The Effect of Linseed Oil on the Properties of Lime-Based Restoration Mortars
Total Page:16
File Type:pdf, Size:1020Kb
Allma Mater Studiiorum – Uniiversiità dii Bollogna DOTTORATO DI RICERCA Science for Conservation Ciclo XXII Settore/i scientifico disciplinari di afferenza: CHIM/12 TITOLO TESI THE EFFECT OF LINSEED OIL ON THE PROPERTIES OF LIME-BASED RESTORATION MORTARS Presentata da: Eva Čechová Coordinatore Dottorato Relatore Prof. Rocco Mazzeo Prof. Ioanna Papayianni Esame finale anno 2009 Abstract THE EFFECT OF LINSEED OIL ON THE PROPERTIES OF LIME-BASED RESTORATION MORTARS The traditional lime mortar is composed of hydrated lime, sand and water. Besides these constituents it may also contain additives aiming to modify fresh mortar´s properties and/or to improve hardened mortar´s strength and durability. Already in the first civilizations various additives were used to enhance mortar´s quality, among the organic additives, linseed oil was one of the most common. From literature we know that it was used already in Roman period to reduce water permeability of a mortar, but the mechanism and the technology, e.g. effects of different dosages, are not clearly explained. There are only few works studying the effect of oil experimentally. Knowing the function of oil in historical mortars is important for designing a new compatible repair mortar. Moreover, linseed oil addition could increase the sometimes insufficient durability of lime-based mortars used for reparation and it could be a natural alternative to synthetic additives. In the present study, the effect of linseed oil on the properties of six various lime- based mortars has been studied. Mortars´ compositions have been selected with respect to composition of historical mortars, but also mortars used in a modern restoration practise have been tested. Oil was added in two different concentrations – 1% and 3% by the weight of binder. The addition of 1% of linseed oil has proved to have positive effect on mortars´ properties. It improves mechanical characteristics and limits water absorption into mortar without affecting significantly the total open porosity or decreasing the degree of carbonation. On the other hand, the 3% addition of linseed oil is making mortar to be almost hydrophobic, but it markedly decreases mortars´ strength. However, all types of tested lime- based mortars with the oil addition showed significantly decreased water and salt solution absorption by capillary rise. Addition of oil into mortars is also decreasing the proportion of pores which are easily accessible to water. Furthermore, mortars with linseed oil showed significantly improved resistance to salt crystallization and freeze-thaw cycles. On the base of the obtained results, the addition of 1% of linseed oil can be taken into consideration in the design of mortars meant to repair or replace historic mortars. Eva Čechová List of symbols and abbreviations List of symbols and abbreviations A [mm2] area on which the load is applied (compressive strength testing) ASTM American Standard Testing Method b [mm] width of specimen c [MPa] compressive strength C [kg/(m2.min0,5)] coefficient of water (salt solution) absorption C2S Dicalcium silicate 2CaO. SiO2 C3A Tricalcium aluminate 3CaO. Al2O3 C3S silicate 3CaO. SiO2 C4AF Tetracalcium aluminoferrite 4CaO. SiO2. Al2O3. Fe2O3 Ca coefficient of pores accessibility to water -1 -2 Cv [g.h .m ] water vapour permeability coefficient C-S-H Calcium silicate hydrate d [mm] depth of specimen Edyn [GPa] dynamic modulus of elasticity e.g. exempli gratia (= for example) EN European Standard f [MPa] flexural strength Ff [N] maximum load applied to the specimen (flexural strength test) Fc [N] maximum load applied to the specimen (compressive strength test) φ angle with vertical direction ii List of symbols and abbreviations g [m.s-2] gravity acceleration, g = 9.81 m.s-2 h [m] distance reached by water in the capillary h0 [m] height of water above entrance pore Δh/Δt [m.s-1] capillary absorption rate i.e. id est (= that is) l [mm] distance between the axes of the support rollers L [m] length of the specimen m0 [kg] mass of the empty vassel m0 [kg] mass of the dry specimen m1 [kg] mass of the empty container m2 [kg] mass of the container and test specimen m10 [kg] mass after 10 minutes m90 [kg] mass after 90 minutes mA [kg] mass of the empty pycnometer mB [kg] mass of the pycnometer filled with distilled water mC [kg] mass of the pycnometer filled with ethanol mD [kg] mass of the specimen mE [kg] mass of the pycnometer filled with ethanol and the specimen mfm [kg] mass of vassel with fresh mortar mh1 [kg] mass of the saturated specimen after 48 hours weighed hydrostatically mh2 [kg] mass of the saturated surface dry specimen after vacuum evacuation weighed hydrostatically mSSD1 [kg] mass of the saturated surface dry specimen after 48 hours iii List of symbols and abbreviations mSSD2 [kg] mass of the saturated surface dry specimen after vacuum evacuation n [Hz] fundamental frequency in longitudal mode of vibration of the specimen v [m.s-1] ultrasonic pulse velocity η [Ns.m-2] water viscosity OPC Ordinary Portland Cement p48 [%] porosity after 48 hours, i.e. porosity easily accessible to water P [%] porosity accessible to water, i.e. open porosity H 2O r [m] capillary radius RH [%] relative humidity ρ [kg.m-3] density of the material (dynamic modulus of elasticity testing) -3 a [kg.m ] apparent density -3 ρb [kg.m ] bulk density of fresh mortar -3 -3 H O 2 [kg.m ] distilled water density at 20 ºC, H2O = 998,2 kg.m -3 C [kg.m ] density of ethanol at 20 ºC -3 ρl [kg.m ] loose bulk density -3 ρp [kg.m ] particle density determined σ [N.m-1] surface tension of the water T [s] pulse transit time τ [h] time between two successive measurements (water vapour permeability test) Θ contact angle between water and the solid surface iv List of symbols and abbreviations V [m3] capacity of the container 3 Vfm [m ] volume of fresh mortar wt weight (percentage per weight) WA [%] water absorption after vacuum evacuation WA48 [%] water absorption after 48 hours v Table of contents Table of contents 1 INTRODUCTION .............................................................................................................. 1 2 THEORY .......................................................................................................................... 3 2.1 DEFINITION OF MORTAR .......................................................................................................... 3 2.2 MORTAR COMPOSITION .......................................................................................................... 5 2.2.1 Binders ....................................................................................................................... 6 2.2.1.1 Terminology on lime...................................................................................................... 6 2.2.2 Aggregate .................................................................................................................. 7 2.2.3 Water ......................................................................................................................... 8 2.2.4 Additives and admixtures .......................................................................................... 8 2.3 TYPES OF MORTAR .................................................................................................................. 9 2.3.1 Lime mortar ............................................................................................................... 9 2.3.1.1 Binder properties .......................................................................................................... 9 2.3.1.2 Hardening process ....................................................................................................... 10 2.3.2 Hydraulic mortars .................................................................................................... 12 2.3.2.1 Cement mortar ............................................................................................................ 13 2.3.2.1.1. Binder properties .................................................................................................... 14 2.3.2.1.2. Hardening process .................................................................................................. 16 2.3.2.2 Hydraulic lime mortar ................................................................................................. 17 2.3.2.2.1. Binder properties .................................................................................................... 17 2.3.2.2.2. Hardening process .................................................................................................. 18 2.3.2.3 Pozzolanic mortar ........................................................................................................ 18 2.4 DETERIORATION OF MORTARS ................................................................................................. 19 2.4.1 Physical deterioration .............................................................................................. 20 2.4.1.1 The effect of water ...................................................................................................... 20 2.4.1.2 The effect of salts ........................................................................................................ 20 2.4.2 Chemical (environmental) weathering .................................................................... 24 2.4.2.1 Degradation of lime mortars (4) ................................................................................... 25 2.4.2.2 Degradation