A new approach is developed for predicting strain-controlled, low cycle fatigue life at elevated temperature using a proposed energy measure of fatigue damage. This measure of damage, defined as the net tensile hysteretic energy of the fatigue cycle, can be approximated by the damage function σTΔεp, where σT is the maximum stress in the cycle and Δεp is the inelastic strain range. The damage function is applied to predicting effects of hold time and frequency, when time-dependent damage occurs, through failure relations incorporating a variation of Coffin's frequency modified approach. Failure equations are developed for two postulated categories of time-dependent damage.
The paper reports on the performance of 34 different concrete mixes containing glass crushed to ¾-in. (19-mm) maximum size as coarse aggregate and six reference mixes made with gravel of the same size. Two cements of alkali equivalent 0.58 and 1.13, classifiable as low and high alkali (ASTM C 150-72), in amounts ranging from 400–900 lb/yd3 (237–534 kg/m3 were used in combination with glass both with the fines removed and in the as-crushed condition. Partial cement replacement with fly ash and mixing of glass with gravel aggregate were included in an attempt to find a suitable method of overcoming the expected adverse effects of the reaction between glass and cement alkalis. On the basis of compressive strength, flexural strength, expansion, and visible surface deterioration recorded up to an age of one year, the results show that in many cases the direct combination of glass with portland cement yields concrete which exhibits marked strength regression and excessive expansion due to alkali-aggregate reaction. The conditions under which performance is satisfactory appear to relate to limiting maximum values of cement content and alkali equivalent. Replacement of 25 to 30 percent by weight of the cement, whether low or high alkali, appears to be an effective and widely applicable method of ensuring good long-term concrete performance, although the minimum required in any given case may be related to cement composition.
Empirical equations are developed for evaluating the guard-gap correction for guarded electrodes, taking into account the ratio of gap width to electrode spacing, the ratio of the electrode thickness to the gap width, and the permittivities of the material in the gap and between the electrodes. Exact equations are then developed for calculating specimen permittivity, thickness, and dissipation factor from two-fluid measurements, for the first time taking into account the change in effective area when the specimen is inserted between the electrodes, the dissipation factor of the specimen, and that of the liquid. Series resistance and inductance and change in spacing of the electrodes between the first and second set of readings are also taken into account. The accuracy of the equations is estimated to be such that they will not significantly affect the accuracy of two-fluid measurements. Sample calculations are included.
The hydration of tricalcium silicate (C3S) in the presence of various salts has been investigated by means of conduction calorimetry. The salts used have been classified into four groups on the basis of their reactions with C3S. The temperature dependence of hydration has been examined for C3S by itself and in the presence of four salts. The apparent activation energy varies with extent of hydration, decreasing initially to a nearly constant value, and falling off again as diffusion control sets in.
The paper describes a basic analytical method for calculating the surface area of fine aggregate particles (sands and fillers). Equations were derived for direct determination of the specific surface using data of actual size distribution, fineness, and shape properties of the particles. Practical calculation examples are given and compared with other conventional methods and with experimental determination of the surface area. In general, the method is flexible and affords a desirable degree of accuracy according to a proper partitioning of the size range into fractions. Results of the calculated surface areas were very close to values obtained experimentally. This indicates the advantages of the suggested method over some other useful methods for surface area calculations. The suggested method is basic and general and can be applied to any technology where the surface area of fine particles is an important factor.
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