Working Mechanisms and Design Principles of Comb-like Polycarboxylate Ether Superplasticizers in Cement Hydration: Quantitative Insights for a Series of Well-Defined Copolymers

Journal Article · Sat May 29 00:00:00 EDT 2021 · ACS Sustainable Chemistry & Engineering

DOI:https://doi.org/10.1021/acssuschemeng.0c08566· OSTI ID:1785296

Javadi, Ali ^[1]; Jamil, Tariq ^[2]; Abouzari-Lotf, Ebrahim ^[3]; Soucek, Mark D.  ^[1]; Heinz, Hendrik  ^[4]

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1. Department of Polymer Engineering, University of Akron, Akron, Ohio 44325, United States
2. Department of Chemical and Biological Engineering, University of Colorado-Boulder, Boulder, Colorado 80309, United States, Department of Mechanical Engineering, NED University of Engineering and Technology, Karachi 75270, Pakistan
3. Helmholtz Institute Ulm (HIU), Electrochemical Energy Storage, Helmholtzstraße 11, D-89081 Ulm, Germany, Department of Environment and Green Technologies, Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, 54100 Kuala Lumpur, Malaysia
4. Department of Chemical and Biological Engineering, University of Colorado-Boulder, Boulder, Colorado 80309, United States

Cement and concrete are the most widely used building materials and contain comb copolymers such as polycarboxylate ethers (PCEs) as hydration and setting modifiers. The working mechanisms of these additives in cement hydration have remained uncertain, which limits the rational design of additives and of new cement materials with lower CO₂ footprint. We identified quantitative correlations between PCE copolymer structure, adsorption, and cement setting properties for a series of copolymer structures and concentrations, combined with insights into conformations and adsorption mechanisms by atomistic simulations. The PCE copolymers have only a small fraction of polydispersity compared to earlier studies, and molecular dynamics simulations utilize Interface force field models for C-S-H phases that enable order-of-magnitude more accurate insights into the dynamics of the nanoscale polymer interfaces compared to earlier models. Two distinct sets of property correlations were discovered. (1) The carboxylate content of the PCEs, i.e., the molar density of ionic side groups per unit mass, correlates with the adsorbed amount of polycarboxylate ethers onto cement pastes, the conductivity of the cement paste, and the retardation of the acceleration period of cement hydration. (2) The combination of the ionic character of the polymer backbone and the length of non-ionic polyethylene glycol (PEG) side chains correlates with the water-to-cement ratio necessary for processing, zeta potentials, and fluidity of the cement pastes in mini slump tests. Simulations indicate that PCE adsorption onto cement particles involves migration of calcium ions in the acrylate backbone onto the calcium silicate hydrate surface, or calcium hydroxide surfaces, followed by ion pairing of the anionic polymer backbone with the positively charged mineral surface. PEG side chains exhibit no affinity to the mineral surface. The best fluidity and water reduction are achieved using an optimum ratio of the volume of PEG side chains to the volume of the anionic backbone, balancing sufficient surface bonding through the ionic backbone and minimization of interparticle forces by the non-ionic PEG side chains. Here, a charge density too low prevents effective adsorption, and a charge density too high leads to multilayer deposition and ionic agglomeration forces between coated particles that reduce the fluidity and increase the necessary water-to-cement ratio. The proposed mechanism supersedes prior models and provides quantitative metrics for the rational design of polymer additives for cement and related particle dispersions.

• Research Organization: Univ. of Colorado, Boulder, CO (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC02-06CH11357; AC05-00OR22725
• OSTI ID: 1785296
• Alternate ID(s): OSTI ID: 1804311
• Journal Information: ACS Sustainable Chemistry & Engineering, Journal Name: ACS Sustainable Chemistry & Engineering Vol. 9 Journal Issue: 25; ISSN 2168-0485
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
superplasticizer
copolymer
cement
adsorption
molecular dynamics simulation
C-S-H gel
hydration reaction
slump flow
thermoresponsive polymers
hydration
electrical conductivity
copolymers