Influence Of Recycled Aggregate Defects On The Durability Of Recycled Aggregate Concrete

In this thesis, recycled aggregates were treated with sulfuric acid solution, then, experimental investigations were conducted to study the influence of attached mortar and damage in stones on the properties of recycled aggregates and durability properties of recycled aggregate concrete.Recycled aggregates were soaked by sulfuric acid solution with different concentrations (1mol/L,2mol/L and3mol/L) and for different days (3d,5d and7d), then, the optimum concentration and soaking time (3mol/L for7days) for sulfuric acid solution to remove the attached mortar of recycled aggregate was confirmed, the removal rate of attached mortar can be above90%. The basic performances, including water absorption test, apparent density test, crushed value test and soundness test, were conducted on natural aggregate and two kinds of recycled aggregates (untreated recycled aggregate and recycled aggregate soaked by3mol/L sulfuric acid solution for7days). Durability properties tests, including chloride ion penetration resistance test, frost resistance test and water penetration resistance test, were conducted on concrete (W/B=0.60and W/B=0.26) made with the three kind of aggregates above. Influence of attached mortar and damage in stones due to crashing processing on the basic performances of recycled aggregate and the durability properties of recycled aggregate concrete respectively were obtained from analysis of the results of tests above, In order to research the damage in stones due to sulfuric acid treatment, natural limestone aggregates were also soaked by sulfuric acid, the basic performance and mass change of natural aggregate before and after sulfuric acid treatment were compared. Meanwhile, the mass changes of three other kinds of natural aggregates (dolerite, basalt and granite) before and after sulfuric acid treatment were determined.Furthermore, stereoscopic microscope was used to observe the cutting sections of recycled and natural concrete, the observed results were obtained to explain the macroscopic experimental results mentioned above.The experimental results are as follows.The results of water absorption test, apparent density test, crushed value test and soundness test indicate that attached mortar and damage in stones due to crashing process both have a certain negative effect on the properties of recycled aggregate. For apparent density, crushed value and soundness, the negative effect of attached mortar is the primary factor to reduce the properties of recycled aggregate, and damage in stones due to crashing processing has a slightly negative effect to reduce these properties of recycled aggregate. For water absorption, the negative effect of damage in stones due to crashing processing is the primary reason to reduce this property of recycled aggregate, and attached mortar has a slightly negative effect to reduce the properties of recycled aggregate. Compared to the negative effect of attached mortar and damage in stones due to crashing process on recycled aggregate, the negative effect of damage in stones due to sulfuric acid treatment was insignificant. After sulfuric acid treatment, granitic aggregate has a relatively small mass lose, which indicated that the sulfuric acid had the minimum damage to granitic aggregate among the four kinds of natural aggregates.The results of the durability property tests of concrete indicate that damage in stones due to crashing processing and attached mortar both have a certain negative effect on the chloride ion penetration resistance test, frost resistance test and water penetration resistance test of recycled aggregate concrete. At a high water/binder ratio (W/B=0.60), damage in stones due to crashing processing is the primary factor for inducing the decrease of chloride ion penetration resistance of recycled aggregate concrete, and attached mortar has a slightly negative effect on the chloride ion penetration resistance of recycled aggregate concrete; attached mortar is the primary result in the decrease of frost resistance and water penetration resistance of recycled aggregate concrete, and damage in stones due to crashing processing has a slightly negative effect on the frost resistance and water penetration resistance of recycled aggregate concrete. At a low water/binder ratio (W/B=0.26), attached mortar is the primary parameter for the decrease of chloride ion penetration resistance, frost resistance and water penetration resistance of recycled aggregate concrete, and damage in stones due to crashing processing has a slightly negative effect on the chloride ion penetration resistance, frost resistance and water penetration resistance of recycled aggregate concrete.The observed results from stereoscopic microscope can verify the experimental conclusions further.