RILEM Recommended Test Method: AAR-3—Detection of Potential Alkali-Reactivity—38 °C Test Method for Aggregate Combinations Using Concrete Prisms

Abstract

The former version of this method was initially developed by RILEM following an international trial. This trial showed that the method can reliably differentiate reactive and non-reactive combinations.

Annex A—Additional Information

(Comments relate to clauses as numbered in the method)

1.1 A4.7 Specimen Storage

The seal of the airtight lid is critical in preventing significant loss of the water in the pail and hence in maintaining high humidity around the specimens. It is important regularly to check the water level in the container and to refill as necessary.

Plastic racks can be used to hold the prisms in place vertically in the container. The racks with the prisms are placed in the containers which are lined with a layer of either terry cloth or geotextile, ~7 mm in thickness.

The plastic racks should be made in such a way that there is enough clearance at the bottom to keep the prisms about 40–50 mm above the bottom of the pail. About 25 mm of water would then be placed at the bottom of the container.

The temperature-controlled room can be either different size ovens (which have a fairly limited capacity in some cases) or walk-in insulated chambers. Figures A.1 and A.2 show a typical laboratory set-up.

Fig. A.1

Concrete prism specimens in the storage container

Fig. A.2

Storage of containers

1.2 A4.8 Casting, Curing and Measuring Environment

Cooling to a standard temperature is necessary to obtain reproducible results. In countries with hot climates, however, it may occasionally be necessary to allow the casting, curing and measurement to be carried out in a room maintained at a temperature higher than the preferred 20 °C, up to a maximum of 27 ± 2 °C and not less that 65 % ± 5 RH.

Note A15: A controlled temperature of 20 °C is preferred and strongly recommended for this stage of the test. Whatever standard temperature might be adopted (20 °C or another value up to 27 °C) for a particular test, it is essential that the same procedure and the same temperature are used consistently throughout the test. However, use of a temperature other than 20 °C will necessitate reconsideration of the expansion limits.

1.3 A5.2 Calculation of Sodium Hydroxide to Be Added to the Mixing Water

Example calculation for determining the amount of sodium hydroxide (NaOH) to be added to the mixing water to increase the alkali content up to 1.25 % sodium oxide equivalent by mass of cement:

Cement content of 1 m³ of concrete = 440 kg

Assumed content of superplasticizer = 2.0 kg

Specified amount of Na₂O eq. in concrete = 440 × 0.0125 = 5.50 kg

Amount of Na₂O eq. in cement (1.0 %) = 440 × 0.01 = 4.40 kg

Amount of Na₂O eq. in superplasticizer (1.0 %) = 2 × 0.01 = 0.02 kg

Amount of Na₂O eq. to be added per m³ = 5.50 – 4.40 – 0.02 = 1.08 kg

The conversion factor Na₂O eq. to NaOH is 1.291.

Amount of NaOH required (to be added to the mixing water) = 1.08 × 1.291 = 1.39 kg

The purity of the technical grade NaOH to be used is 98 %

Amount of technical grade NaOH required (to be added and mixed together

with the first half of the mixing water) = (1.39/98) × 100 = 1.42 kg

1.4 A5.3 Aggregates—Standard Aggregate Materials Test

The aggregate fractions should be combined in mass proportion calculated on a saturated surface dry basis according to Table A.1 given below which gives the recommended aggregate grading curve range to achieve a matrix suited for production of workable and stable concrete. In order to meet these requirements, it is necessary to know the particle size distribution curve of each aggregate.

Table A.1 Recommended aggregate grading curve range

Note A16: Gaps between two fractions should be avoided. For example, sand 0/2 (2–0  mm) should not be tested with an aggregate 8/16 (16–8  mm).

Note A17: With some reactive aggregates it has been found that there is a proportion of reactive constituents in the aggregate that leads to a maximum expansion. This proportion is called the ‘pessimum’ content, and the relationship between expansion and content of reactive constituents is called the ‘pessimum behaviour’ of the reactive aggregate.

1.5 A6 Concrete Mix Design

Preparation of the aggregates

Pre-wetted fine aggregates are used in order to ensure a workable and homogeneous concrete. This shall be done using the following procedure:

Determine the water absorption (WA_f) and initial water content (W_i) of the fine aggregate according to the standards/methods valid in the place of use. Weigh out a sufficient quantity of the fine aggregate, place it into a tray and add a sufficient amount of water calculated to achieve a water content of 5 ± 2 %. Mix the wetted fine aggregate thoroughly and store in sealed containers for at least 16 h. Measure the final water content (W_f) of the fine aggregate.

The coarse aggregate should be used without pre-wetting, but the water absorption (WA_c) and the water content (W_c) should be measured.

The amount of water added to the mix to achieve the prescribed free water content of 220 kg/m³ is then calculated, taking into account both the water absorption and the measured water content of the fine and coarse aggregates. The water absorptions of most fine aggregates will be less than the intended water content (i.e. 5 ± 2 %). For most coarse aggregates, the water content will be lower than their water absorptions. In the cases where the water content (W) is higher than the water absorption (WA), the contribution from the aggregate (W_free) to the free water content of the mix can be calculated as:

Contribution from the aggregate = [(measured water content of the aggregate – water absorption of the aggregate)/100] × [calculated mass of the dry aggregate]

or

$$ {\text{W}}_{\text{free}} = \, \left[ {\left( {{\text{W }} - {\text{ WA}}} \right) \, /{ 1}00} \right]\,\times\,[\left( {{\text{quantity}}_{\text{ssd}} {\text{ of the aggregate}}} \right)/( 1 { } + {\text{ WA}}/{1}00)] $$

(A.1)

In the case of where the water absorption of the aggregate is higher than its water content, the extra water needed (W_extra) at the mixing stage, to bring the aggregate to a saturated surface dry state, can be calculated as:

Extra water needed = [(water absorption of the aggregate – measured water content of the aggregate)/100] × [calculated mass of the dry aggregate]

or

$$ {\text{W}}_{\text{extra}} = \, \left[ {\left( {{\text{WA }} - {\text{ W}}} \right) \, /{ 1}00} \right]\,\times\,\left[ {\left( {{\text{quantity}}_{\text{ssd}} {\text{ of the aggregate }}} \right)/\left( { 1 { } + {\text{ WA}}/{1}00} \right)} \right] $$

(A.2)

Concrete mix design

A worked example is presented below, see Tables A.2, A.3, A.4, A.5 and A.6.

Table A.2 General concrete mix design

Table A.3 Typical properties of the materials

Table A.4 Calculation of the concrete mix design—stage 1

Table A.5 Calculation of the concrete mix design—stage 2

Table A.6 Final concrete mix design—quantities to be added to the mix

An example of concrete mix design calculation made with one coarse and one fine aggregate is shown (the calculation is the same for more aggregates).

For the mix design it is necessary to know:

• The water absorption (WA) of each aggregate. The values can be determined according to EN 1097-6 [12], ASTM C127 [13] or ISO 7033 [14];

• The densities on an oven dry (ρ_rd) and saturated surface dry (ρ_ssd) basis of all fractions. The values can be determined according to EN 1097-6 [12], ASTM C127 [13] and 128 [15] or ISO 7033 [14];

• The water content (W) of each aggregate. The values can be determined according to EN 1097-5 [16] or ASTM C566 [17].

Assume that the content of superplasticizer (with density 1.1 kg/m³ and water content 80 %) required is 2.0 kg/m³ and that the amount of technical grade NaOH (with density 2.1 kg/m³) required is 1.4 kg/m³—see example in Annex A5.2.

The volumetric weight and the air content of the fresh concrete should be measured, according respectively to EN 12350-7 [18]/ASTM C1170 [19] and EN 12350-6 [20]/ASTM C173 [21]/ASTM C231 [22]. The ratio between the theoretical and the measured volumetric weights of the fresh concrete should be 1.000 ± 0.015 (which corresponds to 440 ± 6 kg of cement). This will ensure the correct amount of alkali from the cement in the fresh concrete.

Calculation of the quantity (X) of coarse aggregate (saturated surface dry) in 1 m³ of concrete:

Aggregate volume = 1000 – 143 − 220 − 15 − 2 − 1 = 619 L/m³

(X/2.68 kg/L) + (4/6 × X)/2.68 kg/L = 619 L/m³

X = 995 kg/m³

Calculation of the quantity (4/6 × X) of fine aggregate (saturated surface dry) in 1 m³ of concrete:

4/6 × X = 4/6 × 995 kg/m³ = 663 kg/m³

The contribution from the fine aggregate (W_free-f) to the free water content can be calculated according to Eq. A.1:

W_free-f = [(6.2 – 1.1)/100] × [(663)/(1 + 1.1/100)] = 33.4 kg (~33 kg)

The extra water needed (W_extra-c) at the mixing stage to bring the coarse aggregate to a saturated surface dry state can be calculated according to Eq. A.2:

W_extra-c = [(0.8 – 0.3)/100] × [(995)/(1 + 0.8/100)] = 5.0 kg

Example of fresh concrete properties measured:

Slump = 120 mm (target is 100–180 mm)

Air content = 1.4 % (target <3 %)

Measured volumetric weight = 2327 kg/m³

Ratio between the theoretical and measured volumetric weights = (2320/2327) = 0.997 (target is 0.985–1.015).

If the ratio is outside the range, the quantity of aggregate should be increased/decreased (without changing the proportion between the different aggregates) in order to meet the requirement of the weight ratio (0.985–1.015).