This survey was conducted in large part to determine the specifics of the labor shortages not whether or not they were occurring especially which crafts
This survey was conducted in large part to determine the specifics of the labor shortages Û not whether or not they were occurring Û especially which crafts are being affected in which parts of the country, said TAUC CEO Steve Lindauer.
From Precast/Prestressed Concrete Institute and High Concrete Group’s Mark Adams÷
Addressing the question Self-consolidating Concrete: Use it or lose it? representatives from two PCI member producers conclude that a single answer is insufficient. A discussion of their companies’ experiences adopting self-consolidating concrete (SCC) allowed the producers to clarify how one determines whether to pursue SCC, in what likely will be higher-cost mixture proportions, for a given project or product line.
Jeffrey Everett of The Shockey Precast Group and High Concrete Group’s Paul Ramsburg traced their respective companies’ pathways to standard SCC production, sharing basic considerations, questions to ask, challenges to overcome, and final results after implementation. Their primary points can be summarized in five steps.
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First things first Û At the outset, producers must consider their motivation for adopting SCC, i.e., Is the decision driven by product novelty and others’ use of it, or does SCC offer a means to advance business objectives and address customer needs? Determine what results are desired. In the cases of both Shockey and High Concrete, producers wanted to improve casting efficiency, reduce cycle times, ensure product quality, and reduce overall costs.
Comparing the new with the old requires a system of measurement that allows tracking the changes. Whether noting square feet per hour, hours per piece, or any other relevant production parameter, benchmarks will be needed for evaluation. Both companies had established productivity and quality data, so at trial time, comparing new results with existing operations was a straightforward process.
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Create new SCC mixture proportions Û The optimum SCC mix for an application is largely specific to a given plant, location, aggregate options, and admixture supplier. A prime consideration is mix rheology, providing as much self-consolidation as possible to minimize external vibration requirements, while resisting segregation. Freedom from bug holes is of little use if the coarse aggregate falls out of suspension. Variation inevitably will occur in local sand options, aggregate density and gradations, cementitious powder selections, and their respective proportions, along with admixture dosage rates. Both companies developed their mixtures internally until they had predictable, user-friendly designs.
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Determine where risk may be involved with SCC use Û Questions may arise regarding strand bond or particular issues in the case of a customer-specific project. Running tests in conjunction with current production minimizes research and development costs. Also to be gained are valuable experience in a production environment and compilation of statistics to help make business decisions.
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Run trials Û Once an appropriate method to perform a case study has been determined, communication of goals to all parties handling the product is indispensable, including the casting team and quality-control specialists. Evolution of mix proportions should be anticipated as trials progress; such developments typically do not occur overnight, but rather through continuous testing. Further, results from a single test should not lead to discouragement.
Over time, both companies have learned what attributes are critical to successful SCC. Difficulties often arise through variations in incoming raw materials. Control of batch water during mixing is a crucial component, as mix proportions tend to be highly sensitive to water content. Too little or too much water can impact workability, flowability, and resistance to segregation.
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Review the results achieved Û Final assessment must address whether original business objectives were met. In evaluating how SCC costs compare with those incurred for normal production, any increases in the cost of concrete along with any reductions in labor, patching, or other factors must be considered.
Are SCC trials successful or close to being successful? In some markets, local aggregates may not suit an SCC design without significant chemical admixture dosages. High dosage rates may raise the cost per yard of SCC to a level that becomes difficult to recover. Moreover, some applications do not lend themselves to high-flow mixtures, at least not using traditional forms, so SCC is not a solution for every casting challenge precasters face. Accordingly, evaluation of the opportunities that SCC offers is unique to each facility’s operational and financial situation. The question of how SCC may fit into an operation is one that needs to be answered through careful investigation.
Nevertheless, results at Shockey and High Concrete have been rewarding. Both cite reduced casting-cycle time and labor requirements for placement, minimized or completely eliminated patching, improved product appearance, and Û most importantly Û a net savings to the bottom line.
COMPARISONS
Average daily concrete: 650 cubic yards
| Conventional | SCC | |
|---|---|---|
| Batching | 2 | 2 |
| Transport | 3 | 3 |
| Placing | 10 | 5 |
| Vibration | 2 | 0.5 |
| Floating/Finish | 2 | 2 |
| Clean-up | 2 | 0.5 |
| Patching | 6 | 1 |
| Casting crew size | 27 | 14 |
| Daily casting time | 11 | 9 |
| Worker hours | 297 | 126 |
| 171 worker hour savings @ $23 = $3,933 daily savings | ||
One company’s records compare conventional concrete and SCC with respect to labor requirements in their casting process.