The stone aggregates constitute over 90% of the mass of a pavement and hence its properties play a very vital role in design of satisfactory unbound as well as bituminous mixes. Also since the aggregates availability ...The stone aggregates constitute over 90% of the mass of a pavement and hence its properties play a very vital role in design of satisfactory unbound as well as bituminous mixes. Also since the aggregates availability is continuously becoming scarce, attempts have to be made to identify use of some marginal as well as inferior aggregates without sacrificing the desirable qualities of resulting mixes. One of the most important properties therefore is the combined index of aggregates which deals with aggregates shape and is the sum of flakiness and elongation indices of aggregates measured related to their thickness and length respectively. The Ministry of Road Transport and Highways （MoRTH） specifies an upper limit of 30% combined index for different types of bituminous mixes. In the field, many times the aggregates supplied have combined index of more than 30%. A pre determined mix such as bituminous concrete, dense or semi dense bituminous macadam etc. has to be designed using such aggregates. It may be easy to design the mix but to get the aggregates with desirable combined index is often very difficult. In order to overcome this, in many projects, secondary crushers are used to crush the aggregates for the second time just to bring down the combined index. This obviously increases the project cost. It is quite possible that the aggregates with higher combined index may be suitable for a particular type of mix. It is therefore appropriate to study what type of a bituminous mix can be satisfactorily prepared depending on the availability of aggregates with generally higher values of combined index. Hence, it was attempted to determine the usual Marshall test properties of two most commonly used types of bituminous mixes namely bituminous concrete and dense bituminous macadam using aggregates with combined index 30%, 40% and 50%. It was found that aggregates with higher combined index are more suitable to design dense bituminous macadam mix than bituminous concrete.展开更多
文摘The stone aggregates constitute over 90% of the mass of a pavement and hence its properties play a very vital role in design of satisfactory unbound as well as bituminous mixes. Also since the aggregates availability is continuously becoming scarce, attempts have to be made to identify use of some marginal as well as inferior aggregates without sacrificing the desirable qualities of resulting mixes. One of the most important properties therefore is the combined index of aggregates which deals with aggregates shape and is the sum of flakiness and elongation indices of aggregates measured related to their thickness and length respectively. The Ministry of Road Transport and Highways （MoRTH） specifies an upper limit of 30% combined index for different types of bituminous mixes. In the field, many times the aggregates supplied have combined index of more than 30%. A pre determined mix such as bituminous concrete, dense or semi dense bituminous macadam etc. has to be designed using such aggregates. It may be easy to design the mix but to get the aggregates with desirable combined index is often very difficult. In order to overcome this, in many projects, secondary crushers are used to crush the aggregates for the second time just to bring down the combined index. This obviously increases the project cost. It is quite possible that the aggregates with higher combined index may be suitable for a particular type of mix. It is therefore appropriate to study what type of a bituminous mix can be satisfactorily prepared depending on the availability of aggregates with generally higher values of combined index. Hence, it was attempted to determine the usual Marshall test properties of two most commonly used types of bituminous mixes namely bituminous concrete and dense bituminous macadam using aggregates with combined index 30%, 40% and 50%. It was found that aggregates with higher combined index are more suitable to design dense bituminous macadam mix than bituminous concrete.
