Above: Measuring the deflection of a notched concrete prism during a study of the mechanism of crack propagation in reinforced concrete structures. Below: Determining the size and distribution of air voids in a polished, hardened concrete specimen. Air voids have a definite effect on the durability of concrete (page 150).

In other projects the mechanisms by which fires are extinguished were studied, as was the effectiveness of various fire retardants. Improved measuring techniques were sought for heat pumps and air conditioning units, and performance of air-to-air heat pumps was evaluated. With a view to protecting the perishable cargoes in refrigerated trailers, chilled air distribution inside these vehicles was investigated.

Several problems related to the moisture menace in construction were studied. An apparatus was constructed, and a method devised, for measuring water vapor permeance through building materials. The moisture problem in underground pipe insulation was studied, and test methods for moisture barrier materials for use in underground heat distribution systems were worked out. To combat moisture in flat insulated roofs as a threat

to economy and efficiency of air-conditioning and heating, roof specimens were studied and information obtained with which to prepare specifications for self-drying roofs.

Air Void Systems in Hardened Concrete. The quantity and distribution of entrained air in concrete is related to the production of durable concrete, and especially to the concrete's resistance to freezing and thawing and salt scaling. In this connection, knowledge of the amount and size distribution of air voids in the hardened concrete is essential for study of the mechanisms by which damage occurs and of the means to produce the more lasting concretes. To secure the needed knowledge, a linear-traverse apparatus is being developed, to enable polished specimens to be traversed under a microscope to determine the distribution of bubble sizes. Electronic counters and a digital recorder are used in the apparatus. When it is ready, work will commence on an automatic method for obtaining the bubble-size measurements, and this will mean saving in time and in operator fatigue. Creep and Shrinkage of Structural Lightweight Concretes. In recent years expanded shale aggregates have been used extensively in reinforced concrete structures. In order to formulate satisfactory standards and design practices for lightweight aggregate concretes, in structures subjected to high sustained stresses, the Bureau conducted experiments on the creep and shrinkage in expanded shale concretes. This work is supported by the Expanded Shale Clay and Slate Institute. The creep properties are being determined for concretes of different strengths and different stress levelstrength ratios. For purposes of comparison, parallel tests are being made on specimens of normal weight concretes.

Characterization of Cement Compounds by Infrared Spectros

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Infrared absorption spectra were obtained for a number of compounds which occur in portland cement, or are related to compounds formed in the hydration of portland cement. The patterns, in many cases, were found sufficiently distinctive to identify single phases. In addition, infrared was used to distinguish between water of crystallization and hydroxyl groups and to detect hydrogen bonding. Most of the stable combined water in the calcium silicate hydrates was found to be in the form of hydroxyl groups, and all of the calcium silicate hydrates showed some degree of hydrogen bonding.

Crack Propagation and the Fracture of Concrete. Knowledge of the mechanism of propagation of cracks in concrete is necessary for better understanding of the behavior of reinforced concrete structures. Experiments on the properties of concrete beams with crack-simulating notches indicated that the concept of a critical strain energy release rate being a condition for rapid crack propagation and consequent fracture was appli cable to concrete. Estimates of critical strain energy release rates based on the locally elevated stress fields in the vicinity of a crack yielded values for beams with different notch depths which were in close agreement.

Calcium Aluminate Complex Salts. The complex compounds of calcium salts with tricalcium aluminate, important in the hydration, hardening, and durability of cements, were further investigated. A thermochemical study of calcium aluminate monocarbonate was completed, and one on the corresponding monosulfate and tricarbonate compounds is under way. Extinguishment of Fires. Investigations were continued and expanded in regard to the mechanism by which extinguishing agents suppress combustion reactions. Experiments on extinguishment of diffusion flames by halogenated inhibitors gave results which appear to be more readily explained in terms of reactions, or other properties of the intact inhibitor molecules, than in terms of reactions of the halogen fragments obtained from the pyrolytic degradation of the inhibitor. A search of the literature revealed an unexpected correlation between the efficiency of an extinguishing agent and the yield of negative halogen ions produced in the dissociative resonance capture of low-energy electrons by inhibitor molecules. The subject is receiving further study. Flammability of Materials. The radiant panel test for flammability, developed by NBS and recently adopted as an ASTM tentative method, was the subject of cooperative studies to determine its usefulness for evaluating performance of fire retardant and other paint systems. Data obtained indicate the method provides a sensitive way of measuring the relative effectiveness of paints in reducing surface flammability of the base material. Results show that when the paint is applied to a hardboard base, rather than to the commonly used fiberboard base, the test provides a superior method of measuring the paint's fire-retardant effectiveness. The study further indicates that commonly available alkyd or latex base paints, when applied at coverage rates in the range of 250 to 125 ft2/gal, are effective fire retardants.

Heat Pump Studies. Experiments were conducted to improve measuring techniques for heat pumps and air-conditioning units, in which accurate determinations of average wet and dry-bulb temperatures of a stream of moving air are required. An apparatus was built to study the principles and techniques for mixing a nonhomogeneous air stream for precise temperature measurement. This apparatus includes a means for providing a known degree of nonhomogeneity before the air stream enters the mixing device as well as precise measurements of the wet and dry-bulb temperatures after the air stream leaves the mixing device. Performance data on orifices, baffles, screens, and rotating blades are being correlated with fluid mechanics. theory to develop mixing devices that will provide more precise determinations of the "state condition" of an air stream. The suitability of thermometers, thermistors, and thermocouples for measuring dry-bulb temperatures in an air stream for a range of velocities from 300 to 2,000 ft/min was investigated.

Field Studies of Air-to-Air Heat Pumps. Field studies of air-to-air heat pumps were sponsored by the Office of the Chief of Engineers, the

Bureau of Yards and Docks, and the U.S. Air Force. The studies were carried out under summer and winter conditions in three housing projects of the Air Force. The purpose was to obtain data on performance factor, as well as on use of supplementary resistance heat, the contribution made to heating and cooling loads by the miscellaneous uses of energy in the houses, and the relation between computed and measured heating and cooling loads. Similar data on energy use in three other Air Force housing projects employing gas heating equipment and electric air-conditioning units were obtained for comparison.

extinguishment are part of a broad fire research program.

ness of a fire inhibitor is investigated (page 151).

Here the effective

Water Vapor Permeance of Building Materials. The building industry long has recognized that control of moisture and its migration in and through building materials is a major problem. However, present techniques for measurement of the permeance of water as vapor do not give results of sufficient precision. Therefore, there is a critical need for reference standards in this area and for test methods for making measurements consistent with established standards. With a view to this need an apparatus was constructed, and a method, based on an indirect gravimetric procedure, was devised to measure water vapor permeance. The method eliminates many errors and variables inherent in most procedures. The same basic equipment also can be adapted for study of radioactive tracer techniques, reducing the time for a single determination from days to minutes.

Two materials in film form were selected for possible reference samples. They were polyethylene terephtholate for low permeance, and polycarbonate film for higher permeance. Ultimately, it is expected the method and the reference samples can be used for the calibration of techniques and equipment in other laboratories.

Underground Heat Distribution Systems. Investigations of underground pipe insulation systems were essentially completed under the sponsorship of the Office of the Chief of Engineers, the Bureau of Yards and Docks, and the U.S. Air Force. The investigations revealed the necessity for long-term integrity of the moisture barriers used to protect the insulation. Moreover, the provision of air passages around or through the insulation to permit moisture removal by ventilation was demonstrated to be useful as an aid to protection and preservation of insulating materials.

An air-pressure test was recommended, to establish initially the absence of leaks in the moisture barrier of field installations, where free water is likely to be in contact with the heat-distribution system. Desirable physical characteristics and test methods for moisture barrier materials for use in underground heat distribution systems were worked out. A report on the investigation is being prepared for publication.

Moisture in Flat Insulated Roof Constructions. The actual insulating effect of insulated flat-roof constructions may depart greatly from the design values, due to moisture in the insulation. The moisture may be in the insulation when it is installed, or it may get into it later. As a result, the air-conditioning or heating of a building may be impaired, and the operating cost for these services may become excessive.

In an investigation sponsored jointly by the Office of the Chief of Engineers, Bureau of Yards and Docks, and U.S. Air Force over the past 5 years, tests of about 60 roof specimens under conditions simulating natural winter and summer roof exposures with daily solar heating were conducted. The results demonstrated that many common insulated flat-roof constructions are markedly reduced in insulating value by moderate amounts of moisture, and that under service conditions, substantial drying of wet constructions often is impracticably slow. However, some constructions were found to