Carbonated Hydroxyapatite Substituted with Magnesium for Stone Consolidation

Carbonated hydroxyapatite (CHAp) is an inorganic compound with various applications that presents better homogeneity and consolidating effect than HAp [1]. [...]

Effectiveness and Compatibility of a Novel Sustainable Method for Stone Consolidation Based on Di-Ammonium Phosphate and Calcium-Based Nanomaterials

External surfaces of stones used in historic buildings often carry high artistic value and need to be preserved from the damages of time, especially from the detrimental effects of the weathering. This study aimed to test the effectiveness and compatibility of some new environmentally-friendly materials for stone consolidation, as the use thereof has been so far poorly investigated. The treatments were based on combinations of an aqueous solution of di-ammonium phosphate (DAP) and two calcium-based nanomaterials, namely a commercial nanosuspension of Ca(OH)2 and a novel nanosuspension of calcite. The treatments were applied to samples of two porous stones: a limestone and a sandstone. The effectiveness of the treatments was assessed using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, ultrasound pulse velocity test, colour measurements, and capillary water absorption test. The results suggest that the combined use of DAP and Ca-based nanosuspensions can be advantageous over other commonly used consolidants in terms of retreatability and physical-chemical compatibility with the stone. Some limitations are also highlighted, such as the uneven distribution and low penetration of the consolidants.

Effect of Different Silicic Acid Ester on the Properties of Sandstones with Varying Binders

This study deals with the effect of using different silicic acid ethyl esters (SAE) on diverse sandstones and to estimate their influence on the properties of the treated stones. Prismatic samples of Baumberger Sandstone (BST), Sander Sandstone (SST) and Nievelsteiner Sandstone (NST) with the dimensions 50 mm×50 mm×100 mm were treated with three different consolidating agents based on silicic acid ethyl ester (KSE 100, KSE 300, KSE 510) in three different procedures (vacuum, 1- and 5- time impregnation). The aim of this study is to demonstrate that differences in application, for instance varying stone consolidation agents, other treatment procedures as well as using sandstone samples with different binders (BST: calcareous, SST: clayey, NST: quartzitic), cause in each case different results concerning the strengthening effect and the success of a consolidation action. Laboratory measurements were performed on treated and untreated material in order to estimate the effectiveness of stone consolidation actions. To detect the influence of subsequent treatment procedures, water vapour diffusion resistance (WVDR) and capillary water absorption (CWA) measurements were carried out. Furthermore, the effectiveness of a stone consolidation was analysed by measuring ultrasound velocity, compressive strength, flexural strength, bond strength by pull-off and the porosity of the stone samples. Due to varying treatment procedures the investigated sandstones showed different petrophysical and mechanical properties (no strengthening effect up to “over-treating”). Different treatment procedures lead to increasing amounts of strengthening agent in the pore space of the investigated stones and as a result to higher values in WVDR (except BST and NST samples), ultrasound velocity and to an improvement in mechanical strength (except compressive strength of NST). This applies in particular to 1-time, 5-time and vacuum impregnated SST and 5-time treated NST and BST, regardless of the used stone strengthener. On the other hand, these different treatment procedures lead often to a decreased CWA and to a reduction in total porosity. The performed measurements indicate a development in strength in case of 5-time and vacuum treatment, but also an increase of the possibility of sealing the pores, especially for SST samples.