Giacomo Betti

Preliminary In-Situ Evaluation of an Innovative, Semi-Flexible Pavement Wearing Course Mixture Using Fast Falling Weight Deflectometer

In the last forty, years semi-flexible pavements have been successfully employed, especially in those areas subjected to heavy and slow-moving loads. They usually comprise a wearing course of Grouted Macadam, a composite pavement material that provides significant advantages in comparison to both concrete and asphalt pavements. On the other hand, the laying process of this material is a two-stage operation, and the realization complexity leads to long realization times and high initial costs. Therefore, the use of semi-flexible pavements has been limited to some fields of application and areas. Recently, an innovative material has been developed to be used as an alternative to Grouted Macadam for semi-flexible pavement wearing course realization. This material should provide similar or even superior characteristics compared to traditional Grouted Macadam. This will reduce semi-flexible pavement construction time and avoid the need for dividing the laying process. This paper presents an experimental program involving the use of FastFWD, as an APT device, to evaluate in-situ properties and performance of this material. The achieved results regarding the validation of this new material by means of FastFWD appear promising both in terms of the material’s properties and resistance to dynamic load repetitions.

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.

Active filler’s effect on in situ performances of bitumen emulsion recycled mixtures

This paper address the in situ performance over time of different bitumen emulsion stabilized mixtures blended with different types of fillers (cement, lime and mineral filler), monitored during the first year from construction. Results are part of a more extensive research program aimed to investigate the effects of using lime as active filler in cold recycled mixtures, both with bitumen emulsion and foam bitumen. A specific test track has been designed on a construction road near Florence in order to evaluate the evolution of mixture performance over time. Short term bearing capacity has been evaluated by means of LWD (Lightweight tests) after 4 h from compaction while FWD tests have been performed after 24 h, 14 days, 28 days and 9 months to monitor the mid-term performances. Up until mid-2014 tests road was not yet opened to traffic so the mixtures experienced only construction traffic loads. Results obtained positively support the use of lime as active filler in the bitumen emulsion stabilized material and underline the effect of different blends of fillers in the material behaviour. 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.

Effect of active fillers on cracking performance of bitumen-stabilised materials

A laboratory investigation was conducted to evaluate the effect of active fillers on the cracking resistance of bitumen-stabilised mixtures. Nine types of stabilised mixtures composed by 100% recycled aggregates, different blends of fillers (cement, lime and common filler) and bitumen emulsion or foamed bitumen as stabilising agents were used to build three consecutive experimental sections on a constructing road. Cores of the trial sections were tested in a laboratory according to a Superpave Indirect Tensile Test (IDT) procedure developed for quasi-brittle materials. An in-house-developed Digital Image Correlation (DIC) software code was applied. The results show the benefit of the active filler to the mixture’s cracking resistance in terms of increased tensile limits to failure. Significant damage has shown to be strongly more localised in mixtures containing active fillers. Among all the blends, the more promising blend combination consists in 1% of cement, 2% of lime and 1.5% of traditional filler.

Subgrade and Foundation Dynamic Performance Evaluation by Means of Lightweight Deflectometer Tests

Evaluation of the in situ bearing capacity of subgrade and foundation layers is carried out by means of enhanced dynamic testing devices such as the lightweight deflectometer (LWD). These devices offer many practical advantages over traditional plate load tests and allow simulation of real conditions of loads induced by heavy vehicle traffic. Devices provided with a load cell and a geophone can acquire load–deflection time histories, sampling data every 0.25 ms, with a high level of accuracy. LWD data are used mainly to calculate the surface modulus of the tested materials with the Boussinesq equation; procedures specifically developed for estimating the material compaction level achieved on-site are coming into use. This paper focuses on the use of the LWD for investigating the performance of subgrade and foundation layer materials for stiffness (bearing capacity) and compaction achieved. Great effort has been devoted to improving deflectometric tests, correlating energy loss (energy spent to deflect the tested surface, determined as the area enclosed by the load–deflection graph) to the performance of tested materials, especially for compaction level achieved on site. The influence of load frequency is evaluated and described. The results, obtained at two trial fields, confirm the reliability of the LWD in roadwork quality control and for a staged design approach to earthworks.