RU2402767C2 - Method to test asphalt-concrete mixtures for caking - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: cylindrical sample is deformed by introduction of cone tip into through cylindrical hole of smaller diametre until sample is damaged. At the same time diagram of tip insertion is registered in coordinates "load-movement". The diagram is used to identify caking index as energy spent to damage the sample.

EFFECT: improved accuracy and reproducibility of test results, and development of capabilities for process automation.

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Description

The invention relates to testing equipment, and in particular to methods for determining the characteristics of mechanical properties (CMS) of road-building materials.

Known methods for determining the caking properties of cold asphalt mixtures, namely, that the sample is formed in a heated cylindrical form under load and after a certain time visually assess the integrity of the sample extracted from the mold (see GOST 12801-98 “Materials based on organic binders for road and airfield construction Test methods ", clause 6.1.5). These methods do not provide quantitative indicators for assessing caking and can only be used for preliminary screening of samples.

Closest to the technical nature of the claimed is a method of testing asphalt concrete mixtures for caking, consisting in the fact that a cylindrical sample is deformed by introducing a conical tip into a through cylindrical hole of a smaller diameter, located in the center of the sample along its axis, until the tip is destroyed or introduced to the entire height sample and on the basis of the adopted criteria determine the caking index (see. Materials and products for the construction of roads. / Under the editorship of Professor N.V. Gorelysheva. M .: Transpo Hg. 1986. 288 pp. 185-186). With this method, the above disadvantages are eliminated. The disadvantage of this method is the low accuracy due to the influence of subjective factors on the result. Here, clotting is estimated by a conditional indicator - the number of strokes of the falling cargo at the tip necessary for the complete destruction of the sample (see GOST 12801-98, clause 25.4). In this case, the criterion for the end of the test “to complete destruction” is not objectively determined, and the indicator itself - the number of strokes - admits the fundamental possibility of overstating the result due to the fact that the destruction of the sample can occur at the very beginning of the last impact, which nevertheless will be fully counted.

The test itself is time-consuming, requires constant involvement of the laboratory assistant and cannot be automated due to the lack of a clear objective criterion for its completion (visual assessment of failure).

The purpose of the invention is to increase the accuracy and reproducibility of test results, as well as creating opportunities for automation of the process by eliminating subjective factors.

This goal is achieved by the fact that the method of testing asphalt concrete mixtures for caking, namely, that the cylindrical sample is deformed by introducing a conical tip into the through cylindrical hole of a smaller diameter, located in the center of the sample along its axis, until the tip breaks or penetrates to the entire height of the sample, and based on the accepted criteria, the caking index is determined, supplemented with operations in which the load on the sample and the movement of the tip are measured, as a criterion for the end Nia slump tests take load, and caking index for receive operation (energy) of the sample fracture, breaking load or depth of penetration of the tip.

Comparative analysis with the prototype shows that the proposed method is characterized in that the load on the sample and the movement of the tip are additionally measured, the drop in load is taken as the criterion for the end of the test, and the work (energy) of fracture of the sample, breaking load or the depth of penetration of the tip, is taken as the caking index.

The drawing shows a diagram of the method. It can be implemented on any machine (press) for testing asphalt concrete materials or other similar testing equipment.

The test sample 1 is mounted on a fixed support (plate) 2 of the press connected to the force sensor 3. A conical tip 5 is connected to the movable support 4, which receives movement from the press drive (not shown) at a speed V. On the press frame 6 or on the support 2 (to exclude the influence of the flexibility of the press on the measurements) a tip displacement sensor 7 is installed, the measuring rod of which interacts with the support 4. The communication unit 8 is used to convert and transmit signals from the sensors.

The test is as follows. When the press drive is turned on, the support 4 moves, and the tip (indenter) 5 is inserted into the central hole of a smaller diameter d _{0 of} sample 1, due to the difference in diameters, forcibly deforming it and exciting force P (test load), which is sensed by the force sensor 3 and converted into proportional an electrical signal transmitted by the communication unit 8 to a indicating device or printer. Similarly, from the sensor 7, a signal is transmitted proportional to the movement (penetration) l of the tip 5.

For illustration, the drawing shows an exemplary diagram of the implementation of the tip in the coordinates P-l.

When the breaking load P _{r is} reached, its value drops, which serves as an objective criterion for the destruction of the sample. The drop rate to be taken into account can be set. The load P _p corresponds to the penetration value of the tip l _p . The hatched area of the diagram corresponds to the work (energy) spent on the destruction of the sample, and is equal to:

In its physical sense, this value can be taken as an objective indicator of caking.

To increase the reproducibility of the results, integration can be carried out not from 0, but starting from the final l ₀ corresponding to the selected initial measuring load P ₀ .

If the diagram is close to linear, then we can accept:

In the General case, the measurement of work (integration) can be carried out using a hardware-software device, implemented, for example, using a computer (not shown).

The test can also be carried out to a predetermined penetration depth l _{3 of the} tip, in particular to the entire height of the sample h (l ₃ = h), for which a displacement sensor is used, or to a predetermined load value P ₃ , for example, P ₃ = P _p .

The possibility of a correlation between caking indices determined by the proposed and known analogue method can be approximately estimated as follows.

According to the known method, when a sample is destroyed by a load of mass m falling from a height H and the number of strokes n, the work of destruction

_And = nmgH

where g is the acceleration of gravity.

With the proposed method, the work of destruction, determined by the area of the diagram P-l, is equal to A _P. From the equality of work A _P = A _And we find:

_And = nmgH

With accepted standard values (see GOST 12801-98, p. 25.1):

m = 0.5 kg; h = 0.2 m we have:

And _P = n · 1 J

those. the work (energy) of the destruction of A _P according to the proposed method, expressed in J (Nm), is numerically equal to the number of strokes n before the destruction by the known method.

The presence of a relationship between caking indicators allows the use of previously obtained test data and norms while accumulating new statistics. Moreover, the proposed method can be used both as the main one and as an additional or auxiliary one, using the park of testing machines (presses) already available in the laboratories.

Claims (1)

A method for testing caking mixtures of asphalt concrete mixtures, namely, that a cylindrical sample is deformed by introducing a conical tip into a through cylindrical hole of a smaller diameter located in the center of the sample along its axis, until the tip breaks or penetrates to the entire height of the sample, and based on the accepted criteria, it is determined caking index, characterized in that in order to increase the reproducibility of the results, a tip penetration diagram is additionally recorded in the “load” coordinates -moving ”and from the diagram determine the caking index of asphalt concrete as the energy spent on the destruction of the sample.

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