# Strength and Compressibility of Ammonia-Soda Residue from the Solvay Sodium Plant
## 2 Experimental Procedure
### Test Methods  
Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were used to identify the mineral composition of waste material and to investigate the microstructure of ASR. The specimen was dried under 105 \({}^{\circ}\)C. The 1-2 cm grey inclusions inside the white cement were recognised and separated for the phase and elemental analyses. Two X-ray diffraction patterns on both samples were collected at Bragg-Brentano geometry by using an in-house PANalytical X'Pert PRO MPD diffractometer and exploitation of monochromatic X-ray radiation of \(\lambda\) = 1.5406A. The data was recorded with step 0.08\({}^{\circ}\) in a range of 5-90\({}^{\circ}\). The phase identification was performed using X'Pert High Score Plus. The SEM images and elemental analyses were obtained using a JEOL JSM-7100F scanning electron microscope and an EDAX \"Octane Pro\" SDD Energy Dispersive X-Ray Spectrometer. Thin layers of both samples were spread on top of aluminium stumps covered by carbon tape. The SEM images and EDS spectra were taken at 15.0 keV with a working distance of 10.0 mm. For imaging, the samples were additionally coated by a 10 nm layer of carbon. The physical properties of the ASR were determined as per the relevant International Organization for Standardization (ISO). The conventional grain size analysis was conducted in accordance with ISO 17892-4 standard [38], and the density of soil skeleton (G\({}_{\text{s}}\)) was determined using the pycnometric method as per ISO 17892-3 [39]. The isotropically consolidated drained triaxial compression tests (CID) were carried out using the VJ-Tech triaxial compression apparatus. An appropriate testing procedure was adopted to gather high-quality data by performing full saturation with water, including increases of back-pressure, consolidation, and the choice of the loading rate. The samples with dimensions: diameter 50 mm and height 90 mm were formed. The height was measured before each test. The samples placed in the cell were sealed with airtight membranes and double O-rings. The porous disks and the paper filters were placed at the bottom and the top of the sample, ensuring the free water flow. The saturation of the specimens was done by the ramp method. In this technique, the cell pressure and back-pressure at the specimen's faces are ramped, and the B-check is performed at regular intervals to examine whether the required Skempton's pore pressure coefficient B (B-parameter) has been reached. The B-parameter was calculated as the ratio of the increase in the excess pore water pressure to the applied stress increment. A mean total stress increment of 50 kPa was selected for all the B-checks. The ASR specimen was assumed to be saturated if the B-value was sufficiently high (the analysis criterion of B > 0.98 was expected). To achieve the isotropic consolidation stage, the confining pressure on both end faces of the specimen was applied for one hour to establish target effective stresses between 50 and 400 kPa. For all the tests, the time needed to complete dissipation did not exceed 2 h.  
The shearing and consolidation stages were carried out using one-way drainage conditions. The final loading rate was estimated to be ca. 50% of the maximum rate determined based on the consolidation results. Adopting such a rate limit results from the previous preliminary study [40]. The constant rate of strain (CRS) consolidation tests were performed in a Multi-Purpose Consolidation Cell (MPCC) produced by VJ-Tech. In the CRS test, the load increases continuously while a constant strain rate remains constant, so the continuous recording of stresses and strains can be made. The most important parameter that must be determined before starting the CRS test is the strain rate [41; 42]. If the strain rate is too low, the pore pressure is very small or not generated at all during the test, leading to erroneous values of hydraulic conductivity (k\({}_{\text{v}}\)) and coefficient of consolidation (c\({}_{\text{v}}\)).