Compressive strength and permeability of steam-cured mortar incorporating high volume fly ash with different activation degrees by wet milling

Abstract

High volume fly ash (HVFA) cementitious material has received widespread attention because of its great economic and environmental benefits, but the slow strength development restricted its practical application. In present work, fly ash (FA) with different activation degrees was prepared through wet milling technique. Specimens incorporating 50 wt% FA with single and combined activation degrees were designed. Compressive strength, capillary absorption, chloride permeability, chemically combined water and pore structure of steam-cured high volume fly ash mortar (HVFM) were investigated, and the cost and CO2 emission were also evaluated. Results indicated that it is possible to compensate the early low strength and improve the late strength of HVFM by optimizing the proportion of FA with different activation degrees. The HVFM containing 10 wt% raw fly ash (RFA, D50 = 19.7 μm, 28-day reactivity index = 83%), 15 wt% FA wet milled for 70 min (FA1, D50 = 4.29 μm, 28-day reactivity index = 103%) and 25 wt% FA wet milled for 6 h (FA2, D50 = 2.51 μm, 28-day reactivity index = 128%) almost achieved the highest compressive strength at both early and late ages. The anti-permeability was also obviously improved by the combination of FA with different activation degrees, attributing to larger amounts of hydrates and more complicated pore structure. The combination of FA with different activation degrees helps to ensure the early compressive strength while also having additional environmental and economic benefits.