The use of additives to supplement or replace cement in concrete is a well-studied topic. The use of fibers, polymers, minerals, and even nanomaterials has been considered for improving concrete properties such as permeability and strength, and these issues are constantly under investigation. In this study, the mechanical properties and permeability of concrete containing calcium carbonate (CaCO3) nanoparticles and fly ash are investigated. For this purpose, concrete specimens with different proportions of nanoparticles and fly ash were prepared and aged for 7 days and 28 days to investigate the mechanical properties via compressive strength tests, tensile strength tests, and flexural strength tests under three-point loading and also to study the permeability properties via full water absorption tests and the testing of penetration depth under water pressure. To determine the distribution of nanoparticles and their size and microstructure, scanning electron microscopy (SEM) images were obtained, and energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses were performed. The results show the positive effect of CaCO3 nanoparticles in filling concrete pores, which leads to increased strength and reduced permeability. In general, the SEM images and EDS and XRD analyses showed that there was a good correlation between the materials used in the concrete and also that the nanoparticles were appropriately distributed in the concrete samples.

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Abstract-With regard to the importance of road accidents and the resulting costs, which include human, economic and social losses, the study and modeling of road accidents will be inevitable in identifying the causal factors of accidents. This article analyzes the construction of a model for the severity of fatal road accidents taking into account of the characteristics of the driver, motor vehicle, road and the environmental conditions of the roads of the country. In order to construct the accidents severity model, the Logit function of fatality likelihood is used. The function's output varies between zero and one. As the output becomes closer to one the likelihood of fatality will be more, and as it approaches the zero the likelihood of fatality will come down. In such models, such factors as elderly drivers, the existence of motorcycles and bicycles, inattention to the front, exceeding the authorized speed, unauthorized deviation to left due to overtaking, passing unauthorized place, illiteracy of drivers, etc. will increase the severity of accidents, and such factors as clear weather, standard road width, etc. will decrease fatal accidents. The factors are discussed in detail in this article.Index Terms-Road accident, highways, logit model, accident indexes.

Compared to the motorway network, rural and urban roads are very unsafe. Advanced Driver Assistance Systems can be used to increase traffic safety, thereby improving the conditions for effective deployment of the underlying network for integrated traffic management. In this study, we have identified ADA systems that are expected to have a high impact on traffic safety by coupling characteristics of accidents to the functionality of different ADA systems. Based on the results of this study, Intelligent Speed Adaptation (ISA) and Intersection Crash Avoidance systems appeared most likely to substantially improve the safety on nonmotorway roads. ISA was selected for further analysis due to the likelihood of its near future introduction. Microscopic simulation model was used to quantify the impacts on traffic safety for an urban highway with controlled intersections near the south of Tehran metropolitan. Depending on the penetration level, the results of the simulation study showed that the decrease in the total number of accidents ranges from 4% to 19%.