Towards a Low Carbon Concrete

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The current environmental crisis could be tackled by reducing greenhouse gas emissions. One possible solution is the decarbonization of the cement industry, as the cement industry contributes to about 8% of global CO2 emissions since every ton of Ordinary Portland Cement (OPC) emits about 0.97 tons of CO2. Alternative cement formulations such as calcium sulfoaluminates (CSA), which mainly constitute of ye’elimite (C4A3$) phase could potentially reduce CO2 emissions due to the lower quantity of limestone used for production and lower clinkering temperature. Moreover, calcium sulfoaluminate (CSA) cement are promising candidates that can substitute OPC because of its rapid strength gain, shorter curing time, and lower shrinkage. Yet, the production process of CSA or similar family cement still lacks some economical and process viability. The novelty of GORD Institute’s cement processing technology compared to conventional cement production is the use of sulfur burning as the source of heat and sulfates, required in the production of CSA, which enables a significant reduction in the amount of fuel used in the process and limestone to be calcined, thus a reduction in the carbon footprint with a comparable operational cost to conventional cement. The utilization of sulfur doesn’t only preserve the mineralogy ye’elimite phase in CSA cement but also provides improvements in the mechanical properties of the resultant concrete product, outperforming ordinary Portland Cement. Extensive laboratory experiments and pilot scale studies were conducted in the development stage of this technology to investigate its viability. The findings and hypothesis of the project can be outlined in several publications cited here [1–3]. For lab-scale studies, a configuration designed by GORD was used in all experiments, which included an electrically heated furnace that resembles a kiln, mass flow controllers, and a scrubber to neutralize and clean excess SO2 gas. The SO2-containing atmosphere is composed of a mixture of nitrogen, oxygen, and sulfur dioxide at different partial pressures. Numerous ye’elimite and alpha prime belite clinkers were successfully prepared with desired mineralogy avoiding sulfur volatilization upon using the SO2-containing atmosphere technology. These clinkers were then characterized, and their performance was tested through hydration studies, compressive strength, etc. Results showed that a new generation of low-carbon footprint and low-cost cement could potentially be commercialized. Subsequent to the lab scale studies, a series of trials were conducted at a pilot scale at the IBU-Tec Research and Development site in Weimar, Germany. Clinkers with satisfactory proportions of ye’elimite and belite (35 – 40 wt. % and 40-45 wt. % respectively) and low anhydrite contents (≤ 5 wt. %) were produced that showed superior properties compared to OPC in terms of compressive strength, sulfate resistance, and shrinkage. The proposed schematic for the SO2-containing atmosphere pilot scale plant is very similar to the conventional OPC process but only differs in the addition of sulfur to the precalciner and kiln burners, a modified raw feed composition, and a wet scrubber to generate gypsum. Only limited modifications are required to adapt a traditional cement plant to the GORD process and, along with the easy worldwide availability of raw materials such as sulfur, the technology presented here is one of the few opportunities which have the potential to change worldwide cement production away from the traditional Portland cement process. Moreover, there are many kilns with high-sulfur content fuels as well as wet scrubbers to meet emissions standards, the only change is that these are mandatory elements of our process. This innovation could imply a change in the paradigm of cement production and consumption in countries with large sulfur reserves, such as Qatar. The proposed novel cement processing technology has been proven to produce clinker, at pilot scale, which outperform the mechanical strength properties needed by industrial standards. Therefore, given the actual technology readiness level of GORD Institute’s CSA (TRL 6) and the feasibility of its potential commercial production, the proposed project will target the scale-up of the process in terms of: • Construction and utilization of SO2 containing pilot kiln to produce a range of product formulations while optimizing the sulfurous fuel. • Construction of a unique pilot plant designed to achieve the high thermal efficiency of industrial kilns. This high thermal efficiency is essential to prove the GORD Institute process as the formulation chemistry is directly linked to the quantity of sulfur burnt, which itself is proportional to the heat requirement; thus, industrial efficiencies are required to optimize and prove full-scale production. • Demonstration of SO2 capture within the pilot kiln pre-heater cyclone stack to provide reassurance to industrial partners that the scrubbing can be carried out effectively. The technology presented here is one of only a few key developments which have the potential to change worldwide cement production from the traditional Portland cement process. The GORD Institute approach has already been proven at the pilot scale, however, further product and process development toward full-scale production is needed. Refernces: [1] A. Elhoweris, I. Galan, F.P. Glasser, Stabilisation of α ′ dicalcium silicate in calcium sulfoaluminate clinker, Adv. Cem. Res. 32 (2020) 112–124. https://doi.org/10.1680/jadcr.18.00050. [2] Y. Al Horr, A. Elhoweris, E. Elsarrag, The development of a novel process for the production of calcium sulfoaluminate, Int. J. Sustain. Built Environ. 6 (2017) 734–741. https://doi.org/10.1016/j.ijsbe.2017.12.009. [3] I. Galan, A. Elhoweris, T. Hanein, M.N. Bannerman, F.P. Glasser, Advances in clinkering technology of calcium sulfoaluminate cement, Adv. Cem. Res. 29 (2017) 405–417. https://doi.org/10.1680/jadcr.17.00028.