# Life Cycle Assessment of Substitutive Building Materials for Landfill Capping Systems in Vietnam
###### Abstract
Regarding the legal requirements for the landfill sealing layers, the demands of the German Landfill Act (Dep V, 2009) [57] were considered. According to that legislation, landfills were divided into classes, depending on their hazard potential. Class I refers to \"Above-ground landfill for moderately contaminated excavated earth and rubble and comparable mineral commercial waste\". Class II refers to waste with a higher level of pollutants that also has a higher biological content than that in landfill class I. Higher landfill classes refer to hazardous waste landfills that are anyhow excluded from the implementation of substitutive building materials. The general approach to the pre-feasibility assessment of the substitutive building materials comprised the following steps:  
* Selection of potential materials that are available in large amounts in Vietnam and are considered residues based on literature research;
* Procurement of these materials and performance of a general soil mechanical characterisation of the pure materials;
* Development of mixture scenarios for the materials based on their properties and existing experiences;
* Soil mechanical investigations for several mixture scenarios to assess feasible mixtures that meet the requirements of the existing legislation on landfill sealing layers;
* Those mixtures that met the legal requirements for landfill sealing layers in terms of hydraulic conductivity have been considered for potential implementation and, in this regard, for the LCA. The key parameter for the assessment of leachate formation through a sealing system or component is the hydraulic conductivity of the sealing material. It describes the gravitational flow rate at which water seeps into the ground through interconnected voids of materials, described in hydrology through the permeability coefficient \(\mathrm{kf}\)[58]. The German legislation for surface sealing systems requires \(\mathrm{kf}\leq 5\times 10^{-9}\) m/s for landfill class I (simple landfills for construction rubble) and \(\mathrm{kf}\leq 5\times 10^{-10}\) m/s for class II (pre-treated municipal waste landfill). The investigations have been performed according to the existing German (Deutsches Institut fur Normung) DIN norms, summarized in Table 2. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Methodology** & **According to Norm** \\ \hline Water content & The water content was determined based on & \\ Water content & DIN 18121 Part 1 by oven drying. The & \\ Water content & sample in its natural state was weighed and & \\  & then dried together with a pan in the & \\  & Memmert drying oven at 105 \({}^{\circ}\)C. After & \\  & cooling, the sample was weighed again. The & \\  & mass difference corresponds to the amount of & \\  & pore water evaporated by oven drying. & \\ \hline Grain density & The test procedure for determining the grain & \\  & density using a helium pycnometer is & DIN 66137-2 (analogue to ASTM D854) \\  & regulated by DIN 66137-2: Gas pycnometry. & \\ \hline Grain size distribution & The grain size distribution & \\  & using a combined dry sieving with a sieving & \\  & machine (mesh size (mm): 8, 4, 2, 1, 0.5, 0.25, 0.125, and 0.063) and anemeter (elutriation) & \\  & to classify very fine fraction. & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: DIN norms applied for the soil mechanical lab tests. For the lab study, the selected materials were Asian rice husk ash and milled brick waste. Moreover, fly ash was taken into consideration as a potential sealing layer, based on wide relevance and usage among similar construction applications that had already proved the hydraulic conductivity of that material type [59; 60]. The mix ratio for the mineral sealing layer was elaborated in Tables 3 and 4. The alternative materials were made as a partial replacement for the conventional layer in different mixes.