effectively reduces drying shrinkage, and enhances the compaction effect, thereby comprehensively improving the crack resistance of concrete structures.

[0085] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A calcium-magnesium composite expansion agent for concrete with hydration heat regulation, characterized in that, The magnesium expansion component, the calcium expansion component, the hydration heat regulating component, the humidity control component, and the plasticizing component are mixed to obtain the hydration heat regulating type calcium-magnesium composite expansion agent. The magnesium expansion component is a low-activity magnesium oxide expansion agent with a MgO content of ≥90% and a reaction time of 400-600s. The calcium expansion component is ion-doped and physically coated double-modified calcium oxide-calcium sulphoaluminate expansion clinker. The hydration heat regulating component includes a starch derivative and a nano-regulating material. The nano-regulating material includes at least one of nano calcium carbonate, nano silicon dioxide, nano titanium dioxide, and nano iron oxide. The humidity control component is a porous carbon material prepared by mixing rice husk with an ammonium chloride solution, followed by filtration, drying, and calcination. The plasticizing component is a slump-preserving superplasticizer.

2. The compound expansive agent for controlling the hydration heat of concrete according to claim 1, characterized by, The low-activity magnesium oxide intumescent agent is prepared by calcining magnesite at 1100-1200°C for 30-60 min, and then grinding to a specific surface area of 300-400 kg / m 2 to obtain the low-activity magnesium oxide intumescent agent.

3. The compound expansive agent for controlling the hydration heat of concrete according to claim 1, characterized by comprising 5 to 15% of the magnesium compound, 5 to 15% of the calcium compound, 0.1 to 1% of the dispersant, and 0.1 to 1% of the defoamer. The raw materials for preparing the raw meal in the preparation process of the ion-doped and physically coated double-modified calcium oxide-calcium sulphoaluminate expansive clinker include, in percentage by weight, limestone 80-90%, hard gypsum 5-10%, bauxite 1-5%, iron slag 0.5-2%, and zinc oxide 1-5%; the specific surface area of the limestone, hard gypsum, bauxite, and iron slag is 300-500 kg / m 2 ; the zinc oxide is of analytical purity, the CaO content in the limestone is ≥50%, the SO3 content in the hard gypsum is ≥48%, the Al2O3 content in the bauxite is ≥40%, and the Fe2O3 content in the iron slag is ≥30%; the water-solid ratio is (0.1-0.2):1; the calcination temperature is 1300-1350℃, and the calcination time is 30-60 min; the mass ratio of the clinker to the modified polyethylene wax powder is 100:(0.5-2); and the specific surface area of the ion-doped and physically coated double-modified calcium oxide-calcium sulphoaluminate expansive clinker is 200-300 kg / m 2 .

4. The compound expansive agent for controlling the hydration heat of concrete according to claim 1, characterized by, The slump-preserving superplasticizer has a slump-preserving time of ≥2h and a water-reducing rate of ≥20%.

5. The compound expansive agent for controlling the hydration heat of concrete according to claim 1, characterized by comprising 5 to 15% of the magnesium compound, 5 to 15% of the calcium compound, 0.1 to 1% of the dispersant, and 0.1 to 1% of the defoamer. The mass ratio of the starch derivative to the nano-regulating material in the hydration heat regulating component is 20-25:

1.

6. The compound expansive agent for controlling the hydration heat of concrete according to claim 1, wherein The starch derivative includes at least one of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and malt dextrin.

7. The method for preparing the hydration heat regulating type compound calcium and magnesium swelling agent according to any one of claims 1 to 6, characterized in that, In the preparation process of the porous carbon material, the concentration of the ammonium chloride solution is 0.5-2mol / L, the mass ratio of the rice husk to the ammonium chloride solution is 1:(5-20), the soaking temperature is room temperature, the soaking time is ≥12h, the calcination temperature is 400-600℃, and the calcination time is 30-60min. The magnesium expansion component, the calcium expansion component, the hydration heat regulating component, the humidity control component, and the plasticizing component are mixed to obtain the hydration heat regulating type calcium-magnesium composite expansion agent.

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