vane. This effect in soil tests has previously been noted by Wilson [16d]. No cracks were noted at the higher shear strengths and the pastes and mortars appeared attached to both sides of each vane. Regardless of the interpretation and/or significance of the three phases of hardening of neat cement pastes and mortars observed in these exploratory tests, it appears that the vane shear apparatus offers an excellent means for studying this phenomenon. It also appears that the apparatus would offer a means for studying the effects of different admixtures on cements. The apparatus may also be used to determine the consistency of cement pastes and mortars, obtaining the values in terms of g/cm2 instead of percent flow on a flow table or penetration of a cylinder or needle of specified weight and diameter. As indicated earlier, many papers [14-18] have been published on the use of the vane-shear apparatus for measuring the shear strength of soils. Among the variables that have been studied and reviewed by Brand [18] are the vane geometry (height to diameter ratio) and the number of blades, the effect of the rate of strain, the mode of failure, the effect of inhomogeneity, anisotropy, and effect of soil disturbance. The last three items would possibly not affect the tests on neat pastes or mortars as conducted in the present studies. More work is necessary and certain refinements in both apparatus and techniques appear desirable. In correlating these values for rate of hardening with existing time of set tests it would be desirable to have an apparatus rugged enough to measure a shear strength of 20,000 to 30,000 g/cm2 (about that corresponding to final set as determined by the Gillmore apparatus) after which compressive strength measurements could be made to follow further strength development. It would have been possible to increase the range of the instrument used by using smaller vanes and a shallower depth of paste or mortar. It appeared desirable to use only the one size vane (1 cm diameter) in each series of tests, changing the springs as necessary to make the measurements of the more mature pastes. With the neat cement pastes, there was the problem of relatively large occluded air bubbles making some of the measurements of questionable value when the air bubbles were in the shear plane. The use of larger vanes would give a better ratio of diameter of vane to diameter of bubbles of occluded air, but more air bubbles would be present in the shear plane and it would not be possible with the apparatus used to follow the strength development past the time of initial set. Another problem with the small vanes was their tendency to tilt as the mortar or paste was vibrated into place. This could possibly be remedied by using some type of jig for holding them in place until after the mortar or paste had been vibrated in place around the vanes. For measurements of consistency of freshly mixed pastes or mortars, the larger vanes (2 or 3 cm) appear desirable because they do not tilt as readily as the 1 cm vanes. In preliminary tests using a 2.5 x 2.5 x 28 cm mold, the specimen cracked lengthwise instead of shearing out a cylinder. This occurred only at the higher shearing values but prompted the use of briquette molds with more rigid sides in later tests. This also helped to isolate the vanes to a greater extent. In calculations of shear resistance the effect at the end of the vane was ignored. This may or may not have had an effect. Brand [18] indicated that with a vane of height twice the diameter the end effect would account for only 3 to 4 percent of the shear value. With a 212 to 1 ratio for height to diameter, the end effect should be less. Although polytetrafluoroethylene was used as a base, there was some bond between the cement paste and the plastic at the later ages. The effect of method of placement and amount of vibration used in forming the paste and mortar specimens and setting of the vanes requires further study. Some preliminary tests with lighter gage brass vanes indicated that they were deformed at high shear values. During the past 20 years, much research has been conducted relating the shear of soils as measured by the vane-shear apparatus and shear tests conducted by other means. There have also been published discussions of the nature of the shear, the stresses involved, the effect of pore-water pressure or dilatency at the edge of the vane, and how the linear stresses are translated to a circular stress to shear out a cylinder. Very little appears to be known with respect to the distribution of the stresses on the boundary between soil and the testing device. The authors are not aware of any photoelastic studies of the stresses generated by a turning vane of the type used. Although the apparatus appears very simple, there are, as indicated by a review of many articles on soil mechanics, still many unknown factors which need further study and clarification. Although a four-bladed vane was used in these tests on pastes and mortars, a shear-vane having the configuration of a spline shaft may possibly be better for use in concrete in order to avoid having large aggregates in the shear plane. The edges away from the lead edges of the splines would have to be cut back or beveled to avoid friction with the mortar. 7. Summary and Conclusions The results of exploratory studies indicated that a modified vane shear apparatus offers a means for determining the early strength development in portland cement pastes and mortars. The shear tests indicated what appear to be three distinct phases in the setting and early hardening process as postulated earlier by various authors as cited. Three phases were evident in each of the six cements tested and in both neat cement pastes and in cement-sand mortars. The rate of increase of shear resistance with time as well as the duration of the different phases differed with the different cements. 8. References [1] Bogue, R. H., The Chemistry of Portland Cement, 2nd edition, p 647-690 (Reinhold Publishing Corp., New York, 1955). [2] Lea, F. M., and Desch, C. H., The Chemistry of Cement and Concrete, (Revised edition), p 215-260. (St. Martin's Press Inc., New York, 1956). [3] Greene, Kenneth T., Early hydration reactions of portland cement, Proceedings of the Fourth International Symposium on the Chemistry of Cements, Nat. Bur. Stand. (U.S.), Monogr. 43, Vol. 1, p 359, Aug. 1962. [4] Schwiete, H. E., Ludwig, U., and Jäger, P. Investigations in the system 3 CaO Al2O3 CaSO, CaO H2O, Symposium on Structure of Portland Cement Paste and Concrete, Highway Research Board, NRC SP 90 p 353, 1966. [5] Budnikov, P. P., Strelkov, M. I., Some recent concepts on portland cement hydration and hardening, Symposium on Structure of Portland Cement Paste and Concrete, Highway Research Board, NRC, SP 90 p 447, 1966. [6] Kondo, R., and Ueda, S., Kinetics and mechanisms of the hydration of cements, Proceedings of the Fifth International Symposium on the Chemistry of Cement, Vol. II, p 203, Tokyo, 1968. See also Discussion by Stein, H. N., Proceedings of the Fifth International Symposium on the Chemistry of Cement, Vol. II, p 248, Tokyo, 1968. [7] Ish-Shalom, Moshe, and Greenberg, S. A., The rheology of fresh portland cement pastes. Proceedings of the Fourth International Symposium on the Chemistry of Cements, Nat. Bur. Stand. (U.S.), Monogr. 43 Vol 2, p 731, Sept. 1962. [8] Hershel, W. H., and Pissapia, E. A., Factors of workability of portland cement concrete, Proc. A.C.I. Vol. 32, p 631-658 (1936). [9] Tuthill, L. H., and Cordon, W. A., Properties and uses of initially retarded concrete, A.C.I., Proc. Vol. 52, p 273, Nov. 1955, and Discussion, A.C.I., Proc. Vol. 52, p 1187, Dec. 1956. [10] Kelly, T. M. and Bryant, D. E., Measuring the rate of hardening of concrete by bond pullout pins, Proc. ASTM, Vol. 57, p 1029, 1957. [11] Whitehurst, E. A., Use of the soniscope for measuring setting time of concrete, Proc. ASTM Vol. 51, p 1166 and p 1176, 1951. [12] Kelly, T. M., Setting Time. Significance of tests and properties of concrete and concrete-making materials, ASTM STP 169A, p 102, 1966. [13] Steinour, Harold, H., The Setting of Portland Cement, A Review of Theory, Performance and Control, Bulletin 98, Research and Development Laboratories of the Portland Cement Association, Research Department, Nov. 1958. [14] ASTM Symposium on Vane Shear Testing of Soils, ASTM STP 193 (1957). (a) Osterberg, J. O., Introduction, p. 1. (b) Gibbs, H. J. An apparatus and method of vane shear testing of soils, p 9. (c) Fenske, C. W., Deep vane tests in Gulf of Mexico, p. 16. (d) Hill, W. C., Vane in-place shear device developed (e) Eden, W. J., and Hamilton, J. J., The use of a field [15] ASTM Symposium on Soil Exploration, ASTM STP No. 351 (1963). (a) Liu, T. K., and Thornburn, T. H., Investigation of surficial soils by field vane test, p 44. (b) Hall, E. B., Shear-strength of soft clayey soil by field and laboratory methods, p 53. [16] ASTM Symposium on Laboratory Shear Testing of Soils, ASTM, STP 361 (1965). (a) Roscoe, K. H., Schofield, A. N., and Thurairjah, A An evaluation of test data for selecting a yie criterion for soils, p 111. (b) Rowe, P. W., Stress Dilatancy Performance of Clays p 135. (c) Schmertmann, J. H., Generalizing and measuring the Hvorsley effective components of shear resistance p 147. (d) Wilson, N. E., Laboratory vane shear tests and the influence of pore-water stresses, p 377. [17] ASTM Symposium on Vane Shear and Cone Penetration Resistance Testing of In-Situ Soils, ASTM STP 399 (1965). (a) Andresen, A., and Sollie, S., An inspection vane p 3. (b) Eden, W. J., An evaluation of the field vane test in sensitive clay, p 8. (c) Miller, E. A., and Hall, E. B., A comparison of soil shear strengths as determined with field and labora tory vane shear apparatus, p 18. (d) Sibley, E. A., and Yamane, G., A simple shear test for saturated cohesive soils, p 39. [18] Brand, E. W., The Vane Shear Test and its use for Strength Measurements of Cohesive Soils, Bulletin, The International Union of Testing and Research Laboratories for Materials and Structures (RILEM) Bulletin 36 Sept. 1967. [19] Segalova, E. E., and Solovyeva, E. S., Study of the mechansm of structure formation in cement suspensions and effect of admixtures of hydrophilic plasticizers on these processes, Reports of Symposium on the Chemistry of Cements. State Publication of Literature on Structural Materials, Moscow (1956). Translated from Russian by Margaret Corbin, Portland Cement Association, Skokie, Ill. [20] Rehbinder, P. A., Physico-chemical concepts of the mechanism of setting and hardening of mineral binders Reports of Symposium on the Chemistry of Cement, State Publication of Literature on Structural Materials, Moscow (1956). Translated from Russian by Margaret Corbin, Portland Cement Association, Skokie, Ill. [21] Sivertsev, G. N., Some experimental preliminaries for the formation of a general theory of cement hardening based on colloid chemistry, Reports on the Chemistry of Ce ments, State Publication of Literature on Structural Materials, Moscow, (1956) Translated from Russian by Margaret Corbin, Portland Cement Association, Skokie, Ill. [22] Budnikov, P. P., and Strelkov, M. I., Some recent concepts on portland cement hydration and hardening. Symposium on Structure of Portland Cement Paste and Concrete. SP 90, Highway Research Board, Wash., D.C (1966). [23] Schwiete, H. E., Ludwig, U., and Jäger, P., Investigations in the systems 3 CaO Al:O1•CaSo1•CaO⚫H2O, Symposium on Structure of Portland Cement Paste and Concrete. SP 90, Highway Research Board, NRC, Wash., D.C. (1966). Appendix A Modifications of the shear apparatus linkage are indicated in figure 2a. Part "A" of figure 2a is attached to the spring portion of the apparatus by means of a set screw. Part "B" is hooked over part "A" and acts as a universal joint when torque is applied. Actually the contact is on the sides of the hook when the spring portion and part "A" are lowered onto the load transfer device "C". The upper section of part "C" is square in cross section and somewhat larger in the midsection than at the top or bottom and fits rather loosely in order to act as a universal joint with the tom hollow portion of part "B". The bottom of t "C" has notches at right angles to fit over and age the vanes, part "D", and transfers the torque the vanes. Some details of the 2 cm vane are icated in part "E". The worm-gear for loading the spring in the apatus used had a 30 to 1 ratio. The gear was turned the rate of 1 revolution per second. With different ength springs, the rate of loading would then be ferent and no account was taken of this in comcations of shear resistance. In making a shear test, the load transfer device "C" s placed on the vane "D" which was previously bedded in cement paste or mortar. The mold with ortar and vane were aligned under part "B" and spring (with screw loading device and indicator) gether with parts "A" and "B" were lowered onto e parts "C" and "D" until part "B" lost contact th part "A" on the horizontal part of the hook. rque was then applied, noting the maximum number of degrees that the spring was rotated before shear failure occurred. Appendix B, Calibration An inverted Tee with arms each approximately 12 cm long as indicated in figure 2b was attached to the shear apparatus in place of the vane. The cord was attached to the inverted Tee at 10 cm from the center. The cord was horizontal from the Tee to the pulley and at right angles to the Tee. The balance cradle and vertical portion of the cord from the pulley to the cradle were weighed and additional weights added, noting the combined weights and the number of degrees of spring rotation necessary to raise the balance pan off its support. The results of spring rotation with the different weights were plotted for each of the springs and the values for grams force at 1 cm radius per degree rotation calculated for use in expressing experimental shear values. U. S. GOVERNMENT PRINTING OFFICE: 1970 O 389-783 |