In built up media (complex built environment), the materials are simultaneously exposed to a series of physical, chemical and microbiological stress factors that act synergistically with disturbing electromagnetic fields and cause material degradation - with consequences on the durability and safety in exploitation of buildings and installations. The main generative sources of disturbing fields (stray current generators) on built up media are railroads with DC or AC traction with various operating voltage and frequency, medium and high voltage overhead power lines and unbalanced currents from a three-phase power system. The generated stray currents cause destruction both in metallic elements of built structures (railroads, power installations) and in neighbouring constructions and installations (belonging to other administrations) with negative environmental implications.

The corrosion state of an underground metallic pipeline of �161 mm and 565 m length was assessed by specific electrical and electrochemical measurements. The investigated pipe, buried in 1997, was protected against corrosion by successive layers of bituminous material with a total thickness of 1 to 1.2 mm. The pipeline crosses three electrified railway lines (50 Hz - 28 kV), and then its route is approximately parallel to these lines; thus, the induced AC voltages between line and ground were calculated obtaining values between 4.05 and 7.1 Vrms, in good agreement with the values measured in the accessible points. The measurements regarding the insulation capacity against corrosion of the bituminous insulation, performed at one month and after 19 years of burial, showed an increase of the average cathode current density needed for obtaining the protection potential in the range �1.00 � �1.28 VCu/CuSO4 of approx. three times (from 6.65 up to 19.96 mA/m2), in good agreement with the evolution of the insulation resistance measured between the steel pipe (having a contact area with the ground of 270.5 m2) and a ground socket of 4 W, which decreased from 995 to 315 kW. Following the analysis and processing of the field collected data, it is considered that, by implementing a cheap cathodic protection system (without cathodic current power supply), based on the rectification of the AC induced voltage, the safe operation period of the investigated pipeline may be extended by at least 50 years.

The influence of fly ash adittion (90 % fraction [ 100 mm) on the cement mortar characteristics was studied. The XRD, XRF, SEM and FTIR determinations indicated that fly ash used has a hollow microstructure of microsphere and cenosphere whose total content in SiO2, Al2O3 and Fe2O3 is 88.63 % and that of CaO and MgO of 8.55 %. The mechanical, thermal and dielectric determinations made on mortar samples with content of fly ash in the 0-40 % range have highlighted fact that the mechanical strength of cement mortars is maximal at 20 %, the increase in fly ash content leads to a decrease in relative density and thermal conductivity as well as and to increased dielectric losses tgd.

In order to prevent incidents due to uncontrolled gas leakage and explosion/fires were devastating look at the factors that determine the safety in operation of gas networks made of polyethylene. Sustainability and safety in operation, lines of distribution networks and installations for use in natural gas represents a complex issue with implications for economic, social and environmental. Underground natural gas pipes are subjected to a series of prompts both static and dynamic which could lead to. damage. The complexity of the problems stemming from the diversity of stress factors acting on the related pipelines supply natural gas. In this context, the authors analyse the behaviour of pipelines under the effect of the stresses to which they are subject by using finite element modelling.

The structural and physicochemical changes that lead to the aging of the bituminous insulation of underground metallic pipelines were determined through various investigations (XRD, dielectric spectroscopy and thermal analysis � coupled techniques TG + DTA + DTG). The resistance to moulds of the bituminous insulation was evaluated by using specific microbiological methods and the dominant microbiological species found in the soil where the investigated bituminous material was exposed for 19 years were identified. The measurements carried out on samples taken from site showed that the bituminous material used in the anti-corrosive isolation of steel pipes has a very low resistance to microorganisms; thus, the dielectric qualities of bitumen deteriorate substantially (tg� increases 3-4 times). The exposure of the bituminous insulation to different climatic conditions and to solar radiation (UV-IR) leads to a decrease in the dielectric losses in the insulation and to an increase in crystallinity and thermo oxidative reactivity of bitumen, thus leading to a significant decrease in the material�s resistance to the action of fungi.