Per Goltermann

Reinforced Concrete T-Beams Externally Prestressed with Unbonded Carbon Fiber-Reinforced Polymer Tendons

Unbonded carbon fiber-reinforced polymer (CFRP) offers promise for use in prestressing applications due to its minimal creep and relaxation, low weight and high resistance to degradation. This study highlights the potential of CFRP rods in external and unbonded prestressing applications. A series of experiments were conducted on seven beams prestressed with unbonded external CFRP tendons anchored using a newly developed anchorage and post-tensioning system. The experiments investigated the effects of varying the initial tendon depth, prestressing force, and the presence of a deviator. The experimental results were compared to those observed with analogous beams prestressed with steel tendons, predictions made using an analytical model adapted from the literature and common beam theory. Results showed that steel and CFRP tendons had very similar effects on the structural behavior of the strengthened beams. Minor differences were observed that could be attributed to the difference between the modulus of elasticity of the CFRP and the steel used in the tests. Reinforced concrete beams prestressed with external bonded CFRP tendons exhibited the expected increase in strength, stiffness, and failure load, as well as decreased ductility, relative to unstrengthened beams. Under the loads examined in this study, the bending of CFRP tendons due to beam deflection did not significantly affect the tendon’s performance. Although the models predicted the beams’ load-bearing behavior accurately, they were less effective at predicting the stress experienced by the tendons. The findings from this study contribute to a better understanding of structural behavior of reinforced concrete beams post tensioned with external unbonded CFRP tendons throughout the load scheme.

Numerical Simulation and Experimental Validation of an Integrated Sleeve-Wedge Anchorage for CFRP Rods

The tensioning of carbon-fiber-reinforced polymer (CFRP) rods for prestressed concrete applications or posttensioning repair and strengthening has been met with mixed success. This is primarily because of limitations inherent in the use of traditional wedge anchors typically used for steel tendons. Recently, an integrated sleeve-wedge anchorage has been successfully developed specifically for CFRP rods. This paper presents a numerical simulation of the newly developed anchorage by using ABAQUS. The three-dimensional (3D) finite-element (FE) model, which considers material nonlinearity, uses hexagonal elements for the barrel, CFRP rod, and tetrahedral elements for the integrated sleeve wedge. The simulated barrel surface strains are shown to compare well with optically measured strains; however, the numerical results are shown to be sensitive to the mechanical properties of the anchorage and CFRP rod and especially the transverse elastic modulus of the CFRP rod. Finally, the simulated strain distributions ...

GREENLANDIC WASTE INCINERATION FLY AND BOTTOM ASH AS SECONDARY RESOURCE IN MORTAR

Today, 900 tons incineration fly ash is shipped abroad annually from Greenland for deposits, whereas the 6,000 tons incineration bottom ash is deposited locally. These incineration ashes could be valuable in concrete production, where the cement has to be shipped to Greenland. For this purpose, the effects on compressive strengths of mortars by substituting cement or sand by raw, washed and electrodialytically treated fly ash or bottom ash were investigated. Parts of the experimental fly ash had been pre-treated by either washing with distilled water or electrodialytically treated to remove salts and by the latter method, also heavy metals. Mortar samples were cast where cement (5%–20%) or sand (5%–10%) was replaced with fly ash or bottom ash, together with references without replacements. The compressive strengths were measured after 7, 14, 28 and 42 days. Replacing cement by fly ash resulted in lower compressive strength at 20% content of fly ash. At 5% replacement with raw fly ash a compressive strength similar to the reference was seen. However, using washed and electrodialytically treated ash lead to lower strengths. The lowest compressive strength was seen when replacing both sand with bottom ash and cement with fly ash. Based on the compressive strength tests, it is found that using Greenlandic incineration ashes in mortar as 5% cement replacement could consume all ash instead of disposals, and could thus turn the ashes into a local resource and simultaneously reduce the import of cement.