During road construction, granular materials for the unbound base course (UBC) and cement-bound base course (CBC) are mostly compacted by vibratory rollers. A widespread laboratory test for determining the optimal moisture content (OMC) and maximum dry density (MDD) of the mixture for installation in UBC and CBC is the Proctor test. Considering that the Proctor test does not produce any vibrations during compaction, this paper compares the Proctor test and the vibrating hammer test. The examination was conducted on UBC and CBC with varying cement content and aggregate types. All mixtures were compacted by both methods with the aim of determining the compaction and strength characteristics. The results indicated the high comparability of the two test methods for mixtures with natural aggregate in terms of MDD, OMC, density and strength characteristics (California bearing ratio (CBR) for UBC and 28-day compressive strength for CBC). For mixtures with higher cement content, the OMC difference depending on the laboratory compaction method used can be significant, so the laboratory compaction method should be chosen carefully, particularly for moisture-susceptible materials. This paper also reveals that by increasing the proportion of rubber in the mixture, the compaction and strength characteristics differ significantly due to the compaction method. Therefore, when using alternative and insufficiently researched materials, the compaction method should also be chosen carefully.

This paper aims to assess the influence of clogging on paving material (pervious concrete) drainage characteristics as well as the influence of the properties of an unbound base layer on drainage characteristics of the whole paving system. The clogging influence has been studied measuring the drainage characteristics on pervious concrete flags before and after their clogging, according to ASTM C1701-09. Additionally, the drainage characteristics of uncontaminated pervious concrete as a paving material was assessed using the falling head method. To assess the influence of properties of an unbound base course (UBC) on drainage characteristics of the whole paving system, the unbound base layer was compacted in two different levels of compaction and the drainage characteristics were measured (according to ASTM C1701-09). It is concluded that pervious concrete prepared with a smaller aggregate fraction is more prone to clogging. Regarding the influence of UBC, it is important to find a balance between pervious concrete infiltration and UBC exfiltration rate, particularly in a case of pervious concrete flags made of coarse aggregate.

Road construction relies on natural material exploitation and it is necessary to find new ways of reducing its negative environmental impact. Simultaneously, number of tyres placed on Croatian (and world) market is constantly growing and the need for waste tyres management will begin to increase due to the wear and tear of tyres in use at the moment. This paper presents a review of latest international and domestic researches on waste rubber application in road construction with special emphasize on Croatian researches within this topic. Preliminary results of ongoing research on waste rubber application in cement bound mixtures are also presented.

Crumb rubber (CR) obtained from end-of-life tyres (ELT) has gained significant attention in the sustainable design of asphalt pavements in recent years, showing a promising perspective in the enhancement of pavement performance related to its structural and functional properties. Existing research on CR influence on pavement performance mostly focused on peculiarities of asphalt mixture modification procedures—dry and wet processes, CR content in the mixture and CR particle size. In this study, a laboratory-based experimental investigation of CR effect on two different mixture gradations, namely dense-graded and gap-graded mixtures with three different binder contents, was performed. CR was added in mixtures through binder modification, with a constant CR content of 18% by binder weight in all mixtures. Volumetric properties—maximum mixture density, bulk density and void characteristics, alongside mechanical properties determined by the Marshall test method—were determined on unmodified and modified mixtures. The goal was to evaluate the influence of CR modification with respect to three different binder contents. The results showed that gap-graded mixtures are more sensitive to change in CR modified binder content in comparison to dense-graded mixtures in terms of air voids content. Furthermore, the mechanical properties of CR-modified mixtures were slightly enhanced in gap-graded mixtures, showing a promising potential of CR modification for pavement performance. However, the choice of optimal binder content in CR-modified mixtures was shown to be a critical mixture design parameter due to the increased sensitivity of binder content change to the analysed voids properties and permanent deformations.

The high stiffness of cement-bound aggregate (CBA) is recognized as its main drawback. The stiffness is described by the modulus of elasticity, which is difficult to determine precisely in CBA. Incorporating rubber in these mixtures reduces their stiffness, but mathematical models of the influence of rubber on the mechanical characteristics have not previously been defined. The scope of this research was to define a prediction model for the compressive strength (f_c), dynamic modulus of elasticity (E_dyn) and static modulus of elasticity (E_st) based on the measured ultrasonic pulse velocity as a non-destructive test method. The difference between these two modules is based on the measurement method. Within this research, the cement and waste rubber content were varied, and the mechanical properties were determined for three curing periods. The E_dyn was measured using the ultrasonic pulse velocity (UPV), while the E_st was determined using three-dimensional digital image correlation (3D DIC). The influence of the amount of cement and rubber and the curing period on the UPV was determined. The development of prediction models for estimating the f_c and E_st of CBA modified with waste rubber based on the non-destructive test results is highlighted as the most significant contribution of this work. The curing period was statistically significant for the prediction of the E_st, which points to the development of CBA elastic properties through different stages during the cement-hydration process. By contrast, the curing period was not statistically significant when estimating the f_c, resulting in a simplified, practical and usable prediction model.

Digital image correlation (DIC) is a method of point displacement measurement by an optical system. If two cameras are used for capturing the same point displacement, three-dimensional data are obtained using the 3D-DIC method. The areas of application of this method in pavement construction are diverse, but it is mainly used for displacement monitoring during standard tests of the failure of specimens due to load application. Furthermore, DIC technology was used only for testing particular material characteristics and assuming their influence on the overall pavement system. Within this research, DIC was applied in two areas: defining material mechanical characteristics and analyses of pavement structure behaviour under cyclic loading. The scope of this research was to gain more insights into DIC’s potential application within pavement behaviour analyses, specifically on cement-bound granular material (CBGM) characterisation. Results from this study confirm the suitability of 3D-DIC technology for pavement material characterisation. Furthermore, it is shown that certain trends of material behaviour defined on the simple material level of each independent pavement layer will significantly differ when it is placed in the system, and this kind of complex analysis is possible by using 3D-DIC technology.