# Early Age Assessment of a New Course of Irish Fly Ash as a Cement Replacement
## 1 Introduction  
Coal-powered electrical energy in Ireland will be phased out entirely by 2025. The only coal-fired power station in Ireland is located at Moneypoint in Co. Clare on the west coast. Coal-burning for electricity generation in Ireland will be phased out by 2025, when the plant was due for decommissioning, but, due to the current energy crisis, it will continue operations as a back-up until 2029. Moneypoint, which generates up to 915 MW and has been operational since 1987, has several million tonnes of unconditioned (\"wet\") fly ash deposited over a 25-acre ash field. Between now and 2028, when the station is scheduled to be finally decommissioned, a further 800,000 tonnes of fly ash may be deposited, based on projected operation patterns. The ash stored on site has been separated into three deposits from 1985 to 1995, 1995 to 2005 and 2005 to present. This paper presents a characterisation and hydration study of the ash dating from 1985 to 1995. Subsequent publications will present the two other deposits.  
Significant reductions in current carbon dioxide (CO\({}_{2}\)) levels proposed by the European Union (80% by 2050 [1]) have been adopted by member states, including Ireland. The production of Portland cement (PC) contributes to 8% of worldwide greenhouse gas emissions [2]. Cement production in Ireland is currently at 5 million tonnes annually, which releases circa 4 million tonnes of CO\({}_{2}\) into the atmosphere. Therefore, partially replacing or blending Portland cement with suitable supplementary cementitious materials (SCMs) would yield substantial reductions in CO\({}_{2}\) emissions per tonne of cement. Current cement standards [3] define two types of siliceous fly ash blends that permit cement replacement by fly ash of up to 20% (CEM II/A-V) or 35% (CEM II/B-V). With a 35% replacementlevel (CEM II/B-V), typical in the US and UK, an annual reduction of circa 650,000 of CO2 could be realised, representing 2% of Ireland's total carbon emissions annually. With over 12 million tonnes of concrete produced annually in Ireland, CEM II/B-V cement could utilise up to 750,000 tonnes of Moneypoint fly ash each year.  
In order to investigate the suitability of this fly ash as a suitable cement replacement in concrete, building on previous work [4, 5], this paper presents the initial findings of its characterisation, including moisture content and the XRF and XRD over time of hydrating samples. To observe how it performed in concrete, the compressive strength of concrete samples was assessed using 100 mm cubes. Fly ash has been used at CEM I replacement levels of 0, 10, 25 and 35% to demonstrate the optimum point of replacement, which is in accordance with EN 197 [3]. In addition, in order to improve thermodynamic predictions, a suite of phase equations to represent the behaviour of the ash amorphous/glass phase during hydration has been developed, taking into account its oxide proportions. These equations are added to the PHREEQC input file for fly ash replacement levels from 5 to 35% in 5% steps and replace the traditional method of adding additional CaO, Al2O3, etc. to represent the glass in fly ash. This approach can also be used to represent the glass phase in most SCMs.