Adobe Conservation: Evaluation of Silicone and Acrylic Consolidants
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Since soil and water were the most accessible building materials, humans used the mixture of soil and water to fabricate mud bricks or adobe. Iran, Syria, and Iraq have numerous mud brick buildings, and Arg-e Bam, located in Iran, was one of the most famous earthen monuments in the world; it was destroyed in a massive earthquake in 2003. In this research adobe samples were fabricated and different consolidants were applied to the samples. To determine the most effective consolidant, the tests were performed on the treated adobe. The soil for this research was supplied from Godfrey, a site near Kingston, Ontario, Canada. The soil was mixed with kaolin to achieve a similar grain size distribution to that of soil found in Bam. This research used four specific consolidant materials: a 5% (w/v) solution of Paraloid B-72 in toluene; a 50% (v/v) solution of methyl trimethoxy silane (MTMOS) in ethanol; a 50% (v/v) solution of ethyl silicate (TEOS) in ethanol; and Conservare H, which is the commercial brand of ethyl silicate. The research also studied the effects of Paraloid B-72 on surfaces previously treated with methyl trimethoxy silane and ethyl silicate. The chemicals were applied to the samples by brushing. After treatment, different physical properties were measured. The tests included study of density, porosity, water absorption, depth of penetration, abrasion resistance, hardness, compressive strength, bending strength and colour changes. Chemical analysis (X-ray diffraction) was used to study the chemical components of the soil and scanning electron microscopy showed changes to the treated surfaces after application of the chemicals. This research can be used as a guide in choosing the consolidants in adobe consolidation depending on the priorities defined in each building conservation project. Also, by applying all the same tests to samples made from the actual soil from Bam, this research can be used to evaluate how grain size distribution can affect the physical properties of the consolidated samples. By considering only the grain size of the soil used for adobe fabrication, the results from this research produced the following conclusion of consolidation of adobe from Bam; if the colour change is important, then the recommended consolidant is MTMOS or TEOS; if the colour change is not important, then the recommended consolidant is Paraloid B-72. The comparison among all the consolidants and their results, except results from failure strength, leads to the conclusion that the best consolidant is TEOS followed by a second coat of Paraloid B-72.