Active control method for concrete shrinkage and creep based on aggregate characteristics and water-binder ratio

Abstract

The application discloses a kind of based on aggregate characteristics and water-binder ratio concrete shrinkage and creep active control method, comprising the following steps: determining the physicochemical properties and mechanical properties of pure cement;According to the data of pure cement determined, actively control preparation low shrinkage type high-strength mortar;According to the low shrinkage type high-strength mortar prepared by active control, combined with active control admixture aggregate and water-binder ratio, low shrinkage type concrete with expected creep degree and strength is prepared.The technical problems of poor engineering applicability of the prior art for concrete shrinkage and creep control method, and not considering the influence of aggregate elastic modulus on concrete shrinkage are solved.

Description

Technical Field

[0001] This invention relates to the field of building construction materials technology, and more specifically, to an active control method for concrete shrinkage and creep based on aggregate properties and water-cement ratio. Background Technology

[0002] Currently, concrete undergoes shrinkage and creep during hydration and under subsequent stress, leading to structural cracking and stress relaxation. Existing design systems often neglect concrete deformation, severely impacting structural durability. Minimizing concrete shrinkage is now a consensus in high-performance concrete design; however, lower creep is not always better. For structures requiring high concrete volume stability, such as prestressed concrete and railway sleepers, strict control of creep is essential. Furthermore, concrete deformation is not entirely without benefit; for large-volume concrete structures, situations like support settlement causing stress necessitate increased creep to disperse concentrated stress within the structure. Therefore, developing low-shrinkage concrete with actively controllable creep has significant engineering implications for improving concrete quality.

[0003] Concrete shrinkage mainly occurs during the early stages of hydration and the later stages of drying. Early-stage shrinkage is primarily influenced by the cementitious material itself. At this stage, due to the low concrete strength and good deformation properties, concentrated stress is less likely to form within the concrete. During drying shrinkage, the shrinkage process is further limited by the aggregate because the hydration gel and aggregate have formed a spatial framework. However, when the elastic modulus of the aggregate is insufficient, it cannot inhibit shrinkage. During concrete creep, the microstructure of the cementitious gel changes, producing viscoplastic deformation similar to fluid flow. This deformation increases over time. Eventually, when the deformation is transferred to aggregates with higher elastic moduli, the creep begins to stabilize due to the aggregate interlocking effect. Therefore, concrete creep is also influenced by the combined effects of cementitious materials and concrete aggregates. Generally, aggregates with high elastic moduli can inhibit creep growth. However, when the elastic modulus of the aggregate is too high, the cement shrinkage cannot coordinate with the deformation, leading to concentrated stress within the gel. This concentrated stress makes the concrete highly susceptible to brittle failure at both the micro and macro levels.

[0004] Based on the above, the industry has reached a consensus that the selection of raw materials and the water-cement ratio of hydration gel are the main factors affecting concrete shrinkage and creep, and that a lower water-cement ratio results in a smaller shrinkage value compared to a higher water-cement ratio.

[0005] Regarding the creep properties of adhesives, the inventors disclosed a method for actively controlling concrete creep using the elastic modulus of mineral admixtures in Chinese patent CN103787606B. This method involves designing mix proportions by observing the microstructure of concrete paste at 28, 90, and 180 days, and controlling concrete creep by adjusting the mineral admixtures. However, large amounts of mineral admixtures significantly affect concrete strength, a factor this technical solution fails to consider, thus not meeting engineering design requirements. Furthermore, this method does not account for the influence of aggregate elastic modulus, resulting in poor engineering applicability. Chinese patent CN111798931A discloses a mix proportion design method for prestressed concrete using manufactured sand and gravel aggregates based on deformation control. However, this technical solution does not provide specific mix proportion adjustment methods, leading to poor engineering applicability, and it also fails to consider the influence of aggregate elastic modulus on concrete shrinkage.

[0006] Building upon previous research, this invention has conducted extensive experimental studies on the single and combined effects of water-cement ratio and aggregate elastic modulus on shrinkage and creep, achieving significant results. Based on this, a technical solution for the active control of concrete shrinkage and creep based on aggregate properties and water-cement ratio is proposed. Summary of the Invention

[0007] Therefore, this invention provides an active control method for concrete shrinkage and creep based on aggregate properties and water-cement ratio, in order to solve the technical problems of poor engineering applicability of existing methods for controlling concrete shrinkage and creep, and the failure to consider the influence of aggregate elastic modulus on concrete shrinkage.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] An active control method for concrete shrinkage and creep based on aggregate properties and water-cement ratio includes the following steps:

[0010] Determine the physicochemical properties and mechanical properties of pure cement;

[0011] Based on the measured data of pure cement, the preparation of low-shrinkage high-strength mortar is actively controlled;

[0012] Based on the actively controlled preparation of low-shrinkage high-strength mortar, and combined with actively controlled admixtures and water-cement ratio, low-shrinkage concrete with the expected creep and strength is prepared.

[0013] Based on the above technical solution, the present invention is further described as follows:

[0014] As a further aspect of the present invention, the determination of the physicochemical properties and mechanical properties of pure cement specifically includes:

[0015] The physicochemical and mechanical properties of pure cement were determined. During the determination of these properties, the specific surface area of ​​the cement was measured using a laser particle size analyzer. The specific surface area of ​​the cement used was 360–370 m². 2 / kg.

[0016] As a further aspect of the present invention, the step of actively controlling the preparation of low-shrinkage high-strength mortar based on measured pure cement data specifically includes:

[0017] Based on the measured pure cement data, the mix proportions were actively controlled to prepare low-shrinkage high-strength mortar with predetermined early strength and low shrinkage value. A strength prediction model was established based on the predetermined early strength, and an elastic modulus prediction model was simultaneously established based on the strength prediction model to obtain elastic modulus prediction data.

[0018] As a further aspect of the present invention, the method of actively controlling the mix proportion to prepare a low-shrinkage high-strength mortar with predetermined early strength and low shrinkage value based on measured pure cement data specifically includes:

[0019] Fly ash and mineral powder are mixed in a certain proportion to form a composite mineral admixture;

[0020] By using fly ash and mineral powder as mineral admixtures, the heat of hydration of cement can be reduced, and mineral admixtures can be used as micro-aggregates to form a spatial skeleton to reduce the early shrinkage of concrete.

[0021] Continue to incorporate silica fume as an early strength conditioning phase to compensate for the strength loss caused by the incorporation of mineral admixtures;

[0022] Gypsum is further incorporated as an early shrinkage regulating phase. By incorporating gypsum during the hydration process, ettringite crystals are generated. The micro-expansion effect caused by the ettringite crystals is used to adjust the early shrinkage, and finally, a low-shrinkage mortar that meets the strength requirements is designed and formed.

[0023] Based on the above proportions, the amounts of mineral admixtures, silica fume, and gypsum are determined according to the predetermined early strength and low shrinkage value control requirements to form a low-shrinkage mortar phase.

[0024] As a further aspect of the present invention, the step of establishing a strength prediction model based on a predetermined early strength, simultaneously establishing an elastic modulus prediction model based on the strength prediction model, and obtaining elastic modulus prediction data specifically includes:

[0025] Define the early compressive strength σ of mortar at 28 days. m0 ;

[0026] The mortar strength σ over 360 days mt The prediction model is:

[0027] σ mt =σ m0 ·kt (1)

[0028] Where, k t It is a time correction parameter; the strength of the mortar changes with the time t corresponding to 28d to 360d.

[0029] Based on experimental data, the elastic modulus and strength σ of mortar can be determined. mt The correlation between them allows for the fitting of the elastic modulus E of the low-shrinkage mortar phase. mt Predictive model:

[0030] E mt =0.0081σ mt +0.5909+R1 (2)

[0031] R1 is a correction coefficient, which represents the change in the elastic modulus of the mortar with time t.

[0032] As a further aspect of the present invention, the preparation of low-shrinkage concrete with the desired creep and strength based on actively controlled low-shrinkage high-strength mortar, combined with actively controlled admixtures and water-cement ratio, specifically includes:

[0033] Based on the expected creep and strength of low-shrinkage concrete, a prediction model for concrete creep and a prediction model for strength are established based on the predicted elastic modulus of low-shrinkage high-strength mortar, the characteristic data of admixtures, and the water-cement ratio data. Through the prediction models for concrete creep and strength, the admixtures and the water-cement ratio are actively controlled to prepare low-shrinkage concrete with the expected creep and strength.

[0034] As a further aspect of the present invention, the step of establishing a concrete creep prediction model based on the expected creep and strength of the prepared low-shrinkage concrete, using the elastic modulus prediction data of low-shrinkage high-strength mortar and the characteristic data of admixture aggregates, specifically includes:

[0035] Aggregates include coarse aggregates and fine aggregates. When the elastic moduli of the coarse and fine aggregates are the same, the elastic modulus E of the low-shrinkage mortar phase is determined based on concrete creep as determined by experimental data. mt The correlation between the values ​​was used to establish the 360-day creep C of concrete. ct The prediction model is:

[0036] C ct = -34.5E mt +71.465+R2 (3)

[0037] Where R2 is the correction factor, and C is the 360-day creep coefficient of concrete. ct With the elastic modulus E of the low-shrinkage mortar phase mt Synchronous changes;

[0038] When the elastic modulus of coarse aggregate is inconsistent with that of fine aggregate, the creep C of the prepared concrete will be different. ctd The prediction model is:

[0039] C ctd =C ct E r / E dr (4)

[0040] Among them, E r / E dr It is the correction coefficient when the elastic modulus of aggregates is inconsistent. The elastic modulus of concrete is predicted by the elastic modulus of mortar. The premise is that the elastic modulus of aggregates used in making concrete is the same as that of mortar. Therefore, when the elastic modulus of aggregates and mortars are different, it is necessary to make corrections, that is, to make linear corrections by formula (4).

[0041] As a further aspect of the present invention, the establishment of a concrete creep prediction model based on the elastic modulus prediction data of low-shrinkage high-strength mortar, the characteristic data of admixture aggregates, and the water-cement ratio data specifically includes:

[0042] When the elastic modulus of aggregates is consistent, with a water-cement ratio of 0.36 as the benchmark, the 360-day creep C of concrete is... ctr The linear relationship between the water-cement ratio Rw and the water-cement ratio is as follows:

[0043] C ctr =C ct (1.935R w +0.3026+R3) (5)

[0044] Where R3 is the correction factor, and C is the 360-day creep coefficient of concrete. ctr With water-cement ratio R w When the aggregate materials are consistent and the water-cement ratio changes synchronously, the effect is achieved through (1.935R). w +0.3026+R3) corrects for the effect of water-cement ratio;

[0045] When the elastic modulus of aggregates is inconsistent, it is necessary to add a correction component E to the aggregates. r / E dr 360d creep C of concrete ctr The linear relationship between the water-cement ratio Rw and the water-cement ratio is as follows:

[0046] C ctr =C ctd (1.935R w +0.3026+R3)

[0047] That is, C ctr = (-34.5E) mt+71.465+R2)E r / E dr (1.935R w +0.3026+R3) (6)

[0048] Therefore, by substituting equations (1), (2), (3), (4), (5), and (6) into the calculation, the creep degree C of concrete after 360 days is obtained. ctr The prediction model is:

[0049] C ctr =(-34.5(0.0081σ) mt +0.5909+R1)+71.465+R2)·E r / E dr ·(1.935R w +0.3026+R3)(7).

[0050] As a further aspect of the present invention, the concrete strength prediction model established based on the elastic modulus prediction data of low-shrinkage high-strength mortar, the characteristic data of admixture aggregates, and the water-cement ratio data specifically includes:

[0051] Concrete later-stage strength σ ct The prediction model is:

[0052] σ ct =σ m0 ·k t ·k a ·(E dr / E r )·k Rw (8)

[0053] Where, k a This refers to the influence coefficient of admixtures, such as the influence coefficient of water-reducing agents and early-strength agents; E dr / E r k is the aggregate correction factor. Rw This is the correlation coefficient between the water-cement ratio and the adhesive ratio.

[0054] As a further aspect of the present invention, the following steps are also included:

[0055] When the raw materials are of the same type, concrete creep is also affected by the particle size range. Taking the particle size of 5-31.5 mm as the benchmark, concrete creep shows a trend of first increasing and then decreasing as the particle size decreases.

[0056] The concrete 360-day post-creep C ctr The predictive model forecasts concrete creep values. When the concrete creep exceeds the expected design value, the creep is adjusted through the following methods:

[0057] 1) Select coarse aggregates with a specific elastic modulus to ensure that the elastic modulus of the aggregates is not less than 270 kgf / mm². 2 This is to avoid the inability to suppress concrete shrinkage due to insufficient elastic modulus of concrete aggregate;

[0058] 2) Reduce aggregate particle size to 5-25mm;

[0059] 3) While ensuring the strength of the concrete, select a specific water-reducing agent to reduce the water-cement ratio.

[0060] When the creep of concrete is lower than the design value, the creep can be increased through the following three methods:

[0061] 1) Select coarse aggregates with a specific elastic modulus to ensure that the elastic modulus of the aggregates is not less than 310 kgf / mm². 2 This is to avoid the inability to coordinate deformation during concrete shrinkage due to excessively high elastic modulus of concrete aggregate, which could lead to concentrated stress inside the concrete.

[0062] 2) Reduce aggregate particle size to 5-20 mm;

[0063] 3) Reduce the water-cement ratio and the proportion of mineral admixtures to ensure concrete strength;

[0064] When a single adjustment method cannot meet the creep design requirements, at least two adjustment methods should be combined to meet the expected design requirements.

[0065] The present invention has the following beneficial effects:

[0066] 1. This invention divides concrete into two parts: mortar and aggregate. Based on a large amount of experimental data and mathematical statistics, it establishes a predictive model for concrete creep that considers mortar strength, aggregate elastic modulus, and water-cement ratio. The model is simple, intuitive, and highly applicable, and provides theoretical support for other related technologies.

[0067] 2. Concrete shrinkage and creep are complementary and both have a significant impact on the durability of concrete and its stability in engineering applications. Therefore, considering both simultaneously, this invention achieves synchronous control of shrinkage and creep through comprehensive adjustment of mineral admixtures, aggregates, etc., resulting in a significant improvement in technical performance.

[0068] 3. Due to the presence of various mineral admixtures in cement, the performance of cement produced by different manufacturers varies significantly. Therefore, the technical approach of controlling concrete shrinkage and creep based on cementitious materials has certain limitations. Compared to cementitious materials, aggregates have more stable physical and chemical properties. Thus, a method was established to control concrete shrinkage by using the elastic modulus and particle size range of aggregates as parameters. Based on a large amount of experimental data, a simple and feasible adjustment scheme was developed. The implementation process is simple and the engineering applicability is strong.

[0069] 4. This invention breaks through the traditional concept of low shrinkage and low creep in concrete and establishes a technical approach for bidirectional adjustment of low shrinkage and creep, which has stronger engineering applicability compared with other technical solutions. Attached Figure Description

[0070] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The structures, proportions, sizes, etc., drawn in this specification are only used to complement the content disclosed in the specification, so that those skilled in the art can understand and read them. Any modifications to the structure, changes in the proportional relationships, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0071] Figure 1 This is a schematic diagram of the process of adding gypsum to produce ettringite in the active control method for concrete shrinkage and creep based on aggregate properties and water-cement ratio provided in an embodiment of the present invention.

[0072] Figure 2 This diagram illustrates the relationship between mortar strength and elastic modulus in the active control method for concrete shrinkage and creep based on aggregate properties and water-cement ratio provided in this embodiment of the invention.

[0073] Figure 3 This diagram illustrates the relationship between the mortar elastic modulus and concrete creep in the active control method for concrete shrinkage and creep based on aggregate properties and water-cement ratio, as provided in an embodiment of the present invention.

[0074] Figure 4 This is a schematic diagram illustrating the influence of aggregate particle size on creep degree in the active control method for concrete shrinkage and creep based on aggregate properties and water-cement ratio provided in an embodiment of the present invention.

[0075] Figure 5 This is a schematic diagram illustrating the influence of aggregate hardness and water-cement ratio on concrete creep in the active control method for concrete shrinkage and creep based on aggregate properties and water-cement ratio provided in an embodiment of the present invention. Detailed Implementation

[0076] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0077] The terms "upper," "lower," "left," "right," and "middle" used in this specification are merely for clarity of description and are not intended to limit the scope of the invention. Any changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0078] like Figures 1 to 5 As shown, this invention provides an active control method for concrete shrinkage and creep based on aggregate properties and water-cement ratio. This method breaks through the traditional concept of low shrinkage and low creep in concrete, establishing a technical approach for bidirectional adjustment of both shrinkage and creep. Concrete is divided into mortar and aggregate components, and based on data and mathematical statistics, a predictive model for concrete creep is established, integrating mortar strength, aggregate elastic modulus, and water-cement ratio. The overall approach is simpler and more intuitive, providing theoretical support for other related technologies and exhibiting stronger engineering applicability compared to other technical solutions. Specifically, the method includes the following steps:

[0079] Step S1: Determine the physicochemical properties and mechanical properties of pure cement;

[0080] In step 1), when determining the physical and chemical properties of pure cement, the selected cement is P.Ⅱ42.5R cement for engineering use, which meets the relevant provisions of Chinese standard GB175-2007.

[0081] Furthermore, the specific surface area of ​​the cement was determined using a laser particle size analyzer.

[0082] Preferably, the specific surface area of ​​the cement used is 360–370 m². 2 / kg.

[0083] Step S2: Based on the measured pure cement data, actively control the preparation of low-shrinkage high-strength mortar;

[0084] Specifically, based on the measured pure cement data, the mix proportions are actively controlled to prepare low-shrinkage high-strength mortar with predetermined early strength and low shrinkage value. A strength prediction model is established based on the predetermined early strength, and an elastic modulus prediction model is established simultaneously based on the strength prediction model to obtain elastic modulus prediction data.

[0085] In step 2), fly ash and mineral powder are mixed in a certain proportion to form a composite mineral admixture.

[0086] By using fly ash and mineral powder as mineral admixtures, the heat of hydration of cement is reduced, and the mineral admixtures are used as micro-aggregates to form a spatial skeleton, thereby reducing the early shrinkage of concrete.

[0087] Furthermore, silica fume is added as an early strength-regulating phase to compensate for the strength loss caused by the incorporation of mineral admixtures.

[0088] Furthermore, gypsum is further incorporated as an early shrinkage regulator to facilitate the formation of ettringite crystals during hydration (see reference). Figure 1 By utilizing the micro-expansion effect induced by ettringite crystals, early shrinkage is adjusted, ultimately resulting in a low-shrinkage mortar that meets strength requirements.

[0089] Based on the above proportions, the amounts of mineral admixtures, silica fume, and gypsum are determined according to the predetermined early strength and low shrinkage value control requirements to form a low-shrinkage mortar phase.

[0090] Preferably, the fly ash used is Grade I fly ash, with a specific surface area 2 to 2.3 times that of cement and an elastic modulus of 100 to 130 GPa.

[0091] Preferably, the slag used is S95 grade slag, with a specific surface area of ​​0.9 to 1.1 times that of cement and an elastic modulus of 70 to 80 GPa.

[0092] Preferably, the silica fume used is a high-density silica fume, with a dosage of 4-10% and a specific surface area that is 0.9-1.1 times that of cement.

[0093] Preferably, the gypsum used contains more than 90% CaSO4, with an admixture amount of 3-7%, and a specific surface area that is 2.7-3.0 times that of cement.

[0094] According to GB50203-2011, the early compressive strength σ of mortar at 28 days is defined as... m0 .

[0095] The mortar strength σ over 360 days mt The prediction model is:

[0096] σ mt =σ m0 ·k t (1)

[0097] Where, k t It is a time correction parameter; the strength of the mortar changes with the time t corresponding to 28d to 360d.

[0098] like Figure 2 As shown, based on experimental data, the elastic modulus and strength σ of the mortar are related. mt The correlation between them allows for the fitting of the elastic modulus E of the low-shrinkage mortar phase. mt Predictive model:

[0099] E mt =0.0081σ mt +0.5909+R1 (2)

[0100] R1 is a correction coefficient, which represents the change in the elastic modulus of the mortar with time t.

[0101] Step S3: Based on the actively controlled low-shrinkage high-strength mortar, and combined with actively controlled admixtures and water-cement ratio, prepare low-shrinkage concrete with the expected creep and strength.

[0102] Specifically, based on the expected creep and strength of low-shrinkage concrete, a concrete creep prediction model and a strength prediction model are established based on the elastic modulus prediction data of low-shrinkage high-strength mortar, the characteristic data of admixture aggregates, and the water-cement ratio data. Through the concrete creep prediction model and the strength prediction model, the admixture aggregates and the water-cement ratio are actively controlled to prepare low-shrinkage concrete with the expected creep and strength.

[0103] In step 3), based on the expected concrete creep and strength requirements, aggregates with specific elastic moduli and water-reducing agent dosages are selected to prepare creep-controlled low-shrinkage concrete.

[0104] First, to facilitate engineering applications, the Vickers hardness of the selected aggregate is measured using a Vickers hardness tester.

[0105] Preferably, the square cone apex angle of the Vickers hardness tester is 136°.

[0106] Furthermore, aggregates include coarse aggregates and fine aggregates. When the elastic moduli of coarse aggregates and fine aggregates are the same, such as... Figure 3 As shown, based on the concrete creep determined by experimental data and the elastic modulus E of the low-shrinkage mortar phase... mt The correlation between the values ​​was used to establish the 360-day creep C of concrete. ct The prediction model is:

[0107] C ct = -34.5E mt +71.465+R2 (3)

[0108] Where R2 is the correction factor, and C is the 360-day creep coefficient of concrete. ct With the elastic modulus E of the low-shrinkage mortar phase mt Synchronous changes.

[0109] When the elastic modulus of coarse aggregate is inconsistent with that of fine aggregate, the creep C of the prepared concrete will be different. ctd The prediction model is:

[0110] C ctd =C ct E r / E dr (4)

[0111] Among them, E r / E drIt is the correction coefficient when the elastic modulus of aggregates is inconsistent. The elastic modulus of concrete is predicted by the elastic modulus of mortar. The premise is that the elastic modulus of aggregates used in making concrete is the same as that of mortar. Therefore, when the elastic modulus of aggregates and mortars are different, it is necessary to make corrections, that is, to make linear corrections by formula (4).

[0112] Furthermore, when the elastic modulus of aggregates is consistent, with a water-cement ratio of 0.36 as the benchmark, the 360-day creep C of concrete is... ctr The linear relationship between the water-cement ratio Rw and the water-cement ratio is as follows:

[0113] C ctr =C ct (1.935R w +0.3026+R3) (5)

[0114] Where R3 is the correction factor, and C is the 360-day creep coefficient of concrete. ctr With water-cement ratio R w When the aggregate materials are consistent and the water-cement ratio changes synchronously, the effect is achieved through (1.935R). w +0.3026+R3) corrects for the effect of water-cement ratio.

[0115] When the elastic modulus of aggregates is inconsistent, it is necessary to add a correction component E to the aggregates. r / E dr 360d creep C of concrete ctr The linear relationship between the water-cement ratio Rw and the water-cement ratio is as follows:

[0116] C ctr =C ctd (1.935R w +0.3026+R3)

[0117] That is, C ctr = (-34.5E) mt +71.465+R2)E r / E dr (1.935R w +0.3026+R3) (6)

[0118] Therefore, by substituting equations (1), (2), (3), (4), (5), and (6) into the calculation, we obtain the creep degree C of concrete after 360 days. ctr The prediction model is:

[0119] C ctr =(-34.5(0.0081σ) mt +0.5909+R1)+71.465+R2)·E r / E dr ·(1.935R w+0.3026+R3)(7)

[0120] Concrete later-stage strength σ ct The prediction model is:

[0121] σ ct =σ m0 ·k t ·k a ·(E dr / E r )·k Rw (8)

[0122] Where, k a This refers to the influence coefficient of admixtures, such as the influence coefficient of water-reducing agents and early-strength agents; E dr / E r k is the aggregate correction factor. Rw This is the correlation coefficient between the water-cement ratio and the adhesive ratio.

[0123] Furthermore, when the raw materials are of the same type, concrete creep is also affected by the particle size range, such as... Figure 4 As shown, with a particle size of 5–31.5 mm as the baseline, concrete creep shows a trend of first increasing and then decreasing as the particle size decreases.

[0124] Furthermore, in the engineering design, the water-cement ratio is initially assumed to be 0.36, with coarse and fine aggregates of the same material. The coarse aggregate particle size range is 5–31.5 mm. The concrete mix design is carried out using conventional design methods. The mortar strength requirements are calculated based on the concrete strength prediction model. Early creep is controlled by mineral admixtures and gypsum. The concrete creep value is further predicted using the aforementioned prediction model. When the concrete creep exceeds the design value, the creep can be adjusted according to the site conditions through the following methods:

[0125] 1) Select coarse aggregates with higher elastic modulus, while ensuring that the elastic modulus of the aggregates is not less than 270 kgf / mm². 2 This is to avoid the inability to suppress concrete shrinkage due to insufficient elastic modulus of concrete aggregate.

[0126] 2) Reduce aggregate particle size to 5-25mm.

[0127] 3) While ensuring the strength of the concrete, select a high-efficiency water-reducing agent to reduce the water-cement ratio.

[0128] Furthermore, when the creep of concrete is lower than the design value, the creep can be increased in the following three ways:

[0129] 1) Select coarse aggregates with a lower modulus of elasticity, while ensuring that the modulus of elasticity of the aggregates is not less than 310 kgf / mm². 2This is to avoid the inability to coordinate deformation during concrete shrinkage due to excessively high elastic modulus of concrete aggregate, which could lead to concentrated stress within the concrete.

[0130] 2) Reduce aggregate particle size to 5-20mm.

[0131] 3) Reduce the water-cement ratio and the proportion of mineral admixtures to ensure concrete strength.

[0132] Furthermore, when a single adjustment method cannot meet the creep design requirements, multiple adjustment methods can be combined to meet the design requirements.

[0133] Verification of concrete creep regulation effect based on aggregate and water-cement ratio:

[0134] The selected materials for this project are P.Ⅱ42.5R ordinary Portland cement, S95 slag produced by Xi'an Delong Powder Engineering Materials, and fly ash produced by Shaanxi Hancheng Datang Shenglong. Their chemical compositions are as follows:

[0135] Table 1 Physical properties and elemental composition of cementitious materials

[0136]

[0137] Manufactured sand was selected as the fine aggregate, and five other aggregates with different hardness were selected as the coarse aggregate. The aggregate particle size ranged from 5 to 31.5 mm, and the content of needle-like and flaky particles (16 to 19 mm) did not exceed 3%. Their hardness values ​​are as follows:

[0138] Table 2. Results of aggregate hardness test

[0139]

[0140] Using a base water-cement ratio of 0.33 and the same mix proportions, concrete was prepared. A stress level of 0.4 was selected, and creep tests were conducted on the concrete after 28 days of curing. The test results are as follows: Figure 5 As shown, regardless of the type of aggregate used, the creep of concrete increases with the increase of the water-cement ratio. Furthermore, concrete creep increases with the increase of aggregate hardness. While pebbles and granite have similar hardness, their creep is greater due to their smooth surfaces. Additionally, from... Figure 3 As can be seen, when using the same type of aggregate, the creep of concrete is closely related to the particle size distribution. As the particle size decreases, concrete creep first decreases and then increases. When the aggregate particle size is between 5 and 25 mm, the particle size is moderate, the spatial structure is good, and the creep is lowest. However, when the particle size is further reduced to 5 to 20 mm, the particle size is too small, the spatial skeleton is insufficient, and the concrete creep increases. From the above, it can be seen that the concrete creep adjustment method proposed in this invention is simple.

[0141] The following are examples:

[0142] Example 1

[0143] The prepared concrete is for bridge pavement, which requires good deformation characteristics under the lateral tensile stress generated by vehicle traffic to prevent cracking. Therefore, the concrete creep is maximized while meeting the concrete strength requirements. The design concrete strength is 35 MPa, and the design creep is 45 × 10⁻⁶. -6 / MPa.

[0144] Jidong Cement P.Ⅱ42.5R Portland cement was selected as the main cementitious material. Mortar mix design was carried out according to the strength design value. A series of mortar specimens were prepared for different water-cement ratios, silica fume content, and gypsum content, and their 28-day strength and shrinkage values ​​were measured to select a low-shrinkage mix ratio that met the strength requirements. Finally, S95 grade slag with a low elastic modulus and a specific surface area of ​​390 m² was selected as the mineral admixture. 2 / kg, the selected mineral admixture dosage was 65%, the water-cement ratio was 0.36, the silica fume dosage was 4% to improve the early strength of concrete, the gypsum dosage was 5% to reduce the early shrinkage of concrete, and polycarboxylate superplasticizer was used to adjust the workability of concrete. According to the design code for ordinary concrete JGJ55-2011, the mix proportion was designed according to the strength design value. The creep prediction model calculated that its creep did not meet the design requirements. Based on the above concrete creep adjustment method, pebbles with lower hardness and better smoothness were finally used as aggregate, and the particle size was adjusted to 5-20mm to further increase the creep. The engineering verification showed that the pavement performance was good.

[0145] Example 2

[0146] The prepared concrete serves as a flexible connection between buildings. Due to the possibility of uneven foundation settlement causing cracking in the connecting beams, the concrete is required to possess certain creep properties. The design strength of the concrete is 40 MPa, and the design creep degree is 30 × 10⁻⁶. -6 / MPa.

[0147] Jidong Cement P.II 42.5R Portland cement was selected as the main cementitious material. Mortar mix design was carried out according to the strength design value. A series of mortar specimens were prepared for different water-cement ratios, silica fume content, and gypsum content, and their 28-day strength and shrinkage values ​​were measured to select a low-shrinkage mix ratio that met the strength requirements. Finally, fly ash and mineral powder were selected in a 1:1 ratio to prepare a mineral admixture with a suitable elastic modulus and a specific surface area of ​​390 m². 2 / kg, the selected mineral admixture dosage was 60%, the water-cement ratio was 0.36, the silica fume dosage was 7% to improve the early strength of concrete, the gypsum dosage was 3% to reduce the early shrinkage of concrete, and polycarboxylate superplasticizer was used to adjust the workability of concrete. According to the design code for ordinary concrete JGJ55-2011, the mix proportion was designed according to the strength design value. The creep prediction model calculated that its creep did not meet the design requirements. Based on the above concrete creep adjustment method, quartzite with low hardness and good smoothness was finally used as aggregate, the particle size was adjusted to 5-31mm, the water-cement ratio was adjusted to 0.34, and the creep of concrete was adjusted. The engineering verification showed that the structural stability was good.

[0148] Example 3

[0149] The prepared concrete is prestressed concrete. To reduce prestress loss and ensure the normal use of the structure, the concrete creep should be minimized. The design strength is 50 MPa, and the design creep is 15 × 10⁻⁶. -6 / MPa. Jidong Cement P.Ⅱ42.5R Portland cement was selected as the main cementitious material. Mortar mix design was carried out according to the strength design value. A series of mortar specimens were prepared for different water-cement ratios, silica fume content, and gypsum content, and the 28-day strength and shrinkage value were measured to select a low-shrinkage mix ratio that met the strength requirements. Finally, Grade I fly ash with a high elastic modulus and a specific surface area of ​​390 m² was selected as the mineral admixture. 2 / kg, the selected mineral admixture dosage was 40%, the water-cement ratio was 0.36, the silica fume dosage was 5% to improve the early strength of concrete, the gypsum dosage was 4% to reduce the early shrinkage of concrete, and polycarboxylate superplasticizer was used to adjust the workability of concrete. According to the design code for ordinary concrete JGJ55-2011, the mix proportion was designed according to the strength design value. The creep prediction model calculated that its creep did not meet the design requirements. Based on the above concrete creep adjustment method, limestone with low hardness and good smoothness was finally used as aggregate, the particle size was adjusted to 5-25mm, and the water-cement ratio was adjusted to 0.32 to further reduce the creep of concrete. The engineering verification showed that the structural stability was good.

[0150] Shrinkage and creep of the concrete from Examples 1 to 3 were tested over 360 days. The results are as follows:

[0151] Table 3. Adjustment parameters and performance indicators of concrete prepared in the examples.

[0152]

[0153] As shown in Table 3, after optimizing the mix proportion using the aforementioned prediction model, the prepared concrete exhibits a low shrinkage rate (the shrinkage value of ordinary concrete is generally 800–1500), effectively preventing the formation of initial cracks caused by early concrete shrinkage. Simultaneously, the creep rate meets design expectations well, ensuring concrete strength. Verification shows that this invention can effectively control concrete strength, shrinkage, and creep through the synergistic effect of raw material design, water-cement ratio, and aggregate elastic modulus. In particular, its creep rate can be bidirectionally controlled according to design requirements, and the proposed adjustment rules are simple and effective, demonstrating good engineering applicability.

[0154] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for actively controlling concrete shrinkage and creep based on aggregate properties and water-cement ratio, characterized in that, Includes the following steps: Determine the physicochemical properties and mechanical properties of pure cement; Based on the measured data of pure cement, the preparation of low-shrinkage high-strength mortar is actively controlled; Based on the actively controlled preparation of low-shrinkage high-strength mortar, combined with actively controlled admixtures and water-cement ratio, low-shrinkage concrete with the expected creep and strength is prepared. The process of actively controlling the preparation of low-shrinkage, high-strength mortar based on measured pure cement data specifically includes: Based on the measured pure cement data, the mix proportions were actively controlled to prepare low-shrinkage high-strength mortar with predetermined early strength and low shrinkage value. A strength prediction model was established based on the predetermined early strength, and an elastic modulus prediction model was simultaneously established based on the strength prediction model to obtain elastic modulus prediction data. The preparation of low-shrinkage high-strength mortar with predetermined early strength and low shrinkage value based on measured pure cement data specifically includes: Fly ash and mineral powder are mixed in a certain proportion to form a composite mineral admixture; By using fly ash and mineral powder as mineral admixtures, the heat of hydration of cement can be reduced, and mineral admixtures can be used as micro-aggregates to form a spatial skeleton to reduce the early shrinkage of concrete. Continue to incorporate silica fume as an early strength conditioning phase to compensate for the strength loss caused by the incorporation of mineral admixtures; Gypsum is further incorporated as an early shrinkage regulating phase. By incorporating gypsum during the hydration process, ettringite crystals are generated. The micro-expansion effect caused by the ettringite crystals is used to adjust the early shrinkage, and finally, a low-shrinkage mortar that meets the strength requirements is designed and formed. Based on the above proportions, the amounts of mineral admixtures, silica fume, and gypsum are determined according to the predetermined early strength and low shrinkage value control requirements to form a low-shrinkage mortar phase; The process of establishing a strength prediction model based on a predetermined early strength, simultaneously establishing an elastic modulus prediction model based on the strength prediction model, and obtaining elastic modulus prediction data specifically includes: Define the early compressive strength σ of mortar at 28 days. m0 ; The mortar strength σ over 360 days mt The prediction model is: s mt =s m0 ·k t (1) Where, k t It is a time correction parameter; the strength of the mortar changes with the time t corresponding to 28d~360d. Based on experimental data, the elastic modulus and strength σ of mortar can be determined. mt The correlation between them allows for the fitting of the elastic modulus E of the low-shrinkage mortar phase. mt Predictive model: E mt =0.0081σ mt +0.5909+R1 (2) Where R1 is the correction coefficient, and the elastic modulus of the mortar changes synchronously with time t; The preparation of low-shrinkage, high-strength mortar based on active control, combined with actively controlled admixtures and water-cement ratio, to obtain low-shrinkage concrete with the expected creep and strength specifically includes: Based on the expected creep and strength of low-shrinkage concrete, a concrete creep prediction model and a strength prediction model are established based on the elastic modulus prediction data of low-shrinkage high-strength mortar, the characteristic data of admixture aggregates, and the water-cement ratio data. The low-shrinkage concrete with the expected creep and strength is prepared by actively controlling the admixture aggregates and the water-cement ratio through the concrete creep prediction model and the strength prediction model. The step of establishing a concrete creep prediction model based on the expected creep and strength of the prepared low-shrinkage concrete, using the elastic modulus prediction data of low-shrinkage high-strength mortar and the characteristic data of admixture aggregates, specifically includes: Aggregates include coarse aggregates and fine aggregates. When the elastic moduli of the coarse and fine aggregates are the same, the elastic modulus E of the low-shrinkage mortar phase is determined based on concrete creep as determined by experimental data. mt The correlation between the values ​​was used to establish the 360-day creep C of concrete. ct The prediction model is: C ct =-34.5E mt +71.465+R2 (3) Where R2 is the correction factor, and C is the 360-day creep coefficient of concrete. ct With the elastic modulus E of the low-shrinkage mortar phase mt Synchronous changes; When the elastic modulus of coarse aggregate is inconsistent with that of fine aggregate, the creep C of the prepared concrete will be different. ctd The prediction model is: C ctd = C ct AND r / AND dr (4) Er / Edr is the correction coefficient when the elastic modulus of aggregates are inconsistent. The elastic modulus of concrete is predicted by the elastic modulus of mortar. The premise is that the elastic modulus of aggregates used in making concrete is the same as that of mortar. Therefore, when the elastic modulus of aggregates and mortars are different, correction is required, i.e., linear correction by formula (4). The concrete creep prediction model established based on the elastic modulus prediction data of low-shrinkage high-strength mortar, the characteristic data of admixture aggregates, and the water-cement ratio data specifically includes: When the elastic modulus of aggregates is consistent, with a water-cement ratio of 0.36 as the benchmark, the 360-day creep C of concrete is... ctr The linear relationship between the water-cement ratio Rw and the water-cement ratio is as follows: C ctr = C ct (1.935R w +0.3026+R3) (5) Where R3 is the correction factor, and C is the 360-day creep coefficient of concrete. ctr With water-cement ratio R w When the aggregate materials are consistent and the water-cement ratio changes synchronously, the effect is achieved through (1.935R). w +0.3026+R3) corrects for the effect of water-cement ratio; When the elastic modulus of aggregates is inconsistent, it is necessary to add a correction component E to the aggregates. r / E dr ， 360d Creep C of Concrete ctr The linear relationship between the water-cement ratio Rw and the water-cement ratio is as follows: C ctr = C ctd (1.935R w +0.3026+R3) That is, C ctr = (-34.5E mt +71.465+R2) E r / E dr (1.935R w +0.3026+R3) (6) Therefore, by substituting equations (1), (2), (3), (4), (5), and (6) into the calculation, the creep degree C of concrete after 360 days is obtained. ctr The prediction model is: C ctr = (-34.5(0.0081σ mt +0.5909+R1)+71.465+R2)·E r / E dr ·(1.935R w +0.3026+R3)(7); The concrete strength prediction model established based on the elastic modulus prediction data of low-shrinkage high-strength mortar, the characteristic data of admixture aggregates, and the water-cement ratio data specifically includes: Concrete later-stage strength σ ct The prediction model is: s ct =s m0 ·k t ·k a ·(E dr / E r )·k Rw (8) Where, k a This refers to the influence coefficient of admixtures, such as the influence coefficient of water-reducing agents and early-strength agents; E dr / E r k is the aggregate correction factor. Rw This is the correlation coefficient between the water-cement ratio and the adhesive ratio.

2. The active control method for concrete shrinkage and creep based on aggregate properties and water-cement ratio according to claim 1, characterized in that, The determination of the physicochemical and mechanical properties of pure cement specifically includes: The physicochemical and mechanical properties of pure cement were determined. During the determination of these properties, the specific surface area of ​​the cement was measured using a laser particle size analyzer. The specific surface area of ​​the cement used was 360–370 m². 2 / kg.

3. The active control method for concrete shrinkage and creep based on aggregate properties and water-cement ratio according to claim 1, characterized in that, It also includes the following steps: When the raw materials are of the same type, concrete creep is also affected by the particle size range. Taking a particle size of 5~31.5mm as the benchmark, concrete creep shows a trend of first increasing and then decreasing as the particle size decreases. The concrete 360-day post-creep C ctr The predictive model forecasts concrete creep values. When the concrete creep exceeds the expected design value, the creep is adjusted through the following methods: 1) Select coarse aggregates with a specific elastic modulus to ensure that the elastic modulus of the aggregates is not less than 270 kgf / mm². 2 This is to avoid the inability to suppress concrete shrinkage due to insufficient elastic modulus of concrete aggregate; 2) Reduce aggregate particle size to 5~25mm; 3) While ensuring concrete strength, select a specific water-reducing agent to reduce the water-cement ratio; When the creep of concrete is lower than the design value, the creep can be increased through the following three methods: 1) Select coarse aggregates with a specific elastic modulus to ensure that the elastic modulus of the aggregates is not less than 310 kgf / mm². 2 This is to avoid the inability to coordinate deformation during concrete shrinkage due to excessively high elastic modulus of concrete aggregate, which could lead to concentrated stress inside the concrete. 2) Reduce aggregate particle size to 5~20mm; 3) Reduce the water-cement ratio and the proportion of mineral admixtures to ensure concrete strength; When a single adjustment method cannot meet the creep design requirements, at least two adjustment methods should be combined to meet the expected design requirements.

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