Multi-scale structure of in-situ polymerized cementitious composites with improved flowability, strength, deformability and anti-permeability

In-situ polymerization of polymers with cement can greatly improve the engineering performances of cementitious composites, the structural mechanisms, however, remain still not fully established. Herein in-situ polymerization modified cementitious composites (iPMCC) with sodium acrylate (SA) in different dosages (0%, 4% and 8%) were fabricated. Flowability, strength, deformability, and water sorptivity of the iPMCCs were tested, and the multi-scale structures in terms of pore size distribution, microscopic morphology, chemical characteristics, and solid structure of calcium-silicate (-aluminate)-hydrates were characterized. Results demonstrate that, compared with neat cement paste, the iPMCC with 4% SA showed the improvement of flowability by 35.1%, the increases of flexural and compressive strength by 109.0% and 11.8%, the rises of flexural and compressive deformation energy by 458.8% and 161.0%, and the decrease of water sorptivity by 19.1%. The in-situ SA polymerizations lead to substantial pore refinement, but macro defects in the iPMCC with 8% SA. Cross-linked sodium polyacrylate networks formed in the cement matrix and interacted with the cement hydrates, accounting for the improved strength, deformability, and water resistance. Cement hydration depression by polymers was evidently supported by the NMR data. The findings would deepen the understandings of multi-scale structure of cementitious composites with polymers, enabling development of highly ductile and durable construction materials.

Automated summary

In-situ polymerization of sodium acrylate (SA) in cementitious composites significantly improves their flowability, strength, deformability, and water resistance. The addition of 4% SA in the modified cementitious composites (iPMCC) results in a 35.1% improvement in flowability, a 109.0% increase in flexural strength, an 11.8% increase in compressive strength, a 458.8% rise in flexural deformation energy, a 161.0% rise in compressive deformation energy, and a 19.1% decrease in water sorptivity compared to neat cement paste. The in-situ SA polymerizations refine the pores in the iPMCC, but the presence of macro defects is observed in the iPMCC with 8% SA. The formation of cross-linked sodium polyacrylate networks in the cement matrix enhances the strength, deformability, and water resistance of the iPMCC.