It has been known for a long time that strained, microcrystalline or cryptocrystalline quartz-bearing
aggregates may cause alkali-silica reactions in concrete. Studying the relationship between deformation
processes and microstructural characteristics of rocks, the reason for this behaviour can be better
understood. Orthogneisses from the metamorphic basement of the Sierra Chica, Córdoba (Argentina), which
were locally and differentially deformed in ductile shear zones, were used to analyse such behaviour.
Petrographic analyses, accelerated mortar bar tests (ASTM C 1260, 2005) and chemical test (ASTM C 289,
1994) were conducted. Furthermore, corrosion tests were performed on polished rock surfaces using 1 N
NaOH solution. It was seen that the reactivity of the quartz-bearing mylonites increased by ~30% with
respect to the non-mylonitised sample due to the increment in the strained quartz content and specially
with the extended subgrain development. The mylonitised rock affected by superimposed cataclasis and the
development of pseudotachylytic veins incremented its reactivity by ~97% with respect to the nonmylonitised
sample due to the combined effects of subgrain formation, grain size reduction and the
formation of glassy material. It was also the only sample that showed significant differences in surface
corrosion confirming the high reactivity of the rock. These results agree with expansion values measured on
the accelerated mortar bar test and with silica leached in the chemical test. We believe that the simultaneous
use of different tools to evaluate the potential alkali reactivity of the rocks in concrete is a good strategy
rather than the use of isolated tools, which could lead to confusing interpretations of the process and
therefore result in erroneous decisions.
It has been known for a long time that strained, microcrystalline or cryptocrystalline quartz-bearingaggregates may cause alkali-silica reactions in concrete. Studying the relationship between deformationprocesses and microstructural characteristics of rocks, the reason for this behaviour can be betterunderstood. Orthogneisses from the metamorphic basement of the Sierra Chica, Córdoba (Argentina), whichwere locally and differentially deformed in ductile shear zones, were used to analyse such behaviour.Petrographic analyses, accelerated mortar bar tests (ASTM C 1260, 2005) and chemical test (ASTM C 289,1994) were conducted. Furthermore, corrosion tests were performed on polished rock surfaces using 1 NNaOH solution. It was seen that the reactivity of the quartz-bearing mylonites increased by ~30% withrespect to the non-mylonitised sample due to the increment in the strained quartz content and speciallywith the extended subgrain development. The mylonitised rock affected by superimposed cataclasis and thedevelopment of pseudotachylytic veins incremented its reactivity by ~97% with respect to the nonmylonitisedsample due to the combined effects of subgrain formation, grain size reduction and theformation of glassy material. It was also the only sample that showed significant differences in surfacecorrosion confirming the high reactivity of the rock. These results agree with expansion values measured onleached ปูนเร่ง แถบทดสอบ และซิลิก้าในการทดสอบสารเคมี เราเชื่อว่าการเกิดการใช้เครื่องมือต่าง ๆ เพื่อประเมินศักยภาพด่างเกิดปฏิกิริยาของหินในคอนกรีตเป็นกลยุทธ์ที่ดีแทนที่จะใช้เครื่องมือแยก ซึ่งอาจทำให้สับสนตีความกระบวนการ และจึง ทำให้ตัดสินใจพลาด
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