## 2 Materials and Methods
### Test Programme  
Self-compacting lightweight concrete (SCLC) does not yet have specific standards or guidelines for handling. Therefore, the characterization of SCLC in its fresh state has been conducted following the same parameters and standards as conventional self-compacting concrete. Thus, to evaluate fluidity, apparent viscosity, visual stability, and passing ability, tests were performed according to the parameters established by [28], as described in Table 6.  
Following this, the fresh bulk density was determined by weighing the metal moulds before and after concrete placement. The difference in weight, divided by the volume of the mould, provides the bulk density of the fresh concrete. Studying the characteristics of hardened SCLC is essential to assess performance at different ages and ensure compliance with standard requirements. After hardening, dry bulk density was determined at 7 and 28 days. Four samples were measured, and the average was considered as the final value. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Test** & **Property Evaluated** & **Reference** \\ \hline \multirow{2}{*}{Slump flow} & Filling ability and & \multirow{2}{*}{[29]} \\  & segregation resistance & \\ \hline \multirow{2}{*}{T500} & Filling ability and apparent & \multirow{2}{*}{[29]} \\  & viscosity (fluidity) & \\ \hline \multirow{2}{*}{Visual stability index} & Presence of bleeding & \multirow{2}{*}{[29]} \\  & and/or segregation & \\ \hline \multirow{2}{*}{J-ring} & Passing ability & [30] \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Tests and properties evaluated for SCLC in the fresh state. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Composition** & **SCLC-EC** & **SCLC-SBA50** & **SCLC-SBA90** & **SCLC-SMR37** \\ \hline Cement & 449.31 & 468.74 & 476.48 & 457.53 \\ \hline Metakaolin & 44.93 & 46.87 & 47.65 & 45.75 \\ \hline Fine aggregate & 831.22 & 867.17 & 881.49 & 846.43 \\ \hline Lightweight coarse aggregate & 336.98 & 396.09 & 528.89 & 410.40 \\ \hline Water & 181.97 & 189.84 & 192.97 & 185.30 \\ \hline Superplasticizer (\% of fines) & 1.00 & 0.82 & 1.30 & 1.30 \\ \hline Water-to-cement ratio & 0.405 & 0.405 & 0.405 & 0.405 \\ \hline Aggregate-to-fines ratio & 2.36 & 2.45 & 2.69 & 2.50 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Consumption of materials for the self-compacting lightweight concrete used in the study (kg/m\({}^{3}\)). Axial compressive strength tests were performed following the recommendations of [31] at 7 and 28 days. Four samples were used for each age, and the average was considered. The same test specimens from the dry bulk density test were used. Twenty-four hours before the tests, the concrete specimens were sulphur-capped to level the faces, ensuring uniform load distribution in the mechanical press. The compressive strength test was conducted using a Shimadzu AG-X 300 kN press with a loading rate of 0.30 MPa/s, following the specifications of [31; 32]. In addition to bulk density and compressive strength, the efficiency factor (EF) was another parameter used to evaluate the SCLC. The EF is determined by the ratio of compressive strength at 28 days to the bulk density of the concrete. For each mix, the EF was calculated using the compressive strength values at 28 days and the average dry bulk density values. The diffusion coefficient of chloride ions was assessed using the method established in [33], following the specifications of [34]. This test provides information on the resistance to chloride ion penetration in concrete by determining the diffusion coefficient. As it is accelerated by an electric current, it is possible to characterise the concrete in up to 72 h, depending on the quality of the concrete tested. The concretes were tested 186 days after casting, with specimens measuring 50 \(\pm\) 5 mm in height and 100 \(\pm\) 2 mm in diameter and 4 specimens for each design. The specimens were prepared by wet curing up to 28 days and outdoor curing up to the date of the test.