ACI 211.6T-14 AGGREGATE SUSPENSION MIXTURE PROPORTIONING MIETHOD.
Step 1: Select the maximum size of aggregate Select the largest maximum size of aggregate that is practical for the application. As required by ACI 318, the nominal maximum size of aggregate should not exceed: a) One-ffth of the narrowest dimension between sides of forms; b) One-third the depth of slabs; or c) Three-fourths of the minimum clear spacing between individual reinforcing bars, bundles of bars, or preten- sioning strands. Increased maximum size of aggregate typically results in increased packing density of the combined aggre- gate, reduced concrete plastic viscosity, increased concrete slump and slump fow, increased segregation poten- tial, and reduced passing ability. Step 2: Select combined aggregates Select the relative amounts of fne, intermediate, and coarse aggregates based on grading, shape, angularity, and texture. The selection of aggregates should balance each of these factors. For example, adding a poorly shaped aggregate to improve grading could have an overall negative effect on concrete. In most cases, the combination of aggregates resulting in maximum packing density is not optimal for workability. Instead, a slightly fner grading is typically preferred. If the combined aggregates contain less than 5 percent passing the No. 200 (75 μm) sieve, this fne material can be considered negligible to the volume of paste and accounted for as part of the combined aggregate. Other- wise, include all aggregate material passing the No. 200 (75 μm) sieve as part of the powder. Grading—There is no universally optimal grading for concrete, or even a particular type of concrete, such as self-consolidating concrete (SCC). The best grading for a mixture depends on the application and the aggregate. As a starting point, select a blend of fne and coarse aggregate best matching the 0.45 power curve or fner and without an excess or defciency of material on two consecutive sieves.
Step 7: Select w/p and admixture doses for workability Adjust both the w/p and admixture doses to achieve the desired workability. Use data from trial batches or past experience to select the w/p. If the powder content consists of only cement and supplementary cementi- tious materials, the w/p is equal to the w/cm. One common practice is to adjust the w/p to achieve a certain slump without mid- or high-range water-reducing admixture (HRWRA), which is sometimes referred to as a water slump, then adjust the dose of mid-range water- reducing admixture or HRWRA to the target slump. Alternatively, use a fxed dose of admixture and adjust the w/p, or vary both the w/p and admixture doses simultaneously. When making these adjustments, consider the rheology of the concrete; decreasing the w/p from an accept- able value for a given application may result in concrete with high viscosity that is described as sticky or cohe- sive, whereas increasing the w/p may be prone to segregation and bleeding.ACI 211.6T pdf download.