Effect of surfactants on the distribution of natural rubber latex in cement and geopolymer composites based on X-ray computed tomography

Abstract

The production of natural rubber latex (NRL) has increased significantly and its use, particularly in construction materials, has been promoted and studied. The presence of NRL in cement composites reduces crack formation and improves ductility. However, the incorporation of NRL in cement composites leads to coagulation of the NRL and fast setting; the use of a surfactant is recommended to avoid these problems. This study investigated two types of surfactant, an anionic surfactant (sodium dodecyl sulfate, SDS) and a nonionic surfactant (Tween 20). An NRL-fly ash geopolymers was also studied for comparison. The three-dimensional microstructure, including the pore and rubber distribution in the NRL composite, was investigated by X-ray micro-computed tomography (micro-CT). The test results show that both surfactants generate pores in the composites. The fine pore formation in the NRL geopolymer composite was found to be better than in the NRL-cement composite. In the NRL cement, Tween 20 generated 2.72% of pores by volume, which was slightly lower than the 3.05% generated by SDS. In the geopolymer system, fast setting of the geopolymer took place with Tween 20. A low pore percentage of 1.67% was obtained for SDS. The agglomerated NRL appeared in various shapes and sizes, particularly at the surface and corners of both NRL composites. A high level of agglomeration of NRL with a plate shape was found in the cement composite with SDS (anionic surfactant). A smaller NRL particle size and better distribution of NRL was found in the geopolymer compared with the cement composite. The results thus confirm that the surfactants can be used to disperse NRL in the cement and geopolymer composites.