CN210427574U

CN210427574U - An experimental device for testing the free shrinkage properties of concrete

Info

Publication number: CN210427574U
Application number: CN201821649898.5U
Authority: CN
Inventors: 韩春秀; 张久长; 罗强军
Original assignee: Yunnan Minzu University
Current assignee: Yunnan Minzu University
Priority date: 2018-10-11
Filing date: 2018-10-11
Publication date: 2020-04-28
Anticipated expiration: 2028-10-11

Abstract

The utility model discloses an experimental device for testing the free shrinkage performance of concrete in the field of civil engineering. Aiming at the difficulty of using in-situ long-term load experiments to obtain the constrained shrinkage performance of concrete in practical engineering, a practical new experimental device that can be operated in the laboratory without constraints to make concrete shrink freely is proposed. The free shrinkage of concrete can be obtained through experiments. The mechanical properties of restraint shrinkage in engineering can be obtained indirectly through calculation. The device is simple in components and small in size, and can be placed in a space with less interference such as the corner of the room. The temperature and humidity requirements are low, and the same indoor environment can be maintained. The instrument for measuring strain uses a vibrating wire strain gauge and a micrometer to compare the same position. It can be tested and compared and analyzed; the data collection adopts a portable data acquisition instrument, which can be charged for a long time, small in size, and easy to operate; the experimental results can be compared with the results of the test block shrinkage coefficient written calculation.

Description

Experimental device for test concrete free shrinkage performance

Technical Field

The invention belongs to the technical field of civil engineering structure experiments, and relates to an experimental device for testing the free shrinkage performance of concrete.

Background

Shrinkage is a physical property inherent to concrete that tends to cause cracking of the concrete over its service life. Concrete used in actual engineering is often constrained in cross sections (such as composite beams) or structural supports and the like, the constraint in the cross sections can cause the redistribution of cross section stress of a composite structure, and a shrinkage secondary internal force which changes along with time can be caused for a statically indeterminate structure, so that the final stress state of the cross sections is changed and the deflection is increased, the value of the final stress state can be as much as several times of the elastic deformation, the concrete is very unfavorable for a structure with strict deflection requirements, and sufficient attention is paid to the concrete constraint shrinkage performance.

However, the shrinkage-restraining properties of concrete in engineering are quite complex, involving a considerable number of influencing factors, almost all of which, together with the results they produce, are themselves random variables. In order to obtain the parameters, an in-situ experiment is usually required on an engineering site, the shrinkage belongs to long-term mechanical properties, the time consumption is long, the duration is generally more than 1 year, long-term data measurement is required, the conventional strain gauge reading needs to be conducted with alternating current, short-term data is observed, the purpose of stably, long-term and accurately obtaining effective data of a test piece cannot be achieved, and meanwhile, the in-situ experiment is greatly influenced by environmental disturbance and experiment space. Concrete shrinkage in actual engineering is constrained shrinkage, and in order to obtain shrinkage mechanical properties, the concrete shrinkage is very difficult to realize through in-situ long-term load mechanical experiments. If the free shrinkage test can be carried out on the concrete and then the constrained shrinkage calculation is carried out through the structural mechanics principle, the mechanical property rule of the constrained shrinkage in the engineering can be indirectly obtained.

Disclosure of Invention

To the problem of adopting the long-term load experiment operation difficulty of normal position in order to obtain concrete restraint shrinkage performance in the actual engineering, provide one kind can be in the laboratory operation, do not add the practical novel experimental apparatus that retrains and make concrete free shrinkage, can obtain concrete free shrinkage data through the experiment, can indirectly obtain the mechanical properties of restraint shrinkage in the engineering through calculating. The experimental device comprises an external vibrating wire strain gauge 1; a dial gauge displacement gauge 2; a micrometer strain gauge 3 with the gauge length of 150 mm; a steel plate cushion block 4 having dimensions of 400mm × 400mm × 10mm in length × width × height; a concrete block 5 having a length × width × height of 515mm × 100mm × 100 mm; a steel bar support 6 with the size of 600mm by 400mm and the diameter of 20 mm.

The device has the advantages that: the device is simple in component, small in size, capable of being placed in a room corner and other space positions with small interference, low in temperature and humidity requirements, capable of keeping the same indoor environment, capable of placing a hygrothermograph near a test piece to obtain an environment influence coefficient, and capable of performing in-situ comparison test on strain measurement instruments by adopting a vibrating wire type strain gauge and a micrometer and performing data comparison analysis; the data collection adopts a portable data acquisition instrument which can be charged for a long time, has small volume and is convenient to operate; the experimental result can be compared with the result of calculating the shrinkage coefficient of the test block.

Drawings

FIG. 1 is a schematic diagram of: the concrete free shrinkage scale model experiment device is subjected to axonometric drawing;

FIG. 2 is a diagram of: concrete specimen top view.

The reference numbers in the figures are: 1 is an external vibrating wire strain gauge; 2 is a dial gauge displacement meter; 3 is a micrometer gauge with the gauge length of 150 mm; 4 is a steel plate cushion block having dimensions of 400mm × 400mm × 10mm in length × width × height; 5 is a concrete block having a length, width and height of 515mm, 100mm and 100 mm; 6 is a steel bar support with a height x width dimension of 600mm x 400mm and a diameter of 20 mm.

Detailed Description

The invention is realized by the following technical scheme:

1) pre-manufacturing a steel bar support 6 with the height multiplied by the width of 600mm multiplied by 400mm and the diameter of 20mm, and welding four feet of the steel bar support 6 on four sides of a steel plate cushion block 4 to ensure that the steel bar support 6 is vertical to the steel plate cushion block 4 along the height direction; a template with the length, the width and the height of 515mm, the width and the height of 100mm and 100mm is supported at the center of a steel plate cushion block 4, a concrete test block 5 is manufactured, the concrete grade is C30, the template is disassembled when the maintenance is carried out for 28 days, the steel plate cushion block 4, a steel bar support 6 and the concrete test block 5 form an experimental model, the model is placed at an indoor corner with relatively small artificial disturbance on the same day, and the floor area of an operation space is about 4 square meters. The same 3 models were made, and a hygrothermograph was placed near the model, and the ambient temperature and humidity were recorded each morning and evening each day from the day the test piece was placed.

2) On the day of placing the model (namely 28 th day of concrete curing), the upper ends of 1 dial indicator displacement meters 2 are fixed to the cross points of the steel bar supports 6, and the lower ends of the 1 dial indicator displacement meters are in contact with the upper surface of the test block 5; 2, sticking the external vibrating wire strain gauges 1 to two side surfaces of the test block 5 close to the upper edge of the test block by using bar-planting glue; and (3) sticking the 2 micrometer strain gauges with the gauge length to the upper edge of the test block 5 close to the test block by using bar-planting glue, wherein the two side faces of the test block are different from the two side faces of the vibrating wire strain gauges 1.

3) On the day that the model was placed (namely 28 th day of concrete maintenance), 1 and 3 install the back, adopt portable data acquisition instrument switch-on vibrating wire formula strainometer 1 to carry out the first day and measure, carry out the first day reading to amesdial strainometer 3 simultaneously, follow-up measurement time point to 1 and 3 does: once daily for month 1, every 3 days for

month

2 and 3, and every 7 days for month 4 to 12, with a time span of one year.

Claims

1. An experimental device for testing the free shrinkage performance of concrete comprises an externally attached vibrating wire strain gauge (1), a dial gauge displacement meter (2), a dial gauge strain gauge (3) with the gauge length of 150mm, a steel plate cushion block (4) with the dimensions of 400mm multiplied by 10mm with the dimensions of length multiplied by width multiplied by height, a concrete test block (5) with the dimensions of 515mm multiplied by 100mm with the dimensions of length multiplied by width, and a steel bar support (6) with the dimensions of 600mm multiplied by 400mm with the diameter of 20mm with the dimensions of height multiplied by width, wherein the steel plate cushion block (4), the steel bar support (6) and the concrete test block (5) form an experimental model, four feet of the steel bar support (6) are welded on four sides of the steel plate cushion block (4), so that the steel bar support (6) is vertical to the steel plate cushion block (4) along the height direction, a template with the dimensions of 515mm multiplied by 100mm multiplied by height is adopted at the center of the steel plate cushion block (4) to manufacture the concrete test block (5), the concrete grade of the concrete test block (5) is C30, the maintenance period is 28 days, the concrete test block (5) enables concrete to shrink freely without constraint, the upper end of 1 dial indicator displacement gauge (2) is fixed to the cross point of the steel bar support (6), the lower end of the concrete test block contacts with the upper surface of the concrete test block (5), 2 external-attached vibrating wire strain gauges (1) are adhered to the concrete test block (5) through bar-planting glue and are close to the two side faces of the upper edge of the concrete test block (5), 2 dial indicator strain gauges (3) with the gauge length of 150mm are adhered to the concrete test block (5) through bar-planting glue and are close to the upper edge of the concrete test block (5) and are located on the two side faces different from the external-attached vibrating wire strain gauges (1).

2. The experimental device for testing the free shrinkage performance of the concrete according to claim 1, wherein the external vibrating wire strain gauge (1) is used for data acquisition through a portable data acquisition instrument.