Improving mechanical properties of 3D printed mortar through synergistic effects of fly ash microspheres and nanosilica

Fly ash microspheres (FAM), being a superfine fly ash, and nanosilica (NS), being an ultrafine amorphous silica, have proven to be useful for enhancing the performance of traditional cement-based materials. To explore the possibility of improving the performance of three-dimensionally printed (3DP) mortars by the combined addition of FAM and NS, a series of 3DP mortars with varying water/cementitious materials (w/cm) ratios, FAM contents and NS contents were made and their performance was evaluated. The results showed that optimising the water reducer dosage could make the 3DP mortars achieve great extrudability, buildability and dimensional stability. The w/cm ratio, FAM content and NS content were the main factors determining the mechanical properties of the 3DP mortar. The co-addition of FAM and NS enhanced the flexural, compressive and bond strengths by percentage increases larger than the sum of the percentage increases owing to individual addition of FAM and NS. Hence, FAM and NS should better be used together to release their synergistic effects for the design of 3DP mortar.