An Experimental Study of pH Value and Flexural Strength of Cement Sand Mortar with Surface Untreated Multi-Walled CNTs

Abstract

Background/Objectives: The paper describes the study carried out on test specimens of cement mortar composite admixed with multi-walled carbon nanotubes (CNTs) in order to investigate the physical property changes under nano-level hydration. Methods/Statistical Analysis: In this study, the standard engineering tests such as pH value identification, flexural strength test and compression strength tests were carried out for both control and test specimens which were cast and cured as per Indian Standard specifications. Test specimens of cement mortar composite consisted of ordinary Portland cement and river sand added with 0.2% (by weight of cement) pristine multi-walled CNTs ultrasonicated but without any surface treatment. Findings: The pH value of ultrasonicated multi-walled CNTs dispersed in de-ionised (DI) water was first determined and found to be 6.85. The pH of control mix without multi-walled CNTs was 12.64 and the pH of test mix with multi-walled CNTs was 12.37. The percentage addition of multi-walled CNTs was very small and hence the reduction in alkalinity was found to be equally small. Flexural strength of test specimens showed 23%, 31.41% and 31.46% increase at 7, 28 and 45 days respectively over control specimens. Compressive strength of test specimens showed 6.1% increase at 28 days over control specimens. Application/Improvements: In view of improvement in flexural strength in mortar, addition of multi-walled CNTs to concrete elements may help in improving their performance under dynamic loading. Further improvements are required to study the effect of an increased percentage addition of multi-walled CNTs without any surface treatment and without any surfactant in cement sand mortar (1:3).