Shrinkage and strength of alkaline activated ground steel slag/ultrafine palm oil fuel ash pastes and mortars

• The more amorphous alkaline-activated binder; the better is its strength and shrinkage.
• Ground steel slag up to 60% in AAGU paste reduced the shrinkage significantly.
• The shrinkage of AAGU is influenced by base materials pore menisci radii.
• Low NaOHaq to Na-silicate proportion reduced shrinkage of AAGU product.

This study evaluated the contributions of steel slag and activators ratio to the shrinkage of the alkali-activated ground steel slag (G)/ultrafine palm oil fuel ash (U) or AAGU pastes and mortars. The base materials were combined such that G/U+G varied from 0 to 0.8 (pastes) and 0–0.6 (mortars) with the use of 10M-NaOHaq and Na2SiO3aq (Ms = SiO2/Na2O of 3.3) as activators whose ratios (Na2SiO3aq/10M NaOHaq) were varied as 1.0/1.0 and 2.5/1.0. The findings revealed that steel slag reduced the AAGU shrinkage through pore-refinement, elimination of microcracks, and improvement in the microstructural density and strength. The changing of Na2SiO3/10NaOH ratio in the synthesis of AAGU products from 2.5 to 1.0 slightly reduced the shrinkage through the modification of amorphousity and nature of the products (C-A-S-H/C-S-H). The maximum 90-day slag-free AAGU paste and mortar shrinkages were 60.80 × 103 με and 11.82 × 103 με but reduced to 25.88 × 103 and 2.71 × 103 με, respectively as G/(U+G) = 0.4 in AAGU0.4.