Abstract
A new concept is introduced for active rheology control of cementitious materials using stimuli-responsive polymers. RAFT polymerization of methacrylic acid (MAA) and 2,2,6,6, tetramethyl-4-piperidyl methacrylate (TMPMA) was employed to prepare poly(MAA-co-TMPMA) as precursor for the preparation of poly(MAA-co-TEMPO), a redox-responsive copolymer containing 2,2,6,6-tetramethylpiperidine-1-oxyl group. Poly(MAA-co-TEMPO) is soluble in alkaline water and undergoes a redox switch when electrically triggered, oxidizing the TEMPO group to the oxoammonium cations (TEMPO+). The observed active stiffening control is hypothesized to result from adsorption of the negatively charged copolymer with the TEMPO side chains on cement particles and (partial) desorption of the zwitterionic copolymer with the TEMPO+ side chains. The new chemical admixtures could enhance flowability of cement pastes at low W/C ratio and sharply increase storage modulus when applying an electric potential of 1 V. Poly(MAA-co-TEMPO) acts as smart superplasticizer that can actively alter the rheology of cementitious materials upon applying an electric voltage.
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