The working mechanisms of low molecular weight polynaphthalene sulfonate superplasticizers Alexander Mezhov a,⇑ , Simon Ulka a , Youri Gendel a , Charles E. Diesendruck b , Konstantin Kovler a a Faculty of Civil and Environmental Engineering, Technion –Israel Institute of Technology, Israel b Schulich Faculty of Chemistry, Technion –Israel Institute of Technology, Israel highlights  All PNS types up to critical dosage demonstrate the same adsorption behavior and zeta potential development.  At the critical dosage dispersing ability is governed by the increment of zeta potential value.  Above the critical dosages, the plasticizing effect is governed by both increment in surface charge and air content.  Above the saturation dosages, air content changes are not significant, while the amount of non-adsorbed polymer increases.  The polymer with lowest molecular weight retards hydration the most. article info Article history: Received 19 June 2019 Received in revised form 4 December 2019 Accepted 16 December 2019 Keywords: Polynaphthalene sulfonate (PNS) Rheology Yield stress Zeta potential Retardation of hydration Air entrainment abstract Polynaphtalene Sulfonate (PNS) superplasticizers are one of the most commonly used admixtures in con- crete production. Yet, PNS working mechanism has been studied in the context of the effect it has on indi- vidual properties, limiting the overall understanding of the parallel effects this admixture creates. This study connects the microscopic behavior of PNS of different molecular weights to their effect on the macroscopic properties of the cementitious system, including dispersing ability, air entrainment and retardation as a consequence of the molecular adsorption on cement and free PNS in solution. Our results confirmed that changes in macroscopic properties are not only a consequence of the adsorbed polymer but also of the non-adsorbed, which in turn reduces paste viscosity due to an increment in air entrain- ment. The induction period at the low dosage is equal for all polymers, while at the high dosage polymer with the lowest molecular weight retards hydration the most. Ó 2019 Elsevier Ltd. All rights reserved. 1. Introduction Since their introduction in the early 1930s, superplasticizers (SPs) have become an important component in the production of concrete, allowing additional control over rheological and mechan- ical properties of both fresh and hardened concrete. Among numerous types of SPs available, polynaphthalene sulfonate (PNS), is one of the most popular ones in use in construction. PNS is a linear anionic surfactant made from the polymerization of naphthalene sulfonate and formaldehyde, typically presenting molecular weights ranging from 1000 to 20,000 g/mol [1]. The degree of polymerization (DP – average number of repeating units) is considered an important factor that defines the effectiveness of PNS as a superplasticizer [2]. It was found that plasticizing effects are only observed in oligomers containing at least five repeating units, i.e. ~1000 g/mol [1]. Upon addition to the aqueous disper- sion, PNS is adsorbed on the surface of cement particles, hence most previous studies focus on the relationship between polymer adsorption to cement dispersion. In general, it has been shown that the absorption efficiency increases with DP [3,4]. Early studies claimed that the amount of adsorbed polymer is directly correlated to the dispersion ability of the admixture [5], but later studies pointed to a plasticizing effect by non-absorbed polymer in the solution [6], which explains previous findings of an optimum molecular weight in terms of admixture efficiency [1]. Since PNS is an anionic surfactant, adsorption on the cement grains induces an increment of negative zeta potential [7], leading to electrostatic repulsion between the particles. Evidently, this fact is in agreement with the DLVO (Derjaguin, Landau, Verwey and Overbeek) theory, which describes the balance of the inter- particle forces in an aqueous dispersion as a function of the dis- tance between particles. Without the superplasticizer, the zeta potential is the result charge of all cement phases found on the https://doi.org/10.1016/j.conbuildmat.2019.117891 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: alexander.m@technion.ac.il (A. Mezhov). Construction and Building Materials 240 (2020) 117891 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat