Abdullahi Ali Mohamed

Effects of Recycled Aggregates on Water-Cement Ratio for Concrete

Recycled aggregate differs from primary aggregate in that it constitutes of two types of materials: the primary aggregate and the attaching cement mortar. This study was conducted in order to investigate the effects on water-cement ratio for concrete cast with recycled aggregates derived from different origins (hollow blocks & structural concrete elements) and different mixed proportions of recycled aggregate contents. The outcomes of test indicate that higher water cement ratios are required for concrete cast with recycled aggregates as compare to those cast with primary aggregates. Also there appear no obvious relationships or consistencies that can be drawn among types of recycled aggregate.

Performance of asphaltic concrete incorporating styrene butadiene rubber subjected to varying aging condition

The influence of styrene butadiene rubber (SBR) on asphaltic concrete properties at different aging conditions was presented in this study. These aging conditions were named as un-aged, short-term, and long-term aging. The conventional asphalt binder of penetration grade 60/70 was used in this work. Four different levels of SBR addition were employed (i.e., 0 %, 1 %, 3 %, and 5 % by binder weight). Asphalt concrete mixes were prepared at selected optimum asphalt content (5 %). The performance was evaluated based on Marshall Stability, resilient modulus, and dynamic creep tests. Results indicated the improving stability and permanent deformation characteristics that the mixes modified with SBR polymer have under aging conditions. The result also showed that the stability, resilient modulus, and dynamic creep tests have the highest rates compared to the short-term aging and un-aged samples. Thus, the use of 5 % SBR can produce more durable asphalt concrete mixtures with better serviceability.

Design of Unbound Pavement Layer Materials Based Upon the Shakedown Concept

This study aims to introduce an alternative design method for unbound pavement layer materials based upon shakedown theory. The kinematic shakedown theorem that describes the ultimate response of an elastic/plastic structure to cyclic loads is used to predict whether stable behaviour in the unbound granular materials layer occurs or excessive rutting will develop. This method seeks the mechanism, from within a class of mechanisms that minimises the shakedown limit load for pavements consisting of layers of Mohr-Coulomb material obeying the associated flow rule. The basic concepts are outlined together with the most recent calculations of the critical design shakedown load. The influence of the of design parameters such as, the strength, stiffness and depth of the base-course material as well as the consequences of load distribution are discussed.