Use of nanocrystal seeding chemical admixture in improving Portland cement strength development: application for precast concrete industry

摘要

This paper summarises an investigation into the potential advantages to the precast concrete industry of using a new 'seeding' type of chemical admixture in Portland cement (PC) based concrete mixes. Results indicated that the addition of 2-4% nanocrystal seeding chemical (NCS) admixture by weight of PC can provide a doubling of early strength, particularly at 6 and 12 h. This strength gain could lead to the turnover of moulds in precast concrete plants being completed twice in 24 h, thus increasing production capacity. Isothermal conduction calorimetry, X-ray diffraction and thermogravimetric analysis techniques were used to investigate the reasons for the improvement in compressive strength development. Results indicated that the increase in early compressive strength is due to an acceleration of early hydration of PC in presence of the NCS. Indeed, after 6 h, the degree of hydration was more than 50% greater when NCS was used. This paper also highlights the possibility of the NCS chemical admixture being used in conjunction with supplementary cementitious materials (SCMs) in PC blended concrete mixes. 2% NCS was added to a blend containing 70% PC and 30% ground granulated blast furnace slag (GGBS). Results indicated that early strength values were greater compared to the blend without NCS and comparable to the 100% PC mix.