Influence of Two Polymer-Based Superplasticizers (Poly-naphthalene Sulfonate, PNS, and Lignosulfonate, LS) on Compressive and Flexural Strength, Freeze-Thaw, and Sulphate Attack Resistance of Lime-Metakaolin Grouts.

Adrián Duran,José Fernández,Jesús González-Sánchez,José Alvarez,Íñigo Navarro-Blasco,Rafael Sirera

doi:10.3390/polym10080824

Abstract

A new range of grouts prepared by air lime and metakaolin (MK) as a pozzolanic admixture has been obtained by using as dispersing agents two polymers, namely poly-naphthalene sulfonate (PNS) and lignosulfonate (LS), with the aim of improving the fluidity of the fresh grouts. Fluidity and setting times of the grouts were assessed. Differences in the molecular architecture and in the anionic charge density explained the different adsorption of the polymers and the different performance. The higher anionic charge of PNS and its linear shape explained its better adsorption and effectiveness. The pozzolanic reaction was favoured in grouts with PNS, achieving the highest values of compressive strength (4.8 MPa after 182 curing days). The addition of PNS on lime grouts slightly decreased the frost resistance of the grouts (from 24 freeze-thaw cycles for the polymer-free samples to 19 or 20 cycles with 0.5 or 1 wt % of PNS). After the magnesium sulphate attack, grouts were altered by decalcification of hydrated phases and by formation of hexahydrite and gypsum. A protective role of portlandite against magnesium sulphate attack was clearly identified. Accordingly, the polymer LS, which preserves a significant amount of Ca(OH)2, could be an alternative for the obtaining of grouts requiring high sulphate attack resistance.

Highlights

IntroductionGrouts based in lime (either air or hydraulic lime) have, in the first approach, an adequate chemical and mechanical compatibility with ancient supports, but may need several additions in order to provide a suitable flowability to fill all the cracks and voids [4,5,6]
Heritage [1,2,3]
This paper focuses on a new range of grouts prepared by air lime, MK as pozzolanic admixture and a polymer-based SP

Summary

Introduction

Grouts based in lime (either air or hydraulic lime) have, in the first approach, an adequate chemical and mechanical compatibility with ancient supports, but may need several additions in order to provide a suitable flowability to fill all the cracks and voids [4,5,6]. These grouts should fulfil mechanical and durability requirements to guarantee their safe applicability [7,8].

Methods

Results

Conclusion