Influence of Defoamer on the Properties and Pore Structure of Cementitious Grout for Rebar Sleeve Splicing

Grout sleeve splicing of rebar is a major technology in prefabricated buildings, and cementitious grout for rebar sleeve splicing (hereinafter called grout) is an essential material for this technology. Grout, with its excellent mechanical properties, improves the stability of rebar sleeve splicing. In this study, the mechanical properties of grout were improved by introducing an admixture in the form of a defoamer, and the influence of the defoamer on the fluidity, loss rate of fluidity, wet apparent density and strength of the grout was investigated. The action of the defoamer in regulating the pore structure of the grout was further analyzed using the mercury intrusion porosimetry (MIP) method. The results showed that when the dosage of defoamer was increased from 0 to 0.025%, the fluidity of the grout initially increased and then decreased, but there was no change in the loss rate at 30 min. The wet apparent density increased continuously, whereas the flexural and compressive strength generally increased initially and then tended to stabilize. The MIP test results showed that the defoamer increased the pore volume of the grout in the range of 6 nm to 30 nm and decreased the pore volume in the range of 30 nm to 60 mu m. However, in the 60 mu m to 300 mu m pore size range, the pore volume increased when the dosage of the defoamer was 0.0025% and 0.0075%, and decreased when the dosage was 0.005% and 0.001%. The porosity of the grout initially decreased and then increased slightly as the dosage of the defoamer increased from 0 to 0.01%. The introduction of defoamer can optimize the pore structure of grout and then improve its mechanical properties. The influence of defoamer on grout properties and pore structure were systemically studied with a view to providing technical and theoretical guidance for rebar sleeve-splicing technology in prefabricated construction.