Mark B. Snyder, Ph.D., P.E., Pavement Engineering and Research Consultants, LLC (PERC) Bridgeville, Pennsylvania ACPA Mid-Year Meeting Workshop June 13, 2017
A Hallmark of good concrete pavements 50-year-old (and TH10 near St, Cloud, MN; 9” PCC Constructed 1952 older) PCC pavements are common ◦ CA, TX, NY, IA, MN, ON Belknap Place San Antonio, TX 1914 Construction
Service life of original PCC surface = 50+ years (SHRP2 Definition) No premature failures or materials-related distress Reduced potential for cracking, faulting, spalling, etc. Maintain desirable ride and surface texture characteristics with minimal M&R Design and Build it Right & Stay Out As Long As Possible
A combination of materials, mix design, structural design, and construction activities selected and implemented to ensure acceptable long-term pavement performance. It’s A System!
Concrete durability problems ◦ “D” -cracking, ASR, freeze-thaw damage, deicing chemical attack, etc. Joint failures ◦ Dowel corrosion or misalignment ◦ Faulting and Spalling ◦ Mid-panel crack deterioration Construction issues ◦ Foundation settlement, sawing errors, over-finishing, etc. Fatigue failures are rare …
Address each potential failure mechanism in design and/or construction specifications.
Address each potential failure mechanism in design and/or construction specifications ◦ Structural (layer materials and thicknesses, panel dimensions, dowel size and spacing, etc.) ◦ Materials Concrete (mix proportions, air void system, permeability, aggregate durability, etc.) Steel (corrosion protection) Foundation (drainage, erosion-resistance, etc.) ◦ Construction (compaction, curing techniques/materials and timing, sawing, surface texture design/construction, dowel alignment, etc.)
80 Std Design 70 Expected Performance LIfe, Years 60 50 40 30 20 10 0 Slab Dowel Concrete Concrete Construction Foundation Drainage Thickness Corrosion Aggregate Matrix Dur. Parameters Support Parameters Resist Dur.
• Match performance potential for design components (strengthen “weak links”) • “Cafeteria” approach may not produce LLCP LLCP requirements are project-specific!
80 Std Design Improved Design and Construction Specs 70 Improved Materials Expected Performance Life, Years Improved Des, Matls & Const 60 50 40 30 20 10 0 Slab Dowel Concrete Concrete Construction Foundation Drainage Thickness Corrosion Aggregate Matrix Dur. Parameters Support Parameters Resist Dur.
Increased Slab Thickness ◦ Old “rule of thumb”: 1 add’l inch PCC doubles ESAL capacity ◦ But … PCC thickness may not be controlling design life! PavementME analyses indicate no added structural benefit above 13 – 13.5 inch pavement thickness for current design loads Control Panel Dimensions ◦ Curl/warp stresses increase with panel size ◦ Old “rules of thumb”: Max panel dimension = 18-24*thickness Max aspect ratio (L/W or W/L) = 1.5
Slab sizes and thicknesses for same top stress (350 psi) Thickness: 6.3 inches PCC Thickness: 10 inches PCC Slabs: 5.9 ft x 5.9 ft Slabs: 14.8 ft x 11.8 Source: TCPavements
DURABILITY ◦ Concrete aggregate (quality and grading) ◦ Cement paste (reduced permeability) w/(c+p) Use of SCMs Increased air content Corrosion-resistant dowel bars
Must be highly durable ◦ DF > 90 (AASHTO T161 Proc A) ◦ ASTM C1260 dilation < 0.8 percent Angular, rough-textured, abrasion-resistant ◦ Improved interlock, enhanced paste bond, durable in construction Photo Credits: PCA Graded (with fine aggregate) to minimize paste content ◦ Reduced permeability and shrinkage Low absorption, low CTE preferred ◦ e.g., basalt, granite, some limestones, etc.
Resistant to AAR (ASTM C1260 dilation < 0.8%) Graded (with coarse aggregate) to minimize paste content ◦ Reduced permeability, shrinkage >30 percent siliceous sand for microtexture Low absorption preferred Photo Credit: PCA
Maximum 500 lb/c.y. cementitious content (with properly - graded aggregate blend) ◦ Volumetric stability ◦ Reduced potential for chemical attack Source: Peter Taylor/National Concrete Pavement Technology Center Fly ash to reduce permeability and water bleeding, increase long-term strength ◦ Typically 15 – 25 percent replacement of cement ◦ Class F for ASR mitigation Consider GGBFS for ASR mitigation, early strength gain
Reduce allowable w/(c+p) for higher strength, lower permeability ◦ PennDOT: 0.40 target, 0.42 max ◦ MnDOT: 0.40 max with incentives down to 0.37 Use Supplemental Cementitious Materials (SCMs) to densify paste ◦ Higher strength ◦ Reduced permeability Source: Portland Cement Association
Ho How SCMs w SCMs Wor ork Cement Ceme nt C-S-H + + = = more C-S-H CH CH Wate ter + SCM + + SCM + Wate ter (w/c = 0.365, RCP: @ 28 days) 9000 8000 7000 RCP (Coulombs) 6000 5000 4000 3000 2000 1000 0 Class F Class C1 Class C2 GGBFS All fly ash 25% replacement, GGBFS 35% Source: National Concrete Pavement Technology Center
Increase plastic air content ◦ Standard: 6.5% +/- 1.5% ◦ HPCP: 8.5% +/- 1.5%. Require 28-day RCP of <2500 coulombs. W/(C + P) < 0.40 (incentive to 0.35) Require minimum 30 percent siliceous fine aggregate (microtexture/friction) Optimize total aggregate grading ◦ “ Shilstone ” approach ◦ 0.45 Power gradation ◦ 8-18 /7-18 grading bands
Must be highly corrosion-resistant Structural design must provide: ◦ Good load transfer ◦ Sufficiently low bearing stress ◦ Sufficiently low overall and differential deflection Many possibilities: ◦ 316L stainless steel (solid, clad, sleeved or tubes) ◦ Zinc alloy-clad or – sleeved steel ◦ FRP-clad steel ◦ Low carbon, high-chrome composite ◦ Special epoxy-coated steel ◦ FRP (requires larger bars and/or closer spacing for equivalent behavior)
Minnesota’s program includes all areas of construction Program applies to the entire industry (agency, contractors and consultants alike)
Photo credit: PCA Certification of batching equipment Pre-qualification of contractor INSPECT, INSPECT, INSPECT ◦ Flexural strength ◦ Air Content ◦ Unit Weight ◦ Water/cementitious ratio ◦ Thickness ◦ Smoothness ◦ Dowel alignment Photo credit: ACPA ◦ Field operations
Certified batch plants and operators ◦ Stockpile moisture management Adequate number of trucks to ensure concrete is fed to paver at consistent and useful rate. ◦ Avoid paver stops/starts. Control delivery time, mix temperature. Never allow retempering!
Don’t Add Excess Water Adding 1 gal. of water to 1 yd 3 of concrete: Increases slump 1 in. • Decreases compressive strength by 200 psi • Wastes the effect of 1/4 sack of cement • Increases shrinkage by 10% • Increases permeability by up to 50% • Increases risk of air void • problems Cons Constr truc uction tion
Microwave Oven Testing of Water Content in Freshly Mixed Concrete – AASHTO T 318
Need proper and timely curing with effective process PAMS curing compounds were developed to be used in applications requiring extremely durable concrete ◦ Originally developed to replace the old chlorinated rubber curing compounds, which are no longer manufactured Offers better water retention than current resin and wax technologies (Minnesota Study: up to 5x more effective!) Offers improved sealing characteristics for additional protection Concrete cured with PAMS has increased abrasion resistance, hardness, resistance to de-icing chemicals Source: W.R. Meadows
◦ Timeliness is essential ◦ Consider use of HIPERPAVIII) Photo credit: PCA ◦ Proper depth (consider section thickness variance)
Benefits: ◦ Significant extension of service life ◦ Reduction of maintenance/rehabilitation frequency ◦ Reduced LCC Initial Costs ◦ 3 – 16 percent of paving costs ◦ Much lower percentage of project costs (considering R.O.W., noise walls, adjacenet structures, traffic control, etc.)
Total project cost ~ $18.4M Total paving cost ~ $3.7M (20.1% of project cost) Incremental cost of HPCP ~ $610,000 ◦ 16.5 percent of paving costs ◦ Only 3.4 percent of project costs! Mn/DOT economic analysis: ◦ LCCA of HPCP = 5% lower than conventional concrete pavement ◦ This doesn’t include user cost savings – potentially huge!
LLCP design and construction can be accomplished with the knowledge and tools that we already have! Structural design for desired traffic loading over performance period Materials design for durability (resistance to exposure) All design components must meet performance requirements (no “weak links”) QA/QC is essential (more intense effort required) Examples: MN, WI, PA, CA (and more …)
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