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This study aims to investigate the autogenous shrinkage-reducing mechanisms of the novel polymer-type shrinkage-reducing admixture (SRA) with water-reducing function. For comparison, the traditional polyether-type SRA was also used. The development of autogenous deformation, hydration rate, internal relative humidity (RH), electrical resistivity, ions and SRAs concentration in pore solutions and crystal content of cement pastes were comprehensively investigated. Unlike the polyether-type SRA mixture which has an expansion period at early age, a relatively slow and monotonous evolution of shrinkage was observed for the polymer-type SRA mixture. It is concluded that the delay and regulation effects on cement hydration of the novel SRA obviously influence the microstructure development and the evolutions of various performances of cement pastes comparing to the polyether-type SRA. Furthermore, both the self-desiccation status induced capillary pressure and the crystallization pressure induced expansion stress contribute to the shrinkage-reducing behaviors of SRAs on the autogenous deformation of the cement pastes.

The development of high performance air entraining agents for concrete is of great importance. In this work, gemini surfactants (a new class of surfactants) have been utilized as air entraining agents for the first time. Three gemini surfactants modified with different anionic groups (sulfonic, sulfate and phosphate groups) were designed and synthesized. The surface tensions and foam heights of their solutions were tested. Using them as the air entraining agents, the air contents and air-void parameters of the cement mortars were tested. The study results clearly show that the gemini surfactants have higher surface activity, foamability, foam stability and air entraining performance compared with the corresponding single-chained surfactants, and the sulfate group modified gemini surfactant has the highest performance. These surfactants are tested merely as model compounds; however, they show higher air entraining ability compared with the benchmark surfactants used in the industry, indicating great potential for practical applications.