June 5th – June 8th , Telč, Czech Republic
FROST RESISTANCE OF LIME-BASED MORTARS WITH LINSEED OIL
C. Nunes, Z. Slı́žková, D. Křivánková 1
Summary: The recent findings in mortar additives that grant hydrophobic properties to
mortars show that by restraining water penetration, damage from frost and salt can be
decreased. The aim of the present research is to assess the ability of lime-based mortars
enriched with 1.5 % linseed oil (by the weight of the binder) to resist to frost damage. The effect of linseed oil addition was studied in two different mortar mixtures: air lime mortar and
air lime-metakaolin mortar. Specimens three months of age were subjected to freeze-thaw
ageing tests. Ageing effect was evaluated by means of ultrasonic measurements, mechanical
tests and porosity measurements. Improved durability of lime-based mortars with linseed
oil addition has been confirmed making the present formula a promising recipe for mortar
reconstructions.
Keywords: mortar, linseed oil, durability
1 Introduction
Today’s lime mortars with compositions similar to ancient mortars, and thus more suitable to ensure the aesthetical and functional compatibility with pre-existing materials, have presented durability problems mainly
when exposed to weathering agents like water and freeze-thaw cycles [1].
Nowadays air lime mortars are very porous and their mechanical strength and durability are low when
exposed to water and frost even though if only occasionally. One way to improve the strength and durability
of air lime mortars is to partially replace air lime by other materials such as pozzolanas. The promising
pozzolanic material in this regard is metakaolin, substance extensively used also in the ancient times. The
properly designed air lime-metakaolin mortar may be promising for mortar repairs. It achieves much higher
mechanical strength than pure air lime mortar but it is not strong enough to generate stress leading to failure
in the original system [2, 3, 4].
The main goal for using oil as an additive for mortars relies in its hydrophobic properties. Hence, it may
be a very efficient additive to improve durability by restraining water penetration. Linseed oil was one of the
main lipid additives used for mortar formulas in ancient times according to ancient treatises, e.g. Vitruvius [5],
Pliny [6], Palladio [7]. However, there is lack of information about the formula composition and preparation
technique. Owing to the proved influence of oils on the improvement of mortars durability [7] the aim of
this paper is to study mechanical resistance of lime-based mortars (lime and lime-metakaolin) enriched with
1.5 %-w linseed oil (to the weight of binder) to freeze-thaw cycles.
2 Experimental study
All the mortars were prepared in laboratory conditions with a binder: aggregate proportion of 1:3 (by weight),
using a siliceous sand as aggregate. Lime-metakaolin mortars proportion corresponds to 0.75:0.25:3-w. The
percentage weight of linseed oil added in respect to the weight of binder was 1.5 %.
1
Mgr. Cristiana Nunes, Zuzana Slı́žková, Ph.D., Mgr. Dana Křivánková, Institute of Theoretical and Applied Mechanics AS CR,
v.v.i., Prosecká 76, 190 00 Prague 9, email:{nunes, slizkova, krivankova}@itam.cas.cz
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XIIIth Bilateral Czech/German Symposium
Binder and aggregate were mechanically mixed using an automatic mortar mixer. The amount of water
was chosen so that each mortar could get comparable consistencies using the flow table test (170 ± 5 mm)
though water/binder ratios were very similar for all mortars (1.03 ± 0.05 mm). Mortars were mechanically
compacted in prismatic 40×40×160 mm casts. During the first day inside the casts and for 6 days afterwards
the samples were stored at 90 ± 5 % of relative humidity. The mortar beams were then stored until testing
days under controlled ambient at a temperature of 20 ± 5◦ C and 60 ± 10%.
Frost cycles were performed with samples 90 days of age. Specimens were dried to constant mass at 60◦ C
before being tested. The freezing tests were performed based on the Czech standard SN 72 2452 [9]. Samples
were immersed in water at ambient temperature (20 ± 5◦ C) until achieving constant mass. After saturation
in water samples were subjected to (−20 ± 5◦ C) in a freezer during 4 hours and then thawed in water at
ambient temperature (20 ± 5◦ C) for at least 2 hours before performing another cycle. Three samples were
subjected to the freezing cycles and a group of 3 specimens was used as a reference for the frost-exposed
materials. They were kept at room temperature in water for the whole time of the cycling procedure (about
1month).
The ageing process was monitored during the testing procedure after each 5 cycles by means of ultrasonic
measurements. The experiment was carried out using a USG 20 device (Krompholz Geotron Elektronik,
FRG) with a 250 kHz vibrator (USG -T) and receiver (USE-T). Ultrasound probe was used to measure the
time of wave propagation. Transmission mode technique was used: one transmitter and one receiver were
placed in the extremities of the specimens (along the length direction).
Freezing cycles were interrupted when specimens showed moderate to severe degradation. Flexural and
compressive strength were then determined based on the Czech standard ČSN EN 1015-11 [10] using a
universal traction machine, following the classic method of performing the compressive test with half samples
obtained from the flexural test. Half of each specimen 40 × 40 × 160 mm remaining from the mechanical
tests were also used for open porosity and bulk density determinations after being dried to constant mass at
60◦ C. These test were performed by total saturation with water under vacuum and hydrostatic weighing as
defined in the table ČSN EN 1936 [11].
3 Results and discussion
Lime mortar samples crumbled after one freezing cycle. Lime with linseed oil mortar was subjected to ten
cycles after which the samples showed moderate degradation by binder powdering and, consequently, sand
disintegration. Ultrasonic measurements revealed a slight decrease on the wave velocity propagation after 10
cycles (Fig. 1). After 10 cycles it was decided to perform flexural and compressive strength tests. Prior to
the mechanical tests, samples were dried to constant mass at 60C. The results of mechanical strength after
freezing tests are shown in Fig. 2.
Regarding lime-metakaolin mortars the results of ultrasound test show a clear drop-off on the wave velocity propagation after 5 and 10 cycles whereas for the linseed oil mortar there is no variation along the
20 cycles performed (Fig. 1). Furthermore, aged and reference specimen’s values are practically equal although slight fissuration of the specimens could be noticed after 17 cycles. Concerning lime-metakaolin
(LM) mortar, after 10 cycles specimens exhibited moderate to severe fissuration. Mechanical properties of
aged specimens were assessed on LM mortar after 10 cycles and on lime-metakaolin-oil (LMO) mortar after
20 cycles (Fig. 2).
The results derived with mechanical tests with mortars with linseed oil point to almost the same flexural
and compressive strength of aged and reference specimens. Furthermore, the results are in agreement with
the ones obtained using the ultrasonic test. Lime with oil (LO) and LMO aged and reference specimens
show similar values for flexural and compressive strength as well as for ultrasonic velocity. The increment
on lime-metakaolin mortars strength is assigned to the hydraulic reactions that are potentiated by water.
Porosity as well as bulk density values does not reveal evidences of damage (Tab. 1), hence, a relationship
between porosity and mechanical features cannot be established. Porosity of all mortar types is quite similar
and it is in agreement with the similar water/binder ratio used to achieve the same consistency.
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June 5th – June 8th , Telč, Czech Republic
Figure 1: Variation of ultrasonic pulse velocity versus ageing cycles: Lime-Oil mortar (left); LimeMetakaolin mortar (middle); LMO: Lime-Metakaolin-Oil mortar (right)
Figure 2: Flexural and compressive strength after freezing test (L: Lime mortar; Lime+Oil mortar; LM:
Lime+Metakaolin mortar; LMO: Lime+Metakaolin+Oil mortar
Table 1: Open porosity and bulk density (average values ± standard deviation) of tested mortars
Mortar
L
LO
LO
LO
LM
LM
LM
LMO
LMO
LMO
Condition
Not Aged
Not Aged
Age Reference
Aged
Not Aged
Age Reference
Aged
Not Aged
Age Reference
Aged
Porosity [%]
32.01 (± 0.19)
35.75 (± 0.27)
34.20 (± 0.23)
35.28 (± 0.62)
34.35 (± 0.13)
34.90 (± 0.14)
36.49 (± 0.25)
32.41 (± 0.50)
35.96 (± 1.56)
36.40 (± 2.35 )
25
kg
Bulk density m
3
1767.82 (± 0.18)
1637.83 (± 6.56)
1634.54 (± 2.34)
1609.49 (± 15.16)
1688.80 (± 0.95)
1669.62 (± 4.37)
1627.12 (± 8.22)
1611.06 (± 7.84)
1680.43 (± 10.95)
1594.40 (± 38.79)
XIIIth Bilateral Czech/German Symposium
4 Conclusions
Improved durability of mortars with linseed oil addition has been confirmed by testing their freeze-thaw
resistance. L mortar was destroyed after 1 cycle whereas LO endured 10 cycles and exhibited only moderate
apparent degradation but significant drop in mechanical strength. LM mortar with 10 cycles decreased its
strength down to the same range of LMO values mortar with 20 cycles meaning that linseed oil also improved
considerably the hydraulic mortar resistance.
A possible explanation for the similar values obtained with aged and reference mortars with oil both with
ultrasonic and mechanical tests is that linseed oil might improve elasticity of the mortar matrix. As a result,
the freezing process itself does no cause the material degradation. This can be inflicted by water dissolution
process but further researchmust be done in order to unveil these results.
Ultrasonic velocity was expected to evolve according to variations of physical parameters influenced by
the damage. Ultrasonic test proved to be a good means for monitoring material ageing as the results are in
agreement with the ones obtained with the mechanical tests. Further research will be focused on quantitative
interpretation of data acquired by studying the influence of parameters other than porosity and mechanical strength on ultrasonic measurements like water content and aggregate properties (pore size distribution,
volume concentration and modulus of elasticity).
Acknowledgment
The present study was supported by the Czech national project MK ČR NAKI DF11P01OVV0080 entitled
”High Valuable and Compatible Lime Mortars for Application in the Restoration, Repair and Preventive
Maintenance of the Architectural Heritage”
References
[1] Veiga, R. As Argamassas na Conservação (Mortars in Conservation), Actas das 1a as Jornadas de
Engenharia Civil da Universidade de Aveiro, Aveiro University, Lisbon (2003).
[2] Fortes-Revilla, C., et al. Modelling of slaked lime-metakaolin mortar engineering characteristics in
terms of process variables, Cement and Concrete Composites 28 (2006).
[3] Slı́žková, Z. Charakteristiky malt modifikovaných metakaolinem aplikovaných na historických objektech, Seminář, Metakaolin 2009, Fakulta stavebn VUT v Brně (2009).
[4] Válek, J., Slı́žková, Z., Zeman, A. Mechanické a fyzikálnı́ zkoušky vápenných malt přı́davkem
metakaolinu a jejich vhodnost pro opravy památkově chránných objektů. Seminář, Metakaolin 2007,
Fakulta stavebn VUT v Brně (2007).
[5] Maciel, J. Vitrvio: Tratado de Arquitectura, 3rd Ed., UTL-IST, Lisbon (1999)
[6] Bostock, J. & Riley, H.T. Pliny: The natural history, Vol. 6, H.G. Bohn, London (1857)
[7] Tavernor, R. & Schofield, R. Andrea Palladio: The four books on architecture. 1570, MIT, Massachusetts (1997)
[8] Rovnanı́ková, P., Omı́tky, STOP, Prague (2002)
[9] ČSN 72 2452, Zkouška mrazuvzdornosti malty
[10] ČSN EN 1015-11, změny A1 Zkušebnı́ metody malt pro zdivo - Část 11: Stanovenı́ pevnosti zatvrdlých
malt v tahu za ohybu a v tlaku
[11] ČSN EN 1936, Zkušebnı́ metody přı́rodnı́ho kamene - Stanovenı́ mrné a objemové hmotnosti a celkové
a otevřené pórovitosti
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