Steel fiber-reinforced concrete contains short discrete fibers that must be uniformly distributed and randomly oriented throughout the concrete to improve its structural properties. Construction procedures for slabs-on-ground don’t differ greatly from those used in conventional concrete, but there are some key SFRC slab installation items that should be kept in mind to make the project go smoother. Mixture selection, mixing methods, placing, finishing, and jointing for steel fiber-reinforced concrete slabs are covered.

Concrete slabs-on-ground are popular for research facilities because they don’t exhibit the resonance characteristics of suspended slabs. Occasionally, a slab-on-ground separates from the subgrade, leaving a void that allows the floor to behave more like a suspended slab and may lead to cracking. To detect these voids, determine their horizontal extent, and verify that corrective actions have been successful, the frequency-dependent response of the slab to an impact load can be measure using impulse-response testing. The results of one such study, with measurements before and after remediation by grout injection, are presented.

In contrast to traditional strip methods for two-way slab design, finite element analysis (FEA) automatically provides deformation compatibility and a full equilibrium load path. Designers using FEA, however, have often blindly ignored twisting moments that occur on the edges of the elements because they are not sure how to account for them. This assumption may be unconservative where torsion is high. The available methods for explicitly incorporating twisting moments in the design of slabs based on FEA results are discussed in this article.

The structural design and rigorous analysis of a foundation system supporting dynamic equipment is complex. Therefore, designers often follow rules of thumb for their design. These rules of thumb, however, may lead to oversized foundations. To optimize slab size while avoiding resonance and ensuring minimal human perception of vibrations, practical guidelines and recommendations for design are presented. The effects of changes in foundation dimensions, operational speed of the equipment, and modulus of subgrade reaction on a slab’s natural frequency and peak displacement are also discussed.

One of several projects related to oil and gas exploration on Sakhalin Island, located on the east coast of Russia and north of Japan, was recently completed. The construction of mass concrete foundations for much of the equipment faced two main challenges that compounded each other: they were constructed during the coldest time of the year, when the daily mean temperature in the coldest month can drop to only -11.4 °C (11.5 °F), and the concrete contained a high slag cement content blended cement for durability. These technical challenges, along with difficulties brought on by language and cultural barriers, are discussed.

In response to the economic downturn, the ACI Board of Direction approved motions to help ACI members maintain their connections to the Institute.

The Holcim Foundation has named the winners of the second cycle of the Global Holcim Awards for Sustainable Construction. The awards competition seeks innovative, future-oriented, and tangible construction projects to promote sustainable responses to the technological, environmental, socioeconomic, and cultural issues affecting building and construction on local, regional, and global levels.

At first glance, the use of alternating bar sizes for reinforcement in walls and slabs may seem to enhance design efficiency, but it usually doesn’t optimize the overall cost of the project. Before the decision is made to specify alternating bar sizes, several issues should be considered.

Highlights of the ACI Spring 2009 Convention in San Antonio.

Is Power Floating Required with a Broom Finish?:

I’m working in an estimating department on a project for a bus depot and maintenance facility. The original contract specified a concrete slab with a coarse broom finish in the area where heavy buses are moving. After a bid was accepted, the floor finish was changed to a steel trowel finish, creating an additional work order. In the course of negotiations, the contractor stated that the original bid did not include power floating because it’s not required for a coarse broom finish. The contractor claimed that power floating is only required for a fine broom finish and that a coarse broom finish could be started almost immediately after placing. Our construction manager claims that power floating is necessary for early start of the rough broom finish and that ACI documents confirm his position. Is it possible to obtain information to support either of the claims?

Temporarily Stopping Construction: An Update:

The Concrete Q&A column in the April 2009 issue of CI responded to a question regarding protection of reinforcing bars extending out of concrete against corrosion when temporarily stopping construction. At the end of that column, we mentioned that there were probably several other options not mentioned in the article and asked CI readers to send us any particularly successful options that they had used.