Influence of constituents on the properties of self compacting repair materials

The paper presents the results of laboratory tests and field application in a highway bridge of self compacting repair materials. Three commercially available repair materials and one specially designed self compacting concrete were used in the study. The properties investigated were shrinkage, creep, elastic modulus and modulus of rupture. In addition, the field investigation determined flowing characteristics, compactibility and placing procedure of the flowing materials. The laboratory results show that the constituents of the mixtures greatly influence the basic properties of the materials. Inclusion of coarse aggregate in the mixture generally lowered the free shrinkage and modulus of rupture. Creep was highest in the material with polymer modification but creep recovery was lowest where large size aggregate was present. The elastic modulus was also influenced by the addition of coarse aggregate and copolymers The field results show that the materials can be placed and compacted satisfactorily without the aid of mechanical equipment

Long-term performance of high-stiffness repairs in highway structures

This paper presents the results of field monitoring of repair patches in two reinforced concrete highway bridges, Lawns Lane Bridge on the M1 and Gunthorpe Bridge across the River Trent. The repairs were applied by spraying (guniting) repair materials to compression members of the bridges. The structural members were unpropped during repair and throughout the 60 week monitoring period. The strains in the repair patches were monitored with vibrating-wire gauges. Four different repair materials were investigated whose elastic modulus was greater than that of the substrate concrete (E-rm > E-sub). The results show that efficient repairs are achieved with E-rm> E-sub, the optimum relationship being E-rm > 1.3E(sub). This enables the repair material to shed a significant proportion of its shrinkage strain to the substrate, thereby reducing restrained-shrinkage tension. It also enables the repair to attract externally applied load from the substrate in the long term. The effect of creep and shrinkage on the performance of the repair patch is also determined. Overall, the results show that current repair standards have limitations with respect to repair material specifications

Factors affecting the efficiency of repair to propped and unpropped bridge beams

This paper presents the results of laboratory and field investigations of bridge beams repaired both under propped and unpropped conditions. In the laboratory beams were repaired using hand-applied repairs. Repairs to beams in two highway, bridges were carried out using both hand-applied and flowing repairs. The repair materials used were commercial products of wide-ranging properties (shrinkage, creep and elastic modulus). Both low stiffness repair materials of elastic modulus, E-rm, less than the substrate E-sub, and high stiffness repair materials (E-rm > E-sub) were used. The repairs were applied in the tensile zone of the beams. Strain distributions in the different phases of repair patches were monitored under service loading for a period of up to 240 weeks. The results show that high structural efficiency is achieved with repairs having E-rm > E-sub, other properties (shrinkage and creep) being within reasonable limits. Such repairs ave less plane to restrained shrinkage cracking and show a capacity for load redistribution into the repair patch. Low stiffness repairs (E-rm < E-sub), on the other hand, are prone to restrained shrinkage cracking and are ineffective in load-sharing with the substrate. Repairs to propped flexural members developed erratic and non-uniform load distribution in the different phases upon reapplication of load. Composite action between the repair patch and the substrate results in cracking in the repair patch, rendering the repairs structurally inefficient

Evolution of the structural and magnetic properties of sputtered Tb_xFe_73Ga_27-x (7 at.% ≤ x ≤ 11 at.%) thin films upon the increase of Tb content.

Tb_xFe_73Ga_27-x (7 at.% ≤ x ≤ 11 at.%) ternary alloys have been obtained by cosputtering from Tb_33Fe_67 and Fe_72Ga_28 targets. In contrast with other Tb-Fe-Ga compounds that consist of just one structural phase, the diffraction pattern of the Tb_7Fe_73Ga_20 shows the presence of two different phases related to binary Tb -Fe and Fe-Ga alloys. This microstructure evolves as the Tb content is increased, and for a Tb of 11 at.% X-ray diffractometry only evidences the presence of a phase close to the TbFe_2. Although none of the studied samples show perpendicular magnetic anisotropy, there is a significant component of the magnetization perpendicular to the sample plane. The increase of the Tb content on the compounds from 7 at.% to 11 at.% enhances this component most probably due to the shift of the microstructure towards one similar to the TbFe_2

Tailoring the magnetic anisotropy and domain patterns of sputtered TbFeGa alloys

We report the magnetic anisotropy and domain configuration of cosputtered TbFeGa alloys. The layers were deposited from two targets with compositions TbFe2 and Fe3Ga, respectively. The structural and magnetic properties do not only depend on the composition but also on the growth conditions. Alloys with the same composition but deposited using a DC or a pulsed power source in the TbFe2 target exhibit a different magnetic anisotropy. The perpendicular magnetic anisotropy, the size and topology of domain patterns can be tailored by changing the evaporation parameters of TbFe2. The width of the stripe domain increases from 235 to 835 nm when using the DC source in the TbFe2. We correlate this effect with Tb enrichment of the TbxFe1−x phases present in the samples

Influence of resistivity on current and potential distribution of cathodic protection systems for steel framed masonry structures

The present paper presents the influence of resistivity on the current and potential distribution of cathodic protection (CP) systems for steel framed masonry structures. The work involves both experimental measurements and boundary element analysis and follows on from earlier experiments employing sand as a simple model for masonry encasement that has been reported elsewhere. Factors such as the size and type of masonry, moisture content and width of mortar joints will affect the resistance of the path through which the CP currents pass and thereby influence the distribution onto the steel surface. To represent such variations in resistance, it has been necessary to construct a small scale specimen replicating, as far as possible, actual applications on steel framed structures. The results from the laboratory specimen and numerical modelling are in sufficient agreement to confirm the validity of the modelling approach and allow the results to be employed for the purposes of design and development

Dual function carbon fibre fabric strengthening and impressed current cathodic protection (ICCP) anode for reinforced concrete structures

A novel technique has been proposed and researched in which carbon fibre reinforced polymers (CFRP) are employed to provide both structural strengthening and electrochemical corrosion protection to reinforced concrete (RC) elements suffering from corrosion related damage. In this paper, CFRPs fabric was used for both flexural strengthening of pre-corroded reinforced concrete beams and operated in a dual functional capacity as an impressed current cathodic protection (ICCP) anode. After a period of ICCP operation at high current density either at constant value or adjusted values, the beams were subjected to flexural testing to determine the load- deflection relationships. The potential decays of the steel met recognised ICCP standards and the CFRP fabric remained effective in strengthening the corroded reinforced concrete beams. The bonding at CFRP fabric anode and concrete interface was improved by using U-shaped wrapping and therefore the ultimate strength of dual function of CFRP fabric with U-shaped wrapping increased significantly