2010 Concrete Streets and Local Roads How to Interpret Mix Designs and Batch Tickets Joe Hug, P.E. Technical Services Manager The Monarch Cement Company A Unique Building Material Concrete Properties • • • • • Strength Durability Sustainability Versatility Economical – These and many other properties depend on the relative amounts and properties of the individual components Mix Design vs. Proportioning • Mix Design – Process of determining required and specifiable properties of a concrete mixture • Mix Proportioning – Process of determining the quantities of ingredients for a given set of requirements – Determine the most economical and practical combination of readily available materials that will produce the required properties Integrated Materials and Construction Practices for Concrete Pavement What makes a good Concrete Mix? • The contractor’s need to handle, place, consolidate and finish the concrete • The specifier or owner requirements for strength, durability, and sometimes, color and appearance. What are we looking for? • Compliance with contract documents • Compliance with building code • Ingredients – – – – Cementitious materials W/Cm ratio Fine and Coarse Aggregates Admixtures • Proportioning – Fresh Properties – Hardened Concrete Properties Individual Specification Requirements • • • • • • • • • • • • • Compressive Strength Flexural Strength Freeze/Thaw and Deicing Chemicals Shrinkage Abrasion Sulfate Exposure Sea water exposure Acid Attack ASR D-Cracking Lightweight or Heavyweight concrete Color …Etc. Cement • ASTM C 150 • AASHTO M 85 Comparing Cements Cement A Cement B C3S (%) 57 59 C2S (%) 13 15 C3A (%) 7 4.6 Blaine Fineness m2/kg 405 342 Equivalent alkalies 0.71 0.40 3-day cube strength (psi) 4,240 3,760 7-day cube strength (psi) 5,800 4,690 141 160 Initial Vicat (minutes) Supplementary Cementitious Materials • Fly Ash – ASTM C 618 – AASHTO M 295 • Slag – ASTM C 989 – AASHTO M 302 • Silica Fume – ASTM C 1290 Requirements for Concrete Exposed to Deicing Chemicals Cementitious Materials Max. Percent of Total Cementitious Materials by Weight Fly Ash or other pozzolans conforming to ASTM C 618 25 Slag (ASTM C 989) 50 Silica Fume (ASTM C 1240) 10 Total fly ash or other pozzolans, slag, & silica fume 50 Total of fly ash of other pozzolans & silica fume 35 ACI 318 – Table 4.3.1 Water Properties • Drinkable or Potable • No pronounced taste or odor • Excessive impurities will affect setting time and concrete strength Water Cement(itious) Ratio W Cm • The weight of water in the mix (not including the water absorbed by the aggregate • The weight of cement(itious) material in the mix Influence of W/CM on Strength and Permeability W/CM ratios for exposure conditions ACI 318 Recommended W/CM for strength ACI 211 Compressive Strength, psi W/CM alone does not control strength 8000 Mix 1 7000 Mix 2 6000 Mix 3 5000 4000 3000 2000 1000 0 0.40 0.45 0.5 0.55 0.6 0.70 Water-Cementitious Ratio (w/cm) Source: ACI 211 Charge Passed, Coulombs W/CM alone does not control permeability 8000 Portland cement 7000 SCM1 SCM2 6000 Ternary Blend 5000 4000 3000 2000 1000 0 0.70 0.55 0.45 Water-Cementitious Ratio (w/cm) Source: ACI 232, 233, 234 Not all W/CM ratios are equal Air Air Water Cement Paste Water Cement Significance of Aggregates in the Concrete Mixture • Represent 60% to 80% of the concrete volume • Represent 70% to 85% of the concrete weight Aggregate Properties • Two categories: Fine & Coarse Aggregate • Inert granular materials • Clean, Hard, Abrasion resistant, and Free of deleterious materials Aggregate Properties • Meet requirements of ASTM C 33 • History • Grading – particle size distribution Significance of Grading • No Deficiency of One Size • No Excess of One Size • Gap Grading • More Paste for a Workable Mix Good Grading Reduces Voids Results of Gap Grading CONTINUOUSLY GRADED MIXTURE No. 4 & 8 GONE INCREASED MORTAR TO FILL VOIDS Dispersion of Aggregates Aggregate Size Maximum Aggregate Size • 1/5 the minimum dimension between formed surfaces • 1/3 the thickness of the slab • ¾ the minimum clear spacing between reinforcing bars • ¾ the minimum clear cover between rebar and forms Aggregates must be resistant to freezing and thawing damage Aggregates must be non-reactive (unless steps are taken to mitigate) Weathering Probability Map ASTM C 33 Design Air Content • Air in the mix provides resistance to freeze/thaw damage Will the concrete mix meet the required strength? Will the concrete mix meet the required strength? f’c Specified Strength The strength the concrete needs to be to assure structural requirements are met. f’cr Required Average Strength The average strength of the concrete to ensure that “no” tests fall below the specified strength. Number of Tests f’c f’cr 5 0 Compressive Strength, psi Proportioning from Field Data Equation A: f'cr = f'c+ 1.65*k*s Equation B: f'cr = (f'c-500) + 2.33*k*s f’c = specified 28-day compressive strength s = standard deviation of test data k = constant based on number of data points n = number of data points k = 1.3 – n/100 where 15<n<30 k=1 where n>30 Proportioning from Field Data Specified Strength, f'c Required Average Strength, f'cr <3000 psi f'c + 1000 3000-5000 f'c + 1200 >5000 f'c + 1400 ACI 318 Documentation of Average Strength • Test record must contain at least 10 consecutive tests encompassing a period of time of not less than 45 days. • Shall represent materials, quality control procedures, and conditions similar to those expected ACI 318 Proportioning by Trial Mixtures • Three cylinders are cast from each of at least three trial mixtures at different w/c ratios using materials, proportions, and consistencies required for the job. Compressive Strength (PSI) Proportioning by Trial Mixtures 6500 6000 5500 5000 4500 4000 3500 3000 0.3 0.35 0.4 w/cm 0.45 0.5 Design Slump Placement Method Concrete Admixtures Admixture Check • Review manufacturer’s technical data sheet • Description – Type, applications, features, benefits, etc. • Check chloride content • Check dosage rates and compare to design • How does admixture affect setting times, air content, slump loss, etc. • Can it be added onsite? If so, how many times? • Call technical representative for more info ASTM C 94 Requirements • Cement and other Cementitious Materials ± 1% (0.3% scale capacity for small loads) • Aggregate ± 2% for individual batchers (0.3% scale capacity for small loads) ± 1% for cumulative batchers (0.3% scale capacity for small loads) • Water ± 1.5% or ± 1 gallon (whichever is greater) • Admixtures ± 3% or minimum dosage (per 100 lb. Cement) NRMCA Plant Certification Aggregate Absorption Oven Dry None Air Dry Less than potential absorption Saturated, Surface dry Damp or wet Equal to potential absorption Greater than absorption Moisture Correction In Summary • A good mix design is one that meets the owners requirements and satisfies the contractor’s need to place and finish. • There is not one perfect mix for every application. • A mix should be tested to verify that the requirements are being met. • The batch ticket provides assurance that the approved mix was provided. Any Questions?