Estudio del desarrollo de la resistencia de morteros con árido reciclado fino mediante ultrasonidos y estimación del agua/cemento efectiva

Resumo

The use of fine recycled aggregate for concrete and mortar manufacturing has a double advantage from the view point of construction sustainability. On the one hand, the amount of waste left in landfills has been reduced, and on the other hand, the use of natural aggregates has been reduced, which implies a minor exploitation of the quarries. In the Spanish regulation EHE-08, annex 15 of the recommendations for the utilization of concrete recycled aggregate, the percentage of substitution of coarse aggregate has been limited to 20%. The standard does not consider the use of fine recycled aggregate. Instead, it specifies that studies should be carried out for its utilization. Therefore, it is interesting to have a major control of the compressive strength of mortars and concretes made with fine recycled aggregate. In addition to the study of 28-days compressive strength of mortar with different percentages of substitution of fine recycled aggregate, we have developed a method for controlling the strength evolution by ultrasound from early ages to 28 days. Mortars with substitutions of 0 %, 20 % and 50 % were studied. Two variables have influence on the results of compressive strength of these mortars: one variable is the percentage of substitution with negative influence on strength, and another variable is the effective water/cement ratio. Due to the fact that the recycled aggregate has a major absorption, many authors emphasize the need for a correction of water in order to have the same effective water/cement ratio. In spite of having increased the percentage of substitution of recycled aggregate, effective water/cement ratio was reduced. We have decided not to do any alteration of the water due to the disparity of theories about how this correction should be done. In order to control this variable, a study has been done with a calibrated cementometer to quantify the reduction of the effective water/cement ratio due to the major absorption of the arid recycling.