Search

ABSTRACT Rutting in asphalt mixes is a common type of distress in pavements with thick asphalt layers. It is more severe for pavements subjected to high pavement temperatures, slow moving, [...]

ABSTRACT Hydrated lime has traditionally been used as filler primarily for its ability to improve the moisture resistance of bituminous mixes. However, studies carried out in the past showed that [...]

This paper presents the details of a laboratory study on the evaluation of the fatigue characteristics of asphalt mixtures containing Recycled Asphalt Pavement (RAP) material using controlled stress indirect tensile fatigue test (ITFT). The effect of different aggregate gradations on the fatigue performance of RAP mixes is the main focus of the study as this helps us to identify the proportion of RAP that can be used from fatigue performance consideration. Two dense mixes and three gap graded mixes, both with different percentages of RAP, were investigated. VG 30 viscosity grade virgin binder was used. The fatigue test was conducted at 25°C. Laboratory fatigue life determined under stress controlled mode increased with increase in the RAP content for all the five aggregate gradations. The corresponding ‘Initial strain vs fatigue life’ trends suggest a decrease (for any specific strain level) in the fatigue life with an increase in the RAP content. However, analysis of the fatigue performance of typical pavement sections with different RAP contents do not suggest any significant detrimental effect of increasing the RAP content for pavements with thick bituminous layers. Use of open graded mixes permits the use of larger binder contents and higher RAP contents in the mix. Fatigue lives of RAP mixes are longer for gap graded mixes compared to dense graded mixes. The fatigue lives of RAP mixes are found to correlate very well with fatigue parameters of the virgin-RAP binder blends prepared in suitable proportions.

Background: This paper mainly focuses on the reliability study of cycloplegic autorefractor measurements over other methods in young children. Material and Method In a prospective study, 200 school children aged 8 to 15 years were evaluated for refractive errors in a period of one year. Non-cycloplegic autorefraction, followed by cycloplegic conventional retinoscopy and cycloplegic autorefraction was performed. Cyclopentolate eye drops(1 %) are used for this purpose. Fundus examination was performed in all children to exclude any posterior segment pathology. Post-mydriatic assessment was performed after one week. Results Post-mydriatic test values are used as gold standard. There is a no significant difference between cycloplegic autorefractor spherical power, cylindrical power and axis measurements against Post mydriatic test values. The difference is statistically significant in case of non -cycloplegic autorefraction. Conclusion Autorefraction with cycloplegia can be substituted for the conventional cycloplegic retinoscopy for both spherical and astigmatic refractive errors in young children. Note: This study was conducted by first author at Department of Ophthalmology, Rangaraya Medical College, Kakinada, India in the year 2002-2003. Keywords: Autorefractor, Cycloplegic autorefraction, Non-cycloplegic autorefraction, Table of Contents Abstract Introduction Material and Methods Results Discussion Conclusion References Introduction Conventional cycloplegic retinoscopy is widely used method to determine the refractive errors in patients of all age [...]

Rutting in bituminous layers is a major mode of distress, especially in pavements with thick bituminous layers. Different binder and mix rutting specifications are adopted by agencies worldwide to address the issue of rutting in bituminous mixes. The wheel tracking test is also widely used to evaluate the rutting potential of bituminous layers which depends on the aggregate gradation, binder type and also on the method of mix design adopted. The present study was conducted to examine the relationship between laboratory wheel track rutting and field rutting of different mixes prepared with different aggregate gradations, binder types and binder contents selected using different compaction efforts. Fifteen pavement sections with different surface mixes were constructed on a national highway. Loose bituminous mixes collected from the field were compacted to prepare specimens for wheel tracking tests. Two sets of specimens were prepared to have (a) 7% air voids and (b) an air void content similar to that observed in the field 1 day after construction. The rut depths measured using a wheel tracking machine correlated very well with field rut depths measured after 1 year when the laboratory specimens were prepared at the same initial air void content as achieved in the field. As expected, the rut depth measured in the laboratory wheel tracker for specimens prepared with 7% air voids did not correlate well with 1 year rut depths of field mixes which had different initial air void contents. Limiting wheel tracking test rut depths have been identified on the basis of comparison of the field rutting performance of different mixes and the corresponding laboratory rutting performance of the mixes. Limiting criteria have been proposed for two limiting rut depths of 10 and 20 mm and for different traffic levels.

For accurate prediction of pavement performance, it is necessary that the effect of ageing on different mix parameters is accounted for. The short-term- and long-term-aged bitumen viscosities estimated using Global Ageing System (GAS) models are used in the Mechanistic Empirical Pavement Design Guide for the estimation of dynamic modulus. Comparison of the viscosities of the bitumens extracted from field- and laboratory-aged asphalt mixes with the viscosities predicted using the GAS model suggests over-prediction for high temperature and lower bitumen film thickness (FT) combinations and under-prediction for low temperatures and high film thicknesses. That the ageing codes used in the GAS model are not sensitive to FT and temperature also has been established in this study. The new statistical model proposed in this study based on fixed effect regression modelling approach for estimating the short-term-aged bitumen viscosity as a function of bitumen type, FT and temperature has been found to predict the short-term-aged viscosity more accurately compared to the GAS model. The predictions with the new model are particularly better for certain combinations of temperature and FT for which large errors are observed in the predictions made with GAS models. The paper also proposes short-term-ageing conditions (sample weight and exposure time) to be adopted for bitumen in a Rolling Thin Film Oven to simulate the field ageing occurring in asphalt mixes having different film thicknesses.

The beneficial effect of hydrated lime added as filler to bituminous mixes in improving the moisture damage resistance of mixes has been known for a long time. However, the effect of binder modification using hydrated lime is less explored. Similarly, very little information is available on the influence of hydrated lime on the moisture resistance of bituminous mixes under critical conditions of high temperature and slow rate of loading. Extensive experimental investigations were conducted in the present study to quantify the relative beneficial effect of addition of hydrated lime in dry and wet methods on the moisture resistance of bituminous mixes. In the dry method, 1.5% and 2% lime (by weight of dry aggregate) was added as filler whereas in the wet method, VG30 and VG40 bitumen were modified using 20% and 30% lime (by weight of virgin binder). The moisture damage resistance of these mixes was evaluated by conducting different tests such as indirect tensile strength, dynamic modulus and dynamic creep tests to assess the sensitivity of different mix parameters in estimating the moisture resistance and to measure the influence of moisture damage on the mechanical properties and rutting performance. The performance of the conventional and lime-modified mixes was also compared with that of polymer and crumb rubber-modified bituminous mixes since lime-modified mixes have been evaluated in this study as possible alternatives to PMB and CRMB mixes, which are popularly used for roads with high traffic volumes. Lime-modified mixes were found to have the best moisture resistance compared to unmodified mixes and PMB- and CRMB-modified mixes. Evaluation of moisture damage in terms of dynamic modulus and dynamic creep tests was found to be significantly more sensitive to moisture damage compared to tensile strength ratio. The beneficial effect of lime has been observed to be significantly more under more severe conditions of high temperature and slow rate of loading compared to lower temperature and high frequency conditions.