When I think back on changes in concrete slab construction during my 50 years, nothing stands out like three inventions of the 1980s that changed the way we constructed slabs: the laser screed, the riding trowel and float dishes, and the early-entry Soff-Cut saw.
With vibratory truss screeds and other equipment, we typically placed slabs in narrow strips that limited the amount of slab we could place in a day—a 10,000-square-foot placement was large. The laser screed allowed much larger, more block-like placements that were far more level than before; our FL numbers increased at least 50%. Soon we were placing 20,000 to 50,000 square feet at a time with far fewer construction joints.
The ability to strike off much larger placements would not have been as beneficial if we had to continue using walk-behind power trowels. Riding trowels were the perfect accompaniment to the laser screed because we could finish much larger areas with less labor. We also increased the flatness of the floors, especially after the introduction of float dishes (pizza pans). Our FF numbers jumped at least 30% with proper use of riding trowels and float dishes.
I did much of the early investigation into the Soff-Cut saw for ACI 302 in the late 1980s and early 1990s. We successfully sawed and prevented out-of-joint cracking in slabs from 4 to more than 12 inches thick, even though we had the saw cut as shallow as 5/8 inch. The saw enabled us to cut much earlier than the wet cut saws we had been using for decades, minimizing cracking and saving overtime.
These innovations were conceived and developed largely by concrete contractors. And improvements have continued, enabling us to have greater productivity and quality of slab construction.
—Jerry A. Holland
Read more highlights from 50 Years of Concrete Construction Progress.