Colored Concrete Pavements: Are They Here To Stay?

Transcription

1 Colored Concrete Pavements: Are They Here To Stay? 18 th Annual TERRA Pavement Conference February 5 th, 2014 Tom Burnham, P.E. Minnesota Department of Transportation Office of Materials and Road Research

2 Acknowledgements Ally Akkari Co-Principal Investigator- (formerly MnDOT) Gerard Moulzolf, Willy Morrison American Engineering Testing, Inc. Larry Sutter Michigan Tech University Steve Olson, John Pantelis, Eric Plemel MnDOT Funding provided by LRRB

3 LRRB Investigation 929 Investigation and Assessment of Colored Concrete Pavement 2 year study ( ) Principal Investigator(s): Tom Burnham MnDOT Ally Akkari (formerly MnDOT) Subcontractor American Engineering Testing, Inc. Gerard Moulzolf Willy Morrison Larry Sutter (Mich Tech)

4 Colored Concrete Why use it on or near roads? Architectural effects: Streetscaping Safety: Delineation

5 Streetscaping

6 Delineation

7 Looks great!...but colored concrete pavements cost more! Are they here to stay? Unfortunately, there s TROUBLE brewin

8 And it s called: Early Distress

9 Cty Hwy 14, Main Street, Centerville

10 Hwy 96, Vadnais Heights

11 Some Low Profile Locations

12 Potential Causes Construction practices Hand placement Over-finishing surface Lack of proper curing Materials related reduction in durability Low air content (less freeze/thaw resistance) Low strength (poor paste-to-aggregate bond?) Pigment related incompatibilities

13 Potential Causes Chemical attack Deicing chemicals Pigment reactions Project design Slow drainage and minimal slopes Loss (or lack) of joint sealant

14 Project Tasks Phase 1: Locate projects throughout Minnesota Investigate extent of problems Observe construction practices Preliminary petrographic analysis Phase 2: Further investigate preliminary findings related to material distress (lab study) Recommendations for specifications, repairs, and alternatives

15 Phase 1 Findings

16 Observations of Performance Good to poor Many projects recently completed Distresses focused on joint regions Some cracking due to thermal expansion restraint Smooth surface textures Plow damage

17 Good Performance Benton Dr and 2 nd St, Sauk Rapids (Built 2007)

18 Not So Good Performance Cty Rd 14, Main Street, Centerville (Built 2008)

19 Cty Hwy 14, Main Street, Centerville

20 Secondary Ettringite

21 Alkali Silica Reaction

22 Petrographic Analysis Results Concentrated micro-cracking through the depth of the joints A poor bond between paste and aggregate High water to cement ratios (up to 0.50) Paste has high porosity Initially adequate hardened air content system System now filled with secondary ettringite near joints, significantly reducing freeze/thaw resistance Surprising presence of ASR near aggregates typically used for concrete in Minnesota Chemical alteration of paste Possible chemical attack

23 Phase 1 Conclusions Construction practices not principal cause of observed distress Mix designs must be improved High w/cm = very porous concrete Focus further on materials related distress Pigment related incompatibilities? What s causing ASR? Cause for chemical attack?

24 Phase 2 Further Investigation of Distress Chemical analysis of pigments Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectrometry (EDX) analysis of core samples Assemble trial mixes to investigate effect of pigment volume and w/cm on durability Investigate potential for thermal expansion distress

25 Chemical Analysis of Pigment

26 SEM Image Green = Iron Blue = Magnesium

27 SEM Image Green = Iron Blue = Magnesium

28 SEM Image Green = Iron Blue = Magnesium

29 Summary of SEM Investigation Magnesium chloride solutions are permeating the concrete, likely as a result of deicer exposure Appears to be strong evidence of paste dissolution There appears to be an affinity for iron by magnesium ions

30 Summary of SEM Investigation Good evidence the fine aggregate is reacting in the presence of the magnesium and undergoing partial dissolution Some fine aggregates are dissolving and could be resulting in an increased alkali loading of the concrete Increased potential for alkali-silica reaction (ASR)

31 Freeze/Thaw Durability Lab Mix, SSD (pcy) (1) Mix #1-Control- No pigment w/cm Mix #3-Pigment 4% w/cm Mix #3-Pigment 4% w/cm Mix #4-Pigment 6% w/cm Lafarge Davenport (lbs) Portage Fly Ash (lbs) Lakeville +3/4", Coarse Aggregate. (lbs) Lakeville -3/4", Coarse Aggregate. (lbs) Lakeville -1/2", Coarse Aggregate. (lbs) Lakeville Fine Aggregate (lbs) Water (lbs) Vinsol Resin, Air Entrainer (oz/cwt) Pigment, % by weight of cementitious Water to Cementitious Ratio Fresh Properties Unit Weight, pcf Slump (in) Air Content (%) Average (2) ASTM C666, Rapid Freezing and Thawing, Proc. A, Relative dynamic modulus, % 300 Cycles Notes: (1) Mix design provided by MnDOT. Mix identified as "Mix 3A21 HEF" July Mix adjusted for higher water to cementitious requirements of this study. (2) Average of three 3x3x11-1/4-in beams.

32 ASR Testing ASTM C1567 Test Results for Coarse Aggregate, % Expansion % Expansion Mix #1-Control-0.43 w/cm Mix # w/cm; Pigment 4% Mix # w/cm; Pigment 4% Mix # w/cm; Pigment 6% days 7 days 11 days 14 days 21 days 28 days Time, days

33 ASR Testing ASTM C1567 Test Results for Fine Aggregate, % Expansion % Expansion Mix #1-Control-0.43 w/cm Mix # w/cm; Pigment 4% Mix # w/cm; Pigment 4% Mix # w/cm; Pigment 6% days 7 days 11 days 14 days 21 days 28 days Time, days

34 Phase 2 Investigation of Thermal Performance Observation of distress likely caused by thermal expansion

35 Thermal expansion distress

36 Thermal expansion distress

37 Cast instrumented test slabs at MnROAD Light Red Dark Brown

38

39 Test Slab Results Light red slab on average 5% warmer than non-colored slab Dark brown slab on average 35% warmer than non-colored slab Darker slabs will expand more for a given change in air temperature Need to be cognizant of potential for thermal incompatibilities when placing colored and non-colored concrete sections next to each other

40 Phase 2 Conclusions Early distress is occurring in several locations Placement practices have not been deemed to be the primary cause for the distress High porosity (high w/cm ratio) mixes are susceptible to intrusion by deicing chemicals Must consider thermal compatibility with surrounding areas Chemical attack and ASR has been identified in both field samples and lab produced mixes

41 Recommendations Limit use of magnesium-based deicers on colored concrete Decrease porosity of mixes via a low w/cm ratio (0.40) Investigate whether ASR mitigation possible (higher % Class F flyash?) Consider alternative ways to produce colored concrete (other than full-depth color) Surface staining Pavement surface marking products

42 What s next? Draft final report to be released by early March 2014 (Tech Brief available in lobby) Recommended construction specifications Repair techniques Alternative coloring solutions Final report available June 2014 Solicit interest in Phase 3 to further investigate causes of distress and solutions for mitigation and repair?

43 Questions? Office of Materials and Road Research