Evaluation on comprehensive properties of slag-cement based self-compacting mortar modified with hybrid addition of limestone powder and unground rice husk ash

Exploring new friendly filler applicable for self-compacting concrete/mortar is always encouraged to persuade a phenomenon of sustainable development. The current study aims at assessing synergistic influences of limestone powder (LP) and unground rice husk ash (URHA) additions respectively as partial replacements of slag and fine aggregate (FA) in ranges of 10 to 50 mass.% and 10 to 50 vol.% on comprehensive performances of a slag-cement self-compacting mortar (SCM). Experimental results indicated that an increment of either LP or URHA amount remarkably increased viscosity of the fresh SCMs. Sole addition of LP partially replacing slag at 10 mass.% led to the hardened SCMs with the enhanced flexural and compressive strengths, strength efficiency (SE) of cement, and durability performances except a slight increase in drying shrinkage. By using LP as partial substitution of slag at 10 mass.%, addition of URHA partially replacing FA at 10 vol.% substantially improved both the mechanical strengths and durability in terms of ultrasonic wave velocity (UPV) and sulfate resistance of the modified SCMs, which was attributed to the additional hydration products detected from X-Ray diffraction technique. Compared with the reference SCM without additive, the modified SCM containing mixture of LP and URHA respectively replacing slag and FA at 10 mass.% and 10 vol.% had compressive strength increased at 15.3%, flexural strength increased at 27.6%, UPV increased at 3.8% at 28 days. Especially, in this study, hybrid addition of LP and URHA respectively replacing slag and FA at 10 mass.% and 10 vol.% was also considered as the optimum amounts for maximizing the SE of cement at up to 0.252 MPa/(kg/m3) in SCMs.