1114
4540.027
Landgren, R; J.A. Hanson; D.W. Pfeifer
Bulletin 183
Article
Portland Cement Association
1965
47-65
Y
This study was initiated to investigate difficulties encountered in lightweight concrete mix control when the moisture contents of the aggregate stockpiles vary considerably.The mix proportioning procedures of the existing ACI Standard 613A-59 were used as a basis for comparison in the investigation. This procedure utilizes the concept of the “specific gravity factor” as the aggregate weight-to- volume ratio. The specific gravity factor is found by trial mix procedure. Theoretical analysis indicates that this factor can be more precisely determined directly, by simple pycnometer procedures using the aggregate alone. The values of the specific gravity factors as obtained with the pycnometer are almost linearly related to the aggregate moisture content (absorbed plus free water) in the range of moisture contents investigated. Further theoretical studies indicate that the water added at the mixer (to maintain a constant slump regardless of aggregate moisture) may be predicted by consideration of the pycnometer specif c gravity factor and the water requirement of control mixes.
These theoretical considerations were confirmed by pycnometer tests and trial mixes containing a number of different lightweight aggregates in which the moisture contents of the fine and coarse fractions varied. The trial mixes produced satisfactorily constant levels of workability, yield, compressive strength, and unit weights of the concrete despite wide variations of aggregate moisture content.
It appears that a better determination of the relative volumes of the fine and coarse aggregates has been achieved, and thus closer control may be obtained when moisture contents vary. The suggested procedures seem adaptable to simple and direct proportioning of lightweight concrete under field construction conditions.