AN INITIAL ANALYSIS OF THE EFFECT OF GYPSUM PLASTER IN RECYCLED MORTARS FROM CD WASTE

摘要

For one type of recycling unit a study was made of the use of recycled sands containing gypsum plaster impurities as mortar for laying masonry. Such mortars, when in contact with moisture, can cause the outset of delayed ettringite and affect the performance of the masonry depending on the porosity of the materials used. Materials characteristic of the region of the recycling plant produced 4 recycled sands (0% up to 0,5% of theoretical sulfate contamination). The mortars were produced with a cement content around 220 kg/m~3, including a reference mortar of cement, lime and quartz sand. The materials quantities used, density and consistency of mortars in the plastic state; and in the hardened state at 63 days of age, the compressive strength, flexural modulus, static and dynamic modulus of elasticity, water absorption and apparent porosity are described in this paper. In between the 63rd and 175th days the mortars were submitted to 8 cycles of 7 days at > 95% R.U., alternating for 7 days at 40 ℃. At the end of 8 cycles there was dimensional change and loss of tensile and compressive strength in all mortars studied. Analysis of the microstructure will confirm if such alterations can be associated to delayed ettringite.