Synthesis, characterization, and water uptake property of alkali-silica reaction products

Abstract

The reaction mechanism of alkali-silica reaction (ASR) is poorly understood due to the difficulties to directly characterize ASR products in concrete. In this study, ASR products with initial Ca/Si of 0.25 and (K+Na)/Si ratio 0.5 with different K/Na ratios are synthesized at 80 o C. The synthesized ASR products are characterized by different techniques, also the solution chemistry is analyzed and saturation indices are calculated. The results show that crystalline and nano-crystalline phases are formed in the presence of both alkalis and calcium. No ASR product is present in the absence of calcium. All synthesized crystalline ASR products highly resembles the crystal structure of shlykovite, indicating that a substitution of K in shlykovite by Na can occur. Its silicate sheet structure has strong similarity to the ASR products formed in concrete according to Raman spectra, while some differences are observed in their morphologies and basal peak of the XRD patterns.

An in-situ 3D micro-XRD investigation of water uptake by alkali-silica-reaction (ASR) product

“…The basal spacings of the other products, ranging from ~10 Å to 13.5 Å, seem inert to the moisture change. Lab-synthesis attempts indicated that their basal spacings are more determined by the synthesis temperature [19,26]. A compression as high as 2 GPa was also proven to result in a permanent basal spacing reduction of ~1 Å for ASR products with basal spacing around 12.2 Å from field concrete samples [31].…”

“…Upon increasing R.H. to 97%, the 7.43 Å basal peak vanished while a new basal peak appeared 13 Å was often observed [17,19]. When the synthesis temperature dropped to 40 °C, a product with basal peaks at 10.8 Å and 8.9 Å was reported [26].…”

“…This project was funded by the Swiss National Science Foundation (SNF) Sinergia project Alkali-silica reaction in concrete (ASR), grant number CRSII5_17108. Paul Scherrer Institut, 19 Villigen (Switzerland) was acknowledged for provision of synchrotron radiation beamtime at beamline microXAS of the SLS and the Interdisciplinary Center for Electron Microscopy (CIME, EPFL) for their support in the sample preparation.…”

“…They were both reproduced in recent laboratory synthesis attempts. Although multiple basal spacing values were found for ASR products from the field and lab-synthesis [31], it was noted that they all seem not able to swell or shrink upon a significant R.H. change [19,26,28]. Temperature is found to affect the formation of different types of crystalline ASR products with varying basal spacing, i.e., 12.0 Å (<40 °C), 10.8 Å (around 40 °C), and 13.1 Å (60-80 °C for K-shlykovite) [26,29,30].…”

“…Compared with the calcium silicate hydrate (C-S-H, the main hydration product in Portland cement concrete), the ASR gel has a much higher content of Na+K and a much lower content of Ca [15][16][17][18]. This compositional difference results in a higher degree of silicate polymerization in the ASR product (Q 3 dominant) than in C-S-H (Q 1 /Q 2 dominant) [16,19]. It is proposed that ASR product expands upon up-taking water to its gel structure, leading to a local stress development and initiation of cracks in concrete [13][14][15].…”