Production of carbon negative concrete for jointed plain concrete road slab construction.

Abstract

Under the context of elevated greenhouse gases emission, how to reduce carbon emissions and increase carbon absorption is the focus of current research on climate change. Concrete is a convection building material the second most consumed material on earth after water which is in its production characterized with significant quantities of emissions and with little lifecycle carbon dioxide absorption through a process of carbonation. This project mainly focused on the production of carbon negative concrete through the utilization pozzolana cement and incorporation of steel slag an industrial in concrete. The materials were obtained from various places and characterized to obtain their properties. The concrete mix design was carried out and there after the life cycle carbon footprint of the concrete was obtained. The amount of steel slag that is need to be incorporated in the concrete to make the carbon neutral concrete was obtained and it was 903.35Kg. Mix ratios incorporating steel slag and using the pozollana cement were obtained. Different test was carried out on the concrete to be produced to assess it strength properties and it was realized that upon the incorporation of steel slag in the mix the compressive and tensile strength increased up to 80% replacement of steel slag and later on decreased. The durability of the samples was assessed and found that it decreased with the increase in the replacement of steel slag for coarse aggregates. Carbonation tests were carried out and it was found that the incorporation of steel slag increases the amount of carbon dioxide uptake which thus confirm the participation of steel slag in the carbon uptake. The optimum mix that was considered after performing all those test was the one with an 80% replacement of coarse aggregates with steel slag and it had a compressive strength of 38.9N/mm2 at 28 days and the normal concrete had a compressive strength of 33.N/mm 2 at 28 days. The carbon uptake by the optimum mix ratio observed was 0.29% and for the normal concrete was 0.075% after seven days of exposure. The sample with the optimum mix ratio was assessed for its durability upon cyclic loading and it was noticed that the durability increases until when a stress of 20% the compressive strength is applied and when exceeded, the durability of the carbon negative concrete decreases as cracks start developing. The plain concrete slab was designed in accordance to the ACI 318 for both the carbon negative concrete and normal concrete and later on simulated using ansys to confirm the safety of the designs. An economic analysis was carried out on the project to assess it worth and it was found out that it is more worth and cheaper to construct a carbon negative concrete road slab than a normal concrete road slab. Key words: carbon negative concrete, normal concrete, pozzolana cement, steel slag, carbonation.