Materials selection for concrete overlays : the final report Page: 77
xviii, 192 p. : col. ill. ; 28 cm.View a full description of this report.
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7 days (psi) 28 days (psi)
Mixture
No. Average Average
7 909 867
8 511 776
9 691 938
10 687 845
11 675 820
12 805 836
13 542 801
14 692 809
15 736 850
16 715 817
17 740 871Based on the statistical analysis, it was determined that the 7-day flexural strength was
most affected by the following variables: SCM content and sacks of cement. The 7-day flexural
strength could be accurately modeled by the following regression model:
7 day flexural strength= 692- 130 SCM content + 28 sacks of cement, and R2
= 89%. (4-5)
Thus, the 7-day flexural strength is mainly controlled by first-order effects and a unit
change in the SCM content have about four times the influence than a unit change in the sacks of
cement.
With regards to the 28-day flexural strength, the value for Mixture 9 appeared to be an
outlier. Thus this value was ignored in the analysis. The following variables were found to be
most significant: SCM content, sacks of cement, and SCM content*SCM content. This yielded
the following regression model (in coded units):28-day flexural strength
(SCM content)2, and R2835 - 37 SCM content + 45 sacks of cement - 40
86%. (4-6)Thus the 28-day flexural strength is more sensitive to changes in the SCM content than
the 7-day flexural strength. The fine aggregate content was not found to be a significant variable
(but in general increasing the fine aggregate ratio slightly decreased the flexural strength).
With a constant mixture design, flexural strength change due to fiber addition was also
explored. Fiber addition slightly improved 7-day (or early age) strength in some specimens.
However, fiber addition slightly decreased 28-day strength in all specimens. The results are
provided in Figure 4.17.77
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Kim, Dong H.; Fowler, David W.; Ferron, Raissa P.; Trevino, Manuel M. & Whitney, David P. Materials selection for concrete overlays : the final report, report, July 2012; Austin, Texas. (https://texashistory.unt.edu/ark:/67531/metapth303706/m1/97/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.