Determining the water - cement ratio , cement content , water content and degree 1 of hydration of hardened cement paste : Method development and validation on 2 paste samples

7 We propose a new method to estimate the initial cement content, water content and free water/cement ratio (w/c) 8 of hardened cement-based materials made with Portland cements that have unknown mixture proportions and 9 degree of hydration. This method first quantifies the composition of the hardened cement paste, i.e. the 10 volumetric fractions of capillary pores, hydration products and unreacted cement, using high-resolution field 11 emission scanning electron microscopy (FE-SEM) in the backscattered electron (BSE) mode and image analysis. 12 From the obtained data and the volumetric increase of solids during cement hydration, we compute the initial 13 free water content and cement content, hence the free w/c ratio. The same method can also be used to calculate 14 the degree of hydration. The proposed method has the advantage that it is quantitative and does not require 15 comparison with calibration graphs or reference samples made with the same materials and cured to the same 16 degree of hydration as the tested sample. This paper reports the development, assumptions and limitations of the 17 proposed method, and preliminary results from Portland cement pastes with a range of w/c ratios (0.25-0.50) and 18 curing ages (3-90 days). We also discuss the extension of the technique to mortars and concretes, and samples 19 made with blended cements. 20