Lime has been used in historic building as a binder
in mortars for over last decades. Today, lime is still used as the primary
binder in many mixes or in the conservations of old historic buildings, usually
in the form of lime putty or Hydraulic lime. Hydrated lime is used in modern
cement based mortars mainly for its properties as a plasticiser.
Occurrence of lime
Lime is obtained from calcination of calcareous rock
with high percentages of calcium carbonate, from which calcium oxide
(quicklime) is obtained. Quicklime is very reactive in the presence of water and
cannot be used before being transformed to calcium hydroxide by reaction with
When an excess of water is added in to the calcium oxide
(quicklime) to produced calcium hydroxide. The paste is known as slake lime.
It is produced by slaking quicklime (CaO )with an excess
of water for extended periods of time until a creamy texture is produced. It is
called lime putty. The effect of extended exposure of lime putty to water indicates
that portlandite crystals, Ca(OH)2, undergo both an important size reduction
and a shape change from prism to plate like crystals agglomerated as aggregates.
Types of lime
Following are the types of lime on the bases of the hydration
Hydraulic lime (HL)
Non hydraulic lime
Hydraulic lime (HL) is a general term for varieties of lime (calcium
oxide), or slaked lime (calcium hydroxide), used to make lime mortar which set through hydration. Hydraulic lime provides a faster initial set and
higher compressive strength than air lime and eminently hydraulic
lime will set in more extreme conditions including under
There are two basic types of hydraulic limes:
Natural hydraulic lime (NHL)
hydraulic lime (NHL) is produced by heating (calcining) limestone that
naturally contains clay and other impurities: no materials may be added to
create the hydraulicity.
Natural hydraulic limes (NHL) are binders in
conformity with the EN 459-1:2010. This type of binder is obtained by firing marly
limestone at a temperature similar to the one used to produce air lime, and
consists of calcium silicates, calcium aluminates and calcium hydroxide.
It is classified as a binder with hydraulic properties
, having not only a hydraulic curing but also an aerial curing obtained by carbonation
with atmospheric carbon dioxide. This double type of curing can be very
beneficial for a variety of applications, particularly in conservation or
rehabilitation interventions of existent and historic buildings .
Artificial hydraulic lime (AHL)
hydraulic lime (AHL) or artificial lime (AL) becomes hydraulic when hydraulic
and/or pozzolan materials
are added either before or after burning in a lime kiln. Artificial limes are
more specifically identified as hydraulic lime (HL), as defined European Norm 459
(EN-459), “Consists of lime and other materials such as Portland
cement, blast furnace slag, fly ash,
limestone filler and other suitable materials”
Non-hydraulic lime is softer and sets much more
slowly. The carbonation process is very slow and the material remains soft and
flexible. This of course, can be extremely advantageous if that’s what is
required. The hydraulic lime is available in degrees of strength, is faster
setting and more durable.
The addition of inorganic or organic substances to
artificial materials such as mortars and bricks is an ancient practice in the
field of construction. … Nevertheless, none of these studies deals with the
effect that those admixtures have on mortars in which a pozzolan is blended to
the binder (aerial lime)
In modern era different organic and inorganic material
is adding to improve the lime characteristic. These materials are divided in to
Additives (i.e. Pozzolans, mineral
fillers, ceramic powder) that are used in lime based mortars with the aim to
improve certain properties or obtain special performances mainly related to the
increase of mortar strength,
Admixtures, added in low amounts (i.e.
Not higher than a 5% of the total mass) in order to produce a permanent
modification in the fresh or hardened mortar, such as density decrease, workability
improvement or waterproofing.
Natural hydraulic lime mortar with graphene
Methods to identify the Lime Properties
There are different methods to identify the lime properties.
Some of them are discussed below,
Thermogravimetry (TGA) and X-ray diffraction (XRD)
The mineralogical phases of both internal and external
zones of mortar samples were determined by means of two different techniques:
thermogravimetry (TGA) and X-ray diffraction (XRD). In the first case, it was
employed a Shimadzu TGA-50H thermogravimetric analyser, working in air in a
temperature range of 25–950 _C, with a heating speed of 5 _C/min. For the XRD
analysis, it was used a Panalytical X’Pert PRO MPD diffractometer, with
automatic loader and X’Celerator detector, 4–70_ 2h explored area.
X-Powder Software Package
The identification of the mineral phases was
performed by using the X-Powder software package 29. For the textural study,
mortars fragments were metalized with a carbon layer and the microstructure
analysed by using a Carl Zeiss Leo-Gemini 1530 field emission scanning electron microscope (FESEM).
Micrometics Autopore III 9410 Porosimeter (Mercury Injection Porosimetry, MIP)
Open porosity (Po, %) and pore size distribution
(PSD, in a range of 0.002 < r < 200 lm) were determined using a Micrometics Autopore III 9410 porosimeter (mercury injection porosimetry, MIP). Mortar fragments of ca. 1 cm3 were oven-dried for 24 h at 60 _C before the analysis. Flexural and compressive strength were measured by means of a hydraulic press INCOTECNIC-Matest. According to the EN 1015-11 28 standard, flexural assays were carried out on three samples per mortar (of 4 _ 4 _ 16 cm). The six samples obtained after the flexural rupture were used for the compressive assays.