# Waste Rubber-Modified Cement-Bound Base Course: Laboratory Characterisation and Field Application
## 1 Introduction  
The importance of essential functional road networks has been recognised since ancient Roman times. Traditional road construction relies on natural material utilisation and, even today, large quantities of stone, gravel, and sand are still built into kilometres of newly constructed roads. Road traffic is an essential means of transportation globally for passengers and inland freight transport. According to Eurostat [1], in 2022, there were 313 million motor vehicles registered in the EU and the motorisation rate surpassed 1 car per 2 inhabitants. Consequently, more than 3.5 million tons of end-of-life tyres (ELTs) were generated in 2019 [2]. This is a waste material that needs to be sustainably addressed. On the other hand, the European Commission's strategic plan outlined the creation of a sustainable transport area to reduce transport's impact on the environment as one of its specific objectives. From this, two objectives may be highlighted: making road construction sustainable and environmentally friendly, and solving the problem of ELT accumulation. With the increase in road traffic and heavy vehicle loads, the task of and requirements for pavement construction have become more demanding. A new trend in pavement construction is the use of new materials with enhanced resistivity to crack occurrence and prolonged service life. Waste rubber (WR), originating from ELTs, is frequently used in the asphalt industry, where its positive effect on the properties of modified asphalt is well known [3; 4; 5; 6; 7]. As a potentially limiting feature, its higher production cost is highlighted, ranging from 20 to 30% in comparison to the direct costs of conventional asphalt mixtures [5]. Used as a replacement for the fine aggregate fraction in cement-bound base courses, WR is known to reduce strength (both compressive and tensile) but improve strain capacity, toughness, and fatigue life, reducing the appearance of shrinkage cracks and the velocity of crack propagation [8; 9; 10; 11]. WR also improves frost resistance and the tensile-to-compressive strength ratio [12] and it can improve the deformation capacity and fatigue performance of cement-bound aggregate [13]. It improves strain capacity and possesses a lower propensity for cracking, owing to restrained shrinkage and improved sound insulation [11]. To improve the mechanical characteristics of cement-based grouting materials, a 2% concentration of silane coupling agent solution may be used for the surface treatment of waste rubber powder, improving toughness, volume stability, and strength. The solution improves the structural distribution and bonding characteristics of the interface between the rubber powder and cement particles [14]. Adding rubber may also reduce the thermal diffusivity, thermal conductivity, and specific heat capacity of the rubberised cement-stabilised base materials, with the potential to reduce both the temperature and temperature fluctuation within semi-rigid pavement structures [15]. In addition to extensive laboratory research, there will be a need for large-scale experimental and numerical models, as pointed out in [11]. The objectives of this paper are to present laboratory test results of WR-modified cement-bound mixtures based on the requirements set out for CBC construction, and to gain practical experience via a field application (a large-scale experiment). Numerical models dealing with the optimal WR-modified mixture from this research are presented in [16; 17]. The greatest advantage of using waste materials in road construction is the reduction in waste being disposed of in landfills. Furthermore, to repurpose waste materials for new applications, a certain amount of energy is required for processing. This typically involves mechanical treatment [18]. Specifically, rubber only requires mechanical processing, such as shredding, which is an established process that does not necessitate additional research or financial investment.