Showing 166-170 of 172 search results

The Sky’s the Limit

Due to the development of powerful high-range water-reducing admixtures and viscosity modifying admixtures, it is now possible to very efficiently and economically build high-rise concrete structures. These admixtures allow concrete to be pumped from the first to the highest floor, so it is no longer necessary to use cranes to transport and place concrete. This article shows how the construction of high-rise buildings has evolved from entirely structural steel structures to almost exclusively reinforced concrete structures, by discussing the construction of some landmark structures built from 1968 to the present.

Available in the following language(s): Spanish, French, Polish

A Field Study of Adhesive Anchor Installations

In theory, the knowledge is available to ensure reliable fastenings with adhesive anchors and to give designers and installers confidence and flexibility in myriad applications. However, with the failure of adhesive anchors in Boston, MA, the installation and use of these types of anchors has been called into question. To figure out what can be improved with regard to the use of adhesive anchors, adhesive anchor installations with injection systems were monitored on 23 job sites in five locations scattered over the U.S. Critical aspects were examined to determine gaps between actual and recommended practice and to come up with proposals to improve installation practices.

Available in the following language(s): French

Raising the Grade

ASTM Subcommittee A01.05, Steel Reinforcement, has made a significant revision to A706/A706M "Standard Specification for Low-Alloy Steel Deformed and Plain Bars for Concrete Reinforcement." The specification was developed in the early 1970s in response to the structural engineering community’s requirements for steel reinforcing bars with controlled tensile properties for use in earthquake-resistant structures and restricted chemical composition for weldability. As of December, 2009, it includes requirements for bars with a minimum yield strength of 80 ksi (550 MPa) (designated as Grade 80 [550]). The increased yield strength was especially encouraged by structural engineers, bar producers, bar fabricators, and contractors from seismically active areas because higher strength bars can help reduce congestion of reinforcement and enhance constructibility, especially in earthquake-resistant structures.

Available in the following language(s): Spanish

U.S. Cement Specifications

Recently, ASTM International and the American Association of State Highway and Transportation Officials (AASHTO) have revised their cement standards to bring them more closely in line with each other. ASTM standards are used more often in commercial construction and AASHTO standards are used more often in transportation projects; there is some overlap in the use of the different standards. The organizations undertook the harmonization effort to help promote consistency and enhance durability.

Available in the following language(s): Spanish

Concrete Q & A: Number of 4 x 8 in. Cylinders Required for a Test Result

We’re building a multistory reinforced concrete frame building and using 4 x 8 in. (100 x 200 mm) cylinders for acceptance testing at 28 days. The engineer of record says we need to average three cylinders for a test result instead of the two cylinders per test we were planning on. What is the standard number of cylinders that comprises a valid test? And if it is three, when did the requirement change from two to three cylinders?

Available in the following language(s): Spanish