Micro-expansion material suitable for PCCP (prestressed concrete cylinder pipe) joint filling as well as preparation method and application of micro-expansion material

Abstract

The invention discloses a micro-expansion material suitable for PCCP (prestressed concrete cylinder pipe) joint filling as well as a preparation method and application thereof, and the micro-expansion material is prepared from the following components (raw materials and mass fraction) in terms of 100 parts of total mass of a mixture: 28-32 parts of cement, 7-11 parts of desulfurization tower bottom ash, 3-5 parts of raw slag, 40-44 parts of fine aggregate, 0.02-0.03 part of a volume stabilizer, 0.06-0.08 part of a surfactant, 0.004-0.006 part of a water retention thickener and 14-15 parts of water. The preparation method comprises the following steps: drying and grinding solid materials except water, fully mixing and packaging to obtain the dry blend of the micro-expansion material. The micro-expansion material mixture prepared by the invention has excellent flowability and can realize normal-pressure pouring. The hardened consolidated body test piece prepared by the invention has excellent impermeability and expansibility in a whole maintenance period from plasticity to hardening while meeting the strength requirement of the bell and spigot joint protective mortar, and solves the cracking risk caused by shrinkage of the traditional cement-based joint material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of solid waste recycling and cement-based grouting materials, in particular to a micro-expansion material suitable for PCCP joint filling, a preparation method and application. BACKGROUND

[0002] Prestressed concrete cylinder pipe (PCCP) has become an indispensable key pipeline type in national large-scale water transfer and distribution projects, urban main water supply pipe networks and industrial water systems due to its high bearing capacity, good durability and large single pipe length. The entire PCCP pipe network system is formed by connecting single pipe bodies through socket joints. These joint parts are the discontinuity points of the continuity of the entire pipeline structure, and are also the weak links of waterproofing, corrosion prevention and stress transmission. In order to ensure the long-term safe and stable operation of the pipe network, the annular cavity formed by the socket joint of PCCP after installation needs to be filled and protected. The performance of the joint filling material used for this purpose directly determines the sealing, durability and overall structural cooperation ability of the joint. Specifically, the material must have excellent waterproof and anti-seepage performance to block the intrusion of external groundwater and corrosive media; it must be able to effectively transmit and buffer the stress caused by water hammer, ground changes and other factors to protect the socket structure from damage; at the same time, it must have excellent adhesion to the pipe body concrete and long-term volume stability to ensure the integrity and compactness of the filling body itself. Therefore, the development of a high-performance PCCP joint filling material is of great technical significance and engineering value for the protection of national major infrastructure projects.

[0003] Around the issue of improving the performance of cement-based joint filling materials, the existing technology research mainly focuses on improving the workability, mechanical properties and single-period volume compensation ability. In terms of material composition, high-strength, low-hydraulic-heat Portland cement is commonly used as the main cementitious material, and finely ground mineral admixtures (such as fly ash, slag powder) are compounded to improve the compactness and later strength of the paste. To meet the stringent requirements of the narrow and complex space of PCCP joints for material fluidity, high-performance polycarboxylic acid superplasticizer is usually used to greatly reduce the mixing water content, thereby obtaining a high-fluidity grouting paste. On this basis, to compensate for the inherent chemical shrinkage and drying shrinkage of cement-based materials during hardening, existing technologies usually introduce single-mechanism expansion components. For example, calcium sulphoaluminate (CSA) or calcium oxide (CaO) based expansion agents are used, which generate ettringite (AFt) or calcium hydroxide crystals during hardening to produce expansion, in order to offset the later shrinkage. Another technical route is to use metal-based gas-producing components (such as aluminum powder), which react with the alkaline environment generated by cement hydration in the plastic stage of the paste, and produce a certain volume expansion of the paste by generating tiny hydrogen bubbles.

[0004] Although the prior art improves the performance of the joint filling material to some extent, in-depth analysis of its full-cycle service process in the PCCP application scenario can find that the traditional scheme relying on a single expansion mechanism still has deep technical limitations in achieving the full cycle and synergy of volume stability from the plastic stage of the paste to the long-term hardening stage. For example, the mismatch between the expansion compensation effect and the material shrinkage process in time, and the uncontrollable risk of late expansion. SUMMARY

[0005] The present application aims to solve the problems existing in the prior art and provide a micro-expansion material suitable for PCCP joint filling, a preparation method and application thereof.

[0006] The technical scheme provides a micro-expansion material composition suitable for PCCP joint filling, which comprises a cementitious material system, and the composition realizes compensation for the volume shrinkage of the composition from the plastic stage after water mixing to the final setting and hardening through the synergistic effect of the following two functional components:

[0007] a) a plastic stage expansion component, which uniformly releases gas through its own chemical decomposition reaction when the composition is in a plastic flow state, to provide early volume expansion to resist and compensate for the volume shrinkage in the plastic stage;

[0008] b) a hardening stage expansion component, which participates in the hydration reaction and generates a crystalline product with expansion properties after the composition completes initial setting and enters the sustained hardening stage, to provide late and long-term volume expansion to resist and compensate for the volume shrinkage in the hardening stage and improve the structural density of the final hardened body.

[0009] Preferably, the effective component of the plastic stage expansion component is azodicarbonamide, and the particle size is in the range of 5-15 μm; the hardening stage expansion component comprises desulfurization tower bottom ash.

[0010] Preferably, in the desulfurization tower bottom ash, the content of calcium sulfate is between 20% and 30% by mass fraction, and the content of lime is between 30% and 50% by mass fraction.

[0011] Preferably, it further comprises raw slag, which is high-temperature molten slag directly discharged from an iron-making blast furnace without water quenching or other rapid cooling treatment.

[0012] Preferably, it further comprises:

[0013] a) a surfactant in the form of a powder, which is prepared from a polycarboxylic acid high-performance water reducing agent;

[0014] b) a water-retaining thickening agent in the form of a powder, the effective component of which is hydroxypropyl methyl cellulose.

[0015] According to another aspect of the present application, there is also provided a micro-expansion material composition, the components of which, in mass parts, constitute a dry mix of the composition:

[0016] Cement: 28-32 parts;

[0017] Desulfurization tower bottom ash: 7-11 parts;

[0018] Raw slag: 3-5 parts;

[0019] Fine aggregate: 40-44 parts;

[0020] Volume stabilizer: 0.02-0.03 parts;

[0021] Surfactant: 0.06-0.08 parts;

[0022] Water-retaining thickening agent: 0.004-0.006 parts.

[0023] Preferably, the fine aggregate is continuously graded river sand, and its particle size is in the range of 0.08 mm to 2.36 mm.

[0024] According to another aspect of the present application, there is also provided a dry mix micro-expansion material composition, which comprises cement and fine aggregate, and the composition further comprises:

[0025] a) Desulfurization tower bottom ash as an expansion source for generating expansive hydration products during the setting and hardening stage of the composition; and

[0026] b) Volume stabilizer, the active ingredient of which is azodicarbonamide;

[0027] The particle size of azodicarbonamide is in the range of 5 μm to 15 μm, so that it can provide effective early volume expansion by releasing uniform bubbles during the plastic stage of the composition after mixing with water.

[0028] According to another aspect of the present application, there is also provided the use of the micro-expansion material composition of any of the above embodiments in filling the joint of a prestressed concrete cylinder pipe (PCCP).

[0029] A method for preparing a dry mix of a micro-expansion material suitable for filling the joint of a PCCP, comprising the following steps:

[0030] (1) After drying treatment of the desulfurization tower bottom ash and raw slag respectively or jointly, grinding them to a specific surface area in the range of 200 m 2 / kg to 300 m 2 / kg;

[0031] (2) Adding the treated desulfurization tower bottom ash and raw slag, cement, and fine aggregate after drying treatment into a mixer in a predetermined ratio, and mixing to obtain a base dry mix;

[0032] (3) Pre-mixing the volume stabilizer, the surface active agent and the water-retention thickening agent to obtain an admixture powder;

[0033] (4) Adding the prepared admixture powder into the mixer containing the base dry material prepared in step (2) through a feeder and mixing again to finally obtain a dry mixture.

[0034] The micro-expansion material mixture prepared by the present application has excellent fluidity and can be filled and constructed under normal pressure. The hardened and consolidated body test piece prepared by the present application meets the strength requirement of the joint protection mortar of the socket joint, has excellent impermeability and expansion during the whole curing period from plasticity to hardening, and solves the cracking risk caused by shrinkage of the traditional cement-based joint material. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The contrast curve diagram of the volume change rate of the composition described in Embodiment 1 of the present application and different technical solutions with time.

[0036] Figure 2 The contrast relationship diagram of the internal expansion stress and the tensile strength development of the composition described in Embodiment 1 of the present application and a high-dosage crystalline expansion agent scheme.

[0037] Figure 3 The contrast column chart of the influence of different components on the construction performance of the material.

[0038] Figure 4 The contrast column chart of the influence of different expansion components on the 7-day expansion effect of the material.

[0039] Figure 5 The contrast column chart of the influence of different components on the 28-day mechanical properties of the material. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0041] In order to solve the problems existing in the prior art, the applicant has conducted in-depth research:

[0042] Firstly, for the plastic stage of the material, i.e. within several hours from the water mixing to the initial setting, the paste will produce significant plastic shrinkage due to water evaporation, aggregate settlement and cement particle flocculation. This shrinkage occurs very early, and if not compensated in time, it is extremely easy to form a small void or interface crack between the top of the joint filling body and the PCCP pipe wall, which will pose a major hidden danger for future leakage. However, the hydration reaction rate of the mainstream calcium sulphoaluminate (CSA) or calcium oxide (CaO) type expansive agent in the prior art is relatively slow, and the onset time of the expansion effect is usually after the initial setting of the material, which is obviously time-lagged in resisting and compensating the plastic shrinkage occurring within several hours. In other words, when the late expansion starts to take effect, the initial defects caused by early shrinkage have already been formed. That is, it is found that the plastic shrinkage occurs very early, while the traditional crystalline expansive agent starts too slowly, resulting in a missed early compensation and forming initial defects.

[0043] Secondly, for the hardening stage of the material, if a gas-producing type of expansive agent (such as aluminum powder) is used to solve the early expansion problem, its action time is too concentrated in the plastic stage, and once the paste loses its fluidity, its expansion process also basically stops, and it cannot compensate for the self-shrinkage and late drying shrinkage continuously generated in the hardening process. If the dosage of the calcium sulphoaluminate (CSA) type expansive agent is simply increased to pursue a higher total expansion rate, a new risk will be faced. Because the expansion process occurs in the hardening stage when the material has already formed a rigid skeleton, if the excessive crystalline expansion stress cannot be effectively released, it will cause micro-cracks in the material or excessive extrusion stress on the external constraint (PCCP pipe wall), thereby damaging the structural integrity and long-term durability of the material itself. In short, in the hardened body which has already formed a rigid structure, pure crystalline expansion will generate a huge internal stress, which will easily lead to cracking of the material itself if not released, i.e. the risk of expansion leading to cracking.

[0044] Therefore, how to construct a relay type expansion mechanism that can accurately match the shrinkage characteristics of the material at different stages, and realize the balance of expansion energy, has become a technical problem with depth and challenge in this field that needs to be solved urgently.

[0045] It should be noted that, unless otherwise specified, the various raw materials used in the embodiments of the present application are all commercially available conventional products, and the test methods used, unless otherwise specified, are all conventional methods.

[0046] Example 1 provides a micro-expansive material composition suitable for PCCP joint filling.

[0047] In this embodiment, the dry mixture of the composition is composed of the following components in mass fraction:

[0048] Cement, 28-32 parts; desulfurization tower bottom ash, 7-11 parts; raw slag, 3-5 parts; fine aggregate, 40-44 parts;

[0049] Volume stabilizer, 0.02-0.03 parts; surfactant, 0.06-0.08 parts; water-retaining thickening agent, 0.004-0.006 parts.

[0050] Preferably, cement, 30 parts; desulfurization tower bottom ash, 9 parts; raw slag, 4 parts; fine aggregate, 42 parts; volume stabilizer, 0.03 parts; surfactant, 0.07 parts; water-retaining thickening agent, 0.005 parts.

[0051] To achieve the technical effects of the present application, the key components in the above-mentioned formula are defined and controlled as follows:

[0052] The cement used is P·I 42.5 Portland cement. In some alternative embodiments, P·II 42.5 Portland cement or other cement meeting the GB175 standard can also be used.

[0053] In the dry-mixed composition of the present application, cement is used as the main cementitious material, and its amount can be set in the range of 28 to 32 parts by mass. This range is a basic guarantee for ensuring that the composition can form the basic mechanical strength and durability after hardening. Within this range, the cement can fully hydrate with water, providing the necessary alkaline environment and structural framework for the reaction of other functional components, especially the expansion component.

[0054] Further, the amount of cement is preferably controlled in the range of 29 to 31 parts by mass. Compared with the aforementioned wider range, this preferred range is more conducive to balancing the strength development, cost control, and expansion efficiency of the material. Too high a cement amount can increase the self-shrinkage of the material, which may offset part of the expansion effect; while too low a cement amount can affect the final mechanical properties. Therefore, 29 to 31 parts is a range that achieves a more optimal synergy between various performance indicators.

[0055] As the best embodiment of the present application, the amount of cement is 30 parts by mass. Experimental data show (as shown in Example 1) that when the amount of cement is 30 parts, the composition has the best comprehensive performance in terms of flowability, delamination degree, full-cycle expansion rate, and final strength, etc. under a specific ratio with other components, achieving the optimization of technical effects.

[0056] The volume stabilizer is a chemical additive used to provide early expansion during the plastic stage of the composition. In the present application, it specifically refers to a powder with effective ingredient of azodicarbonamide.

[0057] For example, the azodicarbonamide used has an effective content of not less than 95%. The particle size is controlled to be 10 μm by laser particle size analyzer, which falls within the range of 5-15 μm defined in claim 4.

[0058] The particle size of azodicarbonamide is controlled to be in this micron level, the motivation is that when it is in contact with the mixed water and the alkaline environment of cement to produce gas, it forms uniform dispersed tiny bubbles which are harmless to the structure of hardened body. These micro-bubbles generate sufficient expansion stress in the plastic stage to resist the volume loss of the material due to bleeding, settlement and autogenous shrinkage; at the same time, the micro-porous structure formed after hardening can be used as the release point of the later expansion stress, reducing the risk of cracking of the hardened body due to later excessive expansion.

[0059] In the present application, the volume stabilizer used as the expansion core in the plastic stage can be set in the range of 0.02-0.03 parts by mass. This range is the critical range to ensure that effective expansion can be generated in the plastic stage of the paste to resist early shrinkage. When the amount is less than 0.02 parts, the gas production is insufficient and the expansion effect is not obvious (as shown in Example 4).

[0060] Further, it is preferred to control the amount of volume stabilizer in the range of 0.025-0.03 parts by mass. This is a higher efficiency interval, which can more reliably provide the desired early expansion rate, and lay a more solid foundation for the subsequent interfacial adhesion and overall density.

[0061] As the best embodiment of the present application, the amount of volume stabilizer is 0.03 parts by mass. As shown in the comparison of Example 1 with Examples 3 and 4, the early expansion rate (0.852% at 3d) generated by the amount of 0.03 parts is much higher than that of lower dosage, which fully proves that this amount is the choice to achieve the best early volume compensation effect.

[0062] The desulfurization tower bottom ash refers to the solid discharge precipitated at the bottom of the flue gas desulfurization tower in the steel industry, which is used as the expansion source in the hardening stage in the present application.

[0063] For example, the desulfurization tower bottom ash used is analyzed by chemical composition, and the content of calcium sulfate is 25% and the content of lime is 40% by mass fraction. This numerical combination falls within the ranges of 20%-30% and 30%-50% defined in claim 5, respectively.

[0064] The calcium sulfate and active calcium oxide (lime) enriched in the desulfurization tower bottom ash will react with the aluminum phase (such as C3A) in the cement in the later stage of cement hydration and the long-term maintenance process, to generate a crystalline product with expansibility, mainly ettringite (AFt). This reaction process is slow and persistent, which can exactly compensate for the self-shrinkage and drying shrinkage of the cement stone in the later stage of hardening, thereby ensuring the volume stability of the material in the whole cycle.

[0065] In the present application, the desulfurization tower bottom ash as the core hardening stage expansion component, the amount thereof can be set to 7 to 11 parts by mass. This range ensures that there is enough late-stage expansion source (calcium sulfate and lime) in the system, which can continuously generate an expansive crystalline product after the material hardens, to compensate for the volume shrinkage in the later stage.

[0066] Further, the amount of desulfurization tower bottom ash is preferably controlled in the range of 8 to 10 parts by mass. In this narrower range, the rate and total amount of late-stage expansion are more easily controlled, which can not only ensure sufficient expansion, but also avoid the potential risk of damage to the structure skeleton formed due to excessive expansion, thereby making the long-term dimensional stability of the material better.

[0067] As the best embodiment of the present application, the amount of desulfurization tower bottom ash is 9 parts by mass. As shown in the comparative data of Examples 1, 6, and 7, the late-stage expansion effect provided by 9 parts of desulfurization tower bottom ash forms a perfect relay with the early-stage expansion effect provided by 0.03 parts of volume stabilizer, realizing a smooth and continuous expansion curve from the plastic stage to the hardening stage, which is better than other ratios.

[0068] The raw slag is high-temperature molten slag directly discharged from an iron-making blast furnace without water quenching or other rapid cooling treatment. This choice is different from the granulated blast furnace slag commonly used in the building materials industry, which is treated by water quenching to excite activity.

[0069] The use of raw slag instead of water-quenched slag is motivated by simplifying the slag disposal process, avoiding secondary water pollution and a large amount of energy consumption in the water quenching process, and conforming to the green and environmental protection technology trend. In the system of the present application, the raw slag can still provide a certain hydration activity after being ground, and can optimize the particle size distribution of the slurry.

[0070] The fine aggregate used in this example is continuous gradation natural river sand, and the particle size is controlled in the range of 0.08 mm to 2.36 mm by sieving method.

[0071] The use of continuous gradation river sand in this range can form a compact skeleton structure to ensure the strength and impermeability of the hardened body, and the reasonable upper limit of particle size (2.36 mm) ensures that the slurry can smoothly pass through the narrow gap of the PCCP joint.

[0072] The surface active agent is in a powder form, prepared by vacuum drying of polycarboxylic acid high performance water reducing agent, with a water reducing rate of not less than 30%. The water retaining thickening agent is also in a powder form, with an effective component of hydroxypropyl methyl cellulose (HPMC), and a viscosity of 2% aqueous solution of about 8×10³ mPa·s.

[0073] The powder form is to facilitate its uniform premixing in dry mixture. The polycarboxylic acid surface active agent provides strong dispersion, greatly reduces the water consumption, and gives the slurry high fluidity. The HPMC, as a macromolecular polymer, can lock water through its long chain structure and the hydrophilicity of hydroxyl groups, and improve the cohesiveness of the slurry, preventing bleeding and delamination due to excessive fluidity. The synergistic effect of the two is the key to achieving high fluidity and high stability of the material.

[0074] The dry mixture sample of the embodiment is prepared according to the method described in the following embodiment 2. The prepared dry mixture is mixed with water in a mass ratio of 100:17, and its performance is tested, and the results are shown in the following table 1 as embodiment 1. The test results show that the composition in this ratio has a consistency of 118 mm and a delamination degree of only 4 mm, with excellent pourable construction performance; the 7-day vertical expansion rate reaches 0.948%, showing excellent full-cycle expansion performance; and the 28-day compressive strength reaches 48.7 MPa, meeting the engineering design requirements.

[0075] The amount of raw slag can be set in the range of 3 to 5 parts by mass. Further, it is preferred to control the amount of raw slag in the range of 3.5 to 4.5 parts by mass. As the best embodiment of the present application, the amount of raw slag is 4 parts by mass.

[0076] The amount of fine aggregate can be set in the range of 40 to 44 parts by mass. Further, it is preferred to control the amount of fine aggregate in the range of 41 to 43 parts by mass. As the best embodiment of the present application, the amount of fine aggregate is 42 parts by mass.

[0077] The amount of surface active agent can be set in the range of 0.06 to 0.08 parts by mass. Further, it is preferred to control the amount of surface active agent in the range of 0.065 to 0.075 parts by mass. As the best embodiment of the present application, the amount of surface active agent is 0.07 parts by mass.

[0078] The amount of water retaining thickening agent can be set in the range of 0.004 to 0.006 parts by mass. Further, it is preferred to control the amount of water retaining thickening agent in the range of 0.0045 to 0.0055 parts by mass. As the best embodiment of the present application, the amount of water retaining thickening agent is 0.005 parts by mass.

[0079] The research found that the reaction of the desulfurization tower bottom ash occurred in the hardening stage when the material had lost its fluidity and formed a rigid structure. It provides volume compensation by generating expansive crystals such as ettringite. In the rigid space that is completely dense and has no elasticity, the growth of crystals will generate huge internal expansion stress. When this stress exceeds the tensile strength of the material itself, it will cause internal micro-cracks in the material, i.e. expansion cracking. This is a serious safety hazard and is an inherent risk of traditional large-dose expansion agent application.

[0080] In this scheme, the gas-producing reaction of the volume stabilizer as a precursor in the plastic stage is equivalent to pre-embedding hundreds of millions of size-controllable micro-pressure relief capsules or buffer spaces inside the entire material. By controlling the particle size of azodicarbonamide between 5 μm and 15 μm, it is ensured that these pre-set spaces are size-beneficial micron-sized pores rather than harmful macroscopic holes.

[0081] When the subsequent desulfurization tower bottom ash begins to react and generate expansive crystals, the expansion stress generated during the growth process can be absorbed and released by this pre-set micro-pore network. The crystals can directly grow into these micro-pores, allowing the internal stress to relax in place without accumulating indefinitely in the substrate. Therefore, the micro-pore structure formed has a certain release effect on the expansion stress after hardening, reducing the risk of cracking caused by expansion of the hardened paste. The reaction product of the precursor (micro-pore structure) provides a safe environment for the reaction of the later substance, resolving the cracking risk that may be caused by the later expansion.

[0082] In the traditional scheme, due to the risk of later cracking, designers often dare not use a sufficient amount of crystalline expansion agent, resulting in insufficient expansion compensation in the later stage, which cannot completely offset the hardening shrinkage, and the efficiency of the expansion agent is artificially limited.

[0083] Since the reaction product of the precursor (micro-pore structure) has already provided a safe pressure relief channel for the reaction of the later substance, it means that the dosage of the later substance (desulfurization tower bottom ash) can be optimized to a more ideal and efficient level without excessive concern about its negative effects. Under the premise of safety, the expansion reaction of the later substance can be more relaxed and more fully carried out. The expansion energy generated is no longer a destructive force that needs to be guarded everywhere, but can be effectively utilized as a constructive force. These energies are efficiently used to fill the capillary pores generated during the hydration process of the cement stone, to compensate for the long-term self-shrinkage and drying shrinkage, and ultimately to significantly improve the overall density and impermeability of the hardened body.

[0084] Embodiment 2, the embodiment provides a method for preparing the aforementioned micro-expanding material dry mixture.

[0085] The fine aggregate, desulfurization tower bottom ash and raw slag are respectively placed in an electrically heated blast drying device at 105°C-110°C for drying. Specifically, the final moisture content of the fine aggregate is controlled to be less than 0.5%, and the final moisture content of the desulfurization tower bottom ash and raw slag is controlled to be less than 0.4%. The motivation of this step is to remove the free water in the raw materials, to ensure the storage stability of the dry mixture and the accuracy of the water-material ratio during subsequent water mixing.

[0086] The desulfurization tower bottom ash and raw slag dried in step (1) are sent into a grinding device based on the principle of ball milling for grinding. The grinding time and rotating speed are adjusted to control the final specific surface area to be 250m 2 / kg, which falls within the range of 200m 2 / kg to 300m 2 / kg defined in claim 11. The purpose of this step is to grind the solid waste raw materials with relatively high inertness to a certain fineness, so as to increase the specific surface area and reactivity.

[0087] This embodiment adopts a two-step mixing method, specifically as follows:

[0088] First step of mixing: the treated cement, desulfurization tower bottom ash, raw slag and fine aggregate are added into a V-shaped mixer according to the proportions described in embodiment 1. The mixer is set to a stirring speed of 60r / min, and the mixing time is 900s, so that the mixture is a uniform solid particle-based dry material.

[0089] Second step of mixing: in another small mixing device, the three powder additives of volume stabilizer, surfactant and water-retention thickening agent are premixed according to the proportions described in embodiment 1, to obtain a mixed powder of additives. Then, the mixed powder is added into the still stirring dry material through a feeder, and the mixing is started again for 300s, to obtain the final, uniform dry mixture product.

[0090] The two-step mixing method, especially the premixing of the extremely small amount of additives (about 0.004% in total) and then adding them into the main material, can greatly improve the uniformity of the dispersion of these trace components in the whole, and avoid the performance fluctuations caused by uneven dispersion.

[0091] Embodiments 3-10: To further prove the necessity and beneficial effects of the key technical features of the present application, embodiments 3-10 are set as a comparison. The formulations of the embodiments are the same as those of embodiment 1 except for the following differences.

[0092] Embodiment 3: Compared with embodiment 1, the difference lies in that the amount of volume stabilizer is reduced from 0.03 parts to 0.02 parts.

[0093] Embodiment 4: Compared with embodiment 1, the difference lies in that the amount of volume stabilizer is further reduced to 0.01 parts.

[0094] Example 5: Compared with Example 1, the difference lies in that no volume stabilizer is added.

[0095] Example 6: Compared with Example 1, the difference lies in that the amount of desulfurization tower bottom ash is reduced from 9 parts to 5 parts, and the amount of cement is correspondingly increased from 30 parts to 34 parts.

[0096] Example 7: Compared with Example 1, the difference lies in that no desulfurization tower bottom ash is added, and the amount of cement is correspondingly increased from 30 parts to 39 parts.

[0097] Example 8: Compared with Example 1, the difference lies in that no raw slag is added, and the amount of cement is correspondingly increased from 30 parts to 34 parts.

[0098] Example 9: Compared with Example 1, the difference lies in that no surfactant is added.

[0099] Example 10: Compared with Example 1, the difference lies in that no water-retaining thickening agent is added.

[0100] The compositions prepared in Examples 1 and Comparative Examples 3-10 are all mixed according to a unified water usage of 14.5 parts of water (equivalent to about 170 parts of water per 1000 parts of dry mixture). The test method for the performance of the mixture (consistency, delamination degree) refers to the “Standard Test Methods for Basic Performance of Building Mortar” (JGJ / T 70-2009). The test method for vertical expansion rate refers to the “Technical Specification for Application of Concrete Admixtures” (GB 50119-2013). The test method for compressive strength after hardening refers to the “Test Rules for Hydraulic Concrete” (SL / T 352-2020).

[0101] The test results are summarized in Table 1 below. Table 1 Performance Test Results of Examples

[0102]

[0103] As can be seen from Comparative Examples 1, 3, 4, and 5, the dosage of the volume stabilizer directly affects the early (3d) vertical expansion rate. Example 5, which does not add a volume stabilizer, has a 3d expansion rate of negative value, showing early shrinkage. This proves the necessity of the volume stabilizer for compensating for plastic shrinkage, providing support for the effect of the expansion component in the plastic stage.

[0104] As can be seen from Comparative Examples 1, 6, and 7, the dosage of the desulfurization tower bottom ash significantly affects the expansion development in the later stage (3d to 7d). Example 7, which does not contain desulfurization tower bottom ash, has a 7d expansion rate that is basically unchanged from 3d or even slightly shrinks. This proves the necessity of the desulfurization tower bottom ash for providing expansion in the hardening stage, providing support for the effect of the expansion component in the hardening stage.

[0105] Comparative Example 1 and 9, Example 9 lacking surfactant, has a consistency of only 53 mm, losing flowability.

[0106] Comparative Example 1 and 10, Example 10 lacking water-retaining thickening agent, has a delamination degree of up to 28 mm, with serious bleeding segregation. This proves the necessity of the synergistic effect of the two admixtures for ensuring excellent construction performance.

[0107] Example 11: Scenario application of product use

[0108] Take 100 kg of dry mixture prepared in Example 1, add 17.0 kg of water, and stir for 3 minutes using a forced mortar mixer to form a uniform grout. Visually observe that the grout is in a uniform flow state, with no bleeding or segregation.

[0109] Pour the grout from the top of a simulated PCCP pipe bell and spigot joint with an outer diameter of 3 meters. The grout fills the entire annular joint cavity smoothly within 5 minutes by relying on its own weight, until it overflows from the exhaust hole on the other side, without the need for any external pressure or vibration.

[0110] After 28 days of curing, disassemble and dissect the simulated joint. Observe that the hardened filling has a smooth surface and uniform internal structure, with no visible cracks, holes, or hollow defects. The hardened body is tightly bonded to the concrete base surface of the pipe and the steel bell ring, with no gaps. The application results show that the composition of the application can well meet the technical requirements for PCCP joint filling, with a full and dense filling effect.

[0111] Example 12: A micro-expansive material suitable for PCCP joint filling and a preparation method thereof.

[0112] To achieve the above performance requirements, the following compounding scheme is adopted: cement 28-32 parts, desulfurization tower bottom ash 7-11 parts, raw slag 3-5 parts, fine aggregate 40-44 parts, volume stabilizer 0.02-0.03 parts, surfactant 0.06-0.08 parts, water-retaining thickening agent 0.004-0.006 parts, and water 163-177 parts.

[0113] Preferably, the micro-expansive material for PCCP joint filling has a mix proportion of: cement 30 parts, desulfurization tower bottom ash 9 parts, raw slag 4 parts, fine aggregate 42 parts, volume stabilizer 0.03 parts, surfactant 0.07 parts, water-retaining thickening agent 0.005 parts, and water 170 parts.

[0114] Preferably, the cement is P•I 42.5 or P•II 42.5 Portland cement.

[0115] Preferably, the desulfurization tower bottom ash and the raw slag are dried at 105-110°C, and the water content is controlled to be less than 0.4%. The dried desulfurization tower bottom ash and the raw slag are ground to a sieve residue of not more than 1.0% on a 0.150mm sieve.

[0116] Preferably, the fine aggregate is continuously graded natural river sand, which is dried at 105-110°C, and the water content is controlled to be less than 0.5%. The particles with a particle size of not less than 0.08mm and not more than 2.36mm are taken by sieving according to the national standard ISO B square hole sieve.

[0117] Preferably, the content of the effective component (azo dicarboxamide) of the volume stabilizer is controlled to be more than 95%, the particle size is controlled to be between 5μm and 15μm, and the raw material ratio of hydrazine hydrate to urea in the synthesis process is controlled to be between 1:2.0 and 2.2.

[0118] Preferably, the water-reducing rate of the surfactant is not less than 30%.

[0119] Preferably, the content of the effective component (HPMC) of the water-retaining thickening agent is not less than 90%, the powder particle size is controlled to be between 100μm and 150μm, and the polymer molecular weight is controlled to be between 8×10 4 ~2×10 5 ; the viscosity of a 2% mass fraction powder particle aqueous solution is controlled to be between 7×10 3 mPa•s and 1×10 4 mPa•s.

[0120] A preparation method of a micro-expansion material suitable for PCCP joint filling, the preparation method comprising the following steps:

[0121] (1) drying the fine aggregate, the desulfurization tower bottom ash and the raw slag respectively;

[0122] (2) grinding the dried desulfurization tower bottom ash and the raw slag to a specific surface area of 200m 2 / kg~300m 2 / kg;

[0123] (3) adding the treated cement, the desulfurization tower bottom ash, the raw slag and the fine aggregate into a mixer in proportion, and mixing to obtain a uniform solid particle dry material;

[0124] (4) fully mixing the volume stabilizer, the surfactant and the water-retaining thickening agent, and adding the mixed powder into the mixer through a feeder, and mixing again according to the method of step (3) to obtain a dry mixture.

[0125] (5) the grinding method used in step (2) is a grinding equipment based on the principle of ball milling, and the stirring rate of the mixer in step (3) is not less than 60r / min, and the mixing time is not less than 900s.

[0126] Preferably, the mixing machine has a uniformity of mixing of not less than 98%.

[0127] The PCCP joint filling micro-expansion material prepared by the application is prepared by using cement, desulfurization tower bottom ash, blast furnace raw slag and natural river sand as main materials, using volume stabilizer (effective component is azodicarbonamide), surfactant (effective component is powder polycarboxylic acid) and water-retaining thickening agent (effective component is HPMC) as admixtures, and compounding in specific amount, so that the PCCP joint filling micro-expansion material has sufficient mechanical properties, and meanwhile, the volume stability of the material from plasticity to hardened consolidation body from construction to service is considered, and the cracking risk of the traditional cement-based joint material caused by shrinkage is fully inhibited.

[0128] The PCCP joint filling micro-expansion material prepared by the application uses azodicarbonamide as the effective component of the volume stabilizer, can continuously release the expansion amount in the plastic stage of the mixture, offsets the shrinkage cracking tendency caused by the autogenous volume deformation of the cement hydration reaction, and uses the calcium sulfate salt crystal in the desulfurization tower bottom ash and the lime component to provide the expansion release amount of the material after hardening and consolidation. Through the above-mentioned means, the material can produce sufficient expansion effect in the plastic and hardened stages, ensures the bonding performance of the joint material and the outer protective mortar of the PCCP bell and spigot, and improves the joint compactness. In particular, the fineness of the volume stabilizer particles is controlled to be between 5 μm and 15 μm, because in this scale, the pores introduced in the mixture system are small-sized gel pores and capillary pores which are beneficial to the durability of the mortar, on the one hand, the mixture can produce expansion effect in the plastic stage, and on the other hand, the microporous structure formed has a certain release effect on the expansion stress after hardening, and reduces the cracking risk of the hardened paste caused by expansion.

[0129] The PCCP joint filling micro-expansion material prepared by the application highlights the reuse of solid waste resources, uses the desulfurization tower bottom ash and the blast furnace raw slag as raw materials, and especially the application of the raw slag avoids the secondary pollution and energy loss in the cold quenching disposal process of the granulated blast furnace slag.

[0130] The prepared PCCP joint filling micro-expansion material of the application uses high-performance polycarboxylic acid powder water reducing agent and macromolecular hydroxypropyl methyl cellulose (HPMC) as a surface active agent and water retaining thickener, so that the material has excellent fluidity, meets the construction conditions of pressureless joint filling, and optimizes the uniformity of the mixed system in the plastic stage, so that the compactness and uniformity of the joint filling are guaranteed during pressureless joint filling construction. In particular, the process of grinding after freeze-drying is used, so that the originally liquid polymer can be added to the dry-mixed mortar in a solid form, significantly improving the convenience of construction mixing, and control indexes for the particle size of the powder water retaining thickener and the viscosity of the aqueous solution are proposed, which meet the thickening effect of the additive on the viscosity of the mixed system.

[0131] In the present application, in view of the problem that the expansion compensation effect and the shrinkage process in the plastic stage of the material are mismatched in time, a volume stabilizer with specific particle size (5-15 μm) of azodicarbonamide as an effective component is introduced. When the dry-mixed material is mixed with water, azodicarbonamide will immediately undergo a rapid chemical decomposition reaction in the alkaline environment formed by cement hydration, releasing uniform, dispersed and small-sized nitrogen bubbles. This gas production process almost synchronously occurs with the plastic shrinkage process of the slurry, and the internal expansion pressure generated thereby can immediately and effectively resist and compensate for the early volume loss caused by bleeding, settlement and other reasons. The time difference problem that the traditional calcium sulphoaluminate (CSA) type expansion agent cannot compensate for the plastic shrinkage is solved. In other words, the present application adopts a fast-to-fast strategy to completely eliminate the early defects before they are formed.

[0132] In view of the problem that the insufficient expansion amount or excessive expansion stress in the later stage leads to cracking, the problem is solved through the synergistic effect of two levels:

[0133] The present application uses desulfurization tower bottom ash as an expansion component in the hardening stage. After the volume stabilizer completes its mission in the plastic stage, the active calcium sulfate and calcium oxide in the desulfurization tower bottom ash begin to participate in the secondary hydration reaction in the hardened cement stone framework, continuously generating ettringite and other expansion crystalline products. This process is persistent and gentle, providing a continuous and long-term expansion energy for compensating for the self-shrinkage and drying shrinkage in the middle and later stages of hardening. This solves the problem of lack of follow-up expansion in the later stage when using a gas-producing type expansion agent alone.

[0134] The uniform distribution of billions of tiny bubbles generated by the volume stabilizer (azodicarbonamide) in the plastic stage will form a network of micro-porous structure in the cement matrix after hardening. When the later desulfurization tower bottom ash hydration produces a crystalline expansion stress, these micro-pores act as a pressure buffer pad and stress release point. The expanding crystals can grow into these pre-set micro-pores, so that the macroscopic expansion stress is effectively relaxed and released, avoiding stress concentration. Therefore, the expansion produced by the present application is a resilient and flexible expansion, which can provide sufficient volume compensation to ensure compactness, and will not cause the matrix to crack due to excessive stress. This perfectly solves the risk of cracking caused by the hard collision of traditional high-dosage expansion agents in rigid systems.

[0135] In summary, the present application fundamentally solves the inherent contradictions and limitations of the prior art in the control of volume stability throughout the cycle by the ingenious coupling of expansion components with two different mechanisms and acting in different time windows, and the clever design of creating favorable conditions for later reactions using early products.

[0136] In short, the early use of azodicarbonamide (volume stabilizer) for rapid gas production characteristics precisely corresponds to and compensates for the shrinkage in the plastic stage. The later use of slow hydration and crystallization of desulfurization tower bottom ash continuously compensates for the long-term shrinkage after hardening.

[0137] The micro-porous structure network formed in the early stage acts as a micro-buffer capsule for releasing the crystalline expansion stress in the later stage. When the expanding crystals grow, their stress can be absorbed and relaxed by these pre-set micro-pores, thereby avoiding the formation of destructive stress concentration in the rigid matrix.

[0138] The above describes the preferred embodiments of the present application in detail, but the present application is not limited to the specific details in the above embodiments, and various equivalent transformations of the technical solutions of the present application can be made within the technical concept of the present application, which all belong to the protection scope of the present application.

Claims

1. A micro-expandable material composition suitable for PCCP joint filling, comprising a gelling material system, characterized in that: The composition compensates for the volume shrinkage of the composition during the entire cycle from the plastic stage after adding water to the final setting and hardening through the synergistic effect of the following two functional components: a) a plastic stage expansion component, which releases gas uniformly through its own chemical decomposition reaction when the composition is in a plastic flow state, providing early volume expansion to counteract and compensate for the volume contraction in the plastic stage; b) The expansive component in the hardening stage, which, after the composition completes initial setting and enters the continuous hardening stage, participates in the hydration reaction through its own components and generates an expansive crystalline product, providing late and long-term volume expansion to counteract and compensate for the volume shrinkage in the hardening stage, and improve the structural density of the final hardened body.

2. The micro-expandable material composition according to claim 1, characterized in that: The active ingredient of the expansion component in the plastic stage is azodicarbonamide, and the particle size is in the range of 5 μm to 15 μm; The expansion component in the hardening stage contains desulfurization tower bottom ash.

3. The micro-expandable material composition according to claim 2, characterized in that: In the desulfurization tower bottom ash, the calcium sulfate content is between 20% and 30%, and the lime content is between 30% and 50%, calculated by mass fraction.

4. The micro-expandable material composition according to claim 1, characterized in that: It also includes raw slag, which is the high-temperature slag directly discharged from the iron-making blast furnace without water quenching or other rapid cooling treatment.

5. The micro-expandable material composition according to claim 1, characterized in that: Also includes: a) Powdered surfactant, prepared from polycarboxylic acid high-performance water reducer; b) Water-retaining thickener in powder form, the active ingredient is hydroxypropyl methylcellulose.

6. The micro-expandable material composition according to claim 1, characterized in that: The components of the dry blend composition are as follows: Cement: 28-32 parts; Desulfurization tower bottom ash: 7~11 parts; Original slag: 3~5 parts; Fine aggregate: 40~44 parts; Volume stabilizer: 0.02~0.03 parts; Surfactant: 0.06~0.08 parts; Water-retaining thickener: 0.004~0.006 parts.

7. The micro-expandable material composition according to claim 6, characterized in that: The fine aggregate is continuously graded river sand with a particle size ranging from 0.08 mm to 2.36 mm.

8. A dry-mixed micro-expandable material composition comprising cement and fine aggregate, characterized in that: The composition also contains: a) Desulfurization tower bottom ash, which serves as an expansion source for generating expansive hydration products during the coagulation and hardening stage of the composition; and b) Volume stabilizer, the active ingredient of which is azodicarbonamide; The particle size of azodicarbonamide is in the range of 5 μm to 15 μm, so that it can provide effective early volume expansion by releasing uniform bubbles in the plastic stage after the composition is mixed with water.

9. Use of the slightly expansive material composition according to any one of claims 1 to 8 in filling joints of prestressed concrete cylinder pipes (PCCP).

10. A method for preparing a dry mix of a micro-expanding material suitable for PCCP joint filling, characterized in that: The following steps are involved: (1) Dry the desulfurization tower bottom ash and the original slag separately or together, and grind them until their specific surface area reaches 200m 2 / kg to 300m 2 / kg range; (2) Adding the treated desulfurization tower bottom ash and raw slag, cement and dried fine aggregate into a mixer in a predetermined proportion and mixing them to obtain basic dry materials; (3) premixing a volume stabilizer, a surfactant, and a water-retaining thickener to obtain an admixture mixed powder; (4) The prepared admixture mixed powder is added to the mixer containing the basic dry material prepared in step (2) through a feeder, and mixed again to finally obtain a dry mixed material.

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