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CN111721627B - Device and testing method for ultra-early tensile creep of cement-based material - Google Patents

Device and testing method for ultra-early tensile creep of cement-based material Download PDF

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CN111721627B
CN111721627B CN202010530249.9A CN202010530249A CN111721627B CN 111721627 B CN111721627 B CN 111721627B CN 202010530249 A CN202010530249 A CN 202010530249A CN 111721627 B CN111721627 B CN 111721627B
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cement
creep
mold
cement paste
mould
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CN111721627A (en
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赵庆新
贾雅丽
马千里
刘辉
钱泉
王建强
王冬丽
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Suzhou Cti Technology Co ltd
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Yanshan University
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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
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/36—Embedding or analogous mounting of samples
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/36—Embedding or analogous mounting of samples
    • G01N2001/366—Moulds; Demoulding
    • 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
    • G01N2203/0014—Type of force applied
    • G01N2203/0016—Tensile or compressive
    • G01N2203/0017—Tensile

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Abstract

本发明提供一种用于水泥基材料超早期拉伸徐变的装置及测试方法，其包括拉伸运动组件、模具和试件承载框架组件。主体框架由截面尺寸相同，长度不等的角钢焊接组成，主体框架的上部为角钢焊接的长方体，四角设有等长的角钢；模具沿长度方向的两端，对称设有等长的螺杆，模具沿宽度方向的两端设有细缝，模具挡板对称分布在模具上表面的两端。测试方法首先是对空模具和含有水泥净浆或者砂浆的模具进行受力测试，得出水泥净浆或者砂浆在模具中所受荷载占总荷载的比例α，然后测试水泥净浆和砂浆的初凝时间，最后通过改进的逐步计算法得到水泥基材料超早期的徐变计算模型。本发明具有操作方便、造价合理，测试数据稳定性好、精度高，占地面积小等优点。

Figure 202010530249

The invention provides a device and a testing method for ultra-early tensile creep of cement-based materials, comprising a tensile motion component, a mold and a test piece bearing frame component. The main frame is composed of welded angle steels with the same cross-sectional size and different lengths. The upper part of the main frame is a cuboid welded with angle steels, and the four corners are provided with equal-length angle steels; the two ends of the mold along the length direction are symmetrically provided with equal-length screws. Both ends along the width direction are provided with slits, and the mold baffles are symmetrically distributed on both ends of the upper surface of the mold. The test method is to test the force of the empty mold and the mold containing the cement paste or mortar first, and obtain the ratio α of the load of the cement paste or mortar in the mold to the total load, and then test the initial cement paste and mortar. setting time, and finally the super-early creep calculation model of cement-based materials is obtained through the improved step-by-step calculation method. The invention has the advantages of convenient operation, reasonable cost, good test data stability, high precision, small footprint and the like.

Figure 202010530249

Description

Device and testing method for ultra-early tensile creep of cement-based material
Technical Field
The invention relates to the field of concrete, in particular to a device and a testing method for ultra-early tensile creep of a cement-based material.
Background
With the rapid development of engineering technology in China, the application field of concrete is wider, and the problem of durability of the concrete is solved. The main causes of deterioration in durability of concrete are cracking and crack propagation of concrete. For early cracks in concrete, creep, especially tensile creep, can redistribute internal forces in the concrete, thereby greatly reducing the risk of crack occurrence, and the ultra-early performance of cement-based materials plays a key role in later crack resistance. Therefore, the tensile creep property of the cement-based material plays an important role in the crack resistance of concrete.
At present, the method for testing creep deformation of cement-based materials at home and abroad is mainly an embedded tensile test method. The embedded tensile test method is characterized in that an embedded pull rod is fixed at two ends of a mould through two side plates before concrete pouring, a template is removed after a test piece is formed, and a testing machine transmits tensile force to the test piece through the embedded pull rod; and placing displacement meters at two ends of the test piece during molding of the test piece, and measuring the size change of the test piece through the displacement meters. However, the method is used for testing the tensile creep of the concrete at the age of 8h at the earliest, and the tensile creep of the cement-based material in the period from initial setting to final setting (6-8h) cannot be measured; and the above stretching method causes load eccentricity and stress strain unevenness. The development of a shrinkage testing device which can accurately test the ultra-early tensile creep deformation of the cement-based material and has low cost is urgently needed.
Most of the existing cement-based material tensile creep calculation models are applied to concrete, but the tensile creep calculation models of the concrete are very complex and cannot be applied to creep calculation of set cement and cement mortar. And the creep model is generally used for the calculation of long age, and the calculation of short age is not accurate enough. There is a need to develop a model that allows for ultra-early creep calculations for cement-based materials.
By combining the super-early self characteristics of the cement-based material, a device and a test method capable of semi-quantitatively testing the super-early creep of the cement-based material are developed, and the super-early tensile creep performance of the cement-based material can be contrastively analyzed by the method.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a device and a test method for ultra-early tensile creep of a cement-based material.
The invention provides a device for ultra-early tensile creep of a cement-based material, which comprises a tensile motion assembly, a die, a laser measurer and a test piece bearing frame assembly, wherein the tensile motion assembly and the die are respectively positioned on the test piece bearing frame assembly, the tensile motion assembly is connected with the die, and the laser measurer is positioned above the die. The test piece bearing frame assembly comprises a main body frame, a track base plate, a bolt nut and an inclined support rod, wherein the main body frame is formed by welding a plurality of angle steels with the same cross section size and different lengths, the upper part of the main body frame is a cuboid welded by the angle steels, the four corners of the main body frame are respectively provided with the angle steels with equal lengths, the track base plate is positioned at the upper end of the main body frame and is fixedly connected with the angle steels at the two ends of the upper part of the main body frame through the bolt nut, and the two ends of the inclined support rod are respectively fixedly connected with the angle steels at the four vertex angles of the main body frame; the mould, it includes screw rod, mould baffle and slit, the mould is along length direction's both ends, and the symmetry is equipped with isometric screw rod, the mould is equipped with the slit along width direction's both ends, mould baffle symmetric distribution is in the both ends of mould upper surface. The stretching movement assembly comprises a hanging plate, a specially-made bearing, a bearing fixing rod, a steel strand, a lever, a tension baffle plate, a stay wire bolt and a fixing rod, wherein the steel strand comprises a first steel strand, a second steel strand, a third steel strand, a fourth steel strand, a fifth steel strand and a sixth steel strand, two ends of the bearing fixing rod respectively penetrate through an inner ring of the specially-made bearing and fixedly connected with an inclined supporting rod, first ends of the first steel strand, the second steel strand and the third steel strand are respectively fixedly connected with the hanging plate, second ends of the first steel strand, the second steel strand and the third steel strand penetrate through an outer ring of the specially-made bearing and fixedly connected with a first end of the lever respectively, the lever and the tension baffle plate are respectively positioned on two sides of the upper portion of the main body frame, a first end of the tension baffle plate is fixedly connected with an angle steel at one end of the upper portion of the main body frame by welding, the first ends of the fourth steel strand, the fifth steel strand and the sixth steel strand are respectively connected with the second end of the lever, the third end of the lever is fixedly connected with the main body frame through a fixing rod, the second ends of the fourth steel strand, the fifth steel strand and the sixth steel strand are connected with the first end of the stay bolt, the second end of the stay bolt is connected with the screw rod at the first end of the mold, and the screw rod at the second end of the mold is fixedly connected with the second end of the tension baffle.
Preferably, the lever includes a first lever, a second lever and a third lever, and the lengths of the first lever, the second lever and the third lever are not equal to each other.
Preferably, the number of the hanging plate, the special bearing, the bearing fixing rod, the lever, the mold and the stay wire bolt is equal.
Preferably, the mould is made of polyurethane material, the elastic modulus of the polyurethane material does not change along with the increase of the using times, and the elastic modulus is stable to 60 MPa.
In another aspect of the present invention, a test method for ultra-early tensile creep of a cement-based material is provided, which specifically includes the following steps:
s1, fixing the water-cement ratio, gradually increasing the doping amount of the mineral admixtures in the cementing material, changing the combination and respective proportion of the mineral admixtures under the same doping amount, and designing the mixing ratio;
s2, coating Vaseline lubricant on the track backing plate;
s3, adjusting the distance between the laser measurer and the mould baffle plate to 26mm, and simultaneously connecting the laser distance measurer with a UT7808 dynamic and static strain acquisition analyzer;
s4, carrying out stress test on the empty mold and the mold containing the cement paste or the cement mortar;
s41, loading a load on the empty die to obtain the deformation of the empty die;
s42, loading a load on the mould containing the cement paste to ensure that the deformation of the mould containing the cement paste is the same as that of the empty mould, and obtaining the stress load of the mould containing the cement paste;
s43, loading a load on the mold containing cement mortar to ensure that the deformation of the mold containing cement mortar is the same as that of the empty mold, and obtaining the stress load of the mold containing cement mortar;
s44, obtaining the stress load of the cement paste or the cement mortar in the mold through the external force difference value of the empty mold and the mold containing the cement paste or the cement mortar, and respectively calculating the proportion alpha of the load of the cement paste or the cement mortar in the mold to the total load, thereby obtaining the proportion of the stress of the cement paste or the cement mortar to the external force load;
s5, respectively pouring the clean cement paste and the cement mortar into the mold, the Vicat instrument and the penetrometer;
s51, stirring the cement paste, and pouring the stirred cement paste into a mold and a Vicat instrument;
s52, stirring cement mortar, and pouring the stirred cement mortar into a mold and a penetrometer;
s6, testing the initial setting time of the cement paste and the cement mortar;
s61, measuring when the cement paste is initially set in the mould and the Vicat instrument, and loading an initial load on the hanging plate;
s62, continuously placing increasing loads on the hanging plate, repeating the steps in the same way, and stopping measurement when the cement paste is subjected to creep cracking;
s63, recording the initial load m of the cement paste1Total load m2Initial strain ε1Total strain epsilon2Elastic strain of each stage ∈i', creep strain ε at each stageiExperimental values such as cement proportion alpha and the like;
s64, measuring after the cement mortar is initially set in the mold and the penetrometer, and loading an initial load on the hanging plate;
s65, continuously placing increasing loads on the hanging plate, repeating the steps in the same way, and stopping measurement when the cement mortar is subjected to creep cracking;
s66, recording the initial load m of cement mortar1Total load m2Initial strain ε1Total strain epsilon2Elastic strain of each stage ∈i', creep strain ε at each stageiExperimental values such as cement proportion alpha and the like;
s7, finishing the experimental values measured in the step S5 to calculate the stress sigma (tau) borne by the cement paste or the cement mortar at any momenti) And creep coefficient at the time of cracking
Figure GDA0002601335360000042
And creep degree C (t), and drawing a creep curve to obtain a creep calculation model of the cement-based material in the ultra-early stage;
s71, converting the stress change curve into a plurality of sections of extremely fine gradient change curves by improving a step-by-step calculation method, and then carrying out creep calculation on each gradient;
and S72, obtaining the creep coefficient and the creep degree of the cement-based material at any time by using the creep calculation model, and drawing a creep curve changing along with time.
Preferably, in step S4, the stress test indicates that the mold and the cement mortar are deformed synchronously when the mold is subjected to an external force and the cement mortar or cement mortar in the mold has not cracked; in the case of synchronous deformation, the internal force applied to the mold and the cement paste or the cement mortar is considered to be distributed by the ratio of the elastic modulus of the cement paste or the cement mortar to the elastic modulus of the mold and the ratio of the cross-sectional area of the cement paste or the cement mortar to the cross-sectional area of the mold.
Preferably, the ratio formula of the internal force of the cement paste or cement mortar to the external force load is as follows:
Figure GDA0002601335360000041
F(t)＝E(t)×ε(t)×A
F'(t)＝E'×ε(t)×A'
E(t)＝191.4326t
wherein:
alpha (t) -the proportion of the internal cement paste or cement mortar stressed in the external force when the mould is stressed by the external force;
f (t) -the change of the stress of the cement paste or the cement mortar along with the time;
f' (t) -the change in mold force over time;
e (t) -the variation of the modulus of elasticity of the cement paste or cement mortar with time;
e' -modulus of elasticity of the mold;
epsilon (t) -the strain of the cement paste or cement mortar and the mould;
a-the cross-sectional area of the cement paste or cement mortar;
a' -the section area of the die, which is the section area of the U-shaped groove;
t-time after initial setting of cement;
the proportion formula of the experimental method of the cement paste or the cement mortar with stress accounting for the external force load is as follows:
Figure GDA0002601335360000051
wherein:
alpha-the proportion of the internal cement paste or cement mortar stressed in the external force when the external force is applied to the mould; f. of1-the mould is subjected to a tensile force when it contains cement paste or cement mortar;
f2the mold is subjected to tension forces when it does not contain cement paste or cement mortar.
Preferably, in step S7, the cement is subjected to a stress σ (τ) at any timei) The calculation formula of (a) is as follows:
Figure GDA0002601335360000052
wherein:
σ(τi) -cement tauiStress applied at any moment;
αi—τithe stress ratio of cement in the mould is always kept;
α1water in mould when test piece loads initial loadThe mud stress ratio;
αcthe ratio of the stress of the cement in the mould when the test piece is subjected to creep cracking;
Ni—τithe total tension on the mold at all times;
N1-the total tension to which the mould is subjected when the mould is loaded with an initial load;
a-the cross-sectional area of the cement paste or cement mortar;
creep coefficient of cement-based material in tensile cracking
Figure GDA0002601335360000053
And the creep degree C (t) are calculated as follows:
Figure GDA0002601335360000061
wherein:
τ0a starting age for the cement-based material;
τiis the desired age of the cement-based material;
m1is the initial load of the test piece;
mcthe total load loaded for the test piece when the test piece is cracked and damaged;
εe(τ0) Is formed by an initial load m1The induced initial elastic strain;
εe(τi) For cement in moulds at τiTotal elastic strain at time;
εc(τi) Is tauiCreep strain at time;
ε(τi) Is tauiTotal strain at time.
Compared with the prior art, the invention has the following advantages:
1. the invention adopts the polyurethane material mould, the mould and the cement-based material are bonded together to generate synchronous deformation, so that the cement-based material can be tested without demoulding, and the ultra-early stretching creep measurement can be carried out on the cement-based material in a viscoelastic-plastic state;
2. the displacement measuring device adopts the infrared sensor, is not in direct contact with the test piece, and has small floor area and simple and convenient operation;
3. the invention provides a calculation model according to the super-early self characteristics of cement-based materials, and the model can be applied to the super-early creep calculation of short-age set cement and cement mortar.
Drawings
FIG. 1 is a schematic diagram of the overall structure of the apparatus for ultra-early stage tensile creep of cement-based materials according to the present invention;
FIG. 2 is a schematic diagram of the structure of a mold in the apparatus for ultra-early tensile creep of cement-based materials according to the present invention;
FIG. 3 is a schematic representation of the ultra-early tensile creep of a cement-based material in an apparatus for ultra-early tensile creep of a cement-based material according to the present invention;
FIG. 4 is a graph of the net cement slurry force ratio over time for an apparatus for ultra-early tensile creep in cement-based materials in accordance with the present invention;
FIG. 5 is a graph showing the creep degree of a cement-based material with a mineral admixture content of 70% in an apparatus for ultra-early tensile creep of a cement-based material according to the present invention;
FIG. 6a is a graph of the creep rate of 10% ultra-fine fly ash set cement as it is creep cracked in an apparatus for ultra-early tensile creep of cement-based materials in accordance with the present invention;
FIG. 6b is a graph of creep rate at creep cracking of 20% and 30% class II fly ash set cement in an apparatus for ultra-early tensile creep of cement-based materials according to the present invention;
FIG. 7a is a graph showing the creep rate of a 40% S95 slag cement slurry at creep cracking in an apparatus for ultra-early tensile creep of cement-based materials in accordance with the present invention; and
FIG. 7b is a graph of the creep rate of a 30% S115 slag ash cement slurry at creep cracking in an apparatus for ultra-early tensile creep of cement-based materials in accordance with the present invention.
The main reference numbers:
the steel strand tensioning device comprises a hanging plate 1, an inclined supporting rod 2, a special bearing 3, a steel strand 4, a first steel strand 41, a second steel strand 42, a third steel strand 43, a fourth steel strand 44, a fifth steel strand 45, a sixth steel strand 46, a bearing fixing rod 5, a bolt nut 6, a main body frame 7, a lever 8, a first lever 81, a second lever 82, a third lever 83, a fixing rod 9, a stay wire bolt 10, a track backing plate 11, a mold 12, a tension baffle 13, a screw rod 14, a laser measurer 15, a mold baffle 16 and a fine seam 17.
Detailed Description
The technical contents, structural features, attained objects and effects of the present invention are explained in detail below with reference to the accompanying drawings.
An apparatus for ultra-early tensile creep of cement-based materials, as shown in fig. 1, includes a tensile motion assembly, a die 12, a laser gauge 15, and a specimen carrying frame assembly. The stretching motion assembly and the die 12 are respectively positioned on the test piece bearing frame assembly, the stretching motion assembly is connected with the die 12, and the laser measurer 15 is positioned above the die 12.
The test piece bearing frame assembly comprises a main body frame 7, a rail base plate 11, a bolt nut 6 and a diagonal support rod 2. Main body frame 7 is the same by a plurality of cross sectional dimension, and the angle steel welding that length is unequal is constituteed, and main body frame 7's upper portion is angle steel welded cuboid, and the four corners is equipped with isometric angle steel respectively, and track backing plate 11 is located main body frame 7's upper end to through the angle steel fixed connection at bolt and nut 6 and main body frame 7 upper portion both ends, the angle steel fixed connection of bolt and nut 6 and four apex angles that are located main body frame 7 are passed through respectively at the both ends of bearing diagonal pole 2.
A die 12 comprising a screw 14, a die dam 16 and a slot 17. Two ends of the die 12 in the length direction are respectively stuck with a symmetrical screw rod with the length of 30mm, two thin slits 17 with the length of 30mm and the depth of 1mm are arranged at intervals of 40mm on two sides of the die in the width direction, and the die baffles 16 are symmetrically distributed at two ends of the upper surface of the die 12. The mold 12 is made of polyurethane material, and the elastic modulus thereof is not changed along with the increase of the use times and is stable at 60 MPa.
The stretching movement assembly comprises a hanging plate 1, a special bearing 3, a bearing fixing rod 5, a steel strand 4, a lever 8, a stretching baffle 13, a stretching bolt 10 and a fixing rod 9, wherein the steel strand 4 comprises a first steel strand 41, a second steel strand 42, a third steel strand 43, a fourth steel strand 44, a fifth steel strand 45 and a sixth steel strand 46.
Two ends of a bearing fixing rod 5 respectively penetrate through an inner ring of a specially-made bearing 3 and are fixedly connected with an inclined support rod 2, first ends of a first steel strand 41, a second steel strand 42 and a third steel strand 43 respectively are fixedly connected with a hanging plate 1, second ends of the first steel strand 41, the second steel strand 42 and the third steel strand 43 respectively penetrate through an outer ring of the specially-made bearing 3 and are fixedly connected with a first end of a lever 8, the lever 8 and a tension baffle plate 13 are respectively positioned on two sides of the upper portion of a main body frame 7, a first end of the tension baffle plate 13 is fixedly connected with an angle steel at one end of the upper portion of the main body frame 7 in a welding mode, first ends of a fourth steel strand 44, a fifth steel strand 45 and a sixth steel strand 46 are respectively connected with a second end of the lever 8, a third end of the lever 8 is fixedly connected with the main body frame 7 through a fixing rod 9, second ends of the fourth steel strand 44, the fifth steel strand 45 and the, the second end of the stay bolt 10 is connected with the screw 14 of the first end of the mold 12, and the screw 14 of the second end of the mold 12 is fixedly connected with the second end of the tension baffle 13.
And a lever 8 including a first lever 81, a second lever 82, and a third lever 83, the first lever 81, the second lever 82, and the third lever 83 each having an unequal length.
The hanging plates 1, the special bearings 3, the bearing fixing rods 5, the levers 8, the dies 12 and the stay wire bolts 10 are equal in number.
The test method for the ultra-early tensile creep of the cement-based material specifically comprises the following steps:
s1, fixing the water-cement ratio, gradually increasing the mixing amount of the mineral admixture in the gelled material, and changing the combination and respective proportion of the mineral admixture under the same mixing amount to design the mixing ratio. The mixing ratio is used for verifying the feasibility of the test method for the ultra-early tensile creep of the cement-based materials with different proportions.
And S2, coating Vaseline lubricant on the track backing plate 11.
And S3, adjusting the distance between the laser measurer 15 and the die baffle 16 to 26mm, and simultaneously connecting the laser distance measurer 15 with a UT7808 dynamic and static strain acquisition analyzer.
S4, carrying out stress test on the empty mold and the mold containing the cement paste or the cement mortar;
s41, loading a load on the empty die to obtain the deformation of the empty die;
s42, loading a load on the mould containing the cement paste to ensure that the deformation of the mould containing the cement paste is the same as that of the empty mould, and obtaining the stress load of the mould containing the cement paste;
s43, loading a load on the mold containing cement mortar to ensure that the deformation of the mold containing cement mortar is the same as that of the empty mold, and obtaining the stress load of the mold containing cement mortar;
s44, obtaining the stress load of the cement paste or the cement mortar in the mold through the external force difference value of the empty mold and the mold containing the cement paste or the cement mortar, and respectively calculating the proportion alpha of the load of the cement paste or the cement mortar in the mold 12 to the total load, thereby obtaining the proportion of the stress of the cement paste or the cement mortar to the external force load.
S5, respectively pouring the clean cement paste and the cement mortar into the mold, the Vicat instrument and the penetrometer;
s51, stirring the cement paste, and pouring the stirred cement paste into a mold and a Vicat instrument;
and S52, stirring cement mortar, and pouring the stirred cement mortar into the mold and the penetrometer.
S6, testing the initial setting time of the cement paste and the cement mortar;
s61, measuring when the cement paste is initially set in the mould 12 and the Vicat instrument, and loading an initial load on the hanging plate 1;
s62, continuously placing increasing loads on the hanging plate 1, repeating the steps in the same way, and stopping measurement when the cement paste is subjected to creep cracking;
s63, recording the initial load m of the cement paste1Total load m2Initial strain ε1Total strain epsilon2Elastic strain of each stage ∈i', creep strain ε at each stageiCement ratio of alpha, etcExperimental values;
s64, measuring after the cement mortar is initially set in the mould 12 and the penetrometer, and loading an initial load on the hanging plate 1;
s65, continuously placing increasing loads on the hanging plate 1, repeating the steps in the same way, and stopping measurement when the cement mortar is subjected to creep cracking;
s66, recording the initial load m of cement mortar1Total load m2Initial strain ε1Total strain epsilon2Elastic strain of each stage ∈i', creep strain ε at each stageiAnd cement content alpha and the like.
S7, finishing the experimental values measured in the step S5 to calculate the stress sigma (tau) borne by the cement paste or the cement mortar at any momenti) And creep coefficient at the time of cracking
Figure GDA0002601335360000102
The creep degree C (t) and drawing a creep curve to obtain a creep calculation model of the cement-based material in the ultra-early stage;
s71, converting the stress change curve into a plurality of sections of extremely fine gradient change curves by improving a step-by-step calculation method, and then carrying out creep calculation on each gradient;
and S72, obtaining the creep coefficient and the creep degree of the cement-based material at any time by using the creep calculation model, and drawing a creep curve changing along with time.
The stress ratio was 0.2. Loading initial load on the a point test piece, generating elastic strain ab on the test piece, and generating creep strain ba after a fixed period of time (the creep time of the test is 1min)1(ii) a Then adding increasing load, wherein the increasing load applied in the test is the loading stress with the stress ratio of 0.02, and the increasing load generates elastic strain a1b1After waiting for the same time, creep strain b is generated1a2(ii) a Then adding the same increasing load to generate elastic strain a2b2Waiting for the same time to generate creep strain b2a3Loading increasing load until cement paste or cement mortar stone cracks, and generating elastic strain anbnIn creep strain phase b of cement-based materialsnan+1Cracking failure, slow allergy at this stage of the process bnc, as shown in fig. 3. The creep coefficient and the creep degree are calculated according to the model of FIG. 3, which only considers the elasticity and the creep action, τiThe time of day is expressed as the desired age, tau, of the cement-based material0The time of day is expressed as the age of onset of the cement-based material.
In step S4, the stress test indicates that when the mold 12 is subjected to an external force and the cement paste or cement mortar inside the mold 12 has not yet cracked, the mold 12 and the cement paste or cement mortar deform synchronously; in the case of simultaneous deformation, the internal force experienced by the mold 12 and the cement paste or cement mortar is considered to be distributed by the ratio of the modulus of elasticity of the cement paste or cement mortar to the modulus of elasticity of the mold 12 and the ratio of the cross-sectional area of the cement paste or cement mortar to the cross-sectional area of the mold 12.
In step S4, the formula of the ratio of the internal force of the cement paste or cement mortar to the external force load is as follows:
Figure GDA0002601335360000101
F(t)＝E(t)×ε(t)×A
F'(t)＝E'×ε(t)×A'
E(t)＝191.4326t
wherein:
alpha (t) -the proportion of the internal cement paste or cement mortar stressed in the external force when the mould is stressed by the external force;
f (t) -the change of the stress of the cement paste or the cement mortar along with the time;
f' (t) -the change in mold force over time;
e (t) -the variation of the modulus of elasticity of the cement paste or cement mortar with time;
e' -modulus of elasticity of the mold;
epsilon (t) -the strain of the cement paste or cement mortar and the mould;
a-the cross-sectional area of the cement paste or cement mortar;
a' -the section area of the die, which is the section area of the U-shaped groove;
t-time after initial setting of cement.
The force ratio of the cement paste as a function of time is plotted according to a formula, as shown in FIG. 4, in which time is calculated from the initial setting of the cement paste.
In step S4, the ratio formula of the cement paste or cement mortar to the external force load is as follows:
Figure GDA0002601335360000111
wherein:
alpha-the proportion of the internal cement paste or cement mortar stressed in the external force when the external force is applied to the mould;
f1-the mould is subjected to a tensile force when it contains cement paste or cement mortar;
f2the mold is subjected to tension forces when it does not contain cement paste or cement mortar.
In step S7, the cement is subjected to stress σ (τ) at any timei) The calculation formula of (a) is as follows:
Figure GDA0002601335360000112
wherein:
σ(τi) -cement tauiStress applied at any moment;
αi—τithe stress ratio of cement in the mould is always kept;
α1the ratio of the stress of the cement in the mould when the test piece is loaded with the initial load;
αcthe ratio of the stress of the cement in the mould when the test piece is subjected to creep cracking;
Ni—τithe total tension on the mold at all times;
N1-the total tension to which the mould is subjected when the mould is loaded with an initial load;
and A is the cross-sectional area of the cement paste or cement mortar.
In step S7, the creep coefficient of the cement-based material at the time of tensile cracking
Figure GDA0002601335360000123
And the creep degree C (t) are calculated as follows:
Figure GDA0002601335360000121
Figure GDA0002601335360000122
wherein:
τ0a starting age for the cement-based material;
τiis the desired age of the cement-based material;
m1is the initial load of the test piece;
mcthe total load loaded for the test piece when the test piece is cracked and damaged;
εe(τ0) Is formed by an initial load m1The induced initial elastic strain;
εe(τi) For cement in moulds at τiTotal elastic strain at time;
εc(τi) Is tauiCreep strain at time;
ε(τi) Is tauiTotal strain at time.
The apparatus and test method for ultra-early tensile creep in cement-based materials according to the present invention are further described with reference to the following examples:
example 1
In order to verify the feasibility of the test method for the ultra-early tensile creep test of cement-based materials with different proportions, four groups of gelled materials with different proportions and with the mineral admixture doping amount of 70% are prepared by adjusting the fineness and the doping amount of the fly ash and the slag, and the influence of the mineral admixture on the creep degree of the set cement with the loading age of 20min is researched. The mixing ratio is shown in Table 1, and the test results are shown in FIG. 1.
TABLE 1 test mix proportions
Figure GDA0002601335360000131
S1, fixing the water-cement ratio, gradually increasing the mixing amount of the mineral admixture in the gelled material, and changing the combination and respective proportion of the mineral admixture under the same mixing amount to design the mixing ratio. The creep degree of the cement paste creep process with the mixing ratio number D will be described by performing the test with the mixing ratio shown in table 1 and by referring to fig. 1.
And S2, coating Vaseline lubricant on the track backing plate 11.
And S3, adjusting the distance between the laser measurer 15 and the die baffle 16 to 26mm, and simultaneously connecting the laser distance measurer 15 with a UT7808 dynamic and static strain acquisition analyzer.
S4, carrying out stress test on the empty mold and the mold containing the cement paste;
s41, loading a load 12N on the empty die to obtain the deformation of the empty die, wherein the deformation is 0.20 mm;
s42, loading a load on the mould containing the cement paste to ensure that the deformation of the mould containing the cement paste is 0.2mm as same as that of the empty mould, and obtaining that the stress load of the mould containing the cement paste is 32N;
s44, obtaining the stress load of the cement paste in the mould through the external force difference value of the empty mould and the mould containing the cement paste, and respectively calculating the proportion of the load of the cement paste in the mould 12 to the total load to be 62.5%, thereby obtaining the proportion of the stress of the cement paste to the external force load.
S5, pouring the cement paste into the mold, the Vicat instrument and the penetrometer;
and S51, stirring the cement paste, and pouring the stirred cement paste into a mold and a Vicat instrument.
S6, testing the initial setting time of the cement paste;
s61, measuring the cement paste 20min after the initial setting of the mould 12 and the Vicat instrument, and loading an initial load m on the hanging plate 11100g, at which an initial elastic strain ab of 1142X 10 was generated-6Generating creep strain ba within 20-21min1Is 857 multiplied by 10-6And obtaining the stress sigma (tau) borne by the cement pastei) The creep degree of the cement paste at 21min is 0.006MPa, and the creep degree of the cement paste at 21min is 0.134(1/MPa) according to a creep degree calculation formula;
s62, continuously placing increasing loads m on the hanging plate 11 ′ 20g, from increasing load m1 ′ Induced elastic strain a1b1Is 214X 10-6Creep strain b1a2Is 143X 10-6(ii) a At this time, the total creep strain at the stage when the creep strain at 21min is 20-22min is 143X 10-6+857×10-6＝1000×10-6(ii) a At this time, the stress ratio of the cement paste is 67.6%, the stress of the cement paste is 0.007MPa, and the creep degree of the cement paste is 0.141(1/MPa) in 22 min. Repeating the steps, and stopping measurement when the cement paste is subjected to creep cracking (27-28 min);
s63, recording the initial load m of the cement paste1100g, total load m2260g, initial strain ε1Is 1142 is multiplied by 10-6Total strain epsilon2Is 5211 × 10-6Elastic strain of each stage ∈i' is 214X 10-6Each stage is strained byiAre respectively 143X 10-6、214×10-6、214×10-6、286×10-6、286×10-6、357×10-6And 214X 10-6The cement paste ratio α is 67%, 68.1%, 69.1%, 70.8%, 71.7%, 72.5%, 73.8%, 73.9%, and other experimental values.
S7, finishing the experimental values measured in the step S5 to calculate the stress sigma (tau) borne by the cement paste at any momenti) And creep coefficient at the time of cracking
Figure GDA0002601335360000141
Degree of creep C (t), and plottingObtaining a creep calculation model of the cement-based material in the ultra-early stage by using a creep curve;
s71, converting the stress change curve into a plurality of sections of extremely fine gradient change curves by improving a step-by-step calculation method, and then carrying out creep calculation on each gradient;
and S72, obtaining the creep coefficient and the creep degree of the cement-based material at any moment by using the creep calculation model, and drawing a creep curve changing along with time.
As can be seen from FIG. 5, the cement-based materials doped with fly ash and slag with different fineness and doping amount have obviously different creep, the cement-stone creep degree curves with different mixing proportions have basically consistent line types, and the stability of test data is good.
Therefore, the tensile creep of the cement paste from initial setting to final setting can be obtained by adopting the cement-based material ultra-early tensile creep test method. Drawing a creep curve according to the test data, analyzing and comparing the creep degrees of cement paste with different mixing ratios, and further researching the ultra-early creep performance of the cement-based materials with different mixing ratios.
Example 2
Creep degree of cement-based materials in different loading ages during creep cracking: a tensile creep test was carried out using a polyurethane mold with a part of cement replaced by fly ash and slag, respectively, at the mixing ratio shown in Table 3, and the influence of fly ash and slag on the tensile creep of set cement was expressed by the creep degree at the time of cracking of the cement-based material. For the cement stone doped with the mineral admixture, when the mixing amount of the fly ash is not changed, the mixing amount of the slag is changed, and the creep degree of the cement-based material during cracking is shown in figures 6 and 7. The time in the figure is calculated by beginning after the initial setting of the cement, and the loading period is respectively 20min, 40min and 60 min.
TABLE 3 test mix proportions
Figure GDA0002601335360000151
S1, fixing the water-cement ratio, gradually increasing the mixing amount of the mineral admixture in the gelled material, and changing the combination and respective proportion of the mineral admixture under the same mixing amount to design the mixing ratio. The creep degree at cracking of the cement paste with the mixing ratio of C1 is described with reference to FIG. 3 by referring to Table 3.
And S2, coating Vaseline lubricant on the track backing plate 11.
And S3, adjusting the distance between the laser measurer 15 and the die baffle 16 to 26mm, and simultaneously connecting the laser distance measurer 15 with a UT7808 dynamic and static strain acquisition analyzer.
S4, carrying out stress test on the empty mold and the mold containing the cement paste or the cement mortar;
s41, loading a load 16N on the empty die to obtain the deformation of the empty die, wherein the deformation is 0.31 mm;
s42, loading a load on the mould containing the cement paste to ensure that the deformation of the mould containing the cement paste is 0.31mm as same as that of the empty mould, and obtaining that the stress load of the mould containing the cement paste is 40N;
s44, obtaining the stress load of the cement paste in the mould through the external force difference value of the empty mould and the mould containing the cement paste, and respectively calculating the proportion of the load of the cement paste in the mould 12 to the total load by 60.0 percent, thereby obtaining the proportion of the stress of the cement paste to the external force load.
S5, respectively pouring the cement paste into the mold, the Vicat instrument and the penetrometer;
s51, stirring the cement paste, and pouring the stirred cement paste into a mold and a Vicat instrument;
s6, testing the initial setting time of the cement paste;
s61, measuring the cement paste 20min after the initial setting of the mould 12 and the Vicat instrument, and loading an initial load m on the hanging plate 11100g, at which an initial elastic strain ab of 1142X 10 was generated-6And obtaining the stress sigma (tau) borne by the set cementi) Is 0.006MPa, and is,
s62, continuously placing increasing loads m on the hanging plate 11' 20g, so reciprocating, stopping the measurement when the cement paste cracks slowly (28-29 min);
s63, recording the initial load m of the cement paste1100g, total load m2260g, initial strain ε1Is 1142 is multiplied by 10-6Total strain epsilon2Is 5496X 10-6Elastic strain of each stage ∈i' is 214X 10-6Creep strain ε at each stageiComprises the following steps: 214 x 10-6、214×10-6、286×10-6、286×10-6、357×10-6、357×10-6、464×10-6And 464 × 10-6The cement paste content alpha is 70.8%, and other experimental values.
S7, finishing the experimental values measured in the step S5 to calculate the stress sigma (tau) borne by the cement paste at any momenti) And creep coefficient at the time of cracking
Figure GDA0002601335360000161
The creep degree C (t) is 0.271(1/MPa), and a creep curve is drawn to obtain an ultra-early creep calculation model of the cement-based material;
s71, converting the stress change curve into a plurality of sections of extremely fine gradient change curves by improving a step-by-step calculation method, and then carrying out creep calculation on each gradient;
and S72, obtaining the creep coefficient and the creep degree of the cement-based material at any time by using the creep calculation model, and drawing a creep curve changing along with time.
For the set cement mixed with mineral admixture, when the slag mixing amount is not changed, the fly ash mixing amount is changed, and the creep degree of the set cement during creep cracking is shown in figure 6.
By analyzing the figure 6, the creep of the set cement is increased along with the increase of the S95 slag content when the content of the ultra-fine fly ash is the same; when the doping amount of the class II fly ash is the same, when the doping amount of S115 slag is increased, the tensile creep of the set cement is increased. Both S115 and S95 slag increase the creep of the set cement at an ultra-early stage, and the increase in creep is greater with greater loadings, as compared to neat cement without mineral admixtures.
As can be seen from FIG. 7, as the amount of slag is the same, the creep of set cement increases as the amount of ultrafine fly ash increases; when the doping amount of the class II fly ash is increased, the tensile creep of the set cement is increased when the doping amount of the class II fly ash is the same as the doping amount of S115 slag. Compared with cement paste without mineral admixture, the addition of fly ash can improve the ultra-early creep of the set cement, and the increase of the creep is larger when the addition amount is larger.
As can be seen from fig. 6 and 7: 1) when the cement is doped, the creep of the doped cement is increased compared with the cement without the mineral admixture, and the creep of the cement is increased along with the increase of the doping amount of the cement and the mineral admixture. 2) As the loading period increases, the creep of the set cement decreases, because the hydration of the cement proceeds, the strength of the set cement gradually increases, and the creep of the set cement decreases. Therefore, the difference of the doping amount and combination of different mineral admixtures on the creep influence of the set cement can be obtained through the test method.
The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims (8)

1. An apparatus for ultra-early tensile creep of cement-based materials, which comprises a tensile movement assembly, a die, a laser measurer and a test piece bearing frame assembly, wherein the tensile movement assembly and the die are respectively positioned on the test piece bearing frame assembly, the tensile movement assembly is connected with the die, the laser measurer is positioned above the die,
the test piece bearing frame assembly comprises a main body frame, a track base plate, a bolt nut and an inclined support rod, wherein the main body frame is formed by welding a plurality of angle steels with the same cross section size and different lengths, the upper part of the main body frame is a cuboid welded by the angle steels, the four corners of the main body frame are respectively provided with the angle steels with equal lengths, the track base plate is positioned at the upper end of the main body frame and is fixedly connected with the angle steels at the two ends of the upper part of the main body frame through the bolt nut, and the two ends of the inclined support rod are respectively fixedly connected with the angle steels at the four vertex angles of the main body frame; the mould comprises screw rods, mould baffles and slits, wherein the screw rods with equal length are symmetrically arranged at two ends of the mould along the length direction, the slits are arranged at two ends of the mould along the width direction, and the mould baffles are symmetrically distributed at two ends of the upper surface of the mould;
the stretching movement assembly comprises a hanging plate, a specially-made bearing, a bearing fixing rod, a steel strand, a lever, a tension baffle plate, a stay wire bolt and a fixing rod, wherein the steel strand comprises a first steel strand, a second steel strand, a third steel strand, a fourth steel strand, a fifth steel strand and a sixth steel strand, two ends of the bearing fixing rod respectively penetrate through an inner ring of the specially-made bearing and fixedly connected with an inclined supporting rod, first ends of the first steel strand, the second steel strand and the third steel strand are respectively fixedly connected with the hanging plate, second ends of the first steel strand, the second steel strand and the third steel strand penetrate through an outer ring of the specially-made bearing and fixedly connected with a first end of the lever respectively, the lever and the tension baffle plate are respectively positioned on two sides of the upper portion of the main body frame, a first end of the tension baffle plate is fixedly connected with an angle steel at one end of the upper portion of the main body frame by welding, the first ends of the fourth steel strand, the fifth steel strand and the sixth steel strand are respectively connected with the second end of the lever, the third end of the lever is fixedly connected with the main body frame through a fixing rod, the second ends of the fourth steel strand, the fifth steel strand and the sixth steel strand are connected with the first end of the stay bolt, the second end of the stay bolt is connected with the screw rod at the first end of the mold, and the screw rod at the second end of the mold is fixedly connected with the second end of the tension baffle.
2. The apparatus of claim 1, wherein the lever comprises a first lever, a second lever, and a third lever, wherein the first lever, the second lever, and the third lever each have unequal lengths.
3. The apparatus for ultra-early tensile creep of cement-based materials of claim 1, wherein the number of said hanging plates, said specialized bearings, said bearing securing rods, said levers, said molds and said stay bolts are equal.
4. The apparatus of claim 1, wherein the mold is made of polyurethane material, and the elastic modulus of the polyurethane material is not changed with the increase of the use times and is stable at 60 MPa.
5. A test method for the ultra-early tensile creep of cement-based materials, according to any of claims 1 to 4, characterized in that it comprises the following steps:
s1, fixing the water-cement ratio, gradually increasing the doping amount of the mineral admixtures in the cementing material, changing the combination and respective proportion of the mineral admixtures under the same doping amount, and designing the mixing ratio;
s2, coating Vaseline lubricant on the track backing plate;
s3, adjusting the distance between the laser measurer and the mould baffle plate to 26mm, and simultaneously connecting the laser distance measurer with a UT7808 dynamic and static strain acquisition analyzer;
s4, carrying out stress test on the empty mold and the mold containing the cement paste or the cement mortar;
s41, loading a load on the empty die to obtain the deformation of the empty die;
s42, loading a load on the mould containing the cement paste to ensure that the deformation of the mould containing the cement paste is the same as that of the empty mould, and obtaining the stress load of the mould containing the cement paste;
s43, loading a load on the mold containing cement mortar to ensure that the deformation of the mold containing cement mortar is the same as that of the empty mold, and obtaining the stress load of the mold containing cement mortar;
s44, obtaining the stress load of the cement paste or the cement mortar in the mold through the external force difference value of the empty mold and the mold containing the cement paste or the cement mortar, and respectively calculating the proportion alpha of the load of the cement paste or the cement mortar in the mold to the total load, thereby obtaining the proportion of the stress of the cement paste or the cement mortar to the external force load;
s5, respectively pouring the clean cement paste and the cement mortar into the mold, the Vicat instrument and the penetrometer;
s51, stirring the cement paste, and pouring the stirred cement paste into a mold and a Vicat instrument;
s52, stirring cement mortar, and pouring the stirred cement mortar into a mold and a penetrometer;
s6, testing the initial setting time of the cement paste and the cement mortar;
s61, measuring when the cement paste is initially set in the mould and the Vicat instrument, and loading an initial load on the hanging plate;
s62, continuously placing increasing loads on the hanging plate, repeating the steps in the same way, and stopping measurement when the cement paste is subjected to creep cracking;
s63, recording the initial load m of the cement paste1Total load m2Initial strain ε1Total strain epsilon2Elastic strain of each stage ∈i', creep strain ε at each stageiCement proportion alpha;
s64, measuring after the cement mortar is initially set in the mold and the penetrometer, and loading an initial load on the hanging plate;
s65, continuously placing increasing loads on the hanging plate, repeating the steps in the same way, and stopping measurement when the cement mortar is subjected to creep cracking;
s66, recording the initial load m of cement mortar1Total load m2Initial strain ε1Total strain epsilon2Elastic strain of each stage ∈i', creep strain ε at each stageiCement proportion alpha;
s7, finishing the experimental values measured in the step S5 to calculate the stress sigma (tau) borne by the cement paste or the cement mortar at any momenti) And creep coefficient at the time of cracking
Figure FDA0002950793210000031
And creep degree C (t), and drawing a creep curve to obtain a creep calculation model of the cement-based material in the ultra-early stage;
s71, converting the stress change curve into a plurality of sections of extremely fine gradient change curves by improving a step-by-step calculation method, and then carrying out creep calculation on each gradient;
and S72, obtaining the creep coefficient and the creep degree of the cement-based material at any time by using the creep calculation model, and drawing a creep curve changing along with time.
6. The method for testing the ultra-early tensile creep of a cement-based material according to claim 5, wherein in step S4, the stress test means that the die is deformed synchronously with the cement paste or cement mortar when the cement paste or cement mortar in the die is not cracked when the die is subjected to an external force; in the case of synchronous deformation, the internal force applied to the mold and the cement paste or the cement mortar is considered to be distributed by the ratio of the elastic modulus of the cement paste or the cement mortar to the elastic modulus of the mold and the ratio of the cross-sectional area of the cement paste or the cement mortar to the cross-sectional area of the mold.
7. A test method for the ultra-early tensile creep of a cement-based material, which utilizes the test method of claim 5, wherein the proportion formula of the internal force of cement paste or cement mortar to the external force load is as follows:
Figure FDA0002950793210000032
F(t)＝E(t)×ε(t)×A
F'(t)＝E'×ε(t)×A'
E(t)＝191.4326t
wherein:
alpha (t) -the proportion of the internal cement paste or cement mortar stressed in the external force when the mould is stressed by the external force;
f (t) -the change of the stress of the cement paste or the cement mortar along with the time;
f' (t) -the change in mold force over time;
e (t) -the variation of the modulus of elasticity of the cement paste or cement mortar with time;
e' -modulus of elasticity of the mold;
epsilon (t) -the strain of the cement paste or cement mortar and the mould;
a-the cross-sectional area of the cement paste or cement mortar;
a' -the section area of the die, which is the section area of the U-shaped groove;
t-time after initial setting of cement;
the proportion formula of the experimental method of the cement paste or the cement mortar with stress accounting for the external force load is as follows:
Figure FDA0002950793210000041
wherein:
alpha-the proportion of the internal cement paste or cement mortar stressed in the external force when the external force is applied to the mould;
f1-the mould is subjected to a tensile force when it contains cement paste or cement mortar;
f2the mold is subjected to tension forces when it does not contain cement paste or cement mortar.
8. A method for testing the ultra-early tensile creep of a cementitious material as in claim 5, wherein the cement is subjected to a stress σ (τ) at any time in step S7i) The calculation formula of (a) is as follows:
Figure FDA0002950793210000042
wherein:
σ(τi) -cement tauiStress applied at any moment;
αi—τithe stress ratio of cement in the mould is always kept;
α1the ratio of the stress of the cement in the mould when the test piece is loaded with the initial load;
αccreep cracking time die for test pieceThe ratio of cement stress is provided;
Ni—τithe total tension on the mold at all times;
N1-the total tension to which the mould is subjected when the mould is loaded with an initial load;
a-the cross-sectional area of the cement paste or cement mortar;
creep coefficient of cement-based material in tensile cracking
Figure FDA0002950793210000051
And the creep degree C (t) are calculated as follows:
Figure FDA0002950793210000052
Figure FDA0002950793210000053
wherein:
τ0a starting age for the cement-based material;
τiis the desired age of the cement-based material;
m1is the initial load of the test piece;
mcthe total load loaded for the test piece when the test piece is cracked and damaged;
εe(τ0) Is formed by an initial load m1The induced initial elastic strain;
εe(τi) For cement in moulds at τiTotal elastic strain at time;
εc(τi) Is tauiCreep strain at time;
ε(τi) Is tauiTotal strain at time.
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