Use of biomass fly ash for mitigation of alkali-silica reaction of cement mortars T.C. Esteves a , R. Rajamma b , D. Soares c , A.S. Silva c , V.M. Ferreira b , J.A. Labrincha a,⇑ a University of Aveiro, Department of Ceramics and Glass Engineering/CICECO, 3810-193 Aveiro, Portugal b University of Aveiro, Department of Civil Engineering/CICECO, 3810-193 Aveiro, Portugal c National Laboratory for Civil Engineering (LNEC), Materials Department, 1700-066 Lisbon, Portugal article info Article history: Received 6 April 2011 Received in revised form 22 June 2011 Accepted 23 June 2011 Available online 22 July 2011 Keywords: Alkali-silica reaction Mitigation Biomass fly ash Metakaolin Mortars abstract The degradation of large concrete structures over time is well known. One of the main reasons is the reac- tion that occurs between the cement paste and some reactive siliceous aggregates, which causes a signif- icant expansion that depends on the employed materials and exposure conditions of the structure. This process is known as alkali-silica reaction (ASR) and affects several structures worldwide, including major dams and bridges in long time run. In this work the effect of fly ashes from biomass combustion in the mitigation of the ASR was investigated. The fly ashes were collected from two industrial plants located in the central area of Portugal: (i) a thermal power plant (BFA 1 ), (ii) co-generation process of a pulp and paper industry (BFA 2 ). The fly ashes were characterised by different techniques to determine the fol- lowing properties: particle size distribution (laser interference), loss on ignition and thermal behaviour (TG/DTA), chemical (XRF) and phases (XRD) composition and pozzolanic activity (EN 196-5:2005). These biomass fly ashes were irregular in shape and fine in size. The chemical characterisation revealed signif- icant differences in CaO and SiO 2 contents, but both fly ashes can be considered as class C fly ashes if com- pared with those generated from the coal combustion. Accelerated mortar-bar tests were conducted according to ASTM C1260/ASTM C1567 to evaluate the behaviour of the biomass fly ash in the ASR inhibition mechanism. The expansive behaviour was studied on mortars where the cement was partially replaced (20–30 wt%) by the biomass fly ashes. This substitu- tion tends to reduce the expansion upon accelerated curing conditions, and BFA 2 is more effective than BFA 1 . But the incorporation of biomass fly ash in the blend along with metakaolin (MK), 20% BFA + 10% MK did a significant improvement in the expansion results, indicating the effective use of biomass fly ash along with metakaolin in mitigating the ASR. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Since a long time, it has been observed that some aggregates incorporated in concrete develop reactions that damage the struc- tures. In concretes and mortars, the occurrence of internal expan- sive phenomenon is normally recognized as alkali-aggregate reaction (AAR). According to the nature of the constituents of the aggregate, these reactions can be classified as: (i) alkali-silica reac- tion, (ii) alkali-silicate reaction, and (iii) alkali-carbonate reaction. In particular, the alkali-silica reaction (ASR) is responsible for the deterioration of concrete structures [1]. This phenomenon involves long, complex and costly repairs. Damage due to ASR in concrete is a phenomenon that was first recognized in 1940 by Stanton in North America [2]. However, ASR mechanisms are not yet enough understood. The influencing factors that favour ASR are: (i) use of reactive aggregates, (ii) strong alkalinity, (iii) water or high moisture levels. Other factors can play a significant role, such as the porosity of the concrete, external temperature and alkalis introduced by some mineral additives or admixtures or by the water [3]. Several studies have been published about the ASR, and it is widely accepted that ASR gel product is formed by the reactions between alkali cations (K + , Na + ) and hydroxyl groups (OH À ) pres- ent in the pore solution and poorly crystallized siliceous minerals found in some aggregates that results in the expansion and crack- ing of the concrete [4]. The use of industrial wastes, such as fly ash or blast-furnace slag have been proved effective means of control- ling the deleterious expansions due to ASR [5,6]. Researchers have proved the significant possibility of using biomass fly ash, another industrial waste material for cement replacement [7–9]. However, biomass fly ash is excluded from additions in concrete according to the current standards because of its non-coal origin. Recently, the new standard EN-450-1 included fly ash obtained from co- combustion of specific co-combustion biomass materials up to 20% by mass of the total fuel. Class C fly ashes with high CaO con- tent are also reported to be useful in mitigating ASR and biomass fly ashes usually are high calcium fly ashes. [7,10]. 0950-0618/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2011.06.075 ⇑ Corresponding author. Tel.: +351 234370250; fax: +351 234370204. E-mail address: jal@ua.pt (J.A. Labrincha). Construction and Building Materials 26 (2012) 687–693 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat