DURA CEO Adj. A/Prof. Ir. Dr. Voo Yen Lei presented at the Precast/Prestressed Concrete Institute PCI Convention & National Bridge Conference which was held on March 1 – 5, 2016, in Nashville, Tennessee, USA. The event, which is the largest tradeshow in North America dedicated to precast concrete, was hosted by both PCI together with The Precast Show.
DURA Technology was invited to be part of The Precast Show and Dr Voo was given 1.5 hours to deliver a lecture for the National Bridge Conference (NBC) Education Sessions, where more than 200 attendees including industry experts, stakeholders especially the FHWA, and professionals in the precast construction industry attended. It included over 35 education sessions on topics such as research, marketing, business, productivity, and technical transportation. During the talk, Dr Voo has demonstrated some of the successful stories on the application of UHPC bridges in Malaysia and he has also shown how UHPC technology can be a cost saving and sustainable technology solution for bridge construction. The lecture summarised the following results:
(1) The UHPC mixes were simplified. A relatively low cost but high strength micro steel fibers with tensile strength over 2700 MPa were identified. Most importanly, the resulting concrete met all the engineering properties requirements for use of UHPC in major bridge members and systems. They include minimum characterictis compressive strength of 150 MPa and characterictis flexural strength of 20 MPa.
(2) It was decided to have a large geometrical volume mixer, 12 m3 and above. It was also decided not to precast a product whose size requires more concrete than allowed in one mixing cycle. The corresponding product weight would be about 20 tonnes. This way, there would be no waiting for fresh concrete delivery and no concern about cold joints. Also, the process eliminates concern about such factors as differential setting time, thermal gradient and differential shrinkage. Thus, highly consistent products are produced with virtually no internal residual stresses.
(3) Use four standardized cross section shapes: (i) decked bulb tees, (ii) spliced segmented U-girders, (iii) pretensioned full length I-beams for spans less than 24 m, and (iv) segmental box-girder shapes for relatively long spans. The span achieved for the fourth shape has been 100 m to the date of this writing. There are significant, counter-intuitive, benefits to making relatively small pieces. They can be made in small indoors facility. They can be shipped in multiple ways including enclosed trucks and ship containers. They can be handled at the site with small equipments.
(4) Use straight pretensioning where possible. However, most applications involve spliced post-tensioned beams, with straight bottom flange post-tensioning. The segment interfaces are match cast, with dry or epoxy joints.
(5) Simplify design of most bridges by eliminating the need for time dependent stress-redistribution analysis, since creep and shrinkage of this material are negligible. However, creep growth of camber and deflection may still be considered by the designer in construction geometrics.
The event provided DURA with opportunities in networking and knowledge expansion and sharing with other professionals in the industry.