|
|
|
|
HYDRAULIC MORTARS
According to
history, around the fourth century B.C., the Greeks discovered that selected
soils of volcanic origin, mixed with slaked lime, formed mortars which could
harden in very humid conditions and were even water-resistant. The Romans added to this knowledge by discovering that the
Neapolitan tuff found near Pozzuola created a highly efficient hydraulic
reaction, and named the mortar formed by this material “Pozzolana”. When
they extended their territories beyond Italy and were thus distanced from their
pozzolana quarries, the Romans looked for other deposits and materials with the
same characteristics. In the Greek
islands, they found the tuff of Santorini, and in the Syrian regions, pumice
stone; in the north as well as in the central part of Europe, they used trass
from the Rhine region (Eiffel). Finally,
the Romans discovered another hydraulic mortar, using a blend of lime and ground
baked earth. This mortar, now known
as “Cocciopesto”, allowed the Romans to bypass natural quarries and to make
hydraulic mortars anywhere in their Empire. With
these hydraulic mortars, the Romans created a new building technique using
“Roman concrete” - a mixture of lime, pozzolana, cocciopesto and loose
stones cast in wooden shuttering or encased structures. Cupolas
of the classical period were frequently made of concrete and here pozzolana were
replaced by the lighter pumice stone, or the concrete was reinforced using
stacked hollow bricks or tubes to produce a lighter structure. Although
Vitruvius has passed down information to us on these materials and techniques,
of which knowledge existed in the Middle Ages, they disappeared until the 18th
century, as their hydraulic components could not be found.
Only the use of hollow bricks was to continue, where the mixture was
often empirical and of dubious quality. Frequently,
as early as, and certainly after, the Roman period, it can be seen from the
different uses and buildings that there was perfect knowledge of a hydraulic
binder made up from marly or clay ridden limestone. This product is now known as
natural hydraulic lime. MODERN MORTARS
In
the post-war reconstruction period, the use of Portland cement in construction
increased, progressively replacing lime, which, until then, had been the basic
element of building technology. The expanding use of this new binder satisfied
all the criteria required in the building sector which was being transformed
from a craft activity into a commercial industry. As the use of cement developed
and its performance characteristics increasingly met the demand for production
volume with shorter setting times, the ability of craftsmen to make and apply
the traditional products faded and became almost obsolete. This
evolution of cement caused a drastic reversal of concepts in that a mixture of
cement and sand is now known as “traditional mortar”, although this
“tradition” is little more than a process adopted in post war years to
satisfy the demand for mass building. The
failures that have been caused by this flawed concept in post war years to
satisfy the demand for mass building, led to the search for alternative
solutions. Technicians recognise
the need to follow the old recipes of the past, while adapting everything to fit
the modern approach and fall in line with the needs of work on an industrialised
site. Fortunately
the old skills have survived, as have documents that detail how to produce
traditional lime mortars. A
combination of these can help to bridge the gap following the demise of the
craftsman’s knowledge in the use of natural products. Unilit
Lime products have
been conceived for the restoration market by the considered evaluation of a
modern manufacturing process to produce traditional restoration products. HYDRAULIC LIME
Pliny
informed us that certain bituminous rocks, when subjected to burning, turned
into water-resistant lime. Vitruvius confirms this, but attributes the
characteristic of these “pebbles” to the fact that they are mixed with
pozzolana tuff. In
the Middle Ages, it is known that certain impure limestones from specific
quarries were used to produce limes, which had to be slaked on use because they
hardened fast and set under water. Among
the many authors of treatises in the Renaissance, Palladio mentions these
characteristics in connection with certain limes originating from the “Colli
Eurganei”. The study of hydraulic lime predominantly took place during the
second half of the eighteenth century, when burning selected argillaceous
limestones, known as “septaria”, at approximately 800oC produced
a hydraulic lime known as “Roman cement”. In
the 19th century, Smeaton, Forst and Vicat produced a lime whose characteristics
they were to define, by burning marls; this lime became known as “natural
hydraulic lime” to distinguish it from the lime which was then produced using
Portland cement by-products. The latter became known as “mainly hydraulic
lime”, but is very different from natural lime, as it behaves chemically and
physically like Portland cement. Finally,
the progress of technology has led to the production of an “artificial”
hydraulic lime, produced by mixing limestone and clay before burning.
It can be claimed to have the same characteristics as natural lime,
although the manufacturers do not always follow the procedure, and are inclined
to mix after burning. NATURAL HYDRAULIC LIME
Natural
hydraulic lime is produced by burning marly limestone at between 800o
and 1000oC. At these
temperatures, the formation of calcium silicates, aluminates and
ferro-aluminates can be noted. However,
the temperature does not release other salts, and the behaviour in the setting
phase is the same as for lime. This
is important for the elasticity of the mortars and their porosity, although
natural hydraulic limes are stronger than air-slaked lime mortars and are
unaffected by humidity before final carbonisation. Natural
hydraulic lime is therefore a substitute compatible with air-slaked lime, both
for the refurbishment and strengthening of historic buildings. Their
fast setting characteristics tolerates the aggression of the modern-day acid
atmosphere, and their porosity prevents the formation of salts in old,
contaminated walls. SAN ROMEDIO HYDRAULIC LIME
Natural
hydraulic lime has been produced in the San Romedio Mines since the last
century. This lime pit was acquired in the early 20th century by the
company Tassullo S.p.A and grew to commercial viability in achieving its
present-day quality level due to the group’s technological innovation and
development. In
depth knowledge of the chemical and physical aspects of hydraulic lime has been
gained using the company’s modern laboratory facilities, with more advanced
research geared to enhancing characteristics of a product on the basis of
quality and consistent performance. From
the chemical viewpoint, natural hydraulic lime, used in the composition of
renders and “small concretes” is a bicalcic silicate.
This special binder, of a hydraulic nature, does not suffer from the
presence of damp or water in the walls, but thrives on it to produce a set. The
binder is produced by the burning at low temperature of special marls extracted
from deposits, which are geologically identified.
After burning, the product is partially slaked, finely milled and ground
to obtain extremely porous grains of high specific surface. The
lime content resultant can, if necessary, be enriched with silicates by adding
pozzolana. THE PRODUCTS
In
the composition of mortars and renders, inert quarry materials obtained from
siliceous rocks are selected according to their degree of purity and
compatibility with the binder. The
products obtained have the following characteristics : ·
optimum inert
material / binder ratio ·
appropriate
variable grading curve ·
controlled
degree of plasticity ·
low elastic
modulus ·
low
hydro-soluble salts content In
terms of performance, this creates consistent quality from the outset, the
elimination of any failures arising from the use of unsuitable inert materials
(stability of dimensions, hollowness, cracking) and ease of application so that
special application skills are not required. UNILIT
- HD System offers a complete range of insulating, strengthening and stabilising
products based on natural hydraulic lime, using the characteristics of this
binder (for each type of structure) so that correct restoration can be carried
out using traditional materials, which are also user friendly on a building
site. In
addition, the specification evaluation should extend to the investigation of
thermo-hygrometric assessment using the Glaser test, hygrometric analysis of the
surfaces, determination of the quantity and type of the hygroscopic salts
contained in the structure, simulation of the materials according to ancient
techniques. These are designed to
assist the specifier in the refurbishment, restoration and conservation sector. BIO-ECOLOGICAL CONSTRUCTION
Building
well for a better life The
endeavours dedicated to achieving the high quality of natural hydraulic lime and
its by-products could not fail to highlight the damage caused by the use of
processes that are incompatible with the environment. On
the basis of experience acquired over a decade of marketing within Northern
Europe, and to satisfy care for protection of mankind and the environment, we
have produced a product range aimed at specifiers who are aware of this problem. Bio-ecological
architecture plays a vital role by making not only specialists, but public and
private enterprise aware of the need to protect a healthy and viable planet for
future generations. In
accordance with National and Community legislation, we must respect quality
parameters both in the production cycle and in the products themselves,
minimising the harmful effects while promoting the maximum degree of recycling. We
are at the forefront of production of bio-ecological mineral binders and we
offer the market a constantly developing family of products. THERMAL INSULATION
Building
insulation is a major factor in energy saving. Efficient construction design is
becoming of significant importance under current legislation and the developers
must opt for structures that are suitable from the technical, economic and
aesthetic points of view. This applies not only to new construction, but also to
the growing market of remodelling and refurbishment. Internal
insulation can be selected where regular heating during a short period of the
day applies as the behaviour of the structure is not altered, and if the space
is heated over a regulated period. Temperature
+ 20oC Saturation
pressure Relative
pressure Cold
bridge prevention Internal
insulation prevents the structure from absorbing heat and reflects the wave
towards the occupants. In thermal controlled heating systems a wall mass acts as
an accumulation and exchange capacitor as, during the periods when the system is
turned off, the “wave return” produced by the structure, maintains the room
temperature at a near-constant level. The
same phenomena applies externally where in hot climates the structure absorbs
less heat and abrupt temperature changes brought about by summer rains, which
causes dampness, condensation and fungal attack. The
mineral insulation mortar Unilit 20
is designed to provide protection for the outer walls. It has a two-fold action
- it provides thermal resistance to the wall fabric and stabilises the
hygrometric balance, due to its high vapour permeability. By
this process an improvement in overall thermal performance is achieved, without
modifying the external appearance and the hygrometric and physiological balance.
Materials are of high quality, environmentally sensitive and easy to apply. The
natural hydraulic lime formula also makes it possible to apply UNILIT 20 to
structures with special historic and architectural importance.
Restrictions imposed for the protection of architectural properties
against the use of incompatible or
unsuitable technologies are met. DAMP ERADICATION
The
discovery of dampness should be investigated as without proper analysis there is
a risk that the incorrect remedy will be selected. Factors
that govern the performance of a structure include thickness, temperature,
ventilation and transmission of heat through the structure.
All these phenomenon control the movement of vapour and thereby the
structure’s ability to perform as a dry element.
This balance can be adversely affected by the incorrect specification of
decorative finish, impervious sealers or cementitious renders. Speed of
evaporation g/m2h Second
phase First
phase Drying
out of wall Percentage
of average humidity in volume Equally
drastic measures such as “forced” dehumidification will reduce the visible
damage but not solve the problem. HYGROSCOPIC SALTS
The
accumulation of excess moisture behind the weathering course and subsequent
evaporation lead to hygroscopic salt deposits. These increase as the cycle of
crystallisation and rehydration advance, leading initially to the spalling of
finishes and ultimately the background. Many
people are currently focusing on this phenomenon to provide a cure by mechanical
extraction. In so doing, they
neglect to tackle the cause of the initial dampness which is critical to the
long term solution. Research
proves there are requirements for new techniques utilising materials that
combine resins with modern binders. Much research has been carried out in modern
construction but not in preservation, restoration or refurbishment. The
effective compromise is found in combining modern manufacturing processes with
traditional materials. The
performance of these, proven over centuries of use, will ensure the best
results. Natural
hydraulic lime can become the vital link between the needs of the sensitive
conservator with those of the modern day specifier.
Unilit is based on a
specific blend of natural hydraulic lime that has historically been used for
mortars and renders. The improved
setting of the product by comparison to wet lime is achieved by a combination of
the extraction process, baking, hydraulicity control and the selection of
compatible aggregates. This
process enables us to determine its capabilities and limitations and so ensure
that the most appropriate binder is specified in all aspects of the restoration
process. STABILISATION AND CONSOLIDATION
Over
recent years the demand for products for use in the consolidation of retaining
walls has increased. Several
European authorities have undertaken experimental studies to increase awareness
in this diverse field. The
aim of consolidation is to stabilise and rejuvenate weakened structures taking
account of the physical and mechanical properties of the original construction. This is achieved by using modern day lime products of
comparable constituents to ensure compatibility and ease of application on old
structures. The
apparent flaws in certain aspects of synthetic processes have restored faith in
the value of traditional building techniques utilising lime to ensure quality
and durability at a realistic cost. From
the research carried out, two processes have been demonstrated to be suitable
for stabilisation and rejuvenation of aging structures. SUPERFICIAL REINFORCEMENT
This
technique is frequently adopted on structures where settlement, vibration or
seismic shocks have caused damage to the fabric of historic structures. By
the use of wholly compatible lime products we are able to provide solutions that
are both physically and aesthetically in harmony with the old structure. Natural hydraulic lime mortar applied as a mass, without
shuttering, adheres effectively to and maintains the structural integrity and
vapour permeability. Where
continued movement is envisaged, stainless steel reinforcement lathing or brick
mesh are incorporated to enhance stability. INJECTION
Consolidation
or stabilisation by injection enables the equilibrium in the physical properties
of the structure to be retained without affecting the performance of the
structural components. The
importance of injection lies in its capacity to homogenise the structural mass
without altering its physical and mechanical characteristics.
Use of synthetic injection processes where the products are stronger than
the elements within which they are applied can cause structural stress and
cracking. Natural hydraulic lime is
especially suitable due to its vapour permeability, mechanical resistance,
excellent penetration due to its fluidity and feeble content of soluble salts.
|
|
Arte Constructo bvba - Molenberglei 18 - B- 2627 Schelle (Belgium) tel: +32 (0)3 880.73.73 fax: +32 (0)3 880.73.70
made by stevensschool
|
