Influence Of Recycled Aggregate Defects On The Mechanical And Durability Properties Of Recycled Aggregate Concrete Prepared With Crushed Granite-aggregate Concrete

The recycling process will have an adverse effect on recycled aggregates (RA), thus affecting the mechanical and ductility properties of recycled aggregate concrete (RAC). The chemical corrosive effect of sulfuric acid on recycled aggregates produced from crushed granite-aggregate concrete is negligibly weak compared with the damage caused by crushing process, therefore, the effect of adhered mortar and gravel damage on the performance of RAC is very special.The effect of adhered mortar and gravel damage on the performance of RA and RAC was carefully analysed in this thesis using recycled aggregates produced from crushed granite-aggregate concrete.Test results of aggregates properties were analysed comparatively in this thesis to study the influences of these two defects on three different types of coarse aggregates: natural aggregates (NA), RA, and recycled aggregates with a soaking treatment in3mol/L sulfuric acid for7days (RA-H). Furthermore, concretes at two water/binder ratios (0.26and0.60) were fabricated using these three types of aggregates, and were separately named as natural aggregates concrete (NAC), RAC, and concrete made of sulfuric acid treated recycled aggregates (RAC-H). Experiment programs were conducted and the results of compressive strength, splitting tensile strength, fracture energy, static modulus of elasticity, chloride ion-resistant permeability, water-resistant permeability and frost-resistance tests were presented and analysed comparatively to evaluate the effects of adhered mortar and gravel damage on the mechanical and durability properties of these three type of concretes mentioned above.Test results revealed that both adhered mortar and gravel damage caused by crushing process can have negative effects on the properties of RA. The crushing value, apparent density, and ruggedness of RA were mostly affected by the mortar adhered, while the increase in water absorption of RA was mainly caused by gravel damage.The results of mechanical test carried out on specimens at both water/binder ratios indicated that the decrease in compressive strength and splitting tensile strength of RAC was mainly caused by adhered mortar, while the decrement of fracture energy can be attributed to the damage of gravel incurred during crushing process. Moreover, the modulus of elasticity of RAC mainly depended on the adhered mortar in the case of low water/binder ratio, but on the degree of gravel damage in the case of high water/binder ratio. Overall, the mechanical properties of RAC at low water/binder ratio were mainlyaffected by the adhered mortar, while in the case of high water/binder ratio, the main influential factor was gravel damage.The results of the durability tests revealed that the chloride ion penetration resistance, water penetration resistance, and frost resistance of RAC are worse than NAC, which can be related to the two defects of RA. Adhered mortar was the main factor which caused the worse performance in those three durability indices mentioned above in the case of low water/binder ratio. In the case of high water/binder ratio, the adhered mortar mainly affected the water penetration resistance and frost resistance of RAC, but not the chloride ion penetration resistance, which was mostly influenced by gravel damage.