Hasan Böke

Ettringite formation in historic bath brick–lime plasters

Abstract Two types of historic hydraulic brick–lime plasters from a selected Ottoman bath are examined to characterize their technology and the appropriateness of their use in bath. The first type of plaster is original and structurally sound, while the historic repair plaster is the second type and is found to have deteriorated despite being exposed to the same environment. This difference is investigated by comparing their raw material compositions and the pozzolanic activities of the brick powders used in the plasters. Although these results showed no significant differences, ettringite crystals are detected in the historic repair ones by XRD, FTIR, and SEM-EDS analysis. The repair plaster may have lost its integrity owing to the expansion generated by the growth of ettringite crystals in the plaster. In this study, the ettringite formation is discussed in relation to hydration reaction products of lime–brick plasters, possible sources of gypsum, and the climatic conditions of historic bath building.

Reducing Marble-SO2 Reaction Rate by the Application of Certain Surfactants

Sulfur dioxide (SO2), prevalent in the modern urban environment of industrial countries, attacks calcite (CaCO3)in marble. As a result, a gypsum (CaSO4·2H2O) crust is produced at rain-sheltered surfaces while areas exposed to rain experience accelerated erosion. We have investigated theeffect of certain surfactants as protective agents against SO2 attack. We report that the anions oxalate (C2O4-2) and oleate (C17H33COO-) from solutions of their highly soluble alkali salt species areable to replace carbonate (CO3-2) in calcite producingless reactive substrate of oxalate and oleate of calcium. Experiments to measure the protection obtained by these treatments were carried out in the laboratory and field conditions at nearly 1ppm and 10 ppb SO2 concentrations, respectively. We found that these treatments provided significantprotection to marble exposed in sheltered areas, up to 30% reduction of reaction rate by treatment with 2 × 10-4M sodium oleate and up to 14% by a 2 × 10-3 M with potassium oxalate solutions, but become ineffective over long term exposure when applied to surfaces exposed to rain.Carrara marble was used in the reported study. Ion chromatographywas the analytical tool, which allowed precise measurements of ionic concentrations of these salts, the amount of their uptakeby marble, and the thickness of the gypsum crust. X-ray diffraction allowed determination of the new minerals formed at the marble surface by the treatment with surfactants.

Investigation of the Pozzolanic Properties of Bricks Used in Horasan Mortars and Plasters in Historic Buildings

Crushed brick used in historic brick-lime mortars and plasters (Horasan) were characterized for understanding their properties to develop intervention mortars for conservation. Brick powders were separated from original mortars and plasters, and analyzed by XRD, SEMEDS, TGA and pozzolanic activity (PA) measurements. The results showed that the microstructures of brick powders were not completely vitrified, and their XRD analysis failed to show the peaks for high temperature (T>900C) phases. PA measurements of all brick powders showed an ample amount of artificial pozzolan property. Consequently, brick powders aimed for conservation of historic mortars must have high clay contents in addition to being low-fired (T<900C) in order to produce maximum conversion into amorphous phase for ideal PA values.