Synergistic effects of micro-silica and nano-silica on strength and microstructure of mortar

Micro-silica (MS), of much finer size than cement, has been proven to be effective in improving the strength and durability of concrete. With the advent of nanotechnology, nano-silica (NS), of even finer size than MS, is now available for production of concrete, especially high-performance concrete (HPC). To investigate the combined effects of MS and NS on the strength and microstructure of mortar or the mortar portion of HPC, an experimental program was launched, in which mortar mixes with various water, MS and NS contents but a constant workability were produced for cube strength measurement and microstructure imaging. From the test results, it was found that even a very small NS content of only 1-2% has substantial positive effects on the cube strength and microstructure, but a very high superplasticizer demand. More importantly, the combined addition of MS and NS has significant synergistic effects on strength and microstructure. These results suggest that NS should not be added alone but should be added together with MS to exploit their synergistic effects for maximum performance. (C) 2017 Elsevier Ltd. All rights reserved.