Estimating the amount of material without significant losses at the end of hybrid casting is a problem addressed in this study. To minimize manufacturing costs and improve the accuracy of results, a correction factor (CF) was used in the formula to estimate the volume percent of the material in order to reduce material losses during the sample manufacturing stage, allowing for greater confidence between the approved blending plan and the results obtained. In this context, three material mixing schemes of different sizes and shapes (gypsum plaster, sand (0/2), gravel (2/4), and Posidonia oceanica fibers (PO)) were created to verify the efficiency of CF and more precisely study the physico-mechanical effects on the samples. The results show that the use of a CF can reduce mixing loss to almost 0%. The optimal compressive strength of the sample (S1B) with the lowest mixing loss was 7.50 MPa. Under optimal conditions, the addition of PO improves mix volume percent correction (negligible), flexural strength (5.45%), density (18%), and porosity (3.70%) compared with S1B. On the other hand, the addition of PO thermo-chemical treatment by NaOH increases the compressive strength (3.97%) compared with PO due to the removal of impurities on the fiber surface, as shown by scanning electron microscopy. We then determined the optimal mixture ratio (PO divided by a mixture of plaster, sand, and gravel), which equals 0.0321 because Tunisian gypsum contains small amounts of bassanite and calcite, as shown by the X-ray diffraction results.

Gypsum (GPS) has great potential for structural fire protection and is increasingly used in construction due to its high-water retention and purity. However, many researchers aim to improve its physical and mechanical properties by adding other organic or inorganic materials such as fibers, recycled GPS, and waste residues. This study used a novel method to add non-natural GPS from factory waste (phosphogypsum (PG)) as a secondary material for GPS. This paper proposes to mix these two materials to properly study the effect of PG on the physico-mechanical properties and fire performance of two Tunisian GPSs (GPS1 and GPS2). PG initially replaced GPS at 10, 20, 30, 40, and 50% weight percentage (mixing plan A). The PGs were then washed with distilled water several times. Two more mixing plans were run when the pH of the PG was equal to 2.4 (mixing plan B), and the pH was equal to 5 (mixing plan C). Finally, a comparative study was conducted on the compressive strength, flexural strength, density, water retention, and mass loss levels after 90 days of drying, before/after incineration of samples at 15, 30, 45, and 60 min. The results show that the mixture of GPS1 and 30% PG (mixing plan B) obtained the highest compressive strength (41.31%) and flexural strength (35.03%) compared to the reference sample. The addition of 10% PG to GPS1 (mixing plan A) improved fire resistance (33.33%) and the mass loss (17.10%) of the samples exposed to flame for 60 min compared to GPS2. Therefore, PG can be considered an excellent insulating material, which can increase physico-mechanical properties and fire resistance time of plaster under certain conditions.

High CO ₂ emissions and rising energy costs in the construction materials industry have increased the demand for innovative, environmentally friendly and energy-efficient construction materials. Gravel wash mud (GWM) is a widely available industrial by-product generated during gravel mining: its fine particle size and high clay mineral content make it a promising raw material for use in cementitious systems. Quartzite dust is another industrial by-product that can be used to improve the physical properties of cement. A NaOH solution was used as the alkali activator for cement synthesis, avoiding the need for soluble silicates. The calcined kaolinite-rich GWM acts as a highly effective binder in cement formulations containing quartzite dust. Surprisingly, only a small amount of calcined clay is required: a mixture containing 90 wt.% quartzite dust and 10 wt.% GWM significantly reduced the demand for alkali activator and the associated production costs. The curing regime was critical for attaining high strength and was specifically optimized for this cement system. For the formulation containing 90 wt.% quartzite dust and 10 wt.% GWM, compressive strength increased from 2.07 MPa under room-temperature curing to 72.6 MPa under optimized curing conditions, corresponding to a ∼35-fold improvement. To demonstrate a practical application, graphite powder was incorporated as an electrically conductive additive. Variation of quartzite content reduced the electrical resistivity of graphite-containing formulations by approximately five orders of magnitude compared with formulations containing only GWM and graphite, highlighting their potential for resistance-heating and thermal energy-storage applications.