2010 NRMCA - National Ready Mixed Concrete Association

References1Obla, K.H., “How Good is your QC – Part I of Concrete Quality Series,” Concrete InFocus, May-June 2010, Vol. 9, No. 3, NRMCA, pp.17-18.2Obla, K.H., “Sources of Concrete Strength Variation – Part II of Concrete Quality Series,” Concrete InFocus, July-August 2010, Vol. 9, No. 4,NRMCA, pp. 21-23.3ASTM C94, “Standard Specification for Ready Mixed Concrete,” Volume 4.02, ASTM International, West Conshohocken, PA, 2009, www.astm.org.4ACI Committee 117, “Specifications for Tolerances for Concrete Construction and Materials and Commentary,” American Concrete Institute,Farmington Hills, MI, 2006, 70 pp.5ACI Committee 214, “Evaluation of Strength Test Results of Concrete (ACI 214R-02),” American Concrete Institute, Farmington Hills, MI,2005, 20 pp.Table 1. Statistical Summary of Project Slump Test Results Sent by 5 Different Concrete ProducersProducer ID # of measurements Average Slump, in. Slump Range, in. Percent in compliance with C94 tolerance of ±1.5 in.A 305 5.2 1.75 – 6.75 98.0B 57 6.9 5.00-8.00 94.7C 41 7.6 3.50-10.50 73.2D1 304 4.8 2.00-8.00 97.4D2 62 8.4 6.25-9.50 95.2Table 2. Statistical Summary of Project Air Content Test Results Sent by 5 Different Concrete ProducersProducer ID # of measurements Average Air Content, % Air Content Range, in. Percent in compliance with C94 toleranceof ±1.5%A 302 5.6 3.4-6.9 99.7B 57 5.4 3.9-7.1 96.5C 41 2.9 2.2-4.0 90.2*D1 302 2.0 1.0-4.5 92.1*D2 17 1.0 0.8-1.4 100**Non air entrained concrete does not have C94 air content tolerances. So ±0.75% was assumedTable 3. Statistical Summary of Project Test Results Sent by 5 Different Concrete ProducersProducer ID Slump, in. Air Content, % Temperat., o F SD of SD of 7 d 28 day StrengthDensity, Strength,AVG SD AVG SD AVG SD lb/ft3 psi AVG, psi SD, psi Standard ofControl*PredictedSD, psi**A 5.2 0.67 5.6 0.46 68.3 6.3 NA 485 5578 438 Very Good 307B 6.9 0.73 5.4 0.81 68.5 6.8 1.36 624 4952 536 Good 362C 7.6 1.69 2.9 0.46 63.0 10.8 1.26 1701 9450 1258 Fair 890D1 4.8 0.59 2.0 0.45 72.0 6.4 1.51 594 5213 474 Very Good 281D2 8.4 0.76 1.0 0.18 78.0 5.7 0.52 1167 6632 938 Poor 294*Standard of Control per ACI 214**Predicted SD based on slump and air content compliance probabilitiesCONCRETE in focus ı 31