Abstract The standard engineering tests designed to evaluate soundness of aggregate simulate frost action and the response of the aggregate to the frost action. The underlying assumption in the tests is that the freezing of water in aggregate pores causes the breakdown of the aggregate. The aggregates referred to in this particular case are crushed limestone and dolomite used as coarse aggregate in concrete and in bituminous mixes. The soundness refers to the ability of the aggregate to withstand the standard engineering tests without excessive deterioration. There is an established correlation between the "frost" sensitivity or soundness of aggregates and the weathering characteristics of the parent rock in outcrop. As a general rule, the rocks that resist weathering and form resistant ridges, cliffs, and stable road cuts produce aggregate that behaves well in concrete or bituminous mix. Conversely, rocks that present poor natural exposures also behave poorly as construction materials and show excessive deterioration in the standard tests. Since this general rule applies to weathering of rocks under all climatic conditions, as will be shown later, conditions other than frost action would appear to contribute to the breakdown of rocks. The illustrations of field weathering of the so-called frost-sensitive rocks at one extreme and sound rocks at the other are given in Figures 1 through 9. The weathering conditions represented are as follows: 1. Semi-arid climate of southern California. Large temperature changes from freezing to very hot are common. Moisture content is low. Ice formation is minimal. 2. Humid, warm, subtropical

Abstract The sodium sulfate soundness test (ASTM C 88) of crushed stone is one of the principal tests for acceptability of aggregates for use in concrete highway construction in Illinois and in many other places. A study was made to evaluate the properties of carbonate rocks that contribute to failure of the test. Correlations of the physical, chemical, and petrographic properties of 108 coarse aggregate samples with their soundness loss were made by regression anaylsis. Of all properties evaluated, water absorption showed the highest degree of correlation with soundness loss for many types of carbonate rocks. The regression indicates that the percentage of soundness loss increases at a rate of 4 to 5 times the percentage of increase in water absorption for several rock types. Among the rocks the best correlations were found for low-alumina (A1 2 O 3 < 0.9) limestones and for low-alumina dolomites. Stepwise multiple regression analysis indicates that the addition of the dolomite content variable to the regression with absorption significantly increases the correlation of low-alumina limestones. The addition of the specific gravity and hardness (Rockwell, scale K) variables to the regression increases to some extent the correlation for other petrographic classes of carbonate rocks.

Abstract Tests have been performed on cylinders of Texas Granite loaded uniaxially and allowed to creep for several days under constant loads. Loads were increased incrementally after the rock approached stability. At each load increment, lateral creep rate ( ) is initially high and then decreases exponentially with time. At successively higher loads, increases as does the amount of creep necessary for the rock to approach stability. At failure stress, is nearly constant for several days before increasing sharply approximately 2 hr before failure. The axial stress–axial strain curve remains linear to failure. All tests result in violent failure. Curves of stress versus lateral strain show failure initiation (microfracturing) at about 50 of failure stress. Elastic volumetric strain is found not to continue negatively up to the point of failure as suggested by others, but rather it passes through zero and becomes positive at about 60 to 70 of failure stress. Unloading curves show that about 50 of the creep strain at constant load is elastically recoverable. Elastic and nonelastic deformation modes can be explained by a model in which axial microfractures developed during loading produce tiny elastic columns of intact rock that buckle and straighten as the rock is loaded and unloaded.

Abstract For years skidding accidents on streets and highways have been a major cause of property damage, bodily injury, and deaths. Accidents of this sort are caused by a great many things, including the driver's skill and physical condition, the condition of the automobile, and many factors related to the condition of the road surface. It is difficult to correlate the effect of specific road-surface properties with specific accidents. It has been recognized, however, that the aggregate material used in the road surface often plays an appreciable role in the ability of that surface to retain adequate skid resistance. The National Crushed Stone Association (NCSA), beginning with the efforts of A. T. Gold beck in the early 1950s, has been aware of these problems and has been conducting research on aggregates incorporated in mixes of various gradations to determine the role played by the aggregate in this important safety area. Before discussing the aggregate itself, let it be known that the skill with which the engineer proportions the ingredients that go into a road-surface mixture and sees to it that this mixture is properly placed and compacted has perhaps as much effect on the ultimate skid resistance as the properties of the aggregate itself. Faulty mix design or "fat" patches and spots in the surface should be recognized as separate problems unrelated to the type of aggregate in the mix. Nevertheless, it is the engineer's responsibility to see to it that aggregates known to polish under pneumatic-tire traffic at a rapid rate are not used in surface mixtures for heavily traveled roads. His problem is in distinguishing which of these aggregates should be permitted and which should not, particularly if he has had no experience with an aggregate that is being proposed for use. The development of standard laboratory tests to predetermine the polish susceptibility of a given aggregate is one of the main goals of the American Society for Testing and Materials (ASTM) Committees E-17 and D-4, and NCSA is participating actively in both of these committees.

Abstract Poor bond between the mortar and the coarse aggregate is one of the causes of low strength and poor durability of concrete. Some aggregate-paste combinations develop superior bonding that contributes significantly to structural strength. However, there is not yet a systematic presentation of data by which bond strength of paste aggregate interface can be optimized. In order for these data to be developed, there is a need for methods to test the bond strength. A direct tensile test for measuring the bond of rock surfaces to Portland cement paste has been devised using commercially available gripping devices and preparation equipment. The results of a series of tests on selected materials indicate the following order of bonding strength to cement paste: frosted glass, quartz, limestone, neat cement paste, dolomitic marble, augite.

Abstract Geologists who are interested in the processes of rock weathering find greatest excitement in the most intense or greatest amount of weathering, whereas those concerned with the preservation of ancient works of stone art are most pleased with rock that exhibits the greatest resistance to weathering. Preservation of stone may be achieved by determining how rocks weather and then by applying protective measures so as to forestall such action. This paper will review the processes and ways by which rocks are weathered in natural and artificially imposed environments. Recent books on rock weathering include those of Winkler (1973), Carroll (1970), Loughnan (1969), and Ollier (1969); these publications indicate a strong resurgence of interest in the subject following older publications (Keller, 1961, 1966; Reiche, 1945). Additional recent books that devote a significant part to weathering include those by Garrels and Christ (1965), Garrels and Mackenzie (1971), Hunt (1972), Millot (1970), Sweeting (1973), Valeton (1972), and Weaver and Pollard (1973). I will touch on only the most timely, diagnostic, or controversial parts of weathering in this review. Rock weathering may be defined as the response of rocks and minerals to the environment that is generated by the weather and biosphere at and near the Earth's surface, a response in which the component phases characteristically are reduced in size, even to ions released in solution. This definition, as with most geologic definitions, is a compromise; it is too restrictive in some cases, too broad in others, but reduction in size is a good descriptive, nongenetic, common denominator in the role of the weathering process. Rock weathering merges gradually into other geologic processes, such as mineral genesis, diagenesis, and sedimentation.

ABSTRACT The major causes of weathering can be ascribed to two factors: water and temperature. The classical concepts of weathering call upon water (1) to freeze in pores and cracks of rock, and by its volume expansion, cause the rock to break—so-called physical weathering; and (2) to dissolve, hydrate, and leach the rock—chemical weathering. The above concepts explain the end products but do not explain the actual process of weathering in both categories. Weathering of rock under all climatic conditions begins with the interaction of the water molecule and the mineral surface. Water, a highly polar fluid, is attracted to the mineral surface by residual Van der Waal's forces, and forms the extension of that surface. Such water has lower vapor pressure, is unfreezable, and possesses certain "rigidity" and force of "crystallization." The statistical relationship is obtained between the internal surface area of 26 rock specimens and their various physical properties. It is seen that the internal surface area has a significant direct and/or indirect effect on most of the rock properties considered.

Abstract The decay of buildings, stone sculptures, and monuments in the highly industrialized Rhine-Ruhr area of western Germany has been well publicized and documented by photographs taken at known time intervals. Figure 1 shows the weathering of a sculpture above the entry to the parish church at Opherdicke near Unna, Westphalia. The Romanesque relief representing the stoning of St. Stephen was carved about A.D. 1170 and was documented with a photograph taken in 1908. Another photograph taken in 1968 shows considerable damage to the tympanum. The decay rate appears to have accelerated at an almost exponential rate from 1908 until today; the relief has virtually disappeared to beyond recognition. Acids in the atmosphere have dissolved the calcite cement and the calcite of many grains from the Soest Sandstone, which is composed of 64 calcite, 18 glauconite, and only 18 quartz. The heavy assault by air pollution through urbanization and industrialization has caused the acceleration of the weathering rates in urban and industrialized areas. The weathering of stone monuments is caused primarily by mechanical and chemical weathering in varying proportions; that is, the physical and chemical conditions are instrumental in the stone decay, and these conditions differ in rural and urban areas (Table 1).

Abstract For centuries the decay of building and decorative stone has caused concern. As early as 1880, geologists recorded and compared weathering rates of graveyard headstones using the times of the inscriptions for comparison (Geikie, 1880). The poor performance of brownstone, which was widely used in major American cities along the East coast, prompted Julien (1884) to investigate the durability of the building stones in that area. The rapidly decaying stones of the Cologne Cathedral challenged Efes (1974) to study the weathered crust with petrographic and chemical methods. Luckat (1976) correlated the sulfate crusts formed at the surface of the Cologne Cathedral with the sulfate fallout from the atmosphere, which he carefully monitored on many stations of the structure. Photographs, taken at various time intervals and first published by Schmidt-Thomsen in 1969, show the effects of atmospheric attack on sculptures and stone monuments and raise the question whether or not the quantification of weathering processes is possible. Frost, solar radiation, and the presence of salts are recognized to be instrumental in the mechanical destruction of rock and stone. The importance of frost action appears to be secondary. Kieslinger (1930) recognized the subtle volume and pressure changes of entrapped ice working within the capillary system of stone and concrete, also the sudden relief of stress by the change from ice I to ice III, or from ice I to the water phase. The critical pore diameter of stone and concrete for frost action was determined by Larsen and Cady (1969) to be 5µm for concrete; this figure should be a guideline for stone. Winkler (1968) extended the pressure-volume-temperature diagram of ice adding contours of equal density for both ice and water under pressure.

Abstract Many of the over 300 national parks and monuments administered by the National Park Service have historic or cultural properties that must be protected or maintained through stone preservation work. A comprehensive stone preservation program for the widespread National Park System is complicated by a number of factors: the different types of stone involved; their varied use, age, and physical condition; the diversity of climates and environments encountered; and the necessity of preserving the historic, aesthetic, and cultural integrity of each stone structure. Examples from two national monuments illustrate the variety of stone problems that the National Park Service must deal with. One example is the Lincoln Memorial in Washington, D.C., where certain areas of the white Colorado Yule marble exterior are badly decayed after only 50 years exposure to the Washington climate (Figs. 1, 2, 3). Different problems are found at the Chaco Canyon Monument (Fig. 4) in northwestern New Mexico. Here, the 800-yr-old pueblos, built with local sandstone, have developed stone decay problems that range from the disintegration of isolated stones (Fig. 5) to walls being undercut by crumbling rows of stone (Fig. 6).

Abstract The sample for this study consisted of Indiana limestone and several marble varieties. The treatment varied from surface coatings to in-depth impregnation. The chemical tests included exposure to SO 2 -enriched dynamic atmospheres and immersion in carbonic and sulfurous acid solutions. The SO 2 reactions were studied as a function of the formation of calcium sulfite determined by X-ray diffraction. The acid reactions were studied on leached Ca 2+ determined by EDTA titration and atomic absorption. The physical tests included the soundness test based on hydration of Na 2 SO 4 in the pore space of the stone. Chemically, certain epoxies and silicones increased the reaction relative to controls. The epoxies did so by absorption of gases, the silicones by probably acting as semipermeable membranes. The reactivity of immersed specimens was greater than that of specimens in a gaseous environment. The resin films during 20 to 40 hr of reaction, necessary for steady state, were not discolored or damaged. In soundness tests, in-depth impregnations produced far better results than surface treatments. All silicone treatments highly reduced water and water-vapor absorption but did not proportionally increase the soundness. The soundness was improved in fluorocarbon-acrylic copolymers, but here the chemical improvement was at its best. The maximum improvement of soundness was experienced by epoxy-treated specimens. An absolute prediction of the long-range behavior of preservative treatments in a natural environment seems to be difficult. Above tests only indicate the relative merits and permit identification of materials that may actually accelerate the weathering process.

Abstract The outdoor statuary of the city of Venice is being lost at the rate of approximately 5 per year. As in most areas of the industrialized world, this phenomenon stems from accelerated weathering of stone caused by air pollution. In the conservation of these artistic works, it is usually necessary to remove the surface encrustation that forms during the deterioration process; this procedure is required for both aesthetic appearance and physical-chemical stability. Unfortunately, much of the Renaissance statuary of Venice is exceedingly friable and highly soluble, so encrustation divestment has been largely a tedious manual effort. Experiments are described here in which pulsed laser radiation was used to selectively evaporate black encrustations from highly altered Carrara marble statuary. Scanning electron microscopy was employed to determine thresholds for microcracking of the calcium carbonate grains as a function of laser-beam energy. Long-pulse xenon flash-lamp radiation and the air-abrasive technique are found to induce considerably more surface damage than optimum laser cleaning. However, limitations of laser technology suggest that at present it will be impractical to clean marble at a rate greater than a few square metres per day. On the other hand, xenon flash-lamp banks may be readily scaled to rates of tens or hundreds of square metres per day.

Abstract Many historic and modern buildings in Germany are constructed of natural stone. Sandstone, which occurs abundantly in Germany, was most frequently used, but limestone, marble, and volcanic rocks predominate regionally. Since the 19th century, when the idea of preservation of cultural heritage was first proposed and governments established offices for the preservation of monuments, the number of historic objects declared as monuments has become so great that it is almost impossible to maintain that many castles, monasteries, churches, and other historic buildings. One of the most difficult maintenance problems is the preservation of building stones. All methods for stone conservation have proved to be effective for only a short time—usually less than 20 years. For this reason, in 1967 I was put in charge of the development of restoration programs to guarantee application of the most effective method of preservation. A series of tests was developed considering all destructive forces that contribute to the decay of stone, to enable us to choose the best techniques for counteracting destructive forces.

ABSTRACT Borobudur, which is a place of Buddhist pilgrimage, is situated in central Java about 45 km from Yogyakarta. Built at the beginning of the ninth century, it is a step pyramid that faces the top of a hill. Each side of its square base is 123 m long. Four rectangular galleries are topped by three circular terraces, adorned with 72 latticed-stone stupas, each containing a statue of Buddha. At the peak is the central stupa that symbolizes Nirvana; it is 31.5 m high with a diameter of 9.9 m, and its pinnacle is 7 m high. The central stupa entirely encloses a large cell that is empty inside. Borobudur is both a cosmic mountain and a shrine and has the form of a mandala. It is divided into three parts: The hidden foot is illustrated with reliefs that represent the Khamadhatu, the sphere of desire. The four rectangular galleries represent the Rupadhatu or sphere of form. The open galleries, each enclosed by a balustrade, are covered by reliefs over a surface of 3 km 2 (Figs. 1 and 2). The circular terraces around the central stupa make up the Arupadhatu, the sphere of formlessness. There is no decoration around this area. It was only in 1814, under the British administration, that the shrine at Borobudur became known to Westerners. It was partially covered then. Drawings and daguerrotypes were made. In 1882 it was proposed in some reports to remove the reliefs from Borobudur and set them up in a special museum. This proposition was never followed through. Major restoration was carried out by a Dutch engineer, Van Erp, who started work in 1908 and finished it in 1911. During this time, crumbling stupas were rebuilt, pavements were laid, and carvings were cleaned. But this restoration was not sufficient. The Indonesian Government became anxious about the structure of the monument and sought international help for its conservation. P. Coremans went to Borobudur, and as a consequence of his mission, one Indonesian went to Brussels for special training. He is now the chief of the Chemico-Archaeological Department.

Abstract Most objects of art and architecture are dirty due to weathering and accumulations of particulates and combustion residues of fossil fuels. The efflorescences disfigure stone surfaces as well as damage the stone on hydration. The biological growths such as algae, bacteria, mosses, and lichens form unsightly encrustations and contribute toward the decay of stone. The deterioration of metallic enforcements produces damaging salts and seriously blemishes the stone surfaces. The methods of cleaning are chemical, mechanical, physical, and the combinations thereof. The materials commonly used for chemical cleaning are the hydrofluoric acid and ammonium biflouride. These materials are generally used for cleaning granite, noncalcareous sandstone, and unglazed masonry (Clarke, 1972; Stombalov, 1972). These compounds react with the silicate minerals and clean surfaces by removal of some of the masonry material. HF, when used for cleaning calcareous materials, produces a CaF 2 coating that is deemed to be protective by some (Stombalov and Van Asperen de Boer, 1972); Lewin ( in Clarke, (1972) indicated that the CaF 2 layer is highly fractured and, in fact, promotes decay by accumulating chemically active agents. Ammonium biflouride is used mostly in the form of paste in such materials as asbestos and bentonite. These and other absorbent powders (Stombalov and Van Asperen de Boer, 1972) such as starch, chalk, and talc are also commonly used. The paste is slow to clean, but it reduces penetration of active agents into stone pore space. Whereas HF etches surfaces, NH 4 HF 2 is reported to form efflorescences.