Bonded Reinforcement

Free Moisture. The free moisture of a filler is the water present on the surface of the particles. This weakly bound water can sometimes contribute to iaterparticle bonding (reinforcing) or filler—matrix iateraction, ie, biader adsorption or catalysis. A determination of free moisture is usually made by measuriag the percent loss on drying the sample at either 100 or 110°C. 

In many of their complexes PF3 and PPI13 (for example) resemble CO (p. 926) and this at one time encouraged the belief that their bonding capabilities were influenced not only by the factors (p. 198) which affect the stability of the a P M interaction which uses the lone-pair of elecU"ons on p and a vacant orbital on M, but also by the possibility of synergic n back-donation from a nonbonding d , pair of electrons on the metal into a vacant 3d , orbital on P. It is, however, not clear to what extent, if any, the a and n bonds reinforce each other, and more recent descriptions are based on an MO approach which uses all (cr and n) orbitals of appropriate symmeU"y on both the phosphine and the metal-containing moiety. To the extent that a and n bonding effects on the stability of metal-phosphorus bonds can be isolated from each otlier and from steric factors (see below) the accepted sequence of effects is as follows ... 

Adhesion Epoxy Bonding reinforcements on external surface of combustion chamber... 

The most recent theoretical study, by Alhrichs and co-workers, deals with the di(phosphino)carbene Id and (phosphino) (phosphonio)carbenes Ie,f.16 The optimized geometry of the di(phosphino)carbene Id is weakly bent (PCP angle 160.5°) and highly unsymmetrical Only one of the phosphorus centers (P1) is in a planar environment, and it is much more closely bonded to the carbenic center than the other one (P1C 1.533 and P2C 1.765 A). The atomic charges (P1 +1.0, C -0.8, P2 +0.6) indicate that the short P bond is a double bond reinforced by Coulombic attraction, while the nature of the molecular orbitals revealed a slight delocalization of the carbene lone pair into the low-lying a (P-N) orbitals of the two phosphino substituents. The distortion from the symmetrical structure can be viewed as a second-order Jahn-Teller effect. 

As is the case with the 1 //-pyrroles and the 1 //-pyrazoles, structures isomeric with the 1//-imidazoles (1) exist that are nonaromatic because of the presence of a tetrahedral carbon atom in the ring. These structures, the 2H-imidazoles (2) and 4//-imidazoles (3), have properties quite different from their 1H counterparts. They also differ from each other in that the polarities of the two conjugated C=N bonds reinforce one another in structures 3, but are in opposition in structures 2. 

Chemical shift trends for the remaining protons in the 1,3-series and related compounds can be deduced from the representative data given in Table 6. The rules outlined above also satisfactorily accommodate the data for methylene groups adjacent to just one heteroatom in the 1,3-dithiane the opposing effects of the j3 C—C and C—S bonds cancel whereas in the 1,3-dioxane the effect of the C—C and C—O bonds reinforce. At the C-5 methylene group, the axial proton is to lower field of the equatorial proton in the 1,3-dioxane and 1,3-oxathiane but to higher field in the 1,3-dithiane. +... 

Unsaturated bonds reinforce the tendency to cross-linking... 

Figure 2.15 Pullout test of resin-bonded reinforcing bar.

The dipole moment of chloromethane (CH3CI) is greater (1.87 D) than the dipole moment of the C—Cl bond (1.5 D) because the C —H dipoles are oriented so that they reinforce the dipole of the C — Cl bond—they are all in the same relative direction. The dipole moment of water (1.85 D) is greater than the dipole moment of a single O— H bond (1.5 D) because the dipoles of the two O — H bonds reinforce each other. The lone-pair electrons also contribute to the dipole moment. Similarly, the dipole moment of ammonia (1.47 D) is greater than the dipole moment of a single N—H bond (1.3 D). 

Stronger directional preferences are observed for hydrogen bond reinforced ionic interactions, for which analysis of protein-ligand interactions in the Brookhaven... 

Intramolecular hydrogen bonding reinforcing the anomeric effect... 

Fibre-reinforced polymers (FRP) rebars, usually made of an epoxy matrix reinforced with carbon or aramide fibres, have also been proposed both as prestressing wires and reinforcement. Nevertheless, they are not discussed here, because these applications are still in the experimental phase and there is a lack of experience on their durability. In fact, while they are not affected by electrochemical corrosion typical of metals, they are not immune to other types of degradation. FRP are also used in the form of laminates or sheets as externally bonded reinforcement in the rehabilitation of damaged structures this application will be addressed in Chapter 19. 

Eriekson and Plueddemann suggest that particularly in filled systems, complete wetting of the mineral surface will improve adhesion by physical adsorption that would exceed the cohesive strength of the polymer. However, it is difficult to see how physical adsorption provides bond reinforcement when the polymer is in competition with water and possibly other weakly bonded surface layers, and where chemical bonding is also present [12],... 

In general, for externally bonded reinforcement (EBR), fabrics and strips are available. Commonly used fibres include carbon, glass and aramid. 

The advantages of externally bonded reinforcement over other methods of strengthening concrete structures include the ability to strengthen part of a structure whilst it is still in use, minimum effect on headroom, low cost and ease of maintenance (see Fig. 6.8, for example). The method has been in use for over 20 years, mainly to enhance flexural capacity, and has been found to produce effective and economical solutions to particular problems. 

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