On-site monitoring for better selection of stone repairs: a case study

Heritage Science

Table 1 Properties of the materials

	Ostermundigen Blue sandstone	Repair mortar
Porosimetry (mercury intrusion porosimetry)
Average pore radius (µm)	7.9	34.6
Total porosity (%)	17.2	35.1
Hygric swelling at 95% RH ɛ ₉₅ (mm m⁻¹)	0.43	0.49
Hydric swelling ɛ _s (mm m⁻¹)	1.25	5.02
Thermal expansion α (10⁻⁶ K⁻¹)	12.9	32.7
Poisson’s ratio ν (−)	0.2^a	0.4^b
Elastic modulus E (GPa)
Wet	0.43	–
Dry	1.87	2.03
Relaxation modulus
Dry	–	\( E_{0} { \exp }\left( { - ( t/\tau)^{\beta } } \right)^{\text{c}}\)
Tensile strength (MPa)
Wet	0.3	–
Dry	1.0	2.7

The Ostermundigen Blue is a sandstone largely used in built heritage in Switzerland, and the repair mortar studied here is made by mixing the powder of this stone with an acrylic resin
^aTaken from [18]
^bTaken from [19]
^cWith E ₀ the instantaneous elastic modulus of the stone (2.03 MPa), t the time in s, τ the temperature-dependent relaxation time \( \left( {4.87 \times 10^{{ - 59}} \exp \left( {\frac{{3.94\cdot10^{4} }}{T}} \right)s} \right) \) and β an exponent equal to 0.206 [20]