Abstract
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.
Highlights
Alkali –carbonate reaction (ACR) is a kind of alkali–aggregate reaction, which means the alkali in the concrete reacts with dolomite crystals, leading to map-like cracks in the concrete and deterioration of concrete
The modified microbars prepared by dolomitic aggregates and self-made cement were used to systematically investigate effects of the concentration of tetramethyl ammonium hydroxide (TMAH) solution, curing temperature and aggregate grain size on the expansion of dolomitic aggregates
Changing the aggregate grain size for modified microbars and increasing the curing temperature can considerably increase the rate of ACR and accelerate the samples with bigger expansion
Summary
Alkali –carbonate reaction (ACR) is a kind of alkali–aggregate reaction, which means the alkali in the concrete reacts with dolomite crystals, leading to map-like cracks in the concrete and deterioration of concrete. The expansion mechanism is still controversial and mainly can be divided into two kinds: one is the growth of brucite crystal causing the expansion [6] and the other is the ACR just like the alkali–silica reaction (ASR) [7,8,9]. The disagreement still exists, it is widely accepted worldwide that the dolomite in dolomitic limestones interacts with the alkali hydroxides from the concrete pore solution causing a fine intergrowth of calcite and brucite in the alkaline condition. The solution alkalinity increases due to the regeneration of the alkali hydroxide and the reaction will continue until the dolomite is used up
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