Possibility of using dry ryegrass as a partial substitution of Portland cement to produce concrete for reducing carbon footprint of cement

Abstract

Cement production has a significant impact on the environment due to its high carbon footprint during production processes. Altering composition of concrete by reducing proportion of cement could be a way to contribute to climate change mitigation initiatives. This study aimed to investigate the possibility of using dry ryegrass as a partial replacement for cement to produce concrete. Seven concrete samples were prepared by mixing dry ryegrass with varying proportion (i.e., 0.0, 0.2, 0.5, 1.0, 2.0, 5.0 and 10.0%) with a readymade mix of concrete having a 10 to 20% cement ratio. The 28-day mechanical property (compressive strength) of the concrete samples was compared with the 28-day characteristic compressive strengths of the normal strength grades specified in NZS 3109. Samples with 2.0, 5.0 and 10.0% of dry ryegrass mixture did not have enough strength to withhold the compression test and quantifiable measurements could not be obtained. Samples with 1.0% of dry ryegrass mixture had negligible compression strength. The low compressive strength of the sample with 1.0, 2.0, 5.0 and 10.0% of dry ryegrass mixture was associated with the higher water retention by the grass present in the concrete mixture which prevented the curing process. The higher water retention also reduced the effective binding of the aggregate. Average compressive strength of the samples with 0.2 and 0.5% dry ryegrass mixture had 28.13 and 21.58 MPa, respectively. Sample with 0.2% dry ryegrass mixture can be applicable in heavy applications while sample with 0.5% dry ryegrass mixture can be applicable in light applications. Manufacturing a kg of cement produces a kg of CO2 thus, if 0.5% dry ryegrass mixture is used in concrete production, 0.5% CO₂ emission can be reduced. However, even at 0.2% dry ryegrass mixing the strength reduced by 39%. So, it might not be reasonable to go for 0.5% carbon emission reduction at the cost of 40% strength reduction. The results confirmed that the use of dry ryegrass as a partial component of cement for the preparation of concrete is not justifiable.