Title: Some Factors Influencing the Strength of Concrete Containing Admixtures Powdered Aluminum
Author(s): Carl A. Menzel 000
Publication: Journal Proceedings
Appears on pages(s): 165-184
Discusses the effects of small additions of aluminum powder on the strength of several types of concrete and concrete specimens. These effects result primarily from the generation of minute bubbles of hydrogen gas within the paste. This gas tends to expand the volume of the paste and increase the pressure within the mass which may be partially restrained by the confining parts of the mold. This tendency to expand the volume of the paste improves the intimacy of con- tact with adjacent aggregate particles and with em- bedded steel reinforcing bars. Under ordinary condi- tions the compressive strength of plastic concrete is sharply reduced with increase in porosity of the paste that occurs with unrestrained expansion. Under spe- cial conditions, particularly where the expansion restrained, the strength may be increased by the ad- mixture of aluminum powder. In a special case of grouted gravel concrete, marked increases in com-pressive strength were obtained when the expansion of the grout was restrained by the interlocked pieces of gravel and the homogeneity of the mass for this type of concrete was greatly improved. With lean mixes, or with mixes deficient in fine aggregate par- ticles, slight improvements in strength were obtained with 6 x l2-in cylinder specimens but these were small compared to the strengths obtainable with properly designed workable mixes of the same cement content but without aluminum powder.