SPECIFIC ASSESSMENT METHOD OF RAILWAY BALLAST PARTICLE DEGRADATION BASED ON UNIQUE LABORATORY TEST

Dep. «Transport Infrastructure», Szechenyi Istvan University, Egyetem Sq., 1, Gyor, Hungary, 9026, tel. + 36 (96) 613 544, e-mail fischersz@sze.hu, ORCID 0000-0001-7298-9960 Dep. «Transport Infrastructure», Szechenyi Istvan University, Egyetem Sq., 1, Gyor, Hungary, 9026, tel. + 36 (96) 613 544, e-mail nemeth.attila@sze.hu, ORCID 0000-0002-3477-6902 Dep.«Structural and Geotechnical Engineering», Szechenyi Istvan University, Egyetem Sq., 1, Gyor, Hungary, 9026, tel. + 36 (96) 613 541, e-mail harrach.daniel@sze.hu, ORCID 0000-0003-4819-8506 Dep.«Transport Infrastructure», Szechenyi Istvan University, Egyetem Sq., 1, Gyor, Hungary, 9026, tel. + 36 (96) 613 544, e-mail era__juhasz@hotmail.com, ORCID 0000-0002-5544-3146


Purpose
In the EU's 2014-2020 Finance Programme Hungarian railway construction and rehabilitation projects can be financed by more than thousand billion Hungarian Forints, from which quantity of money important railway projects can be executed.The important part of these projects is the ballast that is the most component of superstructure.In nowadays practice it is obvious aspect that required quality ballast [3,5,[13][14][15][16][17][18][19][20][21][22] is achievable in requested quantity.
In the followings the authors point to those criteria because of that the future view is more shaded, and which are prescribed that special rock physics tests (Los Angeles and Micro-Deval abrasion tests) are highly suggested with more real loading conditions than the standardised tests considering available stone-rock qualities' limits.
The grains' original -base rock-dependentabrasion properties can be hardly modified by technology methods, these are mostly depending on «aggregate asset» and rocks' mechanical characteristics.In professional events more and more presentations are made about the fact that environmental, nature-reservational, heritage-protective, etc. regulations hitting the stone-mining industry aggravated year by year generally mean such restrictions [13,14] on the access of the natural wealth that might lead to problems in base material supply and increasing quality hazard on the medium term.
The authors think it a base problem that the ability for railway ballast material is internationally required the Los Angeles abrasion and Micro-Deval abrasion tests [15,16] in the product standard [17].These laboratory tests are not able to simulate the real evolved stresses of railway ballast (it should be mentioned that in case of e.g.asphalt and concrete road pavements' «stone skeleton» [1,10,11] these laboratory tests are not the optimal solution, either).For the objective judgement of conformability special laboratory breakage test has to be used that consider the more real operation circumstances and stresses.
After the international literature review, the authors represent the own, unique solution for a special laboratory test procedure (method) that is able to simulate the stresses more realistic.The results are comparable to the conventional, standardised abrasion (degradation) tests [15,16], the degradation qualifying parameters used internationally [8,9,12], as well as required cycle of ballast cleaning work [2,12].

Methodology
In 2014 an R&D was made with the finance support of Colas Északkő Ltd.; the public information were published in [6,7].Below these results are shortly detailed: -there is no strong correlation between any degradation parameters and their change, as well as the measured and calculated rock mechanic parameters.This result wasn't unexpected because of the base assembly of laboratory tests (rotating steel drum filled with ballast particles with or without steel balls vs. a «box» filled with ballast, pulsated by dynamic cyclic force), -in the article [4] the particle degradation due to tamping technology was examined in the labora-tory, the authors of this paper weren't able to verify neither physical nor mathematical correlation between the Los Angeles abrasion value of the samples and the particles shape parameters, -the time interval values of ballast cleaningscreening work were determined according to earlier experience data of MÁV (Hungarian Railways) and international literature [2,12].
The authors have supplementary plans compared to the research executed in 2014: more accurate measurement of the variation of ballast grains' degradation as a function of pulsating cycles (or elapsed time during the fatigue test) with the manner detailed below: -testing of minimum two types of ballast samples with different rock mechanic properties (ballast samples from Colas Északkő Ltd.), • ballast sample #1: LA RB =19%, M DE RB=17%, • ballast sample #2: LA RB =16%, M DE RB=4%, -fatigue tests connected to railway ballast material samples, definition of PSD (particle size distribution) before and after fatigue tests with the following load cycles: 0.1 million; 0.2 million; 0.5 million; 1 million and 1.5 million; 3 million and 5 million (the authors modified the initial plan and they will execute measurements with maximum 5 million cycles, but in this way they don't have the opportunity to make measurements with 3 separate measures), -separate ballast sample should be for each fatigue test, i.e. the test series will be like the following: • ballast sample should be cleaned and washed (the particles more than 22.4 mm are needed for the tests), • PSD should be determined (BP -before pulsating test), • 0.1 million loading cycles should be utilized, • PSD should be determined (AP -after pulsating test), • the ballast sample has to be thrown away, • another (new) ballast sample should be cleaned and washed (the grains more than 22.4 mm are needed for tests), • PSD should be measured (BP -before pulsating test), • 0.2 million loading cycles should be used, • PSD should be determined (AP -after pulsating test), • the ballast sample has to be thrown away, • etc. until 5 million loading cycles.-F V [12], BBI [9] parameters have to be determined, -grain quantity d<22.4 mm, d<0.5 mm, d<0.063 mm, the ratio d 60 /d 10 , moreover M and λ [8] parameters should be defined, -the goal is to effort determine mathematicalphysical trends and correlation between characteristics (see above point) and loading cycles of fatigue test.
The noticed measurements are also performed using of fresh railway ballast samples from andesite base rocks, as these measurements were executed in the research in 2014.The dynamic fatigue test series were able to be begun in March, 2018, the full results is able to be published in June, 2018.

Findings
In this paper the authors are able to sentence the results until 3 million loading cycles, because the measurements with fatigue tests are done as follows: -

Originality and practical value
According to the Fig. 1-8 the following results can be determined, that are not the final results of the research, and they consider the maximum 3million-fatigue cycles (not the 5 million): -there are significant correlation (R 2 >0.8) related to four calculated parameters from the eight (as a function of number of loading cycles), the regression functions are power regression function: • F V , i.e. the parameter that can forecast the necessity of ballast bed screening, this parameter is recommended by the South African Railways [12], • d<22.4 mm (in mass percent) related to after pulsating, • M and λ parameters [8] that are recommended by researchers from the BME (Budapest University of Technology and Economics) (now the authors used the M and λ ratios: the ratio of numbers after pulsating and before pulsating, respectively).-The regressions are not significant (neither with linear, nor with power regression functions) related to the other four calculated parameters, -in detailed analysis (considering only the significant correlations) the authors can highlight the fact, that «speed» of the breakage (the tangent of the functions) is higher related to ballast sample #2 than ballast sample #1, that is very interesting because both the LA RB and M DE RB parameters are better (lower) for ballast sample #2, -to be able to sentence final results the missing measurements are needed (i.e. the measurements until dynamic fatigue with 5 million loading cycles).

Conclusions
This article introduces a research's results (but not the final results) supported by ÚNKP-17-4 New National Excellence Program of Ministry of Human Capacities.The accurate topic in the ÚNKP project is the «Innovative breakage test method of railway ballast material».In the authors' earlier paper the up-to-date international research achievements were resulted related to conventional (standardized) and non-conventional (non-standardized), additionally seperate laboratory breakage and abrasion test methods and DEM simulations of ballast materials.The research plan was introduced and detailed for 2017 and 2018 years, it can be scored as the enhancement of the earlier research.The authors sentenced the results of the laboratory tests in the consideration of the maximal 3 million fatigue cycles for the two different andesite railway ballast samples.The developed method seems to be adequate for evaluating of the degradtion process of railway ballast material according to railway.

Fig. 1 .
Fig. 1.Function of parameter F V (%) as a function of number of loading cycles related to both ballast samples