CN114018711B - Method for determining change of elastic modulus and shrinkage strain of concrete along with time - Google Patents
Method for determining change of elastic modulus and shrinkage strain of concrete along with time Download PDFInfo
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- CN114018711B CN114018711B CN202111371658.XA CN202111371658A CN114018711B CN 114018711 B CN114018711 B CN 114018711B CN 202111371658 A CN202111371658 A CN 202111371658A CN 114018711 B CN114018711 B CN 114018711B
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
- G01N2203/0075—Strain-stress relations or elastic constants
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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Abstract
The invention discloses a method for determining the change of elastic modulus and shrinkage strain of concrete along with time, which comprises the following steps: s1, selecting two sections of outer tubes with the same size to be fixed on a bottom plate; two sections of inner pipes with different wall thicknesses are selected to be coaxially arranged in the two sections of outer pipes respectively and fixed on the bottom plate; the heights of the outer tube and the inner tube are the same; s2, fixing a plurality of strain gauges on the inner walls of the two sections of inner pipes in a circumferential direction; and connecting the two groups of strain gauges to the strain gauge by wires; s3, simultaneously pouring concrete to be tested in gaps between the two groups of outer pipes and the inner pipes, and covering a plastic film on the top surface of the concrete for sealing after pouring is completed; and S4, measuring strain values of the two groups of inner pipes at different ages, and calculating the elastic modulus and the shrinkage strain of the concrete at each age. The method is simple and reliable in operation, can accurately measure the shrinkage strain values and the elastic modulus of the concrete at different ages, and has the advantages of high data precision, economy, applicability and strong popularization.
Description
Technical Field
The invention relates to the technical field of concrete structures in civil engineering, in particular to a method for determining the change of elastic modulus and shrinkage strain of concrete along with time by using the circumferential strain of two sets of steel pipe sleeve structures.
Background
The concrete structure is the most widely applied engineering structure form, shrinkage is the basic characteristic of concrete, and the concrete is gradually hardened after pouring, and the water is dispersed to generate time-varying shrinkage. The final shrinkage value of concrete is related to various factors such as cement consumption, water-cement ratio, aggregate property, curing condition and component size, and can be generally up to (300-600). Times.10 -6 The commercial pumping concrete can reach (800-1000) x 10 -6 . Shrinkage deformation is restrained and forms tensile stress, and the tensile strength of the concrete is only 1/10-1/20 of the compressive strength, so that the shrinkage is extremely easy to cause concrete cracking, the cracking reaches a certain width to affect structural attractiveness, durability and safety, particularly in ultra-long concrete structures, and the concrete shrinkage often causes the cracking of the concrete structures.
In the rapid development period of China, the construction scale of infrastructures is large and the quantity of infrastructures is large, the problems of shrinkage crack control of ultra-long concrete structures can be solved in the projects, and due to the lack of a perfect concrete shrinkage crack control theory, the problems that shrinkage cracks exceed the standard requirements in a large number of projects each year are solved. The shrinkage of concrete gradually increases along with time, the elastic modulus of concrete also gradually increases along with time, and the measurement of shrinkage strain of concrete and the change rule of the elastic modulus along with time is very difficult, and a large number of test pieces are needed, and the elastic modulus of concrete is measured through experiments at different times, and especially early, the concrete strength is extremely low, and the elastic modulus of concrete is difficult to measure.
The research on the shrinkage strain of the concrete and the time-varying rule of the elastic modulus of the concrete can be directly used for the calculation and analysis of the shrinkage strain and the stress of the ultra-long concrete structure to judge whether the concrete is cracked or not; and the formation and development mechanism of the shrinkage crack of the concrete can be established, so as to guide the shrinkage crack calculation theory of the ultra-long concrete structure. The change rule of the concrete elastic modulus along with time is researched, a theoretical basis can be provided for concrete structure crack control in public facility construction of large airport terminal, exhibition center, stadium and the like, and the concrete elastic modulus crack control method has important practical significance.
Therefore, how to accurately measure the shrinkage strain and the change rule of the elastic modulus of the concrete along with time is a problem to be solved by the technicians in the field.
Disclosure of Invention
In view of the above, the present invention provides a method for determining the elastic modulus and shrinkage strain of concrete with time, which aims to solve the above technical problems.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a method for determining the change of the elastic modulus and the shrinkage strain of concrete with time comprises the following steps:
s1, selecting two sections of outer tubes with the same size to be fixed on a bottom plate; two sections of inner pipes with different wall thicknesses are selected to be coaxially arranged in the two sections of outer pipes respectively and fixed on the bottom plate; the heights of the outer tube and the inner tube are the same;
s2, circumferentially fixing a plurality of strain gauges on the inner walls of the two sections of inner pipes; and connecting the two groups of strain gauges to a strain gauge through wires;
s3, simultaneously pouring concrete to be tested in gaps between the two groups of outer pipes and the inner pipes, and covering a plastic film on the top surface of the concrete for sealing after pouring is completed;
s4, measuring strain values of the two groups of inner pipes at different ages, and calculating the elastic modulus and the shrinkage strain of the concrete at each age.
Through the technical scheme, the invention adopts two groups of inner and outer pipe structures, the outer pipe has the same radius and thickness, the inner pipe has the same radius and different wall thickness; the elastic modulus and the shrinkage strain value of the concrete at any moment can be calculated through two groups of strain values at the same time; the method is simple and reliable in operation, can accurately measure the shrinkage strain values and the elastic modulus of the concrete at different ages, and has the advantages of high data precision, economy, applicability and strong popularization.
Preferably, in the above method for determining the change of the elastic modulus and the shrinkage strain of concrete over time, in step S1, the outer tube and the inner tube are both sealed with the bottom plate. Preventing concrete from leaking from the bottom gap, resulting in error in the experiment.
Preferably, in the method for determining the change of the elastic modulus and the shrinkage strain of the concrete over time, in step S2, two groups of strain gauges are fixed at half the height of the inner wall of the two sections of the inner pipe; the number of the strain gauges in each group is 4, and the strain gauges are uniformly distributed on the inner wall of the inner tube in the circumferential direction. The measuring requirements can be met.
Preferably, in the method for determining the change of the elastic modulus and the shrinkage strain of the concrete over time, in step S3, two sections of the inner side walls of the outer tube are covered with an anti-adhesion plastic layer in advance before the concrete is poured. So that the concrete can shrink freely when shrinking, and no binding force is generated between the concrete and the outer tube.
Preferably, in the method for determining the change with time of the elastic modulus and the shrinkage strain of concrete, in step S4, the strain value of each of the inner tubes is an average value of the plurality of strain gauges at the same time when the strain measurement is performed.
Preferably, in the method for determining the change of the elastic modulus and the shrinkage strain of the concrete over time, the radius of the inner pipe is 100-150 mm, and the height of the inner pipe is 1-1.5 times of the diameter; the wall thickness of one inner tube is 1.5-2.0 times of the wall thickness of the other inner tube, wherein the wall thickness of the inner tube with smaller wall thickness is 4-6 mm.
Preferably, in the method for determining the change of the elastic modulus and the shrinkage strain of the concrete over time, the difference between the radius of the outer tube and the radius of the inner tube is 80 mm-100 mm.
Preferably, in the above method for determining the change of the elastic modulus and the shrinkage strain of concrete over time, in step S4, the radius of the inner tube is R, the radius of the outer tube is R, and the inner tube and the outer tube form an annular elastomer; when the internal compressive stress of the annular elastomer is q and the external compressive stress is 0, the stress state of the annular elastomer is:
radial stress at radius ρ isHoop stress is +.>
The inner diameter of the annular structure formed by the concrete is r, and the hoop stress of the inner side of the annular structure isSince the poisson's ratio effect is less than 5%, the corresponding strain after ignoring the poisson's ratio effect is:
the radius of the inner tube is r, the thickness is t, and the corresponding hoop stress when bearing the radial stress q at the outer side isThe corresponding strain is:
the deformation coordination relationship is as follows:
ε 0 ＝ε c +ε s the method comprises the steps of carrying out a first treatment on the surface of the Formula III
In formulas one to three: epsilon 0 Shrinkage strain for the free state of the concrete; e (E) s 、E c Modulus of elasticity for the inner pipe and the concrete;
from equation IISubstituting the formula I to obtain: />Substituting the formula III to obtain:
modulus of elasticity E of the concrete c Free shrinkage strain ε 0 Strain +epsilon of said inner tube s And said concrete constraint strain = epsilon c + is a function of time, plus a function of time (τ), resulting in:
the two groups of inner pipes are respectively a 1# inner pipe and a 2# inner pipe; the wall thickness of the 1# inner tube is t 1 The wall thickness of the No. 2 inner tube is t 2 The method comprises the following steps of:
the free shrinkage strain of the 1# inner tube is:
the free shrinkage strain of the 2# inner tube is:
and (3) solving a simultaneous formula five to a simultaneous formula seven:
relationship of concrete elastic modulus with time:
relationship of shrinkage strain of concrete with time:
wherein:is the ratio of the radii of the inner tube and the outer tube; />Is the ratio of the thickness to the radius of the No. 1 inner tube,is the ratio of the thickness to the radius of the No. 2 inner tube.
Preferably, in the method for determining the change of the elastic modulus and the shrinkage strain of the concrete over time, the inner tube and the outer tube are both steel tubes. Can meet the experimental requirements.
Compared with the prior art, the invention discloses a method for determining the change of the elastic modulus and the shrinkage strain of concrete along with time, and two groups of test devices are composed of an inner pipe and an outer pipe, wherein the radius and the thickness of the outer pipe are the same, the radius of the inner pipe is the same, the wall thickness is different, and the same distance is kept between the inner pipe and the outer pipe; the inner side of the inner pipe is annularly stuck with a strain gage, the inner pipe and the outer pipe are placed on the bottom plate, and a gap between the inner pipe and the outer pipe and the bottom plate is subjected to sealing treatment; connecting strain gauges of the two-section inner tube to strain gauges; pouring the stirred concrete into the space between the inner pipe and the outer pipe; covering the top surface of the concrete between the inner pipe and the outer pipe with a plastic film to prevent water evaporation; starting strain continuous collection; the elastic modulus and the shrinkage strain value of the concrete at any moment can be calculated by two groups of strain values at the same time. The method is simple and reliable in operation, can accurately measure the shrinkage strain values and the elastic modulus of the concrete at different ages, and has the advantages of high data precision, economy, applicability and strong popularization.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic top view of an experimental apparatus provided by the invention;
FIG. 2 is an exploded view of a set of outer and inner tube structures provided by the present invention;
FIG. 3 is a cross-sectional view of a set of outer and inner tube structures provided by the present invention;
FIG. 4 is a schematic view of the stress of the annular concrete provided by the invention;
FIG. 5 is a schematic view of the inner tube according to the present invention.
Wherein:
1-an outer tube;
2-a bottom plate;
3-an inner tube;
4-strain gage;
5-conducting wires;
6-strain gauge;
7-concrete;
8-plastic film.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to FIGS. 1 to 5, in a certain engineering, the elastic modulus E of concrete at a certain age is measured c (tau) and concrete shrinkage strain epsilon 0 (τ) (free state shrinkage strain) elastic modulus E of steel pipe s ＝20×10 4 MPa,1# steel tube r=120 mm, t 1 =4 mm, 2# steel tube r=120 mm, t 1 =8 mm; r=200 mm, epsilon measured 15 days of age s1 (15)＝231με，ε s2 (15)＝166με。
Yielding α=0.6, β 1 ＝1/30,β 2 =1/15, substituting formula eight and formula nine can result in the concrete elastic modulus and shrinkage strain:
it can be seen that the elastic modulus and shrinkage strain of the concrete can be calculated by the test data, and the method is proved to be feasible and accurate.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the description of the method section.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (9)
1. The method for determining the change of the elastic modulus and the shrinkage strain of the concrete with time is characterized by comprising the following steps of:
s1, two sections of outer tubes (1) with the same size are selected and fixed on a bottom plate (2); two sections of inner pipes (3) with different wall thicknesses are selected to be respectively and coaxially arranged in the two sections of outer pipes (1) and fixed on the bottom plate (2); the heights of the outer tube (1) and the inner tube (3) are the same;
s2, fixing a plurality of strain gauges (4) on the inner walls of the two sections of inner pipes (3) in a circumferential direction; and connecting two groups of strain gauges (4) to a strain gauge (6) through a wire (5);
s3, simultaneously pouring concrete (7) to be tested in gaps between the two groups of outer pipes (1) and the inner pipes (3), and covering a plastic film (8) on the top surface of the concrete (7) for sealing after pouring is completed;
s4, measuring strain values of the two groups of inner pipes (3) at different ages, and calculating the elastic modulus and the shrinkage strain of the concrete (7) at each age;
in the step S4, the radius of the inner tube (3) is R, the radius of the outer tube (1) is R, and the inner tube (3) and the outer tube (1) form an annular elastomer; when the internal compressive stress of the annular elastomer is q and the external compressive stress is 0, the stress state of the annular elastomer is:
radial stress at radius ρ isHoop stress is +.>
The inner diameter of the annular structure formed by the concrete (7) is r, and the hoop stress of the inner side of the annular structure isSince the Poisson's ratio is less than 5%, the concrete (7) constrains the strain ε after ignoring the Poisson's ratio effect c The method comprises the following steps:
the radius of the inner tube (3) is r, the thickness is t, and the corresponding hoop stress when bearing the outer radial stress q isThe inner tube (3) has strain epsilon s The method comprises the following steps:
the deformation coordination relationship is as follows:
ε 0 ＝ε c +ε s the method comprises the steps of carrying out a first treatment on the surface of the Formula III
In formulas one to three: epsilon 0 -a shrinkage strain for the free state of the concrete (7); e (E) s 、E c -modulus of elasticity for the inner pipe (3) and the concrete (7);
from equation IISubstituting the formula I to obtain: />Substituting the formula III to obtain:
modulus of elasticity E of the concrete (7) c Free shrinkage strain ε 0 The inner tube (3) being strained epsilon s And the concrete (7) constrains the strain epsilon c Is a function of time, added to the time function (τ) to obtain:
the two groups of inner pipes (3) are respectively a 1# inner pipe and a 2# inner pipe; the wall thickness of the 1# inner tube is t 1 The wall thickness of the No. 2 inner tube is t 2 The method comprises the following steps of:
the concrete free shrinkage strain corresponding to the 1# inner pipe is as follows:
2# inner tube stationThe corresponding concrete free shrinkage strain is:
and (3) solving a simultaneous formula five to a simultaneous formula seven:
relationship of concrete elastic modulus with time:
relationship of shrinkage strain of concrete with time:
wherein:-the ratio of the radius of the inner tube (3) to the radius of the outer tube (1); />Is the ratio of the thickness to the radius of the No. 1 inner tube,is the ratio of the thickness to the radius of the No. 2 inner tube.
2. Method for determining the change over time of the elastic modulus and the shrinkage strain of concrete according to claim 1, characterized in that in step S1 both the outer tube (1) and the inner tube (3) are sealed with the bottom plate (2).
3. Method for determining the change in elastic modulus and shrinkage strain of concrete over time according to claim 1, characterized in that in step S2 both sets of strain gauges (4) are fixed at half the height of the inner wall of the two sections of inner tube (3).
4. A method for determining the change of the elastic modulus and the shrinkage strain of concrete over time according to claim 3, wherein the number of the strain gages (4) in each group is 4, and the strain gages are uniformly arranged on the inner wall of the inner pipe (3) in the circumferential direction.
5. Method for determining the change with time of the elastic modulus and the shrinkage strain of a concrete according to claim 1, characterized in that in step S3, the inside walls of two sections of the outer tube (1) are previously covered with a layer of anti-adhesion plastic before the concrete (7) is poured.
6. The method according to claim 1, wherein in step S4, the strain value of each inner tube (3) is averaged over a plurality of strain gauges (4) at the same time when the strain measurement is performed.
7. The method for determining the change of the elastic modulus and the shrinkage strain of the concrete with time according to claim 1, wherein the radius of the inner tube (3) is 100-150 mm, and the height of the inner tube (3) is 1-1.5 times of the diameter; the wall thickness of one inner tube (3) is 1.5-2.0 times of the wall thickness of the other inner tube (3), wherein the wall thickness of the inner tube (3) with smaller wall thickness is 4-6 mm.
8. The method for determining the change of the elastic modulus and the shrinkage strain of the concrete with time according to claim 7, wherein the difference between the radius of the outer tube (1) and the radius of the inner tube (3) is 80-100 mm.
9. The method for determining the change of the elastic modulus and the shrinkage strain of concrete with time according to claim 1, wherein the inner tube (3) and the outer tube (1) are both steel tubes.
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| CN109975120A (en) * | 2019-04-18 | 2019-07-05 | 中国建筑材料科学研究总院有限公司 | Concrete restraint stress and deformational stress measuring device and measuring method |
| CN112949105A (en) * | 2019-12-11 | 2021-06-11 | 武汉大学 | Method and system for calculating extrusion stress of isotropic double-tube concrete column |
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