RU2059242C1 - Process of determination of creepage of concrete - Google Patents

Abstract

FIELD: construction industry. SUBSTANCE: process refers to expidited determination of creepage of concrete. Tested sampled are loaded to destruction. Deformations are measured in process of loading. Chart "stress-deformation" is plotted. Values of total and elastic deformations of concrete are found under loading level equal to limit of long-term strength of concrete. Difference of these values is calculated. Creapage of concrete is determined as ratio of found difference to limit of long-term strength. EFFECT: expidited process of determination of creepage of concrete. 1 dwg, 1 tbl

Description

 The invention relates to tests of building materials and can be used to accelerate the determination of creep measures of concrete.

A known method for determining the creep of concrete by measuring strains in the direction of the longitudinal axis of the sample loaded with a constant axial compressive load [1]
The disadvantage of this method is the duration and complexity of the tests.

Closest to the proposed one is a method for determining the creep of concrete, including loading the test samples to failure, measuring strains during loading, and constructing a stress-strain diagram [2]
The disadvantage of this method is the complexity and duration of the tests, which consists in multiple (up to 2x10 ⁶ cycles) loading and unloading of the tested samples. In addition, special equipment is required. The adoption of a certain compressibility of concrete under conditions of instantaneous application of the load as the value of ultimate deformability is erroneous, since the ultimate compressibility of concrete at the time of destruction largely depends on the rate of application of the load and increases with decreasing loading speed.

 The technical result is to eliminate the above disadvantages.

 This is achieved by the fact that in the method for determining the creep of concrete, including loading the test samples to failure, measuring strains during loading, building a stress-strain diagram, the total and elastic strain of concrete is determined from the stress-strain diagram at the loading level, equal to the tensile strength of concrete, then the difference between these values is found, and the creep of concrete is determined as the ratio of the found difference to the tensile strength.

 The invention is illustrated in the drawing.

 The method is as follows.

ε" испытуемого бетона.On concrete prism samples with a size of 100x100x400 mm, axial compression tests determine the prismatic strength of concrete R _b and the initial elastic modulus E _о , longitudinal and transverse strains. According to the data obtained, the upper limit of the microcracking of concrete R is determined in a known manner $\genfrac{}{}{0ex}{}{\text{v}}{\text{t}}$ , numerically equal to the tensile strength of concrete R _s under static loading as the stress at which the ratio of the increment of transverse relative strains to the increment of longitudinal relative strains is 0.5. The relative strain ε _R corresponding to the compressive strength of the concrete (the prismatic strength of concrete R _b ) is determined, the diagram is constructed "

ε "tested concrete.

ε" (точка В). Абсцисса точки В составляет величины полной деформации бетона ε_b при уровне нагружения, равном пределу длительной прочности бетона R_с. Определяют величину упругой деформации бетона ε_el при уровне нагружения, равном пределу длительной прочности бетона R_с по формуле ε_el

Определяют ползучесть бетона по формуле
С_В

В таблице представлены экспериментальные данные по способу, полученные при испытаниях бетонов классов по прочности на сжатие 825-840, изготовленных с применением цементов 19 цементных заводов.On the ordinate axis, mark the point corresponding to the long-term strength of concrete R _s (point N), from which the perpendicular is restored to the intersection with the descending branch of the diagram "

ε "(point B). The abscissa of point B is the total strain of concrete ε _b at a loading level equal to the tensile strength of concrete R _s . The elastic strain of concrete ε _{el is} determined at a loading level equal to the tensile strength of concrete R _s using the formula ε _el

The creep of concrete is determined by the formula
C _B

The table shows the experimental data on the method obtained during testing of concrete of classes of compressive strength 825-840, made using cements of 19 cement plants.

 The method can be implemented during one work shift (more precisely, 2-3 hours). Creep determination can be used in the precast industry to accurately predict structural deformations under prolonged loading. The method is especially effective in solving optimization problems, for example, when choosing starting materials, concrete compositions, conditions of work, because it allows you to get a large amount of information in a short period of time at low labor costs.

Claims (1)

 METHOD FOR DETERMINING CONCRETE CREEP, including loading test specimens to failure, measuring strains during loading and plotting stress strain diagrams, characterized in that the total and elastic strain of concrete is determined from the stress – strain diagram for loading at a level equal to the ultimate strength of concrete, then find the difference of these values, and the creep of concrete is determined as the ratio of the found difference to the ultimate strength.

Images