Determining the water cement ratio cement content, water content and degree of hydration of hardened.pdf

Cement and Concrete Research 39 (2009) 957–965 Contents lists available at ScienceDirect Cement and Concrete Research j ourna l homepage: ht tp: / /ees.e lsev ie /CEMCON/defau l t .aspDetermining the water–cement ratio, cement content, water content and degree of hydration of hardened cement paste: Method development and validation on paste samples H.S. Wong ?, N.R. Buenfeld Concrete Durability Group, Imperial College London, SW7 2AZ, UK? Corresponding author. Tel.: +44 20 7594 5957; fax E-mail address: hong.wong@imperial.ac.uk (H.S. Wo 0008-8846/$ – see front matter ? 2009 Elsevier Ltd. A doi:10.1016/j.cemconres.2009.06.013a b s t r a c ta r t i c l e i n f oArticle history: Received 1 July 2007 Accepted 12 June 2009 Keywords: Backscattered electron imaging (B) Image analysis (B) Microstructure (B) SEM (B) w/c ratioWe propose a new method to estimate the initial cement content, water content and free water/cement ratio (w/c) of hardened cement-based materials made with Portland cements that have unknown mixture proportions and degree of hydration. This method first quantifies the composition of the hardened cement paste, i.e. the volumetric fractions of capillary pores, hydration products and unreacted cement, using high- resolution field emission scanning electron microscopy (FE-SEM) in the backscattered electron (BSE) mode and image analysis. From the obtained data and the volumetric increase of solids during cement hydration, we compute the initial free water content and cement content, hence the free w/c ratio. The same method can also be used to calculate the degree of hydration. The proposed method has the advantage that it is quantitative and does not require comparison with calibration graphs or reference samples made with the same materials and cured to the same degree of hydration as the tested sample. This paper reports the development, assumptions and limitations of the proposed method, and preliminary results from Portland cement pastes with a range of