Microstructural characteristics of concrete added with C-S-H and carbon nanotubes

ABSTRACT

The incorporation of nanomaterials is a possibility for the improvement and modification of characteristics or properties in materials. The incorporation of nanomaterials is a possibility for the improvement or even the creation of some characteristics or properties in materials. The use of carbon nanotubes (CNT) has been researched in concretes to increase the compressive and flexural strength, modulus of elasticity among other characteristics such as reduced permeability. The aim was to improve the hydration kinetics of cement silicates by creating nucleation spaces and growth of crystalline structures making the microstructure denser, as verified by microscopic analysis and porosimetry. Microconcrete specimens had tensile strength tested at 28 days. The percentages of NTC (0.0% and 0.2%) and C-S-H (0.0% and 2.0%) were varied, as well as the Ca/Si ratio (0.8 and 1.2) of C-S-H. In total, 5 types of composites were produced, and their results were compared to the reference material (without additions). The composite C2-0.8 (with 2% C-S-H of Ca/ Si =0.8) presented tensile strength 18.0% higher than the reference material (R), already for the composite CT2-0, 8 (2% C-S-H Ca / Si = 0.8 and 2% CNT) the increase in resistance of 33% compared to the reference. The composite T2 (added only 0.2% of CNT) presented 13% of increase of resistance when compared to material R. The use of NTC, in concrete or other cementitious mixtures, can be enhanced if used in conjunction with C-S-H (precipitate). This improves the hydration of cement silicates by creating nucleation spaces that favor crystalline growth and reduce porosity as seen in electron microscopy analysis and mercury intrusion porosimetry tests performed on the samples.

Key-words
C-S-H; carbon nanotubes; flexural tensile strength