1,721,170 research outputs found
Porous concrete road pavements: analysis of noise emissions and applicative implications from the standpoint of both active safety and freeze and thaw cycles resistance
No full textStarting from previous studies carried out by the same Authors, this research is focused on the definition of the optimal mix design of a road pavement made of new draining porous concrete. An accurate experimental investigation performed on different real-scale laying allowed the Authors to assess a series of structural and superficial characteristics of the road pavement above mentioned, so as to appreciate all its positive aspects, the perfectible ones being, in any case, highlighted. In particular, apart from dealing with the mechanical strength of the structural elements against the passage of heavy vehicles and from assessing such parameters as superficial texture, permeability and porosity, the measurements were concentrated on the behavior of the elements themselves in case of very severe winter environmental conditions, with a special interest for freeze and thaw cycles as well as for the use of de-icing salts. Furthermore, a special care was dedicated to the analysis of noise emissions connected with these new pavements, the measurements being taken by means of appropriate apparatus. In addition, the research assessed the advantages from the standpoint of users safety belonging to the utilization of this structural elements: not only the spray, splash, aquaplaning and light reflection phenomena are dramatically reduced, but a significant decrease in the braking distance is observed for both dray and wet conditions. Therefore, thanks to these remarks, the Authors believe that this innovative road pavements, if the perfectible aspects were faced, could be regularly used with positive implications for both users safety and environment protection
Asphalt concrete pavement reinforcement through the addition of micro-fibres and steel meshes
No full textNowadays the deterioration of the asphalt concrete superstructures is a critical problem in the area of road construction. More specifically, the causes of the degradation can be addressed to the increase of traffic, of axle loads and/or to the use oflarger wheel paths, the influence of the thermal stresses being also important in this negative phenomenon. Form this standpoint, there is a wide diffusion of the so-called "macro-reinforcement techniques ", which have recourse to both different dimensions fibres and meshes inside the asphalt concrete wearing course. So as to assess the real benefits belonging to the application of these techniques, this study is focused on the flexural analysis of traditional and reinforced asphalt concrete specimens by means of the "Three Point Load Apparatus ". the reinforcements used for the process varying. Afterwards, starting from the results obtained from constant strain load tests, some specific parameters taken from the theory of steel fibre reinforced concrete, and accurately adapted for the purpose, were defined; their use allowed the Authors to clearly identify the post-crack resistance of the reinforced asphalt concrete specimens. In conclusion, knowing the load, the deflection and the first-crack toughness, thanks to the comparison of the "toughness indices" and of the "residual strength factor", a classification of the different typologies of reinforcement has been performed identifying, amongst them, the ones whose mechanical performances are more reliable from the viewpoint of the flexural resistance
Design of ports and interports high durability rigid pavements
No full textThe application of severe loads on stocking areas pavements sometimes brings to the onset of stresses which are unforeseen at the design stage. These unexpected tensions can jeopardise the life cycle of the structure and, to certain extents, give origin to cracks which, if not promptly faced, might cause the loss of the mechanical characteristics of the superstructure. Inasmuch this is a pivotal aspect in road design, in this paper the Authors tackled the theme of the dimensioning of rigid pavements for stocking areas. This aspect, faced through the finite element analysis, considers the application of severe loads belonging to different kinds of containers, along with the stresses generated by the straddle carrier, which is the equipment for the movement and the handling of such heavy and cumbersome elements. The analysis of the different loading areas showed that the wheeled vehicle is responsible, during the handling manoeuvres, for the highest stresses in the structure. Having found this, the Authors dimensioned the different concrete pavements, considering several load conditions and defining the solution which is the best cost-performance compromise, with respect to both durability and mechanical performances required. From this standpoint, eventually, the use of steel fibres to enhance the mechanical performances of the pavements was taken into account
Plastic shrinkage reduction in concrete pavements due to the addition of both steel and polymer modified fibers
No full textEarly shrinkage due to quick drying immediately after pouring is one of the most dangerous phenomenon influencing both performances and durability of concrete pavements in service. At the Laboratory of Roads Construction of the University of Basilicata-Potenza, this aspect was faced by simulating the conditions normally experienced after casting a concrete pavement in a severe environmental surrounding: high temperature and strong wind were indeed considered. Plain and fibre-reinforced concrete elements were tested, the results being therefore compared in order to assess the improvements of performances due to the addition of fibres to the paste. According to the kind of fibre (steel or polymer modified) and to the dosage adopted, different situations were found from the viewpoint of number and width of cracks and both weight and length variation of the elements. The laboratory experiments drove to significant consideration on fibre reinforced concrete pavements, allowing the writers to make a clear comparison amongst the different kind of fibres used: indeed, the behaviour of pavements changed with type (steel or polymer modified), dimensions (length and aspect ratio) and dosage of fibres. The results explained that the longer the element, for steel fibres, and the higher the dosage, for polymer modified elements, the better the performances from the standpoint of plastic shrinkage damages
Resistance of plain and fibre-reinforced concrete road pavements to penetration of de-icing salts
No full textSeveral concrete pavements have been tested at the University of Basilicata in respect of the effects of de-icing salts. These are frequently used in winter on motorways and other roads. The Investigation was specifically concerned with areas where humid conditions are experienced and where pavements are subjected to at least 15 freeze/thaw cycles a year
Assessment of hand involvement in systemic sclerosis by ultrasonography : comment on the article by Elhai et al
No full textConcrete pavements reinforced with polymer-modified and steel fibres
No full textThis project dispels some of the prejudices surrounding the use of micro-fibres in concrete, in particular, that they are secondary reinforcement. Adding PMF fibres significantly increases material toughness
Superficial characteristics and mechanical strength assessment of a wearing course made of new porous concrete
No full textThe use of concrete for road pavements in Italy is still relegated to few applications, especially for those situations where a significant bearing capacity as well as high mechanical characteristics are required. On the contrary, bituminous binders are widely employed for such pavement structures for which excellent performances from the standpoint of smoothness and both drainage and noise reduction are expected. As a matter of fact, this research tried to study a porous concrete wearing course which would guarantee a good behaviour from the point of viewof rainfall water drainage, the outstanding mechanical performances of rigid pavements being in any case not jeopardised. Therefore, the authors made an effort in verifying how, for concrete pavements, both micro and macro texture could be manipulated, starting from the mix design, in order to achieve the above mentioned superficial characteristics. For this purpose, different measurements were performed on several self-made laboratory porous concrete pavements assessing micro and macro roughness of the surface, and the results were compared to the outcomes of similar structural elements made of stone mastic asphalt SMA, and of draining flexible pavements; furthermore, porosity and permeability of the new material were investigated also. Last but not least, as a porous concrete could tend to crumble because of the reduced compactness of the matrix, compared to ordinary concrete, the mechanical properties of such structural elements were assessed also. In particular, compressive strength and impact resistance tests were performed on some porous concrete, plain concrete and SMA specimens, so that any decrease or increase in the performances could be monitored. The outcomes were impressive, and they gave the proof of the fact that both knowledge and techniques on concrete pavements matters are increasing more and more, most of the prejudices about these structural elements being now anachronistic; the more researchers get into this matter, the higher the safety for users, and the large use of concrete pavement structures in many foreign countries is the evidence of the
outstanding performances of this material
Noise emission comparison between porous concrete and porous asphalt road pavements
No full textIn this investigation the Authors developed a particular grading curve for the manufacture of a porous concrete road pavement and assessed the noise emission due to vehicles tyres rolling belonging to its use. In fact, this innovative superstructure, apart from guaranteeing excellent superficial characteristics from the standpoint of grip and rainfall discharge, allows an increase in the users safety, especially in case of severe meteorological conditions, because of the reduction of the phenomena of aquaplaning, splash, spray and lights reflection. In addition, the high material porosity involves a reduction in the noise emissions belonging to vehicles tyres rolling. Therefore, so as to assess the real drop of noise emissions connected to the use of such superstructures in an urban environment, some real scale pavements were manufactured, both with ordinary and porous concrete, the results being outstanding for the latter. Furthermore, in order to get an additional validation of the results obtained, a traditional and a twin- layer draining and noise reducing asphalt pavement were laid, both of them being considered as the state of the art on this matter; a typical bituminous pavement was also investigated from the same standpoint during the research. This comparison showed the high performances of the porous concrete superstructure, the results of all the draining pavements having the same order of magnitude. Thus, the Authors reckon that the investigation on porous concrete road pavements should be improved further by researchers, and it would be worth to issue some Standards which would control the innovative material characteristics as well as its manufacture exactly in the same way it usually happens for asphalt superstructures
Skid resistance of porous concrete: an overall comparison with stone mastic asphalt pavements
No full textThe problems connected with the bad surface characteristics of a road pavement have significant consequences on users safety, most of the times the car drivers being not always totally responsible for the car accidents caused. In case of sever rainfalls, splash, spray and aquaplaning phenomena due to poor surface conditions of the road infrastructure severely reduce visibility as well as the overall safety. These aspects have been successfully faced by porous asphalt and Stone Mastic Asphalt (SMA) pavements, while no remedies where found for concrete pavements from this standpoint. At the Laboratory of Roads Construction of the University of Basilicata (Potenza, Italy), special mix designs were studied in order to find out the best recipe for rigid pavements which could give good results from the point of view of both micro and macro texture, the overall draining performances being at the same time improved. After carefully selecting, amongst the others, the mix which better combined these aspects, several measurements on the skid resistance of the surface were taken by means of the British Pendulum and the sand height method. Hence, the results so found were compared to the outcomes belonging to a usual SMA pavement, the conclusions being impressive: as for the test above mentioned, the authors found that excellent surface characteristics were found, the initial gap existing from this point of view between flexible and rigid pavements being therefore almost filled. Furthermore, the draining performances of the porous concrete pavements were outstanding and the resulting permeability was similar to the corresponding value of typical draining and noise reducing bituminous pavements
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