Internal Curing. A National Perspective on Recent Developments

Transcription

1 Internal Curing 1 A National Perspective on Recent Developments 47 th Annual Mid Atlantic Quality Assurance Workshop Concrete Session February 5, 2014 Reid W. Castrodale, PhD, PE Expanded Shale Clay and Slate Institute

2 Outline 2 Introduction ACI 308/213 Report ASTM C1761 Desorption Wetted Surface Dry Condition States where IC has been used Two Examples of Field Applications Specifications / Special Provisions for IC

3 Internal Curing 3 Internal curing is: modifying a conventional normal weight concrete mixture to provide internal curing of the concrete by replacing a portion of the normal weight fine aggregate with prewetted fine or intermediate lightweight aggregate. ESCSI Guide Specifications for Internally Cured Concrete

4 Internal Curing 4 Internal curing is: modifying a conventional normal weight concrete mixture to provide internal curing of the concrete by replacing a portion of the normal weight fine aggregate with prewetted fine or intermediate lightweight aggregate. ESCSI Guide Specifications for Internally Cured Concrete

5 Internal Curing 5 Internal curing using prewetted lightweight aggregate (LWA) is: Not a new concept It has been known for years Not a new type of concrete It is a modification of NWC Not lightweight concrete (LWC) Density is reduced slightly, but that is not the goal

6 Internal Curing 6 Prewetted LWA is simply used as a method to provide curing water from within the concrete to improve the properties of concrete Prewetted LWA is being used like an admixture

7 ACI 308 / 213 Report 7 Report on Internally Cured Concrete Using Prewetted Absorptive Lightweight Aggregate ACI ( )R 13 (June 2013) Report was a joint effort of ACI 308 Curing Concrete Committee ACI 213 Lightweight Aggregate & Concrete Committee

8 ACI 308 / 213 Report 8 Overview: Introduces the concept of using prewetted LWA to increase cement hydration in internally cured concrete Describes the process benefit and applications of internal curing (IC) Describes mixture proportioning and absorptive material selection Discusses benefits relating to sustainability

9 ASTM C Standard Specification for Lightweight Aggregate for Internal Curing of Concrete ASTM C1761/C1761M 12 (August 2012) Requirements for LWA used to provide water for internal curing (IC) of concrete Test methods for absorption & desorption Recognizes IC with LWA as a source of water to sustain hydration and substantially reduce the early age autogenous shrinkage and selfdesiccation that can lead to early age cracking

10 ASTM C Appendix provides expressions based on the Bentz equation for calculating: The quantity of LWA required for IC The quantity of NWA replaced by LWA

11 ASTM C Quantity of LWA required for IC depends on Total cementitious materials content (C f ) Chemical shrinkage (CS) Desorption of LWA (W LWA ) This is the science More simplified approaches have also been used

12 Desorption 12 Definition in ASTM C1761 Relative quantity of absorbed water that prewetted LWA can release for IC Desorption < Absorption Desorption is typically 85 98% of absorption Example: Absorption = 20% (% of OD mass) Desorption = 0.18 (C1761 Appendix) or Desorption = 90% (more typ. usage % of absorbed water released)

13 Desorption 13 Pores Available for Internal Curing Pores Absorbed Water Pores Desorbed Water Solid Solid Solid Absorbed Water not released for Internal Curing Oven Dry, M OD Wetted Surface Dry, M SD Equil. at 94% RH, M 94

14 Wetted Surface Dry Condition 14 LWA is in the wetted surface dry condition (WSD) after: the prescribed soaking period and the removal of surface moisture Analogous to saturated surface dry condition (SSD) for normal weight aggregate But LWA particles do not reach max. absorption (saturation) even after soaking for 72 hours From ASTM C1761 Section

15 Wetted Surface Dry Condition 15 Consistently getting LWA fines to the wetted surface dry condition can be challenging Currently available methods NYS DOT Test Method No.: NY E Brown paper towel method Can be done in field, but some variability Centrifuge method new approach ACI Appendix B More consistent more operator independent INDOT & Purdue are working on std method

16 Wetted Surface Dry Condition 16 Surface moisture on the LWA must be known so corrections can be made to batch water Absorption of LWA must be known to compute the weight of WSD LWA required to provide the desired quantity of water for IC Absorbed water DOES NOT affect mixing water Absorbed water is released from the LWA only after hydration has begun

17 Some DOTs that have used IC 17 Illinois (Tollway) Bridge decks Indiana Bridge decks Iowa Bridge decks New York Bridge decks Texas Pavements Bridge deck Utah Bridge decks Virginia Bridge decks Ontario, Canada Bridge Decks

18 Field Experience with IC 18 Denver Water Company Lonetree Basin Tank #2 10 M gallon Concrete Water Storage Tank

19 Field Experience with IC 19 Test pour for water tank Highlands Ranch, CO Internal Curing vs. No Internal Curing Concrete placed at 92 F air temp. & 20% RH No conventional curing With internal curing Without internal curing One day after placement

20 Field Experience with IC 20 Indiana DOT Test Slabs constructed in 2010 No difference in finishing was reported Slab without IC cracked after a few months Slab with IC had no visible cracks after 1 year

21 Field Experience with IC 21 Indiana DOT Test Slabs constructed in % +75% +25% Di Bella, et al., Documenting the Construction of a Plain Concrete Bridge Deck and an Internally Cured Bridge Deck, Report TR , IN LTAP Center, June 2012

22 Special Provisions & Guide Specs 22 Several approaches have been used Use the Bentz approach to compute quantity of LWA based on desorption (ASTM C1761) Use a simplified approach that assumes some of the inputs for the Bentz approach (ESCSI calculator on website) Use a very simple approach that specifies the replacement fraction of NWA and minimum absorption of LWA (NYS DOT specs) LWA suppliers can provide additional guidance

23 23 Thank you For more information on Internal Curing using LWA Reid W. Castrodale, PhD, PE