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1 . Change in cement type .
2 . Change in fine aggregate ( washed concrete sand ) type . Sand is approx . 52 % of the volume and is also 52 % of what you visually see with acid etch , sandblast and exposed aggregate finishes . 3 . Change in coarse aggregate type . 4 . Change in mix design characteristics including slump , water / cement ratio or admixtures .
5 . Use of different source materials often meets the same performance and design strength criteria . Therefore , a ready-mix batch plant may use and batch several different sand , rock and cement sources in the course of one day . This is why it ’ s important to check and verify that the Statement of Mix Design uses the sole source materials throughout the duration of the project .
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RULE 4 |
FORMWORK |
Precise formwork leads to precise concrete work , and since concrete is fluid when poured , it will conform to its confining formwork . Precise formwork will result in concrete having crisp and precise edges , smooth grades and even transitions . |
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RULE 3
SUBGRADE PREPARATION
Without a well-graded and compacted subgrade , the best architectural concrete may fail . This is often the most overlooked step in creating a quality concrete installation . Key factors to ensure quality subgrade are :
1 . Subgrade should consist of semi-permeable , non-expansive soils . 2 . Materials must be graded and compacted in accordance with the soils report .
3 . Pipes and conduits must be placed in the subgrade and appropriately backfilled and compacted prior to commencing with concrete installation . On-structure concrete must be covered with drain board prior to placing topping slabs .
4 . Architectural concrete should always be placed over a minimum of two inches of damp , screeded and washed concrete sand . Sand creates a proper slip plane , retains moisture , and provides an avenue for migration of bleed water . This reduces surface cracking , prevents soil-toconcrete surface contamination , and controls bleed water . 5 . Use Mirafi 500x or 600x in natural compacted fill conditions or expansive soil . 6 . For on-structure concrete , always place concrete topping on drain board material .
1 . Form lumber should be S4S ( surfaced four sides ) # 2 grade Douglas fir or better .
2 . Form lumber should be handpicked to be free of crooks , hooks , warps , wanes and / or knots .
3 . Layout should be performed with digital transits for precise alignment . ( Wind blowing on a tight string commonly used for layout can deviate more than two inches in a 150-foot run .) 4 . New material should be used for each new project . 5 . Straight wall forms should be 3 / 4-inch M . D . O . plywood . 6 . Radius forms should be two laminations of plywood with the second lamination being M . D . O . ( facing concrete side ).
7 . For radius forms , two top plates prescribed and laminated and two bottom plates pre scribed and laminated over two by four-inch framing with studs at 16-inch o . c ., and horizontal plates no greater than four feet o . c .
8 . Straight wall plywood joints can be sealed with foam tape , or covered with reveals to prevent bleed water occurrence . Lamination of radius wall forms prevents bleed water leakage .
RULE 5 REINFORCING
Without the use of slab reinforcement , concrete may not be structurally strong enough to support heavy loads or prevent slab displacement from