# Sulfate Resistance in Cements Bearing Bottom Ash from Biomass-Fired Electric Power Plants  
[PERSON]  
1 Departamento de Construccion, Escuela Politecnica de Caceres--Grado de Ingenieria Civil, Universidad de Extremadura, Instituto de Investigacion de Desarrollo Territorial Sostenible (INTERRA), 10003 Caceres, Spain; [EMAIL_ADDRESS] (J.M.M. ); [EMAIL_ADDRESS] (I.F.S.d.B.) Departamento de Cementos y Reciclado de Materiales, Instituto de Ciencias de la Construccion Eduardo Torroja (IEtc-CSIC), 28033 Madrid, Spain; [EMAIL_ADDRESS] (M.I.S.d.R. ); [EMAIL_ADDRESS] (M.F.) Sostenibilidad en Materiales de Construccion, Universidad de Extremadura, Unidad Asociada al CSIC, Departamento de Construccion, Instituto de Investigacion de Desarrollo Territorial Sostenible (INTERRA), Escuela Politecnica de Caceres--Grado de Ingenieria Civil, Universidad de Extremadura, 10003 Caceres, Spain 10003 Caceres, Spain 10003-00  
cementitious matrices, yielding gypsum (CSH\({}_{2}\)), ettringite (C\({}_{6}\)A\(\overline{\rm S}_{3}\)H\({}_{32}\)), and sodium hydroxide (NaOH). The third, NaOH, forms in the presence of alkaline sulfates (Na\({}_{2}\)SO\({}_{4}\)). Because the volume of the resulting end products is 1.2- to 2.2-fold greater than that found in the starting reagents [5], the matrix expands and cracks, increasing permeability and water ingress in structures, and consequently the rate of decay. A second effect of ESA is the steady loss of strength, weight, and cohesion in cement hydration products [6]. From the perspective of durability, the technical implications of using supplementary cementitious materials (SCMs) in cement manufacture can be summarized as: (i) lower reactivity, resulting in less heat of hydration; (ii) lower aluminate phase (C\({}_{3}\)A and C\({}_{4}\)AF) content due to the dilution effect and the presence of the CH needed for the pozzolanic reaction; and (iii) pore system refinement resulting from that reaction (between the SCMs and CH), because the C-S-H gels generated settle in the pores, enhancing concrete impermeability [7; 8; 9]. In addition to these favorable technical effects, SCM use is associated with social and environmental benefits, including the reduction in natural resource deployment and the furtherance of progress in the pursuit of alternative SCMs drawn from industrial waste. The latter contributes to the institution of circular economy principles in construction and compliance with cement industry environmental commitments (lowering CO\({}_{2}\) emissions and energy consumption, among others) [10]. Scientific community sights are presently trained on assessing agroforestry waste as a possible source of SCMs, given that \(140\times 10^{9}\) tonnes of biomass waste are generated yearly [11]. The focus in that line of research has been on waste whose origin lies in: (i) agroforestry biomass consisting primarily of bagasse, rice, and to a lesser extent bamboo ash, laboratory-calcined at different temperatures [12; 13; 14], and (ii) biomass ash or biomass bottom ash from heat and/or power plants [15; 16; 17], \(\sim\)\(10\times 10^{6}\) tonnes of which are generated yearly [18]. Research efforts in connection with the latter have consisted of analyzing the effect of using biomass ash (BA) on the mechanical characteristics of the new mortars. The findings vary depending on the origin and nature of the waste, in addition to the replacement ratio [16; 19; 20]. Very few papers have been published, however, on the behaviour of new eco-cements in aggressive environments (chlorides, carbonation, freeze-thaw), although replacement ratios of over 10% BA have been shown to lower resistance [21]. Blending ordinary Portland cement (OPC) with up to 20% BA has nonetheless been reported to prompt water sorptivity and a decline in swelling- and shrinkage-induced variations in volume [22]. Only one paper has been published to date on sulfate resistance in cements bearing this waste. According to the authors, [PERSON] et al.