Lime Based Mortars. Relationships between Composition Parameters and Mechanical Strength

Author(s): Ioanna Papayianni, Dimitris Papadimitriou
Paper category: Proceedings
Book title: Proceedings of the 5th Historic Mortars Conference
Editor(s):José Ignacio Álvarez, José María Fernández,Íńigo Navarro, Adrián Durán, Rafael Sirera
ISBN:978-2-35158-221-3
e-ISBN: 978-2-35158-222-0
Publisher: RILEM Publications SARL
Publication year: 2019
Pages: 1316-1324
Total Pages: 9
Language : English

Abstract: Lime based mortars are used for repairing Heritage Structures (HS), since they are
considered more compatible to old mortars compared with cement based ones. Apart from
hydrated lime they often contain a hydraulic component such as pozzolan, brick dust or
small percentage of cement (usually ≤30% by mass of the binder content). Hydraulic lime
such as NHL3.5 is also used for repairing HS. Lime based mortars are characterized by low
strength potential and slow strength development rate. The main parameters influencing
the mechanical strength are the type of binder or binding agent, the water to binder ratio
(W/B) and the binder to aggregate ratio (B/A). Furthermore, the curing regime analogous to
the binder type as well as compaction or workmanship applied to mortar play also an
important role in mortar’s strength development.
Trying to find interrelationships between mechanical strength and composition parameters,
a peer review of literature made and 123 different mortar compositions were listed and
categorized according to aforementioned influential parameters. The relevant regulative
frames were kept for the curing conditions and compaction. The water content was the
required for workability 15±2cm expansion measured with flow table (according to EN1015-
3).
The data concerned the compressive and flexural strength of 4x4x16cm mortar specimens at
28-d and 90-d ages. The influential composition parameters were the binding system, W/B
and B/A ratios. The binding systems compared were hydrated lime CL90 (EN 459), hydraulic
lime NHL3.5, lime:pozzolan (1:1), lime:pozzolan:brick dust (10-20% by mass of binder),
lime:cement (10-20% by mass of binder). The evaluation of the results showed that: The
strength development depends mainly on the type of binding systems and W/B ratio. The
stronger the hydraulic content the higher the strength development. The effect of B/A is
relatively low in these mortars which have been cured properly up to testing the mechanical
strength. The rate of strength development (fc28/fc90) ranges from 45-70%, that means the
28-d strength is not representative of the final strength capacity of these mortars. The 28-d
flexural strength of these mortars constitutes the 30-40% of their compressive strength.
The paper contributes to design of lime-based mortars on a scientific basis since diagrams of
strength-W/B have been plotted for each of the studied binding systems.

Online publication : 2019
Publication type : full_text
Public price (Euros) : 0.00