Recycled aggregate concrete enhanced with polymer aluminium sulfate

The large porosity, high water absorption and many inherent micro-cracks in recycled aggregates are the key causes of the weaker mechanical properties, higher drying shrinkage and even vulnerability to early-age cracking in recycled aggregate concrete (RAC). A method of using the polymer aluminium sulfate (PAS) to enhance the mechanical properties and volume stability of RAC is presented. Three basic mechanical properties (compressive strength, flexural strength and elastic modulus) and two volume stability parameters (free drying shrinkage and restrained shrinkage cracking) were evaluated along with a few parallel tests of PAS at the microstructural level. The microstructure of the interfacial transition zone (ITZ) in RAC was characterised by micro-hardness tests and scanning electron microscopy. The test results show that the PAS, due to its chemical function, is capable of effectively increasing the micro-hardness and reducing the inhomogeneity of the ITZ in RAC. These improvements in the microstructur...