Bond Properties of NHL-Based Mortars with Viscosity-Modifying Water-Retentive Admixtures

Tomáš Žižlavský,Martin Vyšvařil,Patrik Bayer

doi:10.3390/min11070685

Abstract

This article studies the influence of biopolymeric viscosity-modifying admixtures with water-retentive function on the physico-mechanical properties of natural hydraulic lime-based mortars and their adherence to the traditional fired-clay brick substrate. The use of admixtures increases the water/binder ratio, which in turn leads to a decrease in the strength of the mortars. The viscosity-modifying function improves the adhesive strength between mortar and pre-wetter brick by increasing the binder paste viscosity, while the water-retentive function along with increased water content may lead to a decrease in adhesive strength. On the contrary, water retention and increased water content are beneficial on a dry surface, while paste viscosity plays only a minor role. When subjected to temperature-varying cycles, the mortars are more prone to in-mortar failure during the pull-off test. The air-entraining function of some admixtures improves the frost resistance of the mortars; however, it would negatively affect the adhesive strength by incorporating pores into the contact zone between the mortar and brick substrate. This study showed that the use of some of the studied admixtures may improve the adhesion of mortar to the brick substrate.

Highlights

IntroductionDurability and longevity are desired characteristics for most products of mankind, especially for civil engineering structures, where the designed lifetime expectancy is rarely less than half a century, and this is usually affected by moral obsolescence and not the degradation of the main structural elements
The decrease is driven by two complementary factors: the water content (w/b), which is prevailing within mortars with lower air content (HPCH, ALGNA, Diutan gum (DG)), and the air content, which leads to a more pronounced drop in the density
The study deals with the influence of biopolymeric viscosity-modifying admixtures with water-retentive function on the physico-mechanical properties of natural hydraulic lime-based mortars and their adherence to the traditional fired-clay brick substrate

Summary

Introduction

Durability and longevity are desired characteristics for most products of mankind, especially for civil engineering structures, where the designed lifetime expectancy is rarely less than half a century, and this is usually affected by moral obsolescence and not the degradation of the main structural elements. Each with its own lifetime expectancy, from several decades for the most exposed and/or least durable materials, e.g., paint finishes on wooden elements, up to several centuries for the main load-bearing structures such as walls. The philosophies of different approaches addressing the repairs of historical buildings are summarised in a two-part paper by A.M. Forster [1,2].

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Results

Conclusion