A time-sharing shrinkage composite expanding agent and a preparation method thereof
By combining time-phased shrinkage-inhibiting composite expansion agents, the problem of mismatched expansion and shrinkage inhibition effects of expansion agents at different stages is solved, achieving expansion compensation in the early and middle-to-late stages, improving the shrinkage performance and strength of concrete, and enhancing its impermeability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUILIN UNIVERSITY OF TECHNOLOGY
- Filing Date
- 2025-12-31
- Publication Date
- 2026-05-29
AI Technical Summary
Existing expansion agents have mismatched expansion and shrinkage suppression effects at different stages, which makes concrete prone to cracking during temperature rise and fall, and existing methods cannot effectively improve the suppression of shrinkage in the plastic stage of concrete.
A time-phased shrinkage-inhibiting composite expansion agent is adopted, which is composed of azo compounds, magnesium oxide, calcium oxide, calcium aluminate-calcium sulfoaluminate cement clinker, pre-absorbent spherical sodium polyacrylate, and core-shell structured polyacrylamide resin/kaolin composite spheres. Through the synergistic effect of different components, early and mid-to-late stage expansion compensation is achieved, forming a porous structure to reduce shrinkage.
It effectively compensates for the chemical shrinkage and drying shrinkage of concrete, improves the density and impermeability of concrete, reduces shrinkage, maintains strength, and improves pore structure and stress state.
Abstract
Description
Technical Field
[0001] This invention belongs to the field of building materials technology, and in particular to a time-separated shrinkage-inhibiting composite expansion agent and its preparation method. Background Technology
[0002] Due to its material properties and construction methods, cement concrete suffers from shrinkage issues such as chemical shrinkage, drying shrinkage, and thermal shrinkage, which can easily lead to cracking. With the increasing demands for concrete strength in major projects, the water-cement ratio has decreased while the amount of cementitious materials used has increased dramatically. While significantly increasing the strength of concrete, this also brings a large amount of heat generated during cement hydration, further exacerbating the risk of cracking due to thermal shrinkage. Shrinkage causes internal cracks in the concrete, resulting in a decrease in its strength, impermeability, frost resistance, and durability. To avoid shrinkage, adding an appropriate amount of expansive agent to ordinary concrete is the most common method used in engineering to control crack formation. For example, micro-expansion cement, a hydraulic cementitious material that expands slightly in volume after hardening, can be used. Concrete volume expansion can also be achieved by adding expansive agents such as magnesium oxide or calcium oxide. However, calcium oxide reacts immediately upon contact with water, expanding rapidly in the early stages, but lacks sustained expansion force in the later stages when water is scarce. Conventional magnesium oxide expansive agents mainly focus on later-stage expansion, with a weaker effect in inhibiting early-stage shrinkage. Therefore, in many cases, it is difficult for a single expanding agent to achieve a good full-time shrinkage suppression effect, which leads to significant drawbacks.
[0003] In actual concrete structures, due to the heat released during cement hydration, the concrete structure undergoes temperature rise and fall processes. During the temperature rise stage, due to the principle of thermal expansion and contraction, the concrete generally expands; however, during the temperature fall stage, the shrinkage due to temperature drop is generally greater, and coupled with autogenous shrinkage and drying shrinkage, it easily causes concrete cracking. Therefore, the optimal solution to solve concrete shrinkage cracking is to match the expansion and contraction suppression throughout the entire time period with the shrinkage characteristics of the concrete, that is, to adjust the shrinkage suppression rate of the expansion agent in different time periods to achieve time-based expansion and contraction suppression.
[0004] For example, Chinese patent (CN103130437A) discloses a method for preparing a concrete expansion agent, which involves melting and calcining gypsum and calcium oxide to form an expanded clinker of calcium oxide coated with gypsum, which is then further ground together with other powders to a specific surface area of 140-400 m². 2 The result was obtained after processing / kg. This method improves the weathering resistance of expanded clinker, but it does not improve its shrinkage inhibition during the plastic stage of concrete. Summary of the Invention
[0005] The purpose of this invention is to provide a time-sequential shrinkage-inhibiting composite expansion agent and its preparation method, so as to solve the problems mentioned in the background art.
[0006] To achieve the above objectives, the present invention provides the following technical solution: a time-sequential shrinkage-inhibiting composite expansion agent, wherein the composite expansion agent is prepared from the following components in parts by weight: 2-8 parts of azo compounds, 20-30 parts of magnesium oxide, 10-30 parts of calcium oxide, 30-50 parts of calcium aluminate-calcium sulfoaluminate cement clinker, 5-10 parts of pre-absorbed spherical sodium polyacrylate, and 5-10 parts of core-shell structured polyacrylamide resin / kaolin composite spheres.
[0007] Furthermore, the kaolin has a particle size of 50-100 μm; the average particle size of the core-shell structured polyacrylamide resin / kaolin composite spheres is 0.3 cm-0.7 cm.
[0008] Furthermore, the spherical sodium polyacrylate is sodium polyacrylate with an effective water-absorbing polymer content of more than 90% and a particle size of 3-5 mm; Furthermore, the raw material mix ratio of the calcium aluminate-calcium sulfoaluminate cement clinker is: 50-60% bauxite, 30-45% limestone, and 5-18% gypsum, which is obtained by calcination at a high temperature of 1500-1700℃.
[0009] Furthermore, the mineral composition range of the clinker is CA: 30-35%, C4A3S: 20-30%, CA2: 25-35%, C2S: 5-15%; Furthermore, the bauxite has the following composition: Al2O3 > 72%, SiO2 < 11%; limestone has the following composition: CaO > 55%, SiO2 < 12%; and gypsum has the following composition: SO3 > 46%. Spherical sodium polyacrylate and polyacrylamide resins possess characteristics such as high water absorption, high water retention, and effective persistence. They can absorb tens or even hundreds of times their own weight in water. Their hydrophilic groups form hydrogen bonds in water or solutions, thereby forming charged groups. These charged groups simultaneously increase the ion concentration inside the resin, increasing the osmotic pressure and providing the driving force for water absorption. Furthermore, when spherical sodium polyacrylate and polyacrylamide resins absorb water, there is not only internal capillary adsorption but also physical adsorption through the polymer network, resulting in strong water retention capacity. Water adsorbed by the internal cross-linked network will not be released due to external mechanical forces (such as stirring). When the spherical resin of this invention is mixed with cement, as the cement hydrates and hardens, the water retained inside the resin is gradually released, forming near-spherical, regular macropores in the cement paste, thus preparing porous, highly absorbent resin aggregate concrete. Due to the water-releasing curing characteristics of the spherical resin of this invention, a high-strength arched shell structure with a high degree of hydration and a dense structure is formed around the spherical regular pores, making this pore structure fundamentally different from the pore structure in conventional foamed concrete.
[0010] Furthermore, the magnesium oxide is obtained by low-temperature calcination at 500-600℃. MgO expanding agent has a delayed micro-expansion effect, mainly acting on expansion in the middle and late stages. The direct driving force for the expansion of MgO expanding agent comes from the swelling force and crystallization pressure of Mg(OH)2 crystals. In the early stage of hydration, Mg(OH)2 crystals are very small, and the expansion of the slurry is mainly due to the swelling force of water absorption. As Mg(OH)2 crystals grow, the crystallization growth pressure of the crystals becomes the main driving force for expansion.
[0011] When calcium oxide is mixed with cement and water, it undergoes a hydration reaction to produce calcium hydroxide, which generates the expansion force of concrete. The source of this expansion is Ca(OH)2, and the volume of the solid phase increases by almost 100% after the reaction.
[0012] This invention uses calcium aluminate-calcium sulfoaluminate cement clinker as an expansive agent. When this expansive agent is added to cement to form expansive concrete or mortar and water, the calcium aluminate (CA) in the system first reacts with CaSO4 in the gypsum to form hydrated calcium sulfoaluminate. This reaction process proceeds synchronously with the cement hydration process. During the hydration of the calcium aluminate expansive agent, ettringite and hydrated aluminum hydroxide gel are simultaneously formed, resulting in a reasonable match between the expansive and cementitious phases, maintaining appropriate expansion while ensuring the strength of the cement paste. The early-formed ettringite has a significant expansion effect, which compensates for the chemical shrinkage and drying shrinkage of the cement paste. Both the calcium sulfoaluminate and calcium oxide expansive agents produce substantial expansion within 7 days. The ettringite also fills and blocks pores, improving the density and impermeability of the concrete, greatly reducing the volume shrinkage of the cement paste, and fundamentally improving the pore structure and stress state of the concrete.
[0013] In the mid-to-late stages of the system, the core-shell structure of polyacrylamide resin / kaolin composite balls continues to play a role in water release, improving the shrinkage compensation efficiency of the composite expansion agent.
[0014] Furthermore, the kaolin content in the core-shell structured polyacrylamide resin / kaolin composite sphere is 30-40 wt%. This core-shell structured polyacrylamide resin / kaolin composite sphere is a porous sphere comprising a polyacrylamide resin matrix as the core and a porous kaolin transport layer as the shell. Polyacrylamide resin has a large water storage capacity, and kaolin minerals have a large specific surface area and are stable. Therefore, this core-shell structured polyacrylamide resin / kaolin composite sphere has excellent water absorption and swelling effect. This core-shell structured polyacrylamide resin / kaolin composite sphere can be combined with sodium polyacrylate to solve the problems of slow water absorption rate, low efficiency, and small capacity of existing resins.
[0015] Furthermore, the preparation method of the core-shell structured polyacrylamide resin / kaolin composite spheres includes the following steps: (1) Kaolin is activated by suspending it in a saturated sodium chloride aqueous solution for 2-3 hours, then dried and ground to 50-100 μm to obtain activated kaolin; (2) Immerse spherical polyacrylamide resin with a particle size of 1-2 mm in deionized water for 1-2 hours to absorb water and swell. (3) Take out the swollen polyacrylamide resin after filtration, and then mix it with activated kaolin. Coating is carried out under the condition of a mass ratio of 1:(10-15) for 5-10 minutes. (4) Dry the product coated in step (3) at 110℃-140℃ for 1-4 hours. After drying, sieve to obtain the core-shell structured polyacrylamide resin / kaolin composite ball.
[0016] In step (3) of this invention, the mass ratio of the swollen spherical polyacrylamide resin to the activated kaolin is 1:(10-15) during the coating process, and the coating time is controlled at 5-10 minutes to ensure the coating effect. If the mixing time is too long, the resin will release too much water, which will affect the coating effect.
[0017] In step (2) of this invention, immersing the spherical polyacrylamide resin in deionized water for 1-2 hours can control the swelling volume of the spherical polyacrylamide resin and better control the resin-clay ratio in the subsequent coating stage. This invention controls the spherical polyacrylamide resin to absorb water to 2-3 times its original volume, ensuring the performance of the spherical polyacrylamide resin. Because if the water absorption and swelling volume of the spherical polyacrylamide resin is too high or too low, it will reduce the water absorption performance of the polyacrylamide resin / kaolin composite spheres or lead to a large breakage rate.
[0018] In step (4) of this invention, the core-shell structured polyacrylamide resin / kaolin composite ball is dried at 110℃-140℃ for 1-4 hours. Under the above temperature and drying time, the activated clay particles can fully interact with the surface of the swollen resin, ensuring that the prepared composite ball forms a porous structure on the surface after drying, while ensuring a high yield and low breakage rate.
[0019] The average particle size of the core-shell structured polyacrylamide resin / kaolin composite spheres is 0.3cm-0.7cm. The particle size of the core-shell structured polyacrylamide resin / kaolin composite spheres of this invention can be adjusted to meet the requirements of different water absorption conditions. Furthermore, the controllable size of the core-shell structured polyacrylamide resin / kaolin composite spheres can meet various dimensional requirements during material use.
[0020] The activated kaolin and polyacrylamide resin of the present invention construct a porous structure on their surface to form a porous transport layer, which increases the specific surface area of the composite sphere; at the same time, the transport layer can quickly liquefy water vapor to form liquid water and transport it to the internal polyacrylamide resin, thereby changing the original water absorption mechanism of high polyacrylamide resin and significantly improving the material's performance. Furthermore, the azo compound is one or a combination of several of the following: azodicarbonamide, azobisisobutyronitrile, isopropyl azodicarbonate, diethyl azodicarbonate, diazoaminobenzene, and barium azodicarbonate. When the azo organic foaming agent is added to concrete, due to the presence of unshared electron pairs on the amino nitrogen atom, the NN and N=N bonds break under certain temperature and alkaline conditions of cement hydration, releasing nitrogen gas. This can generate fine, uniform bubbles, establishing a moderate expansion during the plastic stage of the slurry to compensate for the volume shrinkage caused by plastic settlement and autogenous shrinkage before the cement slurry solidifies after hydration.
[0021] Another object of the present invention is to provide a method for preparing the above-mentioned time-separated shrinkage-inhibiting composite expansion agent, comprising the following steps: (1) 10-30 parts calcium oxide and 30-50 parts calcium aluminate-calcium sulfoaluminate cement clinker, ground to a specific surface area of 300-600 m². 2 / kg; (2) Grind magnesium oxide separately to a specific surface area of 500-800 m². 2 / kg; (3) The materials obtained in steps (1) and (2) above are mixed and homogenized with 2-8 parts of azo compound, 5-10 parts of pre-absorbed water-spherical sodium polyacrylate, and 5-10 parts of core-shell structured polyacrylamide resin / kaolin composite spheres to obtain the composite expansion agent.
[0022] Compared with the prior art, the present invention has the following technical effects and advantages: (1) This invention uses calcium aluminate-calcium sulfoaluminate cement clinker as an expansive agent. When this expansive agent is added to cement to make expansive concrete or mortar and water, the CA in the system first reacts with CaSO4 in gypsum to generate hydrated calcium sulfoaluminate. This reaction process proceeds synchronously with the cement as the hydration process continues. The ettringite formed during the hydration of this expansive agent is generated simultaneously with the hydrated aluminum hydroxide gel, so that the expansive phase and the cementitious phase are reasonably matched, that is, maintaining a moderate expansion while ensuring the strength of the cement stone. The ettringite generated in the early stage has a large expansion effect. The expansion during this period can compensate for the chemical shrinkage and drying shrinkage of the cement stone. Both the calcium aluminate-calcium sulfoaluminate expansive agent and the calcium oxide expansive agent generate a large amount of expansion within 7 days. The ettringite also has the function of filling and blocking pores, improving the compactness and impermeability of concrete, greatly reducing the volume shrinkage of cement stone, and fundamentally improving the pore structure and stress state of concrete.
[0023] (2) The present invention uses low-temperature calcined magnesium oxide and core-shell structured polyacrylamide resin / kaolin composite balls to act on the mid-to-late stage expansion, which reduces the volume shrinkage of cement stone. The core-shell structured polyacrylamide resin / kaolin composite balls improve the shrinkage compensation efficiency of the composite expansion agent, further reducing the shrinkage of concrete. Detailed Implementation
[0024] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.
[0025] Example 1 A method for preparing a time-separated shrinkage-inhibiting composite expansion agent includes the following steps: (1) 10 parts calcium oxide and 30 parts calcium aluminate-calcium sulfoaluminate cement clinker, ground to a specific surface area of 300 m². 2 / kg; (2) Low-temperature calcined magnesium oxide is separately ground to a specific surface area of 500 m². 2 / kg; (3) The materials obtained in steps (1) and (2) above are mixed and homogenized with 2 parts of azo compound, 5 parts of pre-absorbed water spherical sodium polyacrylate and 5 parts of core-shell structured polyacrylamide resin / kaolin composite spheres to obtain the composite expansion agent.
[0026] The kaolin has a particle size of 50 μm; the core-shell structured polyacrylamide resin / kaolin composite spheres have an average particle size of 0.3 cm.
[0027] The spherical sodium polyacrylate is sodium polyacrylate with an effective water-absorbing polymer content of more than 90% and a particle size of 3 mm. The raw material mix ratio of the calcium aluminate-calcium sulfoaluminate cement clinker is: 50-60% bauxite, 30-45% limestone, and 5-18% gypsum, which is obtained by calcination at 1500℃.
[0028] The mineral composition range of the clinker is CA: 30-35%, C4A3S: 20-30%, CA2: 25-35%, C2S: 5-15%; The bauxite has the following composition: Al2O3 > 72%, SiO2 < 11%; limestone has the following composition: CaO > 55%, SiO2 < 12%; gypsum has the following composition: SO3 > 46%. The magnesium oxide was obtained by low-temperature calcination at 500℃; The kaolin content in the core-shell structured polyacrylamide resin / kaolin composite sphere is 30 wt%. The preparation method of the core-shell structured polyacrylamide resin / kaolin composite spheres includes the following steps: (1) Kaolin was activated by suspending it in a saturated sodium chloride aqueous solution for 2 hours, then dried and ground to 50 μm to obtain activated kaolin; (2) Immerse 1mm spherical polyacrylamide resin in deionized water for 1 hour to absorb water and swell. (3) Take out the swollen polyacrylamide resin after filtration, and then mix it with activated kaolin. Coating is carried out under the condition of a mass ratio of 1:10, and the time is controlled at 5 minutes. (4) The product coated in step (3) is dried at 110°C for 1 hour. After drying, it is sieved to obtain the core-shell structured polyacrylamide resin / kaolin composite ball.
[0029] The azo compound is azodicarbonamide.
[0030] Example 2 A method for preparing a time-separated shrinkage-inhibiting composite expansion agent includes the following steps: (1) 20 parts of calcium oxide and 450 parts of calcium aluminate-calcium sulfoaluminate cement clinker, ground to a specific surface area of 450 m². 2 / kg; (2) Grind magnesium oxide separately to a specific surface area of 750 m². 2 / kg; (3) The materials obtained in steps (1) and (2) above are mixed and homogenized with 4 parts of azo compound, 8 parts of pre-absorbed water spherical sodium polyacrylate and 8 parts of core-shell structured polyacrylamide resin / kaolin composite spheres to obtain the composite expansion agent.
[0031] The kaolin has a particle size of 75 μm; the core-shell structured polyacrylamide resin / kaolin composite spheres have an average particle size of 0.5 cm.
[0032] The spherical sodium polyacrylate is sodium polyacrylate with an effective water-absorbing polymer content of more than 90% and a particle size of 4 mm. The raw material mix ratio of the calcium aluminate-calcium sulfoaluminate cement is: 50-60% bauxite, 30-45% limestone, and 5-18% gypsum, which is obtained by calcination at 1700℃.
[0033] The mineral composition range of the clinker is CA: 30-35%, C4A3S: 20-30%, CA2: 25-35%, C2S: 5-15%; The bauxite has the following composition: Al2O3 > 72%, SiO2 < 11%; limestone has the following composition: CaO > 55%, SiO2 < 12%; gypsum has the following composition: SO3 > 46%. The magnesium oxide was obtained by low-temperature calcination at 550℃; The kaolin content in the core-shell structured polyacrylamide resin / kaolin composite sphere is 35 wt%. The preparation method of the core-shell structured polyacrylamide resin / kaolin composite spheres includes the following steps: (1) Kaolin was activated by suspending it in a saturated sodium chloride aqueous solution for 2.5 hours, then dried and ground to 75 μm to obtain activated kaolin; (2) Immerse 1.5 mm spherical polyacrylamide resin in deionized water for 1.5 hours to absorb water and swell. (3) Take out the swollen polyacrylamide resin after filtering, and then mix it with activated kaolin. Coating is carried out under the condition of a mass ratio of 1:12, and the time is controlled at 8 minutes. (4) The product coated in step (3) is dried at 120°C for 2 hours. After drying, it is sieved to obtain the core-shell structured polyacrylamide resin / kaolin composite ball.
[0034] The azo compound is azodicarbonamide.
[0035] Example 3 A method for preparing a time-separated shrinkage-inhibiting composite expansion agent includes the following steps: (1) 30 parts calcium oxide and 50 parts calcium aluminate-calcium sulfoaluminate cement clinker, ground to a specific surface area of 600 m². 2 / kg; (2) Grind magnesium oxide separately to a specific surface area of 800 m². 2 / kg; (3) The materials obtained in steps (1) and (2) above are mixed and homogenized with 8 parts of azo compound, 10 parts of pre-absorbed water spherical sodium polyacrylate and 10 parts of core-shell structured polyacrylamide resin / kaolin composite spheres to obtain the composite expansion agent.
[0036] The kaolin has a particle size of 100 μm; the average particle size of the core-shell structured polyacrylamide resin / kaolin composite spheres is 0.7 cm.
[0037] The spherical sodium polyacrylate is sodium polyacrylate with an effective water-absorbing polymer content of more than 90% and a particle size of 5 mm. The raw material mix ratio of the calcium aluminate-calcium sulfoaluminate cement is: 50-60% bauxite, 30-45% limestone, and 5-18% gypsum, which is obtained by calcination at 1600℃.
[0038] The mineral composition range of the clinker is CA: 30-35%, C4A3S: 20-30%, CA2: 25-35%, C2S: 5-15%; The bauxite has the following composition: Al2O3 > 72%, SiO2 < 11%; limestone has the following composition: CaO > 55%, SiO2 < 12%; gypsum has the following composition: SO3 > 46%. The magnesium oxide was obtained by low-temperature calcination at 600℃; The kaolin content in the core-shell structured polyacrylamide resin / kaolin composite sphere is 40 wt%. The preparation method of the core-shell structured polyacrylamide resin / kaolin composite spheres includes the following steps: (1) Kaolin was activated by suspending it in a saturated sodium chloride aqueous solution for 3 hours, then dried and ground to 100 μm to obtain activated kaolin; (2) Immerse spherical polyacrylamide resin with a particle size of 2 mm in deionized water for 2 hours to absorb water and swell. (3) Take out the swollen polyacrylamide resin after filtration, and then mix it with activated kaolin. Coating is carried out under the condition of a mass ratio of 1:15, and the time is controlled at 10 minutes. (4) The product coated in step (3) is dried at 140°C for 4 hours. After drying, it is sieved to obtain the core-shell structured polyacrylamide resin / kaolin composite ball.
[0039] The azo compound is azodicarbonamide.
[0040] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that core-shell structured polyacrylamide resin / kaolin composite spheres were not used; instead, spherical polyacrylamide resin of the same weight was used instead of core-shell structured polyacrylamide resin / kaolin composite spheres. Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that core-shell structured polyacrylamide resin / kaolin composite balls were not used; instead, activated kaolin of the same weight was used instead of core-shell structured polyacrylamide resin / kaolin composite balls. Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the same weight proportions of unactivated kaolin were used instead of activated kaolin. Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the average particle size of the core-shell structured polyacrylamide resin / kaolin composite balls used is 1 cm.
[0041] The expansion rate and setting time of the blank group and experimental group (Examples 1-3, Comparative Examples 1-4) were tested using reference cement in accordance with GB / T1346~2019; the test results are shown in Table 1: Table 1 Experimental Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Limiting expansion rate % (7d) in water 0.0227 0.0236 0.0233 0.0183 0.0164 0.0143 0.0172 Limiting expansion rate % (21d) in air 0.0216 0.0221 0.0218 0.0172 0.0152 0.0135 0.0189 Setting time (initial setting) / min 124 120 123 136 139 143 133 Setting time (terminus of setting) / min 236 230 235 248 254 261 240 As can be seen from the results in Table 1, the expansion agents obtained in Examples 1-3 of the present invention have a better effect on limiting expansion rate and a shorter setting time; the core-shell structured polyacrylamide resin / kaolin composite balls used in Comparative Example 4 have a larger average particle size and their expansion rate is slightly worse than that of Examples 1-3.
[0042] The expansive agents obtained in Examples 1-3 and Comparative Examples 1-4 of this invention were applied to ultra-high performance concrete. The specific mix proportions of the ultra-high performance concrete are shown in Table 2. Table 2: Concrete Mix Design Table (Unit: Kg) Commercially available cement sand steel fiber fly ash silica ash Water reducing agent Expanding agent water Blank group 600 1000 157 200 200 20 0 150 experimental group 600 1000 157 200 200 20 45 150 The 3-day, 7-day, and 28-day compressive strengths of the concrete obtained in the blank group and the experimental group (Examples 1-3 and Comparative Examples 1-4) were tested according to GB / T50081-2019 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete". Simultaneously, the 28-day total shrinkage rate of the concrete obtained was tested according to GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". The test results are shown in Table 3. Table 3: Test Results Experimental Project Blank group Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Expanding agent dosage / kg 0 45 45 45 45 45 45 45 3d compressive strength / MPa 89.4 87.2 87.4 87.1 86.1 85.0 84.4 86.8 7d compressive strength / MPa 105.5 101.3 101.6 100.8 100.1 99.8 98.4 100.4 28-day compressive strength / MPa 134.6 131.4 131.9 131.1 125.6 124.8 119.9 128.3 <![CDATA[Total shrinkage rate of 28d / 10 -6 > 617 205 198 207 223 241 252 262 Slump / mm 248 256 258 257 253 252 252 253 Expansion / mm 649 656 658 656 654 653 652 655 As can be seen from the results in Table 3, the expansive agents obtained in Examples 1-3 of this invention have achieved outstanding effects in reducing concrete shrinkage, especially Example 2, whose total shrinkage rate after 28 days is only 198 × 10⁻⁶. -6 Furthermore, the compressive strength remains at a high level, and there is no significant decrease in strength when the shrinkage rate is reduced.
[0043] The core-shell structured polyacrylamide resin / kaolin composite spheres used in Comparative Example 4 had a larger average particle size, and their compressive strength, self-shrinkage rate, and other indicators were slightly worse than those in Examples 1-3.
[0044] The test results of Comparative Examples 1-3, which did not use core-shell structured polyacrylamide resin / kaolin composite balls, were all worse than those of Examples 1-3.
[0045] This demonstrates that the use of core-shell structured polyacrylamide resin / kaolin composite spheres plays a crucial role in the production of expansion agents and other effects.
[0046] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.
Claims
1. A time-separated shrinkage-inhibiting composite expansion agent, characterized in that: The composite expansion agent, by weight, consists of the following components: 0.5-8 parts of azo compound, 20-30 parts of magnesium oxide, 10-30 parts of calcium oxide, 30-50 parts of calcium aluminate-calcium sulfoaluminate cement clinker, 5-10 parts of pre-absorbed spherical sodium polyacrylate, and 5-10 parts of core-shell structured polyacrylamide resin / kaolin composite spheres.
2. The time-separated shrinkage-inhibiting composite expansion agent as described in claim 1, characterized in that: The kaolin content in the core-shell structured polyacrylamide / kaolin composite sphere is 30-40 wt%.
3. The time-separated shrinkage-inhibiting composite expansion agent as described in claim 1, characterized in that: The kaolin has a particle size of 50-100μm; the average particle size of the core-shell structured polyacrylamide resin / kaolin composite spheres is 0.3cm-7cm.
4. The time-separated shrinkage-inhibiting composite expansion agent as described in claim 1, characterized in that: The azo compounds are one or a combination of several of the following: azodicarbonamide, azobisisobutyronitrile, isopropyl azodicarbonate, diethyl azodicarbonate, diazoaminobenzene, and barium azodicarbonate.
5. The time-separated shrinkage-inhibiting composite expansion agent as described in claim 1, characterized in that: The raw material mix ratio of the calcium aluminate-calcium sulfoaluminate cement clinker is: 50-60% bauxite, 30-45% limestone, and 5-18% gypsum, which is obtained by high-temperature calcination at 1500-1700℃.
6. The time-separated shrinkage-inhibiting composite expansion agent as described in claim 5, characterized in that: The mineral composition of the clinker ranges as follows: CA: 30-35%, C4A3S: 20-30%, CA2: 25-35%, C2S: 5-15%.
7. The time-separated shrinkage-inhibiting composite expansion agent as described in claim 5, characterized in that: The bauxite has the following composition: Al2O3 > 72% and SiO2 < 11%; limestone has the following composition: CaO > 55% and SiO2 < 12%; and gypsum has the following composition: SO3 > 46%.
8. The time-separated shrinkage-inhibiting composite expansion agent as described in claim 1, characterized in that: The preparation method of the core-shell structured polyacrylamide resin / kaolin composite spheres includes the following steps: (1) Kaolin is activated by suspending it in a saturated sodium chloride aqueous solution for 2-3 hours, then dried and ground to 50-100 μm to obtain activated kaolin; (2) Immerse spherical polyacrylamide resin with a particle size of 1-2 mm in deionized water for 1-2 hours to absorb water and swell. (3) Take out the swollen polyacrylamide resin after filtration, and then mix it with activated kaolin. Coating is carried out under the condition of a mass ratio of 1:(10-15) for 5-10 minutes. (4) Dry the product coated in step (3) at 110℃-140℃ for 1-4 hours. After drying, sieve to obtain the core-shell structured polyacrylamide resin / kaolin composite ball.
9. The time-separated shrinkage-inhibiting composite expansion agent as described in claim 1, characterized in that: The magnesium oxide is obtained by low-temperature calcination at 500-600℃; the spherical sodium polyacrylate is sodium polyacrylate with an effective water-absorbing polymer content of more than 90% and a particle size of 3-5mm.
10. The preparation method of the time-separated shrinkage-inhibiting composite expansion agent according to claims 1-9, characterized in that... It includes the following steps: (1) 10-30 parts calcium oxide and 30-50 parts calcium aluminate-calcium sulfoaluminate cement clinker, ground to a specific surface area of 300-600 m². 2 / kg; (2) Grind magnesium oxide separately to a specific surface area of 500-800 m². 2 / kg; (3) The materials obtained in steps (1) and (2) above are mixed and homogenized with 0.5-8 parts of azo compound, 5-10 parts of pre-absorbed water spherical sodium polyacrylate, and 5-10 parts of core-shell structured polyacrylamide resin / kaolin composite spheres to obtain the composite expansion agent.