Modifying effect of anionic polyacrylamide dose for cement-based 3DP materials: Printability and mechanical performance tests

Abstract

Cement-based materials have been broadly applied as constructional materials in 3D printing (3DP) civil engineering due to their high mechanical strength, yet their non-ideal performance in ductile and compaction during the printing process always limits their further application. To improve the buildability and antisettling capability of 3D printing materials, a new cement-based 3DP material is proposed by partly replacing traditional hydroxypropyl methyl cellulose (HPMC) with anionic polyacrylamide (APAM). To compare the modifying effect of APAM to that of the cement-based 3DP (APAM-3DP) material, the printability, physical–mechanical performance of APAM-3DP material are tested, and the corresponding microstructural characteristics of mortars with different replacement ratios are analysed. The experimental results show that under the same dosage, APAM can reduce the fluidity of cement-based materials, shorten the setting time and slow down the hydration process compared with HPMC. Addition of the appropriate amount of APAM can improve the buildability of cement-based materials by 57 % and the compressive strength of the samples is increased by 7.7%, but the deformation rate is also doubled. When the APAM dosage is appropriate the samples were more prone to brittle failure and overall failure, if the APAM dosage is too large, the sample is prone to ductile failure and local failure. The modification mechanism of APAM was also analyzed from the microscopic pore characteristics and the morphology of hydration products of the samples.