Influence of heat curing period and temperature on the strength of silico-manganese fume-blast furnace slag-based alkali-activated mortar

Abstract

In the reported study, silico-manganese fume (SMF) was developed into an alkali-activated binder (AAB) in combination with blast furnace slag (BFS) by adding NaOH and Na2SiO3. The effect of curing on the resulting AAB was studied by water-ponding, ambient-curing and heat-curing. In the first phase, the period of oven-curing (3–24 h) at 60 °C was optimized. This was then followed by optimizing the oven-curing temperature (25–95 °C) within the period of 6 h. Good synergy of precursors exhibited acceptable fresh properties and formation of notable phases like C-Mn-S-H, K-A-S-H, C-(A)-S-H that were responsible for strength skeleton. Early-age compressive strength gain was approximately 50% of the 28-day maximum values of 46.4 and 43.5 MPa obtained in water- and ambient-cured specimens, respectively. On the contrary, the 3-day strength gain of 42.6 MPa was recorded in oven-cured (60 °C) specimens with linear increment with time up to 24 h. However, a curing period of 6 h was considered optimum from energy and cost benefit points of view. This registered 3-, 7- and 28-day strength of 38, 41 and 45.2 MPa, respectively due to increased crystallinity of the C-A-S-H and quartz phases. The morphology of specimens cured by water-immersion, room temperature and optimum oven conditions was homogeneous, dense and consisted lesser traces of unreacted particles favored by high degree of dissolution and polymerization due to formation of stratlingite and gehlenite that acted as a crack filler and pore blocker.