Potential reactivity of granitic rocks. Petrographic characterization vs accelerated expansion tests

RAMOS, V.; FERNANDES, I.; SILVA, A. S.; SOARES, D.; NORONHA, F.

doi:10.1590/S1983-41952016000100005

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Articles • Rev. IBRACON Estrut. Mater. 9 (1) • Jan-Feb 2016 • https://doi.org/10.1590/S1983-41952016000100005 copy

Potential reactivity of granitic rocks. Petrographic characterization vs accelerated expansion tests

Reatividade potencial de rochas graníticas. Petrografia vs ensaios de expansão

Authorship SCIMAGO INSTITUTIONS RANKINGS

Several cases of alkali-silica reaction involving granitic aggregates have been diagnosed in damaged concrete structures in Portugal. Nonetheless, this kind of rock is usually regarded as slow/late reactive or even non-reactive to alkalis. Granitic rocks are widely exploited in Northern and Central Portugal, representing almost half of the produced aggregates in this country. Project IMPROVE rose from the need to accurately diagnose the potential reactivity of granites to alkalis. The study involved about forty granites collected from different regions in Portugal, from which the results of eight samples are being presented in this paper. The tests carried out include the petrographic analyses of the aggregates and mortar and concrete expansion tests. It was concluded that the content of microcrystalline quartz correlates better with the results of AAR-4.1 than with the other expansion tests.

alkali-silica reaction; granites; petrography; expansion tests; performance

Test	Cement/aggregate	Water/cement	Cement
Test	Cement/aggregate	Water/cement	Type	Na₂O_eq (%)
ASTM C 1260	0.44	0.47	CEM I 42,5 R	0.86 - 0.89
RILEM AAR-4.1	0.25	0.45	CEM I 42,5 R	0.89
RILEM AAR-3	0.25	0.45	CEM I 42,5 R	0.89

Aggregate	Brief petrographic description	Undulatory extinction angle (º) of quartz crystals (mean) and respective class*	Potentially reactive silica forms (< 100 µm) (vol.%) and reactivity class
GR1	Medium-grained granite with porphyritic tendency. Frequent microcracks, especially in quartz and plagioclase crystals, filled by microcrystalline muscovite and oxides.	16.0 Moderate	Quartz inclusions; myrmekites 2.4 Class II
GR2	Coarse to medium-grained porphyritic granite with deformation evidences.	20.0 Moderate	Tectonized quartz; quartz inclusions; myrmekites 21.7 Class II
GR3	Coarse to medium-grained porphyritic granite with abundant microcracks filled by oxides and microcrystalline muscovite.	18.0 Moderate	Quartz inclusions; myrmekites 1.0 Class I
GR7	Coarse to medium-grained porphyritic granite	14.0 Weak	Myrmekites 0.1 Class I
GR17	Medium to fine-grained granite.	15.0 Moderate	Quartz inclusions; myrmekites 1.5 Class I
GR18	Medium-grained porphyritic granite with deformation evidences.	23.0 Moderate	Tectonized quartz; quartz inclusions; myrmekites 4.8 Class II
GR19	Medium-grained granite. Presence of abundant microcracks.	20.0 Moderate	Quartz inclusions; myrmekites 1.4 Class I
GR20	Medium to fine-grained granite. Presence of abundant microcracks.	19.0 Moderate	Quartz inclusions; myrmekites 1.2 Class I

Method	Criteria	GR1	GR2	GR3	GR7	GR17	GR18	GR19	GR20
Petrographic characterization	RILEM AAR-1.1 [ ¹⁵[15] RILEM AAR-1.1. Detection of potential alkali-reactivity, Part 1: petrographic examination method for aggregates. In: NIXON PJ and SIMS I (Eds.). RILEM recommendations for the prevention of damage by alkali-aggregate reactions in new concrete structures, State-of-the-art report of the RILEM Technical Committee 219-ACS, RILEM State-of-the-Art Reports, Springer-Dordrecht, Netherlands v. 17, 2016; p. 35-60.]	Class II	Class II	Class I	Class I	Class I	Class II	Class I	Class I
	LNEC E 461 [ ²⁰[20] LNEC E 461. Betões. Metodologias para prevenir reacções expansivas internas. Especificação LNEC, Lisboa, Portugal, 2007: 6 p.]	Class II	Class II	Class I	Class I	Class I	Class II	Class I	Class I
	Microcrystalline quartz (vol.%)	2.4	21.7	1.0	0.1	1.5	4.8	1.4	1.2
	Undulatory extinction	Mod.	Mod.	Mod.	Weak	Mod.	Mod.	Mod.	Mod.
ASTM C 1260	RILEM AAR-0 [ ¹⁸[18] RILEM AAR-0. Outline guide to the use of RILEM methods in the assessment of the alkali-reactivity potential of aggregates. In: NIXON PJ and SIMS I (Eds.). RILEM recommendations for the prevention of damage by alkali-aggregate reactions in new concrete structures, State-of-the-art report of the RILEM Technical Committee 219-ACS, RILEM State-of-the-Art Reports, Springer-Dordrecht, Netherlands v. 17, 2016; p. 5-34.]	NR	NR	NR	NR	NR	NR	NR	NR
ASTM C 1260	Santos Silva and Braga Reis [ ²¹[21] SANTOS SILVA A, BRAGA REIS MO. Avaliação da reactividade aos álcalis dos agregados para betão. In: Proceedings of the Encontro Nacional de Betão Estrutural, Faculdade de Engenharia da Universidade do Porto, Portugal, 2000; p.23-32.]	NR	NR	NR	NR	NR	NR	NR	NR
RILEM AAR-4.1	LNEC E 461 [ ²⁰[20] LNEC E 461. Betões. Metodologias para prevenir reacções expansivas internas. Especificação LNEC, Lisboa, Portugal, 2007: 6 p.]	NR	PR	PR	NR	PR	PR	NR	PR
	RILEM AAR-0 [ ¹⁸[18] RILEM AAR-0. Outline guide to the use of RILEM methods in the assessment of the alkali-reactivity potential of aggregates. In: NIXON PJ and SIMS I (Eds.). RILEM recommendations for the prevention of damage by alkali-aggregate reactions in new concrete structures, State-of-the-art report of the RILEM Technical Committee 219-ACS, RILEM State-of-the-Art Reports, Springer-Dordrecht, Netherlands v. 17, 2016; p. 5-34.]	NR	PR	NR	NR	PR	NR	NR	PR
	Lindgård et al. [ ¹⁹[19] LINDGÅRD J, NIXON PJ, BORCHERS I, SCHOUENBORG B, WIGUM BJ, HAUGEN M, ÅKESSON U. The EU "PARTNER" Project - European standard tests to prevent alkali reactions in aggregates: final results and recommendations. Cement and Concrete Research, v. 40, 2010; p.611-635.]	NR	PR	PR	NR	PR	PR	PR	PR
RILEM AAR-3	RILEM AAR-0 [ ¹⁸[18] RILEM AAR-0. Outline guide to the use of RILEM methods in the assessment of the alkali-reactivity potential of aggregates. In: NIXON PJ and SIMS I (Eds.). RILEM recommendations for the prevention of damage by alkali-aggregate reactions in new concrete structures, State-of-the-art report of the RILEM Technical Committee 219-ACS, RILEM State-of-the-Art Reports, Springer-Dordrecht, Netherlands v. 17, 2016; p. 5-34.] and LNEC E 461 [ ²⁰[20] LNEC E 461. Betões. Metodologias para prevenir reacções expansivas internas. Especificação LNEC, Lisboa, Portugal, 2007: 6 p.]	NR	PR	NR	NR	NR	NR	NR	NR

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E-mail: arlene@ibracon.org.br

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[TFN01] * Undulatory extinction angle [ ¹⁶[16] LNEC E 415. Inertes para argamassas e betões - determinação da reactividade potencial com os álcalis. Análise petrográfica. Especificação LNEC, Lisboa, Portugal, 1993; 6 p.]: Weak - (0º - 14º); Moderate - (15º - 24º); Strong - (25º - 35º)