Global environmental policy contributes to the development and use of technologies that ensure the smallest possible energy consumption, reduced pollution and less environmental degradation [1
]. Many industry branches generate significant pollution due to the overproduction of by-products [2
]. Such processes include, for instance, the construction of roads, which involves many types of works related to the demolitibnbon of damaged pavements. Waste reduction is achieved through the use of recycling technologies [3
]. Common methods employed to re-use waste materials include deep cold recycling with foamed bitumen [5
] (MCAS) and bitumen emulsion (MCE) [6
The cold recycling technology assumes the construction of the road base with the use of materials from the demolition of old pavement structures. The process takes place at ambient temperature. Shredded materials from the waste in the form of a reclaim, are mixed with the addition of asphalt emulsion or foamed asphalt and a hydraulic binder. As a result, a new, load-bearing capacity of subbase is created while minimizing losses incurred for the purchase of new materials, transport and disposal of old ones. The entire process brings environmental benefits related to the reduction of production, emission of pollutants and energy consumption. Reconstruction of the roadway made in this technology allows for a quick improvement of operational parameters [8
The subbase made of the recycled cold mix can be manufactured in two ways, in the factory “In-plant” or on-site, i.e., “in-place” [9
]. To produce the mixture on-site, specialized recyclers are used, which enable the mixing of individual materials, including the old surface layers that have been crushed earlier. An exemplary in-place recycling facility is shown in Figure 1
At the beginning of the process, the seeder spreads the hydraulic road binder, which may be, e.g., cement, and the well-graded aggregate is subsequently distributed. The recycler, linked by a rigid line with a water cistern, and a cistern containing bitumen or slow decomposition emulsion, mix all the components of the new foundation. The emulsion is pumped straight into the drum. In the case of foamed bitumen, it is formed when the hot bitumen and water come into contact. Both materials are forced with special nozzles into the drum chamber. Cold water, due to contact with hot road asphalt, evaporates rapidly, causing bitumen foam. The binder coats the mineral particles of aggregate with the addition of cement, ultimately providing excellent material for the foundation. After passing the recycler, it is necessary to pre-compact with a steel-rubber roller, because the material is significantly loosened. Another device that is involved in the process is a grader that profiles a new foundation to a specific shape. This is followed by the proper compaction of the layer, using a steel-rubber roller with a smooth drum and a rubber-pneumatic roller, which compacts the whole [10
The second option is to make the foundation using delivered material, that is, transported to the section, from a special factory. A mixture of recycled materials, produced in cold technology in the factory, is placed on a properly prepared substrate. Here, the reclaimed material (with corrected grain size) is mixed with the binder. The advantage of this technology is greater accuracy of dosing ingredients and control of produced material composition. The prepared mixture is transported by self-unloading cars. It is placed along the length using a grader or paver. Next, the new foundation is thoroughly compacted with a set of road rollers. The entire procedure is controlled both by tests on the building site and in the laboratory. The foundation made this way can be covered with an appropriate package of bituminous layers, depending on the traffic load category. An exemplary in-plant recycling facility is shown in Figure 2
Studies have shown that the use of Portland cement in the recycled mixture results in an excessive increase in stiffness [6
], causing the base course to crack due to over-stiffening [11
]. That is why it seems necessary to look for a binder other than Portland cement that will ensure the primary physical and mechanical properties, reduce stiffness, and guarantee a long service life of the recycled base course.
2. Subject of the Test
The subject of the tests is the cold-recycled mixture (CRM). The tests concerned the assessment of the impact of binder type on the properties of the cold-recycled mixture containing two types of binders, i.e., foamed bitumen and bitumen emulsion, as well as Portland cement (CEM I 32.5R) and hydraulic binder. Foamed bitumen and bitumen emulsion were produced from 70/100 penetration grade bitumen for roads. The hydraulic binder was produced by mixing three base ingredients in the following ratio: 40% CEM I 32.5R; 20% Ca(OH)2
and 40% CBD (cement bypass dust). Binders for the test section were prepared on an industrial scale. The recycled mixture was prepared under industrial conditions using the “in situ” method [9
]. The base course layer is dedicated to traffic volume category KR3–4 (0.50 < ESAL100
≤ 7.30 million standard 100-kN axles) [12
The test section was located at an open-pit mine in Świętokrzyskie Province. This location makes it possible to fairly quickly determine the behaviour of the recycled base course with foamed bitumen and bitumen emulsion and with the dedicated binder under high-stress conditions.
The test section was divided into four parts; a diagram and division of the section are shown in Figure 3
. The equipment used to prepare the recycled base course under industrial conditions using the “in situ” method is shown in Figure 4
This way, it will be possible to unambiguously assess the quality of the produced mixture and draw conclusions regarding the impact of the type and kind of the binders on the properties of the cold-recycled mixture.