Abstract
This paper introduces a new method to measure whole cycle length change non-destructively and continuously using a digital image analysis system. The macroscale length changes of mortars containing different shrinkage-reducing admixture (SRA) dosages (0%, 1%, 2% and 5% by cement weight) were first determined using a complementary metal oxide semiconductor (CMOS) image sensor under alternating dry and wet curing conditions. After that, the length change was calculated using developed digital image processing technology (DIPT) software. After that, several significant conclusions could be drawn by combining with the results of systematic tests of the macroscopic and microscale physical properties of the cement mortar using X-ray diffraction, scanning electron microscopy, mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) methods. The test results indicated that SRAs exhibited significant effects on the shrinkage inhibition of cement mortars, whereas the shrinkage reduction behaviour was also affected by varying the curing conditions. The MIP and NMR analyses demonstrated that SRAs reduced the irreversible shrinkage of the cement mortars by decreasing the volume percentage of the 3–50 nm pores and promoting the conversion of calcium silicate hydrate gel from an oligomeric to a high polymerization state thereby improving the volume stability of cement mortars.
Highlights
Current civil engineering technology advancements have enabled rapid global urbanization and overall improvements in lifestyles which have resulted in cementitious materials being the most widely used and successful building materials
This study mainly aimed to investigate the effects of two different shrinkage-reducing admixture (SRA) on the volume stability of cement mortars under a designed alternating wet and dry schedule, accompanied by alternating temperature conditions
The weight loss was determined by placing each sample on a scale and recording the mass change owing to water evaporation per unit of weight at different aging times
Summary
Current civil engineering technology advancements have enabled rapid global urbanization and overall improvements in lifestyles which have resulted in cementitious materials being the most widely used and successful building materials. Their unsatisfactory volume stability, including their unrestrained shrinkage or shrinkage–cracking under restrained conditions, have raised many safety and economic concerns such as crack generation accelerating the damage of concrete and thereby shortening the service life of structures. Several specific high-performance additives have been developed to improve the volume stability of concrete such as expansive agents [2,3], fibres [4,5] and shrinkage reducing admixtures (SRAs) [6]. SRAs could be good additive options, as they exert excellent early shrinkage retardation effects on concrete
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