Internal Curing of Pervious Concrete using Lightweight Aggregate
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The document discusses using prewetted lightweight aggregates for internal curing of pervious concrete. It finds that mixtures containing fine lightweight aggregate had better workability, similar moisture loss, higher strength, improved freeze-thaw durability, and less shrinkage compared to a control mixture without lightweight aggregate. The degree of hydration was also significantly increased, demonstrating that lightweight aggregates can effectively provide internal curing to pervious concrete.
Internal Curing of Pervious Concrete using Lightweight Aggregate
- 1. Internal Curing of Pervious Concrete using Lightweight Aggregate John Kevern and Daron Brown Pervious in Paradise 2014
- 2. The Good Stuff About Pervious • Reduces stormwater volume • Cleans stormwater • Reduces the urban heat island • Quiet • Slip resistant
- 3. The Bad Stuff About Pervious • The mix is different • Not as many/improperly used standards • Has to be cured under plastic • It clogs • It ravels 11/2/2015:3
- 4. Motivation • Internal curing using a super absorbent polymer has shown beneficial to pervious concrete properties • Internal curing is commonly performed using prewetted lightweight fine aggregate in conventional concrete
- 5. Water to Cement Ratio Cement Hydration Products Interlayer gel water water Chemical Shrinkage Excess WaterExcess Cement
- 6. Internal Curing for Concrete • Concrete needs water for hydration • At w/c 0.42 and below self-desiccation (autogenous shrinkage) causes significant internal stresses • Supplying external water to low w/c mixes only impacts the surface
- 7. Internal Curing for Concrete • Supplying additional water internally can mitigate shrinkage stresses in low w/c mixtures • Saturated lightweight aggregates, saturated porous aggregates, super absorbent polymers can supply this extra internal water
- 8. Study Scope • Determine if prewetted lightweight aggregates can provide internal curing to pervious concrete
- 9. Study Mixtures • Control mixture had 7% fine aggregate by volume • 100% of the conventional fine aggregate volume was replaced with lightweight fine aggregate • Admixtures were air, HRWR, and hydration stabilizer *All samples individually placed to control voids at 25% Cement Coarse Aggregate Fine Aggregate Water (pcy) SSD (pcy) SSD (pcy) (pcy) PC(Control) 573 2214 164 195 PC- BDX (BuildexFines) 573 2214 126 (WSD) 195 PC- HPB(Hydraulic Press Brick Fines) 573 2214 145 (WSD) 195 PC- BRF (Big River Fines) 573 2214 98 (WSD) 195 PC- LW (AllHydraulic Press Brick) 573 1127 (WSD) 145 (WSD) 195 Mixture Abs % 16% 19% 39% 11%
- 10. Tests • Unit weight (ASTM C1688 and ASTM C1754) and voids (ASTM C1754) • Moisture loss • Strength • Permeability and infiltration • Freeze thaw durability • Shrinkage • Degree of Hydration
- 11. Moisture Loss (ASTM C156) • 9” x 13” x 2” samples • Moisture loss over 72 hrs at 100°F and 32% relative humidity
- 12. Freeze-Thaw Durability (ASTM C666a)
- 13. Ring Shrinkage (ASTM C1581) Measures strain on inside steel ring
- 14. Results – Basic Properties Fresh Unit Weight ASTMC1688 Avg. (pcf) Avg. (pcf) COV(%) Avg. (%) COV(%) Avg. (in./hr) COV(%) PC (Control) 121.8 116.8 0.4 25.9 2.7 1680 7.8 PC - BDX (BuildexFines) 127.8 113.5 0.1 23.3 3.4 1080 31.1 PC - HPB (Hydraulic Press Brick Fines) 128.8 112.9 0.1 27.6 1.0 1200 18.0 PC - BRF (Big River Fines) 124.6 113.7 0.1 30.3 5.0 1320 49.4 PC - LW (All Hydraulic Press Brick) 76.4 63.3 0.3 42.8 0.9 4600 5.5 Voids ASTMC1754 Permeability ASTMC1754 Mixture HardenedUnit Weight ASTMC1754
- 15. Results – Moisture Loss
- 16. Results – Degree of Hydration
- 17. Results - Strength 0 500 1000 1500 2000 2500 3000 3500 PC PC-BDX PC-HPB PC-BRF PC-LW CompressiveStrength(psi) 7-day 28-day
- 18. Results – Freeze Thaw
- 19. Results – Freeze Thaw
- 21. • Mixture containing prewetted fine lightweight aggregate had better workability than the control as indicated by greater fresh density. • Moisture loss from mixtures containing prewetted fine lightweight aggregate was similar to the control samples. • All lightweight aggregate tested produced significant increases in the degree of hydration over the control mixture. Performance was similar between the aggregate types at 28 and 90 days. Summary and Conclusions
- 22. • Samples containing fine prewetted lightweight aggregate as a replacement for conventional sand had similar compressive strengths to the control mixture at 7 days. At 28 days the fine aggregate samples all were stronger than the control. • Prewetted lightweight aggregate improved freeze- thaw durability. Performance was directly related to the amount of additional pore space provided within the lightweight particles. • All samples containing lightweight aggregate had significantly less shrinkage than the control mixture in ring shrinkage testing. Summary and Conclusions
- 23. Contact Information John T. Kevern, PhD, PE, LEED AP Associate Professor of Civil Engineering 370A Flarsheim Hall, 5110 Rockhill Rd. University of Missouri – Kansas City Kansas City, MO 64110 Phone: 816-235-5977 Fax: 816-235-1260 Email: kevernj@umkc.edu