Reaction mechanisms of tartaric acid in pure Portland Cement hydration and in combination with increased anhydrite content and triethanolamine

The concentration-dependent retarding effect of tartaric acid (TA) on the hydration of pure OPC was studied by heat flow calorimetry, in-situ XRD and pore solution analyses with ICP-MS and HPLC-UV/VIS. Furthermore, the mechanism of action of TA in combination with triethanolamine (TEA) and increased sulfate content was investigated. From this data a model is proposed to describe the altered hydration process. Over 80% of TA could not be found in the pore solution, presumably the consequence of an adsorption mechanism. The residual TA in the pore solution is the factor responsible for the duration of retardation. Once the TA is consumed, aluminate reaction occurred. The consumption of TA is most likely caused by the poisoning of ettringite nuclei. Although ettringite was oversaturated, no precipitation was detected. After the aluminate reaction no TA was detected in the pore solution. The main silicate retarding effect is presumed to be the aluminium concentration.