The use of Sardinian granite by-products from the Sarrabus Gerrei region to be used in road pavement layers

In Sardinia abandoned granite by-products stockpiles deriving from different excavation and processing methods are becoming an environmental and economic concern. Currently, these materials derive mainly from the ornamental quarry industry, very active in the region since late 1900’s, but also from civil engineering works consisting of tunnels, dams and other excavation projects. The storage of granite by-products in such great amount and for long periods produces damage to the environment, in terms of alterations of the landscape that can be temporary but in several cases permanent wen waste deposits become part of the landscape surrounding, subtracting large extensions of land to more important purposes such as agriculture. Also there is the visual and air pollution problem due to the suspension of fine particles in the air that these materials can produce when exposed for years to environmental climate conditions. The possibility of using of such materials that are already been extracted and that for them energy and therefore CO2 emissions has already been spent, would decrease the use of other natural aggregates that have yet to be excavated instead. Reducing the exploitation of non-renewable natural resources and limiting consumption of energy and CO2 emissions. In order to limit and in some cases solve some of these problems this thesis takes in to account the possibility of using granite by-products for road construction purposes. The possibility of using these materials, that in many cases are considered a waste, as a valid alternative to other aggregates that normally are used in pavement layers could decrease road construction costs. In this research granite by-products from the Sarrabus-Gerrei region were studied to evaluate the physical and mechanical properties to assess the possibility of using them to their fullest extent in both unbound and bound pavement layers. Three types of granite byproducts deriving from the same mother rock but subjected to different processes were studied. Two resulting from: Drill and Blast (D&B) and Tunnel Boring machine (TBM) excavation methods. The third material was obtained from the crushing of the larger blocks obtained during D&B excavation. The work reported herein describes test conducted in order to determine the best suitable application according to the type of layer in which use such material, evaluating the possible variations in terms of physical and mechanical characteristics that granite by-product performed when subjected to different processes. A preliminary characterization was conducted evaluating the environmental compatibility of such materials, based on Italian regulations on the use of excavated earth and rocks. The results of such tests were important to assess and determine the possible application in road pavement layers. Firstly, unbound layers were studied, analyzing aggregate properties and performing tests on different mixes. Particular attention was given on the bound layers were both hydraulic and bitumen binders were studied. Soil-cement mixes were prepared using different percentages of Portland cement performing different. Then Hot Mix Asphalt (HMA) samples were analysed in order to evaluate the affinity between granite and bitumen. Difficulties were emerged using this type of aggregates in HMA layers due to adhesion problems between granite and bitumen. Stripping tests were performed and also attention was focused on the adhesion phenomena. In order to better understand such phenomena and evaluate and measure potential parameters, digital image processing was conducted. Good values for the unbound layer, in which granite by-products were tested, were measured. Furthermore, the use of such materials for cemented treated layers was evaluated obtaining as well good results.