Influence and mechanism analysis of different types of water reducing agents on volume shrinkage of cement mortar

Abstract

This study investigated the impact of five commonly employed water-reducing agents on the fluidity of cement paste at varying dosages firstly. The agents considered in this research are sodium lignosulfonate (LS), naphthalene superplasticizer (PNS), aliphatic superplasticizer (HSB), and two types of polycarboxylate superplasticizers (PCEs), specifically PCE-5C and PCE-6C. Subsequently, the impact of water reducing agents on both the total drying shrinkage and autogenous shrinkage of cement mortar was investigated. This was done by maintaining a consistent water-cement ratio, ensuring good workability, and adjusting the dosage of various water-reducing agents to achieve comparable slump flow in the mortar. Furthermore, the study delved into the mechanisms behind the influence of different types of water-reducing agents. The findings indicate the following: 1) Polycarboxylate superplasticizers (PCEs) exhibit superior dispersion performance with cement, trailed by naphthalene superplasticizer (PNS) and aliphatic superplasticizer (HSB), while sodium lignosulfonate (LS) demonstrates the least effective dispersion performance. The fluidity of cement paste is most responsive to variations in the dosage of PCEs, followed by PNS and HSB, whereas the fluidity of cement paste undergoes minimal changes when the dosage of LS is increased. 2) The effects of various water reducing agents on the volume shrinkage of cement mortar are distinct, and their influence is the outcome of multiple factors working in tandem. These factors include the postponement of the exothermic peak during cement hydration, reduction in solution surface tension, and decrease in the proportion of larger pores and smaller-sized capillary pores within the porosity of cement-based materials, and all these aspects collectively contribute to minimizing the volume shrinkage of cement-based materials. 3) In the realm of concrete engineering, opting for PCEs as water-reducing agents has proven effective in reducing the overall drying shrinkage of cement-based materials. Notably, PCE-5C demonstrates a superior ability in minimizing shrinkage compared to PCE-6C.