1. DURABILITY ASSESSMENT OF STONES FOR RENOVATION OF HISTORIC BUILDINGS
Martin KEPPERT, Monika ČÁCHOVÁ, Dana KOŇÁKOVÁ
Department of Materials Engineering and Chemistry, Faculty of Civil Engineering, Czech Technical University in Prague

2. Objectives porous sedimentary rocks – sandstone, marlstone
wide range of properties due to differences in composition (amount of clay matrix, presence of siliceous or calcareous cement)
S 1
S 2
Rock
Porosity
Compressive strength %
MPa
S 1
30.5
8.7
S 2
21.8
25.5
S 3
16.2
81.0
S 4
6.2
109.0
S 3
S 4

3. Methods evaluation of porous stones durability:
ice decay – freezing/thawing cycles of water saturated samples;
evaluation by loss of Youngs modulus or bending strength
salt decay – cyclic crystallization/dissolution of Na2SO4.10H2O
induced by temperature changes between 10 and 40 °C
evaluation by „Dry weigth loss“ (DWL) – loss of weigth of samples due to salt scaling

4. Results Rock Porosity Compressive strength Bending strength
Youngs modulus
DWL %
MPa
GPa
S 1
30.5
8.7
1.3
10.9
S 2
21.8
25.5
3.6
18.0
4.2
S 3
16.2
81.0
11.4
27.5
0.5
S 4
6.2
109.0
18.2
34.4
3.1
Pore size distribution is controling
salt decay :
smaller pores = higher crystallization pressure