CN1558201A

CN1558201A - Concrete early shrinkage stress tester

Info

Publication number: CN1558201A
Application number: CNA2004100135359A
Authority: CN
Inventors: 巴恒静; 高小建
Original assignee: Harbin Institute of Technology
Current assignee: Harbin Institute of Technology
Priority date: 2004-01-19
Filing date: 2004-01-19
Publication date: 2004-12-29
Anticipated expiration: 2024-01-19
Also published as: CN1247983C

Abstract

The concrete early contraction stress measuring instrument belongs to the field of cement and concrete early performance measuring instrument. The instrument includes chuck with movable end and fixed end for holding concrete sample, tension sensor with one end connected to the movable end of the chuck, rolling ball screw with one end connected to the other end of the tension sensor via an elastic assembly, and motor connected via shaft coupler with the other end of the rolling ball screw. The present invention has smooth operation, high measurement precision, capacity of providing great pulling stress and simple operation, and can measure the mechanical parameters of concrete related to the early cracking accurately and quantitatively.

Description

Concrete early-age shrinkage measuring stress instrument

Technical field: the invention belongs to the early stage performance testing apparatus of cement concrete.

Background technology: along with science and technology development, high performance concrete replaces normal concrete to become future thrust gradually.High performance concrete have water-cement ratio low, mix characteristics such as a large amount of high-activity mineral blending materials, thereby it just begins to produce very big self-constriction after initial set, the contraction that moisture loss is caused is more responsive simultaneously, its elastic modulus height, the reason such as little of creeping more are easy to generate the early-age shrinkage cracking in addition.The generation of early-age shrinkage cracking can cause the very big reduction of concrete structure durability energy, receives the concern of engineering and scientific circles.Because the every performance of early concrete is in the quick change procedure, estimates or predict early stage cracking based on the test of traditional shrinkage value and sclerosis back mechanical property, and manage by the form of optimizing structure no longer suitable with the method for avoiding early stage cracking.The mensuration of concrete early-age shrinkage, differential contraction stress, mechanics parameter such as creep can be for deeply understanding early stage cracking mechanism, providing reliable theoretical foundation and research technique for Optimal Structure Designing under constraint condition.External part research institution Preliminary Exploitation goes out similar testing equipment, the domestic any report that does not also have about this kind equipment.The basic functional principle of this equipment is: an end of prism-shaped test specimen maintains static by anchor clamps, and the other end is removable free end, and this free end links to each other with force cell, and its displacement is monitored by a displacement transducer; Can drive free end and produce a displacement when concrete shrinkage, when displacement reaches the control threshold values of setting (as 5 μ m), rotating screw bolt is withdrawn into the original position by a series of precision gear transmissions with free end.In force cell, will measure tension like this, be differential contraction stress.It not only can quantitatively measure stress, the strain that concrete produces because of contraction, can also converse the development of the early stage elastic modulus of concrete, and the value of creeping in early days, is a kind of test method that is worthy to be popularized.The part but this kind equipment still comes with some shortcomings at present: 1), adopt common bolt, screw drive, composite gear deceleration system, be difficult to realize so meticulous micrometric displacement and very big tension is provided from present domestic machining level.When 2) testing test specimen is retracted in the process in original position,, destroy too early because the contraction non-uniform phenomenon that the test specimen section part may exist causes the stressed off-centre of test specimen; 3) test specimen and active chuck are subjected to the base frictional resistance in the process that moves around, and produce certain error; 4) under so big pulling force (20000N) effect, stiff end adopts any steel fixed form all can produce distortion, and the differential contraction stress value that causes measuring is far below actual value.

Summary of the invention: the precision that exists at available coagulation soil differential contraction stress instrument is not high, the easy stressed off-centre of test specimen and destroying too early, test specimen frictional resistance in moving process is big, differential contraction stress value that measures and the big drawback of actual value error, the invention provides a kind of concrete early-age shrinkage measuring stress instrument that can address the above problem, it comprises by the concrete sample 3 of movable terminal chuck 1 with 2 clampings of stiff end chuck, movable terminal chuck 1 links to each other with an end of pulling force sensor 4, the other end of described pulling force sensor 4 is connected with an end of ball-screw 6 by elastic parts 5, and the other end of ball-screw 6 is connected with motor 8 by shaft joint 7.The present invention adopts a kind of precision ball screw to replace original screw drive mode, with the coaxial connection of stepper motor the test specimen movable terminal is stretched, thereby the stability and the transmission efficiency of system mechanics operation have been improved, guaranteed the accuracy of test specimen stretching travel, greatly reduced requirement simultaneously stepper motor power.Utilize the compressibility of combined elastic element strong, elasticity is with the characteristics of the size variation of decrement, the movable terminal that the elastic force that utilizes compresses elastomeric to produce drives test specimen is returned to the original position, can realize like this not having under the condition of reducer casing variable-speed processing, the original required stretching displacement of (several micron) is very in a small amount amplified more than tens times by elastic body, relaxed the each required running path increment of stepper motor.Make motor and the ball-screw can synchronous operation, eliminated the margin of error that to introduce in the general mechanical reduction gear transmission process, make the automatic control section and the motor accuracy requirement of system needn't be too high, thereby improved operability, the transmission accuracy of this instrument and the possibility of generally promoting.Because the elastic modulus of concrete in the setting and harden process constantly increases, the every stretching once pulling force of required increase is increasing, thereby the flexible member combination of having adopted three different elastic modulus elastic body combinations to form, it produces the required pressure of unit deformation along with the total compression amount constantly increases.In order to guarantee that the differential contraction stress instrument has enough range abilities and instrument traveling comfort, four flexible member groups that are symmetrically distributed with respect to the lead screw transmission central shaft have been adopted simultaneously.Test specimen movable terminal chuck is installed in that a kind of precision is very high, bearing capacity is strong, move around on the guide rail of specific alloy made, has alleviated the frictional resistance of instrument base to the mobile terminal greatly, has avoided test specimen deflection to occur at drawing process.Product of the present invention operates steadily, the measuring accuracy height, and very big tension can be provided, and is simple to operate, and it can be accurate, quantitative tests out concrete early-age shrinkage cracking forces associated mathematic(al) parameter.

Description of drawings: Fig. 1 is an one-piece construction synoptic diagram of the present invention, and Fig. 2 is the A-A cut-open view of Fig. 1, and Fig. 3 is the structural representation of combined elastic body 5-1, and Fig. 4 is the syndeton synoptic diagram of test specimen movable terminal and guide rail.

Embodiment one: with reference to Fig. 1, present embodiment comprises by the concrete sample 3 of movable terminal chuck 1 with 2 clampings of stiff end chuck, movable terminal chuck 1 links to each other with an end of pulling force sensor 4: an end of movable terminal chuck 1 and an end of pulling force sensor 4 are simultaneously affixed with the 3rd plate 13, the other end of pulling force sensor 4 is connected with an end of ball-screw 6 by elastic parts 5, and the other end of ball-screw 6 is connected with motor 8 by shaft joint 7.Described elastic parts 5 comprises combined elastic body 5-1, the first plate 5-2, the second plate 5-3 and guide pole 5-4, the end of described combined elastic body 5-1 is connected with the first plate 5-2, the other end of combined elastic body 5-1 is connected with the end of guide pole 5-4, guide pole 5-4 is connected with the second plate 5-3 after vertically passing combined elastic body 5-1 and the first plate 5-2, the centre position of guide pole 5-4 and the second plate 5-3 Joint, thus the through hole that another termination of guide pole 5-4 is passed on the 3rd plate 13 forms guide effect.

With reference to Fig. 2, Fig. 3, combined elastic body 5-1 is four and is symmetrically distributed with respect to the central shaft of ball-screw 6, and each combined elastic body 5-1 is made up of outer spring 5-1-1, medi-spring 5-1-2, the inner spring 5-1-3 of different elastic modulus and the pressing plate 5-1-4 and the orienting sleeve 5-1-5 that are installed in three both ends of the spring heads respectively.70,45,25mm the effective diameter of outer spring 5-1-1, medi-spring 5-1-2, inner spring 5-1-3 is respectively:; Number of active coils is respectively 5,10.5,19.25; Number of total coils is respectively 7,12.5,21.25; Rigidity difference 12.09,4.28,2.02GPa.In addition, require elastomeric end and pressing plate 5-1-4 and orienting sleeve 5-1-5 and tight, the rigidity maximum error of four combined elastic bodies is no more than 5%.

Principle of work of the present invention is as follows: with reference to Fig. 1, concrete sample 3 can produce volumetric contraction in the setting and harden process, thereby driving movable terminal chuck 1 moves to stiff end, simultaneously, concrete differential contraction stress in the setting and harden process constantly increases, maximum can reach more than the 2MPa, for sectional dimension is the test specimen of 76 * 76mm, at this moment the pulling force that born of test specimen stiff end reaches 1178.8kgf, under so big acting force, thereby the steel of any fixed form all can produce distortion and be offset, if do not calculate this side-play amount, the differential contraction stress value that then measures will be less than normal.The present invention adopts and on the instrument base 12 at the stiff end of concrete sample 3 and movable end place a micro-displacement sensor 9 to be installed respectively and to monitor its displacement, on this basis test specimen is compensated the method for stretching, thereby can eliminate this error, when two displacement sums reach control limit value (2 μ m), stepper motor 8 will start voluntarily, test specimen is withdrawn into original length, and this process is by computer controlled automatic; After test specimen was withdrawn into original length, pulling force sensor 4 will be stressed and be noted this value of thrust, is concrete differential contraction stress; Along with the further increase of shrinking, the test specimen two ends can be pulled again, and stepper motor 8 can start by follow procedure again voluntarily, and the value of thrust of pulling force sensor 4 records can further increase; Broken or to a certain regulation length of time, the differential contraction stress evolution of concrete sample will be measured fully until test specimen so repeatedly.

Wherein stepper motor 8 directly is connected with ball-screw 6 by shaft coupling 7, ball-screw 6 left ends are fixed on the fixed board 14 motionless, right-hand member links to each other with the first plate 5-2 by bolt 15, the running meeting of stepper motor 8 directly drives ball-screw 6 and rotates, thereby the first plate 5-2 is moved to the left; The first plate 5-2 is moved to the left power is applied on the combined elastic body 5-1, combined elastic body 5-1 be compressed produce elastic force by guide pole 5-4 with the second plate 5-3 to the Zola; The left end of pulling force sensor 4 links to each other with the second plate 5-3 by bolt, and the right-hand member of pulling force sensor 4 is connected with the 3rd plate 13 by bolt, and the 3rd plate 13 is connected with test specimen movable terminal chuck 1; Thereby the pulling force sensor 4 that moves through of the second plate 5-3 has driven movable terminal chuck 1 and moves test specimen 3 is withdrawn into original length; Because the elastic modulus of combined elastic body 5-1 is less, its pulling force just can spur the very little distance of movable terminal chuck 1 operation when the big stroke of motor 8 runnings, thereby has guaranteed test control accuracy and traveling comfort.It is the three-phase hybrid stepping motor of 130BYG350 that described stepper motor adopts model, and step angle is 0.6 °/1.2 °, and maximum static torque is 35N.m.

With reference to Fig. 4, the bottom and the slide block 10 of the movable terminal chuck 1 of concrete sample 3 are affixed, and slide block 10 is arranged on the guide rail 11, and described guide rail 11 is fixed by base 12.Test specimen movable terminal chuck 1 is fixed on four slide blocks 10 by bolt 16, two guide rails 11 are fixed on the base 12, test specimen movable terminal chuck 1 moves on guide rail 11 by slide block 10 like this, thereby has reduced frictional resistance greatly, has guaranteed that also test specimen is stressed even in drawing process.

Claims

1, a kind of concrete early-age shrinkage measuring stress instrument, it comprises by the concrete sample (3) of movable terminal chuck (1) with stiff end chuck (2) clamping, movable terminal chuck (1) links to each other with an end of pulling force sensor (4), the other end that it is characterized in that described pulling force sensor (4) is connected with an end of ball-screw (6) by elastic parts (5), and the other end of ball-screw (6) is connected with motor (8) by shaft joint (7).

2, concrete early-age shrinkage measuring stress instrument according to claim 1, it is characterized in that described elastic parts (5) comprises combined elastic body (5-1), first plate (5-2), second plate (5-3) and guide pole (5-4), one end of described combined elastic body (5-1) is connected with first plate (5-2), the other end of combined elastic body (5-1) is connected with an end of guide pole (5-4), and guide pole (5-4) vertically passes combined elastic body (5-1) and is connected with second plate (5-3) with first plate (5-2) back.

3, concrete early-age shrinkage measuring stress instrument according to claim 2 is characterized in that described combined elastic body (5-1) is four and is symmetrically distributed with respect to the central shaft of ball-screw (6).

4, concrete early-age shrinkage measuring stress instrument according to claim 2 is characterized in that described combined elastic body (5-1) is made up of outer spring (5-1-1), medi-spring (5-1-2), the inner spring (5-1-3) of different elastic modulus and the pressing plate (5-1-4) and the orienting sleeve (5-1-5) that are installed in three both ends of the spring heads respectively.

5,, it is characterized in that on the instrument base (12) at the stiff end of concrete sample (3) and movable end place, a micro-displacement sensor (9) being installed respectively according to claim 1,2,3 or 4 described concrete early-age shrinkage measuring stress instruments.

6, according to claim 1,2,3 or 4 described concrete early-age shrinkage measuring stress instruments, the bottom and the slide block (10) of movable terminal chuck (1) that it is characterized in that described concrete sample (3) is affixed, slide block (10) is arranged on the guide rail (11), and described guide rail (11) is fixed by base (12).