Preparation and properties of ecological concrete with maize-cob aggregate

Abstract: 52 million tons of maize cobs are produced behind a huge annual output of maize each year in China. A maize cob was normally estimated as 21% of a whole maize. Previous maize cobs are generally discarded or burned as fuel, wasting natural biomass resources, while seriously polluting the environment. Currently, most maize cobs with a low utilization rate are used in the field of feeding, fungus planting, and chemical industry. Actually, maize cobs can serve as insulation materials or non-load-bearing structures, due to the high toughness, moderate strength, sound and heat insulation from the naturally porous structure. But only a few studies were focused on the utilization of maize cobs in construction. Waste concrete after crushing and screening can be an alternative way to prepare recycled aggregates with maize cobs in rural areas. In this study, a light and heat-preservation ecological concrete was fabricated, where maize cobs were broken into particles to serve as coarse aggregates in recycled mortar. The particle gradation of maize-cob aggregate was analyzed under various cement-sand ratios and maize-cob volume contents. A field test was also conducted to evaluate the performances of ecological concrete. The results show that the ecological concrete behaved a high strength with the reasonable particle gradation, when the mass ratio for the small and large particles of maize cob was 1∶1.5. There was little influence of cement-sand ratio on the dry density of ecological concrete. But the recycled sand contributed to the decrease of thermal conductivity and strength. The dry density, thermal conductivity, and strength of ecological concrete decreased obviously with the increase of maize-cob volume content. In the field test, the dry density of ecological concrete was 1 200-1 550 kg/m3, while the thermal conductivity was 0.20-0.26 W/m·K, and the 28d strength was 2.0-5.7 MPa. The thermal conductivity was positively correlated with the 28 d strength of ecological concrete, while both increased as the dry density increased. Ecological concrete with maize-cob aggregate can be expected to replace traditional building material in agricultural and rural construction, due to its light weight, thermal insulation, and high strength. The utilization of maize cobs in ecological concrete can alleviate agricultural wastes occupies and incineration pollution. The treatment of maize cob and recycled sand can also promote the recycling use of solid wastes in agriculture and construction in rural areas.