Effect of Shrinkage Reducing Admixture on the Strength and Shrinkage of Alkali Activated Cementitious Mortar

The effect of a shrinkage reducing admixture (SRA) on the mechanical properties and drying shrinkage of a proprietary alkali activated cementitous material (AACM) was investigated. Five AACM mortar mixes were prepared. SRA replaced the liquid activator at a dosage of 0%, 1%, 2%, 4% and 7%. The liquid/binder ratio was 0.38. The samples were cured in water. The flexural and compressive strengths of all mixes were determined at 1day, 2 days, 7 days and 28 days and the drying shrinkage was determined up to 80 days. The results show that SRA reduced the shrinkage of AACM mortar by up to 69% after 80 days at 7% dosage. However, SRA also reduced the compressive and flexural strengths of AACM mortars. Increasing dosages of SRA reduced the compressive and flexural strength while recording less shrinkage. Regardless of the dosage of SRA, a unique relationship exists between flexural strength and compressive strength, which correlates with the data of previous research. The AACM mortar maintained strength of over 43MPa (greater than 75% of the control mix at 0% SRA dosage) at 7% SRA dosage, which is classified as high strength in accordance with British Standard PAS 8820:2016. (paper)