Alkali silica reaction in mortar formulated from self-compacting high performance concrete containing rice husk ash Ha Thanh Le a,b,⇑ , Karsten Siewert a,1 , Horst-Michael Ludwig a,2 a F.A. Finger-Institute for Building Materials Science, Faculty of Civil Engineering, Bauhaus-University Weimar, Coudraystr. 11, 99423 Weimar, Germany b Institute of Construction Engineering, University of Transport and Communications, Lang Thuong, Dong Da, Hanoi, Viet Nam highlights  The effect of rice husk ash on ASR in mortar formulated from SCHPC was investigated.  The mortar containing reactive greywacke aggregate can be durable when SF and RHA5.7 are used.  SF was significantly more effective than RHA in mitigating ASR in mortar.  RHA had paradoxical effect on ASR especially when coarse RHA is used.  To mitigate ASR, RHA should be ground to very fine particle sizes of at least 5.7 lm. article info Article history: Received 28 November 2014 Received in revised form 6 April 2015 Accepted 9 April 2015 Keywords: Self-compacting high performance concrete Rice husk ash Alkali silica reaction Paradoxical effect Reactive aggregate Non-reactive aggregate abstract In the present study, the resistance of mortar formulated from self-compacting high performance con- crete containing rice husk ash (RHA)/silica fume (SF) and reactive/non-reactive aggregates to alkali silica reaction (ASR) was assessed. For the mortar containing greywacke reactive aggregate, SF is significantly more effective than RHA in reducing expansion of the mortar under accelerated testing conditions (NaOH 1 M at 80 °C). The increase in particle size of RHA increased the expansion of mortar. Surprisingly, the mortars containing coarse RHA, i.e. 15.6 and 7.7 lm, were disrupted after 28 and 56 days of immersion. However, the increase in the fine RHA (5.7 lm) content decreased the expansion of mortar. For the mortar containing non-reactive basalt aggregate, the incorporation of RHA increased the expan- sion, and the samples containing the coarse RHA (15.6 lm) cracked substantially. This indicates that RHA had paradoxical effect on ASR. The results from microscopic investigations show that RHA particles cracked substantially. The cracks also radiated from the RHA particles into the matrix, and ASR gels formed inside the RHA particles. It is suggested that to mitigate ASR by using RHA, RHA should be ground to very fine particle sizes of at least 5.7 lm. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Self-compacting high performance concrete (SCHPC) can be defined as a new generation of concrete on the basis of the concepts of self-compacting concrete (SCC) and high performance concrete (HPC). As a result, SCHPC possesses the adequate self-compactability (filling ability, passing ability and segregation resistance) of SCC and the high strength and good durability of HPC [1]. In order to fulfil these requirements, a high volume of Portland cement, an extensive dosage of chemical admixtures and reactive supplementary cementitious materials (SCMs), e.g. silica fume (SF), are used. Alkali silica reaction (ASR) is a deleterious reaction caused by a reactive aggregate and cement paste pore solution. The reaction between alkali hydroxides in concrete pore solution and amor- phous or poorly crystalline silica phases in aggregates or SCMs forms alkali silica gels which absorb water and expand [2–5]. The high cement content in SCHPC leads to a high amount of soluble alkali in the pore solution. This results in a high probability of http://dx.doi.org/10.1016/j.conbuildmat.2015.04.005 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: F.A. Finger-Institute for Building Materials Science, Faculty of Civil Engineering, Bauhaus-University Weimar, Coudraystr. 11, 99423 Weimar, Germany. Tel.: +49 3643 584765; fax: +49 (0) 3643 584759. E-mail addresses: lehautc@daad-alumni.de (H.T. Le), karsten.siewert@ uni-weimar.de (K. Siewert), horst-michael.ludwig@uni-weimar.de (H.-M. Ludwig). 1 Tel.: +49 (0) 3643 58 4725; fax: +49 (0) 3643 58 4759. 2 Tel.: +49 (0) 3643 584761; fax: +49 (0) 3643 584759. Construction and Building Materials 88 (2015) 10–19 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat