Synergy of Nanoparticles with Supplementary Cementitious Materials in Concrete (ACI Fall 2022, Dallas, TX) This talk will cover a performance-based study on the effects of attapulgite nanoclay and carbon nanotubes (CNTs) on the fresh and hardened properties of mortars with partial cement replacement with fly ash and blast furnace slag. Shear rheology was applied to measure yield stress and viscosity, and the tack test was applied to measure static cohesion. Results show that the additives had differing effects on 100% cement mortars versus blended (50% cement, 25% fly ash, 25% slag). The nanoclays increased yield stress and static cohesion and decreased plastic viscosity in both systems, but these effects were more marked in the cement mortar than in the blended. On the other hand, CNTs increased all measured rheological parameters in the cement mortar and decreased them in the blended. The rheological results highlight the importance of considering the binder system when utilizing additives with exceptional surface. In the hardened state, electrical resistivity, compressive strength, and tensile strength were evaluated. Results indicate that although nanoclays are utilized primarily as a rheological modifier, they have the potential to enhance mechanical properties.

Characterizing and Controlling Interfaces in Concrete (ACI Fall 2022, Dallas, TX) Nano-engineering concrete properties has now emerged as a novel tool for the deployment of advanced cementitious composites necessary for the 21st century civil infrastructure. This study is aimed at characterizing the interface properties of polyvinyl-alcohol (PVA) fibers in strain-hardening cementitious composites (SHCC) incorporating high-volume GP (HVGP) at 0-100% replacement of FA. Single fiber pull-out tests were conducted to characterize the interface properties (i.e., frictional bond, chemical bond, and slip-hardening coefficient) necessary for micromechanical tailoring of SHCC. Results indicate that nanomodification of SHCC matrix and interface properties using nanocellulose (at rates of 0.03-0.10% per cement mass) enabled to significantly alter the pull-out behavior. In fact, the common frictional sliding behavior is shifted to a slip-hardening behavior due to a twofold mechanism imparted by nanomodification (i) meshing the matrix, and (ii) creating a jamming effect, interfering with the pull-out of PVA fibers. This characteristic slip-hardening effect contributed towards enhancing the strain-hardening capacity of SHCC as experimentally validated by uniaxial tensile tests.