in slender CAUs is generally less than the strength determined from these 

 ideal tests. 



70. Kendall and Melby (1990) give a modulus of rupture or pure bending 

 tensile strength of f' r = 984 psi for the Crescent City dolosse. The 

 splitting tensile strength can be estimated as f' t = 0.73 f' r = 718 psi. This 

 value can be thought of as a conservative design strength for the Crescent 

 City case. 



71. High-strength concrete is generally with reference to the com- 

 pressive strength, which might be on the order of 10,000 psi. Because CAUs 

 are generally unreinforced, the CAU designer is interested in the tensile 

 strength. While the American Concrete Institute gives the design relationship 

 for the modulus of rupture of normal weight concrete as £' r = 7 .5j~ f' c (ACI- 

 9.5.2.3), where f' c is the compressive strength in psi, this relationship is 

 not necessarily conservative for high-strength concrete. Saucier (1984) has 

 shown that the ratio between tensile and compressive strengths for high- 

 strength concrete can be maintained. With the use of quality materials, low 

 water-cement ratios, high-range water -reducing admixtures, and very fine 

 silicon-dioxide powder, or silica fume, compressive strengths as high as 

 15,000 psi with corresponding moduli of rupture as high as 1,200 psi can be 

 achieved with little loss in workability. Therefore, high-strength concrete 

 may be a viable alternative for some designs. 



72. High-unit-weight concrete may be a design alternative but very 

 little research has been done in this area. High-unit-weight aggregate could 

 be added to the concrete to achieve more hydraulically stable armor units. 

 From the Hudson equation it can be seen that the armor unit stable weight is 

 inversely proportional to the density cubed. Increasing the concrete density 

 is therefore highly advantageous. As an example, for the Crescent City 

 dolosse, increasing the unit weight from 150 pcf to 160 pcf provides a 23- 

 percent decrease in the dolos design volume. The design stress decreases by 

 4 percent for this 6. 7 -percent increase in unit weight. 



73. The effect of temperature differentials in curing concrete dolosse 

 was investigated by Norman and Alexander (1985). Their conclusion was that, 

 for Crescent City dolosse of waist ratio 0.32, there is little effect on 

 strains from construction-related temperature differentials within the 

 dolosse. For higher waist ratio dolosse, this topic may require further 

 study . 



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