Experiments on cold recycling with foamed bitumen or bituminous emulsion and cement

Throughout the world, cold recycling is a well-established and widely used process, in virtue of the technical-structural, ecological-environmental, economic and safety advantages that it offers. In Italy, although the necessary know-how exists for the technology to be correctly applied, it has seldom been used. Companies have thus found themselves carrying out applications, even important ones, abroad. This paper, describing the results of recent work of cold recycling of road pavements in Kosovo and Italy, comes within the wider context of theoretical studies and experiments conducted at the University of Padova, which are aimed at learning more about the mechanical and rheological characteristics of the materials used in cold recycling technology. The studied superstructures were similar in that there was serious degradation characterised by accentuated visco-plastic flow, with loose chippings and holes scattered all over the surface. For the rehabilitation work in situ recycling with foamed bitumen or bituminous emulsion and cement was used, a method that has attained good levels of reliability. The work in Kosovo, done on regional roads within the ambits of the rebuilding of infrastructures damaged during the 1999 war in the country, and those in Italy, on stretches of minor extra-urban roads in the Province of Vicenza, are characterised by the different depth and type of intervention. For the recycling, cement was used as binder (in amounts varying from 2.5 to 3%), mixed with water (from 2.5 to 2.8%) and 65% acid bituminous emulsion or foamed bitumen (doses from 3.7 to 4%). The indirect tensile strength tests carried out on samples of recycled concrete collected from the sites and compacted with a gyratory compactor demonstrated satisfactory performances, characterised by indirect tensile strength of up to 6.5 daN/cm2 in mixes with up to 6.8% voids. The paving was completed either with a multi-functional 0/20 mm mono-layer surfacing, with an average depth of 7 cm, or with a 0/15 mm bituminous wearing course approximately 4 cm deep on a 0/25 mm base course of 6 cm. The response of the pavements to vehicle stress was found to be fully acceptable.