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

C V Nguyen,G Jones,P S Mangat

doi:10.1088/1757-899x/371/1/012022

Abstract

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.

Highlights

Alkali activated cementitious material is developing significantly as a global sustainable material for the construction industry
The results show that shrinkage reducing admixture (SRA) reduced the shrinkage of activated cementitous material (AACM) mortar by up to 69% after 80 days at 7% dosage
Regardless of the dosage of SRA, a unique relationship exists between flexural strength and compressive strength, which correlates with the data of previous research

Summary

Introduction

Alkali activated cementitious material is developing significantly as a global sustainable material for the construction industry. Kutti [6] stated that the alkali activation of slag produced two main hydration products, a C–S–H gel and a Si-rich gel The latter consists of higher uncombined water content that is eliminated during the drying process, causing substantial shrinkage and, microcracking. 2.4 Drying shrinkage The drying shrinkages of different compositions of AACM mortar mixes (Table 1) were determined according to BS ISO 1920-8:2009: Testing of concrete - Part 8: Determination of drying shrinkage of concrete for samples prepared in the field or in the laboratory [18]. The samples were removed from water at 7 days after casting, dried with a cloth and the first (datum) strain reading was taken with a demec extensometer.

Results and discussion

Relationship between flexural and compressive strengths

Conclusions