Title:
Effect of Coarse Aggregate Characteristics on Lateral Pressure Exerted by Self-Consolidating Concrete
Author(s):
Joseph Assaad and Kamal H. Khayat
Publication:
Materials Journal
Volume:
102
Issue:
3
Appears on pages(s):
145-153
Keywords:
aggregate; column; plastic; rheology
DOI:
10.14359/14441
Date:
5/1/2005
Abstract:
An experimental program was carried out to determine the influence of concentration and nominal size of coarse aggregate on the development of lateral and pore water pressures of self-consolidating concrete (SCC). Nine mixtures prepared with sand-total aggregate ratios (S/A) varying between 1.0 and 0.30 were evaluated. The mixture made with an S/A value of 0.50 was repeated three times with different coarse aggregate gradations of 10-5, 14-5, and 20-5 mm. An experimental column measuring 2800 mm in height and 200 mm in diameter was used to determine lateral pressure and pore water pressure during the plastic stage of cement hydration. Rheological characteristics were assessed to determine the relationship between internal friction and lateral pressure development. Test results show that lateral pressure is significantly influenced by the S/A value. Right after casting, mixtures with S/A values of 1.0 and 0.75 developed initial lateral pressures of 99 and 96% of those corresponding to the hydrostatic pressure, respectively. With the increase in coarse aggregate concentration (S/A of 0.50 to 0.30), the initial relative lateral pressure decreased from 92 to 77%, respectively, and the rate of drop in pressure was more pronounced. This can be related to the increased coarse aggregate volume that reduces the mobility of the mixture and results in less lateral pressure. Irrespective of the S/A value, the measured lateral pressure was found to correspond to the pore water pressure during the plastic stage. The increase in nominal aggregate size from 10 to 14 mm reduced the initial relative lateral pressure from 92 to 85% and increased the rate of pressure drop with time. Further increase in nominal aggregate size to 20 mm led to almost similar pressure as that of the SCC with 14 mm nominal aggregate size. The lateral pressure developed by the plastic concrete is found to be directly related to internal friction resulting from the coarse aggregate concentration. The greater the degree of increase in internal friction, which corresponds to mixtures made with relatively low S/A values, the lesser the magnitude of initial lateral pressure becomes and the faster the drop in pressure.