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Exploratory tests of corrosion of reinforcing steel in concrete by X-radiography
I
resurvey I
regJrVey
Prepared by M.E. Adams, R.S. Bailey, L. Boniface and J.W. Rock
CARBON MATRICES Composite materials made from a porous 213carbon-carbon preform densified with boron nitride by chemical vapour infiltration Hannache, H., Quennisset, LM., Naslan, IL and Heraud, L. Journal of Materials Science Vol 19 (1984) pp 202-212 A low pressure vapour deposition technique w a s used to infiltrate 2D-carbon/carbon preform with boron nitride. The mechanical properties of this composite were investigated using a compression test. The behaviour depended upon the volume fraction of boron nitride: at low volume fractions (<0.2) the material behaved similarly to the 2D-carbon/ carbon composite. At greater volume fraction a decrease in the failure strain was accompanied by increasing failure stress. The oxidation behaviour indicated that the boron nitride does not totally protect the carbon, and at temperatures below 900°C a weight loss is observed. At temperatures greater than 900°C a weight gain is found, and is due to the oxidation of boron nitride. It is possible for an oxidized surface film to provide protection to the boron nitride, however at 1000-1100°C this film appears to vaporize.
CEMENT MATRICES Efficiency of some silane coupling agents and of the method of their application in polyester resin concrete Mani, P , Gupta, A.FL and Krishnamoorthy, S. Journal of Materials Science Iiol 18 (1983) pp 3599-3605 The effects of the mode of application and coupling agent type on the compressive strength of polyester resin concrete has been studied. Two coupling agents, 7-methacryloxypropyltrimethoxy silane and 7-aminopropyltriethoxy silane, and two application methods, pretreatment of the aggregate or addition to the resin, were examined. They found that pretreatment of the aggregate gave the best compressive strength overall; only at optimum loading did addition of the silane to the resin give equivalent results. Of the two coupling agents, the 7 methacryloxy gave better compressive strength than the amino silane. From X-ray examination the authors showed that the silane migrated through the resin to the resin/aggregate interface when initially added to the resin alone.
Exploratory tests of corrosion of reinforcing steel in concrete by X-radiography Sekine, I. and Fujinawa, M.MaterialsEvaluation Vo142 (1984) p 121 The corrosion of steel reinforcing bars in concrete was studied in an accelerated test. 0.4, 1.0 and 2.0% sodium chloride was added to the concrete, and the specimens were then
240
weathered for 1-3 months. After taking care that film exposure or development conditions were constant, it was found that the tan of the density of the X-ray i m a g e - - m e a s u r e d using a densitometer--was proportional to the degree o f corrosion of the steel. The a m o u n t of corrosion was estimated from the weight loss of the steel bars after removal from the concrete. O t h e r factors investigated were the effect of specimen thickness and geometry on the X-ray image.
Fibre reinforced cement and concrete: Part 1 theoretical principles Hannant` DJ. Concrete Vol 18 No 2 (February 1984) pp 25-26 In this theoretical analysis of tensile loading of fibre-reinforced concrete and cement, stress/ strain curves are presented for cases where varying fibre volume fractions influence the load bearing capability of test sections. Fracture mechanics considerations allow calculation of the stress for propagation of inherent and induced cracks in the cement paste. A high V f of stiff, well-bonded fibres increases the matrix cracking strain by stopping flaw propagation. Two modes of failure are proposed: (i) multiple matrix fracture followed by fibre pull-out and (ii) single fracture of the section. The amount of energy absorbed before attaining a certain level of damage depends on the failure mode, and this energy should be predicted using the appropriate material parameter, ie the parameter is related to the unit area of the fracture surface for case (ii), or related to the energy absorbed/unit volume for case (i).
Slow crack growth in bleached cellulose fibre cements Mai, Y.W. and Hakeem, M.I.Journal of Materials Science Letters Iiol 3 (1984) pp 127-130 Slow crack growth resistance curves, for both bleached and unbleached cellulose fibre cements, in terms of stress intensity factor and potential energy release rate are evaluated from measurements of the modified compliance and residual displacement. These latter two parameters are obtained from fracture experiments on double cantilever beams. The composites containing the bleached fibres are found to be stiffer, and have smaller inelastic crack tip zones. The unbleached fibre cements have superior resistance to crack growth.
Slow crack growth in cellulose fibre cements MaL Y.W. and Hakeem, M.I.Journal of Materials Science Vo119 (1984) pp 501-508 Subcritical crack growth in a cellulose fibre-(8% weight fraction of bleached fibre) reinforced cement was investigated using a double cantilever beam technique. The results were expressed in terms of crack growth resistance, which takes into account the effect of residual displacement, particularly important in the testing of wet specimens. The superiority of the wet cement composite over the dry was attributed to an increase in ductility and toughness of the cellulose fibres.
CERAMIC FIBRES Synthesis of continuous silicon carbide fibre part 3. Pyrolysis process of polycarbosilane and structure of the products Hasegawa, Y. and Okamura, K. Journal of Materials Science Iiol 18 (1983) pp 3633-3648 Three methods were used to synthesize the polycarbosilane precursors, which were characterized by a variety of methods. The authors considered that the pyrolysis process could be subdivided into six subregions. In the first stage the precursors lost weight due to evaporation of low molecular weight components. During the second stage a weight increase was observed, due to condensation or polymerization. Sidechain dehydrogenation occurred in the third stage. The fourth stage was regarded as transitional with amorphous products being formed. These products crystallized with further dehydrogeneration in the fifth stage. Finally in the sixth stage crystalline growth of fl-SiC occurred.
GENERAL Accelerated testing of composites Papazian, H.A.Journal of Reinforced Plasticsand Composites Vol 2 (October 1983) p 282 A survey of literature results shows that Zhurkov's phenomenological method of the strength of solids can be used to devise accelerated tests of static and dynamic tension, as well as cyclic failure of composites. Zhurkov's equation is used to show that relatively high loads give rise to failure times at loads at any temperature of interest. Extrapolation to more inaccessible temperatures is also possible, from only a few data points.
Analysis of curved laminated beams of bimodulus composite materials g a m a n a Murthy, P.V. and Ran, K.P.Journalof Composite Materials Vol 17 (September 1983) p 435 An elastic small deflection analysis of typical cantilever curved-sections subjected to different loadings and lay-up schemes has been carried out using a finite element analysis. The results obtained for different loadings and lay-up schemes are presented, and it was found that the neutral (zero axial strain) surface assumes different shapes with these variables and with the radius of curvature. The influence of this is to change the stiffness along the beam length. The iterative method of analysis used can be extended to shell and plate applications from the hollow and solid circular cross-section beams used in this study.
Bounds on the non-local effective elastic properties of composites Diener, G., Hiirrich, A. and Weissbarth, J.
COMPOSITES. JULY 1984
resurvey I
regJrVey
Prepared by M.E. Adams, R.S. Bailey, L. Boniface and J.W. Rock
CARBON MATRICES Composite materials made from a porous 213carbon-carbon preform densified with boron nitride by chemical vapour infiltration Hannache, H., Quennisset, LM., Naslan, IL and Heraud, L. Journal of Materials Science Vol 19 (1984) pp 202-212 A low pressure vapour deposition technique w a s used to infiltrate 2D-carbon/carbon preform with boron nitride. The mechanical properties of this composite were investigated using a compression test. The behaviour depended upon the volume fraction of boron nitride: at low volume fractions (<0.2) the material behaved similarly to the 2D-carbon/ carbon composite. At greater volume fraction a decrease in the failure strain was accompanied by increasing failure stress. The oxidation behaviour indicated that the boron nitride does not totally protect the carbon, and at temperatures below 900°C a weight loss is observed. At temperatures greater than 900°C a weight gain is found, and is due to the oxidation of boron nitride. It is possible for an oxidized surface film to provide protection to the boron nitride, however at 1000-1100°C this film appears to vaporize.
CEMENT MATRICES Efficiency of some silane coupling agents and of the method of their application in polyester resin concrete Mani, P , Gupta, A.FL and Krishnamoorthy, S. Journal of Materials Science Iiol 18 (1983) pp 3599-3605 The effects of the mode of application and coupling agent type on the compressive strength of polyester resin concrete has been studied. Two coupling agents, 7-methacryloxypropyltrimethoxy silane and 7-aminopropyltriethoxy silane, and two application methods, pretreatment of the aggregate or addition to the resin, were examined. They found that pretreatment of the aggregate gave the best compressive strength overall; only at optimum loading did addition of the silane to the resin give equivalent results. Of the two coupling agents, the 7 methacryloxy gave better compressive strength than the amino silane. From X-ray examination the authors showed that the silane migrated through the resin to the resin/aggregate interface when initially added to the resin alone.
Exploratory tests of corrosion of reinforcing steel in concrete by X-radiography Sekine, I. and Fujinawa, M.MaterialsEvaluation Vo142 (1984) p 121 The corrosion of steel reinforcing bars in concrete was studied in an accelerated test. 0.4, 1.0 and 2.0% sodium chloride was added to the concrete, and the specimens were then
240
weathered for 1-3 months. After taking care that film exposure or development conditions were constant, it was found that the tan of the density of the X-ray i m a g e - - m e a s u r e d using a densitometer--was proportional to the degree o f corrosion of the steel. The a m o u n t of corrosion was estimated from the weight loss of the steel bars after removal from the concrete. O t h e r factors investigated were the effect of specimen thickness and geometry on the X-ray image.
Fibre reinforced cement and concrete: Part 1 theoretical principles Hannant` DJ. Concrete Vol 18 No 2 (February 1984) pp 25-26 In this theoretical analysis of tensile loading of fibre-reinforced concrete and cement, stress/ strain curves are presented for cases where varying fibre volume fractions influence the load bearing capability of test sections. Fracture mechanics considerations allow calculation of the stress for propagation of inherent and induced cracks in the cement paste. A high V f of stiff, well-bonded fibres increases the matrix cracking strain by stopping flaw propagation. Two modes of failure are proposed: (i) multiple matrix fracture followed by fibre pull-out and (ii) single fracture of the section. The amount of energy absorbed before attaining a certain level of damage depends on the failure mode, and this energy should be predicted using the appropriate material parameter, ie the parameter is related to the unit area of the fracture surface for case (ii), or related to the energy absorbed/unit volume for case (i).
Slow crack growth in bleached cellulose fibre cements Mai, Y.W. and Hakeem, M.I.Journal of Materials Science Letters Iiol 3 (1984) pp 127-130 Slow crack growth resistance curves, for both bleached and unbleached cellulose fibre cements, in terms of stress intensity factor and potential energy release rate are evaluated from measurements of the modified compliance and residual displacement. These latter two parameters are obtained from fracture experiments on double cantilever beams. The composites containing the bleached fibres are found to be stiffer, and have smaller inelastic crack tip zones. The unbleached fibre cements have superior resistance to crack growth.
Slow crack growth in cellulose fibre cements MaL Y.W. and Hakeem, M.I.Journal of Materials Science Vo119 (1984) pp 501-508 Subcritical crack growth in a cellulose fibre-(8% weight fraction of bleached fibre) reinforced cement was investigated using a double cantilever beam technique. The results were expressed in terms of crack growth resistance, which takes into account the effect of residual displacement, particularly important in the testing of wet specimens. The superiority of the wet cement composite over the dry was attributed to an increase in ductility and toughness of the cellulose fibres.
CERAMIC FIBRES Synthesis of continuous silicon carbide fibre part 3. Pyrolysis process of polycarbosilane and structure of the products Hasegawa, Y. and Okamura, K. Journal of Materials Science Iiol 18 (1983) pp 3633-3648 Three methods were used to synthesize the polycarbosilane precursors, which were characterized by a variety of methods. The authors considered that the pyrolysis process could be subdivided into six subregions. In the first stage the precursors lost weight due to evaporation of low molecular weight components. During the second stage a weight increase was observed, due to condensation or polymerization. Sidechain dehydrogenation occurred in the third stage. The fourth stage was regarded as transitional with amorphous products being formed. These products crystallized with further dehydrogeneration in the fifth stage. Finally in the sixth stage crystalline growth of fl-SiC occurred.
GENERAL Accelerated testing of composites Papazian, H.A.Journal of Reinforced Plasticsand Composites Vol 2 (October 1983) p 282 A survey of literature results shows that Zhurkov's phenomenological method of the strength of solids can be used to devise accelerated tests of static and dynamic tension, as well as cyclic failure of composites. Zhurkov's equation is used to show that relatively high loads give rise to failure times at loads at any temperature of interest. Extrapolation to more inaccessible temperatures is also possible, from only a few data points.
Analysis of curved laminated beams of bimodulus composite materials g a m a n a Murthy, P.V. and Ran, K.P.Journalof Composite Materials Vol 17 (September 1983) p 435 An elastic small deflection analysis of typical cantilever curved-sections subjected to different loadings and lay-up schemes has been carried out using a finite element analysis. The results obtained for different loadings and lay-up schemes are presented, and it was found that the neutral (zero axial strain) surface assumes different shapes with these variables and with the radius of curvature. The influence of this is to change the stiffness along the beam length. The iterative method of analysis used can be extended to shell and plate applications from the hollow and solid circular cross-section beams used in this study.
Bounds on the non-local effective elastic properties of composites Diener, G., Hiirrich, A. and Weissbarth, J.
COMPOSITES. JULY 1984