EXPERIMENTAL STUDY ON EFFECTS OF ADHERED MORTAR CONTENT ON QUALITY OF RECYCLED COARSE AGGREGATE AND PROPERTIES OF CONCRETE

摘要

Although the adhered mortar conternt affects the properties of recycled aggregate concrete, there are few papers describing those effects. This paper presents the results of a series of experimental study on the effects of adhered mortar content on the quality of recycled coarse aggregates and strengths and durability of concrete. 5 kinds of recycled coarse aggregates made with heating and rubbing method, mechanical crashing method and separating lightweight particle with water stream method were tested for specific gravity, absorption and adhered mortar content. Specific gravity in oven-dried condition ranged from 2.35g/cm3 to 2.59 g/cm3, absorption ranged from 1.58% to 5.83% and adhered mortar content ranged from 8.0% to 68.4%, depending on manufacturing method of recycled aggregates. Absorption decreased linearly with the increase of specific gravity. Specific gravity decreased and absorption increased with the increase of adhered mortar content. Recycled aggregates produced by heating and rubbing method showed lower adhered mortar conent corresponding to lower absorption and higher specific gravity, while those made by mechanical crushing method showed higher adhered mortar content corresponding to higher absorption and lower specific gravity. Compressive, tensile and shear strengths, modulus of elasticity, drying shrinkage and carbonation were tested on concrete mixtures with the water cement ratio of 43%, 50% and 60% using 3 kinds of recycled coarse aggregates and river sand. The test results of concrete indicated higher compressive, tensile amd shear strengths and higher modulus of elasticity for concrete using recycled coarse aggregates with lower adhered mortar content, lower absorption and higher specific gravity. Recycled aggregates with higher adhered mortar content also showed significunt adverse effects on drying shrinkage and carbonation. In conclusion, the upper limit of adhered mortar content of coarse recycled aggregates to keep up the quality of aggregates and concrete equal to natural coarse aggregates is considered to be 15%.