Real Solutions for Concrete Mix Design

Transcription

1 oncrete onference, Oct Real Solutions for oncrete Mix Designs Real Solutions for oncrete Mix Design Either you re part of the solution, or you re part of the problem. -Eldridge leaver Pogo Know your needs Write your spec Strength Shrinkage Permeability Freeze-thaw resistance Abrasion resistance ASR resistance Sulfate resistance Specs in balance oncrete is Part of a System No cracks Low permeability Low w/cm Higher cost Greater shrinkage More heat Higher cement 1

2 oncrete onference, Oct Real Solutions for oncrete Mix Designs He that is good with a hammer tends to think everything is a nail. THOU SHALT HAVE A LOW WATER- EMENT RATIO. - Abraham Maslow How did they get 0.26 w/c? PA Bulletin 29 The Nonevaporable Water ontent of Hardened Portland- ement Paste T Powers Grind a cement sample in water for 4-5 days Mix a small bit of cement in a large volume of water Results of a low w/c Add more cement Generate more heat More thermal expansion More autogenous shrinkage More cracking Greater alkalis (ASR potential) Higher cost Less sustainable concrete W/ vs. Strength DM 2 We have found no pavement failures in the U.S. due to low concrete strength. 2

3 oncrete onference, Oct Real Solutions for oncrete Mix Designs ement efficiency Plain cement ement + Ash ement + Admix ement + Admix + Ash What problems do we face? racking Sulfate attack hloride attack ASR Freeze-thaw Abrasion Types of cracking Plastic shrinkage (bleeding & evaporation) Drying shrinkage (excess water) Differential moisture shrinkage (curling) Thermal shrinkage Differential thermal shrinkage Autogenous shrinkage D-cracking Stress cracking Drying shrinkage Water has 2 purposes ombine with cement Lubricate the mix Drying shrinkage excess water Total water is the key urling finer mixes slow bleeding Increasing cement can increase thermal and autogenous shrinkage Keys to decreasing water WATER DEMAND Admixtures are a partial solution (can increase shrinkage) Increase maximum aggregate size Soft aggregate / cleavage planes D-cracking Increase coarse aggregate Optimize aggregate grading (particle shape and texture affect water demand) 3

4 oncrete onference, Oct Real Solutions for oncrete Mix Designs RESULTS OF GAP GRADING HAYSTAK - Optimum Graded Mix olorado Bridge Deck Wisconsin Univ/DOT Research Optimized Aggregate onclusion Wisconsin DOT/Univ Effects of particle distribution on segregation ompressive strength - plus 10 to 20% Air entraining agent - minus 20 to 30% Potential water demand - minus 20 to 30% Potential high spacing factor for air voids Reduced segregation and higher density following extended vibration 4

5 oncrete onference, Oct Real Solutions for oncrete Mix Designs 8/18 Grading Spec Effects of Aggregate Grading on Drying Shrinkage of Florida oncretes I article, March Mcall, King, Whisonant Using the 8-18 rule doesn t always result in concretes with minimal shrinkage Well graded aggregate mix containing 670# of angular manufactured screenings compared to gap graded mixes Strengths and shrinkage comparable on all mixes Use a variety of methods W / R a t i o Percent coarse aggregate P S I Thermal cracking Increasing cement increases heat Early morning placement can cause problems in hot weather (Hiperpave) Avoid high temperature differentials 5

6 oncrete onference, Oct Real Solutions for oncrete Mix Designs Autogenous shrinkage ement + Water => smaller product Increasing cement increases autogenous shrinkage Accelerating strength gain will accelerate autogenous shrinkage (heat, admixtures) Permeability-related related distress w/c is not the full answer to reducing permeability Total water is a major factor Secondary reactions can reduce permeability New generation of admixtures Hydration of Portland ement Hydration of Portland ement ement + Water -S-H + a(oh) 2 + Other Pozzolanic Reaction in oncrete Effect of Pozzolanic Reaction a(oh) 2 + Pozzolan more.. -S-H 6

7 oncrete onference, Oct Real Solutions for oncrete Mix Designs Marin Airport, PR RP variations 28 day Examine the combined mix sk 6 sk 7.5 sk 6 sk + mfg sand ement em + ash em + air Alkali Silica Reactivity ASR Requirements Reactive silica High alkali pore solution Moisture Increasing cement increases alkalis Adding lass F fly ash or GGBFS can reduce ASR Lithium can mitigate ASR Freeze-Thaw Resistance Original studies show need for 9% air as a percent of mortar or 16% air in paste Air void spacing is critical Air Void Analyzer has shown importance of bubble sizes FT damage is a function of paste and aggregate permeability Does P need air entrainment? A PA publication contains the results of tests on high-strength concrete for frost and scaling resistance. All tests were made on concretes with portland cement as the only cementitious material. Durability factors [for freeze-thaw] close to 100 were only achieved without air entrainment when the water-cement ratio was equal to or less than Resistance to scaling of non-air-entrained concrete was only achieved when the watercement ratio was reduced to Air loss in concrete Losses of 3-5% reported behind paver or after pumping Segregation of concrete during placement and at vibrator trails Wisconsin DOT reports well-graded aggregate mixes tend to segregate less Ohio DOT reports well-graded aggregate mixes tend to lose less air 7

8 Nevada Infrastructure oncrete onference, Oct Real Solutions for oncrete Mix Designs Abrasion resistance IAR Study - High fines manufactured sand Proposed revision to ASTM -33 Allow up to 18% passing #200 Dust of fracture only an increase strength, decrease permeability Requires increased Super-P dosage Particle shape critical oncrete & Sustainability Reducing oncrete oncrete s Impact on Sustainability onsider entire life cycle Minimize impact on: Environment & Natural Resources urrent practices provide no incentive for innovation in fact, they stifle innovation. Economics Aesthetics & Human Factors ement production impact Transportation and processing impact 8

9 oncrete onference, Oct Real Solutions for oncrete Mix Designs LEED & sustainability efforts AI (SD) NRMA (Green Star program) PA APA FHWA oncrete Roapmap Improve sustainability Reduce cementitious contents Allow more recycled pozzolans Allow better use of local aggregates Incorporate recycled crushed concrete and reclaimed fresh concrete Encourage innovations Improve our understanding of concrete Pigments Pigments Shift to Performance Strength Modulus of elasticity Durability Low shrinkage/cracking Workability Stability & uniformity Protect reinforcing steel 9

10 oncrete onference, Oct Real Solutions for oncrete Mix Designs JEDDAH INTERNATIONAL AIRPORT Severe mix segregation due to use of aggregate grading standards in a region for which they were not suited. Blind Men & the Elephant Traditional methods causing problems Fixed weights of variable materials result in a variable product. Design of oncrete Mixtures D.A. Abrams, Lewis Inst. Bulletin 1 It is a matter of common experience that the method of arbitrary selection in which fixed quantities of fine and coarse aggregates are mixed without regard to the size and grading of the individual materials is far from satisfactory. SmartPlant: The Next Generation Fixed weights vs. Adjusted SmartPlant Materials Statistics onstruction Maturity Aggregates ement Fly Ash Admixtures 10

11 oncrete onference, Oct Real Solutions for oncrete Mix Designs For a copy of this presentation, go to