**4. Mix proportioning, mixing, and curing procedures**

Mix proportioning of concrete mixes containing one or more SCMs targets the optimization of mix packing order to minimize voids and increase strength, and durability without altering mix slump and/or flowing ability. Different proprietary UHPC mixes are available in the construction market. Examples of proprietary mixes are BSI "Beton Special Industrial," developed by Eiffage, Cemtec developed by LCPC, and Ductal developed by Lafarge. Different non-proprietary, ultra-high performance and high-performance mixes are developed through research programs across the globe.

The primary difference between UHPC and HPC mixes is the reduced strength of HPC (UHPC mix compressive strength exceeds 21.7 ksi [12, 13], and contains a higher percentage of SCMs, and incorporates random steel fibers to increase concrete ductility and post-cracking stiffness).

Supplementary cementitious materials and different steel fibers increase the overall density of concrete mixes. Optimized mixing procedures for concrete with high percentages of SCMs are as follows [14]:


Due to the high packing order of granular materials and the possible inclusion of random steel fibers, high-energy paddle mixers are required to produce mixes with sufficient rheology. Examples of high-energy mixers are shown in **Figure 6**.

Concrete mixes with incorporated SCMs can be cured using regular moisture curing techniques. When very high early strength is required (as in precast/ prestressed concrete industry), thermal curing could be applied. Thermal curing should be gradually applied to avoid developing hair cracks within hardened concrete [14].

**Figure 6.** *High-energy paddle mixers—Used for UHPC and HPC mixing.*
