Effects of varying recycled fine aggregate content and water/cement ratio in bedding mortar

Abstract

This paper presents the results from a research carried out with the aim of analysing the usability of Recycled Fine Aggregates (RFA) produced from Construction and Demolition Waste (CDW), in bedding mortar. Properties of RFA were compared to that of the Natural Fine Aggregates (NFA) in terms of Bulk Density, Fine Fraction, Particle Size Distribution, Water Absorption and Chloride Content and were tested for five mixed proportion scenarios of RFA and NFA at 0%, 25%, 50%, 75% and 100% RFA contents. RFA indicated a water absorption of 6.33% when compared to that of 0.71% for NFA (ordinary river sand). Mortar testing was further divided under three water/cement ratios at 0.5, 0.6 and 0.7. Bulk density gradually decreased with increased RFA content yet recorded an exceptional highest of 1476Kg/m3 at 75%RFA. Results from fine fraction and particle size distribution indicated compatibility of RFA to replace NFA up to 50% RFA. Chloride content analysis indicated allowable RFA replacement levels up to 99% and 44% for bedding mortar and plastering mortar applications, respectively. Though higher water absorption demanded for higher water content, Compressive Strength increased with the increasing RFA content, even above NFA values, reaching a maximum of 15.2 ± 0.50 N/mm2 at 75% RFA for 0.7 water/cement ratio while workability was within the acceptable range at 50% RFA at the same water content. The analysis in terms of fine aggregate properties and mortar properties showed that up to 50%, NFA can be substituted with RFA at water/cement ratio of 0.7 in bedding mortar which will also attribute to a cost reduction of minimum 50%, as well as to greatly reduce the disastrous environmental impacts from sand mining and waste disposal thus enhancing sustainability.