Rock Pore Structure as Main Reason of Rock Deterioration

Abstract

Crashed or dimensional rocks have been used as natural construction material, decoration stone or as material for artistic sculptures. Especially old historical towns not only in Slovakia have had experiences with use of stones for construction purposes for centuries. The whole buildings were made from dimensional stone, like sandstone, limestone or rhyolite. Pavements were made especially from basalt, andesite, rhyolite or granite. Also the most common modern construction material -concrete includes large amounts of crashed rock, especially limestone, dolostone and andesite.However, rock as any other material if exposed to exogenous processes starts to deteriorate. Especially mechanical weathering can be very intensive if rock with unsuitable rock properties is used. For long it had been believed that repeated freezing and thawing in relation to high absorption is the main reason of the rock deterioration. In Slovakia for many years the high water absorption was set as exclusion criterion for use of rocks and stones in building industry. Only after 1989 the absorption was accepted as merely informational rock property and not exclusion. The reason of the change was not the understanding of the relationship between the porosity and rock deterioration, but more or less good experiences with some high porous rocks used in constructions exposed to severe weather conditions and proving a lack of relationship between rock freeze-thaw resistivity and water absorption.Results of the recent worldwide research suggest that understanding a resistivity of rocks against deterioration is hidden not in the absorption but in the structure of rock pores in relation to thermodynamic properties of pore water and tensile strength of rocks and rock minerals.Also this article presents some results of research on rock deterioration and pore structure performed on 88 rock samples. The results divide the rocks tested into two groups -group N in which the pore water does not freeze even when the temperature decreases to -20 ºC, and the second group F in which the pore water freezes. It has been found that the rocks from group N contain critical portion of adsorbed water in pores which prevents freezing of the pore water. The presence of adsorbed water enables thermodynamic processes related to osmosis which are dominantly responsible for deterioration of rocks from group N. A high correlation (R = 0.81) between content of adsorbed water and freeze-thaw loss was proved and can be used as durability estimator of rocks from group N. The rock deterioration of group F is caused not only by osmosis, but also by some other processes and influences, such as hydraulic pressure, permeability, grain size, rock and mineral tensile strength, degree of saturation, etc., and the deterioration cannot be predicted yet without the freeze-thaw test. Since the contents of absorbed water and ratio between adsorbed and bulk water (of which the absorbed water consists) is controlled by the porosity and pore structure, it can be concluded that the deterioration...

Quantifying Rock Fatigue and Decreasing Compressive and Tensile Strength after Repeated Freeze‐Thaw Cycles

“…Water migration outwards from the centre of the block concentrates porewater close to the surface. When the rock temperature decreases below zero in stage II, bulk water in macropores (diameter > 1 mm) freezes first, while capillary water in mesopores (diameter between 0.1 µm and 1 mm) and adsorbed water in micropores (diameter < 0.1 µm) freeze only at lower temperatures (Powers, ; Ondrasik and Kopecky, ). The percentage of micropores is decisive for the durability and susceptibility of porous rocks to freezing and thawing (Kaneuji et al , ; Prick, ).…”

Frost Damage in Tight Sandstone: Experimental Evaluation and Interpretation of Damage Mechanisms

“…There are several pore classification criteria used in different fields. This paper refers to the classification criteria proposed by Ondrášik et al based on Kelvin’s equation [ 39 , 40 ]. Pores of >0.1 mm diameter are called macropores, pores with diameters of 2 μm–0.1 mm are mesopores, pores of 50 nm–2 μm are micropores, and pores of <50 nm are nanopores.…”

NMR Experimental Study on Dynamic Process of Pore Structure and Damage Mechanism of Sandstones with Different Grain Sizes under Acid Erosion

“…However, there is no unified classification standard for the pore radius of sandstones, and sandstones from different areas have different classification standards. According to the pore classification standard proposed by Ondrášik and Kopecký [44] and the pore structure characteristics of the specimens, the pores were divided into three types: micropores (≤100 μm), mesopores (100-1000 μm), and macropores (≥1000 μm). Based on this, the critical pore radius values of these pore types were substituted into equation 4, and the T 2 cutoff time of the three pore types were calculated to be 10 ms and 100 ms. e T 2 spectrum distribution curves of typical specimens from each group are analyzed as follows.…”