Clinkerless slag-silica binder: hydration process and hardening kinetics (part 2)
In part 1 of the studies, it was shown the results of the implementation of the “top–down” nanotechnological principle to obtain clinkerless binder with a high content of microsilica, activated during grinding what allowed to increase their hydraulic activity. Part 2 of the studies have been implemented in order to ensure the possibility of using of clinkerless slag-silica binder, modified by complex additive of SiO2 nanoparticles in combination with a plasticizer (“bottom–up” nanotechnological principle), as a hydraulic binder. For nanotechnological activation the solution of nano-additives, synthesized by the sol–gel process, is used. Experimental results of changes phase composition and microstructure of clinkerless slag-silica binder during hydration and structuration processes; flocculation and hardening kinetics are presented. The laser granulometry method, dynamic light scattering and transmission electron microscopy were used to estimate the particle size of original components. XRD – method, scanning electron microscope were used to estimate phase composition and morphology of the clinkerless binder’s hydration product. The flocculation was evaluated by the penetrometric method. The hardening kinetics was evaluated by the mechanical tests after 1, 3, 7, 14, 28 day of curing. As a result, the distinctive features of the main periods of heterogeneous processes of structure formation of the nano-activated clinkerless slag-silica binder are revealed at the different stages of hardening. It was established that the “bottom – up” nanotechnological principle, implemented through the introduction of SiO2 – nanoparticles into binder paste allows to increase the hydraulic activity of slag due to the catalytic role of nanoparticles and their chemical interaction with slag minerals. As a result, the strength of the of clinkerless slag-silica binder was 35.8 MPa, and it’s setting and hardening rates corresponds to the speed of these processes for Portland cement under normal temperature-humidity conditions.