The aim of the research was to evaluate the properties of foamed bitumen, produced from a Fischer–Tropsch synthetic wax modified 50/70 penetration grade bitumen for use as a binder in road construction layers. The binders were subjected to conventional tests (including penetration, softening point, Fraass breaking point and dynamic viscosity) as well as bitumen-foam-specific testing (including expansion ratio, half-life and foam index at different foaming water contents). Optimum amounts of foaming water and Fischer–Tropsch wax were identified and the binders were classified as relevant for different low-energy bitumen mix production techniques

The paper presents the results of laboratory testing of the physical and mechanical parameters of the recycled material using the foamed bitumen and resistance to the action of water. The tests were performed on the mineral recycled base mixes with foamed bitumen, in which the material from the existing pavement layers was used. The effect of two kind of binding agents (foamed bitumen and Portland cement) was evaluated. The bitumen binder was added to the recycled material in the amount of 2.0% to 3.5%, and hydraulic binder of 1.0% to 2.5% with steps every 0.5%. The effects of different binder materials contents on the air void content, Marshall stability and resilient modulus at temperature 25°C of the recycled mixes were investigated. Moreover, the detrimental effect of water was measured by comparing indirect tensile strength (soaked and unsoaked) and determine tensile strength retained of foamed bitumen mixtures. The results were subject to the optimization process. This allowed to state that if 2.5% foamed bitumen and 2.0% of Portland cement are used, the recycled base course has the required physical and mechanical properties and moisture resistance

Current regulations regarding emissions, as well as the efforts focused on reducing energy intensity of building materials production create a need for implementing new road construction technologies. Particular attention is being paid to the lowering of asphalt concrete production temperature, which is about 160°C. In response to this need warm mix asphalt (WMA) technologies have been developed which allow producing asphalt mixes at temperatures about 20–30°C lower than those of conventional methods. However, it was only after half warm mix asphalt (HWMA) was introduced that the mixing temperature of asphalt concrete with foamed bitumen could be reduced by as much as 60°C. Asphalt pavements constructed with HWMA may have a reduced service life and lower resistance to environmental factors (e.g. water). This paper presents the results from the tests with one freeze cycle and from the moisture sensitivity analysis conducted for the low-temperature asphalt concrete (AC 8) with foamed bitumen and the control mix produced according to conventional hot mix asphalt technology. It was found that the modification of 50/70 bitumen (before foaming) with the addition of 2.5% FT synthetic wax had a beneficial effect on the properties of asphalt concrete mixes under investigation. The ITSR indices were compared having been determined in accordance with procedures based on European and AASHTO standards that are widely used in Poland. The analysis was extended to include the compactibility evaluation of low-temperature bituminous mixes and the impact of air voids on the mechanical parameters. The foamed asphalt concrete modified with 2.5% FT wax was found to satisfy the requirements for moisture resistance determined during the test with one freeze cycle

Hot-mix asphalt (HMA) remains the predominant material for pavement surfacing. Mixing is performed at about 180 °C, depending on the bitumen used. Environmental concerns in terms of emissions and energy demand are fostering new sustainable technologies in road construction. Warm-mix asphalt (WMA) and half-warm-mix asphalt (HWMA) mixtures meet current expectations in that they are produced at lower temperatures, 100–130 °C, ensured by foaming the bitumen with water. The extent of temperature reduction requires that the mixture has adequate moisture and frost resistance, which is particularly important in countries that have a low-temperature climate. Asphalt concrete AC 8 S with 50/70-grade foamed bitumen modified with 0.6 wt.% surface-active agent (SAA) was used in the tests. To provide the AC mixture with the required resistance to climatic factors (water, temperature below 0), hydrated lime was added at 0, 15, 30, and 45 wt.% as limestone filler replacement. The influence of the hydrated lime addition on the air void content and resistance to moisture and frost damage was investigated according to the WT-2 2014 methodology based on EN 12697-12: 2008 and to the modified AASHTO T283 method. The optimum content of hydrated lime for filler replacement was determined through statistical analysis of the test results. With the optimum hydrated lime replacement of 30%, the required level of moisture and frost resistance of HWMA concrete with foamed bitumen is achieved. The results of this study confirmed the suitability of HWMA concrete with foamed bitumen for application in road construction practice.

The paper presents an approach for identifying the optimum range of foamed bitumen and Portland cement contents in recycled mineral-bitumen road base mixtures using simultaneous optimization of response variables (i.e. properties of mixtures estimated from statistical models) with the use of desirability functions. The 16 evaluated mixtures had a common aggregate composition comprising materials from existing pavement layers (reclaimed asphalt pavement and aggregates from recycled crushed stone base layer) and virgin material. The mixtures varied in foamed bitumen contents (2.0% - 3.5%) and Portland cement contents (1.0% - 2.5%). The investigated mixture parameters included: air void content (Vm), indirect tensile strength (ITS), tensile strength retained (TSR) and indirect tensile stiffness modulus (ITSM) at 25°C. The use of the desirability functions and desirability index allowed to identify the effective and optimum range of binding agent dosing for the recycled mixture with respect to all of the measured mixture properties

To ensure the standard properties of half-warm asphalt (HWA) mixes produced with foamed bitumen, the binder needs to have the best possible characteristics. One way to attain this is to modify the bitumen before it is foamed. The 50/70 penetration bitumen used in this study, was modified with a surface active agent (SAA) at different rates (0.2%, 0.4%, and 0.6% by wt.). The effect of the modifier on the bitumen properties (penetration, softening point, the Fraass breaking point, dynamic viscosity at 60 °C, 90 °C, and 135 °C) and on the binder foaming parameters (expansion ratio - ER, half-life - HL, foam index - FI) was investigated and the optimum quantity of foaming water was determined. Statistical analysis of the results showed that the addition of 0.6% SAA had the most beneficial effect on the set of 50/70 bitumen standard properties and foaming characteristics.