Abstract
This paper investigates cement mortars made with waste plastic aggregates (polycarbonate-PC-, polyoxymethylene -POM-, acrylonitrile-butadiene-styrene -ABS-, an ABS/PC blend -ABSC- and polyethylene terephthalate -PET-) as partial sand replacements at 5–20% by volume.Even at 20% plastic content, the strength surpasses the standard strength requirements for masonry, rendering and plastering mortars, with compressive strengths ranging from c.37–71 MPa and flexural strengths reaching 4–9 MPa. Most plastics, in contents up to 15%, enhance the flexural strength of the standard cement mortar which can improve the resistance to tensile stress caused by loading and expansion by frost, salt or swelling clays.The plastic aggregates increase the cement mortar's ability to deform on stress application, delaying failure and turning the typical brittle failure of cement mortars into a ductile failure, a notable asset for those specifying repair mortars for masonry which typically deforms over time.The fall in the mechanical/hygric properties and density caused by the plastic (>15% content), is mainly due to the proliferation of disrupted interfaces rather than to the physical properties of the plastics themselves. There is not significant direct correlation between the properties of the mortars and those of their plastic aggregates – except for the compressive strength. The relationship can sometimes appear inverse, suggesting that larger differences between plastic and cement matrix properties can enhance incompatibility and lower durability. However, the grading, shape and surface characteristics of the plastic particles impact the properties of the resultant mortars. The results highlight the performance of the ABS (best graded plastic) barely rising the hygric properties, even at 15% replacement, and showing high strengths and sealed interfaces.
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