Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Modelling the Pb release during Portland cement alteration   Complex cementitious matrices undergo weathering with environmental exchange
and can release metallic pollutants during alteration. The molecular mechanisms
responsible for metal release are difficult to identify, though this is
necessary if such processes are to be controlled. The present study determines
and models the molecular mechanisms of Pb release during Portland cement
leaching. As Pb release is strongly related to its speciation (i.e. atomic
environment and the nature of bearing phases), the first objective of the
present study was to investigate the evolution of Pb retention sites together
with the evolution of the cement mineralogy during leaching. Complementary and
efficient investigation tools were used, namely X-ray diffraction, micro-X-ray
fluorescence and X-ray absorption fine structures. The second objective was to
reproduce our results with a reactive transport code (CHESS/HYTEC) in order to
test the proposed speciation model of Pb. Combined results indicate that in
both the unaltered core and the altered layer of the leached cement, Pb(II)
would be retained through C-S-H 'nano-structure', probably linked to a Q1 or
Q2P silicate tetrahedra. Moreover in the altered layer, the presence of Fe
atoms in the atomic environment of Pb is highly probable. Unfortunately little
is known about Fe phases in cement, which makes the interpretation difficult.
Can Fe- substituted hydrogranet (C3AH6) be responsible for Pb retention?
Modelling results were consistent with Pb retention through C-S-H in layers and
also in an additional, possibly Fe-containing, Pb-retention phase in the
altered layer.

11
The categories of this paper are: hep-lat
7
The categories of this paper are: hep-th
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
26
The categories of this paper are: bayes-an
3
The categories of this paper are: physics
1
The categories of this paper are: cs
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th