Excess large and unstable air bubbles can reduce the compressive strength of hardened concrete, and traditional defoamers always fail because of adsorption and encapsulation on cement with the progress of cement hydration in later stages. It is necessary to develop a novel defoamer that shows a sustained defoaming ability in fresh concrete. A novel slow-release defoamer for concrete using porous nanoparticles as carriers is reported for the first time. The porous nanoparticles/polyether defoamer composite (SiO2-Def) was prepared via sol-gel method. SiO2-Def is a spherical composite nanoparticle with a size range of 160-200 nm and a uniform pore size distribution. SiO2-Def shows a high load rate of about 16.4% and an excellent release under an alkali and salt environment. It has a weak initial defoaming ability but shows a sustained defoaming ability with time, so that it can avoid the failures of defoamers and eliminate harmful bubbles entrained during the processes of pumping and transportation. Moreover, SiO2-Def produced a higher compressive strength of the hardened cement mortars.
Keywords: bubbles; concrete; defoamers; porous nanoparticles; slow-release.