Mechanical properties and Mullins effect in rubber reinforced by montmorillonite

The present work investigated the properties of rubber vulcanizates containing different nanoparticles (Cloisite 20A and Cloisite Na+) and prepared using different sonication amplitudes. The results showed that a maximum improvement in tensile strength of more than 60% over the reference sample was obtained by the nanocomposites containing 2 wt.% Cloisite 20A and 1 wt.% Cloisite Na+ and mixed with a maximum amplitude of 270 μm. The modulus at 300% elongation increased by approximately 18% and 25% with the addition of 2 wt.% Cloisite 20A and 3 wt.% Cloisite Na+, respectively. The shape retention coefficient of rubber samples was not significantly affected by the mixing amplitude, while the values of the softness measured at the highest amplitude (270 μm) were higher compared to those of mixtures homogenized with lower amplitudes. The loading-unloading and loading-reloading processes showed similar trends for all tested nanocomposites. However, they increased with increasing levels of sample stretching but were not significantly affected by filler content at a given elongation. More energy was dissipated during the loading-unloading process than during the loading-reloading. SEM micrographs of rubber samples before and after cycling loading showed rough, stratified, and elongated morphologies. XRD results showed that elastomeric chains were intercalated in the MMT nanosheets, confirming the improvement of mechanical properties. The difference between the hydrophilic pristine nanoclay (Cloisite Na+) and organomodified MMT (Cloisite 20A) was also highlighted, while the peaks of the stretched rubber samples were smaller, regardless of the rubber composition, due most probably to the decrease of interlayer spacing

Mechanical properties and Mullins effect in rubber reinforced by montmorillonite

The present work investigated the properties of rubber vulcanizates containing different nanoparticles (Cloisite 20A and Cloisite Na+) and prepared using different sonication amplitudes. The results showed that a maximum improvement in tensile strength of more than 60% over the reference sample was obtained by the nanocomposites containing 2 wt.% Cloisite 20A and 1 wt.% Cloisite Na+ and mixed with a maximum amplitude of 270 µm. The modulus at 300% elongation increased by approximately 18% and 25% with the addition of 2 wt.% Cloisite 20A and 3 wt.% Cloisite Na+, respectively. The shape retention coefficient of rubber samples was not significantly affected by the mixing amplitude, while the values of the softness measured at the highest amplitude (270 µm) were higher compared to those of mixtures homogenized with lower amplitudes. The loading-unloading and loading-reloading processes showed similar trends for all tested nanocomposites. However, they increased with increasing levels of sample stretching but were not significantly affected by filler content at a given elongation. More energy was dissipated during the loading-unloading process than during the loading-reloading. SEM micrographs of rubber samples before and after cycling loading showed rough, stratified, and elongated morphologies. XRD results showed that elastomeric chains were intercalated in the MMT nanosheets, confirming the improvement of mechanical properties. The difference between the hydrophilic pristine nanoclay (Cloisite Na+) and organomodified MMT (Cloisite 20A) was also highlighted, while the peaks of the stretched rubber samples were smaller, regardless of the rubber composition, due most probably to the decrease of interlayer spacing

Chemical composition and hazardous effects of leachate from the active municipal solid waste landfill surrounded by farmlands

Landfill leachates are potentially harmful to the environment and to human health.The objective of this study was to characterize leachates in order to analyze whether a relationshipexists between the stored waste and the composition of leachates, and to detect possible leakages ofpollutants into the environment. To achieve these objectives, field data, Global Positioning Systemdata and physico-chemical data were used. Biological tests are becoming increasingly popularin determining leachate toxicity; therefore, two toxicity tests were performed with the seeds ofwhite mustard (Sinapis albaL.) and duckweed (Lemna minorL.). Leachates were sampled from theleachate pond. Groundwater quality was monitored by using drill holes. The research and analysiscarried out are important to determine their potential impact on agricultural areas located near thelandfill. Demonstrably increased (P<0.05) concentrations of heavy metals were detected only inthe leachate pond which closes the landfill body, where it links up with the landfill insulation layer.Water sampled from drill holes reaching into groundwater was not contaminated. The results showedthat the leachates did not leak outside the landfill. Nevertheless, they were found to be phytotoxic.Both toxicity tests showed that the increasing amount of leachates resulted in the increasing growthinhibition of the tested plants. The proper handling of leachates should have been ensured.The research was funded by the Ministry of Agriculture of the Czech Republic, institutional support MZE-RO1720

Reliability of Methods for Determination of Stress History Parameters in Soils

Stress history acquired by any cohesive soil influences, to a large extent, three groups of fundamental properties indispensable in geotechnical design i.e. state of soil, shear strength, and stiffness characteristics. The basic stress history parameter (from which other parameters are derived) determined directly from laboratory tests is a preconsolidation stress σ′p. Since the first method proposed by Casagrande in 1936, value σ′p is determined in the oedometer test as a border between overconsolidated (OC) and normally consolidated (NC) zones. Approach based on division between predominantly elastic, (recoverable) strain, and plastic (irrecoverable) strain is a main principle of several methods of σ′p determination, which have been proposed over the past eighty-six years

Comparison of Changes of Road Noise Level Over a Century Quarter: A Case Study of Acoustic Environment in the Mountainous City

An essential part of a sustainable city is sustainable transport; however, the development of transport has led to the growing noise pollution. It is obvious that the road-traffic noise has negative health impacts on the population in the cities. These effects should be reduced to ensure the sustainability of modern cities. The main purpose of the study was to compare the changes in the noise level in the mountainous city in 2012 and 2016 compared to 1990. A hypothesis was introduced that over the past 26 years, the level and severity of noise during the day and night increased along with traffic and the number of cars. In addition, a comparison of the value of the traffic intensity of passenger cars and trucks during the daytime in the years 2012–2016 was made. Additionally, the noise generated by vehicles during the day and night was compared. On the basis of the results obtained, it can be concluded that the level of noise during the daytime over the last 26 years has clearly decreased. The main factors that reduced the noise level were the improvement of the quality of vehicle fleet, directing transit traffic to the city beltways, as well as the local use of noise barriers. However, the level of noise intensity at night increased significantly. This is due to the increase in the total number of vehicles in the city and their high speed at this time

Capability and limitations in laboratory determination of stiffness parameters of soils

The paper concerns laboratory methods for determination of soil stiffness. Major criterion for selection of analysed equipment is range of strain in which stiffness can be reliably determined. Substantially, various configurations of triaxial apparatus are referred to i.e. with standard cell and with the modified one. Additional system for internal measurement of strain is described and rational (based on test results) for use of it is presented. As to shear wave velocity measurement as a mean to obtain initial stiffness, requirements for proper measurement and interpretation was given. Finally, an approach to determine Poisson’s ratio on the basis of combined results of cyclic triaxial and resonant column tests was presented

Możliwości aparatu trójosiowego ściskania ze względu na określenie nieliniowości rozkładu sztywności gruntu

Reliable evaluation of stress-strain characteristics can be done only in the laboratory where boundary conditions with respect to stress and strain can be controlled. The most popular laboratory equipment is a triaxial apparatus. Unfortunately, standard version of triaxial apparatus can reliable measure strain not smaller than 0.1%. Such accuracy does not allow to determine stiffness referred to strain range most often mobilized in situ i.e. 10-3 ÷ 10-1%, in which stiffness distribution is highly nonlinear. In order to overcome this problem fundamental modifications of standard triaxial apparatus should be done. The first one concerns construction of the cell. The second refers to method of measurement of vertical and horizontal deformation of a specimen. The paper compares three versions of triaxial equipment i.e. standard cell, the modified one and the cell with system of internal measurement of deformation. The comparison was made with respect to capability of stiffness measurement in strain range relevant for typical geotechnical applications. Examples of some test results are given, which are to illustrate an universal potential of the laboratory triaxial apparatus with proximity transducers capable to trace stress-strain response of soil in a reliable way.W artykule wskazano i przeanalizowano błędy jakie wynikają z konstrukcji komory standardowej. Następnie przedstawiono dwie modyfikacje aparatu, które znacząco zwiększają dokładność wyznaczania sztywności gruntu. Pierwsza modyfikacja polega na innej konstrukcji komory aparatu, która charakteryzuje się wewnętrznymi prętami łączącymi. Takie rozwiązanie pozwala na sztywne połączenie górnej części komory z dolną co pozwala m.in. na wyeliminowanie większości błędów braku współliniowości w dwóch płaszczyznach, pozwala na stały dostęp do próbki na etapie przygotowania (depozycja materiału, pomiary średnicy) a także zwiększa dokładność zadawania i pomiaru składowej wartości naprężenia pionowego. Taki rodzaj modyfikacji zwiększa dokładność pomiaru nawet o jeden rząd wielkości. Następnym etapem w doskonaleniu techniki określania charakterystyki naprężenie odkształcenie w aparacie trójosiowym są wewnątrzkomorowe systemy pomiaru przemieszczeń próbki. W artykule przedstawiono system, który według doświadczenia i opinii Autorów jest bardzo efektywny w porównaniu z innymi systemami. System oparty jest na czujnikach mikroprzemieszczeń działających na zasadzie prądów wirowych, których rozdzielczość pomiaru wynosi 1μm. System pomiarowy oparty na konfiguracji sześciu takich czujników pozwala na zwiększenie dokładności pomiaru o następny rząd wielkości. Należy podkreślić, że omówione powyżej modyfikacje aparatu trójosiowego były dokonane samodzielnie, w ramach własnej pracy badawczej a nie w drodze zakupu całego systemu dostępnego komercyjnie. W celu wykazania efektywności przedstawionych modyfikacji aparatu trójosiowego ściskania, w artykule przedstawiono wyniki pomiarów w postaci rozkładu parametrów określających sztywność gruntu tj. modułu odkształcenia E i współczynnika Poissona ν. Wyniki badań przedstawiono dla zagęszczonego i luźnego piasku drobnego przy różnych wartościach naprężenia poprzedzającego ścinanie. Zmienność parametrów przedstawiono w zależności od odkształcenia pionowego dla pomiarów wewnętrznych i zewnętrznych. Wyniki wskazują na istotny wpływ analizowanych czynników tj. zakresu odkształcenia, sposobu pomiaru i stanu materiału reprezentowanego przez wskaźnik porowatości i wielkość naprężenia na przebieg zmienności parametrów określających sztywność gruntu

Applicability of shear wave velocity to evaluate state of granular materials with fines

Evaluation of state of cohesionless soils is a key issue in majority of geotechnical projects, especially when the major concern is liquefaction phenomenon. Standard approaches based on static or dynamic penetration tests are of limited or no use in granular materials containing considerable amount of fines. Therefore, there is a need to look for alternative approaches to identify state of materials containing certain amount of fines. One of a conceivable approaches rests on shear wave velocity (Vs) measurement. It results from the fact that Vs reflects state of stress and void ratio as well. A little is known to what extent shear wave velocity might reflect state of soil, especially, when it contains certain amount of fines. The paper concerns possibility of evaluation of state of cohesionless soils containing fines on the basis of shear wave velocity. The approach is based on hybrid approach i.e. laboratory and field measurement of shear waves velocity which enables projection of correlation between void ratio and normalized shear wave velocity measured in the laboratory for a given soil on a field profile. Thus, the determined void ratio profile is used to determine undrained shear strength on the basis of steady state line determined in the laboratory for the same soil batch. This procedure was carried out for twokinds of soil containing 10 and 36% of fines, which represent a sand-like material and transition zone behavior. Comments concerning applicability of this approach are given in the conclusion

Quality requirements for static liquefaction test of soil in triaxial apparatus

Since in the field of research concerning liquefaction phenomenon, the largest database exists for triaxial tests, this type of apparatus was selected as the most relevant. Available data concerning laboratory research on liquefaction tests for identification of undrained response of sand indicated that the results are very sensitive to even smallest incorrectness in the testing procedure. Besides, due to a complex nature of liquefaction phenomenon, it was considered prudent to undertake some efforts directed to increase the objectivity of tests. Therefore, before commencement of the actual test program for investigation of undrained response of soil, it is necessary to carry out some preparatory experimental work consisting of application of indispensable modification necessary for enhancement of a quality of a triaxial test. The paper presents the key issues pertaining to the implementation of the experiment. Significance of these modifications for desired characteristics is emphasized. Relevance of some upgrading of the equipment for liquefaction tests is exemplified