{"id":175553,"date":"2023-05-25T15:43:24","date_gmt":"2023-05-25T22:43:24","guid":{"rendered":"https:\/\/inbusinessphx.com\/?p=175553"},"modified":"2023-05-25T15:43:24","modified_gmt":"2023-05-25T22:43:24","slug":"asu-designed-fiber-reinforced-concrete-speeds-up-phoenix-rapid-transit-construction","status":"publish","type":"post","link":"https:\/\/staging.inbusinessphx.com\/?p=175553","title":{"rendered":"ASU-Designed Fiber-Reinforced Concrete Speeds Up Phoenix Rapid Transit Construction"},"content":{"rendered":"
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Photo by Charlie Leight\/ASU News<\/figcaption><\/figure>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
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Using fiber-reinforced concrete instead of rebar-supported slabs for constructing Metro Phoenix light rail extensions is giving new meaning to rapid transit. Months of construction time are being reduced to weeks, adding cost savings, sustainability and worker safety to the mix.<\/p>\n

A collaboration between Arizona State University, the Phoenix Valley Metro Regional Transportation Authority and Kiewit-McCarthy, the project\u2019s construction firm, began with a materials upgrade proposal from Barzin Mobasher, an ASU professor of structural engineering in the School of Sustainable Engineering and the Built Environment.<\/p>\n

The project, which extended the light rail by 1.5 miles, incorporated the\u00a0fiber-reinforced concrete design and was completed in early May.<\/p>\n

Reinforcing bar, or rebar, is made of steel and embedded in concrete to strengthen structures. According to Mobasher, more than 60% of the volume of concrete used throughout the world has zero tensile efficiency and is unable to carry load. This makes concrete used in load-bearing structures like the light rail susceptible to cracks, which begin very small and grow unhindered until there is a fault in the structure.<\/p>\n

Incorporating rebar provides the loadbearing strength required for most concrete-based construction. However, laying rebar is costly, leaves a dramatic carbon footprint, presents worker safety risks and above all, takes a great deal of time. As the inevitable concrete cracking escalates and the rebar corrodes, additional maintenance, repair and rehabilitation are required, further adding to costs and neighborhood disruption.<\/p>\n

Mobasher\u2019s proposal simplified challenges for the light rail extension project and delivered a successful new system \u201cjust by making one change in the design criteria \u2013 using fibers in the concrete mix instead of reinforcing with rebar,\u201d he said.<\/p>\n

Instead of using two layers of rebar in cross directions to support the light rail’s electrified track in the extensions, Mobasher\u2019s design and validation approach considered both steel and polymeric fibers added directly into the concrete, completely eliminating the need for rebar reinforcement. Finally, steel fibers were chosen by Valley Metro for the northwest extension project.<\/p>\n

To validate the proposal, a series of serviceability tests were conducted in ASU\u2019s Structural and Materials Lab<\/a>. Testing involved creating full-size mock-ups for both rebar-reinforced concrete and fiber-reinforced concrete, in the same ratios as full-size sections. Side-by-side testing allowed comparisons of\u00a0strength and flexibility\u00a0as well as documentation of concrete cracking and fatigue susceptibility.<\/p>\n

The testing process also projected cost and construction time savings. For example, the\u00a0per mile construction of the extension using rebar was projected at 231 days, while using fiber-reinforced concrete reduced it to\u00a0121 days, with a cost savings of more than $12 million.<\/p>\n

\u201cThe idea of taking several long rebars that are half an inch in diameter, separated by 12 to 18 inches and built into a cage that is 12 inches above ground and replacing them with a fiber material, which is 2 inches long and only 1\/32nd of an inch in diameter and mixed in with the concrete, might seem on scale non-competitive,\u201d Mobasher said.<\/p>\n

\u201cBut if you have thousands of those small fibers distributed in there, they become much more effective in arresting the cracks \u2014 working as small Band-Aids to keep the cracks closed and transfer the load. (Fiber-reinforced concrete) can be designed to bear up to an unprecedented 40% of the tensile load capacity of concrete.\u201d<\/p>\n

\u201cWe did the fatigue tests to simulate conditions for up to 45 years of service at much higher expected loads as proof of concept, and they accepted the proposed approach,\u201d said Mobasher of the approvals from Valley Metro and the city of Phoenix. \u201cIt\u2019s been a tremendous experience for them to save the amount of materials used and, at the same time, to be able to meet the project at costs much lower than the original budget and in a much faster time frame.\u201d<\/p>\n

The Valley Metro project is expected serve as a prototype for similar light rail upgrades nationally and will be presented at an international Fiber-Reinforced Concrete Workshop<\/a>\u00a0hosted by ASU in September.<\/p>\n

Construction time<\/h4>\n

A major obstacle for community approval of light rail transit is months of neighborhood disruption during construction. Using\u00a0fiber-reinforced concrete instead of rebar-supported designs significantly reduces disruption to weeks or, in some cases, days.<\/p>\n

Andrew Haines, project manager for Jacobs Engineering in Tempe, attributed the success of the materials change to \u201cchallenging the accepted.\u201d<\/p>\n

\u201cThere\u2019s an accepted way of doing reinforced concrete in the United States, especially with regard to light rail,\u201d Haines said. \u201cI think engineers get into this track of just, \u2018We\u2019ve got to do it a certain way, that\u2019s how it\u2019s always been done,\u2019 and it\u2019s been very difficult to change that \u2014 to accept something new.<\/p>\n

\u201cThe placement of the concrete with the fibers has been very simple,\u201d Haines said. \u201cThere\u2019s no reinforcement \u2014 there\u2019s no bars in the track slab for workers to try to walk on and perhaps slip on. So, it\u2019s just the prepared earth and the rails are in place and the concrete gets placed around it \u2014 the reinforcement is integral with the concrete.\u201d<\/p>\n

The ability to develop material samples and test them in the ASU labs was a major component of implementing the change, according to Haines.<\/p>\n

\u201cWe did all the right things to get this implemented in the field,\u201d he said. \u201cAnd the result seems to be phenomenal.\u201d<\/p>\n

According to Mobasher, the fibers are added into the concrete mix at the plant before being transported by the ready-mix trucks to the construction site. The entire mix is then discharged and self-consolidates, leaving a smooth, finished concrete surface.<\/p>\n

\u201cThe work that used to take weeks to be done is finished in a matter of hours because we don\u2019t need a crew laying up the steel rebars, connecting them, making sure they are all adequately welded together and that the components are all grounded,\u201d Mobasher said.<\/p>\n<\/div>\n<\/div>\n<\/section>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

Using fiber-reinforced concrete instead of rebar-supported slabs for constructing Metro Phoenix light rail extensions is giving new meaning to rapid transit. Months of construction time are being reduced to weeks, adding cost savings, sustainability and worker safety to the mix. A collaboration between Arizona State University, the Phoenix Valley Metro Regional Transportation Authority and Kiewit-McCarthy, […]<\/p>\n","protected":false},"author":2,"featured_media":175554,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_eb_attr":"","footnotes":""},"categories":[16],"tags":[12],"class_list":["post-175553","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-live-learn","tag-featured-stories"],"_links":{"self":[{"href":"https:\/\/staging.inbusinessphx.com\/index.php?rest_route=\/wp\/v2\/posts\/175553","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/staging.inbusinessphx.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/staging.inbusinessphx.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/staging.inbusinessphx.com\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/staging.inbusinessphx.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=175553"}],"version-history":[{"count":0,"href":"https:\/\/staging.inbusinessphx.com\/index.php?rest_route=\/wp\/v2\/posts\/175553\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/staging.inbusinessphx.com\/index.php?rest_route=\/"}],"wp:attachment":[{"href":"https:\/\/staging.inbusinessphx.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=175553"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/staging.inbusinessphx.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=175553"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/staging.inbusinessphx.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=175553"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}