Discuss About The Evaluation Of Road And Pavement Construction Materials In Civil.
Any construction work in civil engineering requires an understanding of fundamentals of design, and economic aspects. Most importantly however, a civil engineer ought to have in-depth understanding of the properties of the construction material. The asphalt concrete mechanistic-empirical train model is used in this paper to evaluate two tests types: the full scale accelerated and the extra-large wheel tracking (ELWT) test with use of a Heavy Vehicle Simulator (HVS). The ELWT was carried out on three different asphalt mixtures. The ELWT test took place at different temperatures and different tyre inflation pressures. The test occurring at such varied conditions aids in justifying the accuracy of the test by making the conditions in the laboratory as close to environmental conditions as possible. Permanent deformations measured on the asphalts slabs were further modelled by use of the United States Mechanistic Empirical Pavement Design Guide (US MEPDG) strain model. The calibration factors obtained were in the + or – 20% range from unity. From these results, it could be that the differences in the scale, geometry and configuration between the two tests devices were the reason behind the calibration factors as observed from the results.
Key words: Pavement, Asbestos, Asphalt Pavement Analyzer (APA), deformation
The Description of ELWT and the Test program
The test was done on slabs fifty centimeters in width and seventy centimeters in length, the slab should a thickness of twelve centimeters. A small inflated radial tyre (tyre pressure between 500 to 1000kPa) is then used to apply load of up to 25kN on the test slabs (Choi and Kim, 2015). The wheel travels longitudinally with a speed of between 1 to 5 km/h. Air and pavements temperatures were measured continuously while being varied between (5-60) ?C. The high-precision laser beam equipment was used to derive the rutting and or deformation in the test slab (Zhou, 2011)
The standard asphalt mixtures used were three: (AG22) for the base layer bituminous, (ABb22) the binder layer and (ABT11) for surfacing. The ELWT device was used to test these mixtures. The total prepared asphalt slabs were nine with three replicas for each mix. The European standard practices were used to prepare the mixes which were later roller compacted so as to attain the desired quality.
The tyre pressure and the ELWT tests were adjusted in order to account for the different places and or location in the actual construction and or real world conditions. A 10kN load was chosen for the experiment. Temperatures of (10, 20 and 30) ? C for the pavement were used for each mix of the first two asphalt slabs. For the 10 ? C and 20 ? C test load cycles of 14000 were applied. Load cycles of 25, 000 were used for the 30 pavement temperature. The third group of the slab mixture was used at temperatures of ten, fifteen, twenty-five and thirty five degree Celsius with load cycles of 14, 000 being used for the entirety of these temperatures. To guard the slabs against damage for the subsequent tests, increasing temperatures were used (Biligiri, 2013). The velocity of the wheel was maintained at 2.5km/h for the tests run.
HVS test program
The results from this test were used for verification purposes. The HVS method allows for a single and or a twin wheel load with magnitudes ranging from 30kN to 110kN moving at12km/h. Add on facilities were used to alter and control environmental influences for example temperature. The HVS test used was an asphalt surface course with a five-layer system (ABT11), binder layer (ABb22) and (AG22) bituminous base. Fitted in the test structure to measure the deformations were pressure cells and strain gauges.
HVS Test Structure material Properties
The assumptions made include a 0.35 Poisson’s ratio for all materials employed (Saride, Avirneni and Challapalli, 2016). For purposes of converting the speed into frequency, the depth, speed and loading frequency relation in equation 1 below was used.
T (in seconds) loading time, z depth (meters), V (km/h) velocity, fo frequency for loading at To (the temperature of reference), fT frequency at temperature T.
To model the permanent deformations in layers of asphalt, a layer strain approach was utilized following the equation 3 below:
?p,i and ? zi represent the permanent perpendicularly strain and ith sublayer the thickness, respectively, n represents number in total of sublayers, Rd indicates the rut depth.
Asphalt Pavement Analyzer APA, is an example of wheel tracking devices that can be in the evaluation of the rutting action of mixtures of asphalt under loading and environmental conditions simulating the actual parameters (Fakhri and Amoosoltani, 2017). He and Wong, (2007) conducted studies on wheel tracking devices that showed these devices have a great impact on measurement of rut. Papavasiliou and Loizos, (2013) demonstrated that the rutting rate is faster for small wheel-tracking machines as compared to larger devices. It means therefore that larger devices do not offer convenience in the evaluation of permanent deformation model features with a high correlation to the actual conditions in the field as the test specimen’s width is smaller. Li and Li, (2012) successfully utilized ELWT used in this model in the evaluation of permanent deformation in bituminous mixtures.
Even though APT test utilizing HVS are expensive to carry out, they are a close representation of real field conditions (Gao et al., 2018). Project research presented in this paper has demonstrated the utilization of ELWT and APT in estimation of permanent deformation features for asphalt layers. Multiple samples can be tested using this method at varying load rates and speeds. The samples are prepared, loaded and positioned easily. The chamber temperature is also efficiently regulated with heating strips and cooling agents fitted with a controller that has a microprocessor. There is accurate evaluation of rutting being provided by the versatile wheel tester. The advanced drive system allowing for testing of speeds and load rates simultaneously and a one of a kind high pressure system makes APA a suitable test for the study of rutting, moisture susceptibility of cold and hot mixes of asphalt and definitely fatigue cracking.
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