Fundamental Interactions between Multi-Walled Carbon Nanotubes (MWCNT), Ca~(2+) and Polycarboxylate Superplasticizers in Cementitious Systems

摘要

The fundamental interactions between polycarboxylate superplasticizers (PCEs), multi-walled carbon nanotubes (MWCNTs), Ca~(2+) ions and cement were investigated. Two commercial samples of MWCNTs were characterized by SEM and TEM imaging. It was found that only one sample contained mostly individual, non-agglomerated CNTs which were used in further tests. The MWCNT sample reduced cement paste flowability, but increased 28 day compressive strength by ～ 20% and tensile strength by 26%. The relatively modest increase can be attributed to agglomeration of individual CNTs into large bundles (Φ ～ 900 nm, 3.51 × 10~(-5) in.). Agglomeration is caused by adsorption of Ca~(2+) ions onto the initially negatively charged surfaces of CNTs. This way, Ca~(2+) ions present in every cement pore solution impede maximal dispersion of CNTs in the cementitious matrix, thus limiting their potential application as nano reinforcement for concrete.