Study On Effect And Mechanism Of Nano-CaCO₃in Cement-based Materials

Concrete is the main material used in building materials and structures.Extending the service life of concrete structures by improving its brittleness,durability and overall performance is the development direction in the field ofconcrete materials. With the rapid development of nano-technology, introducingnano-technology into the building field has become a new research topic. Basedon the advantages of nano-CaCO₃and fly ash, they were mixed into thecement-based materials. The effect of nano-CaCO₃on the properties ofcement-based materials was studied in this paper. The mechanism and variationrule of performance of cement-based materials with nano-CaCO₃dosage wereanalyzed as well.The main contents and results are as follows:1.The dispersion method ofnano-CaCO₃in cement-based materials was determined. The nano-CaCO₃couldbe dispersed evenly in cement-based materials by mechanical agitation andadding water-reducer.2. The result of fresh cement-based material property testshowed that nano-CaCO₃affected the water demand of fresh slurry little. But thesetting time was reduced with the increase of nano-CaCO₃dosage. The fluidity ofcement decreased as well.3. After re-incorporaticn, the earlier and later modulusof rupture and compressive strength of the hardening cement-materials improved,and it taken on the tendency of reducing firstly and increase afterward with theincrease of nano-CaCO₃dosage. The fold pressure ration increased at the sametime. An optimal dosage range from1.33%to3.1%and an optimal dosage of1.33%of nano-CaCO₃were determined. At this point, the fold pressure ration of28d increased by11.3%.4. The endurancing test proved that adding nano-CaCO₃could increase drying shrinkage of cement-based materials, especially the earlydrying shrinkage, and the dosage of nano-CaCO₃should be lower than2.22%.With the increase of nano-CaCO₃dosage, the resistance to chloride ion and frostincreased first, then decreased and increased finally. The dosage of nano-CaCO₃should be lower than2.22%, and the optimal dosage was1.33%.5. Thesubmicoscopic structures and hydration products of hardening cement-basedmaterials were preliminarily analyzed by SEM and XRD. It showed that the maineffects of nano-CaCO₃modified cement-based materials were nucleation effectand filling effect.6. The overall evaluation of nano-CaCO₃modifiedcement-based materials showed that the dosage of nano-CaCO₃should be lowerthan2.22%. When the dosage of nano-was about1.33%, the performance of thecement-based material is relatively good.