Mechanical properties of early-age concrete reinforced with multi-walled carbon nanotubes

The results of mechanical property tests on early-age concrete reinforced with industrial-grade carbon nanotubes (CNTs) are reported. The objective of the study was to validate the effectiveness of CNTs and establish the development of concrete properties with CNT dosage and concrete age. Ultrasonication, ultraviolet–visible spectrophotometry and scanning electron microscopy were employed to inspect or improve the dispersion quality. The test programme considered four CNT dosages and seven concrete ages, with three replicates. The results indicated that industrial-grade CNTs can lead to increases in cubic compressive strength, tensile splitting strength, prismatic compressive strength and ultimate strain of concrete (up to 34·2, 11·1, 19·4 and 8·3%, respectively) comparable to those obtained with the use of fine nanotube particles; no significant influence was found for the other tested concrete properties. The results of this study also indicated that increases in strengths and strain were most significant during the first 7 d, the period when concrete is most prone to cracking due to shrinkage and hydration heat. This implies that industrial-grade CNTs may have a great potential in reducing early-age concrete cracking with much less health risk and lower testing requirements compared with the use of fine nanotube powders.