Effect of the preparation of lime putties on their properties

Eva Navrátilová,Pavla Rovnaníková,Vilém Neděla,Eva Tihlaříková,Jaroslav Pavlík

doi:10.1038/s41598-017-17527-3

Abstract

In the study of lime as the basic component of historical mortars and plasters, four lime putties prepared from various kinds of lime of various granulometry and by various ways of preparation were evaluated. The rheological properties and micro-morphologic changes, growing of calcite crystals, and rate of carbonation were monitored. The lime putty prepared from lump lime achieves the best rheological properties, yield stress 214.7 Pa and plastic viscosity 2.6 Pa·s. The suitability of this lime putty was checked by testing the development of calcium hydroxide and calcite crystals using scanning electron microscopy and environmental scanning electron microscopy. The disordered crystals of calcium hydroxide exhibit better carbonation resulting in the large crystals of calcite; therefore, the mortar prepared from the lump lime has the highest flexural strength and compressive strength 0.8/2.5 MPa, its carbonation is the fastest and exhibits the longest durability. Also, thanks to the micro-morphological characterization of samples in their native state by means of environmental scanning electron microscopy, the new way of lime putty preparation by mixing was proven. The preparation consists in the mechanical crash of the lime particles immediately after hydration. This enables the properties of putty prepared from lump lime to be nearly reached.

Highlights

In the study of lime as the basic component of historical mortars and plasters, four lime putties prepared from various kinds of lime of various granulometry and by various ways of preparation were evaluated
The non-matured lime putty contains the agglomerates of calcium hydroxide and these agglomerates are covered by a thin film of water, which acts as a lubricant, and so this lime putty is extremely fluid
During the maturation of all the lime putty samples, the regular hexagonal crystals of calcium hydroxide are transformed into smaller irregular crystals which are coated with a layer of hydrogel

Summary

Introduction

In the study of lime as the basic component of historical mortars and plasters, four lime putties prepared from various kinds of lime of various granulometry and by various ways of preparation were evaluated. The lime putty prepared from lump lime achieves the best rheological properties, yield stress 214.7 Pa and plastic viscosity 2.6 Pa·s The suitability of this lime putty was checked by testing the development of calcium hydroxide and calcite crystals using scanning electron microscopy and environmental scanning electron microscopy. Various methods and the temperature of hydration of CaO lead to obtaining lime putty with a different morphology, size, and size distribution of calcium hydroxide crystals. The change in the original prismatic crystals into smaller submicrometre plate crystals with a higher specific surface area leads to an increased adsorption of water and thereby increases plasticity and workability[10,11,15,17]. The prolonged ageing of lime putty leads to a higher viscosity, which is caused by the change in its microstructure and the specific surface area of calcium hydroxide during the ageing process. The mortars prepared from lump lime exhibit higher strengths, but they require over-ageing treatment because of their shrinking

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Conclusion