A.A. Cuadri

End-performance evaluation of thiourea-modified bituminous binders through viscous flow and linear viscoelasticy testing

Straight-run bitumens are no longer suitable in new asphalt mixtures. Consequently, the use of modified bitumens has become more important. In order to both improve binders’ mechanical properties and prevent it from phase separation whilst stored at high temperature, the paving industry is currently developing new modification routes based on reactive agents. This work studies the use of thiourea, which has proven to efficiently broaden the temperature interval over which the binder demonstrates an adequate performance. On the one hand, viscous flow and dynamic shear tests indicate an enhancement in the high in-service temperature strength, along with a reduced thermal susceptibility. On the other hand, results of dynamic flexural tests reveal a significant decrease in the binder glass transition temperature. Finally, the use of master curves and a further frequency/temperature conversion are proposed, in order to attain a suitable viscoelastic characterisation of bituminous binders at low temperatures.

The Effect of Carboxyl Group Content on Water Uptake Capacity and Tensile Properties of Functionalized Soy Protein-Based Superabsorbent Plastics

This manuscript studies the relation between macroscopic properties of the soy protein isolate (SPI)-based superabsorbent polymers (SAP) (e.g., water uptake capacity and tensile properties) and the extent of chemical modification conducted on the protein. The increase in the carboxyl group content, obtained from electrometric titrations, for acylated systems compared to native SPI brings with it an improvement in the protein hydrophilic character, as revealed by the determination of the water imbibing capacity. SEM images show that larger porous regions were developed in the acylated plastics. As for their mechanical properties, static tensile measurements indicated that acylated plastics with greater water uptake values display higher extensibility, compared to the reference sample. These natural-based SAP materials could be appropriate for applications in which maintaining the dimensional stability during service is not crucial (e.g. in agriculture and horticulture).

New foamed/modified bitumen using phosphogypsum waste

This paper describes a new alternative way to produce foamed bitumen, by using phosphogypsum wastes (PG), which is also able to enhance the mechanical behavior of the resulting binder. PG waste is generated worldwide from the production of phosphoric acid and deposited in stacks, causing environmental problems. The results obtained point out that the addition of 10 wt.% PG to a 35/50 paving grade bitumen, when activated with a small amount of strong acid, results in a foamed bitumen with enhanced the rheological properties, especially at high in-service temperatures, after foam collapses. This is mainly attributed to the existence of chemical reactions involving phosphorus compounds contained in the PG, forming new chemical links with some bitumen molecules. Another positive aspect of this technology is that this method produces more stable bitumen foam if compared to the traditional processes, i.e. through direct injection of water. Thus, the combined effect of temperature and the activation agent (sulphuric acid) gives rise to dehydration of the structural water contained in PG yielding foamed bitumen.