Low impact surface hardness testing (Equotip) on porous surfaces – advances in methodology with implications for rock weathering and stone deterioration research

Abstract

The Equotip surface hardness tester is becoming a popular method for rock and stone weathering research. In order to improve the reliability of Equotip for on‐site application this study tested four porous limestones under laboratory conditions. The range of stone porosity was chosen to represent likely porosities found in weathered limestones in the field. We consider several key issues: (i) its suitability for soft and porous stones; (ii) the type of probe required for specific on‐site applications; (iii) appropriate (non‐parametrical) statistical methods for Equotip data; (iv) sufficient sampling size. This study shows that the Equotip is suitable for soft and porous rock and stone. From the two tested probes the DL probe has some advantages over the D probe as it correlates slightly better with open porosity and allows for more controlled sampling in recessed areas and rough or curved areas. We show that appropriate sampling sizes and robust non‐parametric methods for subsequent data evaluation can produce meaningful measures of rock surface hardness derived from the Equotip. The novel Hybrid dynamic hardness, a combination of two measuring procedures [single impact method (SIM) and repeated impact method (RIM)], has been adapted and is based on median values to provide a more robust data evaluation. For the tested stones in this study we propose a sample size of 45 readings (for a confidence level of 95%). This approach can certainly be transferred to stone and rock with similar porosities and hardness. Our approach also allows for consistent comparisons to be made across a wide variety of studies in the fields of rock weathering and stone deterioration research. Copyright © 2016 John Wiley & Sons, Ltd.

A laboratory study of Equotip surface hardness measurements on a range of sandstones: What influences the values and what do they mean?

“…For example, Wilhelm et al (2016b) found much more variable data (and thus a need for much larger sample sizes) from four different British building limestones. For example, Wilhelm et al (2016b) found much more variable data (and thus a need for much larger sample sizes) from four different British building limestones.…”

“…In this paper, values from probe D are expressed as HLD, and those from probe C as HLC (following the notation proposed by Wilhelm et al, 2016b). In this study, Probe D and Probe C have been used.…”

“…Following Wilhelm et al (2016b) we have taken 45 SIM measurements at random locations on each surface and calculated mean and standard deviation. Single impact method (SIM): For this measurement method a number of individual measurements are taken at individual points within a sample area to produce a mean and standard deviation.…”

“…Yilmaz, 2013; Wilhelm et al, 2016b;Asiri et al, 2016;Corkum et al, 2018). Yilmaz, 2013; Wilhelm et al, 2016b;Asiri et al, 2016;Corkum et al, 2018).…”

Bullet impacts and built heritage damage 1640–1939

“…In this study, an Equotip 3 with a D-type probe was used to map variations in weakening of the stone surface. This equipment was originally developed for the testing of metals [22], but is now used in both natural settings [23,24] and the built environment [25]. The surface hardness is measured through rebound of a 3 mm diameter spherical tungsten carbide test tip against the rock surface.…”