In Singapore, although the recycling rate for wood waste is around 77%, recycling rate of horticultural waste is only about 48%. In 2016, the total amount of wastes in Singapore rose to 7.67 million tonnes while the recycling... [ view full abstract ]
In Singapore, although the recycling rate for wood waste is around 77%, recycling rate of horticultural waste is only about 48%. In 2016, the total amount of wastes in Singapore rose to 7.67 million tonnes while the recycling rate of horticultural wastes increased slightly. Out of this total amount of generated wastes, food wastes accounted for 785,500 tonnes, but the average recycling rate of food waste was only 13%. Due to land constraint, Singapore incinerates all combustible wastes and the bottom ash is transferred to an offshore landfill. This landfill – the only one in Singapore – is expected to reach its full capacity in about 30 years’ time. Therefore, it is imperative for Singapore to find ways to minimize and/or recycle its wastes into different types of useful by-products. This study aims to explore the recycling of horticultural and food wastes into additives in cementitious mortar, which is widely used as a building material. Biochar – a by-product of pyrolysis of saw dust and food wastes – was evaluated as an additive in mortar, in terms of compressive and flexural strength (according to ASTM 109 and ASTM 348 respectively), water sorptivity (ASTM C1585), and depth of water penetration (BS EN 12390-8). Experimental findings suggest that addition of 1-2 wt.% of mixed food waste biochar and rice waste biochar in mortar results in similar mechanical strength as the control mix (mortar without biochar), but adding 1 wt.% of mixed food waste biochar leads to 40% and 35% reductions in water penetration and sorptivity respectively. On the other hand, biochar from mixed wood saw dust increases the compressive strength and tensile strength by up to 20%, while depth of water penetration and sorptivity is reduced by about 60% and 38% respectively (compared to control). Furthermore, this study evaluates the use of biochar for enhancing the strength of cement mortar that is reinforced with polypropylene (PP) fibers. It was found that samples containing fibers that were coated with a layer of biochar (added at 1.5% wt.) recorded a 11% improvement in both compressive and flexural strength over control samples (containing PP fibers that were not coated with biochar). The water penetration depth decreased by 62% for samples containing biochar. These results can be explained by the micro-filler effects caused by the biochar particles, which not only strengthens the bond between the surfaces of the PP fibers and the mortar matrix, but also enhances the close-packing effect of the sand particles in the mortar mixture. These results highlight the potential of biochar as a mean of waste recycling that also improves the overall performance of mortar. Socially and economically, this technology has the potential to spur local employment by creating additional purpose to salvage wood and food waste for pyrolysis. Having more durable and stronger buildings reduces the frequency of repairs over the service lifespan of buildings, thus contributing to the economic and environmental sustainability of the building industry.
Keywords: cementitious mortar, food wastes, biochar, horticultural wastes.
6b. Urban and rural development
