LADOTD Specifications on ASR/ACR

Transcription

1 LADOTD Specifications on ASR/ACR Presented by: Brandon M. Johnson, P.E. Justin Morris, P.E.

2 LADOTD Specification on ASR/ACR Alkali Silica Reactivity (ASR) is a swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive silica found in many common aggregates, given sufficient moisture.

3 Alkali Silica Reactivity (ASR) First studied by Thomas E. Stanton in California during the 1930s Can cause serious cracking in concrete. This may lead to critical structural problems eventually forcing the structures demolition.

4 Alkali Silica Reactivity (ASR) Contributing factors: - Sufficient amount of moisture - Reactive forms of silica in aggregate - High-alkali pore solution

5 Alkali Silica Reactivity (ASR) Silica gel + Water Expansion

6 LADOTD Specification on ASR/ACR

7 LADOTD Specification on ASR/ACR Alkali Carbonate Reactivity (ACR) is the process of the degradation of concrete containing dolomitic aggregate. Alkali from the cement may potentially react with the dolomitic crystals present in the aggregate therefore inducing the volumetric expansion of the aggregate.

8 Alkali Carbonate Reactivity (ACR) First studied and tentatively proposed by Swenson and Gillott in the 1950 s Can cause serious cracking in concrete due to the aggregate expanding. This may lead to critical structural problems eventually forcing the structures demolition.

9 ASR/ACR Structural Effects Expansion: The swelling nature of ASR gel increases the chance of expansion in the concrete elements. Expansion due to ACR is due to the reaction inducing the production of brucite. Brucite may be responsible for the volumetric expansion after de-dolomotisation of the aggregate, due to absorption of water therefore causing potential failure of the structure. Tensile Strength: Cracking due to ASR/ACR can significantly reduce the tensile strength of concrete therefore reducing the flexural capacity of beams Fatigue: ASR/ACR reduces the load bearing capacity and the fatigue life of concrete.

10 LADOTD Specification for ASR Sand & Gravel Sources

11 LADOTD Specification for ASR/ACR Limestone Sources

12 LADOTD Specification for ASR/ACR; continued CSA-A A chart (CSA Chart).

13 LADOTD Specification for ASR/ACR; continued AASHTO PP 65-11

14 Proposed LADOTD Specification for ASR Sand & Gravel Sources Perform ASTM C289 If ASTM C289 determines material to be innocuous, PCC material codes are issued. If ASTM C289 determines material to be potentially deleterious/deleterious, no PCC material codes are given and ASTM C1260 must be performed. If ASTM C1260 determines material to be non-expansive, PCC material codes are issued. If ASTM C1260 determines material to be expansive, No PCC material codes are issued and ASTM C1293 must be performed. If ASTM C1293 determines material to be non-expansive, PCC material codes are issued and a 2 year recertification is applied to the PCC material codes from the date of the passing ASTM C1293.

15 Proposed LADOTD Specification for ASR Sand & Gravel Sources; continued If ASTM C1293 determines material to be expansive, no PCC material codes are issued. Source may submit new material for evaluation after 6 months from the date of failure.

16 Proposed LA DOTD Guidelines for ASR/ACR Limestone Sources Determine limestone chemical element composition (Aggregates Chemistry). Review aggregates chemistry for potential reactivity using the CSA-A A chart (CSA Chart). If the chemistry parameters are shown to be outside of the lines of the CSA Chart, perform ASTM C1260 to check for ASR. If ASTM C1260 shows material to be expansive, ASTM C1293 must be performed with a evaluation of the results to determine type of reactivity (ASR or ACR). No PCC material codes will be issued until evaluation is complete and the reactivity type has been determined. If the chemistry parameters are shown to be inside the lines of the CSA Chart, perform ASTM C1105.

17 Proposed LA DOTD Guidelines for ASR/ACR Limestone Sources; continued If ASTM C1105 expansion results are more than the limit listed in section 6.6 of AASHTO PP 65-11; the stone is ACR and no PCC user codes will be issued. If ASTM C1105 results are less than the limit listed in section 6.6 of AASHTO PP 65-11, ASTM C1260 shall be performed to check for aggregate reactivity. If ASTM C1260 shows expansion, ASTM C1293 shall be performed with a evaluation of the results to determine type of reactivity (ASR or ACR).

18 ASTM C1260 Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method) SCOPE Provides a means of detection within 16 days by accelerated mortar bar testing of an aggregate intended for use in concrete for undergoing alkali-silica reaction resulting in potentially deleterious internal expansion. Accelerated test method that is useful for aggregates that react slowly or produce expansion late in the reaction.

19 ASTM C1260 Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method) PROCEDURE Test uses cement conforming to ASTM C150 and aggregate proportioned/graded as per Table 1. TABLE 1 Grading Requirements Sieve Size Passing Retained On Mass, % No. 4 No No. 8 No No. 16 No No. 30 No No. 50 No Three - 1 x1 x11.25 Specimens are immersed in NaOH at 80 C for 14 days. Calculate difference between consecutive readings of the same specimen to the nearest 0.001% and report the averages to the nearest 0.01%.

20 ASTM C1260 Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method) REPORT Type and Source of Aggregate & Cement. Autoclave Expansion & Alkali Content of Cement as: Na 2 O eq = %Na 2 O x %K 2 O Average % Length Change at each reading. Graph of the length change from time of the zero reading to day 16.

21 ASTM C1260 Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method) INTERPRETATION OF RESULTS Expansion < 0.10% is indicative of innocuous behavior in most cases. Expansion between % includes aggregates that are known to be both Potentially Deleterious or Potentially Reactive. Expansion > 0.20% is indicative of potentially deleterious expansion.

22 ASTM C1293 Standard Test Method for Determination of Length Change of Concrete Due to Alkali-Silica Reaction SCOPE Covers the determination of the susceptibility of an aggregate for participation in expansive alkali-silica reaction by measuring the length change of concrete prisms. Best test method for evaluating deleterious ASR potential in terms of providing the strongest correlation to field performance. LA DOTD currently does not have the capability to conduct the test therefore it must be outsourced at the contractor/owner s expense. Takes at least 1 year to complete.

23 ASTM C1293 Standard Test Method for Determination of Length Change of Concrete Due to Alkali-Silica Reaction PROCEDURE Method must be conducted using a straight cement concrete mix. Introduces a higher alkali content to the concrete by adding NaOH to the mixing water as well as using a cement with an alkali content of % Na 2 O eq Three - 4 x4 x11.25 Specimens are immersed in water at 38 C for at least 1 year.

24 ASTM C1293 Standard Test Method for Determination of Length Change of Concrete Due to Alkali-Silica Reaction READINGS/MEASUREMENTS Length change measurements are required at 7, 28, 56 days as well as 3, 6, 9 and 12 months when testing an aggregate for susceptibility to expansion due to ASR. Calculate difference between consecutive readings of the same specimen to the nearest 0.001% and report the averages to the nearest 0.01%.

25 ASTM C1293 Standard Test Method for Determination of Length Change of Concrete Due to Alkali-Silica Reaction INTERPRETATION OF RESULTS Expansion < 0.04% is indicative of innocuous behavior in most cases. Expansion > 0.04% is indicative of a potentially deleterious aggregate.

26 ASTM C1105 Standard Test Method for Length Change of Concrete Due to Alkali-Carbonate Rock Reaction SCOPE Covers the determination of the susceptibility of cement-aggregate combinations to be expansive due to alkali-carbonate reaction by measuring the length change of concrete prisms. Used on Dolomitic Limestones or Calcitic Dolomite. LA DOTD currently does not have the capability to conduct the test therefore it must be outsourced at the contractor/owner s expense. Takes at least 1 year to complete.

27 ASTM C1105 Standard Test Method for Length Change of Concrete Due to Alkali-Carbonate Rock Reaction PROCEDURE Method must be conducted using a straight cement concrete mix. Six - 4 x4 x11.25 Specimens are cast and stored in moist room for at least 1 year. Unlike ASR, the use of SCMs does not prevent deleterious expansion due to ACR. It is recommended that ACR susceptible aggregates not be used in concrete.

28 ASTM C1105 Standard Test Method for Length Change of Concrete Due to Alkali-Carbonate Rock Reaction READINGS/MEASUREMENTS Length change measurements are required at 7, 28, 56 days as well as 3, 6, 9 and 12 months when testing an aggregate for susceptibility to expansion due to ACR. Calculate difference between consecutive readings of the same specimen to the nearest 0.001% and report the averages to the nearest 0.001%.

29 ASTM C1105 Standard Test Method for Length Change of Concrete Due to Alkali-Carbonate Rock Reaction INTERPRETATION OF RESULTS Expansion at 3 months > 0.015% classified as potentially deleteriously reactive. Expansion at 6 months > 0.025% classified as potentially deleteriously reactive. Expansion at 1 year > 0.030% classified as potentially deleteriously reactive. Data for later ages are preferred but the 3-month or 6-month average expansion result may be used if necessary.

30 Questions

31 Alkalis in Concrete Presented by: Justin Morris, P.E. Khalil Hanifa, P.E.

32 Alkalis What is an alkali? ph of an alkali is 7-14 Fresh concrete ph ~12.5 and considered highly alkaline.

33 Alkaline Materials Typically Portland Cement is the contributing factor for alkali content in concrete. (Sodium, Potassium, Lithium, etc.) Other materials factor into the total alkali content of concrete: water, aggregates, supplemental cementitious materials and chemical admixtures.

34 Alkali Content of Materials Alkalis of cement, fly ash and slag are tested in accordance to TR 531 and reported as: Na 2 O eq = %Na 2 O x %K 2 O correction factor reflects the difference in molecular weight between Na 2 O and K 2 O.

35 Quality Control of Materials Alkali content of cement/blended hydraulic cement shall not exceed 0.60% by weight when calculated as: Na 2 O eq = %Na 2 O x %K 2 O Cements with alkali contents of 0.60% or greater shall not be used in concrete.

36 Quality Control of Materials Alkali content of fly ash shall not exceed 2.5% by weight when calculated as: Na 2 O eq = %Na 2 O x %K 2 O Fly ash with an alkali contents between % by weight may only be used with nonreactive (innocuous) aggregates.

37 Quality Control of Materials Alkali content of slag shall not exceed 0.90% but shall be greater than 0.60% by weight when calculated as: Na 2 O eq = %Na 2 O x %K 2 O Slag with an alkali content greater than 0.90% shall not be used in concrete.

38 Alkali Load of Concrete It is important to calculate the alkali load of a concrete mix design, especially when using potentially reactive aggregates.

39 Alkali Load of Concrete The individual responsible for approving a concrete mix design shall request a Certificate of Analysis (CA) for each shipment of cement/fly ash/slag to be used in the design and use the Na 2 O eq number when calculating alkali load.

40 Alkali Load of Concrete The individual responsible for approving a concrete mix design shall verify the Na 2 O eq number for the material and determine if a non-reactive aggregate is needed.

41 Alkali Load of Concrete The total alkali load of the cementitious materials shall not exceed 0.60% if an ASR aggregate is proposed to be used in the concrete mix.

42 Alkali Load Calculation/Example [Cem.(%) x Cem. Alk. Content] + [F.A.(%) x F.A. Alk. Content] < 0.60% Example: 80% Cement (0.53% Na 2 O eq ) & 20% Fly Ash (1.76% Na 2 O eq ) Alkali Load = [0.80 x 0.53] + [0.20 x 1.76] = <0.60 USE INNOCUOUS AGGREGATE

43 Alkali Content of Concrete Total alkali content of concrete: lb alkali/ yd 3 = (lb cement per yd 3 ) x (Na 2 O eq. in cement)/100 lb alkali/ yd 3 = (lb cementitious materials per yd 3 ) x (Na 2 O eq. in cementitious materials)/100 Typical alkali content for concrete ranges between 3-5 lbs./yd 3

44 Other Topics ASR Mitigation Techniques? Class F work better than Class C While Cement is Hydrating, Calcium Hydroxide is being produced and reacts with Fly Ash to reduce permeability.

45 Questions?