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 SCC as defined by ACI (American Concrete Institute) committee 223 . An expansive cement concrete which when properly restrained by reinforcement or other means, will expand an amount equal to or slightly greater than the anticipated drying shrinkage. Subsequent drying shrinkage will reduce these expansive strains, but, ideally, a residual expansion will remain in the concrete, thereby eliminating shrinkage cracking. Minimum shrinkage reinforcement of 0.15% by cross sectional area of concrete shall be provided by using stiff, deformed bar reinforcement, #4 in size (1/2 diameter). Reinforcement will be located in the upper half of the slab by chairing. Reinforcement shall be stopped on either side of the temporary construction joint bulkheads that surround each day of slab placement, and is a single layer spaced as follows: _____Size_______________Distance on Center_______________Thickness of Slab___ ______#4_____________________20_____________________________6_________ ______#4_____________________18_____________________________7_________ ______#4_____________________16_____________________________8_________ ______#4_____________________14_____________________________9_________ ______#4_____________________12____________________________10_________ Shrinkage compensating cement, ASTM C-845 Type K cement, has a shrinkage compensating component interground with the cement, and in order to get more expansion, more cement must be used. Although ASTM C-845 requires the Type K cement to have a minimum amount of expansion in a mortar test, this does not guarantee a minimum expansion of the concrete made with Type K cement. Therefore, testing by ASTM C-878 must be made. This is also true when using a component, which is not interground with cement and is added separately, such as CONEX. In the latter case, the amount of expansion is controlled by the amount of CONEX added. The cementitious factor remains the same as required for the strength desired. The expansion may also be easily verified by a simple in-field test using a clear plastic 10 oz water cup. Fill the cup with the concrete in use and allow to stand, with a wet cloth or sponge on top, for 24-48 hours. Within this period, the cup will crack, indicating that expansive action is occurring due to the CONEX in the mix. This is not to be construed as an indicator of the amount of restrained expansion (RE), but merely as a means of verification of expansion occurring. For an accurate determination of RE, an ASTM C-878 test must be conducted using the in-field concrete. CONEX may be used with most ASTM C-150 cements, including Types V, III, and slag cement. CONEX may also be used along with other cementitious materials, such as fly ash and silica fume. In such cases, the total cementitious should have a minimum of 450 lbs/cu.yd. of Portland cement, unless tests prove that a lower Portland cement content is satisfactory. Where there are sulfate conditions, CONEX may be used with Type V cement or Type II plus a low-carbon fly ash. In the case of the latter, tests should be run to determine the suitability of the fly ash. In both cases, it is recommended that tests be conducted to assure the desired resistance to sulfates. | What is CONEX | Chemistry | Concrete Characteristics | Facts about SCC | CONEX & Floor Slabs | Pre-Stressed | Links | | Return Home | CONEX | Projects | What's New | Our Services | Contact Us | |
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