Precast concrete materials, manufacture, properties and usage - Chapter 5 ppt

... 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...

Ngày tải lên: 08/08/2014, 10:23

... cycle would be about 25 seconds with about 10– 15 seconds in the pressing stage. In the brick process a 4- or 8-drop would take place about every 15 seconds. 6.6.3 Wet and earth-moist mix presses In ... to 15 N/ mm 2 ) and eject. The backing is the earth-moist mix, and the facing the wet mix, and the two are interdiffused by interface cement and water migration. The backing m...

Ngày tải lên: 08/08/2014, 10:23

... 10–20°C/hour, and temperature gradients should be 50 – 150 °C/metre. In rapid cooling of a Jespersen precast unit with an A/C of 6 5, a centre temperature of 90°C, and a surface temperature of 35 C, cracking ... 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...

Ngày tải lên: 08/08/2014, 10:23

... 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 6·9 1·0 6·92 R 56 ... procedures in the manufacture and/ or testing (Assessors and Company). 4. Keeping Record Cards on all machinery, equipment, etc. (Company and Assessors). (See Chapter 5. ) 5. Calibra...

Ngày tải lên: 08/08/2014, 10:23

... concrete I. Title 691′·3 TA683·7 ISBN 0-2 0 3-4 9 05 7-6 Master e-book ISBN ISBN 0-2 0 3-7 988 1-3 (Adobe eReader Format) ISBN 0-8 53 3 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 S...

Ngày tải lên: 08/08/2014, 10:23

... 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 ... strengths above 40 N/mm 2 , nor some sandstones above 50 N/mm 2 . (f) Aggregate variations affect physical, chemical and architectural properties and very few prec...

Ngày tải lên: 08/08/2014, 10:23

... Table 2 .5 illustrates this effect. TABLE 2 .5 TYPICAL EFFECT OF PLASTICISING ADMIXTURE ON PROPERTIES OF A VIBRATED CONCRETE PRODUCT The dosage rates vary from 100 to 1000 ml /50 kg cement and each type ... ADMIXTURES This chapter covers the range of admixtures used in precast concrete products and mortars used with precast masonry. They are all used at relatively low con...

Ngày tải lên: 08/08/2014, 10:23

... 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...

Ngày tải lên: 08/08/2014, 10:23

... following F/C ratios and approximate total water contents were used: F/C 0 0· 25 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 ... one fly ash and F2 was selected. The works mix was a 3/1 by weight sand/ordinary Portland cement mix with a sand grading: Sieve No. Passing % 1·18 mm 100 600 µm 95 300 µm 50 150 µ...

Ngày tải lên: 08/08/2014, 10:23

... resistance. Example 4 Part sandwich cladding panel 150 mm thick with 50 mm cast-in expanded plastics panel taking up 80% of area. k=1·0 for concrete, 0·0 25 for expanded plastics. Solid section: ... 1h Non-air-entrained 0 50 0·30 0·20 Air-entrained 0·40 0· 05 0·01 Fig. 8.18. Defective kerbs with only partial replacement. Copyright Applied Science Publishers Ltd 1982 8 .5. 3 Corrosion...

Ngày tải lên: 08/08/2014, 10:23