Abstract
Low-pH cements are designed to be used in underground repositories for high level waste. When they are based on Ordinary Portland Cements (OPC), high mineral admixture contents must be used which significantly modify their microstructure properties and performance. This paper evaluates the microstructure evolution of low-pH cement pastes based on OPC plus silica fume and/or fly ashes, using Mid-Infrared and Near-Infrared spectroscopy to detect cement pastes mainly composed of high polymerized C-A-S-H gels with low C/S ratios. In addition, the lower pore solution pH of these special cementitious materials have been monitored with embedded metallic sensors. Besides, as the use of reinforced concrete can be required in underground repositories, the influence of low-pH cementitious materials on steel reinforcement corrosion was analysed. Due to their lower pore solution pH and their different pore solution chemical composition a clear influence on steel reinforcement corrosion was detected.
Highlights
IntroductionLow-pH cements have been developed to be used in underground repositories for high level waste
The research on low-pH cementitious materials was initially developed in Canada and Japan [1,2], and subsequently has been addressed from various approaches depending on the type of base cement used: (1) Calcium Silicate Cements; (2) Calcium Aluminate Cements (CAC based); (3) Phosphate Cements; and (4) Magnesia Cements [1,2,3,4,5,6,7,8,9,10]
The feature between 7000 and 7300 cm−1 is the first OH overtone (2ν1, 2ν3, and ν1 + ν3) and it has many components [32,33]: one detectable at 7083 cm−1 corresponding to OH stretching vibrations in portlandite, a broader but less precise shoulder at 7200 cm−1 related to C–S–H gel and a band around 7100 cm−1 related to the presence of Al-bonded O–H groups in ettringite
Summary
Low-pH cements have been developed to be used in underground repositories for high level waste. Cements (OPC) were to be used to produce concrete for underground repositories, their contact with the ground water would create pore water leachates with a pH > 13 The generation of this alkaline plume would have detrimental effects on the engineering bentonite barrier of the repository, as it has low stability at pH > 11 [11]. It is well known that the high alkalinity of the pore solution in conventional OPC materials (pH > 12.6) promotes the formation of a stable passive layer of oxide that protects the rebar from a corrosion process. As the low-pH cement formulations strongly influence the pH value, the formation of this passive layer, as well as its long-term stability, can be affected In this context, when the use of these formulations is considered for reinforced concrete, the durability of the reinforcements in these new.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
