Role of the filler on Portland cement hydration at early ages

The effects of mineral additions, quartz (Q) and limestone (C) fillers, on Portland cement (PC) hydration are ultimately reflected in the mechanical behavior and durability of the resulting concrete. The physical and chemical interactions involved may expedite or retard the hydration rate. The present paper describes the hydration mechanism in Portland cements containing crystalline mineral additions (fillers, non-pozzolanic), based on the reaction rates and amount of products formed. The mineralogical composition of the Portland cements used determines their differential behavior when exposed to sulfate or attacked by chloride, separately. Ground quartz, Q, and limestone, C, were the mineral additions chosen. The results show that direct and non-direct stimulation of the hydration reactions increase with the replacement ratio and, obviously, as a result of the concomitant physic dilution effect. Mixing water would be responsible for direct stimulation. non-direct stimulation, in turn, would occur very early in PC hydration, for the positive and negative electrostatic charge acquired by the particles of fíller during grinding and/or initial mixing, and subsequently the zeta potential is generated as PC hydration progresses.On the other hand, it has also been demonstrated that both of the fillers interact chemically as specified below. Hence, Q filler is influenced by the portlandite of any PC, OPC and/or SRPC (due to its randomly inner texture totally compact, but above all, to its acid chemical character) to originate CSH-gels, although in a very slowly way, and for this reason, its chemical interaction is specific for the portlandite and generic for any PC of C3A significant content. Whereas, Cfiller interacts chemically mainly with the C3A to originate different carboaluminate types, and for this reason, its chemical interaction is specific for the C3A only.Consequently, overall system behavior varies depending on the crystalline mineral addition, the type of PC and the replacement ratio.

► The effects of mineral additions, Q and Cfillers, on PC hydration at early ages.
► Physical interaction: direct and non-direct stimulations of PC hydration.
► Chemical interaction: specificity of Q and C fillers with portlandite and C3A of PC, respectively.
► Technical consequences: Setting times, water for normal consistency amount, chemically combined water and non-pozzolanicity.