A rapid determination method for the early strength of concrete with different grades

Abstract

The present invention belongs to the technical field of concrete, and particularly relates to a method for rapidly determining the early strength of concrete of different grades. The present invention provides a method for rapidly determining the early strength of concrete of different grades. First, the maturity of the concrete is obtained through the concrete age and curing temperature, and then combined with the concrete grade label; the predicted strength of concrete of different grades is calculated respectively according to whether the curing condition is the standard curing condition or the non-standard curing condition. Among them, the strength attenuation coefficient needs to be added under the non-standard curing condition. This method can realize the real-time monitoring and evaluation of the strength evolution of the concrete structure, master the strength evolution law of the concrete at the key parts, provide a scientific basis for construction decisions such as form removal and climbing formwork, and effectively ensure the safety of the concrete structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete, and particularly relates to a method for rapidly determining the early strength of concrete of different grades. Background Art

[0002] Time-variability and volatility are two major characteristics of the performance development of concrete materials. Different from the quality control principle of steel "detect first, then use", the quality control method of concrete materials has always been "pour first, then detect". After the concrete materials are poured, the existing research on the structural state monitoring mainly focuses on the load effect aspects (stress, strain and deformation), while there is a lack of an efficient monitoring and evaluation method for the real-time development state of the mechanical properties of concrete materials, which has an important impact on the structural reliability. Realizing the real-time evaluation of the mechanical properties of concrete entities is of great significance: on the one hand, it has a positive effect and significant social and economic benefits for construction decisions (such as form removal, prestressing operations, withdrawal of curing measures and accelerating the construction process, etc.), real-time quality monitoring and prevention of engineering accidents; on the other hand, mastering the dynamic development of the mechanical properties of concrete entities plays a key role in the research of other related properties. For example, in mass concrete, the hydration heat release during the hardening process causes various different thermodynamic effects, and the understanding and mastery of these phenomena are particularly important for major projects (such as the foundation of super high-rise buildings).

[0003] The strength of concrete is affected by various factors. However, after determining the mix ratio and construction technology, the curing temperature and age will be the key factors affecting the strength growth of concrete. Therefore, how to provide a real-time prediction of the early strength of concrete of different grades under different curing conditions, and realize the real-time monitoring and evaluation of the strength evolution of concrete structures, is a technical problem that needs to be solved urgently by those skilled in the art.

[0004] The information disclosed in this background art section is only intended to increase the understanding of the overall background of the present invention, and should not be regarded as an admission or any form of implication that this information is prior art known to those of ordinary skill in the art. Summary of the Invention

[0005] The present invention provides a method for rapidly determining the early strength of concrete of different grades. Taking the concrete strength grade label and maturity as independent variables, a strength calculation model for rapidly predicting the compressive strength of concrete of different grades is established, providing a simple and effective means for rapidly calculating the early strength of concrete of different grades. This method can realize the real-time monitoring and evaluation of the strength evolution of concrete structures, master the strength evolution law of concrete at key parts, provide a scientific basis for construction decisions such as form removal and climbing of formwork scaffolds, and effectively ensure the safety of concrete structures.

[0006] To solve the above technical problems, the present invention includes the following technical solutions:

[0007] A method for rapidly determining the early strength of different grades of concrete, comprising:

[0008] Step S1: Conduct compressive tests on concrete at different ages under the standard curing conditions in the laboratory to obtain the strength of different grades of concrete at each age, record the corresponding internal temperature change of the concrete, and calculate the maturity using the Nurse-Saul maturity equation, i.e., formula (1):

[0009] M = ∑(T - T 0 )·Δt (1)

[0010] In the formula: M is the maturity, with the unit of °C·h or °C·d;

[0011] T is the average temperature of the concrete within the time interval Δt, with the unit of °C;

[0012] T 0 is the reference temperature, taking -10°C;

[0013] Δt is the time interval, with the unit of h or d;

[0014] Step S2: Calculate the fitting strength of different grades of concrete based on the maturity, i.e., formula (2);

[0015] f = a·(b·(M - c) / (1 + b·(M - c))) (2)

[0016] In the formula: f is the strength of the concrete under the standard curing conditions;

[0017] a, b, c, and d are strength coefficients, all of which are regression constants obtained based on the test results;

[0018] Step S3: Map the obtained different coefficients a, b, c, and d and the concrete grade label to obtain the corresponding relational expressions (3), (4), and (5):

[0019] a = -0.02127C 2 + 2.566C - 15.49 (3)

[0020] b = 2.178e-6C 2 - 0.0001484C + 0.00274 (4)

[0021] c = 0.1261C 2 + 26.83C - 1655 (5)

[0022] In the formula, C is the concrete grade label;

[0023] Step S4: Combine and calculate the relational expressions (3), (4), and (5) to obtain the final concrete strength prediction calculation model applicable to different strength grades under the standard curing condition, that is, Formula (6):

[0024] f = (-0.02127C 2 + 2.566C - 15.49)·{(2.178e-6C 2 - 0.0001484C + 0.00274)·[M - (0.1261C 2 + 26.83C - 1655)] / [1 + (2.178e-6C 2 - 0.0001484C + 0.00274)·[M - (0.1261C 2 + 26.83C - 1655)]]} (6)

[0025] In the formula, f is the concrete strength under the standard curing state, with the unit of MPa; M is the maturity, with the unit of °C·h or °C·d;

[0026] C is the concrete grade label.

[0027] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0028] The present invention provides a method for rapidly determining the early strength of concrete of different grades. Taking the concrete strength grade label and maturity as independent variables, a strength calculation model for rapidly predicting the compressive strength of concrete of different grades is established, providing a simple and effective means for rapidly calculating the early strength of concrete of different grades. This method can realize the real-time monitoring and evaluation of the strength evolution of concrete structures, master the strength evolution law of concrete at key parts, provide a scientific basis for construction decisions such as form removal and climbing formwork, and effectively ensure the safety of concrete structures. The present invention can directly predict the early strength of concrete of different strength grades according to the maturity and concrete strength grade label. The present invention provides a guarantee for the strength prediction of concrete components under the condition of inconvenient on-site construction, and also provides convenience for on-site construction personnel.

[0029] Furthermore, when the concrete curing is in a non-standard curing state, the concrete strength f' under the non-standard curing state is Formula (7):

[0030] f' = γ·f (7);

[0031] In the formula, γ is the strength attenuation coefficient, which is obtained by evaluating the strength of in-situ concrete under the construction site environment

[0032] and calling the strength attenuation coefficient database according to the concrete mix ratio.

[0033] Further, the strength attenuation coefficient database is obtained by large-scale standard curing tests and on-site non-standard curing tests respectively to obtain the corresponding strengths of concrete standard curing tests and on-site non-standard curing tests, and then the strength attenuation coefficient is obtained through the ratio of the two, and then integrated into the strength attenuation coefficient database corresponding to the concrete strength evolution system.

[0034] Further, according to the minimum strength required for the form removal of the concrete component, the form removal time of the component is inversely calculated through formulas (1), (6), and (7), which is the predicted form removal time of the on-site concrete component.

[0035] Further, in step S1, the strength ranges of different grades of concrete are C30 to C60.

[0036] Further, in formula (2),

[0037] When the concrete specimen used is C30, the coefficient a = 42.76; b = 0.0002145; c = -716.9;

[0038] When the concrete specimen used is C35, the coefficient a = 46.21; b = 0.0002860; c = -608.7;

[0039] When the concrete specimen used is C40, the coefficient a = 55.88; b = 0.0002913; c = -312.9;

[0040] When the concrete specimen used is C45, the coefficient a = 56.64; b = 0.0003786; c = -292.7;

[0041] When the concrete specimen used is C50, the coefficient a = 58.49; b = 0.0008248; c = 77.08;

[0042] When the concrete specimen used is C60, the coefficient a = 62.24; b = 0.0016730; c = 394.2.

[0043] Further, in formula (6), the maturity can also be quickly measured by a concrete maturity meter. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is the schematic diagram of the method for quickly measuring the early strength of different grades of concrete in an embodiment of the present invention;

[0045] Figure 2 is the flow chart from the minimum form removal strength to the form removal time of the concrete component in the method for quickly measuring the early strength of different grades of concrete in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] The following further elaborates in detail on the method for rapidly determining the early strength of different grades of concrete proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. According to the following description and the claims, the advantages and features of the present invention will become clearer. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise scales, only for conveniently and clearly assisting in explaining the purpose of the embodiments of the present invention. For the convenience of narration, the "upper" and "lower" directions mentioned hereinafter are consistent with the upper and lower directions of the accompanying drawings, but this should not limit the technical solution of the present invention.

[0047] Example 1

[0048] The following Figure 1 and Figure 2 are used to elaborate in detail on the method for rapidly determining the early strength of different grades of concrete of the present invention.

[0049] Please refer to Figure 1 and Figure 2 , a method for rapidly determining the early strength of different grades of concrete, comprising:

[0050] Step S1: Conduct compressive tests on concrete at different ages under laboratory standard curing conditions to obtain the strength of different grades of concrete at each age. Install 1 temperature sensor in the concrete test block, collect temperature data, record the corresponding internal temperature change of the concrete, and calculate the maturity using the Nurse-Saul maturity equation, that is, formula (1), or rapidly determine its maturity using a concrete maturity meter:

[0051] M = ∑(T - T 0 )·Δt (1)

[0052] In the formula: M is the maturity, with the unit of °C·h or °C·d;

[0053] T is the average temperature of the concrete within the time interval Δt, with the unit of °C;

[0054] T0 is the reference temperature, taking -10 °C;

[0055] Δt is the time interval, with the unit of h or d;

[0056] Step S2: Calculate the fitting strength of different grades of concrete based on the maturity, that is, formula (2);

[0057] f = a·(b·(M - c) / (1 + b·(M - c))) (2)

[0058] In the formula: f is the strength of the concrete under standard curing conditions;

[0059] a, b, c, and d are strength coefficients, all of which are regression constants obtained based on test results;

[0060] Step S3: Map the obtained different coefficients a, b, c, and d to the concrete grade label to obtain the corresponding relationships (3), (4), and (5):

[0061] a = -0.02127C 2 + 2.566C - 15.49 (3)

[0062] b = 2.178e-6C 2 - 0.0001484C + 0.00274 (4)

[0063] c = 0.1261C 2 + 26.83C - 1655 (5)

[0064] In the formula, C is the concrete grade label;

[0065] Step S4: Combine relationships (3), (4), and (5) and calculate to obtain the final concrete strength prediction calculation model applicable to different strength grades under standard curing conditions, that is, formula (6):

[0066] f = (-0.02127C 2 + 2.566C - 15.49)·{(2.178e-6C 2 - 0.0001484C + 0.00274)·[M - (0.1261C 2 + 26.83C - 1655)] / [1 + (2.178e-6C 2 - 0.0001484C + 0.00274) - [M - (0.1261C 2 + 26.83C - 1655)]]} (6)

[0067] In the formula, f is the concrete strength under standard curing conditions, with the unit of MPa; M is the maturity, with the unit of ℃·h or ℃·d;

[0068] C is the concrete grade label.

[0069] Specifically, for the method for rapidly determining the early strength of concrete of different grades provided by the present invention, taking the concrete strength grade label and maturity as independent variables, a strength calculation model for rapidly predicting the compressive strength of concrete of different grades is established, providing a simple and effective means for rapidly calculating the early strength of concrete of different grades. This method can realize the real-time monitoring and evaluation of the strength evolution of concrete structures, master the strength evolution law of concrete at key parts, provide a scientific basis for construction decisions such as form removal and formwork climbing, and effectively ensure the safety of concrete structures. The present invention can directly predict the early strength of concrete of different strength grades according to the maturity and the concrete strength grade label. The present invention provides a guarantee for the strength prediction of concrete components under the condition of inconvenient on-site construction, and also provides convenience for on-site construction personnel.

[0070] In this embodiment, more preferably, when the concrete curing is in a non-standard curing state, the concrete strength f' in the non-standard curing state is given by formula (7):

[0071] f = γ·f (7);

[0072] In the formula, γ is the strength attenuation coefficient, which is obtained by evaluating the strength of in-situ concrete in the construction site environment and calling the strength attenuation coefficient database according to the concrete mix ratio.

[0073] In this embodiment, more preferably, the strength attenuation coefficient database is obtained by large-scale standard curing tests and on-site non-standard curing tests respectively to obtain the corresponding strengths of the concrete standard curing test and on-site non-standard curing test, and then the strength attenuation coefficient is obtained by the ratio of the two, and then integrated into the strength attenuation coefficient database corresponding to the concrete strength evolution system.

[0074] In this embodiment, more preferably, according to the minimum strength required for the form removal of the concrete component, the form removal time of the component is inversely calculated through formulas (1), (6), and (7), which is the predicted form removal time of the in-situ concrete component.

[0075] In this embodiment, more preferably, the strength range of the concrete of different grades in step S1 is C30 - C60.

[0076] In this embodiment, more preferably, in formula (2),

[0077] When the concrete specimen used is C30, the coefficient a = 42.76; b = 0.0002145; c = -716.9;

[0078] When the concrete specimen used is C35, the coefficient a = 46.21; b = 0.0002860; c = -608.7;

[0079] When the concrete specimen adopted is C40, the coefficients are a = 55.88; b = 0.0002913; c = -312.9;

[0080] When the concrete specimen adopted is C45, the coefficients are a = 56.64; b = 0.0003786; c = -292.7;

[0081] When the concrete specimen adopted is C50, the coefficients are a = 58.49; b = 0.0008248; c = 77.08;

[0082] When the concrete specimen adopted is C60, the coefficients are a = 62.24; b = 0.0016730; c = 394.2.

[0083] The above examples are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above examples. The above examples only represent several embodiments of the present invention, and their descriptions are relatively specific and detailed, but they cannot be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for rapid determination of early strength of concrete of different grades. It is characterized in that include: Step S1: Conduct compression tests on concrete of different ages under standard curing conditions in the laboratory to obtain the strength of concrete of different grades at different ages, and record the temperature change inside the corresponding concrete. The maturity is calculated using the Nurse-Saul maturity equation, i.e., formula (1): M = ∑(T - T 0 )·Δt (1) Where: M is maturity, unit: ℃·h or ℃·d; T is the average temperature of concrete in the time interval Δt, in °C; T 0 is the reference temperature, taken as -10°C; Δt is the time interval, in h or d; Step S2, calculating the fitting strength of concrete of different grades according to maturity, i.e., formula (2); f=a(b·(Mc) / (1+b·(Mc))) (2) Where: f is the strength of concrete under standard curing conditions; a, b, c are strength coefficients, which are regression constants obtained based on test results; Step S3, mapping the obtained different coefficients a, b, c and the concrete grade number, can obtain the corresponding relationship equations (3), (4), (5): a = -0.02127C 2 +2.566C - 15.49 (3) b = 2.178e-6 C 2 -0.0001484 C + 0.00274 (4) c = 0.1261C 2 + 26.83C - 1655 (5) In the formula, C is the concrete grade number; Step S4: The relationship (3), (4), and (5) are combined to obtain a concrete strength prediction calculation model applicable to different strength grades under standard curing conditions, that is, formula (6): f = (-0.02127C 2 + 2.566C - 15.49)·{(2.178e-6C 2 - 0.0001484C + 0.00274)·[M - (0.1261C 2 + 26.83C - 1655)] / [1 + (2.178e-6C 2 - 0.0001484C + 0.00274)·[M - (0.1261C 2 + 26.83C - 1655)]]} (6) Where, f is the concrete strength under standard curing conditions, unit: MPa; M is the maturity, unit: ℃·h or ℃·d; C is the concrete grade number.

2. The method for rapidly determining early strength of concrete of different grades according to claim 1, It is characterized in that When the concrete is cured under non-standard curing conditions, the concrete strength f′ under non-standard curing conditions is expressed as formula (7): f = γ·f (7); Where γ is the strength attenuation coefficient, which is obtained by evaluating the strength of solid concrete under the construction site environment and calling the strength attenuation coefficient database according to the mix ratio of concrete.

3. The method for rapidly determining early strength of concrete of different grades according to claim 2, It is characterized in that The strength attenuation coefficient database is obtained through large-scale standard curing tests and on-site non-standard curing tests, respectively, to obtain the corresponding concrete standard curing test and on-site non-standard curing test strength, and then the strength attenuation coefficient is obtained by ratio of the two, and then integrated into the corresponding strength attenuation coefficient database in the concrete strength evolution system.

4. The method for rapidly determining early strength of concrete of different grades according to claim 2, It is characterized in that According to the minimum strength required for concrete component demoulding, the demoulding time of the component is calculated by back-calculating formulas (1), (6), and (7), which is the predicted demoulding time of the on-site concrete component.

5. The method for rapidly determining early strength of concrete of different grades according to claim 1, It is characterized in that The strength range of the different grades of concrete in step S1 is C30-C60.

6. The method for rapidly determining early strength of concrete of different grades according to claim 5, It is characterized in that In the formula (2), When the concrete specimen used is C30, the coefficients a = 42.76; b = 0.0002145; c = -716.9; When the concrete specimen adopted is C35, the coefficients are: a = 46.21; b = 0.0002860; c = -608.7; When the concrete specimen adopted is C40, the coefficients are: a = 55.88; b = 0.0002913; c = -312.9; When the concrete specimen adopted is C45, the coefficients are: a = 56.64; b = 0.0003786; c = -292.7; When the concrete specimen adopted is C50, the coefficients are: a = 58.49; b = 0.0008248; c = 77.08; When the concrete specimen adopted is C60, the coefficients are: a = 62.24; b = 0.0016730; c = 394.

2.

7. The rapid determination method for the early strength of concrete of different grades according to claim 1, characterized in that, the maturity in the formula (6) can also be rapidly measured by a concrete maturity meter.

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