AS 1141.34:2018 – Methods for sampling and testing aggregates Method 34: Organic impurities other than sugar.
2 Principle
The test relies on the reaction of humus material with a sodium hydroxide solution to produce a dark colour In the liquid the intensity of which Is approximately proportionate with the mass content of humus in the fine aggregate. Based on 1917 research, fine aggregate with humus contents that have a resultant solution colour lighter than, or equal to. the Standard colour are expected to have no detrimental effects when used in concrete or mortar products. A darker coloured solution may be the result of humus content and/or reactions from other contaminents and may require further Investigation to determine the extent of possible effects to concrete or mortar properties.
3 Normative references
The following documeuLs are referred to In the text in such a way that some or all of their content constitutes requirements of this document,
AS 1141.2, Met hods [or sampling and testing aggregates. Part 1: DefInitions
AS 1141.2. Met hods for sampling and testing aggregates. Method 2: Basic testing equipment
AS 1141.3.1, Methods for sampling and testing aggregates, Method 3.1: Sampling Aggregates
4 Definitions
For the purpose of this Standard the definitions in AS 1141.1 apply.
5 Safety precautions
Procedures using strong alkalis, including the preparation of dilute solutions of these chemicals, should be carried out with care.
Appropriate documentation should be consulted as to safety precautions.
6 Apparatus
The following apparatus, conforming to the relevant provisions of AS 1141.2. Is required:
(a) Stoppered rectangular clear glass boUles — of approximately 350 mL or greater capacity.
NOTE Suitable bottles were known as graduated prescription bottles. Other containers may be used provided the light path for the comparison test is the same for the test solution and the standard solution Isee (Liuce tO(c)J. European Standard EN 1744-1:2009 specifies a clear, cylindrical stoppered glass bottle approximately 450 mL with an external diameter of 70 mm.
7 Reagents
All reagents shall be of analytical grade. The following reagents are required:
(a) Sodium hydroxide.
(b) Tannic acid.
(c) Ethanol.
(d) Distilled or deionized water.
8 Test portion
By coning and quartering or using sample dividers, take a test portion of approximately 100 g from a laboratory sample obtained in accordance with the procedures of AS 1141.3.1. The test portion shall be used in the condition in which it was received.
9 Solutions required
The Following solutions are required:
(a) Sodium hydroxide solution — A solution of 30 g of sodium hydroxide In 970 ml of distilled or deionized water.
(b) Reference colour solution — Two grams of tannic acid shall be dissolved In 10 ml of ethanol (ethyl alcohol), and the solution diluted to 100 ml with distilled water, then 2.5 ml of the resultant solution shall be added to 97.5 ml of the 3 % sodium hydroxide solution. The mixture shall be shaken vigorously and then allowed to stand in subdued light for 1 h before use. The reference colour solution shall be used within 2 h of its preparation [see Clause lO(c)j.
10 Test procedure
The test procedure shall be as follows:
(a) Pour about 50 ml, of 3 % sodium hydroxide solution into a 250 ml measuring cylinder or similar calibrated clear vessel. Add the fine aggregate to the 125 ml mark and adjust the sodium hydroxide level to the 200 ml mark with more solution (after removal of bubbles by shaking).
(b) Vigorously shake the mixture for not less than 30s, takingcare to ensure that all the fine aggregates are thoroughly wetted by the sodium hydroxide solution and that any lumps are dispersed. After shaking, allow the mixture to stand for 24 h t 15 mm.
(c) At the end of the 24 h standing period, place 100 ml of reference colour solution In a rectangular clear glass bottle, and transfer 100 mL of the supernatant liquid from the test to a similar bottle.
(d) Compare the colour of the test solution to the colour of the reference when both are viewed in similar light conditions and the light paths through the solutions to the viewer are of the same length and angle.
Or, as an alternative to Item (d). either:
(i) Compare the colour of the supernatant liquid, viewed through the thickness of the glass bottle with the colour of a standardized glass sheet. In this case the standardized glass plate shall be compared to the reference solution In a bottle with a light path that allows the viewed colour of the solution to match the colour of the glass plate. Once this Is determined, the test solution shall be contained in a bottle with the same length light path.