Rut Resistant Asphalt Pavements
The author of this article examines the causes and potential cures of asphalt pavement rutting. He explains that rutting on the asphalt pavement surface commonly is the result of an unstable asphalt mix, heavy vehicle traffic, and high pavement temperatures. He notes that this type of rutting is often observed at intersections, bus stops, freeway off ramps, or under extreme loading situations on airport runways or dock loading facilities. He explains how an engineer can determine if rutting in the asphalt pavement surface is due to distress throughout the entire pavement structure or due to failure in the asphalt layer only. He suggests that asphalt mixes can be designed to resist rutting with the proper selection of materials, good construction practices, and use of appropriate mix design methods. Good compaction practices during construction will improve rut resistance by increasing the interlock of aggregate particles in the mix.
Presenting asphalt mixtures flow number prediction model using gyratory curves
Pavement permanent deformations due to lack of shear strength in mixture are a major reason of rutting. Any simple test to determine mixtures resistance to permanent deformation isn’t distinguished in the 1st level of SUPERPAVE mix design method and prevalent methods for evaluating mixture rut resistance are expensive and time-consuming. Two aggregate types, gradations, asphalt cements and filler types were used in this research to present a prediction model for rutting based on flow number. A mathematical model to estimate flow number of dynamic creep test was developed using model parameters and gyratory compaction slope. The model is validated using Neural Network and Genetic Algorithm and makes it possible to evaluate mixtures shear strength while optimum asphalt content is being determined in laboratory. So not only there is no need to expensive test instruments of rutting or dynamic creep but a remarkable time saving in mix design procedure is achievable.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.