Evaluation of glass powder in the mitigation of the alkali-silica reaction (ASR)

The alkali-silica reaction (ASR) is one of the problems that can compromise concrete durability, as the chemical reactions between the reactive aggregate and concrete pore solution, specifically sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺) and hydroxyl (OH^-) in the presence of moisture, trigger expansion and cracking of concrete elements. The use of pozzolanic materials, such as finely ground glass powder (particles smaller than 75μm), to partially replace cement has been widely studied and has demonstrated beneficial results. However, because the behavior of pozzolans towards ASR is not completely understood yet, this work evaluates the effect of incorporating ground glass powder into cementitious composites against ASR. To this end, 8% silica fume was used as a control admixture, and four levels of glass powder (10, 20, 30, and 50%) were incorporated into the cementitious mixture to partially replace cement. Expansion tests were carried out in accordance with NBR15577-4 (ABNT, 2018) on mortar bars using the accelerated test method to assess the mitigation of expansions. The results show that the expansions caused by ASR decreased with the increasing content of glass powder in the cement mixtures. Furthermore, only the 50% level reduced the expansions to a safe value according to the Brazilian standard.

Keywords:
alkali-aggregate reaction; mitigation; pozzolanic materials; glass powder

Components	Values (% mass)
Components	Portland cement	Glass powder	Silica fume	Reactive aggregate
SiO₂	18.76	74.00	94.10	10.94
Al₂O₃	4.15	3.70	< 0.20	1.67
Fe₂O₃	3.56	0.42	< 0.50	1.31
CaO	63.00	9.10	< 0.20	42.54
MgO	0.51	0.74	-	4.70
SO₃	2.79	-	-	0.09
CO₂	4.72	-	-	36.64
Na₂O	0.32	11.00	< 0.20	0.01
K₂O	0.81	0.56	1.28	0.33
Others	1.38	<0.50	1.72	1.77
LOI^* * Loss on ignition (LOI) and **Insoluble residue (IR)	5.89	0.58	3.60	38.16
IR^**	1.34	0.02	-	14.54

Potential reactivity class of the aggregate	Expansion of mortar bars at 30 days - %
Potentially harmless grade R0	Less than 0.19%
Potentially reactive grade R1	Between 0.19 and 0.40%
Potentially reactive grade R2	Between 0.41 and 0.60%
Potentially reactive grade R3	Greater than 0.60%

Methodology	Values	Standard limit
Modified Chapelle NBR 15895 [²⁷27 Associação Brasileira de Normas Técnicas, Materiais Pozolânicos – Determinação do Teor de Hidróxido de Cálcio Fixado – Método Chapelle Modificado, ABNT NBR 15895, 2010.]	1319	> 436 mg Ca(OH)₂/g sample
Performance Index with Portland cement ABNT NBR 5752 [²⁸28 Associação Brasileira de Normas Técnicas, Materiais Pozolânicos – Determinação do Índice de Desempenho com Cimento Portland aos 28 Dias, ABNT NBR 5752, 2014.]	84%	> 90%
Performance Index with Portland cement ASTM C 618-05 [²⁹29 American Society for Testing and Materials, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete, ASTM C618-05, 2010.]	84%	> 75%

IBRACON - Instituto Brasileiro do Concreto Instituto Brasileiro do Concreto (IBRACON), Av. Queiroz Filho, nº 1700 sala 407/408 Torre D, Villa Lobos Office Park, CEP 05319-000, São Paulo, SP - Brasil, Tel. (55 11) 3735-0202, Fax: (55 11) 3733-2190 - São Paulo - SP - Brazil
E-mail: arlene@ibracon.org.br

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[1] Corresponding author: Taís Oliveira Gonçalves Freitas. E-mail: taisfreitas@usp.br