By Dale P Bentz, Chira F Ferraris, Kenneth A Snyder
A most sensible practices advisor is constructed from a synthesis of modern learn on high-volume fly ash (HVFA) concrete combos. those most sensible practices might be utilized by means of the concrete building to accomplish wanted homes and to make sure the (high) functionality of HVFA concrete combos in perform. As such, the file considers all facets of HVFA concrete creation, from the characterization of the beginning fabrics, via mix proportioning and curing thoughts to accomplish wanted houses, to the in-place early-age and long term functionality of the concrete in its clean and hardened states. either mechanical and shipping houses are thought of intimately. viewpoint is confirmed in accordance with a short evaluate of present practices being hired nationally. each one topical part is concluded with a practice-based set of strategies for the layout and building neighborhood. The file is meant to function a invaluable source to those groups, supplying either a learn precis and a advisor to useful steps that may be taken to accomplish the optimal functionality of those sustainable concrete combinations.
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Extra resources for Best Practices Guide for High-Volume Fly Ash Concretes: Assuring Properties and Performance
77) for the OPC concretes, with the two dotted lines indicating ± 20 % from the best fit values. 76). The thin solid line represents the best fit determined for the mortar data in Figure 12. (Taken from ). Relevance to Industry Practice: 1) To achieve acceptable early-age strength, HVFA concretes are commonly proportioned with a lower w/cm than that of the target (100 % OPC) concrete. Because of the spherical shape of many of the fly ash particles and the considerable dilution of the flocculating cement particles in the HVFA mixture, the increase in HRWRA dosage accompanying this reduction in w/cm may not be as large as that which is needed in a non-fly ash concrete.
Long-Term Strength: modify w/cm and/or replace part of fly ash with fine limestone b. Early-Age Strength: switch to a Type III cement, reduce w/cm, and/or use a chemical accelerator c. Setting Times: replace part of fly ash with fine limestone powder d. Shrinkage: employ internal curing (ASTM C1608 and ASTM C1791) or shrinkage-reducing admixture (SRA) e. Rheology: modify HRWA dosage This process is shown schematically below as a flow table (adapted from reference 26). 45 46 Appendix B. ), 3) Select a trial w/cm ratio and determine volume fractions of water and all cementitious (powder) components, 4) Prepare trial mixture and measure performance characteristics, 5) Adjust mixture proportions to obtain desired characteristics, a) if setting time is too long, it can be decreased by replacing a portion of the fly ash with fine limestone powder (optimally about 1 µm median diameter powder); usually in the 5 % to 15 % of total powder volume range b) if early age strength is too low options include i) switch to a Type III cement and first re-evaluate existing mixture with Type III, ii) lower w/cm (or water-to-cement ratio, w/c) based on a plot of strength vs.
Justnes, and B. Lothenbach, Hydration mechanisms of ternary portland cements containing limestone powder and fly ash, Cem. Concr. Res. 41 (3), 279-291 (2011). 60) P. A. Khokhar, R. El Hachem, and A. Loukili, Improvement of the early-age reactivity of fly ash and blast furnace slag cementitious systems using limestone filler, Mater. Struct. 44, 437-453 (2011). 61) J. P. Bentz, and A. Ardani, Enhancing high volume fly ash concretes using fine limestone powder, in Green Cements, ACI SP - , Minneapolis, MN (2013).