Influence of Feeding Sequence on the Fluidity and Fluidity Time of Cement Asphalt Mortar for High-Speed Rail Slab Track

Cement Asphalt Mortar (CA mortar) is one of the most important materials in the non-ballast slab track for High-Speed Rail (HSR) systems. The fluidity and fluidity time of CA mortar are important parameters for this application. Both these requirements are governed by the early age interaction between cement, bitumen emulsion, and admixtures. The present study investigated the influence of the feeding sequence of these primary constituents of CA mortar on its fluidity and fluidity time. Flow time measurement by Brass J funnel was used as a measure of fluidity and the mechanism behind the flow time variation is analyzed through viscosity and adsorption behavior of CA paste. The sieving method was adopted to investigate the adsorption behavior of bitumen droplets on the cement under different feeding sequences. The results showed that adding bitumen emulsion, water, and water-reducing admixture (WRA) initially increased flow time and apparent viscosity, which is not ideal. Test results of adsorption indicated that the increase in particle size was mainly attributed to higher adsorption (adsorption value) resulting in higher viscosity and flowtime. The feeding sequence in which water-reducing admixture (WRA) was premixed with cement and water prior to introducing bitumen emulsion proved to be beneficial to obtain the desired fluidity and fluidity time.