ALBERT

Description: In this paper, the modified microbars prepared by dolomitic aggregates with three kinds of particle size and self-made cement without K + and Na + were cured in 1 and 2 N tetramethyl ammonium hydroxide (TMAH) solution at 20°C, 60°C and 80°C, respectively. TMAH was used as curing solution to exclude the expansion contribution of alkali–silica reaction. Effects of the concentration of TMAH solution, curing temperature and aggregate grain size on the expansion of dolomitic aggregates were systematically investigated to determine the expansion characteristics only caused by alkali–carbonate reaction (ACR). Expansion of modified microbars cured in TMAH solution was measured. The porosities of original and reacted aggregates were also measured. Microstructural studies were carried out by scanning electron microscopy (SEM) and thermo-gravimetric (TG) analysis. The results showed that the aggregate grain size and curing temperature can influence the expansion of modified microbars significantly. When the modified microbars prepared by aggregates with 2.5–5 mm grain size and cured in 1 N TMAH solution at 80°C, the samples exhibited obvious expansion only caused by ACR, which is beneficial to detect the ACR reactivity of dolomitic rocks exclusively in concrete engineering. Based on the pore structure analysis, there was a slight increase (13%) in porosities of aggregates cured for 140 days at 80°C. Rod-like brucite crystals formed in the process of ACR were also found in TG analysis and SEM images.

Description: The exact role of lithium ions (Li + ) in controlling alkali–silica reaction is still unclear. Thus, the effects of Li + on the reaction between reactive silica (quartz glass) and hydroxyl in alkaline solution with or without Ca were investigated by quartz glass powder or slice immersion experiments. When quartz glass was immersed in lithium-containing alkaline solutions, only Li 2 SiO 3 was produced with the absence of Ca, but Li 2 SiO 3 and calcium silicate hydrate (CSH) were formed with the presence of Ca. The quartz glass slice immersion experiment indicated that the mass loss of quartz slices was less than 1% only when Ca was present in the lithium-containing alkaline solution. This was because a dense, low-porosity and strongly bonded production layer mainly composed of CSH and Li 2 SiO 3 crystals was formed on the glass surface and served as a barrier against the diffusion of OH − and alkali ions to the substrate glass.