Method for regulating the suspension stability of light aggregates in a mortar

Abstract

This invention discloses a method for controlling the suspension stability of lightweight aggregates in mortar, comprising: obtaining the apparent density ρ of the lightweight aggregates. a and particle size characteristic parameter d; determine mortar matrix density ρ m The plastic viscosity η of the mortar matrix was tested; the density difference Δρ was calculated, where Δρ = ρ m -ρ a Under the condition of setting the vibration time t, a stability criterion is established: d²·Δρ≤k t ·η, where k t The macroscopic boundary coefficient is used; the minimum mortar plastic viscosity is calculated back-calculated based on the stability criterion; by adjusting the mortar mix ratio, the plastic viscosity η of the mortar matrix is ​​made greater than or equal to the minimum; a quantitative guidance model for guiding the stable suspension of lightweight aggregates is output. This invention establishes a semi-empirical stable suspension determination model with lightweight aggregate particle size characteristic value, aggregate-mortar density difference, and mortar plastic viscosity as variables. The boundary coefficient is calibrated through stability tests, thereby realizing the stable suspension control of lightweight aggregates under specific vibration conditions.

Description

Technical Field

[0001] This invention relates to the field of workability evaluation and control technology for lightweight aggregate concrete (LWAC), and particularly to a method for controlling the suspension stability of lightweight aggregates in mortar. Background Technology

[0002] Lightweight aggregate concrete possesses core characteristics such as light weight, high strength, thermal insulation, and excellent durability, which can significantly reduce the self-weight of the structure while ensuring structural strength.

[0003] However, the workability of freshly mixed lightweight aggregate concrete is the core prerequisite for its successful engineering application.

[0004] Due to environmental factors during on-site transportation and pumping, freshly mixed lightweight aggregate concrete prepared on-site often requires the assistance of vibration compaction during pouring to ensure density.

[0005] While vibration can significantly reduce the yield stress of mortar in fresh concrete and improve its fluidity, this process can easily lead to dynamic segregation of lightweight aggregates. Essentially, the constitutive relationship of vibrated fresh concrete approximately follows a pseudoplastic fluid model with a yield value of zero. Lightweight aggregates, freed from the constraint of yield stress, are easily lifted by buoyancy, ultimately resulting in a significant decrease in the compressive strength and impermeability of the hardened concrete.

[0006] Existing methods for controlling segregation in lightweight aggregate concrete mainly rely on empirical performance indicators, such as segregation degree, or fixed mortar plastic viscosity thresholds set for specific aggregates.

[0007] These methods typically rely on empirical data accumulation and fail to incorporate the three key variables—lightweight aggregate particle size, aggregate-mortar density difference, and mortar plastic viscosity—into a unified quantitative judgment model.

[0008] Therefore, when the type of lightweight aggregate is changed in the project, such as increasing the particle size or decreasing the apparent density, the applicability of the original empirical indicators decreases significantly, which can easily lead to control failure and dynamic segregation problems such as lightweight aggregate floating and stratification.

[0009] Therefore, in order to solve the problem that the existing methods for controlling segregation of lightweight aggregate concrete rely on a fixed mortar viscosity threshold and are difficult to adapt to changes in different lightweight aggregate particle sizes and density differences, it is necessary to provide a stability control method that can simultaneously consider the characteristics of lightweight aggregate particle size, aggregate-mortar density difference, and mortar plastic viscosity, so as to provide a calculable and verifiable control basis for the suspension stability control of lightweight aggregate. This is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0010] In view of this, the present invention provides a method for controlling the suspension stability of lightweight aggregates in mortar, and provides a stable suspension control method based on the matching relationship between lightweight aggregate particle size characteristics, aggregate-mortar density difference and mortar plastic viscosity under set vibration conditions.

[0011] The specific steps are as follows. First, obtain the apparent density ρ of the lightweight aggregate. a The apparent density ρ of the freshly mixed mortar is calculated based on the average particle size characteristic parameter d and the mortar mix proportion. m By combining the above parameters, the net buoyancy force on the lightweight aggregate is obtained. Then, through dimensional analysis, the correlation between the characteristic time of the lightweight aggregate's upward motion and the plastic viscosity of the mortar and the parameters of the lightweight aggregate is obtained. The boundary coefficient is introduced to correct the influence of the engineering vibration condition.

[0012] Subsequently, vibration stratification tests were conducted on lightweight aggregate mortar systems with different parameters. The stratification results after vibration were determined under different plastic viscosity conditions. Based on the stratification limit, the critical plastic viscosity of mortar that meets the suspension stability requirements was obtained.

[0013] Finally, based on the test data, the boundary coefficients were calibrated to establish a system that can simultaneously cover the lightweight aggregate particle size d and the density difference between lightweight aggregate and mortar (ρ). m -ρ a The suspension stability criteria for three key parameters, including mortar plastic viscosity η, are as follows:

[0014] In engineering applications, the minimum threshold of mortar plastic viscosity that meets stability requirements can be calculated directly using this criterion based on the parameters of the lightweight aggregate used. This allows for quick adjustment of the mortar mix ratio and precise control of the suspension stability of lightweight aggregates. It eliminates the need to rely on existing empirical indicators and maintains the accuracy of control even after changing the type of lightweight aggregate, effectively avoiding the problem of lightweight aggregates floating and segregating during vibration.

[0015] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0016] A method for controlling the suspension stability of lightweight aggregates in mortar includes the following steps:

[0017] (1) Obtain the apparent density ρ of lightweight aggregate a and particle size characteristic parameter d;

[0018] (2) Determine the density ρ of the mortar matrix. m And test the plastic viscosity η of the mortar matrix;

[0019] (3) Calculate the density difference Δρ, where Δρ = ρ m -ρ a ;

[0020] (4) Under the condition of setting the vibration time t, establish the stability criterion: d²·Δρ≤kt η, where k t For macroscopic boundary coefficients;

[0021] (5) The minimum mortar plastic viscosity is calculated back-calculated based on the stability criterion. ;

[0022] (6) By adjusting the mortar mix ratio, the plastic viscosity η of the mortar matrix is ​​made greater than or equal to 100%. ;

[0023] (7) Output a quantitative guidance model for guiding the stable suspension of lightweight aggregates.

[0024] Preferably, in step (1), the particle size characteristic parameter d is the average or maximum particle size of the lightweight aggregate, in mm.

[0025] Preferably, in step (2), the plastic viscosity of the mortar is... The results were obtained using a shear rate controlled rheometer, employing a test regime of pre-shear followed by linearly increasing or decreasing shear rate, and fitted based on either the Bingham model or the Herschel-Bulkley model.

[0026] Preferably, in step (4), the vibration time s, boundary coefficient .

[0027] Preferably, in step (4), the macroscopic boundary coefficient k t k is defined as follows: t =18·C s ·v0 / g, where C s The term is a drag coefficient correction term related to aggregate shape and boundary effects, where v0 is the critical safe buoyancy velocity of lightweight aggregate, and g is the acceleration due to gravity.

[0028] Preferably, the critical safe floating speed v0 is the maximum allowable floating speed determined within a set vibration time t to prevent macroscopic dynamic segregation of lightweight aggregate.

[0029] Preferably, in step (4), the stability criterion d²·Δρ≤k t η is derived based on the force balance between net buoyancy and viscous resistance of lightweight aggregate under vibratory liquefaction.

[0030] Preferably, the net buoyancy The viscous resistance , where v is the floating velocity of the lightweight aggregate.

[0031] Preferably, in step (7), the quantification guidance model uses the apparent density ρ of lightweight aggregate. a Particle size characteristic parameter d, mortar matrix density ρm And set the vibration time t as an input parameter, with the minimum mortar plastic viscosity η min For output parameters.

[0032] Preferably, when the lightweight aggregate reaches force equilibrium, the buoyancy is... Let v≤v0, and rearrange the terms to obtain the stability criterion.

[0033] The present invention achieves the following technical effects compared to the prior art:

[0034] 1) This invention improves the particle size of lightweight aggregates by ( ) and the density difference between aggregate and mortar ( The explicit introduction of stability criteria breaks the limitation of setting a fixed viscosity threshold only for a single lightweight aggregate in the traditional segregation resistance evaluation. It can be applied to the stability evaluation of lightweight aggregate systems with different particle sizes and effective densities, and has better material adaptability compared with the fixed viscosity threshold method.

[0035] 2) The minimum plastic viscosity obtained by this invention It can be directly used as a core quantitative indicator to guide the mix design of lightweight aggregate concrete and the adaptive adjustment of admixture dosage, effectively avoiding dynamic segregation and stratification during vibration construction.

[0036] 3) This invention innovatively combines physical profile image analysis with hierarchical quantitative calculation to define the threshold, and uses a binary classification algorithm to calibrate the boundary coefficient, transforming the complex dynamic segregation mechanism of concrete into a definite parameter matching inequality, which significantly reduces the reliance on manual experience in mix design. Attached Figure Description

[0037] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0039] This invention discloses a method for controlling the suspension stability of lightweight aggregates in mortar, comprising the following steps:

[0040] (1) Obtain the apparent density ρ of lightweight aggregate a and particle size characteristic parameter d;

[0041] (2) Determine the density ρ of the mortar matrix. mAnd test the plastic viscosity η of the mortar matrix;

[0042] (3) Calculate the density difference Δρ, where Δρ = ρ m -ρ a ;

[0043] (4) Under the condition of setting the vibration time t, establish the stability criterion: d²·Δρ≤k t ·η, where k t For macroscopic boundary coefficients;

[0044] (5) The minimum mortar plastic viscosity is calculated back-calculated based on the stability criterion. ;

[0045] (6) By adjusting the mortar mix ratio, the plastic viscosity η of the mortar matrix is ​​made greater than or equal to 100%. ;

[0046] (7) Output a quantitative guidance model for guiding the stable suspension of lightweight aggregates.

[0047] In step (1), the particle size characteristic parameter d is the average or maximum particle size of the lightweight aggregate, in mm.

[0048] In step (2), the plastic viscosity of the mortar The results were obtained using a shear rate controlled rheometer, employing a test regime of pre-shear followed by linearly increasing or decreasing shear rate, and fitted based on either the Bingham model or the Herschel-Bulkley model.

[0049] In step (4), the vibration time s, boundary coefficient .

[0050] In step (4), the macroscopic boundary coefficient k t k is defined as follows: t =18·C s ·v0 / g, where C s The term is a drag coefficient correction term related to aggregate shape and boundary effects, where v0 is the critical safe buoyancy velocity of lightweight aggregate, and g is the acceleration due to gravity.

[0051] The critical safe floating speed v0 is the maximum allowable floating speed determined within the set vibration time t to prevent macroscopic dynamic segregation of lightweight aggregate.

[0052] In step (4), the stability criterion is d²·Δρ≤k. t η is derived based on the force balance between net buoyancy and viscous resistance of lightweight aggregate under vibratory liquefaction.

[0053] Net buoyancy The viscous resistance , where v is the floating velocity of the lightweight aggregate.

[0054] In step (7), the quantification guidance model uses the apparent density ρ of lightweight aggregate. a Particle size characteristic parameter d, mortar matrix density ρ m And set the vibration time t as an input parameter to minimize the plastic viscosity of the mortar. For output parameters.

[0055] When the lightweight aggregate reaches force equilibrium, the upward velocity v = d²·Δρ·g / (18·η·C) s Let v ≤ v0, and rearrange the terms to obtain the stability criterion.

[0056] This invention discloses a method for controlling the stable suspension of lightweight aggregates based on a decision model. The core process includes: obtaining the apparent density of the lightweight aggregates. and particle size characteristic parameters Determine the density of the mortar matrix. And test the plastic viscosity of the mortar matrix. ; Calculate density difference ; Set vibration time Establish stability criteria under the condition ; Back-calculate minimum mortar plastic viscosity By adjusting the mortar mix ratio, The final output is a quantitative guidance model.

[0057] The physical and mechanical derivation mechanism of the core stability determination model:

[0058] The core of this invention, which breaks through the traditional empirical threshold, lies in the establishment of a quantitative model based on physical and mechanical equilibrium.

[0059] The derivation process is as follows: During the vibration of freshly mixed lightweight aggregate concrete, the lightweight aggregate loses the constraint of the mortar yield stress, and its motion state in the matrix is ​​mainly governed by the combined net buoyancy and viscous resistance. The net buoyancy force on the lightweight aggregate in the mortar ( )satisfy: Meanwhile, lightweight aggregates experience viscous resistance from the mortar fluid during the floating process. According to Stokes' law and its corrections in engineering fluid mechanics, its resistance can be characterized as: in, For the floating speed of lightweight aggregate, This is a correction term for the resistance coefficient related to aggregate shape and boundary effects. When lightweight aggregate reaches force equilibrium under vibratory liquefaction conditions (i.e.,...) When ), derive the ascent speed. for: At a given vibration time To prevent macroscopic dynamic segregation of lightweight aggregates within 25 seconds, a certain flotation speed is required. It must be less than a certain critical safety speed .

[0060] make By substituting the above equations and rearranging the terms, we can derive the core inequality of this invention: Since the parameter within parentheses integrates time, critical velocity, gravity, and topographic features, this invention defines it as a macroscopic boundary coefficient. .

[0061] Thus, it was established The theoretical model.

[0062] The following specific experiments demonstrate the effectiveness of this boundary coefficient. Calibrate and verify its actual control effect.

[0063] Boundary coefficients of stable suspension model Calibration test: In order to obtain the above boundary coefficients The present invention conducted systematic basic experiments: (1) Obtain basic data on lightweight aggregates and mortar matrix: lightweight aggregates with different apparent densities and particle size ranges, and mortars with different rheological properties were selected.

[0064] The basic properties of lightweight aggregate are shown in Table 1.

[0065] The rheological parameters of the reference mortar with different HPMC / PCE admixtures are shown in Table 2.

[0066] Table 1: Basic Properties of Lightweight Aggregates

[0067]

[0068] Table 2: Rheological parameters of reference mortar with different HPMC / PCE admixtures

[0069]

[0070] (2) Conduct a vibration-compaction stratification test:

[0071] The lightweight aggregate was combined with mortar, and its segregation degree (VI) was tested under 25s high-frequency vibration. Some representative test results are shown in Table 3 below:

[0072] Table 3: Image analysis of the segregation test results and hardened concrete cross-sections for each mix proportion.

[0073] 1 7.8 2052 814 1238 9.5 14.2 no 2 18.9 1864 814 1050 9.5 6.3 yes 3 27.4 1800 814 986 9.5 1.6 yes 4 7.8 2052 814 1238 13.2 25.1 no 5 18.9 1864 814 1050 13.2 11.8 no 6 27.4 1800 814 986 13.2 2.2 yes 7 7.8 2052 814 1238 16 55.3 no 8 18.9 1864 814 1050 16 28.6 no 9 27.4 1800 814 986 16 2.9 yes 10 11.1 1919 1655 264 9.5 3.2 yes 11 18.9 1864 1655 209 9.5 2.8 yes 12 11.1 1919 1655 264 13.2 5.9 yes 13 18.9 1864 1655 209 13.2 3.3 yes 14 11.1 1919 1655 264 16 6.7 yes 15 18.9 1864 1655 209 16 4.1 yes

[0074] Image analysis of the hardened concrete cross-section revealed that the system reached quasi-static suspension when the VI was below 6.7%.

[0075] (3) The final criterion is obtained by calibrating the boundary coefficients:

[0076] Image analysis of the hardened concrete cross-section revealed that the system reached quasi-static suspension when the VI was below 6.7%.

[0077] Using this as a stable label, and based on the data in Table 3, a fitting was performed to finally determine the optimal boundary coefficient k under 25s vibration. t =9326.

[0078] The final criterion is: d2·Δρ≤9326·η.

[0079] Based on the general model established above, the following are some specific control implementation examples under different lightweight aggregate characteristics.

[0080] Example 1: Regulation of large-particle-size, low-density ceramsite

[0081] A lightweight aggregate concrete system has a maximum aggregate size of 16 mm, an apparent density of 715 kg / m³, and a target mortar density of 1953 kg / m³. (1) Calculate the density difference: Δρ = |1953−715| = 1238 kg / m³. (2) Calculate the theoretical minimum plastic viscosity:

[0082] η min =16 2 ×1238÷9326=33.9Pa·s(3)Control: The initial plastic viscosity of the mortar is only 7.3 Pa·s. By adding 0.25% HPMC, its plastic viscosity is increased to 36.0 Pa·s (satisfying ≥33.9Pa·s).

[0083] Testing showed that the VI of the system decreased to 4.5%, and no segregation occurred.

[0084] Example 2: Regulation of medium-sized high-density ceramsite

[0085] A lightweight aggregate concrete system has a maximum aggregate size of 13.2 mm, an apparent density of 1557 kg / m³, and a target mortar density of 2051 kg / m³. (1) Calculate the density difference: Δρ = |2051−1557| = 494 kg / m³. (2) Calculate the theoretical minimum plastic viscosity: η min =(13.2) 2×494÷9326=9.2 Pa·s (3) Adjustment: Since the required viscosity is low, it is only necessary to adjust the mortar-binder ratio or add a trace amount (0.04%) of HPMC to make the mortar viscosity reach 11.5 Pa·s (satisfying ≥9.2 Pa·s).

[0086] The system VI was tested and found to be 3.3%, indicating stable suspension.

[0087] Comparative Example 1: Failure Cases Where Criteria Were Not Met

[0088] Using the same aggregate (η) as in Example 1 min The required viscosity is 33.9 Pa·s, but according to traditional experience, the plastic viscosity of the mortar is only adjusted to 15.0 Pa·s.

[0089] Since 15.0 < 33.9 Pa·s, after 25s of vibration, the measured VI was as high as 55.3%, indicating severe dynamic segregation.

[0090] This demonstrates the necessity of the quantization model of this invention.

[0091] Comparative Example 2: Failure Cases with Fixed Viscosity Threshold

[0092] For the medium-sized high-density ceramsite system in this embodiment, according to the traditional fixed viscosity threshold method, the mortar plastic viscosity is required to be no less than 15 Pa·s. This system meets the requirement after adjustment, but does not meet the criterion proposed in this invention. The final measured VI is 8.1%, and slight segregation has occurred.

[0093] This further verifies the adaptability advantage of the present invention for lightweight aggregates with different characteristics.

[0094] The method of this invention establishes a quantitative stability criterion based on force balance derivation, without relying on fixed empirical thresholds. It can accurately calculate the minimum mortar plastic viscosity required for lightweight aggregates with different characteristics, ensuring stable suspension of lightweight aggregates without segregation, and avoiding material waste and workability loss caused by excessive thickening. It provides clear and reliable quantitative guidance for the control of lightweight aggregate suspension stability in fresh lightweight aggregate concrete, and solves the long-standing industry pain point that the setting of this parameter depends on experience.

[0095] For the medium-sized high-density ceramsite system in this embodiment, according to the traditional fixed viscosity threshold method, the mortar plastic viscosity is required to be no less than 15 Pa·s. This system meets the requirement after adjustment, but does not meet the criterion proposed in this invention. The final measured VI is 8.1%, and slight segregation has occurred.

[0096] This further verifies the adaptability advantage of the present invention for lightweight aggregates with different characteristics.

[0097] For lightweight aggregates with different apparent densities and particle sizes, traditional fixed viscosity thresholds cannot match the coupling effect of the difference between aggregate particle size and density. Either the threshold is set too high, causing unnecessary thickening, wasting additives, and increasing the difficulty of workability adjustment, or the threshold is insufficient, still causing segregation. Only by combining the characteristics of the aggregate itself and calculating the minimum plastic viscosity through the quantitative criteria of this invention can the stable suspension of lightweight aggregates be accurately achieved, while avoiding the performance waste caused by over-adjustment.

[0098] Regarding the failure of this comparative example due to the failure to meet the criterion conditions, it is clear that even if the characteristics of the lightweight aggregate are completely consistent with the qualified control system, macroscopic segregation cannot be avoided as long as the plastic viscosity of the mortar does not reach the minimum requirement calculated by this criterion. This directly confirms the rigid constraint effect of this quantitative criterion on the control of the suspension stability of lightweight aggregate, and also clarifies the necessity of adjusting the viscosity according to the calculation results of this model.

[0099] Even for lightweight aggregate systems with different combinations of apparent density and particle size, stable suspension can be achieved as long as the viscosity requirement given by this criterion is met. Conversely, no matter how other parameters are adjusted, if the plastic viscosity does not meet the requirements, insufficient stability will inevitably occur. This further demonstrates the reliability and necessity of this criterion and provides a clear and feasible quantitative standard for the control of lightweight aggregate suspension stability in the industry.

[0100] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for controlling the suspension stability of lightweight aggregates in a mortar, characterized in that, Includes the following steps: (1) obtaining the apparent density p of the lightweight aggregate a and the particle size characteristic parameter d; (2) The density of the mortar matrix p is determined m and the plastic viscosity of the mortar matrix η is tested (3) calculating a density difference Δρ, where Δρ = p m - p a ; (4) Under the condition of setting the vibration time t, the stability criterion d2- Δp≤ k t ·η is established, where k t is the macroscopic boundary coefficient; (5) According to the stability criterion, the minimum plastic viscosity of the mortar is calculated ; (6) By adjusting the mortar mix ratio, the plastic viscosity of the mortar matrix is ​​adjusted. ; (7) Output a quantitative guidance model for guiding the stable suspension of lightweight aggregates.

2. The method for controlling the suspension stability of lightweight aggregate in mortar according to claim 1, characterized in that, In step (1), the particle size characteristic parameter d is the average or maximum particle size of the lightweight aggregate, in mm.

3. The method for controlling the suspension stability of lightweight aggregate in mortar according to claim 1, characterized in that, In step (2), the plastic viscosity of the mortar The results were obtained using a shear rate controlled rheometer, employing a test regime of pre-shear followed by linearly increasing or decreasing shear rate, and fitted based on either the Bingham model or the Herschel-Bulkley model.

4. The method for controlling the suspension stability of lightweight aggregate in mortar according to claim 1, characterized in that, The step (4) in, the vibration time s, a boundary coefficient .

5. The method for controlling the suspension stability of lightweight aggregate in mortar according to claim 1, characterized in that, In step (4), the macroscopic boundary coefficient k t k is defined as follows: t =18·Cs·v o / g, where C s v is a correction term for the drag coefficient related to aggregate shape and boundary effects. o denoted as ρ, where ρ is the critical safe buoyancy velocity of the lightweight aggregate, and g is the acceleration due to gravity.

6. The method for controlling the suspension stability of lightweight aggregate in mortar according to claim 5, characterized in that, The critical safe floating speed v0 is the maximum allowable floating speed determined within a set vibration time t to prevent macroscopic dynamic segregation of lightweight aggregate.

7. The method for controlling the suspension stability of lightweight aggregate in mortar according to claim 1, characterized in that, In the step (4), the stability criterion d2·Δρ≤k t • η is derived based on the force balance of the net buoyancy and viscous resistance of the lightweight aggregate in the vibrated liquefied state.

8. The method for controlling the suspension stability of lightweight aggregate in mortar according to claim 7, characterized in that, The net buoyancy , the viscous resistance where v is the lightweight aggregate upward velocity.

9. The method for controlling the suspension stability of light aggregates in mortar according to claim 1, characterized in that, In step (7), the quantification guidance model uses the apparent density ρ of lightweight aggregate. a Particle size characteristic parameter d, mortar matrix density ρ m And set the vibration time t as an input parameter to minimize the plastic viscosity of the mortar. For output parameters.

10. The method for controlling the suspension stability of lightweight aggregate in mortar according to claim 9, characterized in that, When the lightweight aggregate reaches a stress balance, the upward velocity... Let v ≤ v o The stability criterion is obtained by rearranging the terms.

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