Active fillers’ effect on in situ performances of foam bitumen recycled mixtures

Cold recycling is one of the most employed rehabilitation techniques for asphalt pavements and it is becoming more and more important as reducing emissions becomes a priority in the reduction of the greenhouse effect. The main advantages of asphalt cold recycling techniques are the use of reclaimed materials and the fact that there is no need of aggregate heating to make the mixtures. This paper describes the evolution with time of in-situ performances of different foam bitumen-stabilised mixtures made with different active fillers (cement and lime), monitored during the first year from construction. Results are part of a more extensive research programme aimed to investigate the effects of using lime as an active filler in cold-recycled mixtures. Mixtures have been laid down on a specifically designed trial section in Italy, close to Florence. Short-term bearing capacity, immediately after construction, has been evaluated using a light weight deflectometer while to evaluate the mid-term performances falling weight deflectometer (FWD) tests have been performed after 24 hours, 14 days, 28 days and 9 months from construction. During these 9 months the test road was not opened to traffic, so the mixtures experienced almost no traffic (only construction traffic loads). This fact allowed to have the curing process without any influences other than the temperature: it means same curing conditions for all mixtures. Subsequent FWD tests are still ongoing to evaluate the evolution over time of pavement bearing capacity due to traffic. Results obtained positively support the use of lime as an active filler in the foam bitumen-stabilised material and allow to underline the effect of different active fillers in the material behaviour, even if all the mixtures underline excellent performances under traffic loading. FWD tests are scheduled to be repeated every 6 months in order to monitor the stiffness evolution of the mixtures and evaluate the nature of traffic damage

Development of a tool to assess in-situ curing of Foamed Bitumen Mixtures

This paper discusses the simplest yet crucial mix design consideration of Foamed Bitumen Mixtures (FBMs); curing. The objective of the present study is to attain better understanding of the curing mechanism of FBMs and lessen the gap between laboratory curing and field evolution of these mixtures. This was achieved by carrying out a laboratory curing study in two phases. The first phase aimed to understand the curing mechanism and to interpret the level of impact of factors such as temperature and time on the curing of FBMs. The effect of these factors on curing was evaluated with reference to stiffness gain and water loss of FBM specimens. The second phase was intended to develop a tool to assess in-situ curing of FBMs. With a view to assessing in-situ strength (or stiffness) the applicability of the maturity method, which is commonly used to estimate in-situ compressive strength of concrete before removal of formwork, to FBMs was evaluated. A strong correlation was found between maturity and the stiffness values obtained from the laboratory tests which resulted in development of maturity-stiffness relationships. The application of the method to assess the in-situ stiffness was presented using three hypothetical pavement sections. The results illustrate the influence of ambient temperature and the importance of cement addition to FBMs