M. Amaranatha Reddy

Investigation of cold-in-place recycled mixes in India

Cold-in-place recycling (CIR) is a popular and cost-effective bituminous pavement rehabilitation technique. India has very limited experience with this technique. A few stretches of national highways were rehabilitated in the recent past using CIR technique. In the present investigation, laboratory experiments were conducted on different cold-recycled mixes prepared using the bituminous material milled from in-service bituminous pavement. The effect of compaction effort, curing time, aggregate gradation and choice of additive on the performance of the cold mixes was investigated. Structural evaluation of a cold-in-place recycled layer was carried out using falling weight deflectometer. Laboratory investigation yielded guidelines on appropriate accelerated curing conditions, compaction effort and optimum fluid content to be adopted for the preparing cold-recycled mixes using the milled bituminous material obtained from typical Indian highways. Structural evaluation of the recycled layer suggested significa...Cold-in-place recycling (CIR) is a popular and cost-effective bituminous pavement rehabilitation technique. India has very limited experience with this technique. A few stretches of national highways were rehabilitated in the recent past using CIR technique. In the present investigation, laboratory experiments were conducted on different cold-recycled mixes prepared using the bituminous material milled from in-service bituminous pavement. The effect of compaction effort, curing time, aggregate gradation and choice of additive on the performance of the cold mixes was investigated. Structural evaluation of a cold-in-place recycled layer was carried out using falling weight deflectometer. Laboratory investigation yielded guidelines on appropriate accelerated curing conditions, compaction effort and optimum fluid content to be adopted for the preparing cold-recycled mixes using the milled bituminous material obtained from typical Indian highways. Structural evaluation of the recycled layer suggested significant increase in the elastic modulus of recycled layer.

Evaluation of the sensitivity of different indices to the moisture resistance of bituminous mixes modified by hydrated lime and other modifiers

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.

An alternative method for short- and long-term ageing for bitumen binders

Short-term ageing of bituminous binders is a well-accepted concept that represents ageing of binders during plant mixing, production, transportation and construction. Simulation of this ageing is carried out in controlled laboratory conditions and these aged binders are used to predict binder rutting performance. Similarly, the simulation of long-term ageing of binders accounts to ageing of the binder during service life of the pavements and these binders are used to characterise the binder response to fatigue performance in the SUPERPAVE test protocol. Two well-established laboratory test methods are generally practised for evaluating the short-term ageing of bitumen binders: (i) the thin film oven (TFO) test method where a pan filled with bitumen is placed on a rotating pan on the horizontal plane and (ii) the rolling TFO (RTFO) method that uses cylindrical glass bottles filled with bitumen which are rolled in the vertical plane. In the case of long-term ageing, simulation is performed in a pressurised ageing vessel (PAV) under constant conditioning of pressure and temperature. The RTFO and PAV are the part of the test protocol of SUPERPAVE specifications. These equipments are costly and may not be available to different agencies and thereby it has become difficult to adopt any studies involving short- and long-term ageing of binders. Any alternative procedure developed that provides similar ageing effects comparable to the SUPERPAVE method would help highway agencies to adopt and study the effect of ageing on binders. Keeping this as the main concern, an attempt is made to develop a cheap and generalised method for short-term and long-term ageing effects using a normal laboratory oven. Six binder types consisting of two each from viscosity grades, penetration-grade polymer-modified binders (PMB) and crumb rubber-modified binders, were considered in this study. Binders were aged in RTFO and PAV ageing and tested for rheological properties using the dynamic shear rheometer. Similarly, these binders were also aged in a normal oven kept at a constant temperature for varying periods of ageing. Test results were compared on the basis of rutting and fatigue criteria to arrive at the time of ageing required in a normal oven that would be similar to RTFO and PAV ageing, respectively. The study revealed that it is possible to correlate ageing methods of SUPERPAVE with a normal oven method and arrive at an alternative method of ageing. In order to compare the actual short-term ageing of one of the modified binders, bituminous mixes were collected from the field during mix production, transportation and compaction, and binders from these were extracted. Rheological parameters of the extracted bitumen from field samples collected during different stages of construction, RTFO and normal oven-aged samples were evaluated and compared. It was found that the actual ageing is different from RTFO and a normal oven ageing and thereby there is a need to carryout a detailed study on ageing characteristics of Indian binders.

Evaluation of rehabilitated urban recycled asphalt pavement

Recycling of pavements is a relatively new technique for India and is gaining popularity in recent times due to several merits the technique has over conventional pavement rehabilitation techniques. The first recycling work of flexible pavements in India was undertaken a decade ago and since then the option of milling and recycling of bituminous layers has been adopted in some parts of urban and high-volume roads in India. However, no research studies were conducted on these works. Foamed bitumen recycled pavement work, which was undertaken on some urban roads of Kolkata city in India, has been reported in this paper. Detailed investigations conducted on the milling and foamed bitumen recycling work have been presented in this paper. Laboratory investigation was carried out on the milled and recycled material. Field evaluation of the pavements was done before and after rehabilitation using falling weight deflectometer. Results indicate that foamed bitumen recycling is a very promising alternative to rehabilitate bituminous pavements and to address the concern of conservation of energy and natural resources.