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Elaich module 5 exercise 5.d advanced


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Elaich module 5 exercise 5.d advanced

  1. 1. Educational Linkage Approach In Cultural HeritageE x e r c i s e 5.DAdvanced CourseModule 5 Monitoring & MaintenanceTopic 5.1 To Monitor or not to Monitor, that is the question! Exercise 5.D Hands on materials: What the contact angle can tell us Authors: Prof. Guido Biscontin, Dr. Francesca Caterina Izzo, Prof. Elisabetta Zendri, Ms. Laura Falchi- Ca’ Foscari University of Venice Objective The aim of this exercise is to help students to understand what a contact angle is, how to measure it and its importance as a monitoring parameter for the behaviour of the relation water/Cultural Heritage materials. Introduction “Monitoring means to carry out evaluation tests at the end of the conservation intervention and over time to control the efficiency of the intervention and of the products in terms of water repellence”. The application of a water repellent on the surface of a building material can change the behaviour in relation with water. This difference can be seen also by measuring the contact angle which gives us the idea of the wettability of the material, that is to say how much water can wet a material. Guidelines Exercise 5.D should be done after the Topic 5.1 of the Module 5 “Monitoring and Maintenance”. Duration: 30 minutes on the first day to prepare samples and treat them with water repellents, 30 minutes for the activity and 30 minutes for writing the report. Type of activity: it is a group activity that should be done in class. The Fig. 1 example of mortar specimen report could be written also as an homework. 1
  2. 2. Educational Linkage Approach In Cultural HeritageE x e r c i s e 5.D Equipment • Stone material samples, preferably regular specimen of: pieces of bricks local stone samples (marble, limestone, sandstone) pieces of mortars • water Fig. 2 applying the treatment • water repellent products such as: linseed, walnut, Vaseline or olive oils; natural wax; commercial water repellents… • brush • syringe without the needle • block notes • protractor • camera Fig. 3 spreading drops of water Before the activity: prepare the equipment needed and copies of the on the treated surface example report and of the data sheets. During the activity: st 1 day: treatment with water repellence products • dry the samples • label the samples and for each different material separate some samples (which will be treated) from others (which will remain untreated) Fig. 5 photo of a drop • apply the oil or wax with a brush all over the surfaces of the chosen samples 135° • dry the treated samples nd 2 day: determination of contact angle • fill up the syringe with water • gently spread some little water drops on the surface of the sample • take orthogonal photos of the samples with the drops of water on the surfaces • measure the contact angle between the surface and the water drop Fig 4 measuring the contact angle 2
  3. 3. Educational Linkage Approach In Cultural HeritageE x e r c i s e 5.D WHAT IF… “…the material absorbs the water drop immediately?!”“Don’t worry! If the material absorb the drop immediately it means that the surface is completely wettable and the contact angle is considered 0° ” Remember! 3
  4. 4. Educational Linkage Approach In Cultural HeritageE x e r c i s e 5.D Report writing: Measure with the protractor the contact angles from the photos you have done. Note down the contact angles of each sample. Calculate the mean of the angles for each material after and before the treatment. Create an histogram of the different contact angles. Mean= (a1+a2+a3+a4+a5)/5 Look at the example: sample nr 1 not treated sample nr 1 treated with drop angle drop angle 1 20 1 120 2 0 2 110 3 15 3 85 4 5 4 98 5 10 5 100 mean 10 mean 102.6 Expected results The samples treated with water-repellent products should have a higher contact angle (as in our examples reported in the previous table). If the contact angle is more than 90°, the surfaces are called hydro-repellent (the water cannot wet the material); the treatment, therefore, is able to protect the materials against the possible damaging action of water. 4
  5. 5. Educational Linkage Approach In Cultural HeritageE x e r c i s e 5.D Report writing: Write the contact angle of different materials and calculate the mean: sample nr not treated sample nr treated with drop angle drop angle 1 1 2 2 3 3 4 4 5 5 mean mean Answer the following questions: 1. What do you observe? 2. Do the different materials react in the same way in contact with water? 3. Do you think the treatments applied are good enough in order to prevent water to enter into on building and/or historical materials? 5