A study on resistance of asphalt concrete exposed to the effect of mycelial fungi

Introduction. In recent years, the issue of improving the quality and service life of road surfaces has been relevant in Russian and worldwide. The main reasons for the early destruction of road surfaces is the quality of individual components and the imperfect composition of asphalt concrete that has pre-set durability. The results of studies, characterizing changes in the roadway surface properties, are of practical value. In this case, we consider the surface hardness of asphalt concrete specimens of various types, subjected to microbiological destruction, which is the property to be studied. The purpose of the work is to study the microbiological resistance of various asphalt concretes, to select and substantiate methods for assessing the biological stability of asphalt concrete subjected to mycelial fungi. Materials and methods. Asphalt concrete specimens contain BND 60/90 bitumen that has the following characteristics: needle penetration depth 0.1 mm at 25 °С – 85; needle penetration depth 0.1 mm at 0 °С — 35; ring and ball softening point 0 °С — 48; extensibility — 83 cm; penetration index — 0.6. Mineral powder, glass cullet powder, and food flour are used as fillers. MP-1 inactivated mineral filler, made of carbonate rock, having the true and average density of 2.71 and 1.71 g/cm3, respectively, was also used. Glass powder was obtained by grinding the waste glass of JSC “Lisma”, Saransk. The chemical composition of glass waste is (in percent for weight): SiO2 — 68.75–72.90; Na2O — 11.9–16.7; K2O — 1.2–3.8; CaO — 5.0–6.0; BaO — 2.2–5.5; MgO — 3.2–3.8; Fe2SO4 — 0.1–0.12; Al2O3 — 1.0–1.5. Food flour was considered as an additive that serves as the nutritional medium for mycelial fungi. Some other components, added to the studied specimens of asphalt concrete, are discussed in the work. The studied property, or hardness, was identified using the Hoppler consistometer. Testing results are provided in the paper. Linear interpolation of experimental data was conducted to identify hardness at the intermediate points to rank the tested asphalt concrete, the standard error between the hardness curve during the exposure and the straight line for the same exposure points. The results of the proposed method are explained graphically using the experimental data. It is assumed that the smaller the root-mean-square error, the more resistant the corresponding composition of asphalt concrete to the effect of mycelial fungi. Results. As a result of the studies and the application of the proposed hardness control methods, the best compositions were identified in terms of resistance to the effects of mycelial fungi. Each group of specimens and compositions of asphalt concrete under study was broken down by their resistance to the effects of the external environment, or mycelial fungi. Conclusions. The results of this research project enable the authors to evaluate the quality of asphalt concrete compositions exposed to the biological environment. The proposed approach to assessing the quality of asphalt concrete compositions can be applied to other building materials and products subjected to certain aggressive media.