5 Concrete constituents as example for the release of dangerous substances
5.6 Mandate M 128 – Products related to concrete, mortar and grout
5.6.2 Concrete admixtures
5.6.2.1 General
Admixtures are defined by the European concrete standard DIN EN 206-1 as material added during the mixing process of concrete to modify the properties in the fresh or hardened state [22]. The European standard for concrete admixtures, DIN EN 934-2, defines admixtures that are suitable for this. The total amount of admixtures added to the concrete may not exceed 5
% by mass (relative to the cement) [76].
Admixtures are used in 60-80 % of the concrete manufactured in ready-mixed concrete plants and on the building site and in 100 % of precast concrete components [84]. Mostly used are concrete plasticisers and liquifiers [26].
The table below provides an overview of concrete admixtures to DIN EN 934-2 [76], their main constituents and their areas of application.
Table 22: Classification of concrete admixtures [according to 23]
Admixture Main constituent Application
Plasticisers Lignosulphonates Melamine sulphonate Naphthalene sulfonate Polycarboxylates
Improving workability and reducing water-cement ratio through improving flowability (lowering the internal friction in the concrete) (two-three times stronger than concrete plasticiser)
Retarders Saccharose Gluconate
Phosphate Ligninsulphonate
Retarding the hydratation of the cement (setting) during the transport of a ready mixed concrete due to influence on the chemical reaction of the cement with water. Prolonging the workability by several hours by delaying the hardening Accelerators Silicates (sodium/potassium water
glass)
Accelerating the development of early strength and hardening of fresh concrete (needed for shotcrete and cold weather applications)
Air-entraining
agents Soap from natural resins (saponified tall oil, balsam and wood rosin) Synthetic non-ionic and ionic tensides
Achieving high freeze/thaw durability through forming tiny, uniformly spaced, air bubbles
Waterproofing
agents Calcium stearate Manufacture of concretes impervious to water (reducing the permeability of concrete through increasing the hydrophobicity of the capillary pore system or closing the pores) Stabilisers Polysaccharides
Nanosilica and colloidal silicic acid Natural rubber modifications Polyacrylates
Polyethylenoxides
For shotcrete and underwater
concrete (prevents segregation of the added water from fresh concrete)
Concrete admixtures do not contain any heavy metal compounds that are actively used, so that the content is very low. The next section shall only consider the release of organic substances by leaching to soil and groundwater.
5.6.2.2 Release of organic substances to soil and groundwater
The information on the concrete admixtures described here was mainly taken from the progress report "Betonzusatzmittel und Umwelt" ("Concrete admixtures and the environment") from the Deutsche Bauchemie e.V., the German industry association for construction chemicals [84]. Other sources are given. The classification as toxicologically unobjectionable is not an assessment according to the DIBt Guideline Soil/Groundwater [20].
Plasticisers and liquifiers
With the exception of polycarboxylates, the admixtures used are considered to be toxicologically unobjectionable. The German Gefahrstoffverordnung – GefStoffV ('Dangerous Substances Ordinance') classifies some of the polycarboxylate compounds as irritants.
Although naphthalene sulphonate is considered to be toxicologically unobjectionable, environmental harm cannot be excluded because the leached compounds are very stable.18 The dosage of liquefying admixtures ranges from 0.2 to 2 % by mass (relative to the cement). An admixture concentration of 40 % produces a concentration of 0.12 % in concrete (cement content 350 kg/m³).
As part of the IBAC study, the leaching behaviour of plasticisers and liquefiers was assessed on cement particles by using batch and short-term static tests, analysing pore water in concrete and examining the sorption behaviour of liquefiers [26]. Until now there have been no results from long-term static tests. The examination on the sorption of liquefiers by cement particles showed that 90 % of the liquefier was already sorbed by the cement particles after 7 days so that only 10 % can be leached out. Analysis of the pore water in concrete showed that after 28 days the concentration of the liquefier had also sunk to 10 % of the initial value. The batch and static tests that were carried out also showed only very slight elution. Under real conditions, it is predicted that there would be less than 1% elution.
On the basis of these results, the IBAC research project classifies plasticisers and liquifiers released in this order of magnitude as not harmful to the environment. There is very little data available on the degradation products of liquefying additives, so it is not possible to draw any conclusions here [26].
Retarders
The agents used for retarders are considered to be toxicologically unobjectionable.
According to the progress report from the Deutsche Bauchemie e.V. (Sachstandsbericht der Deutschen Bauchemie), the German industry association for construction chemicals, the substances are firmly combined in the hardened cement paste matrix so that no leaching is to be expected [8]. However, there were no test results that could have been drawn upon for assessing the leaching [26].
18 For a thorough assessment of sulfonated naphthalenes applied as concrete superplasticisers see: http://e-collection.ethbib.ethz.ch/ecol-pool/diss/fulltext/eth14477.pdf.
Accelerators
Silicates (silicic acid, sodium or potassium salt), aluminates (sodium or potassium aluminate) and carbonates (sodium or potassium carbonate) react alkaline and are classified by the German Gefahrstoffverordnung ('Dangerous Substances Ordinance') [85] as irritating or caustic. The aforementioned substances form poorly soluble calcium salts in the concrete, which are bonded in the hardened cement paste matrix. However, the alkalis are partly leached.
Amorphous aluminium hydroxide and aluminium sulphate are classified as toxicologically unobjectionable. The compounds are alkali-free. They are bonded as calcium aluminate phases in the hardened cement paste so that leaching is not to be expected [26].
Air-entraining agents
Air-entraining agents are manufactured without the addition of additives and auxiliary agents.
Depending on the alkalinity, the German Gefahrstoffverordnung ('Dangerous Substances Ordinance') [85] classifies the agents used as irritating or caustic.
The progress report of the Deutschen Bauchemie states that tenside substances accumulate on the edge of the air voids, whereby the hydrophilic part is embedded in the hardened cement paste matrix [84]. There were no test results for leaching tests [26].
Sealants
Calcium stearate is classified as toxicologically unobjectionable. Since it dissolves with difficulty and reacts hydrophobically, no leaching is to be expected [84]. However, there are no test results available to be able to assess the leaching [26].
Injection aids
Aluminium powder is classified as toxicologically unobjectionable. The hydration products are bonded in the hardened cement paste so that no leaching is to be expected [84, 26].
Stabilisers
The progress report of the Deutsche Bauchemie only provides information on the cellulose ether and starch ether constituents. These are bonded in the hardened cement paste.
Leaching is not to be expected [84].
Recommendations for the release of organic substances from concrete admixtures
With the exception of plasticisers and liquifiers, there is hardly any research data available on the release of dangerous substances from concrete admixtures. The only degradation products considered are for plasticisers and liquifiers, and here only to a limited extent. The IBAC research project comes to the conclusion that the existing data and the properties of the substances used indicate that concrete admixtures have little environmental impact, partly because of the low dosages.
It is not possible to make a conclusive assessment due to insufficient data. Here it would be necessary to conduct leaching tests with concrete test specimens manufactured with the corresponding admixtures. The leaching of organic substances from concrete admixtures is also confirmed by the two following studies. A study by the trade association for Swiss manufacturers of concrete admixtures determined that up to 60 mg/l DOC (dissolved organic carbon) is leached from concrete debris in batch tests [86]. The study conducted by the Institut für Bauforschung der RWTH Aachen – IBAC (Institute for Building Materials
Research at the Technical University of Aachen) reports TOC values (total organic carbon) of up to 12.5 mg/l for a batch test to DIN 38414-S4 with mortar [87].
A basis for more comprehensive studies is also provided by a research project from the Forschungs- und Materialprüfanstalt (FMPA), a research and testing establishment for building materials and structures in Stuttgart, which provides an overview of which concrete admixtures can be released on principle and in quantifiable amounts [88].
5.6.3 Overview of the recommendations for the second standard generation for concrete additions and admixtures
The table below provides a summary of the studies on the environmental compatibility of concrete additions and admixtures described in the previous section and summarises the recommendations for revising the technical specifications.
Table 23: Overview of the recommendations for revising the technical specifications for concrete additions and admixtures
Harmonised product standards
Content/Release of dangerous substances
Recommendations for second standard generation
M 128: Products related to concrete, mortar and grout Release of heavy metals:
Fillers
Heavy metal content comparable with those for sand and gravel and
limestone.
With limestone intercalated with ores, higher contents of individual heavy metals have been measured in individual cases.
Presumably no release of dangerous substances when using fillers from quartz or limestone.
Leaching tests should be conducted if there are indications that ores are intercalated in the limestone.
DIN EN 12878 (Draft)
DIN EN 13263-1 (Draft)
Pigments
Use of inorganic heavy metals that occur in oxidic bonds or other stable compounds.
The stability of pigments in the alkaline environment shall be proved when testing the suitability of the pigments.
No results from leaching tests.
Need for further examination using leaching tests, particularly for organic pigments.
Harmonised product standards
Content/Release of dangerous substances Recommendations for second standard generation M 128: Products related to concrete, mortar and grout
Fly ash
Heavy metal content of fly ash clearly higher (considerably dependent on fuel used).
With batch tests to DIN 38414-S4 with fly ash, the insignificance thresholds ("no effect levels") were exceeded for antimony, arsenic, lead, cadmium, chromium, selenium and zinc. The Z2 values (leachate) of the LAGA-Mitteilung 20 for fly ash were exceeded for arsenic and chromium.
With the long-term static tests, the insignificance thresholds ("no effect levels") were complied with for concrete and mortar.
When using coal fly ash as a concrete addition, the parameters of the LAGA-Mitteilung 20 for fly ash should be tested for.
The use of secondary fuels when producing fly ash should be declared, the compliance with the insignificance thresholds of the DIBt Guideline should be examined with a leaching test.
When using petroleum coke, the nickel and vanadium content should be determined and declared.
Silica fume
Content of heavy metals is less than for Portland cement.
A release of heavy metals is not to be expected.
Release of organic substances to soil and groundwater:
Fly ash
There is very little data available. Results of batch tests have shown that there is very little leaching of organic substances. Values only exceeded in single case with phenol.
There is a need for further investigation as only a few results exist.
DIN EN 450-1 (Draft)
DIN EN 934-2
Concrete admixtures
Plasticisers and liquifiers: The leaching behaviour of plasticisers and liquefiers assessed on cement particles using batch and short-term static tests.
Results from analysing the pore water in concrete show only slight release of organic substances. No results exist yet from long-term static tests. There is no information on degradation products.
Retarders: Substances toxicologically
unobjectionable. These should be firmly bonded in the hardened cement paste. No results from leaching tests.
Accelerators: Bonded in the hardened cement paste. Leaching of alkalis. No results from leaching tests.
Air-entraining agents: No results from leaching tests.
Sealants: Toxicologically unobjectionable. No results from leaching tests.
Injection aids: Toxicologically unobjectionable.
Bonded in hardened cement paste. No results from leaching tests.
Stabilisers: No results from leaching tests.
Because there have only been a few leaching tests, there is a need for further investigation.
Here the results of the leaching tests should be assessed using the DIBt Guideline
Soil/Groundwater.