Combined effects of micro and nano Fe3O4 on workability, strength, packing, microstructure and EM wave absorbing properties of mortar

•Micro Fe3O4 and nano Fe3O4 used together to produce EM wave absorbing mortar.•Adding micro and/or nano Fe3O4 improved strength, packing and microstructure.•Co-addition of micro and nano Fe3O4 has additive effect on EM wave absorption. Fe3O4 (ferroferric oxide) has been proven to be useful for enhancing the electromagnetic (EM) wave absorption performance of cementitious materials. However, there are still few studies on the possible combined usage of micro Fe3O4 and nano Fe3O4 to further enhance the EM wave absorption performance and perhaps also the other performance attributes of cementitious materials. In this research, an attempt to utilize both micro Fe3O4 and nano Fe3O4 to produce EM wave absorbing mortar was made. A series of mortar mixes with varying amounts of micro Fe3O4 and nano Fe3O4 added were tested to investigate their combined effects on the workability, compressive strength, packing density, microstructure and EM wave absorbing properties. The results showed that the combined addition of micro and nano Fe3O4 had little net effect on the workability, but significant positive effects on the compressive strength, packing density and microstructure densification, and more importantly, such combined addition could increase the EM wave absorption performance to higher than possible with only single addition of micro Fe3O4 or nano Fe3O4.