Precast concrete materials, manufacture, properties and usage - Chapter 7 pptx

... expansion and a lower modulus of elasticity than a flint gravel concrete, and both these factors will result in reduced stresses. 7. 2 RELEASE AGENTS AND RETARDERS Release agents for heat-cured concrete ... up and gains strength slowly; a warm-starting concrete, say 25°C, warms up and gains strength more quickly; and a concrete starting at, say 40°C, can be handled within a...

Ngày tải lên: 08/08/2014, 10:23

... process a 4- or 8-drop would take place about every 15 seconds. 6.6.3 Wet and earth-moist mix presses In the production of floor tiles the wet and earth-moist mix mentioned for the five-stage process ... risks of freezing and thawing and the use of de-icing chemicals. A typical mix design could be: 2 7 parts of 10 mm hard stone or crushed rock 1·5 parts of natural sand or sand-gra...

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... concrete I. Title 691′·3 TA683 7 ISBN 0-2 0 3-4 905 7- 6 Master e-book ISBN ISBN 0-2 0 3 -7 988 1-3 (Adobe eReader Format) ISBN 0-8 533 4-9 9 4-0 (Print Edition) WITH 40 TABLES AND 109 ILLUSTRATIONS © APPLIED ... Publishers Ltd 1982 PRECAST CONCRETE Materials, Manufacture, Properties and Usage M.LEVITT ARCS, BSc, DIC, PhD Head—Materials Scie...

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... relevant to precast concrete manufacture leaving mix design to Chapters 5 and 6. 1.5.1 Cement types The most common cements used are ordinary and rapid-hardening Portland (including white), sulphate-resisting ... pre-wetted prior to mixing with the cement and additional water. Some limestones and sandstones have a slower absorption rate, and workability requirements need to be m...

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... and ordinary Portland cements with levels of C3A well under 10% and sulphate-resisting cements are the only types that will apparently benefit. The choice is between the use of plasticising and superplasticising ... Science Publishers Ltd 1982 2 ADMIXTURES This chapter covers the range of admixtures used in precast concrete products and mortars used with precast masonry. T...

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... concrete colour Both the desk-top 100mm square sample and the 300mm square hand- portable samples are misleading in the case of unpigmented materials, and for coloured concretes and mortars they seldom ... agents should be water-in-oil emulsion creams or chemical release agents. Ordinary mineral mould oils and oil-in- water emulsions promote streaking and staining. (c) Pan-type...

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... 0· 37 0·50 0·63 0 75 Total water 0·28 0·32 0·34 0·36 0·38 0·40 Observed and cost-corrected-relative-to-control failing loads (flexure) are shown in Table 4.13. It can be seen that F/C over 0· 37 ... the user, and in this respect vibrated concrete can only take a few per cent of ash and it is hardly economic to set up a second silo in a precast concrete factory to handle such a...

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... accurate and consistent quantity of concrete into the mould. In some precast processes tilting tables are used both to cast the concrete and lift the mould and concrete into the near-vertical ... 240V or three-phase supply under closely supervised nominally dry conditions. 13. Re-vibration of concrete is beneficial if the concrete is re-vibratable and the cost of double ha...

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... particles. The 0 7 is a rapid decay and indicates a silting up and capillary blocking process. Open-textured and honeycombed concretes cannot be tested by this method but the vast majority of precast ... is no solution to the resistance-to- sulphate problems when concrete is not properly made. The intermediate-permeability concretes are those categorised by (c), and even with sul...

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... strength + 0.62 × standard deviation Day no. Average of 10 Standard 0·9 7 0 Accept/ deviation ( σ ) +0·62 σ reject 51 7 4 0·5 6·61 A 52 7 3 0·6 6· 67 A 53 7 1 0·8 6·80 A 54 7 0 1·0 6·92 A 55 ... knowledge, ‘know-how’ and ‘alchemy’, and if one does not know what the variables are doing at any one time control is lost. One can list the factors and control variables one would use i...

Ngày tải lên: 08/08/2014, 10:23