Assessment of the Alteration of Granitic Rocks and its Influence on Alkalis Release

World Multidisciplinary Earth Sciences Symposium 2017

Ferraz, Ana Rita^1 ; Fernandes, Isabel^1,2 ; Soares, Dora^3 ; Silva, António Santos^3 ; Quinta-Ferreira, Mário^4

Department of Geology, Faculty of Sciences, University of Lisbon, Portugal^1

IDL, Institute Dom Luiz, Portugal^2

LNEC, Materials Department, National Laboratory for Civil Engineering, Lisbon, Portugal^3

Department of Earth Sciences, University of Coimbra, Centro de Geociencias, UC, Portugal^4

关键词: Alkali carbonate reaction;    Alkali-aggregate reactions;    Alkali-silica reaction;    Chemical tests;    Concrete cracking;    Granitic rocks;    Interstitial fluids;    Reactive silica;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/95/2/022001/pdf
DOI  :  10.1088/1755-1315/95/2/022001

来源: IOP

【 摘 要 】

Several concrete structures had shown signs of degradation some years after construction due to internal expansive reactions. Among these reactions there are the alkali-aggregate reactions (AAR) that occur between the aggregates and the concrete interstitial fluids which can be divided in two types: the alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR). The more common is the ASR which occurs when certain types of reactive silica are present in the aggregates. In consequence, an expansive alkali-silica gel is formed leading to the concrete cracking and degradation. Granites are rocks composed essentially of quartz, micas and feldspars, the latter being the minerals which contain more alkalis in their structure and thus, able to release them in conditions of high alkalinity. Although these aggregates are of slow reaction, some structures where they were applied show evidence of deterioration due to ASR some years or decades after the construction. In the present work, the possible contribution of granitic aggregates to the interstitial fluids of concrete by alkalis release was studied by performing chemical attack with NaOH and KOH solutions. Due to the heterogeneity of the quarries in what concerns the degree of alteration and/or fracturing, rock samples with different alteration were analysed. The alteration degree was characterized both under optical microscope and image analysis and compared with the results obtained from the chemical tests. It was concluded that natural alteration reduces dramatically the releasable alkalis available in the rocks.