Parametric stress-strain analysis for upstream slope of the asphaltic concrete core rockfill dams in static state

In this study, the effects of various geometric parameters of a dam in 2D static analysis of stress-strain on the upstream slope of the asphaltic concrete core rockfill dams were investigated. For this purpose, first the geometric characteristics of a large number of world's dams were collected and assessed, then by geometric modeling of these dams, many numerical models were developed for static analysis using GeoStudio software in eight height classes, three cases of upstream and downstream slopes, three different shape and thickness of the asphaltic concrete core under different Impounding states including "Full Reservoir", "Half full Reservoir", "End of construction and "Rapid Drawdown on a rigid type of foundation. The results of this study demonstrated that in four different construction and impounding states and in three different cases of slopes, Increasing the height parameter, causes increasing the Maximum total stress, Maximum total strain, Shear strain and Maximum shear stress for all construction and impounding states. The Maximum total stress decreased for all operating situations as the upstream slope reduced. According to the obtained results from the static stress-strain analysis, increasing both vertical and inclined asphaltic concrete core thicknesses, leads to decreasing the Maximum shear stress in Full Reservoir state but it increases in other state of impoundment. Moreover, by comparing the displacements related to specified points on the upstream slopes, increasing the height parameter, leads to increasing both horizontal and vertical displacements, the volumetric strain, deviator strain and deviator stress for all impounding conditions. In the following, the additional results were provided along with diagrams for further analysis.

Asphaltic Concrete Pavement Strength and the Impact of Rainfall

Studies have shown that moisture impacts on the strength of flexible pavement surface of asphaltic concrete. Several investigations and relevant researches treated the effect of subsurface and surface water sources, on the durability of flexible pavements. This study is focused on the surface water sources, as a result of precipitation (rainfall), on the surface of flexible pavements. To conduct this experiment, the considerations made include (i) the continuous exposure of the pavement surface to annual rainfall (ii) application of pavement exposure to moisture in the field. This study considered the amount of rainfall each day, as the duration (age) of pavement exposure to moisture (being under water during rainfall). For the purpose of this experiment, the Owerri to Onitsha about 90km of dual carriage way in south east of Nigeria, was considered. This is a flexible pavement that traverses through the rain forest belt, characterized with high amount of annual rainfall values. Flexible pavement specimens from this road were obtained, cleaned and immersed in water after weighing, to keep vital records of the necessary parameters, before further tests at 7days intervals. Values of strength obtained after days in water, that approximated to the appropriate field situation of exposure to rainfall, showed a consistent loss of strength, from the crushing strength results.

Performance of Fly Ash as Replacement for Non-Renewable Constituent in Asphaltic Concrete for Road Development

The non-renewable constituent used in asphalt concrete consumed large amount of materials resulting an increase in the price of asphalt mixture and consequently the cost of road development. On the other hand, huge industrial waste being generated daily from human activities causes environmental degradations. Thus, the study evaluates the performance of fly ash (FA) in asphalt concrete development targeted for road application. The aggregate, bitumen, and fly ash were characterized before being used. The stone dust in asphalt mixture was replaced with FA in predetermined proportions of 2, 4, 6, and 8% to produce a cylindrical specimen of asphalt mixture concrete. Marshal stability test, flow test, X-ray diffraction (XRD), X-ray Fluorescence (XRF) and Scanning Electron Microscope (SEM) was conducted on the composite samples. From the results, stability values of 7.39, 7.70, 7.90 and 8.22 KN was obtained at 2, 4, 6 and 8% replacements, respectively. Hence, the optimum value of 8.22 KN obtained from 8% partial replacement with FA is adequate for heavy traffic while other partial replacement from 2- 6% with stability within the range of 7.39-7.90 KN is suitable for medium traffic in accordance with the criteria for the marshal mix design method provided by Asphalt institute (1997). Corresponding values of 3.7, 3.5, 3.3 and 3.0 mm was obtained for the flow. The flow, air void, void in mineral aggregates and void filled with bitumen results all satisfied Nigeria general specification for road and bridges (1997). Therefore, fly ash can be used as partial replacement in asphaltic concrete to enhance the performance of the mix with a reduced cost for pavement construction.

Strength Assesment of Asphaltic Concrete using Bitumen, Natural Fibre and Stone Dust: A Critical Review

In this review article, the usage of bitumen, sisal fiber and the sisal fiber for improving the strength parameters of concrete is discussed in detail. Numerous research studies related to the usage of bitumen, sisal fiber and stone dust are studied in detail to determine the results and outcome out of it. Previous research works showed that all, these materials were enhancing the strength and durability aspects of the concrete and depending upon the research studies certain outcomes has been drawn which are as follows. The studies related to the usage of the bitumen or asphalt in concrete so as to produce bituminous concrete or asphaltic concrete, the previous research works conclude that the maximum strength was attained at 5 percent usage of the bitumen and after further usage the general compressive strength of the concrete starts declining. The previous studies related to the usage of the sisal fiber showed that with the usage of the sisal fiber in the concrete, the strength aspects of concrete were improving and the maximum strength was obtained at 1.5 percent usage of the sisal fiber and after his the strength starts declining. Further the studies related to the usage of the stone dust showed that with the usage of stone dust as partial replacement of the natural fine aggregate the compressive strength of the concrete was improving and it was conclude that with the increase in the percentage of the stone dust, the compressive strength of the concrete was increasing.

Effects of Polyethylene Terephthalate and Crumb Rubber on Selected Properties of Asphaltic Concrete

This study investigated the combined effects of polyethylene terephthalate (PET) and crumb rubber (CR) as modifiers on some properties of asphaltic concrete. Asphaltic concrete materials were obtained from a construction site. CR of 9.5 mm size was obtained by sieving, while PET bottles were collected, sorted, washed, dried and shredded by mechanical means. The physical properties of these materials were determined following standard procedure. Bitumen was modified by wet process with PET and characterised. Asphaltic concrete samples with partial replacement of coarse aggregate in the mix with CR were prepared. Samples without modifiers were also prepared as control. These were subjected to Marshall Stability test. The percentage variation for stability and flow between the control and the modified mixes, were 27 % and 0.29 % respectively, while those of the volumetric properties of bulk density, voids filled bitumen (VFB), air voids (VA) and voids in mineral aggregate (VMA) were 0 %, - 0.13 %, 0 % and 0 % respectively. It was concluded that, there was no difference between the flow and volumetric properties of the control and modified mixes. Keywords: Polyethylene terephthalate, crumb rubber, asphaltic concrete, stability, flow, volumetric parameters