Warm-Mix Asphalt Using a Sodium Silicate as an Additive

One of the most widely used asphalt mixtures in pavements is hot-mix asphalt (HMA). During the manufacture and construction of HMAs, high temperatures are used, causing polluting environmental emissions and a large amount of greenhouse gases. One material that has great potential for use in supporting sustainable development in road projects is warm-mix asphalt (WMA). One of the techniques to decrease mixing temperatures (MTs) and produce WMAs is foaming. In the present study, sodium silicate (SS) was used as a water-bearing additive to modify and foam an asphalt cement (AC). Despite its wide potential for use in engineering projects and low cost, SS has not been investigated as a modifying additive in asphalt mixtures. SS foams AC at approximately 80°C. Initially, the evolution of the penetration and softening point of an AC modified with SS (SS/AC ratio=0.25%, 0.50%, 0.75%, 1.0%, 1.25%, and 1.50% by mass) was evaluated. With these tests, the optimum ratio SS/AC=1% was established. On the unmodified (SS/AC=0%) and modified (SS/AC=1%) AC, rotational viscosity, rheology characterization, and visualization in a scanning electron microscope were performed. An HMA (SS/AC=0%, MT=150°C) was used as a control mix. On this HMA and others produced with the modified AC and lower MT (140°C, 130°C, 120°C, and 110°C), tests were performed under monotonic loading [Marshall, indirect tensile strength (ITS), indirect tensile strength in dry condition (ITSD) indirect tensile strength conditioned (ITSC), and Cantabro]. The resistance to moisture damage was also evaluated by calculating the tensile strength ratio parameter (TSR) (TSR=ITSC/ITSD, in percentage). From this experimental phase, the WMA (SS/AC=1%, MT=125°C, 135°C) was defined and tested under cyclic loading (resilient modulus, permanent deformation, and fatigue resistance under controlled stress). Using SS as a modifier of AC, MT could be decreased between 15°C and 25°C, producing a WMA of better or similar performance compared to the control HMA.