A method for calculating the carbonation degree of calcium–silicate–hydrate

The carbonation degree of calcium–silicate–hydrate (CSH) was quantitatively characterised using a direct test method. Nuclear magnetic resonance (NMR) and thermogravimetric methods were used to study different depths of cement paste with a water/cement ratio of 0·35 after 28 d of carbonation. Firstly, based on the hydration and carbonation reaction equations of the CSH, the variation of Ca 2+ can be obtained, and then according to the variation of Ca 2+ to calculate the carbonation degree of CSH. Secondly, the parameter I(Q 2 )/I(Q 1 ) was determined to characterise the structural change of the CSH quantitatively. Finally, the relationship between the CSH carbonation degree and I(Q 2 )/I(Q 1 ) was analysed. The results showed that the carbonation degree of CSH can be expressed as the ratio of the molar content of calcium carbonate carbonated by CSH and the molar content of Ca 2+ in the initial CSH. A good linear relationship was found between the value of I(Q 2 )/I(Q 1 ) and the CSH carbonation degree. Therefore, the NMR method can be used to determine the carbonation degree of CSH.