MEASUREMENT
OF WATER ABSORPTION UNDER LOW PRESSURE
RILEM TEST METHOD NO. 11.4
Introduction
RILEM (Reunion Internationale des Laboratoires D'Essais et de
Recherches sur les Materiaux et les Constructions), with headquarters
in Paris, is the International Union of Testing and Research Laboratories
for Materials and Structures. As with our American Society for
Testing and Materials (ASTM), Technical Committees are formed
within RILEM to develop standard methods for measuring properties
and evaluating the performance and durability of many different
building materials.
One such technical committee, Commission 25-PEM, has developed tests to measure the deterioration of stone and to assess the effectiveness of treatment methods. The standard tests drafted by Commission 25-PEM fall within several categories, including methods for determining internal cohesion (111.), for measuring mechanical surface properties (IV.), and for detecting the presence and movement of water (11.). Within category II., is Test Method No. 11.4, designed to measure the quantity of water absorbed by the surface of a masonry material over a definite period of time.
RILEM Test Method 11.4 provides a simple means for measuring the rate at which water moves through porous materials such as masonry. The test can be performed at the site or in the laboratory and can be used to measure vertical or horizontal water transport. Water permeability measurements obtained in the laboratory can be used to characterize unweathered, untreated masonry. Measurements made at the site (or on samples removed for laboratory testing) can be used to assess the degree of weathering that the material has undergone. Test Method 11.4 can also be used to determine the degree of protection afforded by a water repellent treatment. A description of the equipment and procedure for conducting this test is provided in paragraphs below. The theoretical basis on which the method is based and the several applications of test data are discussed.
Theory
Because masonry building materials are porous, they are all somewhat
permeable to water. The interior structure of a masonry material
is a system of fine interconnected pores. Wetting by liquid water
involves capillary conduction (suction) through this pore system,
proceeding along both vertical and horizontal pathways. Vertical
transport occurs when water enters as ground water at the base
of a structure or as rain water through leaking gutters. Penetration
of driving rain into wall surfaces results in horizontal transport.
(Under actual conditions, the amount of rain penetration depends
on prevailing wind conditions as well as on the composition and
condition of the exposed surface.)
When liquid water comes into contact with a masonry surface, wetting proceeds through the material as a front. Accurate measurements of the advance of this wetting front made on a variety of masonry building materials have demonstrated that the characteristic wetting rate and pattern of each material are directly related to its capillary structure and port size distribution. In fact, rate constants have been measured for brick, limestones and other masonry materials. RILEM Test Method 11.4 provides a simple method for measuring the volume of water absorbed by a material within a specified time period.
Equipment
The equipment necessary for measuring water absorption under low
pressure is simple. The test can be performed at the site or
in the laboratory with a test apparatus available in two forms.
One is designed for application to vertical surfaces and measures
horizontal transport of water, or, its resistance to wind-driven
rain penetration.*
A second form is designed for application to horizontal surfaces and measures vertical transport. Figure 1 illustrates the pipe-like apparatus designed for vertical surfaces. Its flat, circular brim (at the bottom end of the pipe) is affixed to the masonry surface by interposing a piece of putty. The open, upper end of the pipe has an area of 5.7 cm2. The vertical tube is graduated from 0 to 4 cm3 with each gradation representing an increment of 0.1 cm3 (it is therefore possible to estimate to 0.05 cm3.) The total height of the column of water applied to the surface, measured from the center point of the flat, circular brim to the topmost gradation, is 9.8 cm. This corresponds to a pressure of 961.38 pascals (approximately 0.14 psi), or, a dynamic wind pressure of 142.6 kilometers per hour (approximately 88.5 mph). The apparatus designed for application to horizontal surfaces, is similar to the one for vertical surfaces as described above.
*It should be noted that a standard method for measuring water penetration and leakage through masonry is described in ASTM E 514. The ASTM test method is intended to evaluate wall design and workmanship as well as the degree of weathering and the performance of water repellent treatment. It is therefore necessary to conduct the procedure on a test wall built with a minimum height or length of four feet. The wall is exposed to water (3.4 gallons per square feet per hour) in a test chamber for four hours.
Procedure
The testing apparatus is affixed by interposing a tape of putty
between the flat, circular brim of the pipe and the surface of
the masonry material. To ensure adhesion, manual pressure is exerted
on the cylinder. Water is then added through the upper, open end
of the pipe until the column reaches the 0 gradation mark. The
quantity of water absorbed by the material during a specified
period of time is read directly from the graduated tube. The periods
of time appropriate for the test depend on the porosity of the
material on which the measurement is being made; generally 5,
10, 15, 20, 30 and 60 minute intervals provide the most useful
data. In many cases, it may be important to measure water absorption
through the mortar joint as well as through the surface of the
brick (or natural stone) substrate.
Report
Results of the test measurements are presented in the form of
a water absorption graph with the volume of water absorbed in
cubic centimeters reported as a function of time in minutes. The
masonry surface tested must be mentioned in the report.
Applications
Water has long been associated with deterioration processes affecting
masonry materials. Its presence within the interior pore structure
of masonry can result in physical destruction if the material
undergoes wet/dry or freeze/thaw cycling. The latter is particularly
damaging if the masonry material has a high clay mineral content.
Perhaps of greater importance is the fact that the presence of
moisture is a necessary precondition for most deterioration processes.
Pollutant gases are harmful when they are dissolved in water;
fluorescence phenomena are dependent on the migration of salts
dissolved in water; moisture is a requirement for the growth of
biological organisms. Because of these factors, the water permeability
of a masonry material is related to its durability. Thus, results
obtained using Test Method 11.4 can be used to predict potential
vulnerability of untreated, unweathered masonry materials to water-related
deterioration.
Test Method 11.4 also provides useful information when carried out on weathered masonry surfaces. Water permeability of a material is affected when its surface is obscured by the presence of atmospheric soiling or biological growth, or, when there are hygroscopic salts within the interior. The formation of a weathering crust due to mineralogical changes occurring on the exposed (weathered) surface may substantially affect water permeability measurements. By comparing data obtained on masonry that has been exposed to the elements with measurements made on unweathered samples, it is possible to measure the degree of weathering that has occurred.
Finally, RILEM Test Method 11.4 can be used to evaluate the performance of a water repellent treatment. An effective treatment should substantially reduce surficial permeability of the masonry material to water. By so doing, the treatment will reduce the material's vulnerability to water-related deterioration. A comparison of test results obtained on treated masonry samples with those obtained on untreated samples provides information about the degree of protection that can be provided by the water repellent treatment.
References
-
Amoroso, G. and Fassina, V. Stone Decay and Conservation. Amsterdam: Elsevier Science Publishers, 1983. (See especially Chapter 1, "Effects of Water and Soluble Salts on Stone Decay".)
-
Hochman, Harry. "Measuring Water Permeability of Masonry Walls" (Technical Note N-1 179). National Civil Engineering Laboratory, August 1971.
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Sereda, P.J. and Feidman, R.H. "Wetting and Drying of Porous Materials" (Canadian Building Digest 130). Ottawa: National Research Council of Canada, 1975.
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Sinner, Paulus; Winkler, Erhard; and Ibach, Matthias. "Permeability Measurements, an Indication of the State of Weathering and Consolidation of Building Stone". (Unpublished)
-
Stambolov, T. and van Asperen de Boer, J.R.J. The Deterioration and Conservation of Porous Building Materials and Monuments. Rome: ICCROM, 1976.
-
Torraca, Giorgio. Porous Building Materials. Rome: ICCROM, 1981.
Compiled by Frances Gale, September, 1987.
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Updated: April 1, 2004