An impedance measurement technique was used to investigate the effects of aminotri(methylenephosphonic acid) (ATMP), 1-hydroxyethylidene-l,l-diphosphonic acid (HEDP), and diethylenetriaminepenta(methylenephosphonic acid) (DTPMP) on the hydration process and setting behavior of portland cement pastes. It was demonstrated that the impedance and capacitive responses can be used to characterize setting behavior and microstructural development of the hydrating pastes containing these chemical admixtures.
The presence of a long induction period of up to 20 and more than 75 hours is revealed by the impedance curves of pastes containing ATMP, HEDP, and DTPMP at dosages of 0.05% and 0.2%, respectively. This confirms that phosphonates are efficient retarders.
These compounds appear to have strong chelating or complexing capability, potentially poisoning CH and C-S-H nucleation. Stabilization of the C-S-H (metastable) film on the surface of cement
grains appears to cause retarding effect. ADVANCED CEMENT BASED MATERIALS 1995, 2, 182--188 KEY WORDS: Cement hydration, Impedance behavior, Phosphonates, Super-retarders m~l~, etarders such as sugars, casein, dextrin, glycerol, carboxymethyl cellulose, and tartaric i acid are commonly used in concrete practice. Typical applications of retarders in concrete include transport and handling in hot climates, amelioration of long-term strength reduction of steam-cured concrete, and waste reduction and recycling of concrete from ready-mixed trucks. The super-retarding effect of phosphonate compounds, for example, aminotri-(methylenephosphonic acid) (ATMP), 1-hydroxyethylidene-l,l-diphosphonic acid (HEDP) and diethylenetriaminepenta-(methylenephosphonic acid) (DTPMP), on ordinary portland cement (OPC) and its