The objective of this paper is to investigate the coupling effect of cement and organosilicon hydrophobic agents on the water resistance of phosphogypsum. Different weight ratios of Portland cement were added to adjust the alkalinity of this system and further improve the work efficiency of the organosilicon hydrophobic agents. Some macroscopic performances, such as the water absorption, the compressive strength, the flexural strength, and the softening coefficient, were measured to characterize the water-resistance of phosphogypsum. The microscopic characteristics were analyzed via contact angle tests, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) to understand the mechanism of organosilicon hydrophobicity. The results indicated that both the compressive and flexural strengths of phosphogypsum first increased and then decreased with the increase of organosilicon hydrophobic agents. Meanwhile, the surface contact angle continued to increase and the softening coefficient exhibited an obvious increase. When the hydrophobic agent was combined with Portland cement, the softening coefficient of phosphogypsum further increased from 0.80 to 0.99, while the water absorption rate was significantly reduced from 16.0% to 0.8%. Microscopic tests proved that the hydrophobic organic molecules can be polymerized under the high alkalinity, and promote the formation of a hydrophobic film, thus significantly improving the water-resistance of phosphogypsum.

We reveal the critical role of electrolyte pH in efficiency and durability during electrochemical cement clinker precursor production and how to control it.

To address the potential adverse impact of silane on cement hydration, this study systematically investigates the effects of power ultrasound on the mechanical and hydrophobic properties, and the microstructure of silane-modified cement paste. Experimental results showed that ultrasonic treatment within the 240-720 W range significantly enhanced the compressive strength compared to the reference group. In particular, the 480 W group exhibited increases in compressive strength of 36.9 %, 10.7 %, and 7.9 % at 1, 3, and 28 days, respectively. X-ray diffraction and TG analysis revealed that this treatment accelerated the dissolution and hydration degree of the clinker. Contact angle measurements indicated that optimal hydrophobic performance was achieved at 720 W, with a contact angle of 133.0°, representing a 34.2 % increase compared to the reference group. These findings indicate that power ultrasound holds excellent potential for preparing the hydrophobic cementitious materials.

Sulfate and carbonate can cause serious degradation of cement-based materials at low temperature; degradation products generally include ettringite, gypsum and thaumasite. The degradation process is very slow in a natural environment and no useful test method exists to accelerate the degradation process. This study used a voltage of 30 V and an electrical field duration of 20 s to study the acceleration effect of an electrical field on the degradation. Visual observations and compressive strength were used to reflect the degree of degradation. X-ray diffraction, Fourier transform infrared spectroscopy and ion concentration distribution were applied to study the degradation mechanism. The test results indicated that an electrical field can accelerate the degradation within 180 d and that the degradation rate was faster than that associated with full immersion. Moreover, the degree of degradation of a solution with sodium sulfate (Na₂SO₄) as the cathode and magnesium sulfate (MgSO₄) as the anode was higher than that of a solution with magnesium sulfate as both cathode and anode; also the degradation degree of a magnesium sulfate solution under full immersion was higher than that of a sodium sulfate solution under full immersion.