Concrete inFocus - Summer 2013 - (Page OC7)

infocus online connections www.nrmca.org/news/connections Quality on Sustainability Part 14 of Concrete Quality Series Karthik Obla, Ph.D., P.E., Vice-President, Technical Services D ue to increasing focus on sustainable construction, building products are being required to document the environmental impact associated with their manufacture, and to show continuous improvement. For concrete construction, environmental impact can be documented from the source ingredient materials, manufacturing process and the composition of the concrete mixture. In the use phase of concrete buildings and infrastructure there are several advantages that can be documented. This article focuses on the concrete mixture and demonstrates how improved concrete quality can play an important role in developing concrete products with reduced environmental impact and contribute to sustainable development. Target a Low Standard Deviation Parts 1 and 2 of the Concrete Quality series1,2 and benchmark of concrete quality is the Standard Deviation, S, of compressive strength test results. Typically as the concrete quality improves by monitoring and reducing variability associated with ingredient materials, manufacturing and testing, the standard deviation is reduced. Te ACI 318 building code3 for structural concrete4 and ACI 301 specification recognize the use of standard deviation calculated from past projects for a similar concrete mixture to establish the required average compressive strength when designing a concrete mixture for a specified compressive strength. Tis process allows the concrete producer with improved quality control, as indicated by the standard deviation, to target a lower average strength. Table 1 shows the calculated required average strength for a specified strength of 4,000 psi for different levels5 of discussed that a good measure concrete quality as measured by S. A producer with S = 350 psi has to design the mixture for an average strength of 4,470 Table 1. Target Average Strengths for ƒ´c QC Standards (ACI 214) S, psi ƒ´cr , psi Excellent Very Good 350 4,470 Cementitious Content, lb/yd3 447 CO2 footprint, lb/yd3 463 450 4,600 460 476 = 4000 psi Good Fair Poor 550 4,780 478 494 650 750 850 950 1,050 1,150 1,250 5,020 5,250 5,480 5,710 5,950 6,180 6,410 502 518 525 541 548 571 564 587 595 611 618 641 634 657 concrete INFOCUS ı OC7 psi where as a producer with S = 1,250 psi has to target at least 6,410 psi. Based on a simple assumption that a pound of cement equates to a compressive strength of about 10 psi. Table 1 estimates that the cementitious content for the producer with S = 1,250 psi is 43 percent higher than that for the producer with S = 350 psi! Table 1 also includes the environmental impact of one factor: the CO2 presented by Marceau et al.6 footprint—calculated based on data Te CO2 foot- print for the producer with S = 1,250 psi is calculated to be about 41 percent higher than that for the producer with S = 350 psi. Using less cement also conserves natural resources associated with its manufacture. Better Jobsite Curing and Overall Testing Quality A component of the strength standard deviation discussed above is associated with acceptance testing of concrete. Te factors that can increase the component of variability Impact of Concrete http://www.nrmca.org/news/connections http://www.nrmca.org/news/connections

Table of Contents for the Digital Edition of Concrete inFocus - Summer 2013

Corporate Suite
Enviroscene
From Hand Shovels to Keystrokes
Walking on Art
NRMCA’s Design Assistance Program Works for Producers
Maryland Ready Mix Producer Gives Back to Community
Structures That Last
Responsible Sourcing Through CSR Reporting
Index of Advertisers
Responsible Sourcing Through CSR Reporting
White Cement Delivers Beautiful, Profi table Mixes
Impact of Concrete Quality on Sustainability
Tulsa Driver Named NRMCA Driver of the Year

Concrete inFocus - Summer 2013

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