2.8. Metal Leaching Tests

The secondary products of combustion may contain, as already mentioned, certain amounts of toxic substances. The biomass ash used in the research, in particular, usually contains heavy metals. Construction products or concrete may come into contact with the water-repellent environment from the beginning of hydration or after some time. Therefore, it was decided to test the leaching ability of metals from the binder matrices at different times of its hardening.

After each strength test, a half of each mortar bar crushed to grains with the maximum grain size of standard sand (2 mm). Then 150 g were taken and poured over 150 mL of deionized water. The suspension was left unopened for 7 days. It was then filtered and washed using a quality filter so that the beaker was filled with 300 mL of clear filtrate. The filtrate was diluted 10 fold as required by the laboratory in which the tests were performed. Metals were marked according to the standard PN-EN ISO 11885: 2009 [78], and mercury according to the accredited method (No. PB/31/M edition 1 of 26 September 2011) consisting in atomic absorption spectrometry with hydride generation (HGAAS). Metal leachability tests were performed in a specialized accredited laboratory. The concentration of metals was given in units of mass per volume of the filtrate, and then converted into units of mass per 1 kg of binder (without the mass of sand) from which they were washed.