freshconc19.05 - Reading Cement Concrete Concrete Practice...

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DJ Lavery Reading – Cement & Concrete Concrete Practice – British Cement Association Tionestop.com u/n : univulster ; password : newtownabbey Portland cements : pages 4 to 8 Aggregates : pages 10 to 13 Admixtures : pages 15 to 17 Concrete properties : page 18 Curing : pages 45 to 47 Testing : pages 52 to 57
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DJ Lavery Properties of Fresh Concrete Properties of final hardened concrete - Depend on the quality of fresh concrete Depend on good quality control Workability of a concrete mix is defined as The relative ability to be poured, compacted and finished Cohesion Is defined as the relative resistance to segregation Segregation occurs when the constituents separate out High cohesive mixes give good finishes Poor mixes laitance Consistence Can be described as workability with cohesion A term now increasingly used - European standards
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DJ Lavery Properties of Fresh Concrete ‘Workability’ depends on Quantity of water in the mix Internal friction between the particles The volume and nature of the constituents Consistence The consistence specified for a mix will depend on The method of placing, compaction and finishing Ie. Pumped concrete needs a high ‘workability’ Consistence can be altered by using admixtures Consistence testing is empirical Standard tests are made at a standard time prior to placing Slump class Range of slump (mm) S1 10 – 40 S2 50 – 90 S3 100 - 150 S4 160 - 210
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DJ Lavery Properties of Fresh Concrete - Slump Test - BS EN 12350 - 2 Widely used, simple & convenient Conical shaped mould 300mm high, 200mm Ø btm, 100mm Ø top Concrete is placed in 3 layers Each layer tamped with a rod Cone is removed Concrete will slump Slump is measured using the cone as reference If the concrete collapses the test is repeated Poor cohesion:shear slumps Different aggregates can give the same slump for different workabilities Suitable for low to high consistence Detects change in moisture content of aggregate & other changes Slump – to nearest 10mm
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DJ Lavery Properties of Fresh Concrete Slump Test Levelling off Removing the cone Measuring the slump
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