**Table 5.**

*Average mechanical properties of proprietary UHPC mixes [21].*

**Figure 7.** *Different girder sizes providing similar flexure capacity [29].*

#### **4.2 SCMs in HPC mixes**

HPC mixes incorporates different SCMs with variable ratios according to the mix design purpose. Silica fume is used to increase the binder content and improve mix mechanical properties, whereas fly ash is primarily used to increase flowing ability. HPC mixes are produced using similar batching, mixing, and curing procedures as compared to UHPC. Steel fibers are eliminated due to their high cost, while chemicals for increased flowing ability are used to maintain high flowing ability using a low water-to-powder ratio. Different HPC mixes are shown in **Table 6**.

The aforementioned non-proprietary mixes had an average 24-h compressive strength of 80 MPa, and a final 28-day compressive strength of 110 MPa. Detailed compressive strength testing results are shown in **Figure 8**.

Current codes and standard specifications provide equations to estimate concrete mechanical properties as a function of its compressive strength. The American Concrete Institute (ACI) 318 calculates the modulus of elasticity of concrete (MOE) according to the following equation:

$$E\_c = 0.043 \, w\_c^{1.5} \sqrt{f\_c'} \qquad \text{(MPa)} \tag{3}$$


#### **Table 6.**

*Non-proprietary HPC mixes using local materials in the US market.*

*Application of Supplementary Cementitious Materials in Precast Concrete Industry DOI: http://dx.doi.org/10.5772/intechopen.100249*

**Figure 8.**

*Compressive strength test results for non-proprietary HPC mixes.*

Similarly, ACI 318 and AASHTO LRFD specifications use the following equation to estimate the modulus of rupture (MOR) of concrete as

$$f\_r = \mathbf{0.62} \sqrt{f\_c'} \qquad (\text{MPa}) \tag{4}$$

Eqs. (1) and (2) show that the MOE and MOR of concrete, denoted as *Ec* and *fr* respectively, and are correlated with the concrete compressive strength, denoted as *f* 0 *<sup>c</sup>*. Thus, the increase in concrete strength associated with the use of SCMs in mix development results in a significant increase in concrete MOE and MOR.
