Bre Digest 330 Pt3 Alkali-silica Reaction In Concrete

Digest 330

Alkali–silica reaction in concrete

digest

Worked examples

Part 3

2004 Edition

BRE Centre for Concrete Construction

Concrete can deteriorate as a result of an interaction between alkaline pore fluids (principally originating from the Portland cements) and reactive minerals in certain types of aggregates. The mechanism of deterioration is known as alkali–aggregate reaction (AAR); it can occur in a number of forms, the most common being alkali–silica reaction (ASR). This Digest is in four parts Part 1 gives the background to the detailed and simplified guidance contained in Parts 2 and 4. Part 2 gives detailed guidance for minimising the risk of damaging ASR in new construction. Part 3 gives worked examples. Part 4 gives simplified guidance for new construction using aggregates of normal reactivity. ASR induced cracking reflecting vertical reinforcement within a concrete column

How to understand the worked examples In the worked examples shown in the following pages, the concrete constituents and their characteristics have been selected to meet specified requirements for strength and durability. To help the reader to work through the examples: ● general guidance is provided in Table 1 and the section ‘Using Table 1’ on pages 2 and 3 respectively in Part 2 of this Digest; ● specific references to tables are to those in Part 2; ● text shown in bold type refers to text indicated in tables and sections of Part 2.

A BRE research project funded by DTI Construction Sector Unit

2 Example 1 Portland cement

Combination

Combined aggregate[1]

Water

Concrete component

BS 4027 LASRPC

Not specified

Gravel >60% flint

Potable

Alkali (% Na2O eq)

Guaranteed ≤0.60

–

0.01[2]

N/a

Target mean content (kg/m3)

400

–

1795

–

[1] Flint gravel (coarse and fine) [2] Calculated in the combined aggregate from a measured chloride ion content of 0.013%

i

The alkali content of the low alkali sulfate resisting Portland cement (LASRPC) is classified in Table 1 as low alkali PC. If an LASRPC is used with a high reactivity aggregate, the manufacturer’s mean alkali content is used for calculation.

ii The reactivity of the aggregate combination is classified (Table1 and the section ‘Aggregates’ ) as normal. iii The appropriate recommendation in Table 1, located at the intersection of the classifications, is given as: Self-limiting: no mix calculation needed (Note #). iv Reference to Note #, Table 1, indicates: a the appropriateness of LASRPC to BS 4027 (Table 6 for cements in Group A) as a recommended alternative; b the need to calculate whether alkali contributed from other sources exceeds 0.60 kg Na2O eq/m3. Mix water is potable and is deemed to contribute no alkali; no admixture has been selected; accordingly, only a contribution from the combined aggregate needs to be taken into account, as follows: 0.01 x 1795 alkali contributed from the combined aggregate = = 0.18 kg Na2O eq/m3 (below the limiting value). 100 v Since no limit value is given in Table 1 for this classification, no mix calculation is needed. vi From the information obtained, all the conditions appropriate to the recommendations in Table 1 have been met, so there is no need to consider alternative concrete components.

Example 2

Concrete component

Portland cement

Combination

Combined aggregate[1]

Water

BS EN 197-1 CEM I

Not specified

Gravel >60% flint

Potable

[2]

Alkali (% Na2O eq)

Declared mean 0.64

–

0.01

N/a

Target mean content (kg/m3)

465

–

1730

–

[1] Flint gravel (coarse and fine) [2] Calculated in the combined aggregate from a measured chloride ion content of 0.013%

i

The alkali content of the CEM I Portland cement is classified in Table 1 as moderate alkali PC.

ii The reactivity of the aggregate combination is classified (Table 1 and the section ‘Aggregates’) as normal. iii The appropriate recommendation in Table 1, located at the intersection of the classifications, is given as: Limit: ≤ 3.5 kg Na2O eq/m3 (Notes ◊ and §). iv Reference to Note #, Table 1 indicates: a the appropriateness of a CEM I Portland cement (Table 6 for cements in Group A) as a recommended alternative (and the inappropriateness of Note § because it excludes a Portland cement in Group A); b the need to calculate, separately, whether alkali contributed from other sources exceeds 0.20 kg Na2O eq/m3. Mix water is potable and is deemed to contribute no alkali; no admixture has been selected; accordingly, only a contribution from the combined aggregate needs to be taken into account, as follows: 0.01 x 1730 alkali contributed from the combined aggregate = = 0.17 kg Na2O eq/m3. 100 c As 0.17 kg Na2O eq/m3 is less than the limiting value of 0.20 kg Na2O eq/m3, the recommended limit (≤ 3.5 kg Na2O eq/m3) should not be reduced. v Since a limit value (≤3.5 kg Na2O eq/m3) forms the basis for the recommendation, the alkali content of the concrete, derived only from the CEM I Portland cement, must be calculated, as follows: 0.64 x 465 alkali contributed from the Portland cement = = 3.0 kg Na2O eq/m3. 100 As 3.0 kg Na2O eq/m3 is less than 3.5 kg Na2O eq/m3, this recommended limit has been met. vi From the information obtained, all the conditions appropriate to the recommendations in Table 1 have been met, so there is no need to consider alternative concrete components nor a reduced Portland cement content.

3 Example 3 Portland cement

Combination

Combined aggregate[1]

Water

Concrete component

BS EN 197-1 CEM I (32% pfa)

Not specified

Gravel >60% flint

Potable

Alkali (% Na2O eq)

Declared mean of

–

0.03 [2]

N/a

1795

–

CEM I-type component 0.71 Target mean content (kg/m3)

400

[1] Sea dredged gravel (coarse and fine) [2] Calculated in the combined aggregate from a measured chloride ion content of 0.039%

i

The alkali content of the Portland fly ash cement (CEM II/B–V) to BS EN 197-1 is classified in Table 1 as moderate alkali PC. (Note: for the purposes of classification and calculation, the value-to-use is the manufacturer’s declared mean for the CEM I-type component of the Portland cement.)

ii The reactivity of the aggregate combination is classified (Table 1 and the section ‘Aggregates’) as normal. iii The appropriate recommendation in Table 1, located at the intersection of the classifications, is given as: Limit: ≤ 3.5 kg Na2O eq/m3 (Notes ◊ and §). iv Reference to Note §, Table 1, indicates: a the appropriateness of a CEM II/B–V cement to BS EN 197-1 containing 32% pfa (Table 6 for cements in Group B) as a recommended alternative (and the inappropriateness of Note ◊ which applies to a Portland cement containing <25% pfa); b the need to calculate, separately, whether alkali contributed from other sources exceeds 0.20 kg Na2O eq/m3. Mix water is potable and is deemed to contribute no alkali; no admixture has been selected. Accordingly only a contribution from the combined aggregate needs to be taken into account, as follows: 0.03 x 1795 alkali contributed from the combined aggregate = = 0.54 kg Na2O eq/m3; 100 c As 0.54 kg Na2O eq/m3 exceeds 0.20 kg Na2O eq/m3 and a pfa-containing Portland cement is to be used: i the recommended limit should be reduced by the amount of alkali contributed from the aggregate to give a revised limit: 3.5 – 0.5 = 3.0 kg Na2O eq/m3; and ii Table 9 should be checked for its applicability. Referring to Table 9, it can be seen that the table applies only to pfa-containing Portland cements where 25% ≤pfa <30%. In this example, the CEM II/B–V cement contains 32% pfa, which is outside the range. Accordingly, even though all the other conditions for using the table are satisfied, Table 9 and its binder content maxima are inapplicable. v Since a revised limit value (now ≤3.0 kg Na2O eq/m3) forms the basis of the recommendation, the alkali content of the concrete derived only from the CEM I-type component of the Portland cement in the concrete must be calculated, as follows: 68 400 x 0.71 Alkali contributed from the CEM I-type component of the Portland cement = x = 1.9 kg Na2O eq/m3. 100 100 As 1.9 kg Na2O eq/m3 is less than 3.0 kg Na2O eq/m3, this recommended limit has been met. vi From the information obtained, all the conditions appropriate to the recommendation in Table 1 have been met, so there is no need to consider alternative concrete components nor a reduced Portland cement content.

4 Example 4 Portland cement

Combination

Combined aggregate[1]

Water

Concrete component

BS EN 197-1 CEM I

30% pfa

Gravel >60% flint

Potable

Alkali (%Na2O eq)

Declared mean 0.65

Only CEM I component

0.02 [2]

N/a

1695

–

taken into account (text below explains) Target mean content (kg/m3)

350

500

[1] Sea dredged gravel (coarse and fine) [2] Calculated in the combined aggregate from a measured chloride ion content of 0.026%

i The alkali content of the CEM I component of the combination is classified in Table 1 as moderate alkali PC. ii The reactivity of the aggregate combination is classified (Table 1 and the section ‘Aggregates’) as normal. iii The appropriate recommendation in Table 1, located at the intersection of the classifications, is given as: Limit: ≤3.5 kg Na2O eq/m3 (Notes ◊ and §). iv Reference to Note §, Table 1, indicates: a the appropriateness of a combination containing 30% pfa, as a recommended alternative (and the inappropriateness of Note ◊ which applies to a combination with <25% pfa); b the need to calculate, separately, whether alkali contributed from other sources exceeds 0.20 kg Na2O eq/m3. Mix water is potable, and is deemed to contribute no alkali; no admixture has been selected; accordingly only a contribution from the combined aggregate needs to be taken in account, as follows: 0.02 x 1695 alkali contributed from the combined aggregate = = 0.34 kg Na2O eq/m3. 100 c As 0.34 kg Na2O eq/m3 exceeds 0.20 kg Na2O eq/m3 and a pfa-containing combination is to be used: i the recommended limit should be reduced by the amount of alkali contributed from the aggregate to give: a revised limit: 3.5 – 0.3 = 3.2 kg Na2O eq/m3; and ii Table 9 should be checked for its applicability. Referring to Table 9, it can be seen that the table applies only to pfa-containing combinations where 25% ≤pfa <30%. In this example, the combination contains 30% pfa, which is just outside the range. Accordingly, even though all the other conditions for using the table are satisfied, Table 9 and its binder content maxima are inapplicable. v Since a revised limit value (now ≤3.2 kg Na2O eq/m3) forms the basis of the recommendation, the alkali content of the concrete, derived only from the CEM I component of the combination, must be calculated, as follows: 0.65 x 350 alkali contributed from the CEM I component of the combination = = 2.3 kg Na2O eq/m3. 100 As 2.3 kg Na2O eq/m3 is less than 3.2 kg Na2O eq/m3, this recommended limit has been met. vi From the information obtained, all the conditions appropriate to the recommendation in Table 1 have been met,so there is no need to consider alternative concrete components nor a reduced combination content.

5 Example 5 Portland cement

Combination

Pfa

Combined

Water

aggregate[1] Concrete component

BS EN 197-1 CEM I

22% pfa

–

Gravel >60% flint

Potable

Alkali (% Na2O eq)

Declared mean 0.70

(text below explains)

Total acid

0.02 [2]

N/a

Target mean content (kg/m3)

390

500

1695

–

soluble 3.0 110

[1] Sea dredged gravel (coarse and fine) [2] Calculated in the combined aggregate from a measured chloride ion content of 0.026%

i

The alkali content of the CEM I component of the combination is classified as moderate alkali PC.

ii The reactivity of the aggregate combination is classified (Table 1 and the section ‘Aggregates’) as normal. iii The appropriate recommendation in Table 1, located at the intersection of the classifications, is given as: Limit: ≤3.5 kg Na2O eq/m3 (Notes ◊ and §). iv Reference to Note §, Table 1 indicates: ● the inappropriateness of Note §, because the note applies to a combination with ≥25% pfa; Reference to Note ◊, Table 1 indicates: a the appropriateness of a combination containing 22% pfa, as a recommended alternative; b that alkali contributed from the pfa should be calculated in accordance with the recommendations in Table 8 and that the recommended limit (≤3.5 kg Na2O eq/m3) should be reduced by the amount of the contribution. Referring to Table 8: ● for a combination with 22% pfa, one-fifth of the total acid soluble alkali content of the pfa should be taken into account when calculating the contribution from the pfa; 3 x 110 ● alkali contributed from the pfa = = 0.7 kg Na2O eq/m3; 5 x 100 ● revised limit is: 3.5 – 0.7 = 2.8 kg Na2O eq/m3; c the need to calculate, separately, whether alkali contributed from other sources exceeds 0.20 kg Na2O eq/m3. Mix water is potable, and is deemed to contribute no alkali; no admixture has been selected; accordingly only a contribution from the combined aggregate should be taken into account, as follows: 0.02 x 1695 alkali contributed from the combined aggregate = = 0.34 kg Na2O eq/m3. 100 d As 0.34 kg Na2O eq/m3 exceeds 0.20 kg Na2O eq/m3, the revised limit ( ≤ 2.8 kg Na2O eq/m3) should be reduced by 0.3 kg Na2O eq/m3 to ≤ 2.5 kg Na2O eq/m3. v Since a limit value (now ≤2.5 kg Na2O eq/m3) forms the basis of the recommendation, the alkali content, derived only from the CEM I component of the combination, should be calculated as follows: 0.70 x 390 alkali contributed from the CEM I component of the combination = = 2.7 kg Na2O eq/m3. 100 As 2.7 kg Na2O eq/m3 exceeds the revised limit of 2.5 kg Na2O eq/m3, the conditions appropriate to the recommendation in Table 1 have not been met. vi From the information obtained, alternatives should be considered, including: ● the selection of a CEM I component of the combination, with a declared mean alkali content of ≤0.64%, for use with the other concrete components given above; ● the selection of a pfa component of the combination, with a total acid soluble alkali content of ≤2.3%, for use with the other concrete components given above; ● the selection of a proportion of pfa in the combination which is ≥25%, to discount any contributions from the pfa, together with an appropriate adjustment to the target mean combination content to ensure the requirements for strength and durability can still be met; ● the selection of a lower target mean combination content, whilst maintaining the proportion of pfa at 22%, provided the requirements for strength and durability can still be met; ● the selection of an aggregate combination with an alkali content of ≤0.012%, to discount any contribution from the combined aggregate; ● the selection of an aggregate combination of a lower reactivity to satisfy the appropriate alkali limit. Irrespective of the means selected to meet the recommendations, the contingent effects of any change must be carefully considered and the appropriate recalculations carried out.

6 Example 6 Portland cement

Concrete component

BS EN 197-1 CEM I

Combination

Not specified

Combined

Aggregate modifier

aggregate[1]

(Type 1 addition)

Gravel

Pfa to

>60% flint

BS 3892-2 Total acid

Alkali (% Na2O eq)

Declared mean 0.65

–

0.01[2]

Target mean content (kg/m3)

440

–

1755

Water

Potable N/a

soluble 3.0 125

–

[1] Flint gravel (coarse and fine) [2] Calculated in the combined aggregate from a measured chloride ion content of 0.013%

i The alkali content of the CEM I cement is classified as moderate alkali PC. ii The reactivity of the aggregate combination is classified (Table 1 and the section ‘Aggregates’) as normal. iii The appropriate recommendation in Table 1, located at the intersection of the classifications, is given as: Limit: ≤3.5 kg Na2O eq/m3 (Notes ◊ and §). iv Reference to Notes ◊ and § indicates, however, that these provisions apply only to the use of pfa, conforming to BS 3892-1 in a combination. In this example, where a pfa has been used as a Type I addition, refer to the text on page 9, Part 2, ‘Pfa to BS 3892-2 as a Type I addition’. Reference to the text indicates the need to treat the pfa as if it were a component of a combination for the purposes of its: a contribution to the recommended maximum combination content. The maximum has been set at 550 kg/m3 in Table 1. Accordingly, the target mean content of pfa of 125 kg/m3 (+ 3% tolerance on batching = 129) should be subtracted from the maximum, to calculate the maximum content of CEM I Portland cement. This is given as: maximum content of CEM I Portland cement = 550 – 129 = 421 kg/m3. However, the target mean Portland cement content specified is 440 kg/m3. Under these recommendations, 440 kg/m3 is not permissible, so a revised target mean of 408 kg/m3 (421 less 3% tolerance on batching) should be substituted, before progressing to the next step in the calculation procedure; b contribution to the mix alkali content. To calculate contributions to the mix alkali content, the proportion of pfa in the combination should first be calculated as follows: 125 proportion of pfa in the combination = x 100 = 23%. 125 + 408 Referring to Table 8: ● for a combination with 23% pfa, one-fifth of the total acid soluble alkali content of the pfa should be taken into account when calculating the contribution from the pfa; 3 x 125 ● alkali contributed from the pfa = = 0.8 kg Na2O eq/m3. 5 x 100 This contribution from the pfa should be subtracted from the recommended limit ≤3.5 kg Na2O eq/m3 to give: ● a revised limit: 3.5 – 0.8 = 2.7 kg Na2O eq/m3; c the need to calculate, separately, whether alkali contributed from other sources exceeds 0.20 kg Na2O eq/m3. Mix water is potable and is deemed to contribute no alkali; no admixture has been selected; accordingly only a contribution from the combined aggregate needs to be taken into account, as follows: 0.01 x 1755 alkali contributed from the combined aggregate = = 0.18 kg Na2O eq/m3. 100 As 0.18 kg Na2O eq/m3 is less than 0.20 kg Na2O eq/m3, the revised limit of ≤ 2.7 kg Na2O eq/m3 needs no further revision. v Since a limit value (now ≤2.7 kg Na2O eq/m3) forms the basis of the recommendation, the alkali content, derived only from the CEM I component of the combination, should be calculated as follows: 0.65 x 408 alkali contributed from the CEM I component of the combination = = 2.7 kg Na2O eq/m3. 100 As 2.7 kg Na2O eq/m3 equals the revised limit of 2.7 kg Na2O eq/m3, the recommendations appropriate to the use of a pfa as a Type I addition to BS 3892-2 have been met. vi From the information obtained, the target mean cement content should be reduced from 440 kg/m3 to 408 kg/m3 for the recommendations to be met without change to the other specified concrete components (except to a contingent effect on the total content of combined aggregate). ● If using pfa to BS 3892-2 as a modifier of aggregate properties in concrete to be used for minimising the risk of damaging ASR, it would be prudent to target its content within a range approximately 100 to 200 kg/m3. ● At the lower end of the range, step changes in the alkali contributed from the pfa (note to Table 8) can lead to the need to consider alternatives to the specified concrete components. ● At the upper end of the range, as the permitted content of Portland cement reduces, the target mean concrete strength may not be achievable and can lead to the need to consider alternatives to the specified concrete components.

7 Example 7

Concrete component

Portland cement

Combination

BS EN 197-1 CEM I

70% ggbs

Combined aggregate

Water

Crushed greywacke

Potable

plus flint gravel sand Alkali (% Na2O eq)

Declared mean 0.72

Only CEM I component

0.01[1]

N/a

1715

–

taken into account (text below explains) Target mean content (kg/m3)

145

480

[1] Calculated in the combined aggregate from a measured chloride ion content of 0.013%

i

The alkali content of the CEM I component of the combination is classified in Table 1 as moderate alkali PC.

ii The reactivity of the aggregate combination is classified (Table 1 and the section ‘Aggregates’) as high. iii The appropriate recommendation in Table 1, located at the intersection of the classifications, is given as: Limit: ≤ 2.5 kg Na2O eq/m3 (Note
). iv Reference to Note
, Table 1, indicates: a the appropriateness of a combination containing 70% ggbs as a recommended alternative; b the need to calculate, separately, whether alkali contributed from other sources exceeds 0.20 kg Na2O eq/m3. Mix water is potable and is deemed to contribute no alkali; no admixture has been selected; accordingly, only a contribution from the combined aggregate needs to be taken into account, as follows: 0.01 x 1715 alkali contributed from the combined aggregate = = 0.17 kg Na2O eq/m3. 100 c As 0.17 kg Na2O eq/m3 is less than the limiting value of 0.20 kg Na2O eq/m3, according to Note
no reduction to the recommended limit (≤ 2.5 kg Na2O eq/m3) needs to be made. v Since a limit value (≤2.5 kg Na2O eq/m3) forms the basis for the recommendation, the alkali content of the concrete, derived only from the CEM I component of the combination, must be calculated as follows: 0.72 x 145 alkali contributed from the CEM I component of the combination = = 1.0 kg Na2O eq/m3. 100 As 1.0 kg Na2O eq/m3 is less than 2.5 kg Na2O eq/m3, this recommended limit has been met. vi From the information obtained, all the conditions appropriate to the recommendations in Table 1 have been met, so there is no need to consider alternative concrete components nor a reduced combination content.

8 Example 8 Portland cement

Combination

Combined

Water

aggregate[1] Concrete

BS EN 197-1 CEM I

50% ggbs

Gravel >60% flint

Potable

Declared mean 0.85

Only CEM I

0.03 [2]

N/a

1745

–

component Alkali (%Na2O eq)

component taken into account (text below explains) Target mean

225

450

content (kg/m3) [1] Sea dredged gravel (coarse and fine) [2] Calculated in the combined aggregate from a measured chloride ion content of 0.039%

i

The alkali content of the CEM I component of the combination is classified as high alkali PC.

ii The reactivity of the aggregate combination is classified (Table 1 and the section ‘Aggregates’) as normal. iii The appropriate recommendation in Table 1, located at the intersection of the classifications, is given as: Limit: ≤3.0 kg Na2O eq/m3 (Notes ‡ and ◊). iv Reference to Note ‡, Table 1, indicates: a the appropriateness of a combination containing 50% ggbs, as a recommended alternative (and the inappropriateness of Note § which applies to a combination with <40% ggbs); b the need to calculate, separately, whether alkali contributed from other sources exceeds 0.20 kg Na2O eq/m3. Mix water is potable, and is deemed to contribute no alkali; no admixture has been selected, so only a contribution from the combined aggregate needs to be taken into account, as follows: 0.03 x 1745 alkali contributed from the combined aggregate = = 0.52 kg Na2O eq/m3. 100 c As 0.52 kg Na2O eq/m3 exceeds 0.20 kg Na2O eq/m3, according to Note ‡ the recommended limit (3.0 kg Na2O eq/m3) should be reduced by 0.5 kg Na2O eq/m3 to 2.5 kg Na2O eq/m3. v Since a limit value (now ≤2.5 kg Na2O eq/m3) forms the basis of the recommendation, the alkali content of the concrete, derived only from the CEM I component of the combination, should be calculated as follows: 0.85 x 225 Alkali contributed from the CEM I component of the combination = = 1.9 kg Na2O eq/m3. 100 As 1.9 kg Na2O eq/m3 is less than 2.5 kg Na2O eq/m3, this recommended limit has been met. vi From the information obtained, all the conditions appropriate to the recommendation in Table 1 have been met so there is no need to consider alternative concrete components nor a reduced combination content.

References British Standards Institution BS 12:1996 Specification for Portland cement BS 4027:1996 Specification for sulfate-resisting Portland cement BS 3892-1:1997 Pulverized fuel ash. Specification for pulverized fuel ash for use with Portland cement BS 3892-2:1996 Pulverized fuel ash. Specification for pulverized fuel ash to be used as a Type I addition BS EN 197-1:2000 Cement. Composition. specifications and conformity criteria for common cements

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Acknowledgement The authors would like to acknowledge the support of the Department of Trade and Industry in the preparation of this Digest.

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