CN103257220A - Concrete early-stage crack resistance test device and test method - Google Patents

Abstract

The invention relates to a concrete early-stage crack resistance test device and a concrete early-stage crack resistance test method. The device comprises a fixed component and two adjustable stress generators arranged in correspondence along a length direction of the fixed component. Two ends of each adjustable stress generator are respectively connected with the fixed component through adjustable rotation shafts. With the concrete early-stage crack resistance test device provided by the invention, crack resistances of different concretes can be rapidly tested within a few hours, and accurate quantitation and evaluation can be carried out, such that a rapid and accurate method is provided for evaluating concrete material crack resistance. The device is especially suitable for material test at a construction site. The method is sensitive and economically affordable. With the device and the method, standard test method and accordance are provided for evaluating concrete material early-stage crack resistance of projects of airport pavement and other fields, and important guidance is provided for actual concrete works.

Description

The early stage anticracking testing device of a kind of concrete and method of testing

Technical field

The present invention relates to technical field of buildings, be specifically related to the early stage anticracking testing device of a kind of concrete and method of testing, can test out different concrete cracking resistances fast and accurately, be applicable to that the concrete material test is carried out in the building site at the scene.

Background technology

Research about the concrete material cracking performance has become one of important content in the concrete research.The present method of testing of concrete cracking deformation performance mainly is divided under the unconfined condition concrete cracking performance test methods under concrete shrinkage method of testing and the constraint condition.The sex change performance of test concrete under constraint condition, more can be near the behaviour in service of concrete in actual engineering, but still there is not the unified method of testing of estimating concrete material cracking performance under constraint condition in the concrete material standard both at home and abroad at present, various countries are all still under test to the method for testing of concrete cracking performance, do not form unified standard.

The method of testing of concrete cracking performance under constraint condition commonly used mainly contains flat band method, ring method and prism method at present, though these methods can solve certain problem, also exists not enough separately:

1, flat restriction shrinkage cracking test method (flat band method)

Test specimen is tabular in the flat restriction shrinkage cracking test method, and the distortion of test specimen is subjected to the constraint of base or two ends steel form or reinforcing rod.As shown in Figure 1, test specimen is the planar sheet of 600mm * 600mm * 63mm, base also is steel matter, concreting is in punching block, and punching block plastic lining film is after concreting, the constraint of the reinforcing rod around being subjected to when shrinking, the concrete deformation restriction that suffers restraints, restraint stress are during greater than the concrete pulling force, and cracking can appear in test specimen.The principal feature of flat band method is the comparison easy operating, can effectively study the plasticity shrinkage performance of concrete and mortar rapidly.Main dull and stereotyped experimental technique has both at home and abroad at present:

(1) Kraai method (U.S.)

The treadmill test device of this kind research cracking of reinforced concrete and method of testing are proposed by the Kraai of Joseph of Arimathea, Saint (San Jose) state university, provide constraint by the L shaped bar-mat reinforcement that is placed on periphery, die trial inner bottom surface shop layer of plastic film is to reduce concrete constraint.After test specimen is built, with sunlamp and electric fan analog operation environment, after 24 hours, measure fracture length and width.Because the die trial dimensional thickness is 19mm, thinner, the concrete shrinkage cracking after only being suitable for studying mortar and sifting out stone, after through improvement, just can be used for testing the crack on concrete performance.

The method (ACI 544.2R-89 Measurement of Properties of Fiber Reinforced Concrete) in the report of U.S. ACI association is recommended as a kind of method of test synthetic fiber concrete cracking performance.

(2) ICBO (International Conference of Building Officials) standard law (International Academy of Architecture)

In the research of anti-plastic shrinkage and dry shrinkage cracking to concrete, the research group of Parviz Soroushian (U.S. Michigan State University) has adopted a kind of flat test unit that steel plate serves as constraint that bends up.This method adopts single groove to induce the crack to occur, make test effect more outstanding, the crack on concrete performance can be estimated more rapidly, if analyze and disposal route in conjunction with some necessary image, the method for the rough quantitative evaluation concrete cracking performance of a cover can be provided.The method also is recommended as the method that detects the concrete cracking performance by the synthetic fiber concrete standard of ICBO (International Conference of Building Officials) (Acceptance Criteria for Concrete with Synthetic Fibers).

This method die trial size 560mm * 365mm * 114mm provides constraint with the corrugated sheet steel that bends up, and concrete is filled in the mould, and upper surface is exposed in the environment that wind speed is 9.5m/s, relative humidity 40%, continues 3 hours.Because the die trial dimensional thickness is 114mm, can be used for studying concrete and mortar plastic shrinkage and the dry cracking that causes that shrinks.The Purdue university work in this respect of the U.S. is carried out a lot.But this kind method is only established one single groove edge of a knife and is induced the crack, only can characterize knife-edge part crack on concrete performance, and because aggregate skewness in concrete, single groove edge of a knife induces the crack of generation to be subjected to the disturbing effect factor more, and is less to the monolithic concrete representativeness.

More than these two kinds of test methods adopt identical cracking evaluation index, i.e. contraction fissure indexes.According to the width in crack, with the crack be divided into greatly (greater than 3mm), in (2-3mm), little (1-2mm), thin (less than 1mm) four types, define its metric index and be respectively 3,2,1,0.5 each metric index multiply by its corresponding fracture length, is the contraction fissure index of this test specimen after the addition.Estimate improvement degree to concrete and mortar splitting resistance with the Crack Control rate.

Crack Control rate: K=(1-m/m0) * 100%;

Wherein: K represents the Crack Control rate; M is the fracture index of the mortar after the modification; M0 is the fracture index of benchmark mortar.

The treadmill test method has characteristics simple to operation, but flat band method can only provide the inhomogeneous drawdown deformation of part to concrete shrinkage, and there is defective aspect the quantification in crack and the post-processed, for example the Kraai method makes and can't accurately carry out quantitative evaluation to concrete cracking because of the irregularities of crack generation, and the ICBO standard law can only provide the inhomogeneous constraint of part.Therefore flat band method can't characterize crack-resistant performance of concrete accurately.

2, annulus restriction shrinkage cracking test method (ring method)

The circle ring test method is proposed in nineteen forty-two by the Roy Carlson of MIT (Massachusetts Institute of Technology (MIT)) the earliest, is used for studying the splitting resistance of cement paste and mortar at that time.Afterwards, Karlwieghnk and McDonald had also adopted this covering device when the concrete splitting resistance of research, but owing to used the coarse aggregate of different-grain diameter, the die trial size has had bigger change.Cement paste, mortar and concrete circle ring test apparatus structure are similar, and just size is different.As shown in Figure 2, device is made up of a steel annulus and Polyvinylchloride outer shroud mould, and two rings are fixed on the wooden floor, and concrete is shaped to annular test-piece in two rings.Striking time can determine that behind the dismounting external mold, therefore test specimen top silicone rubber seal only allows the test specimen outside surface to shrink according to the needs of research.The test specimen maintenance is under the condition of 20 ℃ and relative humidity 50%, and fracture width is measured with custom-designed microscope.Test index is the total fracture width that causes cracking that shrinks of concrete.

1999 U.S. civil engineer association (AASHTO) recommended a standard concrete ring size: overall diameter is 457mm, and interior diameter is 305mm, highly is 152mm, steel loop thickness 12.7mm ± 0.4mm.After the concrete cast, by being attached to the strain development of 4 strainometer monitoring steel loops on the steel loop, whether every 30min records 1 strain, and observe the crack produce, and determines the cracking time of test specimen with this.It is the time of concrete cracking that the strain value of 1 or more strainometers occur descending time of (being about 20～30 microstrains) is arranged.Width and the cracking pattern in crack, record cracking back.Observe 15d again behind the test specimen cracking, the evolution of record strain and the width in crack.Then with 100 power microscopes along ring short transverse observation fracture width, the height of ring is divided into three parts, namely on average get 3 points along the ring short transverse, according to the mean value of the width reading at three the some places width in crack for this reason.Measure length and the width in crack, with area of cracks (or width) the statement crack on concrete performance in crack.

The deficiency of ring method is: a large amount of research practices show, circle ring test is when the splitting resistance of research grout and mortar, because the contraction of grout and mortar ring can distribute more uniformly along chain rate, so test effect is obvious; And in the concrete because the existence of coarse aggregate, make concrete ring surface water evaporates be subjected to certain obstruction, thereby concrete outside surface can not be shunk uniformly along ring, add coarse aggregate to the restriction peptizaiton in crack, make concrete surface form sightless micro-crack easily, discharge a part of differential contraction stress, thereby, make visible crack breadth extreme and concrete splitting resistance evaluation is affected.So there is following shortcoming in the circle ring test method: the test duration is long, susceptibility is poor.When adopting the ring method test, test specimen will just the incipient crack can occur through the long period usually, can not occur sometimes even because of the susceptibility difference.

The domestic scholar of having also adopted these class methods that the crack on concrete performance has been carried out experimental study in recent years.Circle ring test method subject matter is, the test duration is long, and susceptibility is poor.When adopting the ring method test, test specimen will just the incipient crack can occur through the long period usually, can not occur sometimes even because of the susceptibility difference.

3, prism formula restriction shrinkage cracking experimental technique

The prism method also is a kind of test method of the research shrinkage cracking that generally adopts.The sixties in 20th century, Munich, Germany technology university building materials and member detect the Springenschmid of research institute according to the needs of road and hydraulic engineering construction, develop a cover cracking experimental framework and studied crack on concrete trend (device as shown in Figure 3), and formulated the recommended standard of split test frame by RILEM-TC119.

The split test framework is made up of two steel cross-peens that link to each other by two longitudinal reinforcements.Longitudinal reinforcement is made by the very low steel of thermal expansivity, and like this in the concrete sample hardening process, the spacing between two cross-peens is consistent, and beams of concrete neither can expand and also can not shrink.Can study the restraint stress under the complete constraint condition.Concreting is in the punching block of being made up of bed die 7, tapered end mould 1, leading portion end mould 3, rear end end mould 2, master mould 4 and filling side form 5, template can be regulated by template arrangement for adjusting height 6, rear end constraint crossbeam 10 is stiff end, front end constraint crossbeam 8 is the mobile terminal, controls by stepped hydraulic servo-drive system 14.Concrete early stage elastic modulus also can be measured by this class device simultaneously.In test stand, it is long that level is built 1.5m, and cross-sectional area is the test specimen of 150mm * 150mm.The two ends of beam are fixed in the crosshead, and a crosshead is adjustable, and another is connected on thick and heavy vertical rigidity rod iron, and the constraint crossbeam 9 of side is used for the transversal displacement of confined concrete test specimen 12.For measurement length, laterally be connected on the test specimen main shaft rod iron spacing 500mm with two rod iron concretings.In the sample both sides with the distance of the sensor measurement rod iron on the carbon fiber rod.The sensitivity of sensor is 0.0001mm.The concrete deformation that needs only between two rod irons surpasses 0.001mm, and adjustable crosshead just moves around by step motor, and keeping total deformation is 0, has so just reached longitudinal restraint completely.As the result of crosshead control, the constraining force that produces is by adding continuous the noting of load.Longitudinal framing between the cross-peen has heat insulation layer and cooling system, has also placed strainmeter and power sensor 13 on it to measure concrete meridional stress.During test, cast and vibrated concrete mixture prevent water evaporates in the hardening process in the split test framework.When testing, concrete temperature raises under half adiabatic condition, begins the artificial hypothermia after four days, up to the meridional stress drop, shows that concrete is own through cracking.The Bloom of Israel and Bentur[i] improved test unit under study for action, with the measurement of computer control tension, thereby can clearly know the crack on concrete time.

The deficiency of prism method is: this method is generally used for assessing the cracking that causes because of temperature action, single shaft constraint test findings can provide foundation for the match ratio design and construction of xoncrete structures such as road concrete, mass concrete, provides design guidance for improving concrete cracking resistance.But the major defect of its existence is, the scene that is not easy to carry out is detected, and instrumental sensitivity requires highly, and the cost cost is higher.

Summary of the invention

Technical matters to be solved by this invention provides the early stage anticracking testing device of a kind of concrete and method of testing, can to the concrete that comprises airfield pavement early the cracking resistance in the length of time test, to realize estimating fast and accurately different concrete cracking resistances.

The present invention is in order to solve the problems of the technologies described above, the early stage anticracking testing device of a kind of concrete is disclosed, described device comprises fixed component and along corresponding two the adjustable forcers of answering that arrange of the length direction of fixed component, described each adjustable two ends of forcer of answering are connected with fixed component by adjustable rotation axis respectively.

Further, described each adjustable forcer of answering is made up of two length adjustment devices and two angle regulators respectively, regulates the size of angle between described two length adjustment devices by described two angle regulators.

Further, described each angle regulator comprises angular adjustment slide rail, angular adjustment slide plate and slide plate hold-down nut respectively, described angular adjustment slide plate is fixed on the angular adjustment slide rail by the slide plate hold-down nut, and described angular adjustment slide plate is by angular adjustment slide rail free adjustment.

Further, described each length adjustment device is made up of a plurality of length adjustment side plates and high-performance magnet device respectively, is connected by high-performance magnet device between described adjacent two length adjustment side plates.

Further, described fixed component comprises base plate and stiff end, and described stiff end is vertically installed in the both sides of base plate.

Further, described fixed component adopts all steel material to make.

The invention also discloses a kind of method of concrete being carried out early stage cracking resistance test by the early stage anticracking testing device of concrete, described method comprises the steps:

Steps A is by adding additive to form concrete grout to be measured to concrete;

Step B places above-described proving installation with concrete grout to be measured, makes the concrete test plate (panel);

Step C carries out drying to the concrete test plate (panel) and handles under specific temperature and humidity conditions, treat described concrete test plate (panel) drying after, calculate the average crack width in the crack on the described concrete test plate (panel);

Step D draws the degree of crack-resistant performance of concrete according to the priority of crack time of occurrence and the average crack width that calculates.

Further, described steps A is: by adding the additive of different proportionings to form various test concrete grouts in concrete.

Further, described step B comprises following substep:

Step B11 builds described concrete grout to be measured to proving installation;

Step B12 vibrates to the concrete grout in the proving installation, flushes by tamping and with the proving installation top up to concrete grout;

Step B13, the leveling surface, and use plastic sheeting that it is covered.

Further, the described time that concrete grout in the proving installation is vibrated was less than 12 seconds.

Further, the time of described use plastic sheeting covering is 2 hours.

Further, describedly under the specific temperature and humidity conditions to the withering method of concrete test plate (panel) be: be that 30 ± 2 ℃, humidity are under 50 ± 5% the environment concrete test plate (panel) to be applied the Parallel airflow of 2m/s to making its drying in temperature.

Further, the method for the average crack width in the crack on the described concrete test plate (panel) of described calculating comprises the steps:

Step C11 is divided into N equidistant line segment with the crack on the described concrete test plate (panel);

Step C12 measures and records the fracture width of every equidistant line segment and intersection, crack;

Step C13 asks arithmetic mean to it, with its average crack width as crack on the concrete test plate (panel).

Further, described N is any number between 4～20.

Adopt the beneficial effect of the invention described above technical scheme to be: the early stage cracking resistance measuring technology of concrete provided by the invention, can within a few hours, test out different concrete cracking resistances fast, and quantize accurately and evaluation, for the cracking resistance of estimating concrete material provides quick and accurate method, be particluarly suitable for site and carry out testing of materials; And this method is responsive, comparatively economic and practical, for the early stage cracking resistance of the concrete material that improves airfield pavement and other domain engineering provides means of testing and the foundation of standard, has stronger directive significance for actual concrete works.

Description of drawings

Fig. 1 is the flat concrete cracking proving installation structural drawing that uses at present;

Fig. 2 is the annulus cracking proving installation structural drawing that uses at present;

Fig. 3 is the prism formula restriction shrinkage cracking proving installation structural drawing that uses at present;

Fig. 4 is the structural drawing of the early stage anticracking testing device of concrete in the embodiment of the invention;

Fig. 5 is the force analysis figure when the early stage anticracking testing device of concrete test plate (panel) under constraint condition shrinks in the embodiment of the invention;

Fig. 6 is the force analysis figure of A point and A ' point in the embodiment of the invention;

Fig. 7 is the test plate (panel) force analysis figure of an A-A ' side in the embodiment of the invention;

Fig. 8 is the process flow diagram of the early stage anticracking performance testing method of a kind of concrete in the embodiment of the invention;

Fig. 9 is the diagram of the average crack width in the crack on the described concrete test plate (panel) of the calculating of method of testing in the embodiment of the invention;

Figure 10 is the test result analysis table table 4 of three kinds of method of testings in the embodiment of the invention;

Figure 11 is the table 7 in the embodiment of the invention;

Figure 12 is the table 8 in the embodiment of the invention;

Figure 13 is the table 9 in the embodiment of the invention.

In the accompanying drawing, the list of parts of each label representative is as follows:

1, tapered end mould,

2, rear end end mould,

3, leading portion end mould,

4, master mould,

5, fill side form,

6, template arrangement for adjusting height;

7, bed die,

8, front end constraint crossbeam,

9, side constraint crossbeam,

10, rear end constraint crossbeam,

12, concrete sample,

13, power sensor,

14, Hydrauservo System,

100, base plate,

200, stiff end,

300, adjustable rotation axis,

400, length adjustment side plate,

500, high-performance magnet device,

600, angular adjustment slide rail,

700, angular adjustment slide plate,

800, slide plate hold-down nut.

Embodiment

Part deficiency at method of testing flat band method, ring method and the prism method of present concrete cracking performance under constraint condition, intending proposing a kind of method can make test specimen produce cracking accurately and rapidly, and can provide the fracture evaluation index that the concrete material cracking performance is quantized comparison accurately, and this method is responsive, comparatively economic and practical, is convenient in engineering site operation and use.For the early stage cracking resistance of the concrete material that improves airfield pavement and other domain engineering provides means of testing and foundation.Has stronger directive significance for actual concrete works.

Make the concrete test plate (panel) produce cracking fast under constraint condition, key is constraint condition.Concrete contraction has been subjected to the restriction of constraint condition, and when differential contraction stress during greater than concrete self drag, test plate (panel) namely can begin to occur cracking.Flat band method produces constraint by the reinforcing rod around dull and stereotyped; Ring method produces constraint by the round steel ring of test plate (panel) inwall; The prism method is fixed by an end, and an end moves, and keeps the constant generation constraint of length.Contrast above constraint condition, the present invention intends adopting and answers forcer generation stress to concentrate to provide constraint, thereby makes test plate (panel) ftracture fast under this restrained condition.And accuracy and convenience that crack, cracking back quantizes also are very important requirements, are convenient to DATA REASONING and observation more in order to make test plate (panel) produce the single track crack, and many zigzag cracks can make the late time data collection and handle and produce certain difficulty.And temperature and humidity must keep stablizing within the specific limits in the test condition, and the test data of gained just can be accurate, and the material cracking performance is accurately quantized.

Based on this, the present invention has developed the early stage anticracking testing device of concrete, and dumbbell shape concrete cracking fabricmeter, its ultimate principle is to make proving installation itself have the adjustable forcer of answering, measured material is implemented effectively to ftracture to induce, and provide constraint in the end to the concrete test plate (panel), make the concrete test plate (panel) produce cracking.Through contrast confirmation repeatedly, under the identical situation of other test condition, this method can make test plate (panel) ftracture fast.

Below in conjunction with accompanying drawing principle of the present invention and feature are described, institute gives an actual example and only is used for explaining the present invention, is not for limiting scope of the present invention.

The embodiment of the invention provides a kind of concrete early stage anticracking testing device, Fig. 4 is the structural drawing of the early stage anticracking testing device of concrete in the embodiment of the invention, as shown in Figure 4: the early stage anticracking testing device of described concrete comprises fixed component and along corresponding two the adjustable forcers of answering that arrange of the length direction of fixed component, described each adjustable two ends of forcer of answering are connected with fixed component by adjustable rotation axis 300 respectively.

Wherein, described each adjustable forcer of answering is made up of two length adjustment devices and two angle regulators respectively, regulates the size of angle between described two length adjustment devices by described angle regulator.Described each angle regulator comprises angular adjustment slide rail 600, angular adjustment slide plate 700 and slide plate hold-down nut 800 respectively, described angular adjustment slide plate 700 is fixed on the angular adjustment slide rail 600 by slide plate hold-down nut 800, and described angular adjustment slide plate 700 is by angular adjustment slide rail 600 free adjustment; Described each length adjustment device is made up of a plurality of length adjustment side plates 400 and high-performance magnet device 500 respectively, is connected by high-performance magnet device 500 between described adjacent two length adjustment side plates 400; Described fixed component comprises base plate 100 and stiff end 200, and described stiff end 200 is vertically installed in the both sides of base plate 100.Wherein, needs the when number of described length adjustment side plate 400 is used according to reality and selecting, can be 2,3,4 ..., or 10 are not waited; The magnet arrangement that described high-performance magnet device 500 refers to have powerful magnetic.

In embodiments of the present invention, described fixed component adopts all steel material to make.Both sides stiff end and adjustable answering between the forcer, connected by the adjustable rotation axis that can freely rotate.Stiff end mainly provides the constraint of axial direction, and middle adjustable angle of answering forcer is free adjustment within the specific limits, selects optimal angle thus, and angle too conference makes the concrete sample size narrow, loses the material representativeness; Angle too little can influence the susceptibility of test specimen, so this angle need repeatedly regulate test under the prerequisite that satisfies the requirement of concrete maximum particle diameter, until be adjusted to susceptibility the strongest answer the forcer angle.When carrying out angular adjustment, the length of proving installation both sides side plate is changed, therefore the invention provides length adjustment device, make proving installation both sides side plate within the specific limits according to demand transform length and rely on high-performance magnet device to make the die trial side plate airtight freely, when casting concrete, well having solved infiltration contingent situation such as leak.During adjusting angle, the slide plate by the adjusting angle regulating device can make length adjustment side plate independent assortment angle in the certain angle scope.After answering the angle and side plate length adjustment of forcer, fixed component makes angle and length keep invariable in the whole process of test, determine good best angle answer forcer after, each several part is fixed, can carry out the cracking performance testing experiment.

After concrete is poured into proving installation, under the inducing who answers forcer, make test plate (panel) all produce stress in the both sides of centre and concentrate, the two ends of proving installation all can provide the constraint of axial direction.During concrete shrinkage, be subjected to from the constraint of answering forcer and proving installation end, when differential contraction stress during greater than the concrete drag, test plate (panel) can very fast appearance cracking.Proving installation of the present invention is applicable to the cracking performance evaluation that concrete is early stage, and susceptibility is strong, and is accurately quick, also convenient use at the construction field (site).

Concrete anticracking testing device should provide enough constraints to make concrete material produce cracking under this restrained condition, the size of the restriction ability that can provide directly has been provided the rigidity of proving installation, so the rigidity of cracking resistance testing tool device is very important.The rigidity of this device in principle should be bigger than the test plate (panel) rigidity in 28 length of times of concrete.The rigidity of this proving installation mainly contains stiff end rigidity and angle adjustable section rigidity is formed, and wherein the elastic modulus of steel is E=206 * 10 ³N/mm ², the bending stiffness of stiff end is:

$K_1=\frac{48\mathrm{EI}}{l_1^3}=\frac{48E\×\frac{{\mathrm{bh}}^3}{12}}{l_1^3}=\frac{48\×206\×{10}^3\×\frac{10\×{100}^3}{12}}{{230}^3}=6.78\×{10}^{5}N/\mathrm{mm};$

The bending stiffness coefficient of angle adjustable section is:

${\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="120222160928.png,87561DEST\_PATH\_HDA0000156249740000061.png"\; state="\{\{state\}\}">K</figure-callout>}}_2=\frac{48\mathrm{<figure-callout\; id="2"\; label="EI\; l"\; filenames="120222160928.png,87561DEST\_PATH\_HDA0000156249740000061.png"\; state="\{\{state\}\}">EI</figure-callout>}}{l_{}^{}}=\frac{48E\&times;\frac{{\mathrm{bh}}^3}{12}}{{\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="120222160928.png,87561DEST\_PATH\_HDA0000156249740000061.png"\; state="\{\{state\}\}">l</figure-callout>}}_2^3}=\frac{48\&times;206\&times;{10}^3\&times;\frac{10\&times;{100}^3}{12}}{{170}^3}=9.1\&times;{10}^{5}N/\mathrm{mm};$

The elastic stiffness of angle adjustable section is:

${\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="120222160928.png"\; state="\{\{state\}\}">K</figure-callout>}}_3=\frac{\mathrm{<figure-callout\; id="3"\; label="EA\; l"\; filenames="120222160928.png"\; state="\{\{state\}\}">EA</figure-callout>}}{l_{}}=\frac{E\&times;\mathrm{bh}}{{\mathrm{<figure-callout\; id="3"\; label="l"\; filenames="120222160928.png"\; state="\{\{state\}\}">l</figure-callout>}}_3}=\frac{206\&times;{10}^3\&times;10\&times;100}{450}=4.58\&times;{10}^{5}N/\mathrm{mm};$

So stiffness K by above each several part ₁, K ₂, K ₃Trying to achieve device rigidity is:

$K=\frac{1}{\frac{1}{4K_1}+\frac{1}{4{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="120222160928.png,87561DEST\_PATH\_HDA0000156249740000061.png"\; state="\{\{state\}\}">K</figure-callout>}}_2}+\frac{1}{4{\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="120222160928.png"\; state="\{\{state\}\}">K</figure-callout>}}_3}}=\frac{4}{\frac{1}{6.78\&times;{10}^5}+\frac{1}{9.1\&times;{10}^5}+\frac{1}{4.58\&times;{10}^5}}=8.39\&times;{10}^{5}N/\mathrm{mm};$

Calculate concrete rigidity, choosing the cross section is centre 200mm * 60mm square type cross section, and getting C40 concrete 28d elastic modulus in the length of time is 4 * 10 ⁴N/mm ², length is 1400mm, then this moment, concrete rigidity was:

$K_c=\frac{E_c{A}_c}{l_c}=\frac{E_c\&times;\mathrm{bh}}{l_c}=\frac{4\&times;{10}^4\&times;200\&times;60}{1400}=3.4\&times;{10}^{5}N/\mathrm{mm};$

So this concrete cracking proving installation stiffness K＞K _c, the rigidity of device satisfies the requirement of test concrete material cracking performance.

For proving installation of the present invention better is described, below by specific embodiment principle of the present invention is described, Fig. 5 is the force analysis figure when the early stage anticracking testing device of concrete test plate (panel) under constraint condition shrinks in the embodiment of the invention, as shown in Figure 5, force analysis when being shunk by test plate (panel) under the constraint condition as can be known, behind the casting concrete, concrete produces contraction under dry environment, under the acting force that concrete shrinkage produces, A point place, respectively the concrete test plate (panel) is produced reacting force F1 and F2 on the adjustable both sides AB that answers forcer and AC two surfaces, direction is all perpendicular to each surface.Opposite side A ' some place produces reacting force F1 ' and F2 ' to the concrete test plate (panel) respectively on A ' B ' and A ' C ' two surfaces.Under the concrete shrinkage acting force, test plate (panel) is subjected to the uniform reacting force q1 of constraint of B end simultaneously, in like manner all produces the uniform reacting force q1 ' of constraint, q2, q2 ' at other each ends.

Fig. 6 is the force analysis figure of A point and A ' point in the embodiment of the invention, as shown in Figure 6, with adjustable stressed the decomposition according to the mechanics triangle of answering A point and the A ' point of forcer both sides, analyze as can be known, under the acting force that concrete shrinkage produces, answer on forcer both sides AB and AC two surfaces and respectively concrete is produced reacting force F and F ', reacting force F and F ' are decomposed according to the mechanics triangle, wherein F _1H, F ' _1H, F _2H, F ' _2HBe horizontal direction; F _1V, F ' _1V, F _2V, F ' _2VBe vertical direction.Wherein:

F ₁＝F _1H+F _1V；

F ₁＝F′ _1H+F′ _1V；

F ₂＝F _2H+F _2V；

F ₂＝F′ _2H+F′ _2V；

Concrete to A point place is done force analysis, and when concrete material shrank, adjustable concrete of answering A point place, forcer top under the acting force that concrete shrinkage produces, was subjected to the opposite horizontal force F of left and right sides both direction _1HAnd F _2HEffect, also be subjected to the F of vertical direction _1VAnd F _2VEffect.Answer forcer top A point to exist stress to concentrate, belong to dangerous point.

Fig. 7 is the test plate (panel) force analysis figure of an A-A ' side in the embodiment of the invention, and as shown in Figure 7, the use isolation method is carried out force analysis to the test plate (panel) of an A-A ' side, and the test plate (panel) of an A-A ' side has been subjected to die trial central authorities and has answered the F of forcer _1HAnd F ' _1HAnd the effect of the uniform constraining force in end, the test specimen of an A-A ' side is suffered make a concerted effort be:

F _Close=F _1H+ F ' _1H+ q ₁* d+q ' ₁* d;

Adjustable A point place, the forcer top concrete of answering is at the opposite horizontal force F of direction _1HAnd F _2HEffect under the easiest cracking that at first produces.And the test specimen of an A-A ' side is at F _CloseEffect under, locate to occur cracking at A-A '.So answer forcer induce and end restraint under, the crack of test specimen is the single track crack, trend runs through A-A ', makes gap observation and DATA REASONING more convenient quick.

Another embodiment of the present invention provides a kind of concrete early stage anticracking performance testing method, Fig. 8 is the process flow diagram of the early stage anticracking performance testing method of a kind of concrete in the embodiment of the invention, and as shown in Figure 8: the early stage anticracking performance testing method of described concrete comprises the steps:

Step 801 is by adding additive to form concrete grout to be measured to concrete; In embodiments of the present invention, the additive by adding different proportionings in concrete is tested every kind of concrete grout respectively to form various test concrete grouts.

Step 802 places the above-described proving installation of the present invention with concrete grout to be measured, makes the concrete test plate (panel);

In this embodiment, at first described concrete grout to be measured is built to proving installation; Then the concrete grout in the proving installation is vibrated, flush by tamping and with the proving installation top up to concrete grout, for preventing material segregation, time of vibration is generally in 12s; The back of vibrating is floating, with trowel leveling surface, aggregate is not exposed, and the surface is plain, covers with plastic sheeting immediately after floating, takes off film after 2 hours.

Step 803 is carried out drying to the concrete test plate (panel) and is handled under specific temperature and humidity conditions, treat described concrete test plate (panel) drying after, calculate the average crack width in the crack on the described concrete test plate (panel);

In embodiments of the present invention, it is 30 ± 2 ℃ by test plate (panel) being placed temperature, relative humidity remains in 50 ± 5% the environment concrete test plate (panel) is applied the Parallel airflow of 2m/s to making its drying, be 2m/s such as using fan to regulate its wind speed, directly blow the test specimen surface with electric fan, wind direction is parallel to the test specimen surface and carries out the drying processing.

(pick up counting from casting concrete) after 24 hours and begin to observe crack quantity, width and length.In the test data sheet, fracture length is as the criterion with the naked eyes visible crack, measures its length with steel ruler, being similar to and getting two ends, crack air line distance is fracture length, when obviously bending appears in the crack, represent fracture length with broken line length sum, fracture width is measured with reading microscope (scale division value is 0.01mm).Wherein, the method for the average crack width in the crack on the described concrete test plate (panel) of described calculating is: the crack on the described concrete test plate (panel) is divided into N equidistant line segment; Measure and record the fracture width of every equidistant line segment and intersection, crack; It is asked arithmetic mean, with its average crack width as crack on the concrete test plate (panel).In this embodiment, described N can be between 4～20 value arbitrarily.For example, moving towards with 5 equidistant line segments the crack to be divided into 6 five equilibriums along A-A ' among Fig. 9, recording the fracture width of 5 equidistant line segments and intersection, crack, and ask arithmetic mean, as the average crack width of measuring 24 hours:

$W=\frac{1}{N}\underset{i}{\overset{N}{\mathrm{\&Sigma;}}}\mathrm{Wi};$

Wherein, Wi is the width in crack, i root equidistant line segment place, and unit is mm; N is equidistant line segment bar number (adopting N=5 in the present embodiment).

Except the average crack width after 24 hours as evaluation index, also can be in 24 hours constant duration measure the width in crack, calculate each crack mean breadth constantly, be used for the development trend of research distress in concrete, wherein fracture width unit is in mm.About equidistant line segment bar number, under the condition that does not adopt graphical analysis, be that equidistant bar number is The more the better in principle, this test once selected equidistant bar to count N=20 and N=10 carries out overtesting, and test findings and N=5 difference are very little, are 5 so select equidistant line segment bar number for use.

This method selects for use reading microscope as survey instrument in the quantitative test of distress in concrete, and measurand is the single track crack, so test error only derives from the measuring error of reading microscope.What this test was selected for use is the portable micrometer microscopes of Shanghai optical instrument six factory's JC4-10 types, and the magnification of eyepiece is 10 times, and objective lens magnification is 2 times, and system's magnification is 20 times, and measuring accuracy is 0.01mm.

Step 804 draws the degree of crack-resistant performance of concrete according to the priority of crack time of occurrence and the average crack width that calculates.

The initial time of occurrence of distress in concrete is another important indicator that characterizes the concrete cracking performance.Initial cracking time is more late, illustrates that crack-resistant performance of concrete is more good; Initial cracking time more early illustrates that crack-resistant performance of concrete is more poor.Therefore after concreting, from timing, carefully observe the appearance in concrete Shou Dao crack, this time as the initial time of occurrence in crack, wherein chronomere is in h:mm.

In embodiments of the present invention, in order to check the repeatability of concrete cracking performance testing device, five groups of concrete mixs have been selected for use, every assembly ratio, with 3 identical test plate (panel)s of a collection of making, respectively the fracture width value of each test plate (panel) 24h to be measured and added up, test findings is as shown in table 1 below:

Table 1:

By last table 1 as seen, in five groups of concrete proportionings, all more stable in measured value and the mean value standard deviation of the same batch of test plate (panel) of 24h, MSD maximum standard deviation is in 7%.Therefore use this bright single track inducing concrete cracking performance proving installation can obtain measurement data accurately, and test is repeatable fine.

Below by a specific embodiment and in conjunction with proving installation provided by the invention and method of testing principle of the present invention is further specified, in the present embodiment, prepare the concrete of three groups of grade strength C30, match ratio is as shown in table 2 below, because of the fiber concrete cracking resistance better, the preparation fiber concrete is intended to contrast three kinds of cracking performance method of testings susceptibility of (in this embodiment, method of testing of the present invention being called dumbbell method, board-like leash law and annulus constrained procedure).Fiber adopts cellulose fibre, and volume is respectively 0.9kg/m ³, 1.2kg/m ³, 1.5kg/m ³Test is all carried out in thermostatic constant wet chamber, and temperature remains on 30 ± 2 ℃, and relative humidity remains on 50 ± 5%.Identical at material, under the identical condition of experimental enviroment, the concrete of every assembly ratio all adopts three kinds of methods to test, and three kinds of concrete anticracking method of testings are compared experimental study.

Table 2:

The test findings of three kinds of method of testings shown in the table 4 of following table 3 and accompanying drawing 10, test results and analysis:

For the concrete of three kinds of different fibers contents, dumbbell method, board-like leash law and annulus constrained procedure all show identical cracking trend, and namely volume is 1.5kg/m ³The concrete crack width minimum, and the incipient crack time is the latest; Volume is 0.9kg/m ³Concrete cracking the earliest, the fracture width maximum.This also is consistent with theoretical analysis and practice situation.So using the concrete cracking performance of three kinds of this concrete cracking performance test methods test gained is accurately.

Table 3:

From test findings, volume is 1.5kg/m ³Concrete, the dumbbell shape method ftractures at first, and is better than board-like reinforcing rod leash law, the cracking time of annulus constrained procedure is later than the first two kind method far away; From maximum crack width, the dumbbell shape method is 1.07mm, much larger than 0.64mm and the 0.52mm of other two kinds of methods.Volume is 0.9kg/m ³, 1.2kg/m ³Concrete also show same trend.Maximum crack width is more big, more more significantly reflects the crack on concrete performance, and is convenient to measure, and reduces measuring error.For identical test material, in three kinds of methods, the dumbbell shape method can be the fastest the concrete that makes produce cracking effect and fracture width maximum, therefore from the susceptibility aspect of concrete cracking method of testing, the dumbbell shape method of testing is better than board-like reinforcing rod leash law and annulus constrained procedure.

Test period the aspect, dumbbell shape method and board-like method from begin the test need 24h to end of test (EOT); Ring method susceptibility is poor slightly, need concrete ring to produce cracking at least and could finish test, so test period is longer relatively, and the longest 6d of needs just can finish test in this test.Therefore dumbbell shape method and board-likely be better than ring method in test period, the comprehensive contrast of three kinds of method of testings is as shown in table 5 below:

Table 5:

?	The dumbbell shape leash law	Board-like reinforcing rod leash law	The annulus leash law
				Susceptibility	By force	Stronger	Generally
Test period	Short	Short	Long

[0141]?

Measure operability	Easy	Generally	Complicated
				The engineering application	By force	Stronger	Generally

By above-mentioned experiment as can be known, in the engineering application facet, dumbbell shape method and board-like method are stronger because of susceptibility, can reflect concrete cracking resistance in the short period, and it is comparatively convenient to make horizontal contrast test at actual engineering site.Ring method test period field, engineering site is used less.

In sum, the dumbbell shape method aspect susceptibility, test period the aspect, measure operating aspect, the engineering application facet all is that performance is reasonable, so this test selects the dumbbell shape method as the method for testing of concrete cracking performance in testing.

Concrete Application Example one: the early stage cracking of airfield pavement accounts for more than 50% of airfield pavement cracking, and therefore the research to the concrete early stage cracking resistance of airfield pavement is very necessary and urgent.At present domestic still do not have the measuring technology that can characterize the early stage cracking resistance of airfield pavement concrete, so project team innovates having proposed the early stage cracking resistance measuring technology of dumbbell shape airfield pavement concrete on the basis of summing up existing method of testing.Can a few hours with interior quick comparison with test out different concrete early stage cracking resistances, for the early stage cracking resistance that improves airfield pavement provides means of testing and foundation.Has stronger directive significance for actual concrete works.

Therefore this part research just is being based on the early stage cracking resistance measuring technology of dumbbell shape airfield pavement concrete of domestic initiation, test focuses on the concrete early stage cracking size that contrast is mixed the concrete of PCA-L1 polycarboxylate water-reducer and mixed the FDN water reducer, contrast two kinds of different concrete material cracking resistances, the water reducer kind difference of these two kinds of concrete materials because mixing, and different.Can contrast different types of water reducer to the influence of crack-resistant performance of concrete.Two kinds of water reducers are a kind of to be the PCA polycarboxylate water-reducer; A kind of is the FDN naphthalene water reducer.This example uses two kinds of water reducers of the early stage cracking resistance tester research of dumbbell shape to the influence of the early stage cracking performance of airfield pavement concrete.

Four kinds of match ratios have been selected in this test, and are as shown in table 6 below, and totally 0.53,0.42,0.38 three kind of water cement ratio, more blank concrete, mixing the PCA-L1 poly carboxylic acid is the concrete various aspects of performance of FDN with mixing naphthalene, and wherein naphthalene system and PCA-L1 polycarboxylic acid concrete all adopt 0.42 water cement ratio; Because being lower than 0.4 water cement ratio, naphthalene series concrete is difficult to satisfy the requirement that workability is tieed up vigorous denseness 20s, so adopt the PCA-L1 poly carboxylic acid to prepare the airfield pavement concrete of 0.38 water cement ratio.Four kinds of match ratios, all satisfy the code requirement of " civil airport movement area cement concrete road surface surface construction technical manual " MH 5006-2002, control according to the workability index, reach 20s-25s be as the criterion (the best effort requirement of airfield pavement dry concrete) to tie up vigorous denseness.

Water reducer volume aspect, naphthalene are that the volume of FDN is 2% of cement consumption; 0.42 the PCA-L1 poly carboxylic acid volume of water cement ratio is for being 1.0% of cement consumption; 0.38 the PCA-L1 poly carboxylic acid volume of water cement ratio is for being 1.2% of cement consumption.

Table 6:

The C40 concrete average crack width that mixes two kinds of different water reducers change curve is in time seen the table 7 of accompanying drawing 11, and as shown in the figure, in the 2h of test beginning, the shrinkage factor of N2 (FDN) increases very fast, and N3 increases the slowest, and each group all begins quick growth subsequently; Until the 24h end of test (EOT), each suite line tends to be steady after the 10h, does not have significantly to change, and illustrates that this stage respectively organizes the test specimen fracture width and remain unchanged substantially.N2 (FDN) suite line is apparently higher than N3 suite line, and the N2 curve is in the highest.Two groups of final average crack width values of 24h are N2＞N3 successively, shown in the table 9 of the table 8 of accompanying drawing 12 and accompanying drawing 13.

N3 (PCA), two groups of concrete average crack widths of N2 (FDN) are respectively 1.71mm, 2.84mm during final 24h end of test (EOT).N3 (PCA) test specimen fracture width minimum, N2 (FDN) maximum.From the initial cracking time of two groups of test specimens, N3, the N2 group is respectively 2:00, and 1:10 incipient crack time N2 occurs the earliest, and N3 organizes the latest, N3＜N2.From each group average crack width and initial cracking time, with similar to concrete early-age shrinkage and later stage effect of contraction, other material is all identical with proportioning, and under workability identical (the tieing up vigorous denseness) situation, the concrete cracking resistance of mixing PCA will be significantly better than the concrete of mixing FDN.These two kinds of dissimilar water reducers, the concrete cracking resistance of mixing FDN is the poorest.Therefore mix the PCA-L1 polycarboxylate water-reducer and mix FDN water reducer concrete, the early stage cracking resistance of airfield pavement concrete of mixing the PCA-L1 polycarboxylate water-reducer will obviously be better than the FDN naphthalene water reducer.

Therefore adopt the early stage cracking resistance measuring technology of dumbbell shape can contrast the cracking resistance of different concrete materials fast and accurately, for mix Design and the concrete material of selecting the cracking resistance excellence at the concrete works scene fast provide method of testing and estimate foundation.

The above only is preferred embodiment of the present invention, and is in order to limit the present invention, within the spirit and principles in the present invention not all, any modification of doing, is equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (14)

1. early stage anticracking testing device of concrete, it is characterized in that, described device comprises fixed component and along corresponding two the adjustable forcers of answering that arrange of the length direction of fixed component, described each adjustable two ends of forcer of answering are connected with fixed component by adjustable rotation axis respectively.

2. device according to claim 1, it is characterized in that, described each adjustable forcer of answering is made up of two length adjustment devices and two angle regulators respectively, regulates the size of angle between described two length adjustment devices by described two angle regulators.

3. device according to claim 2, it is characterized in that, described each angle regulator comprises angular adjustment slide rail, angular adjustment slide plate and slide plate hold-down nut respectively, described angular adjustment slide plate is fixed on the angular adjustment slide rail by the slide plate hold-down nut, and described angular adjustment slide plate is by angular adjustment slide rail free adjustment.

4. device according to claim 2 is characterized in that, described each length adjustment device is made up of a plurality of length adjustment side plates and high-performance magnet device respectively, is connected by high-performance magnet device between described adjacent two length adjustment side plates.

5. device according to claim 1 is characterized in that, described fixed component comprises base plate and stiff end, and described stiff end is vertically installed in the both sides of base plate.

6. the device of stating according to claim 1 or 5 is characterized in that, described fixed component adopts all steel material to make.

One kind by the early stage anticracking testing device of concrete to the method that concrete carries out the test of early stage cracking resistance, it is characterized in that described method comprises the steps:

Steps A is by adding additive to form concrete grout to be measured to concrete;

Step B places concrete grout to be measured as each described proving installation of claim 1 to 6, makes the concrete test plate (panel);

Step C carries out drying to the concrete test plate (panel) and handles under specific temperature and humidity conditions, treat described concrete test plate (panel) drying after, calculate the average crack width in the crack on the described concrete test plate (panel);

Step D draws the degree of crack-resistant performance of concrete according to the priority of crack time of occurrence and the average crack width that calculates.

8. method according to claim 7 is characterized in that, described steps A is: by adding the additive of different proportionings to form various test concrete grouts in concrete.

9. method according to claim 7 is characterized in that, described step B comprises following substep:

Step B11 builds described concrete grout to be measured to proving installation;

Step B12 vibrates to the concrete grout in the proving installation, flushes by tamping and with the proving installation top up to concrete grout;

Step B13, the leveling surface, and use plastic sheeting that it is covered.

10. method according to claim 9 is characterized in that, the described time that concrete grout in the proving installation is vibrated was less than 12 seconds.

11. method according to claim 9 is characterized in that, the time that described use plastic sheeting covers is 2 hours.

12. method according to claim 7, it is characterized in that, describedly under the specific temperature and humidity conditions to the withering method of concrete test plate (panel) be: be that 30 ± 2 ℃, humidity are under 50 ± 5% the environment concrete test plate (panel) to be applied the Parallel airflow of 2m/s to making its drying in temperature.

13. method according to claim 7 is characterized in that, the method for the average crack width in the crack on the described concrete test plate (panel) of described calculating comprises the steps:

Step C11 is divided into N equidistant line segment with the crack on the described concrete test plate (panel);

Step C12 measures and records the fracture width of every equidistant line segment and intersection, crack;

Step C13 asks arithmetic mean to it, with its average crack width as crack on the concrete test plate (panel).

14. method according to claim 13 is characterized in that, described N is any number between 4～20.

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