Abstract
Amorphous and crystalline alkali silica reaction (ASR) products formed in aggregates of two different concrete mixtures exposed to the concrete prim test both at 38 °C and 60 °C have been analysed by scanning electron microscope with energy dispersive X-ray spectroscopy and by Raman microscopy. Additionally, amorphous ASR products were synthesized and analysed with Raman microscopy and 29Si nuclear magnetic resonance. Amorphous ASR products display a higher Na/K-ratio than crystalline ones. Both types of products display a structure dominated by Q3-sites (Si-tetrahedra with three bridging oxygen atoms typical for a layer structure) with a secondary amount of Q2-sites (Si-tetrahedra with two bridging oxygen atoms typical for a chain structure). Temperature in the CPT alters the structure of the crystalline ASR. While the Raman spectra of the product formed at 38 °C is identical to the one formed in concrete structures, the one of the 60 °C product corresponds to K-shlykovite.
Highlights
Concrete damages due to alkali silica reaction (ASR) occur worldwide [1]
The goal of this study is to improve the knowledge on ASR products formed in concrete aggregates by investigating:
Still the majority of the cracks in the aggregates are filled only in part with ASR products. In contrast to this situation, the cracks in the cement paste are usually completely filled with amorphous ASR products that have extruded the aggregates simultaneously to crack formation [2]
Summary
The expansion causing the damage is the result of the reaction between the alkaline pore solution in concrete and reactive SiO2 in aggregates causing the subsequent formation of ASR products. ASR products advance towards the interior of the aggregates. This ingress goes together with a simultaneous stress generation, eventually leading to aggregate cracking. Many of these newly formed cracks are not restricted to the aggregates and continue into the cement paste with the concurrent extrusion of ASR products. After the initial crack formation, the mostly empty cracks in the aggregates start to fill with ASR products, again advancing from the periphery of the aggregate towards the interior. In contrast to the initial phase of reaction, where the ASR products are amorphous, the second stage is characterized by the formation of primarily crystalline ASR products
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